US20180363441A1

US20180363441A1 - Method and apparatus for improving wellbore productivity with piezoelectric crystals

Info

Publication number: US20180363441A1
Application number: US16/011,372
Authority: US
Inventors: Azra N. Tutuncu; Ali I. Mese
Original assignee: Individual
Current assignee: Individual
Priority date: 2017-06-19
Filing date: 2018-06-18
Publication date: 2018-12-20

Abstract

A system and method of enhancing production of oil and gas from a reservoir is provided. More specifically, the present invention relates to systems and methods of positioning piezoelectric crystals in a production interval of a well. When activated, the piezoelectric crystals produce displacement (elongation and compaction) and cavitation within the wellbore to move particles within the well and fractures in the reservoir. In one embodiment, a fluid which includes a proppant material and a plurality of piezoelectric crystals is pumped into the well. The fluid may be a hydraulic fracturing fluid. In another embodiment, a plurality of piezoelectric crystals are interconnected to a body of a downhole assembly. The downhole assembly is configured to be positioned within a production interval of a wellbore. In one embodiment, the body includes a hollow bore. In one embodiment, the piezoelectric crystals are interconnected to at least one of an exterior surface of the body and an interior surface of the body within the hollow bore.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority and benefits under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application Ser. No. 62/521,972, entitled “System and Method of Fracture Stimulation and Conductivity Monitoring in Conventional and Unconventional Oil and Gas Production” filed on Jun. 19, 2017, which is incorporated herein in its entirety by reference.

FIELD OF THE INVENTION

The present invention generally relates to systems and methods of enhancing production of oil and gas from reservoirs. More specifically, the present invention relates to systems and methods of positioning piezoelectric crystals within a production interval of a wellbore. In one embodiment, the piezoelectric crystals are mixed with proppants in a hydraulic fracturing fluid to be pumped into the wellbore and fractures. Additionally, or alternatively, piezoelectric crystals may be interconnected to a downhole assembly configured to be placed within the production interval of the wellbore.

BACKGROUND

The exploration and development of unconventional and low permeability reservoirs plays a significant role in meeting and exceeding the U.S. and global energy needs. However, well production generally declines over time. In shale gas formations, shale oil formations, tight sandstone formations, and other unconventional formations with low permeability, the greatest decline in oil and gas production frequently occurs within 6 months to 1 year from the first production.
Current techniques of mapping fractures in a reservoir cannot accurately detect the actual lengths of fractures created during hydraulic fracturing operations. Thus, the effective lengths of fractures detected using current fracture mapping techniques may be shorter than the actual lengths of the fractures. One of the reasons for the shorter lengths is improper placement of the proppants into the fractures. Proper proppant placement within fractures plays a significant role in maintaining conductivity of the fracture once the hydraulic fracturing treatment is completed and production initiated. Inaccurate mapping of fracture length and width along with the overall geometry of the stimulated reservoir volume will cause insufficient transport and placement of proppant into the fractures. The size and shape of the proppants selected for use as well as the resistance of the proppants to local stress changes and to preventing fracture closure also plays a significant role in fracture conductivity.
Crosslinked gel fracturing fluids have been used to provide better proppant suspension. While crosslinked gel fracturing fluids can carry proppants of any size deeper into the fractures due to the higher viscous characteristics, unfortunately, even crosslinked gel fracturing fluids cannot provide satisfactory proppant transport into the fractures under downhole reservoir conditions. Further, cleaning the crosslinked gel fracturing fluids from a wellbore is a significant challenge. Thus, there is often some of the crosslinked gel fracturing fluid which remains within the proppant pack and within the reservoir resulting in damage to the reservoir. This is particularly problematic when crosslinked gel fracturing fluid is used in low permeability gas formations.
Using slickwater to transport and place proppants during hydraulic fracturing reduces the damage caused by crosslinked gel fracturing fluids in the reservoir. As will be appreciated by one of skill in the art, slickwater generally refers to a water-based fluid and proppant combination that has low-viscosity. Chemicals may be added to the water to increase fluid flow and reduce friction. In addition, biocides, surfactants, and scale inhibitors may be added to the slickwater. The use of slickwater is especially beneficial in the hydraulic fracturing of unconventional reservoir formations. Salt ion types of slickwater are particularly beneficial. Various concentrations of slickwater have been formulated to make the slickwater fluid compatible with the proppant selected for a formation associated with a wellbore. However, improper proppant placement and settling, banking within the fractures created during hydraulic fracturing as well as the compaction of the proppant pack and reduction of the proppant pack porosity and permeability with time are strongly dependent on the composition of the fracturing fluid brine. Further, increasing effective stress in the wellbore can crush the proppants if the stresses exceed the proppant strength. The crushed proppants prevent efficient long term production from the well.
Experiments have been conducted using Niobrara shale core samples utilizing distilled water, 2% and 6% NaCl and 2% and 6% MgCl₂solutions flowing through the fractured formation that was filled with monolayer ceramic proppants. The experiments indicated large changes in the stiffness of the formation and an associated reduction of fracture conductivity that was observed occurred faster when stiffness was reduced in spite of the selection of strong proppant.
Applying light or ultralight proppants can help transport the proppants further into the fractures. However, light and ultralight proppants are typically more expensive than denser proppants. The light and ultralight proppants also tend to crush faster than more dense proppants in deeper, high in-situ stress conditions. Unfortunately, crushed proppants introduce additional debris that can also contribute to formation damage. Thus, the use of light or ultralight proppants may be associated with reduced fracture permeability and a decline in fractured reservoir production after a short production time.
Several proppant placement processes have recently been introduced to overcome some of the limitations in the conventional proppant placement techniques. These processes include hybrid fracturing, reverse hybrid fracturing, alternate-slug fracturing, and channel fracturing. Each of these techniques are used to increase the conductivity in the proppant pack, providing highly conductive paths for the flow of oil and/or gas from the reservoir into the wellbore. These techniques have been shown to achieve better proppant placement within the fractures, including placement of proppant into fractures of longer length. However, limitations still exist with the use of these proppant placement processes.
Permeability measurements have been conducted in core samples obtained from several conventional and unconventional reservoir formations. The formations tested include hydraulically fractured Barnett, Eagle Ford, Niobrara and Vaca Muerta shale gas and tight oil formations. Measurements have been conducted under in-situ stress conditions with elevated pore pressure. The samples were first measured in their intact state, prior to application of hydraulic fractures and the mechanical and acoustic/ultrasonic properties were recorded. The samples were subsequently fractured and additional measurements were taken. A selected fracturing fluid with a specific composition was flowed through fractures in the samples at different differential stresses. The permeability and fracture conductivity measurements indicated significant reductions in conductivity and permeability of the fractures in the samples of all formations within short periods of time. The results are evidence explaining the rapid production decline in fractured tight oil and gas shale formations.
Geochemical analysis of the samples after various fluids flowed through the fractured rock identified significant rock-proppant-fluid interactions for specific fluids resulting in dissolution of selected minerals in the matrix. The interactions and dissolution introduce associated reduced stiffness in the formation. As will be appreciated by one of skill in the art, the formation stiffness is measured with Young's modulus. Reductions in formation stiffness cause easier failure that results in grain crushing. The crushed grains as well as other fines may subsequently be transported by fluid flow within the proppant pack in the wellbore as well as within the fractures. The migration of the fines into the proppant pack blocks pore throats within the proppant pack. The embedment of proppants in fracture faces and the migration of fines into the proppant pack results in a reduction of conductivity to the wellbore and an associated decrease in production from the reservoir.
When the fracture conductivity decline results in an uneconomical production level, one method of the improving fracture conductivity and production is refracturing the wellbore. The evaluation of a candidate well to determine the source of production decline is highly important. The evaluation of the candidate well is also important to determine cost and identify a suitable fracturing fluid for continuing the economically viable production status in wells formed in tight sandstones, shale gas, tight oil and other unconventional reservoirs. Refracturing may increase the conductivity and produce an associated increase in production for some limited time, yet temporarily increasing the production will not completely eliminate the production decline. Both hydraulic fracturing and refracturing operations require large amounts of water and chemical additives and raise concerns related to contamination of groundwater and surface water. Further, the cost of transporting the fracturing fluid and proppants to the well are significant. Accordingly, alternate stimulation techniques are needed for economical and environmentally friendly production from tight gas sands, shale gas, tight oil and conventional and unconventional oil and gas reservoirs in the U.S. and worldwide.
Removal of reservoir formation damage using ultrasonic energy has been studied, and acoustic stimulation tools using elastic waves with frequencies typically ranging from KHz to MHz range have been found to remove near-wellbore damage, such as skin effect. The mechanisms behind removal of formation damage using an acoustic streaming approach was not well known until early 1990's. A study of coupling of mechanical and chemical forces and associated modeling on the equilibrium separation distance for acoustic wave propagation that lead to acoustic streaming of small particles oscillating parallel and perpendicular to a plane wall surface revealed the process of acoustic streaming could be utilized in the oil industry.
The efficiency of acoustic cleaning as a function of frequency, output power and the type of fluid interacting with the solid particles has also been studied. Experimental and modeling studies have also shown that ultrasonic cleaning may be a useful stimulation technique in the removal of near wellbore damage caused by drilling and drill-in fluids. Studies have also been conducted to discover the key parameters controlling the efficiency of acoustic cleaning in reservoir conditions. In 2008, one study investigated the effect of fluid type, sonification time and applied sonifier power level on the cleaning efficiency of the near wellbore formation damage caused by fines and solids in drilling and drill-in fluids. In another study, experiments were conducted with dynamic filtration of fully brine saturated reservoir core samples. An experimental study of damage removal near a wellbore in a conventional formation concluded that acoustic cleaning was effective in drilling related applications.
The effectiveness of acoustic stimulation of the screens typically used in frac-pack operations in deepwater applications for production from poorly consolidated reservoirs has also been studied. The screens are often plugged by sand and particles migrating from the formation through fluid flow. This plugging of the screens results in mechanical damage of the screen in these high permeability formations thereby reducing the high-rate production to levels similar to low permeability formations. Acoustic stimulation experiments and modeling have also been conducted to define the mechanisms of plugging in order to determine how to effectively unplug the screens. A field tool for acoustic stimulation that may be used for near wellbore damage removal applications is described in U.S. Pat. No. 7,216,738, which is incorporated herein by reference in its entirety.
Prior art acoustic stimulation tools available in the industry are placed in the well through wireline or tubing. Because of this, prior art acoustic stimulation tools can only be used to eliminate formation damage very near the wellbore. Additionally, the effectiveness of these tools is strongly dependent on the frequency at which the stimulation tools operate. However, all prior art acoustic stimulation tools utilize frequencies which are effective only up to a few inches from the wellbore. Accordingly, prior art acoustic stimulation tools only clean areas very near to the wellbore prior to the proppant packing process when hydraulic fracturing treatment is implemented in the wells. None of these tools generate frequencies which are effective to clean areas more than a few inches away from the wellbore into the reservoir formation.
Another deficiency of all of the prior art stimulation tools is their need for downhole power. The tools can only be used by utilizing power provided by a surface connection or by a downhole battery. Downhole batteries limit usage of the stimulation tool to the life of the battery. Another problem with current stimulation methods and tools is that in order to apply acoustic cleaning or re-fracturing to improve the permeability and fracture conductivity, production from the well must be stopped adding further loss of revenue caused by loss of the production during the treatment in addition to the operation cost of the cleaning/re-fracturing processes.
Due to these and other limitations associated with known systems and methods, there is an unmet need for a system and method of transporting and placing proppants in fractures and cleaning a wellbore and the proppant pack in fractures along a production interval of the well.

SUMMARY OF THE INVENTION

The present invention provides systems and methods of cleaning a wellbore, placing proppant within the fractures along a production interval of a wellbore and/or within the fractures into the reservoir which cannot be implemented using the prior art. The methods and systems of the present invention are more effective than the prior art and without some of the costs and disadvantages. One aspect of the present invention is a novel method for proppant pack placement and removal of production related damage in the proppant pack and real time monitoring of the fracture conductivity.
One aspect of the present invention is a system and a method of positioning piezoelectric crystals within a production interval of a wellbore. In one embodiment, the piezoelectric crystals expand and contract, or move, in response changing conditions within the wellbore. In one embodiment, the movement of the piezoelectric crystals is triggered by changes in one or more of pressure, temperature, and fluid flow within the wellbore. In another embodiment, the movement of the piezoelectric crystals may be initiated by electricity. The movement of the piezoelectric crystals removes particles from proppant packed in the wellbore and fractures in the production interval. More specifically, the movement of the piezoelectric crystals allows particles to migrate out of the proppant pack when the well is flowed. The movement of the piezoelectric crystals also moves the proppant into the fractures. In this manner, the piezoelectric crystals enhance the permeability and flow rates from the wellbore.
Another unique aspect of the invention is that the piezoelectric crystals are self-actuating. When elongation or contraction of the formation or proppant pack takes place as a result of fluid flow, the piezoelectric crystals within the fractures and the proppant pack expand and/or contract. As the piezoelectric crystals move in response to the expansion and/or contraction, the piezoelectric crystals contact each other and neighboring proppant particles. The resulting vibration and displacement create additional drag forces in the proppant pack. These forces push the fines into the neighboring piezoelectric crystal and/or proppant particles. In this manner, the piezoelectric crystals facilitate movement and proper placement of proppants into the induced fractures through the hydraulic fracturing treatment and/or natural fractures that are connected to other natural fractures and hydraulic fractures.
In one embodiment, when there is a reduction in one or more of fluid pressure, temperature, and flow rate, the piezoelectric crystals will contract. In another embodiment, when there is an increase in one or more of fluid pressure, temperature, and flow rate, the piezoelectric crystals will expand or elongate.
It is another aspect of the present invention to provide a hydraulic fracturing fluid which includes a mixture of proppant and piezoelectric crystals. More specifically, in one embodiment, a predetermined ratio of piezoelectric crystals and proppants are mixed together. The hydraulic fracturing fluid with the proppants and piezoelectric crystals may subsequently be pumped together into the wellbore. When the hydraulic fracturing fluid is pumped into the wellbore and fractures of a formation, the piezoelectric crystals are transported into the fractures with the proppant. In this manner, the piezoelectric crystals can be placed in the production interval of the wellbore and into fractures of the formation around the production interval. The piezoelectric crystals can thus be positioned at, or near, the ends of the fractures which are spaced from the wellbore.
The piezoelectric crystals may be substantially evenly distributed within the proppant pack as far away from the wellbore as they can be pumped through the combined induced and natural fracture network introduced during the hydraulic fracturing treatment. The mixture of piezoelectric crystals and proppant is beneficial both during pumping and during production of the well. Specifically, pressure, temperature and flow differentials during hydraulic fracturing cause the piezoelectric crystals to expand and contract. The expansion and contraction of the piezoelectric crystals helps transport and position the proppant within fractures in the formation. Similarly, the piezoelectric crystals included in the hydraulic fracturing fluid also expand and contract in response to production variations. The expansion and contraction is transferred through the proppant pack to fines within the proppant pack. As the well flows, the fines migrate out of the proppant pack and maintain (or improve) fracture conductivity.
It is another aspect of the present invention to provide a downhole assembly which includes piezoelectric crystals. The downhole assembly is configured to be placed within the production interval of the wellbore. The downhole assembly has a body to which the piezoelectric crystals are affixed. Optionally, the body may have a generally cylindrical shape. In one embodiment, the body is solid. Optionally, the body comprises a steel casing or bar. Alternatively, the body is formed of a mesh or screen. Optionally, the body includes a bore with an interior surface. In one embodiment, the piezoelectric crystals are interconnected to an exterior surface of the body. Additionally, or alternatively, in another embodiment, the piezoelectric crystals are interconnected to the interior surface of the bore.
Another aspect of the present invention is a method of monitoring fracture conductivity. The method may be used in production of reservoirs such as tight gas sandstone, shale gas, tight oil, shale oil and other conventional and unconventional formations. In one embodiment, the method includes a 3-D stimulation application as a function of time (i.e., 4D-stimulation) as the method provides real time monitoring of the fractures in the reservoir in proximity to the wellbore through the placed piezoelectric crystals. In one embodiment, the method includes recording data associated with the activation of one or more piezoelectric crystals positioned a wellbore and/or fractures within the reservoir. The data may include frequencies generated by the piezoelectric crystals when activated.
It is another aspect of the present invention to provide a system and method of improving fracture conductivity of a wellbore while the wellbore is in production. In one embodiment, the system and method include a downhole assembly that may be positioned within the wellbore. The downhole assembly is configured to be selectively activated while the wellbore is in production. In this manner, the production of the reservoir and wellbore can be increased without taking the wellbore out of production.
One aspect of the present invention is a system and method of increasing conductivity of fractures of a production zone proximate to a wellbore. In one embodiment, the system and method includes removing damage in the wellbore. For example, in one embodiment, particles associated with proppant, natural or man-made fines, and completion residue are moved out of the fractures with the system and the method of the present invention.
Another aspect of the present invention is a method of increasing fracture conductivity. The method includes positioning piezoelectric crystals in the proppant pack. In one embodiment, the piezoelectric crystals are mixed with the proppant in a hydraulic fracturing fluid. The hydraulic fracturing fluid is then pumped into the wellbore and reservoir. Additionally, or alternatively, the piezoelectric crystals can be interconnected to a downhole assembly of the present invention. In one embodiment, no chemicals are injected into the wellbore with the hydraulic fracturing fluid including that proppant and piezoelectric crystals. In this manner, the system and method of the present invention eliminates, or at least reduces, unintended or inadvertent contamination of ground water and surface water during production from a reservoir. Increasing fracture conductivity without the use of chemicals also reduces costs associated with operating the wellbore and is environmentally safer than prior art methods of increasing fracture conductivity that include injecting chemicals into the wellbore.
Another aspect of the present invention is a system and method of cleaning part or all of a proppant pack in fractures of a hydrocarbon reservoir. More specifically, the system and method of the present invention may be used to clean fractures in the formation. In one embodiment, a downhole assembly of the present invention is positioned in the wellbore. Piezoelectric crystals are interconnected to at least one surface of the downhole tool. Optionally, piezoelectric crystals may also be mixed with the proppant before the proppant is pumped into the wellbore. The piezoelectric crystals are subsequently triggered or activated to clean the proppant pack.
In one embodiment, the piezoelectric crystals are activated through changes in pressure, temperature and/or fluid flow within the wellbore. More specifically, in one embodiment, fluctuations in one or more of pressure, temperature, and fluid flow within the wellbore trigger the piezoelectric crystals. In one embodiment, the piezoelectric crystals do not require external electric power, such as from a battery or an electrical wire.
When triggered, the piezoelectric crystals expand and contract. The expansion and contraction causes displacement in the neighboring proppant particles as well as other piezoelectric crystals creating a chain reaction of self-movement within the proppant pack. In some applications, at specific frequencies and particularly in gas wells, this movement may also cause cavitation within the fluid in the wellbore or in the proppant pack. The cavitation and acoustic streaming caused by the piezoelectric crystal vibration and flow creates drag forces. The drag forces detach the attached fines within fractures in the reservoir and in the proppant pack. In this manner, the piezoelectric crystals restore fracture conductivity. Fluid flow from the wellbore subsequently flushes the fines out of the fractures and the proppant pack. In one embodiment, the fractures can be cleaned from a distal end of each fracture to a portion of each fracture proximate to the wellbore. In another embodiment, the features may be cleaned substantially along the entire fracture length and width into which the piezoelectric crystals are pumped along with the proppant.
Still another aspect of the present invention is a method of enhancing the production of a hydrocarbon reservoir. The method includes, but is not limited to: (1) providing a wellbore extending a predetermined length and depth in the hydrocarbon reservoir; (2) providing a fluid which includes a proppant material and a plurality of piezoelectric crystals; and (3) pumping the fluid into the wellbore. At least one of the plurality of piezoelectric crystals subsequently contracts in response to conditions within the wellbore. In one embodiment, at least one of the plurality of piezoelectric crystals is transported into a fracture in the hydrocarbon reservoir. In one embodiment, the fluid is a hydraulic fracturing fluid. In another embodiment, the fluid includes water.
In one embodiment, the piezoelectric crystals are operable to contract in response to a reduction of at least one of a fluid temperature, a fluid pressure, and a rate of fluid flow. In another embodiment, In one embodiment, the piezoelectric crystals are operable to expand in response to an increase of at least one of a fluid temperature, a fluid pressure, and a rate of fluid flow.
The method may further include selecting a plurality of piezoelectric crystals based on the frequencies the piezoelectric crystals will generate when activated. In one embodiment, the plurality of piezoelectric crystals will generate frequencies of between approximately 0.5 kHz and approximately 1 GHz when activated. In another embodiment, the piezoelectric crystals will generate frequencies of between approximately 1 kHz and 100 MHz when activated. In one embodiment, the plurality of piezoelectric crystals may comprise two or more different materials which exhibit piezoelectricity. Some of the piezoelectric crystals may comprise a ceramic.
In one embodiment, the piezoelectric crystals comprise up to approximately 50% by volume of the fluid. In another embodiment, the piezoelectric crystals comprise up to approximately 25% by volume of the fluid. In still another embodiment, the piezoelectric crystals comprise between about 3% and about 50% by volume of the fluid.
In one embodiment, the piezoelectric crystals and the proppant material are mixed in a one to one ratio (1:1) in the fluid. Alternatively, the ratio of piezoelectric crystals to the proppant is at least one to five (1:5). In another embodiment, the piezoelectric crystals and proppant are mixed in a ratio of not more than five to one (5:1). Accordingly, in one embodiment, the ratio of piezoelectric crystals to the proppant is between approximately 1:5 and approximately 5:1 in the fluid. In another embodiment, the ratio of piezoelectric crystals to the proppant is between approximately 1:1.5 and approximately 1.5:1 in the fluid. Other ratios are contemplated.
Another aspect of the present invention is a fluid for transporting a proppant material and a plurality of piezoelectric crystals into fractures in a hydrocarbon reservoir. The fluid generally includes, but is not limited to: (1) a proppant material; (2) a plurality of piezoelectric crystals; and (3) a liquid selected to transport the proppant material and the plurality of piezoelectric crystals. The fluid can be pumped into a wellbore such that the proppant material and at least one of the piezoelectric crystals are transported into a fracture in the hydrocarbon reservoir. The piezoelectric crystals are operable to expand and/or contract in response to changes in one or more of a fluid temperature, a fluid pressure, and a rate of fluid flow in the wellbore. In one embodiment, the fluid is a hydraulic fracturing fluid. In another embodiment, the liquid includes water.
In one embodiment, the plurality of piezoelectric crystals are operable to generate frequencies of between approximately 0.1 kHz and approximately 1 GHz when activated. In another embodiment, the piezoelectric crystals are operable to generate frequencies of between approximately 1 kHz and 100 MHz when activated. Optionally, the piezoelectric crystals may have a variety of sizes and shapes.
In one embodiment, the piezoelectric crystals comprise up to approximately 50% by volume of the fluid. In another embodiment, the piezoelectric crystals comprise up to approximately 25% by volume of the fluid. In still another embodiment, the piezoelectric crystals comprise between about 3% and about 50% by volume of the fluid.
In one embodiment, the piezoelectric crystals and the proppant material are mixed in a one to one ratio (1:1) in the fluid. Alternatively, the ratio of piezoelectric crystals to the proppant is at least one to five (1:5). In another embodiment, the piezoelectric crystals and proppant are mixed in a ratio of not more than five to one (5:1). Accordingly, in one embodiment, the ratio of piezoelectric crystals to the proppant is between approximately 1:5 and approximately 5:1 in the fluid. In another embodiment, the ratio of piezoelectric crystals to the proppant is between approximately 1:1.5 and approximately 1.5:1 in the fluid. Other ratios are contemplated.
One aspect of the present invention is to provide a novel system and method for placement of a proppant pack in fractures of a wellbore. In one embodiment, the system and method can be used to remove or decrease production related damage to the proppant pack.
It is another aspect of the present invention to provide a system and method of placing proppants into fractures during a hydraulic fracturing operation. In one embodiment, piezoelectric crystals are pumped into a wellbore with proppants. In another embodiment, a downhole assembly is positioned in the wellbore. The downhole assembly includes a screen or a bar to which the piezoelectric crystals are mounted. In both embodiments, the piezoelectric crystals expand or contract. The expansion and contraction is transferred to particles in the proppant pack and causes the proppant to move further into fractures within the formation.
Another aspect of the present invention is a system and method of generating a variety of frequencies with piezoelectric crystals to clean factures in a formation. The frequencies are selected based on characteristics of the formation and the dimensions and geometry of fractures in the formation. For example, the frequencies of the piezoelectric crystals are selected based on the fracture length and width, formation type and mineralogy, gas or oil production, and the in-situ stress characteristics. The frequencies may be from low (kHz) to ultrasonic (MHz) frequencies. The fractures may be naturally occurring or induced, such as by hydraulic fracturing operations. The system and method may be used in vertical, inclined, or horizontal wells which have fracture lengths of tens to hundreds of feet at multiple stages and extending along thousands of feet of the wellbore.
In one embodiment, the system and method includes a downhole assembly including a plurality of piezoelectric crystals. The system and method of embodiments of the present invention can be implemented in a horizontal, a deviated, or a vertical well along the entirety of the production interval. In one embodiment, the system and method include coupling multiple frequency acoustic waves and piezoelectric crystals pumped simultaneously with proppants into the well. Conditions in the well and formation induce mechanical expansion and contraction of the piezoelectric crystals. The expansion and contraction results in different displacements depending on the frequencies of each piezoelectric crystal. In this manner, the cleaning effects generated by the system and method of the present invention can propagate throughout the fracture from the smallest fracture tip to the connection of these fractures into the wellbore as well as into the natural fracture network connected through the hydraulic fracturing treatment.
The system and method of the present invention can be used to clean a majority of the length of a fracture. In one embodiment, a fracture can be cleaned using the system and method of the present invention from a beginning of a fracture proximate to the wellbore to a tip of the fracture distal to the wellbore. Therefore, the cleaning effects are realized for the full length, or a substantial portion of the length, of fractures of horizontal, deviated or vertical wells and in the proppant packed fractures covering the production interval. This cleaning helps to maintain the production interval free of damage for the lifecycle of the well.
One aspect of the present invention is to provide a downhole assembly for positioning proppant in fractures along a production interval of a wellbore to enhance flow rates from the wellbore. The assembly includes, but is not limited to: (1) a body configured to be positioned within the production interval of the wellbore; and (2) a plurality devices interconnected to the body. The devices are operable to expand and contract. Activation of the devices creates displacement and/or cavitation in a fluid within the wellbore. In one embodiment, the devices are piezoelectric crystals. In one embodiment, the piezoelectric crystals have various sizes and frequencies to create the displacement necessary to move proppants of various sizes. Optionally, the piezoelectric crystals are selected based on specific reservoir and fracture characteristics. In another embodiment, the piezoelectric crystals are spaced at predetermined intervals along the device body. In one embodiment, additional piezoelectric crystals are mixed with the proppant and can be pumped together with the proppant into the fractures.
Optionally, the piezoelectric crystals are selected to generate different frequencies when activated. In one embodiment, a first subset of the piezoelectric crystals generate low frequencies. Optionally, the low frequencies may be between approximately 0.1 kHz and approximately 100 kHz when activated. In another embodiment, the first subset of the piezoelectric crystals generate frequencies of between approximately 1 kHz and approximately 10 kHz when activated.
In another embodiment, a second subset of the piezoelectric crystals generate high frequencies. In one embodiment, the high frequencies are between approximately 10 kHz and approximately 1 GHz when activated. Optionally, the second subset of the piezoelectric crystals generate frequencies are between approximately 10 kHz and approximately 10 MHz when activated. In another embodiment, the first subset of the piezoelectric crystals are positioned on an exterior surface of the body. In one embodiment, the second subset of the piezoelectric crystals are positioned on an interior surface of the body. Additionally, or alternatively, the first subset of the piezoelectric crystals may be mixed with the proppant. Similarly, in one embodiment, the second subset of the piezoelectric crystals is mixed with the proppant. In one embodiment, the first subset of the piezoelectric crystals comprise a first material that exhibits piezoelectricity. Optionally, the second subset of the piezoelectric crystals comprise a second material that exhibits piezoelectricity.
In one embodiment, the body comprises a mesh material. Alternatively, the body comprises a solid material. In another embodiment, the body is generally cylindrical. In still another embodiment, the body includes a substantially hollow bore with an interior surface. The piezoelectric crystals can be positioned on at least one of an exterior surface of the body and the interior surface within the hollow bore.
In one embodiment, the downhole assembly is triggered by contraction or elongation in the piezoelectric crystals. The contraction or elongation of the piezoelectric crystals results in displacement of the neighboring proppants. Associated displacements are carried to the neighboring proppants and piezoelectric crystals. In this manner, contraction and elongation of one piezoelectric crystal spreads to other piezoelectric crystals and creates a chain reaction and continues through the proppant pack. The displacement motion is carried further through the proppant all the way into the tip of the hydraulic fractures.
In one embodiment, no downhole battery or surface power is needed to activate the piezoelectric crystals. Optionally, one or more of the piezoelectric crystals can be selectively activated. For example, in one embodiment, the piezoelectric crystals may be activated if a pressure differential is not anticipated for a period of time.
Another aspect of the present invention is a system for improving production of a fluid from a reservoir. In one embodiment, the system includes a mixture of proppant and piezoelectric crystals which are pumped into the well. Additionally, or alternatively, the system can optionally include a downhole tool including piezoelectric crystals. The piezoelectric crystals of the system may be of multiple frequencies. Depending on the selected piezoelectric crystal frequency, a change in the pressure, the flow rate and/or the temperature of the well will result in activation of the of the piezoelectric crystals and cause expansion and contraction of the piezoelectric crystals.
In one embodiment, the downhole tool is interconnected to an electrical source. The electrical source may be a downhole battery. Additionally, or alternatively, the electrical source may be a wire-line to the surface. The piezoelectric crystals can be interconnected to the electrical source. In this manner, electricity can selectively be provided to one or more of the piezoelectric crystals to activate the piezoelectric crystals.
In one embodiment, activation of the apparatus creates displacement and/or movement of particles proximate to the piezoelectric crystals as a result of the piezoelectric crystal characteristics. The displacement and movement causes displacement in the neighboring proppants and other piezoelectric crystals. In this manner, a chain reaction of displacement within the proppant is created. The systems and methods of the present invention may be used to continuously maintain fracture conductivity and associated flow without any decay in production volume throughout the fractures. Further, production from the well may continue while the piezoelectric crystals in the wellbore and fractures expand and contract to clean the well of particles. In one embodiment, the particles are one or more of proppant, fines, and completion residue. The fines may be man-made or naturally occurring.
One aspect of the present invention is a downhole assembly for enhancing flow rates from a wellbore. The downhole assembly comprises: (1) a body for positioning within a production interval of the wellbore; and (2) a plurality of piezoelectric crystals interconnected to the body. Optionally, the piezoelectric crystals are interconnected to an exterior surface of the body. When the downhole assembly is positioned within the wellbore, at least one of the plurality of piezoelectric crystals expands or contracts in response to at least one of a change in temperature, a change in pressure, and a change in fluid flow rate in the wellbore.
In one embodiment, the piezoelectric crystals have predetermined sizes. In another embodiment, the plurality of piezoelectric crystals have sizes and frequencies selected based on characteristics of the wellbore including at least one of the depth, length, temperature, flow rate, hydraulic fracturing interval, reservoir permeability, formation type, and reservoir porosity.
In one embodiment, the body includes a bore defining an interior surface. Optionally, at least one piezoelectric crystal is interconnected to the interior surface of the body.
In another embodiment, a first subset of the plurality of piezoelectric crystals are selected to generate low frequencies when activated. Optionally, the low frequencies are between approximately 0.1 kHz to approximately 100 kHz when activated. Alternatively, the low frequencies may be between approximately 1 kHz to approximately 10 kHz when activated. In one embodiment, the first subset of the plurality of piezoelectric crystals are positioned on the exterior surface of the body.
Additionally, or alternatively, the downhole assembly may optionally include a second subset of the plurality of piezoelectric crystals which are selected to generate high frequencies when activated. In one embodiment, the high frequencies are between approximately 10 kHz and approximately 1 GHz when activated. In another embodiment, the high frequencies are between approximately 10 kHz and approximately 100 MHz when activated. Additionally, or alternatively, the second subset of the plurality of piezoelectric crystals may be positioned on an interior surface of the body.
In one embodiment, the body comprises a solid bar. Alternatively, the body comprises a mesh material. In one embodiment, the first subset of the piezoelectric crystals comprise a first material that exhibits piezoelectricity. Optionally, the second subset of the piezoelectric crystals comprise a second material that exhibits piezoelectricity.
The downhole assembly may further comprise a power source to provide electricity to the plurality of piezoelectric crystals. Optionally, the downhole assembly includes a controller operable to send a signal to activate and deactivate the plurality of piezoelectric crystals.
Another aspect is a method of enhancing a flow rate from a wellbore in a reservoir, comprising: (1) positioning a downhole assembly in a production interval of the wellbore, the downhole assembly generally including (i) a body; and (ii) piezoelectric crystals interconnected to the body; and (2) triggering at least one of the plurality of piezoelectric crystals. When triggered, the at least one piezoelectric crystal expands and/or contracts which causes fines in fractures of the reservoir move to repair and improve the permeability of a hydraulic reservoir proximate to the wellbore.
The method may further comprise flowing fluid from the wellbore. In this manner, the fines are flushed out of the fractures. In one embodiment, the at least one piezoelectric crystal is triggered by a change in a condition within the well bore. More specifically, in one embodiment, the at least one piezoelectric crystal is triggered by a change in one or more of a temperature, a pressure, and a rate of fluid flow in the wellbore.
Optionally, the body comprises a screen or a solid bar for placement in the wellbore. In one embodiment, a first subset of the piezoelectric crystals are operable to generate low frequencies. In one embodiment, the low frequencies generated by the piezoelectric crystals are between approximately 0.1 kHz to approximately 100 kHz. The downhole assembly may optionally include a second subset of the piezoelectric crystals which are operable to generate high frequencies. In one embodiment, the high frequencies generated by the piezoelectric crystals are between approximately 10 kHz to approximately 100 MHz.
The method may optionally include selecting at least one of a pattern, a size, and a frequency of the plurality of piezoelectric crystals. The pattern, size, and/or frequency of the piezoelectric crystals may be based on a characteristic of the wellbore and the reservoir. The method may further comprise selecting piezoelectric crystals of two or more different materials which exhibit piezoelectricity.
Another aspect of the present invention is a method for implementing a 4-D real-time stimulation application. The method comprises: (1) measuring various wellbore and reservoir conditions; (2) determining the changes in production and production related factors from these conditions; and (3) activating a piezoelectric crystal to clean damage from the wellbore and surrounding reservoir to improve production. In one embodiment, the piezoelectric crystal is positioned within a fracture of the reservoir. Optionally, the piezoelectric crystal is positioned within the wellbore. In another embodiment, the piezoelectric crystal is affixed to a downhole assembly positioned in the wellbore.
In one embodiment, a plurality of piezoelectric crystals are positioned in the wellbore. Individual piezoelectric crystals of the plurality of piezoelectric crystals may react differently to changes of pressure, temperature, and flow rate within the wellbore. For example, two piezoelectric crystals may react differently based on differences in their relative size, position within the wellbore or fractures, and differences in their materials. In one embodiment, a first one of the plurality of piezoelectric crystals generates a first frequency when activated. A second one of the plurality of piezoelectric crystals generates a second frequency when activated. By measuring frequencies generated by the piezoelectric crystals, changes in conditions within the wellbore and the fractures in the geologic formation can be determined and located.
Another aspect of the present invention is a method of utilizing acoustic waves in a wellbore. The acoustic waves create acoustic induced drag forces to transport proppants from the wellbore into fractures in the production interval of a well to encourage proper filling of the fracture with proppant. In this manner, the systems and methods of the present invention improve the proppant pack stability and maintenance of the fracture length, width and height throughout the lifecycle production. One method of creating these acoustic waves is by the use of piezoelectric crystals. The piezoelectric crystals may be mixed with the proppant and pumped into the well. Additionally, or alternatively, piezoelectric crystals can be attached to a downhole assembly positioned within the well. Optionally, the downhole assembly includes a screen. In one embodiment, piezoelectric crystals with different frequencies are interconnected to one or more of an inside surface and an outside surface of the screen.
Although generally referred to herein as piezoelectric “crystals,” it should be appreciated that the current invention may be used with any material which exhibits piezoelectricity. Accordingly, the term “piezoelectric crystals” as used herein refers to any type of material which exhibits piezoelectricity. The material may be natural or man-made. The material may be a crystal. Alternatively, the material may be a ceramic. In one embodiment, the piezoelectric crystals are selected to have a hardness that is greater than the proppants.
As used herein, the term “fracture” means a fracture in a reservoir of any type. The fracture may be hydraulically induced (or “man-made”) or an open, natural fracture.
Unless otherwise indicated, all numbers expressing quantities, dimensions, conditions, ratios, ranges, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about” or “approximately”. Accordingly, unless otherwise indicated, all numbers expressing quantities, dimensions, conditions, ratios, ranges, and so forth used in the specification and claims may be increased or decreased by approximately 5% to achieve satisfactory results.
The term “a” or “an” entity, as used herein, refers to one or more of that entity. As such, the terms “a” (or “an”), “one or more” and “at least one” can be used interchangeably herein.
The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Accordingly, the terms “including,” “comprising,” or “having” and variations thereof can be used interchangeably herein.
It shall be understood that the term “means” as used herein shall be given its broadest possible interpretation in accordance with 35 U.S.C., Section 112(f). Accordingly, a claim incorporating the term “means” shall cover all structures, materials, or acts set forth herein, and all of the equivalents thereof. Further, the structures, materials, or acts and the equivalents thereof shall include all those described in the Summary of the Invention, Brief Description of the Drawings, Detailed Description, Abstract, and Claims themselves.
The Summary of the Invention is neither intended, nor should it be construed, as being representative of the full extent and scope of the present invention. Moreover, references made herein to “the present invention” or aspects thereof should be understood to mean certain embodiments of the present invention and should not necessarily be construed as limiting all embodiments to a particular description. The present invention is set forth in various levels of detail in the Summary of the Invention as well as in the attached drawings and the Detailed Description and no limitation as to the scope of the present invention is intended by either the inclusion or non-inclusion of elements or components. Additional aspects of the present invention will become more readily apparent from the Detailed Description, particularly when taken together with the drawings.
The accompanying drawings, which are incorporated herein and constitute a part of the specification, illustrate embodiments of the invention and together with the Summary of the Invention given above and the Detailed Description given below serve to explain the principles of these embodiments. In certain instances, details that are not necessary for an understanding of the disclosure or that render other details difficult to perceive may have been omitted. It should be understood, of course, that the present invention is not necessarily limited to the particular embodiments illustrated herein. As will be appreciated, other embodiments are possible using, alone or in combination, one or more of the features set forth above or described below. For example, it is contemplated that various features and devices shown and/or described with respect to one embodiment may be combined with or substituted for features or devices of other embodiments regardless of whether or not such a combination or substitution is specifically shown or described herein. Additionally, it should be understood that the drawings are not necessarily to scale.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a well formed in a geologic formation;

FIG. 2A is an expanded schematic diagram of a downhole assembly of the present invention positioned within a horizontal segment of the wellbore of FIG. 1;

FIG. 2B is a cross-sectional view of the downhole assembly of FIG. 2A taken along line 2B-2B;

FIG. 3 is a schematic diagram of another embodiment of a downhole assembly of the present invention;

FIG. 4 is a cross-sectional view of the downhole assembly of FIG. 3 taken along line 4-4.

FIG. 5 is a schematic diagram showing piezoelectric crystals pumped together with proppants into a wellbore according to an embodiment of the present invention;

FIG. 6 is a side elevation view of a fracture into which proppants and piezoelectric crystals have been pumped;

FIG. 7 is an illustration of a mixture of proppant and piezoelectric crystals positioned in a section of casing and fractures extending from the casing into a geologic formation;

FIG. 8 is a schematic diagram similar to FIG. 2A and illustrating a downhole assembly positioned in a generally vertical portion of a wellbore and including piezoelectric crystals mixed with proppant in the wellbore and fractures of a geologic formation;

FIG. 9 illustrates forces acting on particles; and

FIGS. 10-12 are graphs of the detachment ratio of particles as a ratio of particles size for various frequencies.

A list of the various components shown in the drawings and associated numbering is provided herein:


Number	Component

1	Well
2	Vertical segment of well
3	Horizontal segment of well
4	Geologic formation
6	Fractures
8	Tip of fractures
10	Casing
12	Casing aperture
14	Proppant
16	Downhole assembly
18	Body
20	Longitudinal axis
22	Exterior surface
24	Hollow bore
26	Interior surface
28	Piezoelectric crystals
30	Power source (optional)
32	Control system (optional)

DETAILED DESCRIPTION

Referring now to FIG. 1, a schematic view of a well 1 formed in a geologic formation 4 is generally illustrated. The well 1 may include a segment 2 that is generally vertical and a segment 3 that is generally horizontal. The segments 2, 3 may be sloped or inclined at various angles. As will be appreciated by one of skill in the art, the well 1 can have a variety of orientations and any number of segments 2, 3.
A downhole assembly 16 is illustrated positioned in the generally horizontal segment 3. Although not illustrated, the downhole assembly 16 may also be positioned in the generally vertical segment 2. Optionally, one or more of a power source 30 and a control system 32 can be operably connected to the downhole assembly 16.
Referring now to FIGS. 2A-2B, an expanded view of a portion of the well 1 is illustrated with one embodiment of a downhole assembly 16 of the present invention generally illustrated within a horizontal segment 3 of the well. The downhole assembly 16 includes piezoelectric crystals 28 and is positioned in a horizontal well 1 while proppant 14 is injected. The downhole assembly 16 is configured to be positioned in a casing 10 positioned in a wellbore which extends into a geologic formation 4. The casing 10 includes a plurality of apertures 12, such as perforations or slots, which allow access to fractures 6 which extend into the reservoir formation 4. The wellbore casing 10 and fractures 6 are illustrated after being packed with a proppant 14. The fractures 6 may extend hundreds or thousands of feet from the casing 10.
The downhole assembly 16 generally includes a body 18. In one embodiment, the body 18 comprises a screen. The screen 18 can be a permanent screen for proppant pack placement and stimulation. Alternatively, the screen can be retrievable for use in another wellbore.
In one embodiment of the downhole assembly 16, a plurality of piezoelectric crystals 28 are attached to the body 18. Specifically, in one embodiment, the piezoelectric crystals 28 can be interconnected to an exterior surface 22 of the body. The piezoelectric crystals 28 are operable to create displacement and/or cavitation and acoustic streaming in a fluid when activated.
Optionally, the body 18 has a cylindrical shape extending along a longitudinal axis 20. In one embodiment, the downhole assembly body 18 is comprised of a mesh material similar to screens used in the wells to prevent sand production.
In one embodiment, the downhole assembly body 18 includes a hollow bore 24. The hollow bore includes an interior surface 26. A plurality of piezoelectric crystals 28 can optionally be interconnected to the interior surface 26.
The piezoelectric crystals 28 can optionally be substantially evenly spaced on one or more of the exterior and interior surfaces 22, 26 of the body 18. In another embodiment, the piezoelectric crystals 28 can have an uneven or random spacing. The spacing between the piezoelectric crystals 28 can be adjusted based on the type of reservoir, reservoir mineralogy and level of damage anticipated. Optionally, a group of piezoelectric crystals can be concentrated at a first portion of the body 18. A second portion of the body 18 may have fewer, or no, piezoelectric crystals 28 depending on the type of the reservoir and the damage to be removed. In this manner, the amount or location of cavitation generated by the downhole assembly 16 can be altered along the length or the diameter of the body 18.
Optionally, in one embodiment, the piezoelectric crystals 28 are of substantially the same size and shape. Alternatively, one or more of the piezoelectric crystals 28 may have a different size or a different shape than others of the piezoelectric crystals. Accordingly, the piezoelectric crystals 28 may or may not be the same size. By selecting piezoelectric crystals 28 of various sizes, the downhole assembly 16 can create a variety of wavelengths that will help detach fines and debris of different sizes from the proppant 14 and fractures 6. The piezoelectric crystals on the body 18 can be placed based on the desired cleanliness of the specific locations of the well.
In one embodiment, various sizes of piezoelectric crystals 28 can be interconnected to the downhole assembly 16 depending on the application. Optionally, the size of the piezoelectric crystals 28 is selected based on one or more of: (i) characteristics of the fractures 6, such as the length, width and height of the fractures; (ii) the density and distribution of the natural fractures; (iii) characteristics of the formation 4 including the compaction properties and strength of the formation; (iv) the petrophysical properties such porosity, permeability, grain size, pore throat size, formation mineralogy and texture; (v) the composition and characteristics of the reservoir fluid; and (vi) the type and petrophysical characteristics of the proppant pack including the proppant size used for packing, porosity, permeability of the proppant pack, and the fracturing fluid composition and characteristics.
In one embodiment, the piezoelectric crystals may be one of material. Alternatively, in another embodiment, downhole assembly 16 may include a plurality of piezoelectric crystals formed of two or more different materials which exhibit piezoelectricity. For example, the downhole assembly 16 may include a first plurality of piezoelectric crystals formed of a first piezoelectric material and a second plurality of piezoelectric crystals formed of a second piezoelectric material. In one embodiment, the first piezoelectric material may have a first hardness and the second piezoelectric material can have a second hardness.
Once the piezoelectric crystals 28 are interconnected to the downhole assembly, the downhole assembly 16 is positioned in the well 1 in sections where the proppant pack will be established. The downhole assembly 16 will create localized vacuums by cavitation during the proppant injection during the fracturing process. The process can be continued throughout the lifecycle of the well as needed. Utilizing the downhole assembly 16 with piezoelectric crystals 28 during the fracture stimulation process will aid in efficient proppant placement for an effective proppant pack from the tip 8 of the fractures 6 to the inside of the casing along the horizontal, inclined or vertical well.
The piezoelectric crystals 28 are triggered during the fracturing to transport the proppant deeper into the reservoir 4 into the tip 8 of the fractures. The piezoelectric crystals 28 trigger automatically based on the piezoelectric crystal properties and the change in pressure, temperature and flow rate within the well. More specifically, piezoelectric contraction and elongation as a result of pressure, temperature and/or flow rate changes cause one piezoelectric crystal 28 to deform neighboring proppants 14 and also other piezoelectric crystals 28. Accordingly, one piezoelectric crystal 28 can transfer electricity to other piezoelectric crystals 28 which activates the other piezoelectric crystals 28 for the continuous stimulation of the proppant pack.
When triggered, the piezoelectric crystals 28 expand and contract which helps efficiently place the proppants in the fractures. After the proppant is placed in the fractures, expansion and contraction of the piezoelectric crystals 28 will help maintain the conductivity and permeability of the fractures as close to initial levels when production started. The piezoelectric crystals 28 will continue whenever changes in one or more of pressure, temperature, and flow rates take place during the lifecycle of the well. When a stable flow rate and pressure are achieved, production from the well will continue until a change in pressure, temperature, or flow rate occurs due to damage of the proppant pack or reservoir. The change will trigger one or more of the piezoelectric crystals 28, causing elongation and/or contraction that stimulate the proppant pack. The stimulation prevents any blockage and damage in the proppant pack and/or formation resulting continuously self-stimulating reservoir to maintain the permeability as close to the initial permeability when the production begins. Fines are dislodged from the proppant pack and then removed from the well by fluid flow.
In one embodiment, the piezoelectric crystals 28 automatically activate in response to changes in conditions within the well. More specifically, changes in one or more of pressure, temperature, and flow rate can cause a piezoelectric crystal 28 to expand or contract automatically. The displacement and cavitation caused by pressure and temperature changes within the well cause the piezoelectric crystal 28 to expand and/or contract. The piezoelectric crystals 28 are self-powered a result of the created electric charge from the contraction or elongation. Accordingly, in one embodiment, no external source power is needed by the downhole assembly 16.
The expansion and contraction of one piezoelectric crystal 28 causes displacement of nearby particles, include proppant, other piezoelectric crystals 28, and fines within the well. The properties of the piezoelectric crystals allow the displacement of nearby piezoelectric crystals. By selecting multiple frequency piezoelectric crystals for the downhole assembly 16, different amounts of displacements can be created at different locations within the casing 10.
As the space is limited downhole, once one piezoelectric crystal 28 expands or contracts, then the displacement is transferred into the neighboring proppants, particles, and piezoelectric crystals 28. This displacement activates other piezoelectric crystals 28 in a chain reaction. Hence, the piezoelectric crystals 28 of the downhole assembly 16 may be continuously activated to clean the well for a long period of time or momentarily depending on the pressure, flow rate and/or thermal stability of the well.
The piezoelectric crystals 28 can be used to produce an acoustic force by a process that coverts electrical energy to mechanical energy and visa-versa. When piezoelectric crystalline matter is subjected to a mechanical force, the crystal becomes electrically polarized. Applied compressional and tensional forces on the crystalline matter generates voltages of opposite polarity, and in proportion to the applied force. Conversely, when piezo crystalline matter is exposed to an electric field, it is elongated or shortened according to the polarity of the field, and in proportion to the strength of the field. Therefore, piezoelectric crystals 28 mounted on the downhole assembly 16 in the wellbore create localized vacuums along the downhole assembly 16 by the piezoelectric crystal caused displacement (contraction and elongation) and in some cases cavitation when the piezoelectric crystal 28 elongates and shortens due to the electrical charge.
Cavitation usually occurs when a liquid is subjected to rapid changes of pressure. The pressure changes cause the formation of cavities in the liquid where the pressure is relatively low, such as during production of the well. When subjected to higher pressure, the voids implode and can generate a shock wave. Cavitation inception occurs when the local pressure falls sufficiently far below the saturated vapor pressure, a value given by the tensile strength of the liquid at a certain temperature. This displacement and/or cavitation creates additional drag forces which help prevent screen out of the proppant-fluid mixture, yet force the proppant-fluid mixture to propagate toward the tip 8 (or distal ends) of fractures 6, toward the space between the wellbore and the screen and all other vertical, deviated and horizontal fractures present in the reservoir. Cavitation is one part of the cleaning mechanism that may take place at a specific pressure and temperature with a specific fluid. The real cleaning is conducted through the particle detachment and carriage of the removed particles with the fluid in the fractures out of the fracture 6 into the wellbore and to the surface.
Spacing of the piezoelectric crystals 28 is important for the piezoelectric crystals 28 to effectively transfer their elongation and contraction to the nearest proppants for continuation of the movement and related stimulation and to accomplish the maintenance of permeability of the well and geologic formation. Accordingly, the location and spacing of the piezoelectric crystals 28 may be selected based on conditions in the wellbore.
Optionally, external power can be supplied to activate the piezoelectric crystals 28. Accordingly, in one embodiment, the downhole assembly 16 is interconnected to a power source 30. One or more of the piezoelectric crystals 28 may be interconnected to the power source. The power source 30 may comprise a battery positioned within the wellbore. Optionally, the battery may be associated with the downhole assembly 16. Additionally, or alternatively, the power source 30 may comprise a fiber optic line. In another embodiment, the power source 30 is a wireline to the surface.
In one embodiment, the piezoelectric crystals can be individually activated. In another embodiment, two or more of the piezoelectric crystals can be activated substantially simultaneously.
The piezoelectric crystals can also be activated in a pattern. For example, a first group of piezoelectric crystals 28 can be periodically activated. A second group of piezoelectric crystals can also be periodically activated. The periods of activation of the first and second groups can be the same or different. In one embodiment, piezoelectric crystals 28A positioned on the exterior surface of the downhole assembly 16 may be activated separately from piezoelectric crystals 28B positioned on the interior surface 26.
Optionally, the piezoelectric crystals 28 can be divided into any number of groups. In one embodiment, a piezoelectric crystal can be in more than one group. For example, a first group may comprise the odd numbered piezoelectric crystals along the length of the body 18. A second group can comprise the even numbered piezoelectric crystals. A third group may include every fifth piezoelectric crystal. Accordingly, the first piezoelectric crystal can be in the first and third groups. A fourth group may comprise piezoelectric crystals positioned on an exterior surface of the body and a fifth group can include piezoelectric crystals positioned within the hollow bore 24 of the body 18. In one embodiment, each group of piezoelectric crystals 28 can be independently activated. In this manner, the downhole assembly 16 may have five or more modes of operation, each mode creating different patterns, intensities, or locations of cavitation in fluid around the downhole assembly.
Piezoelectric crystals can also be grouped according to their position relative to a longitudinal axis 20 of the body 18. For example, a sixth group can include the piezoelectric crystals positioned above the longitudinal axis 20 as illustrated in FIG. 2. A seventh group can include the piezoelectric crystals positioned to the right of the longitudinal axis 20 when viewed in FIG. 2. Other groups of piezoelectric crystals are contemplated.
In one embodiment, a control system 32 is operable to activate one or more of the piezoelectric crystals. Optionally, the control system 32 is interconnected to the power source 30. More specifically, the control system 32 in one embodiment is configured to selectively supply power to one or more of the piezoelectric crystals 28 of the downhole assembly 16.
In one embodiment, the control system 32 of the present invention can assign the piezoelectric crystals 28 to one or more groups. In one embodiment, the control system 32 can assign the piezoelectric crystals 28 to the one or more groups based on one or more of a geometry of the fractures 6 and the formation 4 type.
In one embodiment, the piezoelectric crystals 28 are operable to generate predetermined frequencies when activated. The frequencies generated by the piezoelectric crystals 28 may be selected based on characteristics of one or more of the fractures 6 and the formation 4. For example, the piezoelectric crystals 28 can be selected to generate predetermined frequencies based on at least one of the length and the width of fractures in the geologic formation 4. Additionally, or alternatively, in another embodiment, one or more frequency generated by the piezoelectric crystals is based on the formation type. The frequencies of the piezoelectric crystal 28 may also be selected based on formation type and mineralogy, gas or oil production, and the in-situ stress characteristics.
Optionally, all of the piezoelectric crystals 28 generate the same frequency when activated. In one embodiment, at least some of the piezoelectric crystals generate low frequencies. The low frequencies may be in the low Hz to hundreds of Hz. Optionally, the low frequency piezoelectric crystals generate frequencies of between about 0.1 kHz to less than approximately 1 MHz when activated. In one embodiment, the low frequency piezoelectric crystals 28A are positioned on an exterior surface 22 of the downhole assembly 16. The low frequency piezoelectric crystals 28A generally aid in the cleaning of the proppants 14 within the fractures 6.
In another embodiment, at least some of the piezoelectric crystals 28 generate high frequencies. The high frequencies may vary between low Hz to MHz or hundreds of MHz. Optionally, the high frequency piezoelectric crystals generate frequencies of between about 10 kHz to less than approximately 1 GHz when activated. In another embodiment, the frequencies generated by the high frequency piezoelectric crystals is between about 100 Hz to about 10 MHz. Optionally, the high frequency piezoelectric crystals 28B are positioned within the hollow bore 24 of the body 18. In one embodiment, the high frequency piezoelectric crystals generally aid in cleaning the proppant within the screen 18 of the body of the downhole assembly 16.
The piezoelectric crystals 28 are selected depending on which frequency will work best for the specific formation and/or fracture network. Typically a range of frequencies will be beneficial since the fines and proppants causing damage or reducing the fracture conductivity are multi-sized. Different size of fines can be detached or displaced with different frequencies generated by vibrations of the piezoelectric crystals 28. Further, the material of the fines and other particles to be cleaned from the proppant 14 and the flow of the well may also be considered when selecting frequencies of the piezoelectric crystals 28. Methods of selecting piezoelectric crystals 28 of appropriate frequencies are described hereinafter.
One method of using the downhole assembly 16 includes cleaning the well 1 of drilling fluid, mud cake, and other drilling damage when the target distance for a vertical, deviated or horizontal drilling is reached. Then the downhole assembly 16 of the present invention is connected to the drill pipe, and placed within the vertical, deviated or horizontal well. In one embodiment, the diameter of the downhole assembly 16 is selected based on the target production from the well and the company production management procedures. In one embodiment, the diameter of the downhole assembly may be a diameter as large as the wellbore diameter when the downhole assembly 16 will be permanently placed in the wellbore. Alternatively, the diameter of the downhole assembly may be smaller than the wellbore diameter to allow for retrieval and reuse of the downhole assembly.
The downhole assembly 16 can be retrieved from the wellbore when continued production of the well is uneconomical. In this manner, the downhole assembly can be reused in other wells to reduce costs once. Alternatively, the downhole assembly can be permanently positioned in the wellbore. The permanent deployment of downhole assemblies 16 of the present invention is also economical as it provides a lifetime of reliable fracture stimulation eliminating the need for refracturing or other stimulation procedures. More specifically, because the piezoelectric crystals 28 will automatically expand and/or contract in response to conditions within the well, the downhole assembly 16 will continuously clean the proppant 14 without external power and without input from a technician at the well. Accordingly, the downhole assemblies of the present invention provide a reliable system to clean proppant and improve well productivity without external power or additional labor costs.
Referring now to FIGS. 3-4, another embodiment of a downhole assembly 16B of the present invention is generally illustrated. The downhole assembly 16B is similar to the downhole assembly 16A described in conjunction with FIGS. 2A-2B and includes many of the same, or similar, features. In addition, the downhole assembly 16B operates in a manner similar to the downhole assemble 16A. The downhole assembly 16B can be positioned in a well segment with any orientation, including a horizontal well segment 3 or a vertical well segment 2.
Notably, the downhole assembly 16B includes a body 18 that is solid. Piezoelectric crystals 28 are interconnected to an exterior surface 22 of the body 18. In one embodiment, one or more of a density, a diameter, and a material of the body 18 are selected based on the geometry of the fractures 6 or the formation 4 through which the wellbore is formed. More specifically, one or more of the density, the diameter, and the material of the body 18 can be selected to adjust the displacement and/or cavitation generated by the downhole assembly 16B and the piezoelectric crystals 28. In one embodiment, the body 18 comprises steel casing. Although not illustrated, the body 18 may optionally include a hollow bore the same as or similar to the hollow bore 24 illustrated in conjunction with FIGS. 2A-2B.
The downhole assembly 16 can be used to help displace (or transport) the proppant 14 further into the fractures 6 by utilizing the larger drag forces created by the induced acoustic streaming and acoustic cavitation. The downhole assembly 16 can be employed after the first fluid pad has been implemented, and that coupled with the drag forces introduced by the piezoelectric crystals 28 mounted on the body 18 results in the proppants 14 being displaced further into the fractures 6.
Referring now to FIGS. 5-7, in one embodiment of the present invention, piezoelectric crystals 28C are mixed with proppant 14. The mixture of piezoelectric crystals 28C and proppant 14 can subsequently be pumped into the well 1. The mixture of piezoelectric crystals 28C and proppant 14 can be pumped into the well during, or after, the fracturing operation. In one embodiment, the piezoelectric crystals 28C are mixed with the proppant in a fluid. In this manner, the piezoelectric crystals 28C are transported into the wellbore and into the hydraulically created and naturally existing connected fractures 6. In one embodiment, the fluid is a hydraulic fracturing fluid.
Similar to the piezoelectric crystals 28 used with the downhole assemblies 16 described herein, the piezoelectric crystals 28C may be of equal or varying sizes. In one embodiment, the piezoelectric crystals may be one of material. Alternatively, in another embodiment, the mixture of piezoelectric crystals and proppant may include a plurality of piezoelectric crystals formed of two or more different materials which exhibit piezoelectricity. For example, the mixture may include a first plurality of piezoelectric crystals formed of a first piezoelectric material and a second plurality of piezoelectric crystals formed of a second piezoelectric material. In one embodiment, the first piezoelectric material may have a first hardness and the second piezoelectric material can have a second hardness. Optionally, the first piezoelectric material may react to changes in temperature, pressure, and flow rate within the wellbore differently than the second piezoelectric material.
As generally illustrated, the piezoelectric crystals 28C may be transported to the tips 8 of the fractures 6. More specifically, the piezoelectric crystals 28C can be positioned in the fracture tips 8 outside of the well bore 1 and casing 10.
The size and frequencies of the piezoelectric crystals 28C are selected based on the natural fractures present, the hydraulic fracturing design and characteristics of the formation to be fractured and fractures. In one embodiment, the size and frequency of the piezoelectric crystals 28C as well as the concentration of the piezoelectric crystals 28C in the proppant pack is determined by the fracture volume, reservoir characteristics and in situ reservoir stress magnitudes to determine the level of increases and decreases in the stress and temperatures during the production.
The ratio of the piezoelectric crystals 28C to proppant 14 may also be selected based on the formation, well type, fracture characteristics, and other properties of the well and the proppant. In one embodiment, the piezoelectric crystals and proppant are mixed at approximately a 1:1 ratio by volume. In one embodiment, piezoelectric crystals comprise up to about 80% of the volume of the mixture of piezoelectric crystals and proppant. In another embodiment, the mixture comprises at least about 20% piezoelectric crystals by volume. In still another embodiment, the mixture comprises between about 20% and about 80% piezoelectric crystals and between about 80% and about 20% proppant by volume. In another embodiment, the mixture comprises between about 40% and about 60% piezoelectric crystals and between about 60% and about 40% proppant by volume. In still another embodiment, piezoelectric crystals comprise between about 45% and about 55% of the mixture and the proppant comprises between about 55% and about 45% of the mixture.
In one embodiment, the mixture comprises between about 0.20 wt. % and about 0.80 wt. % piezoelectric crystals and between about 0.20 wt. % and about 0.80 wt. % of a proppant material. In another embodiment, the mixture comprises between about 0.40 wt. % and about 0.60 wt. % piezoelectric crystals and between about 0.40 wt. % and about 0.60 wt. % of the proppant material. In still another embodiment, the mixture comprises between about 0.45 wt. % and about 0.55 wt. % piezoelectric crystals and between about 0.45 wt. % and about 0.55 wt. % of the proppant material.
The mixture of proppant and piezoelectric crystals may subsequently be added to a fluid, such as water or a hydraulic fracturing fluid. The fluid including the mixture of proppant and piezoelectric crystals can then be pumped into a wellbore.
Referring now to FIG. 8, in one embodiment of the present invention, piezoelectric crystals 28C can be mixed with the proppant 14 and pumped into the well 1. A downhole assembly 16A or 16B including additional piezoelectric crystals 28 may also be positioned within the well 1. Although the downhole assembly 16A and piezoelectric crystals 28C are illustrated in a generally vertical segment 2 of the well, as previously described, the downhole assembly 16A and piezoelectric crystals 28C may be positioned in any segment 2, 3 of a well 1.
One method of the present invention includes real-time monitoring of the quality of the proppant pack. More specifically, the proppant pack is monitored between the production interval of the wellbore and the downhole assembly 16 with the piezoelectric crystals 28, along with the proppant pack from the interior of a bore of the downhole assembly to the tip of the vertical/deviated/horizontal natural and induced fracture. This monitoring method may utilize existing fracture mapping techniques such as surface tiltmeter measurements, surface and/or in-well micro-seismic monitoring, or fiber optic monitoring from which the change in the dimensions of the fractures can be determined. The fiber optic monitoring may include one or more of Distributed Temperature Sensing (DTS), distributed acoustic sensing (DAS), Distributed Pressure Sensing (DTP), and others. When continuous stimulation using piezoelectric crystals is used, then the small displacements will be recorded providing information about any change taking place in the fracture dimensions that fracture conductivity is a function of.
The system and methods of the present invention are expected to eliminate the need for refracturing and reduce the associated water use and groundwater contamination risk. Thus, using a downhole assembly 16 including piezoelectric crystals 28 and real-time monitoring of the proppant pack placement, as well as repeated use of the piezoelectric crystal displacement and in some occasions acoustic cavitation induced by the fluctuations in the pressure and temperature in various corners of the proppant pack will result displacement of neighboring piezoelectric crystals and proppants that will not allow settlement and detachment of the fines or any debris received passing through with the produced fluids. Implementing this method and apparatus will also enhance economically viable production with the savings from continuous maintenance and refracturing needs and environmentally friendly production from tight gas sands, shale gas, tight oil and other conventional, deep-water and unconventional resource wells by allowing for higher production rates and reducing the need for refracturing operations.
The methods and apparatus of embodiments of the present invention can also be utilized in deep-water poorly consolidated high permeability reservoir completions. For example, the downhole assemblies 16 can be used in deep-water poorly consolidated reservoirs with gravel completions for efficient gravel packing prior, during, and post frac-pack operations throughout the lifecycle of deep-water and ultra-deep-water wells. The methods and apparatus could be employed during the frac-pack fracture stimulations of these reservoirs. This method and apparatus would help ensure effective gravel packing and would aid the removal of damage within the gravel pack due to the plugging of the pore throats and gas and water blocking through simultaneously pumping piezoelectric crystals of suitable size and frequencies when frac-pack operation is conducted.
Referring now to FIGS. 10-12, the frequencies of the piezoelectric crystals 28 may be selected based in part on characteristics of particles, such as fines, in the proppant or the formation. For the hydrodynamic problem for detachment of fines or particles from surfaces for cleaning, there is no net lift force acting on the particle. There is a tangential force (drag force) that is 1.7 times greater than the drag force created on a sphere in an unbounded medium. A torque is also exerted on the particle. The fluid velocity is evaluated at a distance R, the radius of the particle to be removed, away from the plane wall for calculating drag force:
F _D=1.7(6πμRu| _R)
Here “μ” is viscosity of the fluid, and “u” is the flowing fluid velocity. For a rolling mechanism, torque balance is evaluated as:
F _D *R=F _adhesion *a
can be used to calculate the critical hydrodynamic force at which particle detachment may occur. Here, F_adhesionis the Van der Waals force acting on the particle at equilibrium separation distance, and “a” is the contact radius for a particle calculated using the adhesion force as the body force causing deformation. The adhesion force is calculated considering the distance of separation at the contact zone as well as at the noncontact zone. The calculation of adhesion force and surface force at equilibrium condition is explained in detail in Tutuncu A. N., 1992, Velocity Dispersion and Attenuation of Acoustic Waves in Granular Sedimentary Media, PhD Dissertation, The University of Texas at Austin and Tutuncu A. N. and Sharma M. M., 1992, The influence of fluids on grain contact stiffness and frame moduli in sedimentary rocks, Geophysics, V. 57(12), 1571-1582.
$a^{3} = \frac{3 π}{4} [\frac{(1 - v_{1}^{2})}{π E_{1}} + \frac{(1 - v_{2}^{2})}{π E_{2}}] {RF}_{0},$
where ν₁and ν₂are Poisson's ratios for the spherical particles to be removed, E₁and E₂are the Young's moduli, and R=R₁R₂/(R₁+R₂), F0 is internal force applied from the Hertz theory. See Timoshenko, S., and Goodier, J. N., 1951, Theory of elasticity: McGraw-Hill Book Co.
FIG. 10 is a graph of the detachment ratio as a function of particle size for various frequencies for velocity amplitude u_o=0.1 cm/sec. FIG. 11 is a graph of the detachment ratio as a function of particle size for various frequencies for velocity amplitude u_o=10 cm/sec. FIG. 12 provides a graph of the detachment ratio as a function of particle size for various frequencies for velocity amplitude u_o=20 cm/sec.
The systems and methods described herein improve the transport and placement of proppants into fractures within the production interval of the wells during the hydraulic fracturing operations. The systems and methods of embodiments of the present invention enhance production from wells in conventional and unconventional formations, including tight gas sands, shale gas, tight oil, shale oil and others.
As explained herein, prior art acoustic stimulation tools available can only be used to eliminate some formation damage only very near to wellbore. The prior art acoustic stimulation tools are placed in the well through wireline or tubing and are only useful for eliminating damage near the wellbore. The effectiveness of these tools is strongly dependent on the frequency of the acoustic sensors used. Hence, in all prior art acoustic stimulation tools, the utilized frequencies are effective only up to a few inches from the wellbore resulting in cleaning of damaged proppant only very near to the wellbore. None of the prior art tools have been tested to assist proppant packing into fractures or with low frequencies as disclosed in this invention. Prior art tools are also all much less effective than the system and method of the present invention as the induced fractures in vertical, inclined and horizontal wells are typically designed and executed to be tens to hundreds of feet long with multiple stages over thousands of feet long in horizontal wells.
The systems and methods described in this disclosure can be implemented inside the wellbore along the entirety of the production interval with multiple frequencies. By coupling multiple frequency acoustic waves and piezoelectric induced mechanical elongation and shortening, the cleaning effects can propagate through the entire fracture and wellbore network and can clean damage from the proppant packed well. The fractures can be cleaned from the tip of the fractures into the wellbore. More specifically, the cleaning effects of the system and method of embodiments of the present invention are realized for the full length, or a predetermined portion of the length, of the production interval of a well. Additionally the entire length, or a substantial portion of the length, of the proppant packed fractures can be cleaned with downhole assembly of embodiments of the present invention. The downhole assembly of the present invention may be used in wells of any orientation, including horizontal wells, deviated wells, and vertical wells. Proppant in fractures of any type, such as vertical fractures, deviated fractures, and horizontal fractures can be cleaned using the downhole assembly or piezoelectric crystals pumped together with the proppants during the fracture treatment. The fractures can be one or more of induced fractures and open natural fractures. This cleaning helps to maintain the production interval damage-free for the lifecycle of the well.
Various sizes of piezoelectric crystals can be mixed with the proppant or interconnected on the downhole assembly. The size of the piezoelectric crystals may be selected and optimized based on one or more of: (i) the formation and fracture characteristics such as the length, width and height of the fractures; (ii) the density and distribution of the natural fractures; (iii) formation characteristics including the compaction properties and strength; (iv) the petrophysical properties such porosity, permeability, grain size, pore throat size, formation mineralogy and texture; (v) the composition and characteristics of the reservoir fluid; and (vi) the type and petrophysical characteristics of the proppant pack including the proppant size used for packing, porosity, permeability of the proppant pack, and the fracturing fluid composition and characteristics. Once piezoelectric crystals of appropriate sizes, shapes, and frequencies are selected, the piezoelectric crystals can be mixed with the proppant or interconnected to one or more surfaces of a downhole assembly 16. In one embodiment, the downhole assembly comprises one or more sections. The downhole assembly can be positioned in the well where the proppant pack will be established. When the proppant is pumped into the well, the downhole assembly will create displacement and/or cavitation during starting with the proppant injection during the fracturing process. The piezoelectric crystals 28 mixed in the proppant and/or connected to the downhole assembly 16 will activate (such as by expanding and contracting) throughout the lifecycle of the well as needed and based on conditions in the well. Utilizing the downhole assembly 16 with piezoelectric crystals during the fracture stimulation process will aid in efficient proppant placement for an effective proppant pack from the tip of the induced fractures to within the proppant packed wellbore along the horizontal, inclined or vertical well.
During the production phase of the well, rate of production, wellbore pressure, temperature near the wellbore region, and the conductivity of the proppant pack may be monitored in real time to detect any changes in relative permeability. Any changes in these monitored parameters will provide information on permeability decline. Triggering of the piezoelectric crystals 28 pumped simultaneously together with proppants (such as illustrated in FIGS. 5-8) and/or the piezoelectric crystals 28 of a downhole assembly 16 causes mechanical elongation or contraction of the piezoelectric crystals. Optionally, the piezoelectric crystals 28 may also be activated by an external power source. When shortening of the piezoelectric crystals occurs, it also results in cavitation. The cavitation creates drag forces allowing the cleanup treatment in the proppant pack and in the fracture to recover or improve the permeability in the fractures and in the proppant pack, thus improving productions rates
The piezoelectric crystals 28 can also be deployed with a range of sweeping frequencies. More specifically, a plurality of piezoelectric crystals 28 with different frequencies can be selected and positioned with customized spacing on a downhole assembly. The downhole assembly can thus be configured to remove any proppant damage induced from various fluids used as fracturing fluids, produced fluids including produced water, oil and gas, and fines and particles migrated from the formation into the proppant pack.
The downhole assembly 16 can optionally be reused, once a well is noted to be uneconomic, to reduce costs. The embodiment of the downhole assembly 16A having a body with screens 18 is generally more permanent and is also economical as it provides a lifetime of reliable fracture stimulation eliminating the need for refracturing or other stimulation procedures. The screen mounted with piezoelectric crystals can be designed to provide acoustic cavitation and/or acoustic streaming to aid in fluid flow when deposited near the wellbore region, when the fluid flow is hampered by increased viscosity due to lower temperatures near the wellbore.
This invention is not limited to the applications listed above. More specifically, the methods and downhole tools of the present invention can be used in any type of well which is formed in any geologic formation. Accordingly, the downhole tools and methods described herein can be utilized in deep-water poorly consolidated high permeability reservoir completions. The methods and apparatus can be employed during the frac-pack fracture stimulations of the deep-water reservoir. The method and apparatus of the present invention will also help ensure effective gravel packing and would aid in the removal of damage within the gravel pack due to the fines and particles migrating from the formation into the gravel pack, the plugging of the pore throats, and the gas and water blocking seen in offshore operations. Accordingly, embodiments of the invention will increase production by eliminating proppant pack porosity and permeability damage, and creating an effective proppant pack.
To provide additional background, context, and to further satisfy the written description requirements of 35 U.S.C. § 112, the following references are incorporated by reference herein in their entireties: (1) Beresnev I. A. and Johnson P. A., 1994, Elastic wave stimulation of oil production: A review of methods and results: Geophysics, 59(6), 1000-1017, available at https://library.seg.org/doi/abs/10.1190/1.1443645; (2) Birchak J. R., Ritter T. E., Mese A. I., van Batenburg D., Trainor W., Han W., Yoo K., Kusmer D., Proett M. A., van der Bas F., van der Sman P., Groenenboom J. and Zuiderwijk P., 2005, Acoustic stimulation method with axial driver actuating moment arms on tines, U.S. Pat. No. 7,216,738; (3) Harthy A., Abdulkadir R., Sipra I., 2005, Screen and Near-Wellbore Cleaning and Stimulation Tools Evaluation: Recent Experience in Well operation, SPE 89653, Proc. Coiled Tubing Conference and Exhibition, available at https://www.onepetro.org/conference-paper/SPE-89653-MS; (4) Malhotra M., Lehman E. R. and Sharma M. M., 2014, Proppant Placement Using Alternate-Slug Fracturing, SPE 163851, SPE Journal, V. 19, Issue 5, available at https://www.onepetro.org/journal-paper/SPE-163851-PA; (5) Mese A. I., Soliman M., Robison C., 2005, System and method for treating a fluid in a pipe, U.S. Patent App. Pub. No. 2005/0161081; (6) Liu Y., Gadde P. B. and Sharma M. M., 2006, Proppant Placement Using Reverse-Hybrid Frac, SPE 99580, Proc. SPE Gas Technology Symposium, Calgary, Alberta, Canada, available at https://www.scribd.com/document/334696773/SPE-99580-MS; (7) Soliman M., Mese A. I., Robison C. E., Birchak J. R., Rodney P. F., Han W., Shah V. V., Linyaev, E. J., Proett M. A., 2003, Method and apparatus for treating a wellbore with vibratory waves to remove particles therefrom, U.S. Pat. No. 6,619,394 (also published as PCT Pub. WO 2002/046572); (8) Tutuncu A. N. and Mese A. I., 2008, Experimental Investigation of Ultrasonic Cleaning of Drilling and Drill-In Fluids Damage in Berea Sandstone Cores, SEG 2008-1640, Proc. SEG Annual Meeting, available at https://www.onepetro.org/conference-paper/SEG-2008-1640; (9) Tutuncu A. N. and Roha R., 2008, An Experimental Study for Removal of Near-Wellbore Asphaltene Deposits Using Ultrasonics, SEG 2008-1719, Proc. SEG Annual Meeting, available at https://www.onepetro.org/conference-paper/SEG-2008-1719; (10) Tutuncu, A. N., and M. M. Sharma, 1994, Mechanisms of Colloidal Detachment in a Sonic Field: Paper 63e, Proc. 1st AIChE International Particle Technology Forum, 24-29; (11) Wong S. W., van der bas F., Zuiderwijk P., Birchak B., Han W., Yoo K. and van Batenburg D., 2004, High Power/High Frequency Acoustic Stimulation: A Novel and Effective Wellbore Stimulation Technology, SPE 84118, SPE Production and Facilities Journal, 183-188, available at https://www.onepetro.org/journal-paper/SPE-84118-PA; (12) Zhou J., Sun H., Qu Q., Guerin M. and Li L., 2014, Benefits of Novel Preformed Gel Fluid System in Proppant Placement for Unconventional Reservoirs, SPE 167774, Proc. SPE/EAGE European Unconventional Resources Conference and Exhibition, Vienna, Austria, available at https://www.onepetro.org/conference-paper/SPE-167774-MS; (13) U.S. Pat. No. 5,635,712; (14) U.S. Pat. No. 5,441,110; (15) U.S. Pat. No. 6,935,424; (16) U.S. Pat. No. 7,543,635; (17) U.S. Patent Pub. 2007/0215345; (18) U.S. Pat. No. 9,695,681; (19) U.S. Patent Pub. 2007/0193740; (20) PCT Publication WO2017/105426A1; (21) U.S. Pat. No. 8,646,483; (22) U.S. Pat. No. 6,609,067; (23) U.S. Pat. No. 7,653,488; (24) Iriarte J., Katsuki D. and Tutuncu A. N., 2017, Fracture Conductivity under Triaxial Stress Conditions, Chapter 16 in Hydraulic Fracture Modeling, Editor Yu-Shu Wu, ISBN 978-0-12-812998-2, Elsevier Gulf Professional Publishing, available at https://www.sciencedirect.com/science/article/pii/B9780128129982000163; (25) Iriarte J., Katsuki D. and Tutuncu A. N., 2018, Geomechanical, Geochemical and Permeability Monitoring in Fractured Niobrara Formation under Triaxial Stress State, SPE-189839, Proc. SPE Hydraulic Fracturing Conference, Woodland, Tex., available at https://www.onepetro.org/conference-paper/SPE-189839-MS; (26) Iriarte J., Katsuki D. and Tutuncu A. N., 2018, Geochemical and Geomechanical Changes Related to Rock-Fluid-Proppant Interactions in the Niobrara Formation, SPE-189536, Proc. SPE International Conference and Exhibition on Formation Damage Control, Lafayette, La., available at https://www.onepetro.org/conference-paper/SPE-189536-MS; (27) Tutuncu A. N., Bui B. T. and Suppachoknirun T., 2017, An Integrated Study for Hydraulic Fracture and Natural Fracture Interactions and Re-Fracturing in Shale Reservoirs, Chapter 10 in Hydraulic Fracture Modeling, Editor Yu-Shu Wu, ISBN 978-0-12-812998-2, Elsevier Gulf Professional Publishing, available at https://www.sciencedirect.com/science/article/pii/B9780128129982000102; (28) Tutuncu A. N., 1992, Velocity Dispersion and Attenuation of Acoustic Waves in Granular Sedimentary Media, PhD Dissertation, The University of Texas at Austin; (29) Tutuncu A. N. and Sharma M. M., 1992, The influence of fluids on grain contact stiffness and frame moduli in sedimentary rocks, Geophysics, V. 57(12), 1571-1582; (30) U.S. Pat. Pub. 2018/0100389; and (31) U.S. Pat. Pub. 2018/0134950.
The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limiting of the invention to the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiments described and shown in the figures were chosen and described in order to best explain the principles of the invention, the practical application, and to enable those of ordinary skill in the art to understand the invention.
While various embodiments of the present invention have been described in detail, it is apparent that modifications and alterations of those embodiments will occur to those skilled in the art. Moreover, references made herein to “the present invention” or aspects thereof should be understood to mean certain embodiments of the present invention and should not necessarily be construed as limiting all embodiments to a particular description. It is to be expressly understood that such modifications and alterations are within the scope and spirit of the present invention, as set forth in the following claims.

Claims

What is claimed is:

1. A downhole assembly for enhancing flow rates from a wellbore, comprising:

a body for positioning within a production interval of the wellbore; and

a plurality of piezoelectric crystals interconnected to the body, the piezoelectric crystals having predetermined sizes and being interconnected to an exterior surface of the body, wherein, when the downhole assembly is positioned within the wellbore, at least one of the plurality of piezoelectric crystals expands or contracts in response to at least one of a change in temperature, a change in pressure, and a change in fluid flow rate in the wellbore.

2. The downhole assembly of claim 1, wherein the body includes a bore defining an interior surface.

3. The downhole assembly of claim 2, wherein at least one piezoelectric crystal is interconnected to the interior surface of the body.

4. The downhole assembly of claim 1, wherein a first subset of the plurality of piezoelectric crystals generate low frequencies of between approximately 0.1 kHz to approximately 100 kHz when activated.

5. The downhole assembly of claim 4, wherein a second subset of the plurality of piezoelectric crystals generate high frequencies of between approximately 10 kHz and approximately 100 MHz when activated.

6. The downhole assembly of claim 5, wherein the first subset of the plurality of piezoelectric crystals are positioned on the exterior surface of the body and the second subset of the plurality of piezoelectric crystals are positioned on an interior surface of the body.

7. The downhole assembly of claim 1, wherein the body comprises at least one of a solid bar and a mesh material.

8. The downhole assembly of claim 1, further comprising a power source to provide electricity to the plurality of piezoelectric crystals.

9. The downhole assembly of claim 1, further comprising a controller operable to send a signal to activate and deactivate the plurality of piezoelectric crystals.

10. The downhole assembly of claim 1, wherein the plurality of piezoelectric crystals have sizes and frequencies selected based on characteristics of the wellbore including at least one of the depth, length, temperature, flow rate, hydraulic fracturing interval, reservoir permeability, formation type, and reservoir porosity.

11. A method of enhancing a flow rate from a wellbore in a reservoir, comprising:

positioning a downhole assembly in a production interval of the wellbore, the downhole assembly including:

a body; and

piezoelectric crystals interconnected to the body, a first subset of the piezoelectric crystals operable to generate low frequencies and a second subset of the piezoelectric crystals operable to generate high frequencies; and

triggering at least one of the plurality of piezoelectric crystals, wherein the at least one piezoelectric crystal expands and/or contracts which causes fines in fractures of the reservoir to repair and improve the permeability of a hydraulic reservoir proximate to the wellbore.

12. The method of claim 11, further comprising flowing fluid from the wellbore to flush the fines out of the fractures.

13. The method of claim 11, wherein the at least one piezoelectric crystal is triggered by a change in one or more of a temperature, a pressure, and a rate of fluid flow in the wellbore.

14. The method of claim 11, further comprising selecting at least one of a pattern, a size, and a frequency of the plurality of piezoelectric crystals based on a characteristic of the wellbore and the reservoir.

15. The method of claim 11, wherein the body comprises a screen or a solid bar for placement in the wellbore.

16. A method of enhancing the production of a hydrocarbon reservoir, comprising:

providing a wellbore extending a predetermined length and depth in the hydrocarbon reservoir;

providing a fluid which includes a proppant material and a plurality of piezoelectric crystals; and

pumping the fluid into the wellbore, wherein at least one of the plurality of piezoelectric crystals contracts in response to conditions within the wellbore.

17. The method of claim 16, wherein at least one of the plurality of piezoelectric crystals is transported into a fracture in the hydrocarbon reservoir.

18. The method of claim 16, wherein the plurality of piezoelectric crystals generate frequencies of between approximately 0.1 kHz and approximately 1 GHz when activated.

19. The method of claim 16, wherein the piezoelectric crystals comprise up to approximately 80% by volume of the fluid.

20. The method of claim 16, wherein the at least one of the plurality of piezoelectric crystals contracts in response to a reduction of at least one of a fluid temperature, a fluid pressure, and a rate of fluid flow.