CN111088972A - Hydraulic fracturing production increasing method and target fracturing construction parameter selection method - Google Patents
Hydraulic fracturing production increasing method and target fracturing construction parameter selection method Download PDFInfo
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- CN111088972A CN111088972A CN201911364001.3A CN201911364001A CN111088972A CN 111088972 A CN111088972 A CN 111088972A CN 201911364001 A CN201911364001 A CN 201911364001A CN 111088972 A CN111088972 A CN 111088972A
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/25—Methods for stimulating production
- E21B43/26—Methods for stimulating production by forming crevices or fractures
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B47/00—Survey of boreholes or wells
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B49/00—Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
- G01N3/10—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces generated by pneumatic or hydraulic pressure
- G01N3/12—Pressure testing
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0014—Type of force applied
- G01N2203/0016—Tensile or compressive
- G01N2203/0019—Compressive
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/003—Generation of the force
- G01N2203/0042—Pneumatic or hydraulic means
- G01N2203/0048—Hydraulic means
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0058—Kind of property studied
- G01N2203/006—Crack, flaws, fracture or rupture
- G01N2203/0067—Fracture or rupture
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/02—Details not specific for a particular testing method
- G01N2203/06—Indicating or recording means; Sensing means
- G01N2203/067—Parameter measured for estimating the property
- G01N2203/0676—Force, weight, load, energy, speed or acceleration
Abstract
The application provides a hydraulic fracturing production increasing method and a method for selecting target fracturing construction parameters, wherein the hydraulic fracturing production increasing method comprises the following steps: punching a rock core obtained by sampling a target reservoir to form an eyelet in the rock core; carrying out a core alternating hydraulic fracturing experiment by combining a ground stress field of a target reservoir, applying alternating water pressure to an eyelet of a core to carry out hydraulic fracturing, and selecting target fracturing construction parameters, wherein the target fracturing construction parameters comprise: alternating water pressure frequency, alternating water pressure amplitude and radial well parameters; a windowing pipe channel is put into the target reservoir, and holes are formed in the wall of the casing to complete casing windowing; pulling out the windowing pipe, putting the windowing pipe into a drilling tool, and drilling branch radial holes at the windowing position of the casing pipe; and injecting a fracturing fluid with alternating water pressure into the branch radial holes by combining the selected target fracturing construction parameters to form alternating load on the fracture surface. The application can reduce the frictional resistance of the crack surface, reduce the fracture pressure, realize the slow activation of the natural crack and reduce the risk of inducing the earthquake.
Description
Technical Field
The application relates to the field of unconventional oil and gas reservoir exploitation, in particular to a hydraulic fracturing production increasing method and a target fracturing construction parameter selecting method.
Background
The international petroleum industry recognizes that the efficient exploitation of unconventional oil and gas from "whetstones" is an important development direction and a worldwide problem in the twenty-first century, and the technical advancement of the international petroleum industry becomes an important mark for measuring the national oil and gas exploitation level. The core key of safe and efficient extraction of unconventional oil and gas is that a complex artificial three-dimensional fracture system and effective communication and full reservoir coverage are manufactured in an unconventional oil and gas reservoir with the well depth of thousands of meters by a hydraulic fracturing technology.
In recent years, horizontal well drilling and large-scale hydraulic fracturing well completion technologies are used as the most common technical means for the current unconventional oil and gas scale exploitation, and a modern fracturing production-increasing well completion mode represented by 'long horizontal well section, multi-cluster perforation bridge plug staged fracturing, thousand square sand cubic liquid and industrial operation' prompts the United states to realize 'shale gas revolution', and China also makes great progress in unconventional oil and gas exploration and development of shale gas, dense gas and the like. However, at present, the development effects of unconventional oil and gas resources are uneven, the ecological risk is high, safe and efficient exploitation still faces major challenges, and the following problems mainly exist:
1) fracturing completion operations are costly. Taking the medium petrochemical Ronwei shale gas block as an example, the drilling and completion period required by the vertical depth of a horizontal well of 3800m and the horizontal section length of 1500m is more than 90 days, the operation cost is about 5700 ten thousand yuan, and the total mining cost is more than 60%.
2) The fracture transformation has poor pertinence. The important characteristic of the unconventional compact reservoir is that rock compaction is extremely low in permeability and almost has no natural energy, but weak faces such as bedding, shale, natural fractures and the like are relatively developed and are the material basis for forming a fracture network. At present, the purpose of efficiently activating the natural weak surface is difficult to achieve by a large-displacement, large-liquid-volume and continuous pressure fracturing mode, and the improvement effectiveness is uneven.
3) The ecological environmental protection risk is high. The fracturing of a single well consumes tens of thousands of water, the fracturing flow-back fluid is still difficult to realize complete harmless treatment and recycling, the treatment cost is high (70-120 yuan/m 3 wastewater), and simultaneously, the risk of inducing earthquake exists in the large-energy injected liquid.
It should be noted that the above background description is only for the sake of clarity and complete description of the technical solutions of the present invention and for the understanding of those skilled in the art. Such solutions are not considered to be known to the person skilled in the art merely because they have been set forth in the background section of the invention.
Disclosure of Invention
In order to solve at least one technical problem, the application provides a hydraulic fracturing production increasing method and a target fracturing construction parameter selecting method, which can reduce the frictional resistance of a fracture surface, thereby reducing the fracture pressure, realizing the slow activation and slow energy release of a natural fracture, and reducing the risk of inducing an earthquake.
In order to achieve the above object, the technical solution provided by the present application is as follows:
a hydraulic fracture stimulation method, comprising:
punching a rock core obtained by sampling a target reservoir, wherein an eyelet is formed in the rock core;
carrying out a core alternating hydraulic fracturing experiment by combining the crustal stress field of the target reservoir, applying alternating water pressure to the hole of the core for hydraulic fracturing, and selecting target fracturing construction parameters, wherein the target fracturing construction parameters comprise: alternating water pressure frequency, alternating water pressure amplitude and radial well parameters;
a windowing pipe channel is put into the target reservoir, and holes are formed in the wall of the casing to complete casing windowing;
pulling out the windowing pipe, putting the windowing pipe into a drilling tool, and drilling a branch radial hole at the windowing position of the casing pipe;
and injecting fracturing fluid with alternating water pressure into the branch radial holes by combining the selected target fracturing construction parameters to form alternating load on the fracture surface.
As a preferred embodiment, the radial well parameters include: radial well length and radial well branch number; in the step of drilling a branched radial bore, comprising: radial boreholes of a predetermined length and a predetermined number of branches are drilled in the target reservoir in a direction perpendicular or horizontal to the main wellbore.
As a preferred embodiment, the developing core alternating hydraulic fracturing test further comprises:
measuring the permeability and seismic energy of the fracturing fluid after each core alternating hydraulic fracturing experiment;
changing the experiment working condition, carrying out the experiment of multi-group core alternating hydraulic fracturing, and finally determining the target fracturing construction parameters according to the permeability of the fracturing fluid and the seismic energy measured after each experiment.
In a preferred embodiment, the alternating water pressure frequency in the target fracturing construction parameters is 0.1-10 Hz.
In a preferred embodiment, the ground stress field comprises a minimum principal ground stress and a maximum principal ground stress, the alternating water pressure in the target fracturing construction parameters is 60% -80% of the minimum principal ground stress, and the amplitude of the alternating water pressure is 5 MPa.
As a preferred embodiment, the hydraulic fracture stimulation method further comprises: based on continuous medium mechanics, rock dynamics and a finite difference method, a hydraulic fracturing dynamic and static stress response numerical model is established by using discrete element software, numerical simulation of core alternating hydraulic fracturing is carried out, and the target fracturing construction parameters are verified.
As a preferred embodiment, the step of injecting a fracturing fluid with alternating hydraulic pressure into the branched radial bores comprises: and after the alternating hydraulic fracturing is carried out on the branch radial holes for the first preset time, stopping injecting the fracturing fluid, and after the second preset time, carrying out the alternating hydraulic fracturing.
In a preferred embodiment, the first predetermined time is 1 to 2 weeks, and the second predetermined time is 1 to 2 days.
As a preferred embodiment, the hydraulic fracture stimulation method further comprises: and (3) lowering the detector into a target reservoir through a coiled tubing, and monitoring the activation condition of the natural fracture through the micro-earthquake.
A method for selecting target fracturing construction parameters comprises the following steps:
punching a rock core obtained by sampling a target reservoir, wherein an eyelet is formed in the rock core;
carrying out a core alternating hydraulic fracturing experiment by combining the crustal stress field of the target reservoir, applying alternating water pressure to the hole of the core for hydraulic fracturing, and selecting fracturing construction parameters, wherein the target fracturing construction parameters comprise: alternating water pressure frequency, alternating water pressure amplitude and radial well parameters;
measuring the permeability and seismic energy of the fracturing fluid after each core alternating hydraulic fracturing experiment;
changing the experiment working condition, carrying out the experiment of multi-group core alternating hydraulic fracturing, and finally determining the target fracturing construction parameters according to the permeability of the fracturing fluid and the seismic energy measured after each experiment.
The conventional hydraulic fracturing method has poor improvement effect and serious fracturing fluid leakage. From the microscopic characterization, the surface of the fracture surface has dense hemp micro-convex bodies, so that the fracture surface has high frictional resistance, and the fracture surface is difficult to form shear fractures and tensile fractures through conventional hydraulic fracturing. The invention aims at effectively activating weak surfaces such as open bedding, shale, natural cracks and the like, simultaneously has low liquid amount, low discharge capacity and cyclic injection, improves the complexity of the seam network, reduces the water consumption and reduces the risk of ecological environment. The application provides a hydraulic fracturing production increase method utilizes alternating load activation natural weak face, can adopt certain method to convert continuous rivers into oscillating water flow, applys the alternating water pressure of certain frequency and amplitude to the fracture face, and the alternating load of applying can induce the fracture unstability to promote natural weak face shear slip, the fracture self-supporting is expected to realize the effective activation of natural weak face and improve the oil gas reservoir permeability by a wide margin.
According to the hydraulic fracturing production increasing method and the selection method of the target fracturing construction parameters, fracturing fluid with alternating water pressure is injected into drilled branch radial holes, and alternating load on fracture surfaces is formed. Compared with the conventional reconstruction method, the method adopts constant hydraulic pressure fracturing to facilitate the shearing and expansion of natural fractures. The main manifestations are as follows:
(1) when the alternating water pressure fractures the fracture surface, the alternating water pressure acts on the micro-convex bodies on the surface of the fracture surface and forms a normal load. When the normal load changes in an alternating reciprocating way, the contact state of the normal load and the microprotrusions on the surface of the crack surface changes continuously along with the change of alternating water pressure, and 'jump shearing' is generated. In the mutual shearing process of the concave-convex body between the upper surface and the lower surface of the crack, alternating hydraulic power continuously jumps between the upper surface and the lower surface of the concave-convex body along with the continuous injection of fracturing fluid. Therefore, the upper surface of the concave-convex body has reciprocating loosening-pressing-loosening action, the fatigue failure effect is generated, the frictional resistance of the surface of the crack is reduced, the shearing strength of the crack surface is reduced, and the shear crack is easier to form.
(2) During the injection of alternating water pressure, the fracture undergoes a change from high to low effective positive stress during one cycle of the alternating water pressure, so that the stress is released slowly. This stress relaxation process can lead to pressure diffusion and the release of some of the strain energy and seismic energy stored in the rock mass. And alternating water pressure acts on the surface of the fracture in a reciprocating manner to enable the surface concave-convex body to generate fatigue damage, induce surrounding strata to generate a complex micro-fracture system, generate a small-scale stress triggering earthquake effect on unactivated natural fractures, and increase the permeability of the fracturing fluid.
(3) The hydraulic fracturing production increasing method provided by the embodiment of the application has the characteristic of moderate transformation. The contact state of the microprotrusions on the rough fracture surface is continuously changed by the alternating fluid pressure, and compared with a conventional constant water pressure fracturing method, the direct grinding damage of the microprotrusions is reduced. In the process of activating natural fractures, the energy of the stratum can be slowly released, the seismic energy is reduced, and the risk of inducing earthquakes is reduced.
Specific embodiments of the present application are disclosed in detail with reference to the following description and drawings, indicating the manner in which the principles of the application may be employed. It should be understood that the embodiments of the present application are not so limited in scope.
Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments, in combination with or instead of the features of the other embodiments.
It should be emphasized that the term "comprises/comprising" when used herein, is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps or components.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without inventive labor.
FIG. 1 is a flow chart of a hydraulic fracture stimulation method provided by an embodiment of the present application;
FIG. 2 is a graph comparing stress disturbance to fracture face formation by a hydraulic fracturing stimulation method provided by embodiments of the present application with a conventional hydraulic fracturing method;
FIG. 3 is a graph comparing the alternating water pressure and constant normal load shear friction characteristics under low frequency conditions as provided by the examples of the present application.
Detailed Description
While the invention will be described in detail with reference to the drawings and specific embodiments, it is to be understood that these embodiments are merely illustrative of and not restrictive on the broad invention, and that various equivalent modifications can be effected therein by those skilled in the art upon reading the disclosure.
It will be understood that when an element is referred to as being "disposed on" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and the like as used herein are for illustrative purposes only and do not denote a unique embodiment.
The invention provides a hydraulic fracturing production increasing method for realizing safe and effective activation of natural fractures in unconventional oil and gas reservoirs. The hydraulic fracturing production increase method provided by the embodiment of the application is mainly applied to unconventional reservoirs, and by injecting the fracturing fluid with alternating water pressure into the drilled branch radial holes, the alternating load on the fracture surface is formed, and compared with the conventional modification method in which constant water pressure fracturing is adopted, the method is easier to shear and expand natural fractures. It should be noted that the hydraulic fracturing stimulation method provided by the embodiment of the present application may be applied to a horizontal well section, and may also be applied to a vertical well section, and a specific application scenario is not particularly limited.
As shown in fig. 1, the hydraulic fracture stimulation method includes the following steps:
s1: punching a rock core obtained by sampling a target reservoir, wherein an eyelet is formed in the rock core;
s2: carrying out a core alternating hydraulic fracturing experiment by combining the crustal stress field of the target reservoir, applying alternating water pressure to the hole of the core for hydraulic fracturing, and selecting target fracturing construction parameters, wherein the target fracturing construction parameters comprise: alternating water pressure frequency, alternating water pressure amplitude and radial well parameters;
s3: a windowing pipe channel is put into the target reservoir, and holes are formed in the wall of the casing to complete casing windowing;
s4: pulling out the windowing pipe, putting the windowing pipe into a drilling tool, and drilling a branch radial hole at the windowing position of the casing pipe;
s5: and injecting fracturing fluid with alternating water pressure into the branch radial holes by combining the selected target fracturing construction parameters to form alternating load on the fracture surface.
In this specification, before step S1, an unconventional hydrocarbon dessert reservoir with natural fracture development is selected by comprehensively using data such as earthquake, well logging, numerical reservoir simulation, and the like. And then drilling a well into the target reservoir, and acquiring the ground stress field and sampling of the target reservoir. The drilling method is prior art and will not be described in detail in this application. The ground stress field comprises vertical stress caused by the weight of the overlying rock mass controlled by gravity and tectonic stress controlled by the tectonic movement of the crust. Wherein the tectonic stress comprises two horizontal stress components, a maximum principal stress and a minimum principal stress, respectively. Normally, a natural fracture that propagates after fracturing will extend in a direction perpendicular to the least principal stress, i.e., in a direction parallel to the most principal stress. The measurement method of the ground stress field can adopt a direct measurement method, such as: hydraulic fracturing, acoustic emission, and the like, indirect measurements may also be used, such as: pore wall strain method, etc. In some embodiments, when measuring the crustal stress field of a target reservoir using a hydraulic fracturing method, a section of the wellbore is sealed off with an expandable rubber packer and then pressurized by pumping in liquid while recording the change in hydraulic pressure over time. When the pressure is increased to the point that the wall rock body of the well is broken, the pressure is reduced, the pressure is stopped after stabilizing the pressure for a period of time, and the test is finished after the pressure is reduced to a certain value. And drawing a pressure-time relation curve according to the test result, and calculating the ground stress value according to the elastic mechanics theory.
In the specification, the geostress field of the target reservoir and the core sampling are not in a clear sequence, and after the well is drilled to the target reservoir, the geostress field can be measured firstly and then the sampling is carried out; or sampling first and then measuring the ground stress field; alternatively, sampling and measuring the ground stress field may be performed simultaneously, and the application is not limited thereto.
In step S1, the obtained core is perforated such that perforations are formed in the core. Step S1 is for simulating a step of drilling a radial hole in the target reservoir. The bore formed in the core is used to simulate a radial multilateral well to be drilled in a target reservoir. And then carrying out a core alternating hydraulic fracturing experiment in combination with the ground stress field of the target reservoir, and applying alternating water pressure to the hole of the core to carry out hydraulic fracturing, so that target fracturing construction parameters for carrying out hydraulic fracturing in the target reservoir are selected. The target fracturing construction parameters include: alternating water pressure frequency, alternating water pressure amplitude and radial well parameters.
Specifically, in step S2, the alternating hydraulic fracturing experiment performed on the core is a multi-group experiment performed by changing an experiment condition, the experiment condition may be determined according to the obtained ground stress field, and the experiment condition refers to different fracturing construction parameters, including: different alternating water pressure frequency working conditions, different alternating water pressure amplitude working conditions and different radial well parameter working conditions. In this specification, the pressure of the alternating water pressure does not in principle exceed the original formation stress of the target reservoir. The alternating water pressure frequency, the alternating water pressure amplitude and the radial well are used as variables, and a plurality of groups of experiments of core alternating hydraulic fracturing can be carried out, namely, the alternating water pressure is applied to the core hole to carry out the hydraulic fracturing. In some specific embodiments, a pulse servo fatigue testing machine, an acoustic emission instrument and other equipment can be adopted to design and develop an alternating hydraulic fracturing experiment on the core, and the fracture shear and permeability increasing characteristic of the core under the action of alternating water pressure can be researched.
When alternating fluid pressure acts on the fracture surface, the contact state of the microprotrusions on the fracture surface is changed continuously, and a stress disturbance formed on the fracture surface by the alternating hydraulic fracturing method of the embodiment of the application and the conventional hydraulic fracturing method is shown in a comparison graph in fig. 2. As can be seen from fig. 2, the normal load is created by alternating water pressure acting on the microprotrusions on the fracture face surface. The normal load is subjected to alternating reciprocating change along with the flowing of alternating water pressure to form alternating load on a crack surface, the contact state of the alternating load and the micro-convex bodies on the surface of the crack surface is continuously changed along with the change of the alternating water pressure, and jump shearing is generated, namely, alternating water power continuously jumps between the upper surface and the lower surface of the concave-convex bodies along with the continuous injection of fracturing fluid in the mutual shearing process of the concave-convex bodies between the upper surface and the lower surface of the crack. Therefore, the upper surface of the concave-convex body has reciprocating loosening-pressing-loosening action, the fatigue failure effect is generated, the friction resistance on the surface of the crack is reduced, the shearing strength of the crack surface is reduced, the shearing slippage is promoted, and the shearing crack is easier to form. By adopting the conventional constant hydraulic fracturing method, constant normal load can be formed by the constant water pressure acting on the microprotrusions on the surface of the fracture surface, the contact state of the constant normal load and the microprotrusions on the surface of the fracture surface cannot be changed, and the constant normal load is represented as direct grinding damage to the microprotrusions on the fracture surface, so that no shear stress is formed, and thus no shear fracture can be formed.
The alternating water pressure acts on the fracture surface of the rock core and can generate stress disturbance, the effective stress of the fracture surface can be reduced by mutual superposition of the fluid pressure and the original ground stress, and therefore the alternating water pressure can change the original formation stress distribution and can effectively activate the fracture. In step S2, the developing a core alternating hydraulic fracturing experiment further comprises: measuring the permeability and seismic energy of the fracturing fluid after each core alternating hydraulic fracturing experiment; changing the experiment working condition, carrying out the experiment of multi-group core alternating hydraulic fracturing, and finally determining the target fracturing construction parameters according to the permeability of the fracturing fluid and the seismic energy measured after each experiment.
In the step, alternating water pressure is applied to the original stratum, the stratum is subjected to capacity expansion after shearing and dislocation, a plurality of effective seepage channels are formed in the stratum, fracturing fluid permeates into the seepage channels, the flow conductivity of the fluid is improved, and therefore the oil gas yield can be improved. Therefore, the permeability of the fracturing fluid after each alternating hydraulic fracturing experiment can be obtained, the oil gas yield corresponding to the experimental working condition of the experiment can be reflected, and the target fracturing construction parameters can be determined through the obtained permeability of the maximum fracturing fluid. Furthermore, the seismic energy correspondingly generated under the experimental condition can be reflected by measuring the seismic energy after each alternating hydraulic fracturing experiment, the target fracturing construction parameters are determined by combining the acquired seismic energy and the acquired permeability of the fracturing fluid, and the safety of hydraulic fracturing is ensured. In this specification, the determined standard of the target fracturing construction parameter is the maximum permeability of the fracturing fluid and the minimum seismic energy, and through comparison of the experimental results of each time, the optimum alternating water pressure amplitude, the alternating water pressure frequency and the radial well parameter corresponding to the maximum permeability of the fracturing fluid and the minimum seismic energy can be preferably selected.
In this specification, the radial well parameters include: radial well length and radial well branch number. In the development of the core alternating hydraulic fracturing experiment, the experiment working conditions can also comprise different radial well length working conditions and different radial well branch number working conditions, correspondingly, multiple groups of experiments of core alternating hydraulic fracturing are developed by changing the length of core holes and the number of the core holes, and the radial well parameters are optimized. When alternating water pressure acts on the surface of a natural fracture, the stress field distribution of the fracture surface can be changed, and the natural fracture expansion tendency in the alternating shearing process can be influenced by the alternating water pressure frequency and the alternating water pressure amplitude in the fracturing construction parameters, the length of a radial well and the branch number of the radial well, so that the formation stress is influenced. And determining the optimal radial well parameters through the ground stress field after stress disturbance caused by the alternating water pressure obtained by carrying out multiple groups of experiments.
In a preferred embodiment, the frequency of the alternating water pressure in the target fracturing construction parameters is 0.1-10 Hz. The alternating water pressure in the embodiment is in a low-frequency condition, and the alternating shear damage of the alternating water pressure to the formation of the crack surface microprotrusions can generate powder to form a surface lubricating layer to promote shear slip. Experimental research results show that under the low-frequency condition of 0.1-10 Hz, the alternating shearing has lower friction response compared with the constant normal load, and the friction coefficient can be effectively reduced by the alternating shearing as shown in the experimental results of the alternating normal stress and the constant normal stress shown in figure 3. In addition, alternating water pressure during injection, the fracture undergoes effective positive stress changes from high to low during one cycle of alternating water pressure.
In this embodiment, the alternating water pressure is a low frequency condition, so that the stress can be slowly released when undergoing a change from high to low, and this stress relaxation process can lead to pressure diffusion and release of some of the strain energy and seismic energy stored in the rock mass. Compared with the traditional constant-pressure hydraulic fracturing method, the constant normal load can not effectively relax the stress, and sudden geological disasters can be caused in the environment with complex and fragile geological conditions. The natural crack can suitably be reformed transform to the alternating water pressure of this application embodiment, the reciprocating effect of alternating water pressure makes the surperficial concave-convex body produce fatigue failure on the crack surface, the induced surrounding stratum produces complicated microfracture system, produce the "stress triggering earthquake" effect of small-scale to unactivated natural crack, natural crack can slowly expand, thereby increase the permeability of fracturing fluid, the fracturing fluid can slowly infiltrate in the seam along with the expansion of crack, effectively improve the water pressure in the seam, the leakage phenomenon can be alleviated.
In a preferred embodiment, the alternating water pressure is 60% to 80% of the minimum principal ground stress and the amplitude of the alternating water pressure is 5 MPa. In this embodiment, shear cracks can be created when the alternating water pressure is less than the minimum principal stress. In order to effectively activate natural fractures, promote shear slippage thereof and increase the permeability of the fracturing fluid. Preferably, the alternating water pressure is 60% to 80% of the least principal stress.
Further, in the present specification, the hydraulic fracture stimulation method may further include: based on continuous medium mechanics, rock dynamics and finite difference methods, a hydraulic fracturing dynamic and static stress response numerical model is established by using discrete element software, and alternating hydraulic fracturing numerical simulation research is carried out on a rock core, so that the optimized fracturing construction parameters are verified. In this step, the geostress field of the target reservoir serves as a boundary stress condition for numerical simulation. In addition, the operation and modeling and selection of the numerical simulation study will not be described in detail in this application.
In step S3, a windowing pipe is lowered into the target reservoir and perforated on the casing wall, completing the casing windowing operation. The windowing pipe string can comprise a steering gear, a continuous pipe, a downhole screw motor and a flexible punch, wherein the downhole screw motor drives the flexible punch to rotate, holes are formed in the wall of the casing pipe, and then the windowing pipe string is pulled out to complete casing windowing. Step S3 may be performed after step S2, that is, after the target fracturing construction parameters are determined by performing multiple sets of experiments of alternating hydraulic fracturing on the core, the casing windowing operation in step S3 is performed.
And after the casing windowing operation is finished, a drilling tool is put into the well, and the branch radial hole is drilled at the casing windowing position. Step S4 may include: radial boreholes of a predetermined length and a predetermined number of branches are drilled in the target reservoir in a direction perpendicular or horizontal to the main wellbore. Specifically, the drilling tool includes: coiled tubing, high pressure hoses, jet bits, and downhole turbine-powered drills for driving rotation of the bit. And then, combining the radial well parameters in the target fracturing construction parameters determined in the step, drilling multi-branch radial holes with preset length and preset branch number in the direction vertical to or horizontal to the main shaft through a series of drilling tools which are put into the well.
And after the step of drilling the branch radial hole is finished, and in combination with the target fracturing construction parameters, starting to inject fracturing fluid with alternating hydraulic pressure into the branch radial hole to form alternating load on a fracture surface. Specifically, the existing dynamic fracturing pump or the oil pipe with the hydraulic pulse cavitation jet generator can be adopted to perform alternating hydraulic fracturing on each radial branch well hole, and continuous water flow is converted into alternating hydraulic power which changes periodically. In one embodiment, a hydraulic pulse jet generator is used to perform alternating hydraulic fracturing on each radial branch wellbore, changing the cross-sectional area of the flow channel using the periodic change in impeller rotation, and forming alternating continuous water flow. When the alternating continuous water flow is generated by the method, the impeller continuously changes the flow passage area through high-speed rotation under the action of the impact force of the fluid on the impeller blades so as to generate pulse jet flow, and the adjustment of the alternating water pressure frequency and the alternating water pressure amplitude can be achieved by adjusting the rotation speed of the impeller. Of course, the alternating hydraulic force may be generated by a conventional method, and the present application is not particularly limited. In step S5, the method further includes: and after the alternating hydraulic fracturing is carried out on the branch radial holes for the first preset time, stopping injecting the fracturing fluid, and after the second preset time, carrying out the alternating hydraulic fracturing. In a specific embodiment, the first predetermined time is 1 to 2 weeks, and the second predetermined time is 1 to 2 days. In this embodiment, the alternating hydraulic fracturing may have a plurality of stages, the period of performing the alternating hydraulic fracturing in each stage may be 1 to 2 weeks, and a day or two may be provided between two adjacent periods, so that the alternating hydraulic fracturing is performed intermittently.
In a preferred embodiment, the predetermined length of the radial well is preferably 40 to 60m, and the predetermined number of branches of the radial well is preferably 3 to 6.
In this specification, the hydraulic fracture stimulation method further comprises: the detector is lowered into a target reservoir through a coiled tubing, the activation condition of natural fractures is monitored through micro-earthquakes, and distribution of a reservoir transformation area is monitored and used for monitoring the yield increasing effect after alternating water pressure transformation.
The embodiment of the application also provides a method for selecting target fracturing construction parameters, which comprises the following steps:
s10: punching a rock core obtained by sampling a target reservoir, wherein an eyelet is formed in the rock core;
s20: carrying out a core alternating hydraulic fracturing experiment by combining the crustal stress field of the target reservoir, applying alternating water pressure to the hole of the core for hydraulic fracturing, and selecting fracturing construction parameters, wherein the target fracturing construction parameters comprise: alternating water pressure frequency, alternating water pressure amplitude and radial well parameters;
s30: measuring the permeability and seismic energy of the fracturing fluid after each core alternating hydraulic fracturing experiment;
s40: changing the experiment working condition, carrying out the experiment of multi-group core alternating hydraulic fracturing, and finally determining the target fracturing construction parameters according to the permeability of the fracturing fluid and the seismic energy measured after each experiment.
The hydraulic fracturing yield increase method and the selection method of the target fracturing construction parameters are used for improving unconventional oil and gas reservoirs, the permeability of the unconventional reservoirs is improved, and the yield is improved. The hydraulic fracturing stimulation method can effectively reduce the risk of inducing earthquake. Its advantages and features are:
(1) the method adopts an intermittent low-frequency alternating hydraulic fracturing method, the provided alternating water pressure can induce the formation of micro-cracks, the hydraulic fatigue is generated on the surfaces of the cracks, the fracture pressure is reduced, and finally the effective activation, the slow release of energy, the permeation increase and the yield increase of the natural cracks are realized.
(2) The method solves the engineering problems that natural fractures are difficult to effectively activate and seismic risks exist in the implementation process of unconventional reservoir fracturing reformation, through drilling radial well target communication desserts and combining the action of low-frequency alternating water pressure in the deep part of a reservoir, fracture energy can be gradually released in the fracturing process, the seismic risks are reduced, the reservoir fracturing reformation is carried out to the maximum degree in the area near a main shaft, and a large-range safe production increasing area combining a diversion channel and a shear fracture network is formed.
The above embodiments are merely illustrative of the technical concepts and features of the present application, and the purpose of the present invention is to enable those skilled in the art to understand the content of the present application and implement the present application, and not to limit the protection scope of the present application. All equivalent changes and modifications made according to the spirit of the present application should be covered in the protection scope of the present application.
All articles and references disclosed, including patent applications and publications, are hereby incorporated by reference for all purposes. The term "consisting essentially of …" describing a combination shall include the identified element, ingredient, component or step as well as other elements, ingredients, components or steps that do not materially affect the basic novel characteristics of the combination. The use of the terms "comprising" or "including" to describe combinations of elements, components, or steps herein also contemplates embodiments that consist essentially of such elements, components, or steps. By using the term "may" herein, it is intended to indicate that any of the described attributes that "may" include are optional.
It is to be understood that the above description is intended to be illustrative, and not restrictive. Many embodiments and many applications other than the examples provided will be apparent to those of skill in the art upon reading the above description. The disclosures of all articles and references, including patent applications and publications, are hereby incorporated by reference for all purposes.
Claims (10)
1. A hydraulic fracture stimulation method, comprising:
punching a rock core obtained by sampling a target reservoir, wherein an eyelet is formed in the rock core;
carrying out a core alternating hydraulic fracturing experiment by combining the crustal stress field of the target reservoir, applying alternating water pressure to the hole of the core for hydraulic fracturing, and selecting target fracturing construction parameters, wherein the target fracturing construction parameters comprise: alternating water pressure frequency, alternating water pressure amplitude and radial well parameters;
a windowing pipe channel is put into the target reservoir, and holes are formed in the wall of the casing to complete casing windowing;
pulling out the windowing pipe, putting the windowing pipe into a drilling tool, and drilling a branch radial hole at the windowing position of the casing pipe;
and injecting fracturing fluid with alternating water pressure into the branch radial holes by combining the selected target fracturing construction parameters to form alternating load on the fracture surface.
2. The hydraulic fracture stimulation method of claim 1, wherein the radial well parameters comprise: radial well length and radial well branch number; in the step of drilling a branched radial bore, comprising: radial boreholes of a predetermined length and a predetermined number of branches are drilled in the target reservoir in a direction perpendicular or horizontal to the main wellbore.
3. The hydraulic fracture stimulation method of claim 1, wherein the developing a core alternating hydraulic fracture experiment further comprises:
measuring the permeability and seismic energy of the fracturing fluid after each core alternating hydraulic fracturing experiment;
changing the experiment working condition, carrying out the experiment of multi-group core alternating hydraulic fracturing, and finally determining the target fracturing construction parameters according to the permeability of the fracturing fluid and the seismic energy measured after each experiment.
4. The hydraulic fracture stimulation method of claim 1, wherein the alternating water pressure frequency in the target fracture construction parameters is between 0.1 Hz and 10 Hz.
5. The hydraulic fracture stimulation method of claim 4, wherein the ground stress field comprises a minimum principal ground stress and a maximum principal ground stress, the alternating water pressure in the target fracture construction parameters is 60% -80% of the minimum principal ground stress, and the amplitude of the alternating water pressure is 5 MPa.
6. The hydraulic fracture stimulation method of claim 1, further comprising: based on continuous medium mechanics, rock dynamics and a finite difference method, a hydraulic fracturing dynamic and static stress response numerical model is established by using discrete element software, numerical simulation of core alternating hydraulic fracturing is carried out, and the target fracturing construction parameters are verified.
7. The hydraulic fracture stimulation method of claim 1, wherein the step of injecting a fracturing fluid having alternating hydraulic pressure within the branched radial bores comprises: and after the alternating hydraulic fracturing is carried out on the branch radial holes for the first preset time, stopping injecting the fracturing fluid, and after the second preset time, carrying out the alternating hydraulic fracturing.
8. The hydraulic fracture stimulation method of claim 7, wherein the first predetermined period of time is 1 to 2 weeks and the second predetermined period of time is 1 to 2 days.
9. The hydraulic fracture stimulation method of claim 1, further comprising: and (3) lowering the detector into a target reservoir through a coiled tubing, and monitoring the activation condition of the natural fracture through the micro-earthquake.
10. A method for selecting target fracturing construction parameters is characterized by comprising the following steps:
punching a rock core obtained by sampling a target reservoir, wherein an eyelet is formed in the rock core;
carrying out a core alternating hydraulic fracturing experiment by combining the crustal stress field of the target reservoir, applying alternating water pressure to the hole of the core for hydraulic fracturing, and selecting fracturing construction parameters, wherein the target fracturing construction parameters comprise: alternating water pressure frequency, alternating water pressure amplitude and radial well parameters;
measuring the permeability and seismic energy of the fracturing fluid after each core alternating hydraulic fracturing experiment;
changing the experiment working condition, carrying out the experiment of multi-group core alternating hydraulic fracturing, and finally determining the target fracturing construction parameters according to the permeability of the fracturing fluid and the seismic energy measured after each experiment.
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