RU2645320C2 - Bitumen emulsions for application in oil industry - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: in the method for control of filtration losses in a formation comprising pumping an aqueous liquid containing an emulsion stabilized with a surfactant and having an internal bitumen phase, the bitumen emulsion is converted in the formation by addition of an emulsifying agent initiator. The invention is developed in dependent points of the formula.

EFFECT: increased efficiency of treatment.

14 cl, 3 ex, 5 dwg

Description

BACKGROUND OF THE INVENTION

The invention relates to the intensification of inflow into the well to increase oil and gas production. There are various approaches to stimulate well inflow, and traditionally, such technologies are sensitive to formation characteristics, such as porosity, temperature, stress, and chemical composition. Each inflow intensification operation requires an accurate selection of the composition of the material used to intensify the inflow, and additional options remain.

SUMMARY OF THE INVENTION

One embodiment of the invention is a method for treating an underground borehole, fracture, fluid path and / or formation, comprising injecting into the well an aqueous fluid containing an emulsion with a bitumen internal phase. The emulsion is typically stabilized by a surfactant. The emulsion typically undergoes circulation in a borehole, fracture, fluid path and / or formation.

The circulation of the emulsion is normally initiated by the addition of an agent initiating the circulation of the emulsion. In various embodiments, the emulsion circulation initiating agent is pumped before the fluid containing the emulsion is supplied, or is introduced simultaneously with the fluid containing the emulsion, or introduced in a second fluid, which is supplied with or after the fluid containing the emulsion. Optionally, the initiating agent is in the form of an emulsion and / or encapsulated. In other embodiments, the emulsion reversal initiator exhibits adhesion to subterranean surfaces, or is coated on solid particles in a liquid, or is itself solid particles. Optionally, the liquid containing the emulsion with a bitumen internal phase contains a precursor of the emulsion inversion initiator.

In other embodiments, the fluid comprises proppant (proppant), fibers or particles, or any two or all three of these kinds of materials. Optionally, the fibers or particles or both are degradable.

In a further embodiment, bitumen deposited during or after emulsion treatment is subsequently removed by supplying an organic solvent for bitumen.

In yet a further embodiment, the bitumen emulsion is added only to a portion of the injected fluid (for example, to a portion containing proppant when the proppant is pumped in portions).

Another embodiment is a method for treating an underground formation involving pumping a hydrocarbon-based fluid containing a bitumen emulsion.

Brief Description of the Drawings

Figure 1 is a diagram of a laboratory device for determining filtration fluid loss.

Figure 2 depicts the test results of a bitumen emulsion used to combat filtration losses of fluid in a sand core, followed by purification with diesel oil.

Figure 3 is a diagram of a laboratory setup and slotted nozzles used for bridging tests (initial plug formation).

Figure 4 depicts the results of testing bridging a suspension of bitumen emulsion - fiber in a slit 4 mm wide.

Figure 5 is a diagram of a laboratory setup used for testing emulsion sealing (plugging) proppant-fiber bundles.

DETAILED DESCRIPTION OF THE INVENTION

Although some of the following description is focused on changing the direction of flow and combating mud loss during fracturing, bitumen emulsions and methods of the present invention can be used in many other downhole operations. The invention will be described for the case of processing vertical wells, but equally applicable to wells of any orientation. The invention will be described using hydrocarbon production wells as an example, but it should be understood that the invention can be used in wells for producing other fluids, such as water or carbon dioxide, or, for example, in injection or production wells in underground storage facilities. It should also be understood that in this description of the invention, when describing any range of concentrations or amounts as useful or suitable, etc., it is intended that any and all concentration or amounts in this range, including end points, should be considered as indicated explicitly. In addition, each numerical value must first be perceived as modified by the term “approximately” (if it was not immediately modified in such an explicit way), and then as not modified in such a way, unless otherwise follows from the context. For example, “an interval of values from about 1 to 10” should be taken as indicating any and all possible continuum numbers from about 1 to about 10. In other words, if a certain range of values is given, even if only a few specific values of values are explicitly defined or indicated in a given interval, or even if no values are indicated for a given interval, it should be understood that the inventors imply and believe that any and all values of the quantities in this interval should be considered to to these, and that the inventors have data for the entire interval, and all points in the interval.

We describe the use of commercially available or custom-made bitumen emulsions for a variety of well applications. As an additive to enhance fluid flow, a bitumen emulsion provides benefits by interacting with other materials in the fluid or in the formation, or by interacting with the formation.

We have found that bitumen emulsions, for example when used as additives to fracturing fluids, provide many advantages when performing downhole operations. The emulsion may optionally be inverted in the well, for example, under the influence of chemicals (in a fluid, in another pumped fluid, or in a formation), heat, shear, or due to contact with an uneven or curved surface. As one example of the use of the invention, technical emulsions in a continuous aqueous phase with soft bituminous particles or droplets of an emulsion are easily prepared from bitumen, and when the emulsion is inverted, bitumen adheres to the pores of the formation, preventing mud filtration losses. We have also found that proppant / fiber / bitumen emulsion systems provide better bridging and more stable plugging of natural and artificial cracks and perforations, which are enhanced by the tendency of bitumen to adhere to other surfaces. Reversed bitumen emulsions enhance the adhesion of the fibers to each other, creating a fiber network in the well that prevents the migration of proppant and fine particles and enhances bridging. Due to its good solubility in oil, bitumen released from the emulsion creates a reversible or temporary effect and can be removed by contact with oil or other organic solvents during backwashing or other processing steps.

Bitumen emulsions are well-known materials that are widely used, for example, when lifting heavy oil to the surface using steam injection techniques, as emulsion fuels, in cold paving road surfaces and for waterproofing buildings. In some cases, the problems of transporting heavy oil from the production point to other places were solved by filing in the form of an emulsion. An example is ORIMULSION®, an oil-in-water emulsion consisting of 70 percent Orinoco bitumen and 30 percent water (and a small amount of surfactant), manufactured by PDVSA or commissioned in Venezuela. Bitumen is found in natural conditions, but to deliver this type of oil to refineries, bitumen is converted into a much less viscous oil-in-water emulsion. Note that it should be expected that a water-in-oil emulsion, on the other hand, will exhibit high viscosity.

The concentration of commercially available bitumen emulsions varies depending on the source, but typically ranges from about 40 to about 80 wt.% (Of course, there is no need to use industrially prepared bitumen; the operator can prepare the bitumen independently). A preferred range of values for use in the present invention is from about 50 to about 75 percent. The initial bitumen emulsion is added to other components to obtain a finished fluid for use in an oil field, for example, fracturing fluid or a change in the direction of fluid movement (diversion fluid). The final concentration of bitumen typically ranges from about 1 to about 40 wt.%, Preferably from about 3 to about 30 wt.%. Laboratory tests must be carried out to ensure that bitumen is compatible with other fluid components and that it is possible for each of them to perform its function; appropriate adjustment should be made to the selection or concentration of components.

Since bitumen emulsions are very widely used in terrestrial conditions, they have turned into ordinary mass, inexpensive, well-studied and clearly characterized products that are commercially available almost anywhere in the world. We found that, during downhole operations, bitumen droplets suspended in water affect a number of fluid properties, for example, the ability to transfer proppant or other solids. We have also found that the ability of a bitumen-in-water emulsion to undergo inversion into an emulsion with a bituminous external phase during physical or chemical initiation is useful, for example, for surface modification, aggregation of dispersed materials, control of mud filtration losses, and bridging and plugging for changes in fluid flow direction (fluid deviation).

Typically, the term “bitumen” is defined as a highly viscous, black, sticky mixture of organic liquids, completely soluble in carbon disulfide (CS ₂ ) and having a high content of condensed polycyclic aromatic hydrocarbons. Natural raw bitumen is mined, for example, from tar sands and needs to be heated or diluted to separate from the sand. Another source of bitumen is oil refining processes; refined bitumen is the residual (bottom) fraction obtained by fractional distillation of crude oil. Typically, the lower boiling point is approximately 525 ° C. In this document, we also include in the concept of bitumen a mixture of heavy hydrocarbons (of any origin), which becomes like a solid and sticky at room temperature. In American terminology, such a cleaned residue is usually called asphalt (or asphalt binder). Similarly, in the technical literature, “bitumen emulsion” and “asphalt emulsion” mean the same thing. These emulsions contain up to about 80 wt.% Bitumen and typically from about 1 to about 2 wt.% Chemical additives. There are two main types of emulsions with different affinity for aggregates: cationic and anionic. Heavy oil and bitumen are characterized by high viscosity (i.e., flow resistance, measured in cp) and high density, measured in degrees API (American Petroleum Institute), compared to conventional oil. The World Petroleum Congress defines heavy oil as oil, the viscosity of which in a degassed (dead) state has a value in the range from 100 cP to 10,000 cP at a tank temperature. Heavy oil has a density slightly lower than that of water, with API densities ranging from 10 ° to 20 °. Heavy oil can flow in some reservoirs at well temperature and / or with dissolved gases in situ, but on the surface it is a thick black viscous fluid. Bitumen has a viscosity of more than 10,000 cP. Bitumen is predominantly defined as crude oils or parts of crude oils having a viscosity in the dead state> 10,000 cP. In the absence of viscosity data, crude oils having an API density <10 ° are sometimes referred to as bitumens. Superheavy oil is a heavy oil with API density <10 ° and dead oil viscosity <10000 cP. In comparison, oil with an API density <10 ° is heavier than water. (It should also be noted that the term “oil sands” was created to provide tax incentives in Canada for heavy crude oils found above a certain latitude, where the infrastructure was almost completely absent).

The basics of the stability of bitumen droplets have been studied in detail. The key role of electrostatic repulsion of micronized droplets of bitumen suspended in an aqueous KCl solution has been demonstrated using colloidal particle scattering (CPS); it is believed that the droplets in the bitumen emulsions used in the invention are from about 1 to about 100 microns in size. US patent No. 6613720 discloses a wide range of controlled release methods using emulsions. This patent discloses the controlled release of chemical or biological agents by stabilizing the active ingredients in the dispersed phase of the emulsion, which is then destabilized by a number of different initiators. The only materials disclosed as the dispersed phase were diesel and heptanes, which were described as solvents. In the present invention, the dispersed phase is an agent.

The use of heavy oil in heavy oil-in-water (HO / W) emulsions for downhole operations has been described in SPE 110754, “Innovative Gas Shutoff Method Using Heavy Oil-In Water Emulsion” water) (2008). Please note that in this case it’s not about bitumen, but heavy oil with a viscosity of about 10 and 34 MPa⋅s at 20 ° C and a shear rate> 1 s ^-1 ] Laboratory tests were performed to seal the pores in model cells and porous cores when using HO / W emulsions with different droplet sizes and different rheological characteristics. The flow of an emulsion through porous media is a complex process, which depends both on the properties of the droplets and on the parameters of the solid matrix. The parameters of the emulsion (for example, the concentration of the emulsifier) is regulated depending on the properties of the matrix to achieve the destruction of the emulsion (coalescence of droplets) in a sample with known pore parameters. Droplets can coalesce and form larger droplets when the concentration of surfactant in the solution is reduced to a minimum. Another mechanism described was the coalescence of droplets under the action of high shear forces, which destroy the film at the interface when the droplets are forced to approach each other. The use and effectiveness of a heavy oil-in-water emulsion for blocking a porous sample has been demonstrated for various porous media. Corked porous media can withstand pressure gradients of up to 42 MPa per 1 m (1800 psi (12.4 MPa) per 29 cm of porous medium). The porous medium was completely blocked by heavy oil after injection of 10 pore volumes of the emulsion (only emulsions containing up to 13 percent of heavy oil were used). Typically, the plugging effect for more viscous oils is more pronounced than for oils having a lower viscosity, due to the combined effect of capillarity and viscosity of the injected fluid. The penetration depth of the emulsion depended on the ratio of droplet and channel sizes and on core treatment before washing. The wettability of the solid matrix with water provides a deeper penetration of the heavy oil / water emulsion into the porous formation.

Fighting filtration fluid loss

Fighting fluid filtration losses is often an important requirement for successful fracturing. Efficiency is primarily a function of viscosity and the ability to form a filter cake of a hydraulic fluid for fracturing and permeability and porosity of a formation. If the permeability and porosity of the formation are high, the filtration loss of the fluid is typically fought by increasing the viscosity or the ability to form a filter cake of hydraulic fracturing fluid by adding polymers or having the required particle sizes. Various additives may be used to combat filtration fluid loss. For example, additives include carbonates, salts, minerals, and solid or elastic oil soluble resins. Filtration fluid loss in the formation can be prevented by using additives made from a deformable and / or hydrolyzable material. A typical problem often associated with solid additives to reduce filtration fluid loss is the risk of clogging of equipment, perforations, or formation. Also, after injection into the well, rigid solid particles may not be well placed in the pore space, thereby reducing the effectiveness of the fight against filtration loss of fluid. Reversible formation plugging can be achieved by using degradable additives; decomposition of most of which requires water or hydrocarbon and elevated temperature.

Bridging and plugging

Reversible isolation of a well interval (or flow diversion from this interval) by creating barriers consisting of hydrolyzable polymer fibers has been described. It is also known to use such fibers as additives to prevent fluid loss. US patent No. 7275596 describes the use of fibers for transporting proppant or gravel for fracturing. The industrial application of this patent involves the addition of fiber to low viscosity fluids to prevent the proppant from settling quickly and to ensure uniform proppant placement in the fracture. The patent also describes fibers that, upon completion of processing, can hydrolyze to natural products that do not form a precipitate in aqueous solutions. Fibers and their degradation products are compatible with fluids used in the well. However, creating a high quality barrier in the well remains a challenge; it is difficult to selectively place a barrier in the well having a sufficiently low permeability to reduce injectivity; it is also difficult to control the permeability of the barrier. The use of temporary barriers in wells has been reported (see Ali et al. “Combined Stimulation and Sand Control,” Oilfield Review, vol. 14, No. 2, pp. 30-47) for a method for controlling sand removal while creating temporary barrier containing fibers during fracturing). It is also known to use degradable materials, for example in the form of fibers, to change the direction of flow in a well or insulation. For effective plugging, the fibers must be pumped at a high content in the suspension. This causes the risk of clogging of surface or downhole equipment and therefore significantly limits their use. Additionally, the need to mix and pump the fiber-containing suspension sets limits on some fiber properties (eg, length) to values that are suboptimal for plugging large cracks. Such restrictions reduce the use of fibers for bridging / plugging of cracks, gaps and channels.

US patent No. 3917535 discloses the use of water-based emulsions (with water as the external phase) for acid fracturing. There are also techniques that use water-in-oil emulsions to treat wells. US patent No. 4233165 discloses the preparation of water-in-oil emulsions (the continuous phase was light hydrocarbons), in which the aqueous phase (water droplets less than 10 microns in size) contains acid for acid treatment or transfers reactive solids (for example, zinc carbonates for the reaction with hydrogen sulfide in the drilling fluid). The total concentration of the hydrocarbon phase in the dispersion may be less than 25%. However, this type of emulsion is unsuitable for the purposes described in the present invention. Such a hydrocarbon-based dispersion cannot selectively pad target zones.

Another patent, US patent No. 6939832, discloses a method for the controlled circulation of water-in-oil emulsions for treating wells. The injected liquid was a water-in-oil (W / O) emulsion with a dispersible chemical and a demulsifier (in this case, a surfactant with a cloud point above 40 ° C (or above 60 ° C)). Alternatively, a water-in-oil (W / O) emulsion and a demulsifier are mixed in a formation. In the above examples, the emulsion with a demulsifier lost stability (reversed) at temperatures above 100 ° C, while under ambient conditions the same composition remained stable for several days.

Oil-in-water emulsions have been used as processing fluids (for example, for plugging formations. Examples include those described in US Pat. Nos. 7,231,976 and 7,392,844; US Patent Publications Nos. 2008/0217012 and 2009/0078417; and Patent Publications PCT applications Nos. WO 2001/94742 and WO 1994/28085). None of them disclose the use of bitumen. The oil-in-water emulsion, due to its high viscosity, is itself capable of plugging the formation before its subsequent destruction. In addition, the emulsion serves as an excellent carrier fluid for dispersed materials, such as flow diversion or plugging agents. The use of emulsions can reduce the concentration of expensive gelling agents.

Specially prepared bitumen emulsions (oil-in-water (O / W) type) currently commercially available (including appropriately selected surfactants and other stabilizing agents) remove many of the barriers to use in the field, as these types of emulsions are stable, inexpensive and affordable.

Bitumen emulsions are droplets of bitumen suspended in water and stabilized by one or more surfactants. Surfactants may be anionic, but cationically stabilized emulsions are most widely available. Bitumen emulsions have been proposed as an alternative to hot bitumen in road and residential construction or coating. Bitumen emulsion allows you to work at ambient temperature and in humid conditions. Often bitumen emulsions are used with solid particles such as gravel, crushed stone, sand, etc. When mixed and dried, bitumen is deposited from the emulsion onto solid particles, thereby gluing the particles together. Cationic bitumen emulsions (stabilized by cationic surfactants) are easily handled by contact with anionic surfaces such as carbonates, gravel and other solid materials that are often present or placed in wells.

The bitumen emulsion itself can be a dispersed phase of an aqueous or hydrocarbon based liquid. For example, a hydrocarbon-based continuous phase may contain water droplets, which in turn contain bitumen droplets; such a system is called an O / W / O (oil-in-water-in-oil) double emulsion. Thus, bitumen emulsions can be used in hydrocarbon-based liquids, as well as in water-based liquids, as indicated in other sections of this description. Other suitable double emulsions are W / O / W (water-in-oil-in-water) emulsions. Similarly, triple or quaternary emulsions, such as W / O / W / O, O / W / O / W, W / O / W / O / W and O / W / O / W / O, can be used. Double, triple, etc. emulsions can also be stabilized with surfactants and used as conventional bitumen emulsions.

The circulation of the emulsion in the well can be initiated in several ways, or even combinations of methods. Any such method can be used, for example, contacting bitumen droplets with porous media, interacting with initiating agents (for example, a surfactant having a charge opposite to the charge of a surfactant that stabilizes the emulsion), formation temperature and pH change or shear load. Qualified specialists in the field of downhole operations know a large number of such methods. The conditions and chemicals for initiating the circulation of bitumen emulsions are also known to those skilled in the art of demulsifying heavy oil.

Bitumen-in-oil emulsions used in various methods of the invention are transported to and, optionally, may be stored at the work site. They can then be added to the fracturing fluid or other fluids on their own or with other additives, including proppant and fiber, depending on the purpose of the work.

In addition to fracturing, fluids containing bitumen emulsions are suitable as additives to fluids for processing during drilling and various downhole operations. Examples of applications include controlling mud filtration losses, controlling the bridging and plugging needed to redirect fluid flows, controlling the migration of fine particles, acidizing the matrix (including naturally fractured formations), and controlling backflow.

Bitumen emulsions can be added to fracturing fluids and other well treatment fluids in concentrations from about 0.1 to about 90 wt.%, Preferably from about 0.5 to about 20 wt.%. To prevent filtration loss of fluid through formation pores. , typically from about 1 to about 20 wt.% bitumen emulsion is typically added to the fracturing fluid or drilling fluid. If it is desired to prevent fluid loss through fractures, channels or cracks, a bitumen emulsion is typically pumped with a concentration of from about 0.1 to about 20 wt.%, Together with auxiliary material or substances such as dispersed forms of various materials (e.g. minerals, polymers etc.), often including fibers.

It is known that fiber flocculation plays an important role in effective bridging and plugging. Bitumen emulsion can improve fiber flocculation, thereby providing better bridging and / or plugging of cracks, channels or faults. This, in turn, can provide a change in the direction of fluid movement in the well.

Bitumen emulsions can be used to combat filtration losses of liquids and divert fluids as they are supplied or prepared, or they can be used with an initiating agent. The initiating agent depends on the nature of the surfactant used to stabilize the emulsion. If a cationic surfactant is used, the initiating agent must be anionic. And vice versa. So, for bitumen emulsions stabilized by a cationic surfactant, carbonates, silicates, hydroxides, etc. are used as initiators. For bitumen emulsions stabilized by an anionic surfactant, derivatives of calcium, magnesium, zinc and other cations (salts, hydroxides, complexes, etc.) are used. The initiators may be water soluble or may have limited solubility. They can also be dispersed solid particles (e.g. calcium carbonate). The initiators should be isolated from direct contact with the bitumen emulsion by encapsulation, through the stages of physical separation of the emulsion and initiation, surface modification of the initiator or overstabilization of the emulsion (adding an additional amount of surfactant or stabilization with dispersed materials, etc.), to ensure initiation after a desired period of time after injection, in accordance with the scheme of work.

Bitumen emulsions can be added to liquids online or they can be added by mixing the components of the liquids. Bitumen emulsions can be added to the entire volume of liquid for processing (for example, to combat filtration losses of the liquid in general), or only at certain stages (for example, at the stage or stages of the redirection of fluid flow). To control the reverse flow, a bitumen emulsion is added to the liquid for the final stage of work.

The addition of a bitumen emulsion to a proppant-containing suspension followed by its circulation is used to agglomerate the proppant. The emulsion can be added to proppant plugs if proppant plugs are used during the work; alternatively, portions of the emulsion may be added periodically, while proppant is continuously pumped during the course of the work. In any case, the initiation of the emulsion leads to agglomeration of the proppant with bitumen. In the first case, the dispersion process is prevented. In the second case, the agglomerated proppant will preferably be located near the borehole, in contrast to the non-agglomerated proppant, which will go deeper into the fractures. Agglomeration should occur in the crack, after the passage of fluid through the perforation channels. When proppant and bitumen emulsion are co-injected, the liquid may contain from about 0.1 to about 90 wt.% Bitumen emulsion and from about 24 to about 1200 g / l (from about 0.2 to about 10 ppa (pounds of added proppant)) proppant. A suitable proppant in such cases is mica, and preferred amounts when using mica will be from about 1 to about 20 wt.% Bitumen emulsion and from about 60 to about 240 g / l (from about 0.5 to about 2 ppa) of the proppant.

In situations where the initiator agent injection step is performed before or immediately after the bitumen emulsion step, an inert aggregate (such as fracturing fluid, aqueous surfactant solution, etc.) is required. To prevent unwanted untimely treatment if immediate treatment is not part of the work plan.

After processing, the unwanted residue of the inverted bitumen emulsion formed from the bitumen emulsion is removed with the extracted oil or with a solvent pumped after treatment. Suitable solvents that dissolve bitumen include oil, vegetable oils, diesel, kerosene, etc.

Bitumen emulsions are preferably used at temperatures ranging from about 0 to about 160 ° C.

The present invention can be further illustrated by the following examples.

In this work, we used a bitumen emulsion manufactured by Sibavtoban LLC (Sibavtoban, PLC) (Novosibirsk, Russia). It is a commercially available stabilized cationic type emulsion designated BEC-2 from Sibavtoban and has a bitumen content of approximately 60%.

Example 1: Combating filtration fluid loss

Adding a bitumen emulsion to a linear gel or to other fracturing fluids significantly reduces filtration loss in the laboratory. Additional initiation (reverse agent) was not required. The destruction of the bitumen emulsion in the pores of the core simulating the formation was observed, leading to the deposition of particles of bitumen in the core. During backwashing or refining, bitumen was removed from the formation with oil (e.g., with reverse flow) or washed with one or more organic solvents typically used in industry (such as toluene, diesel oil, and naphtha).

Figure 1 is a diagram of a laboratory device for determining filtration fluid loss. A pump pushes a piston in a cylinder containing fluid pumped through a core. The fluid pressure above the piston was measured. A 10 wt% BEC-2 bitumen emulsion was added to a 2 wt% solution of KCl in deionized water. The mixture was placed in a piston (in the piston) and pumped through a sand core (having a permeability of 137 mD; diameter 17.5 mm and length 23 mm). The sand core was washed with 2 wt.% KCl solution. The tests were carried out at different constant pressure values from 100 to 500 psi (0.68-3.4 MPa). The mass of the effluent at the core outlet was measured. Purification was performed using diesel oil under a pressure of 200 psi (1.36 MPa). The mass of fluid passing through the core was also measured.

Figure 2 shows the test results of a bitumen emulsion used to combat filtration loss of fluid in a sand core, followed by purification with diesel oil. You may notice that a significant reduction in filtration loss of fluid was achieved even in such a short core. The barrier created by the deposition of bitumen was easily removed by washing with diesel fuel.

Example 2: Bridging

Bridging is an important phenomenon for changing the direction of fluid movement; we define it as blocking a channel open for flow by the simultaneous arrival of stable particles whose sizes are smaller than the channel. In addition, for the bridging agent (particulate matter) to be effective after placement, the particles must not be displaced by the flow of carrier fluid and must create an effective barrier to the flow, which is called a “plug”. Typically, to create a cork, the initial barrier formed in the bridging area must be sealed with additional smaller and / or deformable dispersed materials and densified under pressure. The two important characteristics of plugs are the pressure drop that they can withstand and their permeability.

To provide bridging in cracks or cracks of different geometries, proppant and / or fibers can be used. However, when the width of the crack or slit is significantly greater than the size of the dispersed particle, bridging does not occur. Also, even for small fractures, it is necessary to pump high concentrations of dispersed materials, which can lead to clogging of surface equipment, or limited sections of the completed well. In addition, bridging is a function of the speed of the suspension. The lower the speed, the higher the ability for bridging. However, for various reasons, speed limitation will not always be desirable (or achievable) when carrying out hydraulic fracturing.

For example, published laboratory test results (see, for example, SPE 119636, 19-21 January, 2009) showed that a slit 2 mm wide can be covered by degradable fibers 6 mm long and 14 microns in diameter at a concentration of 0.5 wt.% In linear guar gel with a fluid viscosity of 20 cP at 170 s ^-1 and a speed of 1.2 feet / s (0.37 m / s). A 4 mm gap can be covered under the same conditions at a fiber concentration of 1.6%. However, to cover a 6 mm gap with this fiber concentration, it is necessary to reduce the flow rate to about 0.4 ft / s (0.12 m / s). A slot with a width of 8 mm cannot be blocked at all by such fibers in such conditions.

Controlled bridging and sealing of wide cracks is a difficult task, for which there are currently no good solutions. Ideally, bridging should proceed in a controlled manner at a low concentration of dispersed materials and be insensitive to the width of the cracks (which is often a parameter that is not exactly known when the hydraulic fluid pumped by the operator). We found that bitumen emulsion, when added to fracturing solutions or other fluids, increases the ability of fiber suspensions to bridging.

The ability of the fibers to bridging in the presence of a bitumen emulsion reversed by the carbonate anion was studied using the laboratory setup depicted in Figure 3 and channels of various geometries (slot and tunnel). The procedure was based on the technique described in SPE 119636 above.

For a linear slit: Handling a slurry made of 480 ml linear guar gel with a viscosity of 53 cP at 170 s ^-1 , 15 ml of BEC-2 bitumen emulsion, 9 g of polylactic acid fiber (150 ppt (pounds per thousand gallons), 1.8 wt.%), initiated using 10 ml of a 2% solution of NaHCO ₃ to release bitumen. 10 minutes after adding the initiating solution, the suspension was pumped through flat slits ranging in size from 2 mm to 9 mm at a speed of 30 ml / min. Bridging was achieved in all cases, and the pressure rose to more than 450 psi (3.1 MPa), after which an emergency shutdown of the pump was triggered. Under other conditions (for example, lower speeds (which normally enhance bridging), higher fiber concentrations and lower fluid viscosities), cork formation without the addition of bitumen emulsion was not observed even for a 9 mm wide slit. A typical pressure jump during pumping through the cell is shown in Figure 4. A similar experiment without an emulsion did not lead to bridging. A decrease in the concentration of the added emulsion (up to 10 ml for the above suspension) or a decrease in the concentration of fibers (up to 1.2%) led to the absence of bridging.

For a cylindrical hole: The same procedure was used, but using a hole having a diameter of 10.4 mm. Bridging was observed with the following suspension composition: 310 ml of linear gel, 13.2 ml of bitumen emulsion, 100 ppt (1.2%, 3.72 g) of fibers and 6.6 ml of 2% NaHCO ₃ as an initiating agent for the circulation of bitumen emulsion . Without bitumen emulsion, bridging was not observed.

An increase in real-time mutual adhesion of fibers (on-the-fly) in the presence of an initiated or uninitiated bitumen emulsion when pumping a fiber suspension and emulsion into a well provides backflow control. An uninitiated emulsion can provide control by increasing the mutual adhesion of the fibers due to droplets of bitumen between the individual fibers (due to the high viscosity of the bitumen).

Figure 1 shows the results of bridging tests for a slurry consisting of a bitumen emulsion and fibers in a slit 4 mm wide.

The plugs created with a suspension of degradable fibers and a bitumen emulsion are subsequently destroyed in water (the fiber component of the plug) and / or in oil (the bitumen component of the plug), thereby ensuring the reversibility of the plugging of the crack / channel / fault / perforation channel.

Example 3: plugging

The bitumen emulsion added to the liquid not only improves bridging, but also effectively seals the cork by reducing its permeability. The plugging ability of the bitumen emulsion was tested in the laboratory setup shown in FIG. 5. A proppant / fiber pack was obtained by pumping a linear guar gel suspension (120 cP viscosity at 170 s ^-1 ), 40 ppt fiber (0.48 wt.%, 4.8 g / l), 4 ppa proppant (pounds of added proppant ) (480 g / l, size 16/20 mesh) and 3 ppt (0.36 g / l) CaCO ₃ (as a solid initiator for bitumen emulsion) into a steel tube (length 12 cm, diameter 1.1 cm, volume 11 ml). The proppant / fiber pack was heated in a bath to 80 ° C and heated deionized water (at 80 ° C) was passed through the pack at a rate of 10 ml / min (pressure drop was 5 psi (0.034 MPa)) for 1 minute, and then 3 ml / min After that, a 50:50 mixture by weight of water and BEC-2 bitumen emulsion was pumped into the pack. The emulsion was not heated before pumping; when it was pumped into a pack (with conditions typical of a high-temperature formation or fracture), the circulation was initiated by heating, and bitumen precipitated and plugged the pack. Within a minute, the pressure increased significantly; when the pressure increased above 750 psi (5.2 MPa), the safety valve opened. The permeability of the proppant pack immediately changed from very high (equal to 780 D as measured by the pressure drop when pumping water) to small (no flow was observed at a pressure drop of 750 psi (5.2 MPa)).

Claims (14)

1. A method of combating filtration losses in a formation, comprising injecting an aqueous fluid containing an emulsion stabilized with a surfactant and having an internal bitumen phase, characterized in that the formation of the bitumen emulsion is reversed by adding an emulsion initiating agent. 2. The method according to claim 1, characterized in that the initiating agent of the circulation of the emulsion is pumped before the fluid containing the emulsion is supplied. 3. The method according to claim 1, characterized in that the initiating agent of the circulation of the emulsion is pumped simultaneously with the supply of liquid containing the emulsion. 4. The method according to claim 1, characterized in that the initiating agent of the circulation of the emulsion is pumped into the composition of the second liquid. 5. The method according to claim 1, characterized in that the initiating agent of the circulation of the emulsion is pumped after supplying the liquid containing the emulsion. 6. The method according to claim 1, characterized in that the initiating agent of the circulation of the emulsion has adhesion to underground surfaces. 7. The method according to claim 1, characterized in that the initiating agent of the circulation of the emulsion is in the coating on solid particles in a liquid. 8. The method according to claim 1, characterized in that the initiating agent of the circulation of the emulsion is a solid particle. 9. The method according to claim 1, characterized in that the initiating agent of the treatment of the emulsion is encapsulated. 10. The method according to claim 1, characterized in that the liquid contains a precursor of the emulsion treatment initiator. 11. The method according to claim 1, characterized in that the liquid further comprises a proppant. 12. The method according to claim 1, characterized in that the liquid further comprises fibers or particles, or both. 13. The method according to claim 1, characterized in that the liquid further comprises proppant and fibers. 14. The method according to claim 1, characterized in that the precipitated bitumen is subsequently removed by pumping an organic solvent of bitumen.

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