Targeted oil displacement method and system for improving crude oil recovery ratio of heterogeneous oil reservoir

Abstract

The invention belongs to the technical field of oil-gas field development engineering, and discloses a targeted oil displacement method and system for improving the crude oil recovery rate of a heterogeneous oil reservoir, and the method comprises the steps: determining the basic parameters of a heterogeneous reservoir, determining the time required for transporting a capsule polymer to a targeted region, and screening optimal capsule polymer particles; building a quantitative matching relationship between the molecular weight and the concentration of a capsule core polymer and the reservoir permeability and the permeability range, and building a profile control limit standard and fluidity ratio control chart; an injection process of gradient decreasing concentration is adopted, a differential development strategy of oil displacement before profile control is implemented, and the inter-layer and in-layer oil-water flow ratio of a target area of the heterogeneous oil reservoir is dynamically regulated and controlled. Targeted equilibrium displacement of target remaining oil is achieved in an intelligent regulation and control mode of'low-viscosity injection-high-viscosity displacement 'by means of the capsule polymer fluidity time-varying characteristic, the problem of low-permeability layer blockage or high-permeability layer fluid channeling caused by viscosity fixation in traditional polymer displacement is solved, and the crude oil recovery rate of a heterogeneous oil reservoir can be greatly increased.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas field development engineering, and particularly relates to a targeted oil displacement method and system for improving the crude oil recovery rate of heterogeneous reservoirs. Background Art

[0002] Waterflooding reservoirs play a dominant role in the process of oil production. However, due to the long-term scouring of the injected water, the pore structure of the reservoir has changed, the heterogeneity between and within layers has intensified, the water cut of the oilfield has increased, and the oil production has gradually decreased, affecting the later development effect.

[0003] To solve this problem, many oilfields adopt polymer flooding technology to adjust the reservoir heterogeneity in the plane and vertical directions. Chemical flooding mainly based on polymer flooding is an important way to improve the crude oil recovery rate. The addition of polymers can increase the viscosity of the displacing phase, improve the water-oil mobility ratio, and then expand the water phase swept volume and improve the displacement efficiency. However, for heterogeneous reservoirs, after the polymer solution is injected, it is easy to quickly channel along the high-permeability layer, while the low-permeability layer is difficult to be effectively displaced, resulting in prominent interlayer contradictions, low waterflooding sweep efficiency, and a large amount of remaining oil remaining in the low-permeability area and unable to be displaced. If the polymer viscosity is continuously increased, it may cause the reversal of the water absorption profile, resulting in premature plugging of the low-permeability layer and affecting subsequent injection work. In addition, the viscosity characteristics of the polymer solution are relatively fixed, and it is difficult to dynamically adjust according to the actual needs of different regions of the reservoir, and it is difficult to achieve precise displacement of heterogeneous reservoirs. During the deep profile control process, the injected polymer solution undergoes high-speed shearing in the wellbore and near-wellbore areas, resulting in a large viscosity loss (up to 50%), making it difficult to effectively improve the heterogeneity of the middle and deep formations and difficult to start the remaining oil. With the in-depth development of the reservoir, how to targetedly regulate oil displacement to achieve the efficient recovery of crude oil in heterogeneous reservoirs has become an urgent problem to be solved.

[0004] Capsule polymer encapsulates polymers, and the resulting shell layer can effectively protect the polymer from high-speed shear degradation in the near-wellbore area, thereby increasing the viscosity retention rate; at the same time, the response rupture of the shell layer can enable the polymer to be released in a controlled manner to achieve concentrated viscosity increase. Compared with traditional polymer flooding, which increases the viscosity of the entire reservoir at the beginning of injection, capsule polymers can act more accurately on high permeability layers or residual oil-rich areas through delayed release, reducing polymer waste and improving oil recovery efficiency. Preliminary studies have shown that capsule polymers have strong shear resistance and can effectively achieve high polymer viscosity retention. They also have temperature-responsive release characteristics, and the solution viscosity increase shows an S-shaped characteristic. By adjusting the structure and thickness of the capsule polymer shell layer, the capsule polymer can achieve controllable viscosity increase at key locations. The performance of capsule polymers is controllable, and their variable fluidity and gradual viscosity increase performance can achieve targeted displacement of residual oil in heterogeneous reservoirs. However, current laboratory and field applications have not yet involved how to apply the delayed viscosity increase characteristics of capsule polymers to the targeted balanced oil recovery process of heterogeneous reservoirs. How to scientifically optimize and combine capsule polymers based on the permeability differences between layers at the target location of heterogeneous oil reservoirs to maximize their regulation and oil recovery efficiency is still an important issue that needs in-depth analysis.

[0005] Through the above analysis, the problems and defects of the prior art are as follows: (1) Due to the large differences in the permeability of heterogeneous reservoirs in the plane and vertical direction, after the conventional polymer solution is injected, it is easy to flow rapidly along the high permeability layer, while the low permeability layer is difficult to be effectively displaced, resulting in prominent interlayer contradictions, low water drive sweep coefficient, and a large amount of residual oil being retained in the low permeability area and unable to be displaced.

[0006] (2) The viscosity characteristics of conventional polymer solutions are relatively fixed, making it difficult to dynamically adjust according to the actual needs of different areas of the reservoir, and it is difficult to achieve precise displacement of heterogeneous reservoirs.

[0007] (3) During the deep profile control process, the injected polymer solution undergoes high-speed shear in the blasthole and near-wellbore area, resulting in large viscosity loss, making it difficult to effectively improve the heterogeneity of the deep and medium-depth formations and making it difficult to start the remaining oil.

[0008] (4) Currently, there is no technical solution in laboratory and field applications on how to apply the delayed viscosity increase characteristics of capsule polymers to the targeted balanced oil recovery process in heterogeneous reservoirs.

[0009] The viscosity of the existing polymer flooding technology is generally a fixed value. Even if the viscosity can be increased, the initial injection viscosity is still relatively large. The viscosity of the present invention increases gradually, presenting an S-shaped viscosity increase curve. The initial fluid viscosity is similar to the viscosity of water, and has good injectability, so it can play a targeted synergistic role. Summary of the invention

[0010] To overcome the problems existing in the related technologies, the disclosed embodiments of the present invention provide a targeted oil displacement method and system for improving the crude oil recovery rate in heterogeneous reservoirs. The technical solutions are as follows: The present invention is implemented as follows. A targeted oil displacement method for improving the crude oil recovery rate in heterogeneous reservoirs includes the following steps: S1. Determine the basic parameters of the heterogeneous reservoir, clarify the time required for the capsule polymer to migrate to the targeted area, and screen out the capsule polymer particles with appropriate particle sizes and consistent release times; S2. Establish a quantitative matching relationship between the molecular weight and concentration of the capsule core polymer and the reservoir permeability and permeability difference, establish a profile control boundary standard and a mobility ratio control chart, and screen out the optimal core polymer; S3. Adopt an injection process with a gradually decreasing concentration, implement a differential development strategy of first oil displacement and then profile control, and dynamically regulate the interlayer and intralayer oil-water mobility ratios in the target area of the heterogeneous reservoir.

[0011] In step S1, the basic parameters of the heterogeneous reservoir include: the crude oil targeted enrichment area, the permeability of the target reservoir, porosity, heterogeneity degree, reservoir temperature, formation water salinity, pH value, oil phase viscosity, injection flow rate of the injection well, and bottom hole flowing pressure.

[0012] In step S1, to clarify the time required for the capsule polymer to migrate to the targeted area and screen out the optimal capsule polymer, it includes: determining the basic parameters of the heterogeneous reservoir to obtain the time required for the fluid to migrate to the target layer. The determination of the fluid migration time is based on Darcy's law, combined with reservoir physical properties, fluid properties, and heterogeneity characteristics, and is obtained by simulating with numerical simulation software. The expression is: ; In the formula, is the migration time of the capsule in the reservoir, is the distance from the injection well to the target layer, is the reservoir porosity, is the tortuosity, is the effective viscosity of the fluid, is the reservoir permeability, is the pressure difference between the injection well and the target layer, is the retention correction coefficient; Based on the multi-factor response release characterization model of the capsule polymer, select the capsule polymer with appropriate particle sizes and consistent release times. The average particle size of the capsule particles satisfies the average pore throat diameter, and the consistent time means: the migration time of the capsule in the reservoir and the complete rupture release time of the capsule polymer cladding layer; Furthermore, the capsule polymer is a shear-resistant coated particulate with a core-shell structure. The inner core polymer is partially hydrolyzed polyacrylamide, and the molecular weight of the polymer ranges from 8 million to 30 million Daltons. The outer shell is one or several of sodium alginate, polyurethane, and polystyrene. The prepared capsule particles have a particle size range of 0.1 - 10 μm, and the capsule polymer can flow freely in the reservoir pores. The average particle size of the capsule particles and the average pore throat diameter meet .

[0013] Furthermore, the free flow of the capsule polymer in the reservoir pores is based on the resistance coefficient range of 1 - 2 when the capsule polymer is injected into a single core / sand-packed tube.

[0014] Furthermore, the release time of the capsule polymer is related to the thickness of the capsule polymer cladding layer, reservoir temperature, formation water salinity, and pH value. The expression for the complete release time of the inner core polymer is: ; In the formula, is the complete rupture and release time of the capsule polymer cladding layer, is the formation water salinity, is the reservoir temperature, is the thickness of the capsule polymer cladding layer, is the pH value, are all coefficients, is the exponential constant; When the migration distance of the capsule polymer particles is, its concentration is: ; Through indoor dynamic adsorption experiments, analyze the adsorption characteristics and the change law of the adsorption amount of the capsule polymer under the influence of multiple factors, and quantitatively characterize the attenuation law of the capsule particle concentration along the migration distance; the amount of adsorption and retention of the capsule polymer particles along the way is related to the reservoir temperature, capsule polymer concentration, injection flow rate, and aging time of the capsule particles. The adsorption amount of the capsule polymer particles in the unit volume of the reservoir is jointly affected by various factors, and the expression is: ; In the formula, is the migration distance of the capsule polymer particles, is the flow rate, meeting ; is the capsule polymer concentration, is the migration time of the capsule particles in the reservoir, , is the reservoir thickness, is the injection well flow rate, are all coefficients; The expression for the release rate relationship of the capsule polymer at specific temperatures, salinities, and pH values is as follows: ; In the formula, is the cumulative release rate of the polymer molecules encapsulated by the capsule, is the thermal aging time of the capsule polymer, is a coefficient; The relationship between the viscosity and concentration of the polymer released by the capsule polymer is: ; In the formula, is the viscosity, is the concentration of the capsule polymer, are all coefficients.

[0015] In step S2, a quantitative matching relationship between the molecular weight and concentration of the capsule core polymer and the reservoir permeability and permeability contrast is constructed, and a profile control boundary standard and a mobility ratio control model are established, including: In view of the permeability characteristics and permeability contrast of the target area of the heterogeneous reservoir, a single-core / sand-packed tube displacement experiment is carried out to construct a quantitative matching relationship between the molecular weight and concentration of the core polymer and the reservoir permeability and permeability contrast, clarify the boundary chart of the flow or blockage of the core polymer in the specific reservoir permeability, carry out a multi-permeability contrast parallel-core / sand-packed tube displacement experiment, clarify the profile improvement ability of the core polymer with different molecular weights and concentrations in different permeability contrasts, select the core polymer molecules with appropriate molecular weights and injection concentrations matching the reservoir permeability, and establish the profile control and oil displacement process boundary standards applicable to different degrees of heterogeneity.

[0016] Furthermore, the optimal water-oil mobility ratio range for the capsule polymer flooding process is 0.05 - 0.85. Among them, the applicable permeability contrast range for capsule polymer flooding is 1 - 1.5; while when implementing the capsule polymer profile control process, the corresponding reservoir permeability contrast range is 1.5 - 10.

[0017] In step S3, an injection process with a gradually decreasing concentration is adopted to implement a differential development strategy of first oil displacement and then profile control, dynamically regulating the interlayer and intralayer oil-water mobility ratios in the target area of the heterogeneous reservoir, including: for reservoirs with weak heterogeneity, the oil displacement strategy is satisfied. On the premise of controlling the water-oil mobility ratio well, the capsule polymer migrates to the target area for viscosity increase and oil displacement. For reservoirs with strong heterogeneity, a development strategy of first profile control of the high-permeability layer and then oil displacement of the low-permeability layer needs to be implemented; The profile control and flooding process follows the targeted development sequence from the high-permeability reservoir to the low-permeability reservoir: For the targeted high-permeability reservoir High-concentration capsule polymer flooding and profile control are preferentially implemented to the next lower permeability layer The concentration of capsule polymer required to achieve the optimal oil displacement mobility ratio and the displacement pressure are used as the benchmark to determine the injection concentration of capsule polymer required for the layer to ensure the displacement pressure of the layer to effectively displace oil from the reservoir with a lower permeability. Among them, and ; When the layer reaches the upper limit of oil displacement, high-concentration polymer flooding and profile control are implemented in batches for the layer. Taking the optimal oil displacement parameters of the reservoir with a lower permeability as the benchmark, determine the injection concentration required for the layer to control the displacement pressure of the layer to effectively displace oil from the reservoir . Among them, and ; Gradually develop the low-permeability reservoir in the targeted area. When developing the reservoir with the th-level permeability , taking the concentration of capsule polymer corresponding to the optimal oil displacement mobility ratio of the layer and the displacement pressure as the benchmark, inject capsule polymer solutions with decreasing concentrations into the relatively high-permeability reservoir respectively. Among them, ensure that the displacement pressure of each high-permeability layer meets and so as to achieve efficient targeted oil displacement of the layer. Among them, .

[0018] Another object of the present invention is to provide a targeted oil displacement system for improving the crude oil recovery rate of heterogeneous reservoirs. This system is used to regulate the above-mentioned method. The system includes: A capsule polymer screening module for determining the basic parameters of heterogeneous reservoirs, clarifying the time required for capsule polymers to migrate to the targeted area, and screening out capsule polymer particles with appropriate particle sizes and release times; A quantitative matching module for constructing a quantitative matching relationship between the molecular weight and concentration of the capsule core polymer and the reservoir permeability and permeability difference, establishing a profile control limit standard and a mobility ratio control chart, and screening out the optimal core polymer; ​​​​A dynamic regulation module, which is used to implement a differential development strategy of injecting pioneer oil first and then profile control, and adopt an injection process with a gradually decreasing concentration, so as to dynamically regulate the in-layer and inter-layer oil-water mobility ratios in the target area of the heterogeneous reservoir.

[0019] Combining all the above technical solutions, the beneficial effects of the present invention are as follows: Based on the established multi-factor response release model of capsule polymers, mobility ratio control characterization model and along-path adsorption calculation method, the present invention forms a complete technical system from parameter optimization, concentration matching to injection process design. Compared with the "extensive" viscosity increase of traditional polymer flooding, the present invention quantifies the migration concentration change, release law and viscosity evolution of capsule polymers in the reservoir, realizes precise control of the release time of capsule polymers, and provides a scientific and quantitative technical path for the efficient development of the targeted remaining oil enrichment area in heterogeneous reservoirs.

[0020] The present invention adopts an injection strategy of "injecting pioneer oil first and then profile control, with a gradually decreasing concentration". Based on the permeability difference of the target reservoir, the concentration of capsule polymers and the displacement pressure are gradually matched to ensure the balance of displacement pressure between high-permeability layers and low-permeability layers, effectively solving the problem that it is difficult to reach the remaining oil in local areas between layers in heterogeneous reservoirs. This process avoids the problems of plugging of low-permeability layers or channeling of high-permeability layers caused by fixed viscosity in traditional polymer flooding, and realizes the orderly development from high-permeability layers to low-permeability layers.

[0021] The method for targeted balanced displacement of crude oil in heterogeneous reservoirs of the present invention determines the basic parameters of heterogeneous reservoirs, clarifies the time required for capsule polymers to migrate to the targeted area, and optimizes the capsule polymers; based on indoor evaluation experiments, quantitatively characterizes the attenuation law of capsule particle concentration along the migration distance, constructs the matching relationship between the concentration of capsule polymers and the reservoir permeability and permeability difference, establishes the profile control limit standard and mobility ratio control model; adopts the injection method of gradually decreasing concentration to improve the difference in in-layer or inter-layer oil-water mobility ratios in the targeted area of heterogeneous reservoirs. The present invention utilizes the time-varying mobility characteristics of capsule polymers to achieve targeted balanced displacement of target remaining oil in an intelligent control mode of "low-viscosity injection - high-viscosity displacement", which can greatly improve the crude oil recovery rate of heterogeneous reservoirs.

[0022] The present invention can effectively enhance the exploitation intensity of different remaining oil enrichment areas in heterogeneous reservoirs. When targeting a specific area, compared with simply injecting a large amount of viscous polymer solution into the reservoir, the dosage of capsule polymer will be significantly reduced, which helps to reduce the cost of oil exploitation and improve its profit margin. For the displacement of crude oil in heterogeneous reservoirs at home and abroad, traditional polymer flooding technology is mostly adopted, which is difficult to accurately control the action of polymers in different permeable layers and cannot effectively solve the problem that it is difficult to reach the remaining oil in local areas between layers. The present invention has first formed a complete oil displacement technology system based on the multi-factor response release model of capsule polymer, realizing precise control of the release time of capsule polymer, ensuring balanced displacement pressure with the strategy of "first displacing oil and then profile control, and gradually decreasing concentration in a stepped manner", and filling the technical gap in the key technical field of efficient development of targeted remaining oil enrichment areas in heterogeneous reservoirs at home and abroad.

[0023] The present invention can achieve targeted intelligent control of polymers. By quantifying the migration, release and viscosity evolution of capsule polymers in the reservoir and adopting innovative injection strategies and control methods, it effectively takes into account the displacement effects of high and low permeability layers and solves the problem that it is difficult to reach the remaining oil in local areas between layers in heterogeneous reservoirs. The traditional concept tends to use different types of oil displacement agents or different oil displacement processes in different permeable layers, which is complex in operation and poor in effect. The present invention breaks this prejudice, utilizes the time-varying fluidity characteristics of capsule polymers, and realizes balanced displacement of the targeted area in heterogeneous reservoirs with a unified intelligent control method of "injecting at low viscosity - displacing at high viscosity", greatly improving the recovery rate while simplifying the process, and providing a new and effective technical idea for the development of heterogeneous reservoirs. Brief Description of the Drawings

[0024] The drawings here are incorporated into the specification and form a part of this specification, showing embodiments consistent with the present disclosure and used together with the specification to explain the principles of the present disclosure; Figure 1 It is a flow chart of the targeted oil displacement method for improving the recovery rate of crude oil in heterogeneous reservoirs provided by an embodiment of the present invention; Figure 2 It is a route map of the targeted oil displacement method for improving the recovery rate of crude oil in heterogeneous reservoirs provided by an embodiment of the present invention; Figure 3 It is a TEM image of capsule polymer particles provided by an embodiment of the present invention; Figure 4 It is a SEM image of capsule polymer particles provided by an embodiment of the present invention; Figure 5 It is a curve graph showing the relationship between the concentration of capsule polymer and the viscosity corresponding to complete viscosity increase provided by an embodiment of the present invention; Figure 6 It is a graph showing the influence of the viscosity ratio of completely viscosity-increased capsule polymer - oil on the value of improving the recovery rate of crude oil provided by an embodiment of the present invention; Figure 7 This is a comparison diagram of the oil displacement experimental effects of the capsule polymer and the conventional polymer provided by the embodiments of the present invention in a two-dimensional visualization flat plate model. Among them, (a) is the permeability distribution of the two-dimensional flat plate model, (b) is the swept effect of the conventional polymer flooding, and (c) is the wave expansion effect of the capsule polymer flooding; Figure 8 This is a schematic diagram of the targeted displacement of the capsule polymer to improve the heterogeneous reservoir provided by the embodiments of the present invention. Detailed implementation manners

[0025] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following will describe the detailed implementation manners of the present invention with reference to the accompanying drawings. Many specific details are set forth in the following description to facilitate a thorough understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific implementations disclosed below.

[0026] The innovation of the present invention lies in that the present invention quantifies the migration concentration change, release law, and viscosity evolution of the capsule polymer in the reservoir, realizes the targeted viscosity increase and intelligent control of oil displacement of the capsule polymer, and provides a scientific and quantitative technical path for the efficient development of the targeted remaining oil enrichment area in the heterogeneous reservoir.

[0027] Example 1, as Figure 1 shown, the targeted oil displacement method for improving the crude oil recovery rate in the heterogeneous reservoir provided by the embodiments of the present invention includes the following steps: S1. Determine the basic parameters of the heterogeneous reservoir, clarify the time required for the capsule polymer to migrate to the targeted area, and screen out the capsule polymer particles with appropriate particle size and consistent release time; Clarify parameters such as the targeted enrichment point of crude oil, reservoir permeability, porosity, heterogeneity degree, mineral type, reservoir temperature, formation water salinity, pH value, oil phase viscosity, injection flow rate of the injection well, and bottom hole flowing pressure to obtain the time required for the fluid to migrate to the target layer. Based on the multi-factor response release characterization model of the capsule polymer, preferably select the capsule polymer with appropriate particle size and consistent release time.

[0028] S2. Construct a quantitative matching relationship between the molecular weight and concentration of the capsule core polymer and the reservoir permeability and permeability difference, establish a profile control limit standard and a mobility ratio control chart, and screen out the optimal core polymer; Through indoor dynamic adsorption experiments, analyze the adsorption characteristics and the change law of the adsorption amount of the capsule polymer under the influence of multiple factors, and quantitatively characterize the attenuation law of the capsule particle concentration along the migration distance; In view of the permeability characteristics and permeability contrast of the target area in heterogeneous reservoirs, single-core / sand-packed tube displacement experiments are carried out to establish a quantitative matching relationship between the molecular weight and concentration of the core polymer and the reservoir permeability and permeability contrast, clarify the boundary chart of the flow / plugging of the core polymer in the specific reservoir permeability, carry out parallel-core / sand-packed tube displacement experiments with multiple permeability contrasts, clarify the profile improvement ability of the core polymer with different molecular weights and concentrations in different permeability contrasts, optimize the core polymer molecules with appropriate molecular weights and injection concentrations matching the reservoir permeability, and establish the process boundary standards for "profile control" and "oil displacement" applicable to different degrees of heterogeneity.

[0029] On the basis of optimizing the capsule polymer, the polymer encapsulated in the capsule core is optimized, and the molecular weight and concentration of the core polymer are optimized based on the actual reservoir permeability. The optimal water-oil mobility ratio range for the capsule polymer flooding process is 0.05 - 0.85, and the applicable permeability contrast range for capsule polymer flooding is 1 - 1.5; while when implementing the capsule polymer profile control process, the corresponding reservoir permeability contrast range is 1.5 - 10. For reservoirs with weak heterogeneity, the present invention only needs to let it migrate to the target area and increase viscosity for oil displacement under the premise of controlling the water-oil mobility ratio. For reservoirs with strong heterogeneity, a strategy of first profile controlling the high-permeability layer and then displacing the low-permeability layer needs to be implemented.

[0030] S3, adopt an injection process with a gradually decreasing concentration, implement a differential development strategy of first oil displacement and then profile control, and dynamically regulate the interlayer and intralayer oil-water mobility ratios in the target area of the heterogeneous oil reservoir; Reservoirs with weak heterogeneity meet the oil displacement strategy. Under the premise of controlling the water-oil mobility ratio, the capsule polymer migrates to the target area for viscosity-increasing oil displacement. For reservoirs with strong heterogeneity, a development strategy of first profile controlling the high-permeability layer and then displacing the low-permeability layer needs to be implemented; The profile control and displacement process follows the targeted development sequence from high-permeability reservoirs to low-permeability reservoirs: first, for the targeted high-permeability reservoir Give priority to implementing high-concentration capsule polymer flooding, profile control and plugging, and use the capsule polymer concentration required to achieve the best oil displacement mobility ratio for the lower-permeability layer and the displacement pressure as a benchmark to determine the injection concentration of the capsule polymer required for the layer to ensure the displacement pressure of the layer to achieve effective oil displacement for the lower-permeability reservoir ; When the layer reaches the oil displacement upper limit, for the layer, implement high-concentration polymer flooding, profile control and plugging in batches, and use the lower-permeability reservoir Optimal oil displacement parameters Based on the injection concentration required for the , , control , the displacement pressure of the , , and effectively displace the oil in the reservoir ; Gradually develop the low-permeability reservoir in the target area in this way. When developing the lowest-level permeability reservoir , use the concentration of the capsule polymer corresponding to the optimal oil displacement mobility ratio of the layer and the displacement pressure as a reference, and inject capsule polymer solutions with decreasing concentrations into the relatively high-permeability reservoir respectively. Among them, , ensure that the displacement pressure of each high-permeability layer meets and , so as to achieve efficient targeted oil displacement of the layer. Among them, .

[0031] Example 2. The targeted oil displacement system for improving the oil recovery rate of heterogeneous reservoirs provided by the embodiments of the present invention includes: A capsule polymer screening module for determining the basic parameters of heterogeneous reservoirs, clarifying the time required for the capsule polymer to migrate to the target area, and screening out capsule polymer particles with appropriate particle sizes and consistent release times; A quantitative matching module for constructing a quantitative matching relationship between the molecular weight and concentration of the capsule core polymer, the reservoir permeability, and the permeability difference, establishing a profile control limit standard and a mobility ratio control chart, and screening out the optimal core polymer; the mobility ratio control model is a relationship chart established by studying the relationship between the molecular weight and concentration of different capsule core polymers and the viscosity of the oil phase, and its purpose is to screen out the optimal core polymer molecular weight and injection concentration, as Figure 6 shown; A dynamic regulation module for adopting an injection process with gradually decreasing concentrations, implementing a differential development strategy of first displacing oil and then profile control, and dynamically regulating the interlayer and intralayer oil-water mobility ratios in the target area of heterogeneous reservoirs.

[0032] To further prove the positive effects of the above embodiments, the present invention conducts the following experiments based on the above technical solutions.

[0033] There is a heterogeneous reservoir in a certain oilfield with permeabilities of 500 mD and 200 mD respectively, a porosity of 20.1%, a reservoir temperature of 70 °C, a formation water salinity of 6000 mg / L, a formation water pH value of 7.8, and the viscosity of crude oil in the reservoir is 26.8 mPa·s; the time for the fluid to migrate to the target layer is determined based on the following formula: ; In the formula, is the migration time of the capsule in the reservoir, is the distance from the injection well to the target layer, is the reservoir porosity, is the tortuosity, is the effective viscosity of the fluid, is the reservoir permeability, is the pressure difference between the injection well and the target layer, is the retention correction coefficient; In addition, through the sand-packed tube flow experiment, tracer capsules are injected, the breakthrough curve of the concentration at the outlet end is monitored, the breakthrough time of 50% concentration of the tracer is obtained, and a three-dimensional heterogeneous model is established using reservoir simulation software (such as CMG, Eclipse), the reservoir parameters are input, and the time required for the fluid to migrate to the target area is simulated. Thus, the time required for the injected fluid to reach the remaining oil enrichment area is about 10 days.

[0034] The capsule polymer used in this experiment is a shear-resistant coated particulate with a core-shell structure. The inner core polymer is partially hydrolyzed polyacrylamide with a polymer molecular weight of 10 million Daltons; the outer shell is made of polyurethane. Using the interfacial polymerization method, diisocyanate (MDI) is dissolved in the oil phase, and polyol (polyethylene glycol) is dissolved in the water phase (inner core HPAM solution), and the polyurethane shell layer is formed through an interfacial polycondensation reaction. The shell layer thickness is controlled by adjusting the molar ratio of isocyanate to polyol (1.2:1 - 2:1). Its outer shell rupture behavior is affected by temperature, salinity, and pH.

[0035] Through indoor orthogonal experiments, the capsule polymer solution with a concentration of 1500 mg / L is vacuum deoxygenated (oxygen concentration is lower than 20 ppb), sealed in an ampoule bottle for thermal aging experiments, and a characterization model of temperature, salinity, pH, and outer shell thickness is established. The formula is: ; In the formula, is the complete rupture release time of the capsule polymer cladding layer, is the formation water salinity, is the reservoir temperature, is the thickness of the capsule polymer cladding layer, is the pH, are all coefficients, , is an exponential constant; The corrected formula is: ; From it can be seen that: , the average thickness of the capsule polymer cladding layer is obtained is about 115 nm. Preferably, the capsule polymer has a core-shell structure, and the specific structure can be seen in the Figure 3 TEM image in

[0036] The particle size of the capsule particles used in this experiment is 0.8 - 1 μm, and the average particle size of the capsule particles and the average throat diameter meet the requirements. The microscopic image of the capsule polymer can be seen in Figure 4 .

[0037] The capsule polymer used in this experiment has excellent anti-shear performance. Through the anti-shear experiment, a capillary with an inner diameter of 100 μm is used to simulate the injection well borehole, and it is pumped into the capillary at a flow rate of 1 mL / min to simulate the influence of borehole shear on the solution concentration. The viscosity of the polymer solution without the cladding layer drops by more than 50% after shear. At the same viscosity, the capsule polymer is subjected to high-speed shear and then vacuum degassed (oxygen content is less than 20 ppb), and the viscosity after aging at 70 degrees Celsius and complete release is more than 98% of the initial viscosity.

[0038] The injectivity experiment of the capsule polymer was carried out in homogeneous cores with permeabilities of 200 mD and 500 mD respectively, and the resistance coefficient of the capsule polymer injected into a single core in the initial state was 1.25 - 1.35.

[0039] Preferably, when the migration distance of the capsule polymer particles is its concentration: ; Through the indoor dynamic adsorption experiment, the adsorption characteristics and the change law of the adsorption amount of the capsule polymer under the influence of multiple factors are analyzed, and the attenuation law of the capsule particle concentration along the migration distance is quantitatively characterized; the adsorption retention amount of the capsule polymer particles along the way is mainly related to the reservoir temperature, the concentration of the capsule polymer, the injection flow rate, and the aging time of the capsule particles. The dynamic adsorption experiment is carried out, and the capsule polymer is injected into a natural core with a permeability of 500 mD. The maximum absorption peak of the capsule polymer and the change of its absorbance are measured by using an ultraviolet-visible spectrophotometer to determine the change of the capsule polymer concentration in the effluent at the outlet end under different injection stages, and the adsorption amount under the influence of different factors is quantitatively characterized. The adsorption amount of the capsule polymer particles in the unit volume of the reservoir is jointly affected by various factors, and the expression is: ; In the formula, is the migration distance of the capsule polymer particles, is the flow velocity, satisfying ; is the concentration of the capsule polymer, is the migration time of the capsule particles in the reservoir, , is the reservoir thickness, is the injection well flow rate, and the specific flow velocity is determined according to the on-site implementation.

[0040] The release rate relationship of the capsule polymer under the conditions of 70 °C, pH = 7.8, and salinity of 6000 mg / L satisfies , is the cumulative release rate of the polymer molecules encapsulated by the capsule.

[0041] At 70 °C, the relationship between the viscosity of the polymer released by the capsule polymer and its concentration satisfies , is the viscosity, is the concentration of the capsule polymer, and the relationship curve is shown in Figure 5 .

[0042] In this experiment, a homogeneous core with a permeability of 200 mD was used to conduct an optimization experiment on the optimal water-oil mobility ratio. The specific experimental scheme was as follows: the homogeneous core was fully evacuated and saturated with simulated formation water, aged at 70 °C for 24 hours, the crude oil of the target oilfield was injected into the core, and aged at 70 °C for 10 days to fully simulate the reservoir environment. First, a water flooding experiment was carried out, and the simulated formation water with a salinity of 6000 mg / L was injected into the core, and water was flooded until the water cut reached 85%. Then, the fully thickened capsule polymer (concentrations were 500, 1000, 1500, and 2000 mg / L respectively) was injected into the core, and subsequent water flooding was carried out until the water cut reached 98%. Thus, the relationship between different polymer-oil phase viscosity ratios and the enhanced oil recovery values was obtained as shown in Figure 6 . It can be obtained from the curve that when the water-oil mobility ratio is 0.45, the oil displacement effect is better, and the preferred concentration of the capsule polymer is 1500 mg / L. Subsequently, multiple injection slugs (0.05 PV, 0.1 PV, 0.15 PV, 0.25 PV, 0.35 PV, 0.45 PV, 0.5 PV, 0.6 PV) were set, and the enhanced oil recovery effects in different configured slugs were recorded, and the preferred slug was 0.35 PV.

[0043] Compare the oil displacement effects of conventional polymer solutions and capsule polymer solutions with the same fully released viscosity on cores with a permeability of 200 mD. High-speed shear the conventional polymer solution and the capsule polymer solution according to the above method, and then fully trigger the viscosity increase of the capsule polymer. During the experiment, first perform water flooding on the cores saturated with oil, and then inject a conventional polymer solution and a capsule polymer solution with a concentration of 1500 mg / L and an injection volume of 0.35 PV, respectively. The experimental results show that the recovery rate of the conventional polymer flooding after shearing is increased by 8.7% compared with water flooding, while the recovery rate of the capsule polymer solution is increased by 21.33% compared with water flooding, indicating that the recovery rate of the capsule polymer is greatly improved compared with the conventional polymer solution after being injected from the injection well.

[0044] To verify the effectiveness of capsule polymers in oil displacement in actual reservoirs, compare the oil displacement effects of conventional polymer flooding and delayed viscosity increase of capsule polymers based on a two-dimensional visualization flat model. The size of the two-dimensional visualization model is 600*300*35 mm. Establish a high-permeability dominant channel with 60-70 mesh quartz sand, and then establish a low-permeability area with 100-120 mesh quartz sand. Prepare reservoir-simulated oil with silicone oil and crude oil, and perform water saturation and oil saturation operations on the model. Conduct the experiment on the model in an oven at 70 °C. First, perform water flooding until the water cut reaches 95%. Inject a conventional polymer with a concentration of 1500 mg / L and unbroken capsule polymers into the model respectively. The conventional polymer and the capsule polymer have been sheared by a capillary before injection. It can be known from the experimental results that it is difficult for the conventional polymer to have an obvious wave propagation effect after shearing, while the capsule polymer is protected by the outer shell and its viscosity is not significantly affected, and it can achieve rupture and viscosity increase in the sand-packed model, resulting in a delayed wave propagation effect. The experimental results are as Figure 7 shown.

[0045] Carry out an experiment on the resistance increasing performance of fully viscosity-increased capsule polymers with different concentrations and different injection slugs in a core with a permeability of 500 mD, and establish a relationship chart of the resistance coefficient (the ratio of the injection pressure of capsule polymer flooding to the initial water flooding injection pressure) and the residual resistance coefficient (the ratio of the subsequent water flooding to the initial water flooding injection pressure) with the injection concentration and injection slug of the capsule polymer.

[0046] Heterogeneous core displacement experiments were carried out. Cores with permeabilities of 200 mD and 500 mD were selected for water flooding and capsule polymer flooding experimental analysis. Based on the above single-tube oil displacement experiment, the injection pressure of 200 mD under the optimal water-oil ratio and configured slug was determined. Taking this as a benchmark, profile control was carried out on the core with a permeability of 500 mD. Based on the resistance coefficient chart established above, capsule polymers with matching concentrations and injection slugs were selected to effectively profile control the core with a permeability of 500 mD. A capsule polymer solution with a concentration of 2500 mg / L and an injection slug of 0.4 PV was selected. At this time, the injection pressure established for the core with a permeability of 500 mD was higher than that of the core with a permeability of 200 mD, and balanced oil displacement for the cores with permeabilities of 200 mD and 500 mD could be achieved.

[0047] Based on the above experiments, the optimized concentration slugs of the present invention were sequentially injected into the reservoir. In the reservoir, due to the smaller particle size and lower viscosity of the capsule polymer, it would preferentially flow along the high-permeability layer. When it reached the targeted release time, the polymer encapsulated in its core would be released to form a high-viscosity profile control drive. Subsequently, the low-viscosity capsule polymer solution would turn to the low-permeability reservoir, and under the control of the optimal water-oil mobility ratio, efficient oil displacement of the low-permeability targeted remaining oil enrichment area was achieved, as Figure 8 shown.

[0048] As mentioned above, it is only a relatively optimal specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modification, equivalent replacement, and improvement made by those skilled in the art within the technical scope disclosed by the present invention, as long as they are made within the spirit and principle of the present invention, should be covered by the protection scope of the present invention.

Claims

1. A targeted oil displacement method for improving the crude oil recovery rate in heterogeneous reservoirs, characterized in that The method includes the following steps: S1. Determine the basic parameters of the heterogeneous reservoir, clarify the time required for the capsule polymer to migrate to the target area, and screen out the capsule polymer particles with appropriate particle size and consistent release time; S2. Construct a quantitative matching relationship between the molecular weight and concentration of the capsule core polymer and the reservoir permeability and permeability ratio, establish a profile control limit standard and a mobility ratio control chart, and screen out the optimal core polymer; S3. Adopt an injection process with a gradually decreasing concentration, implement a differential development strategy of primary oil displacement followed by profile control, and dynamically regulate the interlayer and intralayer oil-water mobility ratios in the target area of the heterogeneous reservoir.

2. The targeted oil displacement method for improving the crude oil recovery rate in heterogeneous reservoirs according to claim 1, characterized in that In step S1, the basic parameters of the heterogeneous reservoir include: the target enrichment area of crude oil, the permeability of the target reservoir, porosity, heterogeneity degree, reservoir temperature, formation water salinity, pH value, oil phase viscosity, injection flow rate of the injection well, and bottom hole flowing pressure.

3. The targeted oil displacement method for improving the crude oil recovery rate of heterogeneous reservoirs according to claim 1, wherein In step S1, clarify the time required for the capsule polymer to migrate to the target area and screen out the optimal capsule polymer, including: determine the basic parameters of the heterogeneous reservoir, obtain the time required for the fluid to migrate to the target layer, and the determination of the fluid migration time is based on Darcy's law, combined with reservoir physical properties, fluid properties and heterogeneity characteristics, and is obtained by simulating with numerical simulation software. The expression is: ； Wherein, is the migration time of the capsule in the reservoir, is the distance from the injection well to the target layer, is the porosity of the reservoir, is the tortuosity, is the effective viscosity of the fluid, is the permeability of the reservoir, is the pressure difference between the injection well and the target layer, is the retention correction coefficient.

4. The targeted oil displacement method for improving the crude oil recovery rate of heterogeneous reservoirs according to claim 3, wherein The capsule polymer is a shear-resistant coated particulate with a core-shell structure. The inner-core polymer is partially hydrolyzed polyacrylamide, and the molecular weight of the polymer ranges from 8 million to 30 million Daltons. The outer shell is one or several of sodium alginate, polyurethane, and polystyrene. The particle size of the prepared capsule ranges from 0.1 μm to 10 μm, and the capsule polymer can flow freely in the reservoir pores. The average particle size of the capsule particles and the average pore throat diameter meet .

5. The targeted oil displacement method for improving the crude oil recovery rate in heterogeneous reservoirs according to claim 4, characterized in that, The free flow of the capsule polymer in the reservoir pores is based on the resistance coefficient range of 1-2 when the capsule polymer is injected into a single core / sand-packed tube.

6. The targeted oil displacement method for enhancing the crude oil recovery rate in heterogeneous reservoirs according to claim 3, wherein The release time of the capsule polymer is related to the thickness of the capsule polymer cladding layer, reservoir temperature, formation water salinity and pH value. The expression for the complete release time of the core polymer is: ； In the formula, is the complete rupture release time of the capsule polymer cladding layer, is the formation water salinity, is the reservoir temperature, is the thickness of the capsule polymer cladding layer, is the pH value, are all coefficients, is the exponential constant; Migration distance of capsule polymer particles When its concentration is: ； Through indoor dynamic adsorption experiments, analyze the adsorption characteristics of capsule polymers under the influence of multiple factors and the variation law of adsorption capacity, and quantitatively characterize the attenuation law of capsule particle concentration along the migration distance; the amount of adsorbed retention of capsule polymer particles along the way is related to reservoir temperature, capsule polymer concentration, injection flow rate, and capsule particle aging time, and the adsorption capacity of capsule polymer particles per unit volume of the reservoir It is jointly affected by various factors, and the expression is: ； In the formula, is the migration distance of the capsule polymer particles, is the flow velocity, satisfying ; is the concentration of the capsule polymer, is the migration time of the capsule particles in the reservoir, , is the reservoir thickness, is the injection well flow rate, are all coefficients; The expression for the release rate relationship of the capsule polymer at a specific temperature, salinity and pH value is: ； In the formula, is the cumulative release rate of the polymer molecules encapsulated by the capsule, is the thermal aging time of the capsule polymer, is a coefficient; The relationship between the viscosity and concentration of the polymer released by the capsule polymer is: ； Wherein, is the viscosity, is the concentration of the capsule polymer, are all coefficients.

7. The targeted oil displacement method for improving the crude oil recovery rate in heterogeneous reservoirs according to claim 1, wherein In step S2, construct a quantitative matching relationship between the molecular weight and concentration of the capsule core polymer and the reservoir permeability and permeability ratio, and establish a profile control limit standard and a mobility ratio control model, including: For the permeability characteristics and permeability ratio of the target area of the heterogeneous reservoir, implement a single core / sand-packed tube displacement experiment to construct a quantitative matching relationship between the molecular weight and concentration of the core polymer and the reservoir permeability and permeability ratio, clarify the limit chart of the core polymer flowing / plugging in a specific reservoir permeability, implement a multi-permeability ratio parallel core / sand-packed tube displacement experiment, clarify the profile improvement ability of the core polymer with different molecular weights and concentrations in different permeability ratios, select the core polymer molecules with appropriate molecular weight and injection concentration matching the reservoir permeability, and establish the profile control and oil displacement process limit standards applicable to different heterogeneity degrees.

8. The targeted oil displacement method for improving the crude oil recovery rate in heterogeneous reservoirs according to claim 7, wherein The optimal water-oil mobility ratio range for the capsule polymer flooding process is 0.05-0.

85. Among them, the permeability ratio range applicable to the capsule polymer flooding is 1-1.5; while when implementing the capsule polymer profile control process, the corresponding reservoir permeability ratio range is 1.5-10.

9. The targeted oil displacement method for improving the crude oil recovery rate of heterogeneous reservoirs according to claim 1, characterized in that, In step S3, an injection process with a gradually decreasing concentration is adopted to implement a differential development strategy of first driving the pioneer oil and then profile control, dynamically regulating the inter-layer and intra-layer oil-water mobility ratios in the target area of the heterogeneous reservoir, including: for reservoirs with weak heterogeneity, the oil displacement strategy is satisfied. On the premise of controlling the water-oil mobility ratio, the capsule polymer migrates to the target area for viscosity-increasing oil displacement. For reservoirs with strong heterogeneity, a development strategy of first implementing profile control on the high-permeability layer and then driving oil in the low-permeability layer is required; The profile control and flooding process follows a targeted development sequence from high-permeability reservoirs to low-permeability reservoirs: For targeted high-permeability reservoirs Priority is given to implementing high-concentration capsule polymer flooding for profile control and water plugging in the lower-permeability layers The capsule polymer concentration required to achieve the optimal oil displacement mobility ratio and the displacement pressure are used as the benchmarks to determine the injection capsule polymer concentration required for the layer to ensure the displacement pressure of the layer to effectively displace oil from the lower-permeability reservoir wherein , and ; When the layer reaches the upper limit of oil displacement, high-concentration polymer flooding and plugging adjustment are implemented in batches for the layer, and the optimal oil displacement parameters of the reservoir with a lower permeability level are used as a reference to determine the injection concentration required for the layer, control the displacement pressure of the layer to effectively displace oil from the reservoir. Among them, , , and ; Gradually develop the low-permeability reservoir in the targeted area. When developing the reservoir with the -level permeability, use the capsule polymer concentration corresponding to the optimal oil displacement mobility ratio of the layer and the displacement pressure as the benchmark, and inject capsule polymer solutions with decreasing concentrations into the relatively high-permeability reservoir respectively. Among them, , ensure that the displacement pressure of each high-permeability layer meets and , so as to achieve efficient targeted oil displacement of the layer. Among them, .

10. A targeted oil displacement system for improving the oil recovery rate of heterogeneous reservoirs, characterized in that, This system is used to regulate the method according to any one of claims 1-9, and the system includes: A capsule polymer screening module, which is used to determine the basic parameters of the heterogeneous reservoir, clarify the time required for the capsule polymer to migrate to the target area, and screen out capsule polymer particles with appropriate particle sizes and release times; A quantitative matching module, which is used to construct a quantitative matching relationship between the molecular weight and concentration of the capsule core polymer and the reservoir permeability and permeability difference, establish a profile control limit standard and a mobility ratio control chart, and screen out the optimal core polymer; A dynamic regulation module, which is used to adopt an injection process with a gradually decreasing concentration, implement a differential development strategy of first driving the pioneer oil and then profile control, and dynamically regulate the inter-layer and intra-layer oil-water mobility ratios in the target area of the heterogeneous reservoir.

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