A targeted oil recovery method and system for improving crude oil recovery in heterogeneous oil reservoirs

Abstract

The present invention belongs to the technical field of oil and gas field development engineering and discloses a targeted flooding method and system for improving crude oil recovery in heterogeneous reservoirs. The method involves determining the basic parameters of the heterogeneous reservoir, clarifying the time required for capsule polymers to migrate to the targeted area, and screening for optimal capsule polymer particles. A quantitative matching relationship is established between the molecular weight and concentration of the capsule core polymer and the reservoir permeability and permeability range, establishing profile adjustment threshold standards and a mobility ratio control chart. Furthermore, a differentiated development strategy of "pre-oiling followed by profile adjustment" is implemented using a step-by-step concentration injection process to dynamically control the oil-water mobility ratio between and within target layers in the heterogeneous reservoir. The method utilizes the time-varying mobility of the capsule polymer to achieve targeted, balanced displacement of the target residual oil through an intelligent "low-viscosity injection-high-viscosity displacement" approach. This avoids the problems of low-permeability layer blockage or high-permeability layer crossflow caused by fixed viscosity in traditional polymer flooding, significantly improving crude oil recovery in heterogeneous reservoirs.

Description

Technical Field

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

[0002] Water-driven oil reservoirs dominate the oil production process, but due to the long-term scouring of injected water, the pore structure of the reservoir has changed, the heterogeneity between and within layers has intensified, the water content of the oil field has increased, and the oil production has gradually decreased, affecting the subsequent development effect.

[0003] To address this issue, many oilfields use polymer flooding to adjust reservoir heterogeneity both horizontally and vertically. Polymer-based chemical flooding is an important method for enhancing oil recovery. The addition of polymers increases the viscosity of the displacing phase, improves the water-oil mobility ratio, and thus expands the swept volume of the water phase, enhancing displacement efficiency. However, in heterogeneous reservoirs, after injection, polymer solutions tend to rapidly channel through high-permeability layers, while low-permeability layers are difficult to effectively displace. This leads to significant interlayer disparity, low water flooding sweep coefficients, and significant residual oil remaining in low-permeability zones, unable to be displaced. Continuously increasing polymer viscosity can cause a reversal of the water absorption profile, leading to premature plugging of low-permeability layers and compromising subsequent injection efforts. Furthermore, the relatively fixed viscosity characteristics of polymer solutions make it difficult to dynamically adjust to the actual needs of different reservoir regions, hindering precise displacement in heterogeneous reservoirs. During deep profile control, the injected polymer solution undergoes high-speed shear in the blasthole and near-wellbore area, resulting in significant viscosity losses (up to 50%). This makes it difficult to effectively address heterogeneity in mid- to deep-level formations and hinders the activation of residual oil. With the deepening of oil reservoir development, how to regulate oil displacement in a targeted manner and achieve efficient recovery of crude oil from heterogeneous reservoirs has become an urgent problem to be solved.

[0004] Capsule polymers encapsulate polymers, creating a shell that effectively protects them from high-speed shear degradation near the wellbore, improving viscosity retention. Furthermore, the responsive rupture of the shell allows for controlled release of the polymer, resulting in concentrated viscosity enhancement. Compared to conventional polymer flooding, which increases the viscosity of the entire reservoir at the initial injection stage, capsule polymers, through delayed release, can more precisely target high-permeability zones or areas rich in residual oil, minimizing polymer waste and improving oil recovery efficiency. Preliminary studies have shown that capsule polymers exhibit strong shear resistance, effectively achieving high polymer viscosity retention. They also exhibit temperature-responsive release, with solution viscosity increasing in an S-shaped pattern. By adjusting the structure and thickness of the capsule polymer shell, controllable viscosity enhancement can be achieved at key locations. The controllable performance of capsule polymers, coupled with their variable mobility and gradual viscosity enhancement, enables targeted displacement of residual oil in heterogeneous reservoirs. However, current laboratory and field applications have not explored how to apply the delayed viscosity enhancement properties of capsule polymers to targeted, balanced oil recovery in 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 displacement efficiency remains an important topic that needs in-depth analysis.

[0005] Through the above analysis, the problems and defects of the existing technology are as follows:

[0006] (1) Due to the large differences in the permeability of heterogeneous reservoirs in the plane and vertical directions, conventional polymer solutions tend to flow rapidly along the high permeability layer after injection, 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 remaining in the low permeability area and unable to be displaced.

[0007] (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.

[0008] (3) During the deep profile control process, the injected polymer solution undergoes high-speed shear in the blasthole and near-wellbore area, resulting in a large loss of viscosity, making it difficult to effectively improve the heterogeneity of the deep and medium formations and making it difficult to start the residual oil.

[0009] (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 displacement process in heterogeneous reservoirs.

[0010] The viscosity of existing polymer flooding technology is generally a fixed value. Even if the viscosity can be increased, the initial injection viscosity is still large. However, the viscosity of the present invention increases gradually, presenting an S-shaped viscosity increase curve. The initial fluid viscosity is close to that of water, and has good injectability, so it can play a targeted synergistic role. Summary of the Invention

[0011] To overcome the problems existing in the related art, the embodiments disclosed in the present invention provide a targeted oil recovery method and system for improving crude oil recovery in heterogeneous oil reservoirs. The technical solution is as follows:

[0012] The present invention is achieved by providing a targeted oil recovery method for improving crude oil recovery in heterogeneous oil reservoirs, comprising the following steps:

[0013] 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 capsule polymer particles with appropriate particle size and consistent release time;

[0014] S2: Build a quantitative matching relationship between the molecular weight and concentration of the capsule core polymer and the reservoir permeability and permeability range, establish the profile control limit standard and mobility ratio control chart, and screen out the optimal core polymer;

[0015] S3 adopts a step-by-step decreasing concentration injection process and implements a differentiated development strategy of oil production first and then profile adjustment to dynamically control the oil-water mobility ratio between and within the target area of ​​the heterogeneous reservoir.

[0016] In step S1, the basic parameters of the heterogeneous reservoir include: crude oil target enrichment area, target reservoir permeability, porosity, heterogeneity, reservoir temperature, formation water salinity, pH, oil phase viscosity, injection well injection rate and bottom hole pressure.

[0017] In step S1, the time required for the capsule polymer to migrate to the target area is determined, and the optimal capsule polymer is screened. This includes: determining the basic parameters of the heterogeneous reservoir and obtaining 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 obtained through numerical simulation software. The expression is:

[0018] ;

[0019] Where, 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 detention correction factor;

[0020] Based on the multi-factor response release characterization model of capsule polymers, capsule polymers with appropriate particle size and consistent release time are selected. The average particle size of the capsule particles meets the average pore throat diameter. Time consistency refers to the time it takes for the capsules to migrate in the reservoir and the time it takes for the capsule polymer shell to completely rupture and release.

[0021] Furthermore, the capsule polymer is a shear-resistant coated particle with a core-shell structure, the core polymer is partially hydrolyzed polyacrylamide, and the polymer molecular weight ranges from 8 to 30 million Daltons; the shell is one or more of sodium alginate, polyurethane, and polystyrene; the prepared capsule particles have a particle size range of 0.1 to 10 μm, the capsule polymer flows freely in the reservoir pores, and the average particle size of the capsule particles is Average pore throat diameter satisfy .

[0022] Furthermore, the free flow of the capsule polymer in the reservoir pores is based on a resistance coefficient range of 1-2 when the capsule polymer is injected into a single core / sand packing pipe.

[0023] Furthermore, the release time of the capsule polymer is related to the thickness of the capsule polymer shell layer, reservoir temperature, formation water salinity and pH. The expression for the complete release time of the core polymer is:

[0024] ;

[0025] Where, The release time is when the polymer shell of the capsule is completely broken. is the formation water salinity, is the reservoir temperature, is the thickness of the capsule polymer shell layer, is pH, are coefficients, is the exponential constant;

[0026] Migration distance of capsule polymer particles When its concentration is:

[0027] ;

[0028] Through indoor dynamic adsorption experiments, the adsorption characteristics and adsorption variation of capsule polymers under the influence of multiple factors were analyzed, and the attenuation law of capsule particle concentration along the migration distance was quantitatively characterized; the adsorption retention of capsule polymer particles along the process is related to reservoir temperature, capsule polymer concentration, injection flow rate, and capsule particle aging time. The adsorption amount of capsule polymer particles per unit volume of the reservoir is The expression is as follows:

[0029] ;

[0030] Where, is the migration distance of capsule polymer particles, is the flow rate, satisfying ; is the capsule polymer concentration, is the migration time of capsule particles in the reservoir, , is the reservoir thickness, is the injection well flow rate, All are coefficients;

[0031] The expression for the release rate relationship of capsule polymer at specific temperature, mineralization, and pH is:

[0032] ;

[0033] Where, is the cumulative release rate of the polymer molecules encapsulated in the capsule, is the thermal aging time of the capsule polymer, is the coefficient;

[0034] The relationship between the viscosity and concentration of the polymer released by the encapsulated polymer is:

[0035] ;

[0036] Where, is the viscosity, is the capsule polymer concentration, All are coefficients.

[0037] In step S2, a quantitative matching relationship between the molecular weight and concentration of the capsule core polymer and the reservoir permeability and permeability range is established, and a profile control limit standard and a mobility ratio control model are established, including:

[0038] According to the permeability characteristics and permeability extremes of the target area of ​​the heterogeneous reservoir, single core / sand-filled pipe 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 extreme, and to clarify the boundary chart of the flow / blockage of the core polymer in the specific reservoir permeability. Multiple permeability extreme parallel core / sand-filled pipe displacement experiments are carried out to clarify the profile improvement ability of core polymers with different molecular weights and concentrations in different permeability extremes, and to select core polymer molecules with appropriate molecular weight and injection concentration matching the reservoir permeability, and to establish the boundary standards of profile control and oil recovery processes applicable to different degrees of heterogeneity.

[0039] Furthermore, the optimal water-oil mobility ratio range of the capsule polymer flooding process is 0.05-0.85, among which the permeability range suitable for capsule polymer flooding is 1-1.5; and when implementing the capsule polymer profile control process, the corresponding reservoir permeability range is 1.5-10.

[0040] In step S3, a differentiated development strategy of first oiling and then profile control is implemented using a step-by-step decreasing concentration injection process to dynamically control the oil-water mobility ratio between and within the target area of ​​the heterogeneous reservoir. This includes: for reservoirs with weak heterogeneity, the oil displacement strategy is met. Under the premise of controlling the water-oil mobility ratio, the capsule polymer is moved to the target area to increase viscosity and flood the oil. For reservoirs with strong heterogeneity, a development strategy of first adjusting the profile of the high permeability layer and then flooding the low permeability layer is required.

[0041] The flooding process follows a targeted development sequence from high permeability reservoirs to low permeability reservoirs:

[0042] Targeting high permeability reservoirs Prioritize high concentration capsule polymer flooding and plugging to lower permeability layer Capsule polymer concentration required to achieve optimal oil displacement mobility ratio and displacement pressure As a benchmark, determine the injection Capsule polymer concentration required for the layer ,make sure Layer displacement pressure Achieve low permeability reservoir Effective oil displacement, including , and ;

[0043] when When the oil displacement limit is reached, Implement high-concentration polymer flooding and plugging in batches to achieve a lower permeability reservoir. The best displacement parameters As a benchmark, determine The required injection concentration of the layer ,control Layer displacement pressure , for the reservoir Effective oil displacement, including , and ;

[0044] Gradually develop low permeability reservoirs in the target area. Grade permeability reservoir When Capsule polymer concentration corresponding to the optimal oil displacement mobility ratio and displacement pressure As a benchmark, for relatively high permeability reservoirs The capsule polymer solutions with decreasing concentrations were injected respectively, wherein , ensuring that the displacement pressure of each high permeability layer meets and , thereby achieving Efficient targeted flooding of the layer, in which .

[0045] Another object of the present invention is to provide a targeted oil recovery system for improving crude oil recovery in heterogeneous oil reservoirs, the system being used to control the method described, and comprising:

[0046] The capsule polymer screening module is used to determine the basic parameters of heterogeneous reservoirs, clarify the time required for capsule polymers to migrate to the target area, and screen capsule polymer particles with appropriate particle size and consistent release time;

[0047] The quantitative matching module is used to establish a quantitative matching relationship between the molecular weight and concentration of the capsule core polymer and the reservoir permeability and permeability range, establish the profile control limit standard and mobility ratio control chart, and screen the optimal core polymer;

[0048] The dynamic control module is used to adopt a step-by-step decreasing concentration injection process, implement a differentiated development strategy of first oil production and then profile control, and dynamically control the interlayer and intralayer oil-water mobility ratio in the target area of ​​the heterogeneous reservoir.

[0049] Combining all of the above technical solutions, the present invention offers the following beneficial effects: Based on the established multi-factor response release model for capsule polymers, the mobility ratio control characterization model, and the along-the-line adsorption calculation method, this invention forms a complete technical system from parameter optimization and concentration matching to injection process design. Compared to the "extensive" viscosity increase of traditional polymer flooding, this invention quantifies the migration concentration changes, release patterns, and viscosity evolution of capsule polymers in the reservoir, achieving precise control of capsule polymer release time, providing a scientific and quantitative technical path for the efficient development of residual oil-rich areas in heterogeneous reservoirs.

[0050] This invention adopts an injection strategy of "oil injection followed by profile control, with a step-by-step concentration reduction." Based on the target reservoir's extreme permeability, the process gradually matches the capsule polymer concentration with the displacement pressure, ensuring balanced displacement pressure between high and low permeability layers. This effectively addresses the challenge of residual oil in localized areas between heterogeneous reservoir layers. This process avoids the problems of conventional polymer flooding, which can lead to clogging of low permeability layers or crossflow in high permeability layers due to fixed viscosity, enabling orderly development from high to low permeability layers.

[0051] The present invention's targeted balanced displacement method for crude oil in heterogeneous reservoirs determines the basic parameters of the heterogeneous reservoir, identifies the time required for capsule polymers to migrate to the targeted area, and selects the optimal capsule polymer. Based on laboratory evaluation experiments, the method quantitatively characterizes the decay of capsule particle concentration over migration distance, establishes a matching relationship between capsule polymer concentration and reservoir permeability and permeability range, and establishes a profile adjustment threshold standard and a mobility ratio control model. Furthermore, the method employs a step-by-step decreasing concentration injection method to improve the oil-water mobility ratio variation within and between layers in the targeted area of ​​the heterogeneous reservoir. This method utilizes the time-varying mobility of capsule polymers to achieve targeted balanced displacement of target residual oil through an intelligent "low-viscosity injection-high-viscosity displacement" approach, significantly improving crude oil recovery in heterogeneous reservoirs.

[0052] The present invention can effectively enhance the exploitation of different residual oil-rich areas in heterogeneous reservoirs. When targeting specific areas, the amount of capsule polymer used will be significantly reduced compared to simply injecting a large amount of viscous polymer solution into the reservoir, which helps to reduce oil extraction costs and increase its profit margins. Traditional polymer flooding technology is mostly used for crude oil displacement in heterogeneous reservoirs at home and abroad. It is difficult to accurately control the effect of polymers in different permeability layers, and it is impossible to effectively solve the problem of residual oil in local areas between layers. The present invention is the first to form a complete oil displacement technology system based on a multi-factor response release model of capsule polymers, achieving precise control of the release time of capsule polymers, and ensuring balanced displacement pressure with a strategy of "first oiling and then adjusting the profile, and step-by-step concentration reduction". It fills the technical gaps in the industry at home and abroad in the key technical field of efficient development of targeted residual oil-rich areas in heterogeneous reservoirs.

[0053] The present invention can achieve targeted intelligent regulation of polymers. By quantifying the migration, release, and viscosity evolution of capsule polymers in the reservoir, and adopting innovative injection strategies and regulation methods, it effectively takes into account the displacement effects of high and low permeability layers, and solves the problem of residual oil in local areas between layers of heterogeneous reservoirs. Traditional concepts tend to use different types of oil displacement agents or different oil displacement processes in different permeability layers, which is complicated to operate and ineffective. The present invention breaks this prejudice and utilizes the time-varying mobility characteristics of capsule polymers. With a unified "low viscosity injection-high viscosity displacement" intelligent regulation method, it achieves balanced displacement of targeted areas of heterogeneous reservoirs, simplifies the process, and significantly improves the recovery rate, providing a new and effective technical approach for the development of heterogeneous reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and, together with the description, serve to explain the principles of the present disclosure;

[0055] Figure 1 This is a flow chart of a targeted oil displacement method for improving crude oil recovery in heterogeneous oil reservoirs provided by an embodiment of the present invention;

[0056] Figure 2 This is a circuit diagram of a targeted oil displacement method for improving crude oil recovery in heterogeneous oil reservoirs provided by an embodiment of the present invention;

[0057] Figure 3 This is a TEM image of capsule polymer particles provided by an embodiment of the present invention;

[0058] Figure 4 is an SEM image of capsule polymer particles provided by an embodiment of the present invention;

[0059] Figure 5 is a graph showing the relationship between the concentration of the capsule polymer provided in an embodiment of the present invention and the viscosity corresponding to complete thickening;

[0060] Figure 6 This is a graph showing the effect of the polymer-oil viscosity ratio of the fully viscosified capsules provided by an embodiment of the present invention on the crude oil enhanced recovery value;

[0061] Figure 7 : This is a comparison of the oil displacement experimental effects of the capsule polymer provided by the embodiment of the present invention and the conventional polymer in a two-dimensional visualized flat plate model, wherein (a) shows the permeability distribution of the two-dimensional flat plate model, (b) shows the flooding effect of the conventional polymer, and (c) shows the flooding effect of the capsule polymer.

[0062] Figure 8 This is a schematic diagram of improving heterogeneous oil reservoirs by targeted flooding with capsule polymers provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0063] To make the above-mentioned objects, features, and advantages of the present invention more readily apparent, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. The following description sets forth numerous specific details to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0064] The innovation of the present invention lies in: the present invention quantifies the migration concentration changes, release patterns and viscosity evolution of capsule polymers in the reservoir, realizes the targeted viscosity increase and intelligent regulation of oil displacement by capsule polymers, and provides a scientific and quantitative technical path for the efficient development of targeted residual oil-rich areas in heterogeneous oil reservoirs.

[0065] Example 1, as Figure 1 As shown, the targeted oil displacement method for improving crude oil recovery in heterogeneous oil reservoirs provided by the embodiment of the present invention includes the following steps:

[0066] 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 capsule polymer particles with appropriate particle size and consistent release time;

[0067] By clarifying parameters such as the targeted crude oil enrichment point, reservoir permeability, porosity, heterogeneity, mineral type, reservoir temperature, formation water salinity, pH, oil phase viscosity, injection well injection rate and bottom hole pressure, the time required for the fluid to migrate to the target layer is obtained. Based on the multi-factor response release characterization model of capsule polymers, capsule polymers with appropriate particle size and consistent release time are selected.

[0068] S2: Build a quantitative matching relationship between the molecular weight and concentration of the capsule core polymer and the reservoir permeability and permeability range, establish the profile control limit standard and mobility ratio control chart, and screen out the optimal core polymer;

[0069] Through indoor dynamic adsorption experiments, the adsorption characteristics and adsorption capacity variation of capsule polymers under the influence of multiple factors are analyzed, and the attenuation law of capsule particle concentration along the migration distance is quantitatively characterized;

[0070] According to the permeability characteristics and permeability extremes of the target area of ​​the heterogeneous reservoir, single core / sand-filled pipe displacement experiments are carried out to construct a quantitative matching relationship between the molecular weight and concentration of the core polymer and the reservoir permeability and permeability extreme, and to clarify the boundary chart of the flow / blockage of the core polymer in the specific reservoir permeability. Multiple permeability extreme parallel core / sand-filled pipe displacement experiments are carried out to clarify the profile improvement ability of core polymers with different molecular weights and concentrations in different permeability extremes, and to select core polymer molecules with appropriate molecular weight and injection concentration matching the reservoir permeability, and to establish the process boundary standards of "profile control" and "oil displacement" applicable to different degrees of heterogeneity.

[0071] Based on the optimal selection of capsule polymers, the polymer encapsulated within 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 for the capsule polymer flooding process is 0.05-0.85, with a permeability range of 1-1.5 suitable for capsule polymer flooding. When implementing the capsule polymer profile control process, the corresponding reservoir permeability range is 1.5-10. For reservoirs with weak heterogeneity, the present invention simply allows the polymer to migrate to the target area and then conducts viscosity-enhancing flooding while controlling the water-oil mobility ratio. For reservoirs with strong heterogeneity, a strategy of first adjusting the profile of the high-permeability layer and then flooding the low-permeability layer is required.

[0072] S3, adopts a step-by-step decreasing concentration injection process, implements a differentiated development strategy of oil first and then profile control, and dynamically controls the oil-water mobility ratio between and within the target area of ​​the heterogeneous reservoir;

[0073] Reservoirs with weak heterogeneity meet the oil displacement strategy. Under the premise of controlling the water-oil mobility ratio, the capsule polymer is moved to the target area to increase viscosity and flood the oil. For reservoirs with strong heterogeneity, it is necessary to implement a development strategy of first adjusting the profile of the high permeability layer and then flooding the low permeability layer.

[0074] The flooding process follows the targeted development sequence from high permeability reservoir to low permeability reservoir: first, target high permeability reservoir Prioritize high concentration capsule polymer flooding and plugging to lower permeability layer Capsule polymer concentration required to achieve optimal oil displacement mobility ratio and displacement pressure As a benchmark, determine the injection Capsule polymer concentration required for the layer ,make sure Layer displacement pressure Achieve low permeability reservoir Effective oil displacement;

[0075] when When the oil displacement limit is reached, Implement high-concentration polymer flooding and plugging in batches to achieve a lower permeability reservoir. The best displacement parameters As a benchmark, determine The required injection concentration of the layer , ,control , Layer displacement pressure , , for the reservoir Carry out effective oil displacement;

[0076] Thus, the low permeability reservoirs in the target area are developed step by step. Grade permeability reservoir When Capsule polymer concentration corresponding to the optimal oil displacement mobility ratio and displacement pressure As a benchmark, for relatively high permeability reservoirs The capsule polymer solutions with decreasing concentrations were injected respectively, wherein , ensuring that the displacement pressure of each high permeability layer meets and , thereby achieving Efficient targeted flooding of the layer, in which .

[0077] In Example 2, a targeted oil recovery system for improving crude oil recovery in heterogeneous oil reservoirs provided by an embodiment of the present invention includes:

[0078] The capsule polymer screening module is used to determine the basic parameters of heterogeneous reservoirs, clarify the time required for capsule polymers to migrate to the target area, and screen capsule polymer particles with appropriate particle size and consistent release time;

[0079] The quantitative matching module is used to establish the quantitative matching relationship between the molecular weight and concentration of the capsule core polymer and the reservoir permeability and permeability range, establish the profile control limit standard and the mobility ratio control chart, and screen 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. Its purpose is to screen out the optimal core polymer molecular weight and injection concentration, such as Figure 6 As shown;

[0080] The dynamic control module is used to adopt a step-by-step decreasing concentration injection process, implement a differentiated development strategy of first oil production and then profile control, and dynamically control the interlayer and intralayer oil-water mobility ratio in the target area of ​​the heterogeneous reservoir.

[0081] In order to further demonstrate the positive effects of the above embodiment, the present invention conducts the following experiments based on the above technical solution.

[0082] An oilfield has heterogeneous reservoirs with permeabilities of 500 mD and 200 mD, a porosity of 20.1%, a reservoir temperature of 70°C, a formation water salinity of 6000 mg / L, a formation water pH of 7.8, and a crude oil viscosity of 26.8 mPa·s. The time required for fluid migration to the target layer is determined using the following formula:

[0083] ;

[0084] Where, 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 detention correction factor;

[0085] In addition, through sand-filled tube flow experiments, tracer capsules were injected, the concentration breakthrough curve at the outlet was monitored, and the 50% tracer concentration breakthrough time was obtained. A three-dimensional heterogeneous model was established using reservoir simulation software (such as CMG and Eclipse). Reservoir parameters were input to simulate the time required for fluid migration to the target area. It was found that the time required for the injected fluid to reach the remaining oil-rich area was about 10 days.

[0086] The capsule polymer used in this experiment is a shear-resistant, core-shell coated particle. The core polymer is a partially hydrolyzed polyacrylamide with a molecular weight of 10 million Daltons. The shell is made of polyurethane. The polyurethane shell is formed by interfacial polymerization, using a diisocyanate (MDI) dissolved in an oil phase and a polyol (polyethylene glycol) dissolved in an aqueous phase (the core HPAM solution). The polyurethane shell is formed through an interfacial polycondensation reaction. The shell thickness is controlled by adjusting the molar ratio of isocyanate to polyol (1.2:1-2:1). The shell's rupture behavior is affected by temperature, salinity, and pH.

[0087] Through indoor orthogonal experiments, a 1500 mg / L capsule polymer solution was vacuum-deoxygenated (oxygen concentration was less than 20 ppb) and sealed in an ampoule for thermal aging experiments. A characterization model for temperature, mineralization, pH, and shell thickness was established. The formula is:

[0088] ;

[0089] Where, The release time is when the polymer shell of the capsule is completely broken. is the formation water salinity, is the reservoir temperature, is the thickness of the capsule polymer shell layer, is pH, are coefficients, , is the exponential constant;

[0090] The revised formula is:

[0091] ;

[0092] Depend on It can be seen that:

[0093] , the average thickness of the capsule polymer shell layer is obtained The preferred capsule polymer has a core-shell structure. Figure 3 TEM images of .

[0094] The particle size of the capsule particles used in this experiment is 0.8-1μm, and the average particle size of the capsule particles is Average throat diameter satisfy Requirements, microscopic images of capsule polymers are shown in Figure 4 .

[0095] The capsule polymer used in this experiment has excellent shear resistance. Through shear resistance experiments, a capillary with an inner diameter of 100μm was used to simulate the injection well blasthole. The solution was pumped into the capillary at a flow rate of 1mL / min to simulate the effect of blasthole shear on solution concentration. The viscosity of the polymer solution without a shell layer decreased by more than 50% after shearing. At the same viscosity, the capsule polymer was vacuum-deoxygenated (oxygen content less than 20ppb) after high-speed shearing. After aging and complete release at 70 degrees Celsius, the viscosity was more than 98% of the initial viscosity.

[0096] Capsule polymer injectability experiments were carried out in homogeneous cores with permeabilities of 200mD and 500mD, respectively. The results showed that the resistance coefficient of the capsule polymer when injected into a single core was 1.25-1.35 in the initial state.

[0097] Preferably, the migration distance of the capsule polymer particles is When its concentration is:

[0098] ;

[0099] Through indoor dynamic adsorption experiments, the adsorption characteristics and adsorption amount change rules of capsule polymers under the influence of multiple factors are analyzed, and the attenuation rule of capsule particle concentration along the migration distance is quantitatively characterized; the adsorption retention of capsule polymer particles along the process is mainly related to reservoir temperature, capsule polymer concentration, injection flow rate, and capsule particle aging time. Dynamic adsorption experiments are carried out, and capsule polymers are injected into natural rock cores with a permeability of 500mD. The maximum absorption peak of the capsule polymer and its absorbance change are tested using an ultraviolet-visible spectrophotometer, and the change in capsule polymer concentration in the outlet effluent at different injection stages is determined. The adsorption amount under the influence of different factors is quantitatively characterized, and the adsorption amount of capsule polymer particles per unit volume of the reservoir is The expression is as follows:

[0100] ;

[0101] Where, is the migration distance of capsule polymer particles, is the flow rate, satisfying ; is the capsule polymer concentration, is the migration time of capsule particles in the reservoir, , is the reservoir thickness, The injection well flow rate is determined based on on-site implementation.

[0102] The release rate of the capsule polymer at 70°C, pH = 7.8, and salinity 6000 mg / L satisfies the following conditions: , It is the cumulative release rate of the polymer molecules encapsulated in the capsule.

[0103] 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 capsule polymer, the relationship curve is shown in Figure 5 .

[0104] This experiment uses a homogeneous core with a permeability of 200mD to conduct an optimal water-oil mobility ratio optimization experiment. The specific experimental plan is to fully vacuum the homogeneous core to saturate it with simulated formation water, age it at 70℃ for 24 hours, inject the target oilfield crude oil into the core, and age it at 70℃ for 10 days to fully simulate the reservoir environment. First, a water flooding experiment is carried out, and simulated formation water with a salinity of 6000mg / L is injected into the core. The water is driven to a water cut of 85%, and then fully thickened capsule polymers (concentrations of 500, 1000, 1500, and 2000mg / L) are injected into the core. Subsequently, water is driven to a water cut of 98%, thereby obtaining the relationship between different polymer-oil phase viscosity ratios and enhanced oil recovery values ​​as shown below. Figure 6 As shown in the figure, the curve shows that a water-oil mobility ratio of 0.45 achieves optimal oil displacement, with an optimal capsule polymer concentration of 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, and 0.6 PV) were set up, and the enhanced oil recovery (ER) effects of the different slug configurations were recorded. The optimal slug configuration was 0.35 PV.

[0105] The oil displacement effects of a conventional polymer solution and a fully released capsule polymer solution with the same viscosity on a 200 mD permeability core were compared. The conventional and capsule polymer solutions were subjected to high-speed shearing according to the aforementioned method, followed by full viscosity enhancement of the capsule polymer. During the experiment, the oil-saturated core was first flooded with water, followed by injection of a conventional polymer solution at a concentration of 1500 mg / L and a volume of 0.35 PV. The experimental results showed that the conventional polymer flooding after shearing increased the oil recovery by 8.7% compared to the water flooding, while the capsule polymer solution increased the oil recovery by 21.33% compared to the water flooding. This indicates that the capsule polymer significantly improved the oil recovery after injection from the injection well compared to the conventional polymer solution.

[0106] In order to verify the effectiveness of capsule polymer in oil displacement in actual reservoirs, the effects of conventional polymer displacement and delayed viscosity enhancement of capsule polymer were compared based on a two-dimensional visual flat plate model. The size of the two-dimensional visual model is 600*300*35mm. A high permeability dominant channel is established by 60-70 mesh quartz sand, and a low permeability area is established by 100-120 mesh quartz sand. Reservoir simulation oil is prepared by silicone oil and crude oil, and the model is saturated with water and saturated with oil. The model is tested in a 70℃ oven. The experiment is first water-driven to 95% water content. Conventional polymer with a concentration of 1500mg / L and unbroken capsule polymer are injected into the model respectively. Conventional polymer and capsule polymer have been sheared by capillary before injection. The experimental results show that it is difficult for conventional polymer to have a significant wave spreading effect after shearing, while the capsule polymer is protected by the shell and its viscosity is not significantly affected. It can achieve rupture viscosity enhancement in the sand filling model and produce a delayed wave spreading effect. The experimental results are shown as follows: Figure 7 shown.

[0107] Experiments on the resistance enhancement performance of fully viscosified capsule polymers at different concentrations and injection slugs were conducted in 500 mD permeability cores. The relationship between the resistance coefficient (the ratio of the 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) and the capsule polymer injection concentration and injection slug was established.

[0108] A heterogeneous core displacement experiment was carried out, and cores with permeabilities of 200mD and 500mD were selected for water flooding and capsule polymer flooding experimental analysis. Based on the above single-tube flooding experiment, the injection pressure of 200mD under the optimal water-oil ratio and configured slug was determined. Based on this, the profile of the core with a permeability of 500mD was adjusted. Based on the resistance coefficient plate established above, capsule polymers with matching concentrations and injection slugs were selected to effectively adjust the profile of the 500mD permeability core. A capsule polymer solution with a concentration of 2500mg / L and an injection slug of 0.4PV was selected. At this time, the injection pressure established for the 500mD permeability core was higher than that for the 200mD permeability core, and balanced oil displacement could be achieved for the 200mD and 500mD permeability cores.

[0109] Based on the above experiments, the present invention injects the optimized concentration slugs into the reservoir in sequence. In the reservoir, the capsule polymer will preferentially flow along the high permeability layer due to its smaller particle size and lower viscosity. When it reaches the targeted release time, the polymer wrapped in its core will be released to form a high-viscosity profile control drive. The subsequent low-viscosity capsule polymer solution will turn to the low-permeability reservoir. Under the control of the optimal water-oil mobility ratio, efficient oil displacement is achieved in the low-permeability targeted residual oil-rich area. Figure 8 shown.

[0110] The above description is only a preferred specific implementation method of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with this technical field within the technical scope disclosed by the present invention and within the spirit and principles of the present invention should be covered by the scope of protection of the present invention.

Claims

1. A targeted flooding method for improving crude oil recovery in heterogeneous oil reservoirs, characterized in that: The method comprises 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 capsule polymer particles with appropriate particle size and consistent release time; S2: Build a quantitative matching relationship between the molecular weight and concentration of the capsule core polymer and the reservoir permeability and permeability range, establish the profile control limit standard and mobility ratio control chart, and screen out the optimal core polymer; S3, adopts a step-by-step decreasing concentration injection process, implements a differentiated development strategy of oil first and then profile control, and dynamically controls the oil-water mobility ratio between and within the target area of ​​the heterogeneous reservoir; In step S1, the time required for the capsule polymer to migrate to the target area is determined, and the optimal capsule polymer is screened. This includes: determining the basic parameters of the heterogeneous reservoir and obtaining 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 obtained through numerical simulation software. The expression is: Where, t transpot is the migration time of the capsule in the reservoir, L is the distance from the injection well to the target layer, is the reservoir porosity, τ is the tortuosity, μ eff is the effective viscosity of the fluid, K is the reservoir permeability, ΔP is the pressure difference between the injection well and the target layer, and f is the retention correction factor.

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

3. The targeted flooding method for improving crude oil recovery in heterogeneous reservoirs according to claim 1, wherein: In step S1, the capsule polymer is a shear-resistant coated particle with a core-shell structure, the core polymer is partially hydrolyzed polyacrylamide, and the polymer molecular weight ranges from 8 to 30 million Daltons; the shell is one or more of sodium alginate, polyurethane, and polystyrene; the prepared capsule particles have a particle size range of 0.1 to 10 μm, the capsule polymer flows freely in the reservoir pores, and the average particle size d of the capsule particles is equal to the average pore throat diameter d t Satisfy d≤d t / 5.

4. The targeted flooding method for improving crude oil recovery in heterogeneous reservoirs according to claim 3, wherein: The free flow of capsule polymer in reservoir pores is based on a resistance coefficient range of 1-2 when the capsule polymer is injected into a single core / sand packing pipe.

5. The targeted flooding method for improving crude oil recovery in heterogeneous reservoirs according to claim 1, wherein: In step S1, the release time of the capsule polymer is related to the thickness of the capsule polymer shell layer, reservoir temperature, formation water salinity and pH. The expression for the complete release time of the core polymer is: t break =α(βln(S)+γ)·e δ·pH+k·T ·(ξh c +e) Where, t break is the time for the polymer shell of the capsule to completely break and release, S is the salinity of the formation water, t is the reservoir temperature, h c is the thickness of the capsule polymer shell layer, pH is the acidity, α, β, γ, δ, k, ξ, ε are coefficients, and e is the exponential constant; When the capsule polymer particles migrate a distance x, their concentration is: Through indoor dynamic adsorption experiments, the adsorption characteristics and adsorption variation of capsule polymers under the influence of multiple factors were analyzed, and the attenuation law of capsule particle concentration along the migration distance was quantitatively characterized. The adsorption retention of capsule polymer particles along the migration distance is related to reservoir temperature, capsule polymer concentration, injection flow rate, and capsule particle aging time. The adsorption amount of capsule polymer particles per unit volume of the reservoir, q total The expression is as follows: Where x is the migration distance of the capsule polymer particles, v is the flow rate, and C is the concentration of capsule polymer, t age is the migration time of capsule particles in the reservoir, h is the reservoir thickness, Q is the injection well flow rate, and a, b, c, d, f, and g are coefficients; The expression for the release rate relationship of capsule polymer at specific temperature, mineralization, and pH is: Where, is the cumulative release rate of the polymer molecules encapsulated in the capsule, t is the thermal aging time of the capsule polymer, and n is the coefficient; The relationship between the viscosity and concentration of the polymer released by the encapsulated polymer is: μ=iC 2 +jC+m Where μ is the viscosity, C is the concentration of the capsule polymer, and i, j, and m are coefficients.

6. The targeted flooding method for improving crude oil recovery in heterogeneous oil reservoirs according to claim 1, wherein: In step S2, a quantitative matching relationship between the molecular weight and concentration of the capsule core polymer and the reservoir permeability and permeability range is established, and a profile control limit standard and a mobility ratio control model are established, including: According to the permeability characteristics and permeability extremes of the target area of ​​the heterogeneous reservoir, single core / sand-filled pipe 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 extreme, and to clarify the boundary chart of the flow / blockage of the core polymer in the specific reservoir permeability. Multiple permeability extreme parallel core / sand-filled pipe displacement experiments are carried out to clarify the profile improvement ability of core polymers with different molecular weights and concentrations in different permeability extremes, and to select core polymer molecules with appropriate molecular weight and injection concentration matching the reservoir permeability, and to establish the boundary standards of profile control and oil recovery processes applicable to different degrees of heterogeneity.

7. The targeted flooding method for improving crude oil recovery in heterogeneous reservoirs according to claim 6, wherein: The optimal water-oil mobility ratio range of the capsule polymer flooding process is 0.05-0.85, among which the permeability range suitable for capsule polymer flooding is 1-1.5; when implementing the capsule polymer profile control process, the corresponding reservoir permeability range is 1.5-10.

8. The targeted flooding method for improving crude oil recovery in heterogeneous oil reservoirs according to claim 1, wherein: In step S3, a differentiated development strategy of first oiling and then profile control is implemented using a step-by-step decreasing concentration injection process to dynamically control the oil-water mobility ratio between and within the target area of ​​the heterogeneous reservoir. This includes: for reservoirs with weak heterogeneity, the oil displacement strategy is met. Under the premise of controlling the water-oil mobility ratio, the capsule polymer is moved to the target area to increase viscosity and flood the oil. For reservoirs with strong heterogeneity, a development strategy of first adjusting the profile of the high permeability layer and then flooding the low permeability layer is required. The flooding process follows a targeted development sequence from high permeability reservoirs to low permeability reservoirs: High-concentration capsule polymer flooding and plugging are preferentially implemented for the targeted high-permeability reservoir A1. The capsule polymer concentration C2 and displacement pressure P2 required to achieve the optimal oil displacement mobility ratio in the lower permeability layer A2 are used as benchmarks to determine the capsule polymer concentration C1 required for injection into the A1 layer, ensuring that the displacement pressure P1 in the A1 layer can effectively flood the lower permeability reservoir A2, where C1>C2, P1≈P2 and P1≥P2; When the A2 layer reaches the upper limit of oil displacement, high-concentration polymer flooding and plugging are carried out in batches on the A1 and A2 layers. The injection concentration required for the A1 and A2 layers is determined based on the optimal flooding parameters C3 and P3 of the A3 reservoir with the lowest permeability. Control the displacement pressure of A1 and A2 layers Effective oil displacement was carried out in reservoir A3, among which, and Gradually develop low permeability reservoirs in the target area. When developing the nth level permeability reservoir A n When A n The capsule polymer concentration C corresponding to the optimal oil displacement mobility ratio of the layer n and displacement pressure P n As a benchmark, the relatively high permeability reservoirs A1, A2…A n-1 The capsule polymer solutions with decreasing concentrations were injected respectively, wherein Ensure that the displacement pressure of each high permeability layer meets and Thus achieving A n Highly efficient targeted flooding of the layer, where n≥3.

9. A targeted oil recovery system for improving crude oil recovery in heterogeneous oil reservoirs, characterized in that: The system is used to control the method according to any one of claims 1 to 8, and the system comprises: The capsule polymer screening module is used to determine the basic parameters of heterogeneous reservoirs, clarify the time required for capsule polymers to migrate to the target area, and screen capsule polymer particles with appropriate particle size and consistent release time; The quantitative matching module is used to establish a quantitative matching relationship between the molecular weight and concentration of the capsule core polymer and the reservoir permeability and permeability range, establish the profile control limit standard and mobility ratio control chart, and screen the optimal core polymer; The dynamic control module is used to adopt a step-by-step decreasing concentration injection process, implement a differentiated development strategy of first oil production and then profile control, and dynamically control the interlayer and intralayer oil-water mobility ratio in the target area of ​​the heterogeneous reservoir.

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