Method for evaluating self-adapting gel particle injection and plugging performance in low permeability reservoir

Abstract

The application discloses a method for evaluating self-adaptive gel particle injection and plugging of low-permeability oil reservoirs, which adopts a large-displacement constant-flow pump to inject the material, so that the shearing of the material through the sandstone porous medium is closer to the actual situation of an oilfield site; meanwhile, the low-permeability layer and the fractured layer are separated and evaluated through a multi-stage series connection mode, the migration degree of the material and the retention and plugging situation of the material to the fractured layer are quantitatively calculated, and the comparison test is carried out under the same low-permeability oil reservoir geological conditions, so that the relatively simple, fast and accurate material suitable for the application of the target oil reservoir geological conditions is screened out, the material is closer to the real situation of the oil reservoir, the evaluation is more comprehensive and more accurate, and the method can effectively guide the formulation and on-site implementation of the injection process of the pore self-adaptive gel particle in the low-permeability oilfield site.

Description

Technical Field

[0001] This invention belongs to the field of low-permeability reservoir technology and relates to an evaluation method for the injection and plugging properties of adaptive gel particles in low-permeability reservoirs. Background Technology

[0002] Gel particles, as a water-blocking material, are a pre-crosslinked tertiary oil recovery additive. They rely on the viscoelasticity of the gel to bridge and accumulate at formation pore throats, forcing injected water to undergo phase inversion, expanding the water sweep volume, and achieving the effect of reducing water loss and increasing oil production. To ensure better penetration of gel particles into deeper formations with relatively abundant residual oil, the initial particle size of typical gel particles is relatively small, presenting a contradiction between injectability and sealing performance. Furthermore, low-permeability oilfields, due to the presence of natural and artificial fractures, have relatively large permeability variations. In discontinuous phase injection, typical gel particles exhibit disordered sealing, making it difficult to effectively seal water seepage channels in fractures with relatively high permeability.

[0003] Reservoir-adaptive gel particles, a type of water-blocking material, can break up under high-volume water injection conditions by shearing through the pore throats of low-permeability sandstone in the near-wellbore zone. They then gradually migrate deeper into the reservoir with the injected water, accumulating at suitable fracture sites to create a seal, thus exhibiting a certain degree of reservoir adaptability. The initial particle size of this material is relatively large, typically 30μm-300μm. During gel preparation, it is water-saturated and does not expand further in formation water. Its shear-breaking ability determines its ability to penetrate deeper into the reservoir. Currently, evaluating the shear-breaking ability of low-permeability reservoir-adaptive gel particles generally involves high-speed shearing of the material's aqueous dispersion using a high-speed shearing machine, comparing the particle size distribution before and after shearing. However, this method differs significantly from the actual shearing of porous sandstone media in low-permeability reservoirs, failing to accurately reflect the material's condition after shearing within the formation. Furthermore, simply measuring particle size changes cannot characterize the material's fracture-sealing properties after shearing. Meanwhile, the artificial core plugging test commonly used in oilfields to evaluate plugging performance can only provide a qualitative evaluation through changes in core pressure, and cannot quantitatively determine the speed of material migration and the amount of material retained, as well as the degree of plugging within the fracture.

[0004] Chinese patent "A Method for Evaluating the Reservoir Adaptability of Polymer Gel Profile Modifiers" (Application Date: 2014.05.13; Application No.: CN201410200912.3; Publication Date: 2016.02.10; Publication No.: CN103995083A) discloses a method for evaluating the reservoir adaptability of polymer gel profile modifiers. The method involves preparing cemented artificial cores, preparing formation aqueous solutions, and preparing polymer gel profile modifiers. A cemented artificial core is displaced using both the formation aqueous solution and the prepared polymer gel profile modifier, and its residual resistance coefficient is calculated. Another cemented artificial core is displaced using both the formation aqueous solution and pure polymer liquid, and its residual resistance coefficient is calculated. The minimum gelation concentration for a reservoir with known permeability is determined based on the ratio of the calculated residual resistance coefficient to the calculated residual resistance coefficient. This patent can only test the material's sealing effect on the entire core, and cannot quantitatively evaluate the material's shearing, migration, and retention within the core, resulting in inaccurate adaptability evaluation. Summary of the Invention

[0005] The purpose of this invention is to provide an evaluation method for the injectability and plugging properties of adaptive gel particles in low-permeability reservoirs, which solves the problem that existing methods for evaluating adaptive gel particles in permeable reservoirs cannot accurately reflect the injectability and plugging properties, and therefore cannot provide accurate evaluation.

[0006] The technical solution adopted in this invention is an evaluation method for the injection and plugging properties of adaptive gel particles in low-permeability reservoirs, which is implemented according to the following steps:

[0007] Step 1: Prepare an aqueous dispersion of low-permeability reservoir adaptive gel particles;

[0008] Step 2: Based on the actual sandstone pore shear and fracture conditions in low-permeability reservoirs, construct an indoor physical model evaluation platform;

[0009] Step 3: Based on the injection conditions of the target reservoir, simulate the oilfield site and inject pore-adaptive gel particles as water-blocking material. According to the geological conditions of the low-permeability oilfield in actual application, collect the pressure value changes of each layer.

[0010] Step 4: Measure the mass change of each simulated core layer before and after the injection of material, and compare and evaluate the injection performance, migration capacity and retention and sealing capacity of the material.

[0011] The invention is further characterized in that,

[0012] Step 1 is as follows: Select low-permeability reservoir adaptive gel particles with an initial gel particle size of 30μm-300μm as water shut-off material, and then prepare simulated formation water according to the low-permeability formation conditions of the target reservoir; weigh the low-permeability reservoir adaptive gel particles, denoted as M0, add them to the simulated formation water, stir and disperse to prepare a concentration of 1000mg / L to 5000mg / L, continue stirring and dispersing for 5 to 20 minutes, and prepare a total volume of 500 to 1000mL of aqueous dispersion.

[0013] Step 2: The indoor physical model evaluation platform adopts a three-layer series core system. The core system is artificially filled with sand extracted from the strata, and is cylindrical in shape. It is divided into three levels and is held by a core holder.

[0014] Based on the average permeability and fracture size of the low-permeability formation in the target reservoir, core samples of various stages were filled with produced sand. The first-stage core had a permeability of 1 mD to 50 mD and was used to simulate low-permeability formations. The second-stage core had a permeability of 1000 mD to 5000 mD and was used to simulate natural or artificial fractures. The third-stage core had a permeability of 1 mD to 50 mD and was used to simulate subsequent low-permeability formations.

[0015] Each level is connected to a pressure sensor. Simulated core layers and fracture layers with different permeability are artificially filled using sand extracted from the formation. Each layer is connected to a pressure sensor to record the sealing pressure value of that layer, and the collected pressure data is transmitted to a computer in real time.

[0016] The low-permeability reservoir adaptive gel particle aqueous dispersion prepared in step 1 was injected into an intermediate container with stirring. A high-displacement constant flow pump was used to pump the gel particle aqueous dispersion into the core system filled with formation sand constructed in step 2. Pressure sensors collected pressure values ​​at each level in real time. The injectability and migration of gel particles were evaluated by the changes in pressure values. After injecting the low-permeability reservoir adaptive gel particle aqueous dispersion, water injection was continued until the pressure values ​​at each pressure measuring point were basically stable. The highest pressure values ​​P1max, P2max, and P3max at each pressure measuring point were recorded.

[0017] Step 4 is as follows:

[0018] Step 4.1: After injecting simulated formation water into each core sample, weigh them to measure the initial mass, denoted as M. 1b M 2b M 3b After injecting the adaptive gel particle aqueous dispersion into the low-permeability reservoir, continue water injection until the pressure values ​​at each pressure measuring point are basically stable. Then, stop the pump until the pressure returns to zero, and re-weigh the core samples at each level to measure the mass after injection, denoted as M. 1a M 2a M 3a ;

[0019] Step 4.2: Calculate the percentage of the mass difference between the injected gel particles and the initial total mass of the gel particles. This percentage represents the retention and plugging percentage of the adaptive gel particles in each core sample of the low-permeability reservoir, denoted as W1 = (M 1a -M 1b ) / M0×100, W2=(M 2a -M 2b ) / M0×100,

[0020] W3=(M 3a -M 3b ) / M0×100;

[0021] Step 4.3: Compare and analyze the retention of gel particles in core samples of various levels to obtain the injection properties of adaptive gel particles in low-permeability reservoirs after shearing through low-permeability layers and their retention and sealing properties in fracture layers. Quantitatively evaluate the migration speed and retention amount of this water-blocking material, such as pore-adaptive gel particles, as well as their subsequent migration and retention capacity into the deep reservoir.

[0022] Step 4.4: Record the pressure values ​​at each pressure measuring point. If each pressure measuring point has a certain pressure value, it indicates that the adaptive gel particles in the low-permeability reservoir are sheared and broken by the pore throat of the low-permeability layer and enter the deep part of the reservoir with the injected water, indicating good injectability. If, except for the first-level pressure measuring point where the pressure increases significantly, the other two pressure measuring points only show a slight increase, it indicates that the gel particles cannot be effectively sheared and broken by the pore throat of the low-permeability layer and cannot enter the deep part of the reservoir, indicating poor injectability.

[0023] The pumping speed range of the large displacement constant flow pump is 5 to 20 mL / min.

[0024] The intermediate container with stirring has an effective volume of 500–1000 mL.

[0025] The pressure sensor has a maximum range of 20 MPa.

[0026] The beneficial effects of this invention are: the evaluation method for the injection and plugging properties of adaptive gel particles in permeable reservoirs is characterized by its close resemblance to actual oilfield conditions, comprehensiveness, and accuracy. Adaptive gel particles in low-permeability reservoirs are injected into low-permeability formations through a high-flow-rate pump. Under pressure, they undergo shearing in the porous sandstone medium, forming fragmented particles of varying sizes. Gel particles formed after shearing in small pores are also small. In contrast, natural microfractures or artificially inflated fractures have relatively high permeability, resulting in relatively larger particles formed during shearing. This exhibits a certain degree of pore adaptability, forming gel particles of matching size through formation pore selection and achieving a certain degree of plugging performance. Attached Figure Description

[0027] Figure 1 This is a connection diagram of the low-permeability reservoir adaptive gel particle injection and plugging evaluation device of the present invention.

[0028] In the diagram, 1. High-displacement constant flow pump, 2. Intermediate container with agitator, 3. Core holder, 4. Pressure sensor, 5. Computer. Detailed Implementation

[0029] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0030] The present invention provides a method for evaluating the injectability and plugging properties of adaptive gel particles in low-permeability reservoirs, which is implemented according to the following steps:

[0031] Step 1: Prepare an aqueous dispersion of adaptive gel particles for low-permeability reservoirs, specifically following these steps:

[0032] Low-permeability reservoir adaptive gel particles with an initial gel particle size of 30μm-300μm were selected as water shut-off materials. Simulated formation water was prepared according to the low-permeability formation conditions of the target reservoir. The weighed low-permeability reservoir adaptive gel particles, denoted as M0, were added to the simulated formation water and stirred to disperse to a concentration of 1000mg / L to 5000mg / L. The dispersion was continued for 5 to 20 minutes to prepare a total aqueous dispersion of 500 to 1000mL.

[0033] Step 2: Based on the actual sandstone pore shear and fracture conditions in low-permeability reservoirs, construct an indoor physical model evaluation platform, such as... Figure 1 As shown, the indoor physical model evaluation platform adopts a three-layer series core system. The core system is artificially filled with sand extracted from the strata. It is cylindrical in shape, with a diameter of 5cm and a height of 3cm. The whole is divided into three levels and is clamped by core holder 3 to protect the rock sample and seal it.

[0034] Based on the average permeability and fracture size of the low-permeability formation in the target reservoir, core samples of various stages were filled with produced sand. The first-stage core had a permeability of 1 mD to 50 mD and was used to simulate low-permeability formations. The second-stage core had a permeability of 1000 mD to 5000 mD and was used to simulate natural or artificial fractures. The third-stage core had a permeability of 1 mD to 50 mD and was used to simulate subsequent low-permeability formations.

[0035] Each level is connected to a pressure sensor 4. Simulated core layers and fracture layers with different permeability are artificially filled using formation produced sand. Each layer is connected to pressure sensor 4 to record the sealing pressure value of the layer. The collected pressure data is transmitted to computer 5 in real time. According to the actual geological conditions of low-permeability reservoirs, simulated cores with different permeability are constructed in different layers. The permeability of fracture layers is relatively high, and the permeability of low-permeability layers is relatively low.

[0036] Step 3: Based on the injection conditions of the target reservoir, use a large-displacement constant flow pump 1 to simulate the oilfield site and inject pore-adaptive gel particles as water-blocking material. According to the geological conditions of the low-permeability oilfield in actual application, collect the pressure value changes of each layer to characterize the sealing performance.

[0037] The low-permeability reservoir adaptive gel particle aqueous dispersion prepared in step 1 was injected into the intermediate container 2 with stirring. The gel particle aqueous dispersion was pumped into the core system filled with formation sand in step 2 using a high-displacement constant flow pump 1. Pressure sensor 4 collected pressure values ​​at each level in real time. The injectability and migration of gel particles were evaluated by the changes in pressure values. After the low-permeability reservoir adaptive gel particle aqueous dispersion was injected, water injection was continued until the pressure values ​​at each pressure measuring point were basically stable. The highest pressure values ​​P1max, P2max, and P3max at each pressure measuring point were recorded. The pumping speed range of the high-displacement constant flow pump was 5-20 mL / min. The effective volume of the intermediate container 2 with stirring was 500-1000 mL, and the maximum range of pressure sensor 4 was 20 MPa.

[0038] Step 4: Measure the mass change of each simulated core layer before and after the injection of material, and compare and evaluate the injection performance, migration capacity and retention and sealing capacity of the material.

[0039] Step 4.1: After injecting simulated formation water into each core sample, weigh them to measure the initial mass, denoted as M. 1b M 2b M 3b After injecting the adaptive gel particle aqueous dispersion into the low-permeability reservoir, continue water injection until the pressure values ​​at each pressure measuring point are basically stable. Then, stop the pump until the pressure returns to zero, and re-weigh the core samples at each level to measure the mass after injection, denoted as M. 1a M 2a M 3a ;

[0040] Step 4.2: Calculate the percentage of the mass difference between the injected gel particles and the initial total mass of the gel particles. This percentage represents the retention and plugging percentage of the adaptive gel particles in each core sample of the low-permeability reservoir, denoted as W1 = (M 1a -M 1b ) / M0×100, W2=(M 2a -M 2b ) / M0×100,

[0041] W3=(M 3a -M 3b ) / M0×100;

[0042] Step 4.3: Compare and analyze the retention of gel particles in core samples of various levels to obtain the injection properties of adaptive gel particles in low-permeability reservoirs after shearing through low-permeability layers and their retention and sealing properties in fracture layers. Quantitatively evaluate the migration speed and retention amount of this water-blocking material, such as pore-adaptive gel particles, as well as its subsequent migration and retention capacity into the deep reservoir.

[0043] Step 4.4: Record the pressure values ​​at each pressure measuring point. If each pressure measuring point has a certain pressure value, it indicates that the adaptive gel particles in the low-permeability reservoir are sheared and broken by the pore throat of the low-permeability layer and enter the deep part of the reservoir with the injected water, indicating good injectability. If, except for the first-level pressure measuring point where the pressure increases significantly, the other two pressure measuring points only show a slight increase, it indicates that the gel particles cannot be effectively sheared and broken by the pore throat of the low-permeability layer and cannot enter the deep part of the reservoir, indicating poor injectability.

[0044] In this invention, the method for evaluating the injectability and plugging performance of adaptive gel particles in low-permeability reservoirs involves injecting an aqueous dispersion of the test material via a high-volume pump. The migration velocity and plugging capacity are evaluated by recording pressure changes in each layer. A three-layer, serially connected core system is used to test both the shear-fracture injectability of the material under low-permeability geological conditions and the migration velocity and plugging retention in each layer. The three core layers are filled with produced sand from the formation, flexibly constructing complex geological conditions such as low-permeability layers, fracture layers, and water-channeling layers. The core properties are closer to those of actual reservoirs, providing a more accurate assessment of the material's migration, retention, and plugging performance under different permeability conditions. Comparative testing of the mass changes in the sand-filled core layers accurately and quantitatively evaluates the retention and plugging performance. The simulated test parameters are essentially close to the conditions under which adaptive gel particles are injected in low-permeability oilfields. This invention offers closer approximation to in-situ oilfield injection conditions, more comprehensive testing and evaluation, more accurate quantitative testing performance, and better meets the needs of actual reservoir applications.

[0045] Example 1

[0046] Example 1 of this invention describes a method for evaluating the injectability and plugging properties of adaptive gel particles in low-permeability reservoirs, which is implemented according to the following steps:

[0047] Step 1: Prepare an aqueous dispersion of low-permeability reservoir adaptive gel particles

[0048] Low-permeability reservoir adaptive gel particles with an initial gel particle size of 30 μm were selected. Based on the low-permeability formation conditions of the target reservoir, simulated formation water with a certain salinity was prepared. Low-permeability reservoir adaptive gel particles with M0 = 2.50 g were weighed into the simulated formation water, stirred and dispersed to prepare a concentration of 5000 mg / L, and stirred and dispersed for 20 min to prepare a total aqueous dispersion of 500 mL.

[0049] Step 2: Based on the actual sandstone pore shear and fracture conditions in the low-permeability reservoir, construct an indoor physical model evaluation platform. According to the average permeability and fracture size of the low-permeability formation in the target reservoir, use produced sand to fill cores at various levels. The first-level core has a permeability of 1 mD and is used to simulate the low-permeability formation; the second-level core has a permeability of 5000 mD and is used to simulate natural or artificial fractures; the third-level core has a permeability of 1 mD and is used to simulate subsequent low-permeability formations.

[0050] Step 3: Based on the on-site injection conditions of the target reservoir, set the pump speed of the high-flow constant-flow pump to 20 mL / min, and inject the low-permeability reservoir adaptive gel particle aqueous dispersion prepared in Step 1; pressure sensor 4 collects the pressure values ​​at each level in real time, and evaluates the injectability and migration of gel particles by the changes in pressure values. After injecting the low-permeability reservoir adaptive gel particle aqueous dispersion, continue water injection until the pressure values ​​at each pressure measuring point are basically stable, and record the highest pressure value P at each pressure measuring point. 1max =12MPa, P 2max =7MPa, P 3max =3MPa. The presence of pressure values ​​at each pressure measurement point indicates that the adaptive gel particles in the low-permeability reservoir can be sheared and broken by the pore throat of the low-permeability layer and enter the deep part of the reservoir with the injected water, demonstrating good injectability.

[0051] Step 4: After injecting simulated formation water into each core sample, weigh and measure the initial mass, denoted as M. 1b =143.16g, M 2b =126.32g, M 3b =142.68g; After injecting the low-permeability reservoir adaptive gel particle aqueous dispersion, continuous water injection was continued until the pressure values ​​at each pressure measuring point were basically stable. Then, the pump was stopped until the pressure returned to zero, and the mass of each core sample after injection was weighed again and recorded as M. 1a =144.74g,

[0052] M 2a =126.85g, M 3a =142.91g; Calculate the percentage of the mass difference between the injected gel particles and the initial total mass of the gel particles, which is the retention and plugging percentage of the adaptive gel particles in each level of core sample in low-permeability reservoirs, denoted as W1 = (M 1a -M 1b ) / M0×100=63.2%,

[0053] W2=(M 2a -M 2b ) / M0×100=21.2%, W3=(M 3a -M 3b) / M0×100=9.2%; Through comparative analysis, relatively more gel particles were retained and blocked in the first-level low-permeability layer, and a certain amount were also retained in the second-level fracture layer, effectively blocking the fractures. At the same time, some gel particles entered the subsequent low-permeability layer and blocked it. A very small amount of gel particles were displaced from the system by subsequent continuous water injection. The adaptive gel particles of this low-permeability reservoir have good fracture blocking properties.

[0054] Example 2

[0055] Example 2 of this invention describes an evaluation method for the injection and plugging properties of adaptive gel particles in low-permeability reservoirs, which is implemented according to the following steps:

[0056] Step 1: Prepare an aqueous dispersion of low-permeability reservoir adaptive gel particles

[0057] Low-permeability reservoir adaptive gel particles with an initial gel particle size of 300 μm were selected. Based on the low-permeability formation conditions of the target reservoir, simulated formation water with a certain salinity was prepared. Low-permeability reservoir adaptive gel particles with M0 = 1.00 g were weighed into the simulated formation water, stirred and dispersed to prepare a concentration of 1000 mg / L. The mixture was stirred and dispersed for 5 min to prepare a total aqueous dispersion of 1000 mL.

[0058] Step 2: Based on the actual sandstone pore shear and fracture conditions in the low-permeability reservoir, construct an indoor physical model evaluation platform. According to the average permeability and fracture size of the low-permeability formation in the target reservoir, use produced sand to fill core samples at various levels. The first-level core has a permeability of 50 mD and is used to simulate the low-permeability formation; the second-level core has a permeability of 3000 mD and is used to simulate natural or artificial fractures; the third-level core has a permeability of 50 mD and is used to simulate subsequent low-permeability formations.

[0059] Step 3: Based on the on-site injection conditions of the target reservoir, set the pump speed of the high-displacement constant flow pump to 5 mL / min, and inject the low-permeability reservoir adaptive gel particle aqueous dispersion prepared in Step 1; pressure sensor 4 collects the pressure values ​​at each level in real time, and evaluates the injectability and migration of gel particles by the changes in pressure values. After injecting the low-permeability reservoir adaptive gel particle aqueous dispersion, continue water injection until the pressure values ​​at each pressure measuring point are basically stable, and record the highest pressure value P at each pressure measuring point. 1max =16MPa, P 2max =1.3MPa, P 3max =0.1MPa. Except for the first pressure measuring point where the pressure increased significantly, the other two pressure measuring points only showed a slight increase. The gel particles could not be effectively sheared and broken by the pore throat of the low-permeability layer and could not enter the deep part of the reservoir, resulting in relatively weak injection capability.

[0060] Step 4: After injecting simulated formation water into each core sample, weigh and measure the initial mass, denoted as M.1b =138.33g, M 2b =129.26g, M 3b =137.92g; After injecting the low-permeability reservoir adaptive gel particle aqueous dispersion, continuous water injection was continued until the pressure values ​​at each pressure measuring point were basically stable. Then, the pump was stopped until the pressure returned to zero, and the mass of each core sample after injection was weighed again and recorded as M. 1a =139.25g,

[0061] M 2a =129.34g, M 3a =137.92g; Calculate the percentage of the mass difference between the injected gel particles and the initial total mass of gel particles, which is the retention and plugging percentage of adaptive gel particles in core samples of low-permeability reservoirs, denoted as W1 = (M 1a -M 1b ) / M0×100=92.0%,

[0062] W2=(M 2a -M 2b ) / M0×100=8%, W3=(M 3a -M 3b ) / M0×100=0%; Through comparative analysis, the vast majority of gel particles are retained in the first-level low-permeability layer. Due to the relatively hardness of the gel particles, they are not crushed by the compression and shearing of the low-permeability pore throat under the condition of large-volume injection, and cannot enter the second-level fracture layer. The small number of broken gel particles cannot effectively seal the second-level fracture layer, and no particles enter the subsequent low-permeability layer of the third level. The self-adaptive gel particle injection of this low-permeability reservoir is poor and cannot seal the deep fractures of the reservoir.

[0063] Example 3

[0064] Example 3 of this invention describes an evaluation method for the injection and plugging properties of adaptive gel particles in low-permeability reservoirs, which is implemented according to the following steps:

[0065] Step 1: Prepare an aqueous dispersion of low-permeability reservoir adaptive gel particles

[0066] Low-permeability reservoir adaptive gel particles with an initial gel particle size of 150 μm were selected. Based on the low-permeability formation conditions of the target reservoir, simulated formation water with a certain salinity was prepared. Low-permeability reservoir adaptive gel particles with M0 = 2.4 g were weighed into the simulated formation water, stirred and dispersed to prepare a concentration of 3000 mg / L, and stirred and dispersed for 10 min to prepare a total aqueous dispersion of 800 mL.

[0067] Step 2: Based on the actual sandstone pore shear and fracture conditions in the low-permeability reservoir, construct an indoor physical model evaluation platform. According to the average permeability and fracture size of the low-permeability formation in the target reservoir, use produced sand to fill core samples at various levels. The first-level core has a permeability of 32 mD and is used to simulate the low-permeability formation; the second-level core has a permeability of 1000 mD and is used to simulate natural or artificial fractures; the third-level core has a permeability of 11 mD and is used to simulate subsequent low-permeability formations.

[0068] Step 3: Based on the on-site injection conditions of the target reservoir, set the pump speed of the high-displacement constant flow pump to 14 mL / min, and inject the low-permeability reservoir adaptive gel particle aqueous dispersion prepared in Step 1; pressure sensor 4 collects the pressure values ​​at each level in real time, and evaluates the injectability and migration of the gel particles by the changes in pressure values. After injecting the low-permeability reservoir adaptive gel particle aqueous dispersion, continue water injection until the pressure values ​​at each pressure measuring point are basically stable, and record the highest pressure value P at each pressure measuring point. 1max =11MPa, P 2max =9MPa, P 3max =5MPa, and a significant pressure rise was observed at each pressure measurement point. The gel particles were able to be sheared and broken by the low-permeability pore throat and enter the deep reservoir, indicating good injectability.

[0069] Step 4: After injecting simulated formation water into each core sample, weigh and measure the initial mass, denoted as M. 1b =140.21g, M 2b =132.53g, M 3b =141.79g; After injecting the low-permeability reservoir adaptive gel particle aqueous dispersion, continuous water injection was continued until the pressure values ​​at each pressure measuring point were basically stable. Then, the pump was stopped until the pressure returned to zero, and the mass of each core sample after injection was weighed again and recorded as M. 1a =141.06g,

[0070] M 2a =133.56g, M 3a =142.28g; Calculate the percentage of the mass difference between the injected gel particles and the initial total mass of the gel particles, which is the retention and plugging percentage of the adaptive gel particles in each level of core sample in low-permeability reservoirs, denoted as W1 = (M 1a -M 1b ) / M0×100=35.4%,

[0071] W2=(M 2a -M 2b ) / M0×100=42.9%, W3=(M 3a -M 3b) / M0×100=20.4%; Through comparative analysis, the adaptive gel particles of this low-permeability reservoir can be effectively sheared by the pore throat of the low-permeability layer. Except for some retention, the other particles enter the fracture layer with the injected water, which can effectively seal the fractures and form a certain degree of retention and sealing of the subsequent low-permeability layer, thus exhibiting good fracture sealing performance in low-permeability reservoirs.

[0072] Example 4

[0073] Example 4 of this invention describes an evaluation method for the injection and plugging properties of adaptive gel particles in low-permeability reservoirs, which is implemented according to the following steps:

[0074] Step 1: Prepare an aqueous dispersion of low-permeability reservoir adaptive gel particles

[0075] Low-permeability reservoir adaptive gel particles with an initial gel particle size of 200 μm were selected. Based on the low-permeability formation conditions of the target reservoir, simulated formation water with a certain salinity was prepared. Low-permeability reservoir adaptive gel particles with M0 = 1.5 g were weighed into the simulated formation water, stirred and dispersed to prepare a concentration of 2000 mg / L, and stirred and dispersed for 10 min to prepare a total aqueous dispersion of 750 mL.

[0076] Step 2: Based on the actual sandstone pore shear and fracture conditions in the low-permeability reservoir, construct an indoor physical model evaluation platform. According to the average permeability and fracture size of the low-permeability formation in the target reservoir, use produced sand to fill core samples of various levels. The first-level core has a permeability of 45 mD and is used to simulate the low-permeability formation; the second-level core has a permeability of 2000 mD and is used to simulate natural or artificial fractures; the third-level core has a permeability of 10 mD and is used to simulate subsequent low-permeability formations.

[0077] Step 3: Based on the on-site injection conditions of the target reservoir, set the pump speed of the high-displacement constant flow pump to 14 mL / min, and inject the low-permeability reservoir adaptive gel particle aqueous dispersion prepared in Step 1; pressure sensor 4 collects the pressure values ​​at each level in real time, and evaluates the injectability and migration of gel particles by the changes in pressure values. After injecting the low-permeability reservoir adaptive gel particle aqueous dispersion, continue water injection until the pressure values ​​at each pressure measuring point are basically stable. Record the highest pressure values ​​at each pressure measuring point: P1max = 12 MPa, P2max = 10 MPa, P3max = 8 MPa. A significant pressure rise was observed at each pressure measuring point, indicating that the gel particles can be sheared and broken by the low-permeability pore throat and enter the deep reservoir, demonstrating good injectability.

[0078] Step 4: After injecting formation simulated water into each core sample, weigh and measure the initial mass, recording it as M1b = 142.32g, M2b = 129.68g, and M3b = 141.22g. After injecting the low-permeability reservoir adaptive gel particle aqueous dispersion, continue water injection until the pressure values ​​at each pressure measuring point are basically stable. Then, stop the pump until the pressure returns to zero, and weigh and measure the mass of each core sample again after injection, recording it as M1a = 143.16g, M2a = 130.23g, and M3a = 141.56g. Calculate the percentage of the mass difference between the injected gel particles and the initial total mass of the gel particles; this percentage represents the low permeability. The retention and plugging percentages of adaptive gel particles in permeable reservoir cores at each level are denoted as W1 = (M1a-M1b) / M0×100 = 56.3%, W2 = (M2a-M2b) / M0×100 = 36.7%, and W3 = (M3a-M3b) / M0×100 = 22.7%. Comparative analysis shows that the adaptive gel particles in this low-permeability reservoir can be effectively sheared by the pore throat of the low-permeability layer. Except for some retention, the other particles enter the fracture layer with the injected water, effectively plugging the fractures and forming a certain degree of retention and plugging on subsequent low-permeability layers, demonstrating good fracture plugging performance in low-permeability reservoirs.

[0079] This invention provides an evaluation method for the injectability and plugging performance of adaptive gel particles in low-permeability oil reservoirs. A large-displacement constant-flow pump is used to simulate the injection of adaptive gel particle water-blocking material in an oilfield. Based on the geological conditions of the actual low-permeability oilfield, simulated core layers and fracture layers with different permeabilities are artificially filled using produced sand from the formation. The plugging performance is characterized by collecting pressure changes at each layer. Simultaneously, the migration rate and retention of the adaptive gel particle water-blocking material are quantitatively evaluated by measuring the mass of each simulated core layer before and after material injection.

Claims

1. A method for evaluating the injectivity and plugging property of self-adapting gel particles in low-permeability oil reservoirs, characterized in that, The method is implemented according to the following steps: Step 1, preparing a water dispersion of self-adapting gel particles for low-permeability reservoirs; Step 2, building an indoor physical model evaluation platform according to the shear and fracture conditions of the actual sandstone pore of the low-permeability reservoir; Step 3, simulating the oilfield site according to the injection conditions of the target reservoir, injecting the pore self-adapting gel particles as water shutoff material, and collecting the pressure value changes of each level according to the geological conditions of the low-permeability reservoir in actual application; Step 4, measuring the mass changes of each layer of the simulated core before and after the injection of the material, and comparing and evaluating the injection performance, migration ability and retention plugging ability of the material; The step 1 is characterized in that: the low-permeability reservoir self-adapting gel particles with an initial particle size of 30 μm-300 μm are selected as the water shutoff material, and then the simulated formation water is prepared according to the low-permeability formation conditions of the target reservoir; the low-permeability reservoir self-adapting gel particles are weighed and recorded as M0, and then added to the simulated formation water to prepare a water dispersion with a concentration of 1000 mg / L-5000 mg / L by stirring and dispersing for 5-20 min, and the total amount of the water dispersion is 500-1000 mL; The indoor physical model evaluation platform of the step 2 adopts a three-layer core system connected in series, and the core system is artificially filled with formation produced sand and has a cylindrical shape and is divided into three levels, and a core holder (3) is used for clamping; According to the average permeability and fracture size of the low-permeability formation of the target reservoir, the formation produced sand is used to fill the cores of each level, the first level core has a permeability of 1 mD-50 mD and is used to simulate the low-permeability formation, the second level core has a permeability of 1000 mD-5000 mD and is used to simulate natural fractures or artificial fractures, and the third level core has a permeability of 1 mD-50 mD and is used to simulate the subsequent low-permeability formation; Each level is connected with a pressure sensor (4), the formation produced sand is used to artificially fill the simulated core layers and fracture layers with different permeabilities, each layer is connected with a pressure sensor (4) to record the plugging pressure value of the layer, and the collected pressure data are transmitted to a computer (5) in real time; The water dispersion of the low-permeability reservoir self-adapting gel particles prepared in the step 1 is injected into a middle container (2) with stirring, a large-displacement constant-flow pump (1) is used to pump the gel particle water dispersion into the core system filled with formation sand built in the step 2, the pressure sensor (4) collects the pressure values of each level in real time, the injection performance and migration of the gel particles are evaluated through the changes of the pressure values, and after the injection of the low-permeability reservoir self-adapting gel particle water dispersion, the water injection is continued until the pressure values of each level are basically stable, and the highest pressure values P1max, P2max and P3max of each pressure measuring point are recorded; The step 4 is specifically: Step 4.1, after each level of core injection formation simulation water, weighing, measuring the initial mass, recorded as M 1b , 2b , 3b ; after injection of low permeability reservoir self-adapting gel particles water dispersion, continue to inject water, until the pressure value of each level of pressure measuring point is basically stable, stop the pump to zero pressure, re-weighing each level of core injection after measuring the mass, recorded as M 1a , 2a , 3a ; Step 4.2, calculate the mass difference of the two before and after injecting gel particles and the percentage of the total mass of the initial gel particles, that is, the retention and plugging percentage of the self-adaptive gel particles in the low permeability reservoir in each level of core, recorded as W1=(M 1a -M 1b ) / M0x100, W2=(M 2a -M 2b ) / M0x100, W3=(M 3a -M 3b ) / M0x100; Step 4.3, comparing and analyzing the retention of the gel particles in each level of the core, obtaining the injection performance of the low-permeability reservoir self-adapting gel particles after being sheared by the low-permeability layer and the retention plugging performance in the fracture layer, and quantitatively evaluating the migration speed and retention amount of the pore self-adapting gel particles as the water shutoff material and the migration and retention ability of the subsequent into the deep part of the reservoir; Step 4.4, record the pressure value of each pressure point; if each pressure point has certain pressure value, it shows that the low-permeability reservoir self-adapting gel particles are sheared and broken by the pore throat of the low-permeability layer, and enter the deep part of the reservoir with the injected water, and the injection is good; if the pressure of the first pressure point increases greatly, and the pressure of the other two pressure points only increases slightly, it shows that the gel particles cannot be effectively sheared and broken by the pore throat of the low-permeability layer, and cannot enter the deep part of the reservoir, and the injection is poor.

2. The method for evaluating the injectivity and plugging property of the low-permeability oil reservoir self-adapting gel particles according to claim 1, characterized in that, The large-displacement constant-flow pump (1) has a pump speed range of 5-20 mL / min.

3. The method for evaluating the injectivity and plugging property of the low-permeability oil reservoir self-adapting gel particles according to claim 1, characterized in that, The intermediate container (2) with stirring has an effective volume of 500-1000 mL.

4. The method for evaluating the injectivity and plugging property of the low-permeability oil reservoir self-adapting gel particles according to claim 1, characterized in that, The pressure sensor (4) has a maximum range of 20 MPa.

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