Water injection well profile control method based on protection of low-permeability layer and application of water injection well profile control method

Abstract

The invention relates to a water injection well profile control method based on protection of a low permeability layer and application of the water injection well profile control method. The water injection well profile control method comprises the steps that in the first slug, a medium-low permeability layer is temporarily plugged through a temporary plugging agent; in the second slug, a gel profile control agent is used for blocking the high-permeability layer; according to the third slug, the system injected into the high-permeability layer in the early stage is moved to the deep portion of the oil reservoir through the displacement slug, and deep profile control is achieved; and in the fourth slug, a blocking remover is used for conducting blocking removal on the low-permeability layer. The method has the characteristics of simple synthesis process, no by-product, high viscosity and shear resistance, and also has excellent flowability and injectability; after the profile control system prepared by the profile control method simulates shearing of a pump, a pipeline and a stratum, the viscosity retention rate of the profile control system can still reach 92% or above, and the breakthrough pressure reaches 8-11 MPa. Therefore, the effects of high-permeability plugging and medium-low-permeability oil displacement are achieved.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development technology, and specifically to a method for profile control of water injection wells based on protecting low-permeability layers. Background Technology

[0002] The oilfield has entered a "double-high" development stage (peak production and peak recovery rate), characterized by low recovery rate, high overall water cut, and slow oil production. Due to long-term water injection, water channeling has developed, necessitating deep profile control measures. Conventional, general profile control often results in some of the modifier entering low-permeability layers along with high-permeability layers, contaminating them. While mechanical plugging can prevent contamination, the shortened lifespan of downhole tools due to continuous oilfield development increases subsequent construction costs. Conversely, reducing the injection rate can lead to excessively high injection pressure, causing the modifier to enter low-permeability layers and undergo cross-linking reactions, negatively impacting profile control effectiveness and hindering subsequent waterflooding for oil recovery.

[0003] In the prior art, such as publication number "CN102311728B", a chemical pressure-reducing and injection-enhancing agent for water injection wells is provided. Its main components include hexadecyltrimethylammonium bromide, MY / IMC-80BHH corrosion inhibitor, polyaminopolyether methylenephosphonic acid, polyquaternary ammonium salt, citric acid (industrial grade), and hydrochloric acid (industrial grade). The chemical pressure-reducing and injection-enhancing agent is uniformly added to the injection water. By reducing the interfacial tension between oil and water, it increases the permeability of the aqueous phase and the migration speed of the oil-water microemulsion, prevents scale formation, and inhibits the growth of various bacteria, thereby achieving the purpose of pressure reduction and injection enhancement in low-permeability oilfield water injection wells. CN117659972A discloses the present invention of a corn cob granular powder profile control, water plugging, and channeling agent and its application. The main components of this profile control, water plugging, and channeling agent include corn cob granular powder, liquid water glass, and surfactant. Under stirring conditions, corn cob powder is uniformly dispersed in a water glass solution containing a surfactant. During the stirring and dispersion process, the micropores and surface of the corn cob particles are fully wetted by the water glass solution under the action of the surfactant, changing the particle specific gravity and enabling them to be stably suspended in the solution, thus obtaining a corn cob powder profile control, water shut-off, and channeling blocking agent. This profile control, water shut-off, and channeling blocking agent can be prepared with injection water at a suitable concentration and combined with different activation processes to achieve profile control and water shut-off in water-drive reservoirs; CN116444722B discloses a high molecular weight polyacrylamide emulsion water shut-off and profile control agent and its preparation method. The preparation method is as follows: Nitrogen gas is introduced into the reaction vessel, and acrylamide, vinyltriethoxysilane, 2-amino-2-methyl-4-pentenoic acid, 1-vinyl-3-benzylimidazolium bromide, N,N-methylenebisacrylamide, emulsifier, dispersant, buffer salt, and deionized water are added in sequence. The mixture is stirred to obtain a uniform emulsion. An initiator is added to a high-level dropping tank and slowly added to the above reaction vessel. During the dropping process, the solution automatically heats up. After the dropping is completed, the reaction is kept at a constant temperature and then cooled to below 40°C to obtain the product, a water-blocking and profile control agent.

[0004] In summary, existing profile control agent synthesis technologies are not only cumbersome in their synthesis process and generate numerous byproducts, requiring not only the purification of components but also significant time and resources. Furthermore, the profile control agents currently used in the field exhibit poor temperature resistance, acid and alkali resistance, and shear resistance, resulting in poor sealing performance after entering the formation. Moreover, they do not consider implementing protective measures for low-permeability layers, which can easily cause contamination of non-target layers during profile control. Summary of the Invention

[0005] The purpose of this invention is to provide a method for profile control in water injection wells based on the protection of low-permeability layers, addressing the following problems existing in current profile control agent synthesis technologies: ① The synthesis process is not only cumbersome but also generates numerous byproducts; ② Not only is component purification required, but significant time and resources are also incurred; ③ Currently used profile control agents have poor temperature resistance, acid and alkali resistance, and shear resistance, resulting in poor sealing performance after entering the formation and easy contamination of non-target layers. Compared with existing methods for protecting low-permeability layers, this method offers the advantage of producing a profile control agent with a simple synthesis process, no byproducts, high viscosity, and shear resistance, along with excellent fluidity and injectability. This allows for high-permeability sealing and medium-to-low-permeability oil displacement.

[0006] To achieve the above technical objectives, the present invention provides the following technical solutions.

[0007] This invention provides a method for profile control of injection wells based on the protection of low-permeability layers, comprising: The first stage of plugging involves temporarily sealing the medium- and low-permeability layers using a temporary plugging agent solution. The second-stage plug utilizes a gel profile control agent to seal the hyperpermeable layer; the gel profile control agent comprises: a polymer, a crosslinking agent, and additives; The third stage plug utilizes a displacement slug to migrate the previously injected high-permeability layer system to the deeper part of the reservoir, achieving deep profile control; the displacement slug is the same as the first stage plug. The fourth stage involves using a plugging agent solution to unblock the low-permeability layer.

[0008] Furthermore, the temporary plugging agent includes one or more of CQKL-1 type pre-crosslinked gel particles and SAK-3(Ⅱ) type pre-crosslinked gel particles.

[0009] Preferably, the mass concentration of CQKL-1 type pre-crosslinked gel particles in the temporary plugging agent solution is 0.3~0.5%, and the mass concentration of SAK-3(Ⅱ) type pre-crosslinked gel particles is 0.3~0.5%.

[0010] Further, the gelling agent, by mass percentage, preferably consists of 0.4-0.6% polymer, 0.4-0.6% crosslinking agent, 0.3-0.5% additives, and the balance being water.

[0011] Furthermore, the polymer includes anionic polyacrylamide and / or its derivatives; the crosslinking agent includes phenol, formaldehyde, phenolic prepolymer and / or its derivatives; and the auxiliary agent is thiourea.

[0012] Furthermore, the polymer is preferably composed of one or more of urea-based anionic polyacrylamide, benzyl imidazole ionic liquid-modified anionic polyacrylamide, and crown ether grafted modified anionic polyacrylamide; the crosslinking agent is composed of one or more of conventional phenol, formaldehyde, phenolic prepolymer, and hexamethylenetetramine; and the auxiliary agent is thiourea.

[0013] Furthermore, the urea-based anionic polyacrylamide is preferably composed of one or more of di-tert-butyl dicarbonate, o-nitroisocyanate, hydrazine hydrate, trifluoroacetic acid, and di(N-succinimide) sebacate, and has a triple helix structure.

[0014] The benzylimidazolium ionic liquid-modified anionic polyacrylamide is prepared by a Friedel-Crafts alkylation reaction between the benzylimidazolium ionic liquid and polyacrylamide. Furthermore, the benzylimidazolium ionic liquid-modified anionic polyacrylamide is preferably composed of one or more of 1-butyl-3-methylimidazolium bromide ionic liquid, 1-vinyl-3-(pentafluorobenzyl)imidazolium bromide ionic liquid (VIMPFP), polyacrylamide, benzoic acid ester, and triphenylmethane, and has a tubular structure.

[0015] The crown ether grafted modified anionic polyacrylamide is preferably composed of one or more of dibenzo-18-crown-6, 4-formyldibenzo-18-crown-6, polyvinyl alcohol, and polyacrylamide, and has a core-shell structure.

[0016] Furthermore, in the third stage plug, the displacement plug is the same as the first stage plug, that is, the displacement solution is one or more of BPPG and DPPG.

[0017] Preferably, the mass concentration of BPPG in the displacement solution is 0.3-0.5% and the mass concentration of DPPG is 0.3-0.5%.

[0018] Preferably, the unblocking agent is one or more of ammonium persulfate and acetic acid depolymerizing agent.

[0019] Preferably, the mass concentration of acetic acid depolymerizing agent in the unblocking agent solution is 8-12%, and the mass concentration of ammonium persulfate is 35-48%.

[0020] Furthermore, the deep profile control method for water injection wells is applicable to heterogeneous oil reservoirs with a permeability variation coefficient greater than 0.5.

[0021] The present invention has the following beneficial effects: 1. Compared with existing methods for protecting low-permeability layers, the profile control method for water injection wells based on the protection of low-permeability layers provided by this invention has the advantages of simple synthesis process, no by-products, high viscosity, and shear resistance. The apparent viscosity is 100-150 mPa·s, and it has excellent fluidity and injectability. After simulating the shearing of pumps, pipelines, and formations, the viscosity retention rate of this system can still reach more than 92%, and the breakthrough pressure can reach 8-11 MPa.

[0022] 2. This invention introduces an intelligent ultra-high molecular weight polymer to prepare a profile control system suitable for the profile control needs of low-permeability reservoirs that have entered the "dual-high" development stage of long-term water injection and water channel development.

[0023] 3. The slug combination designed in this invention can not only seal high-permeability layers, but also protect low-permeability layers.

[0024] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other design solutions and drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 Permeability (gas permeability) and percentage of each layer in the artificial rock core; Figure 2 Graphs showing the deblocking effects of ammonium persulfate solutions of different concentrations on gel particles; Figure 3 Effects of different concentrations of depolymerizing agent solutions on the unblocking effect of gel particles; Figure 4 The effect of different concentrations of ammonium persulfate plus depolymerizing agent composite solutions on the unblocking effect of gel particles; Figure 5 Displacement pressure curve (evaluation of the protection performance of low-permeability layers based on the combination of particles and unblocking agents). Figure 6 Dynamic changes of unblocked NMR data (evaluation of the protective performance of low-permeability layers based on a combination of particles and unblocking agents); Figure 7 Dynamic changes in NMR data after unblocking (evaluation of the protective performance of low-permeability layers based on a combination of particles and unblocking agents). Figure 8Recovery rate curve (evaluation of the protection performance of low-permeability layers based on a combination of particles and unblocking agents); Figure 9 Dynamic changes in NMR data after unblocking (evaluation of the protective performance of low-permeability layers based on a combination of particles and unblocking agents). Figure 10 Displacement pressure curve (profile modifier bulk slug assembly design); Figure 11 Displacement pressure curve (profile modifier bulk slug assembly design); Figure 12 Displacement pressure curve (profile modifier bulk slug assembly design); Figure 13 Dynamic changes in nuclear magnetic resonance imaging after unblocking (design of the main slug assembly of profile control agent); Figure 14 Dynamic changes in nuclear magnetic resonance imaging after unblocking (design of the main slug assembly of profile control agent); Figure 15 Dynamic changes in nuclear magnetic resonance imaging after unblocking (design of the main slug assembly of profile control agent); Figure 16 Flow rate curve of slug combination mode 1 (profile modifier main slug combination design). Figure 17 Flow rate curve of slug combination mode 2 (profile modifier main slug combination design). Figure 18 Flow rate curve of slug combination mode 3 (profile control agent main slug combination design). Figure 19 Displacement pressure curve (optimization of combined slug injection rate); Figure 20 Displacement pressure curve (optimization of combined slug injection rate); Figure 21 Displacement pressure curve (optimization of combined slug injection rate); Figure 22 Dynamic changes in MRI scans of unblocked slugs (optimization of combined slug injection rate); Figure 23 Dynamic changes in MRI scans of unblocked slugs (optimization of combined slug injection rate); Figure 24 Dynamic changes in MRI scans of unblocked slugs (optimization of combined slug injection rate); Figure 25 Displacement pressure curve (sealing slug and displacement slug design). Figure 26 Displacement pressure curve (sealing slug and displacement slug design). Figure 27 Displacement pressure curve (sealing slug and displacement slug design). Figure 28Dynamic changes in nuclear magnetic resonance imaging (design of sealing sluice block and replacement sluice block); Figure 29 Dynamic changes in nuclear magnetic resonance imaging (design of sealing sluice block and replacement sluice block); Figure 30 Dynamic changes in nuclear magnetic resonance imaging (design of sealing sluice block and replacement sluice block); Figure 31 Oil production curve of profile modification in well area Shi 204.

[0027] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Detailed Implementation

[0028] The invention can be further understood in conjunction with the following detailed description of preferred embodiments and included examples. Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. If any definition of a specific term disclosed in the prior art differs from any definition provided herein, the definition provided herein shall prevail.

[0029] It should be noted that the implementation conditions used in the examples can be further adjusted according to the specific experimental environment, and the implementation conditions not specified are usually those in conventional experiments. Unless otherwise specified, the preparation methods mentioned in this invention are all conventional methods; unless otherwise specified, the various chemical reagents and chemicals mentioned in the following examples are all chemical reagents and chemicals known and commonly used in the prior art.

[0030] In a typical embodiment of this application, a method for profile control of injection wells based on the protection of low-permeability layers is provided, comprising: The first stage plugging method uses a temporary plugging agent solution to temporarily seal the medium and low permeability layers; the temporary plugging agent solution includes one or more of BPPG (i.e., CQKL-1 type pre-crosslinked gel particles; manufactured by Shida Aode (Kaifeng) Technology Co., Ltd.) and DPPG (i.e., SAK-3 (Ⅱ) type pre-crosslinked gel particles; manufactured by Shida Aode (Kaifeng) Technology Co., Ltd.); The second stage plug utilizes a gel profile control agent to seal the hyperpermeable layer; the gel profile control agent includes a polymer, a crosslinking agent, and additives. The third stage plug utilizes a displacement slug to migrate the previously injected high-permeability layer system to the deeper part of the reservoir, achieving deep profile control; the displacement slug is the same as the first stage plug. The fourth stage involves using a plugging agent solution to unblock the low-permeability layer.

[0031] Preferably, the mass concentration of BPPG and the mass concentration of DPPG in the temporary plugging agent solution are 0.3-0.5%.

[0032] Preferably, the gelling agent, by mass percentage, consists of 0.4-0.6% polymer, 0.4-0.6% crosslinking agent, 0.3-0.5% additives, and the balance being water.

[0033] Furthermore, the polymer comprises anionic polyacrylamide and / or its derivatives; The crosslinking agent includes phenol, formaldehyde, phenolic prepolymer and / or its derivatives; The adjuvant is thiourea.

[0034] Furthermore, the polymer is one or more of the following: urea-based anionic polyacrylamide, benzyl imidazole ionic liquid-modified anionic polyacrylamide, and crown ether grafted modified anionic polyacrylamide.

[0035] The crosslinking agent is composed of one or more of phenol, formaldehyde, phenolic prepolymer, and hexamethylenetetramine.

[0036] As a preferred embodiment of the present invention, the urea-based anionic polyacrylamide is preferably composed of one or more of di-tert-butyl dicarbonate, o-nitrophenyl isocyanate, hydrazine hydrate, trifluoroacetic acid, and di(N-succinimide) sebacate, and has a triple helix structure.

[0037] The benzylimidazolium ionic liquid-modified anionic polyacrylamide is prepared by a Friedel-Crafts alkylation reaction between the benzylimidazolium ionic liquid and polyacrylamide; further, the benzylimidazolium ionic liquid-modified anionic polyacrylamide is preferably composed of one or more of 1-butyl-3-methylimidazolium bromide ionic liquid, 1-vinyl-3-(pentafluorobenzyl)imidazolium bromide ionic liquid (VIMPFP), polyacrylamide, benzoic acid ester, and triphenylmethane, and has a tubular structure.

[0038] The crown ether grafted modified anionic polyacrylamide is preferably composed of one or more of dibenzo-18-crown-6, 4-formyldibenzo-18-crown-6, polyvinyl alcohol, and polyacrylamide, and has a core-shell structure.

[0039] In the third stage plug, the displacement plug is the same as the first stage plug, that is, the displacement solution is also composed of one or more of BPPG and DPPG; furthermore, the mass concentration of BPPG in the displacement solution is 0.3~0.5% and the mass concentration of DPPG is 0.3~0.5%.

[0040] As a preferred embodiment of the present invention, the unblocking agent is one or more of ammonium persulfate and acetic acid depolymerizing agent.

[0041] Preferably, the mass concentration of acetic acid depolymerizing agent in the unblocking agent solution is 8-12%, and the mass concentration of ammonium persulfate is 35-48%.

[0042] The present invention further provides an application of the above-mentioned water injection well profile control method based on protecting low-permeability layers, characterized in that: the water injection well profile control method is applicable to heterogeneous oil reservoirs with a permeability variation coefficient greater than 0.5.

[0043] Example 1 The reservoirs in the Shinan Oilfield are all strongly heterogeneous, low-permeability reservoirs with moderate to strong water sensitivity and moderate or higher volumetric flow sensitivity, exhibiting significant differences in recovery rates. For example, the Shinan 31 Qingshuihe Formation reservoir is medium-porosity and low-permeability, with a relatively high caliber recovery rate (30.0%); the Shi 204 Xishanyao Formation reservoir is low-porosity, low-permeability, and highly heterogeneous, with the lowest relative recovery rate. The pressure coefficients in the Shinan Oilfield are all below 1.0, classifying it as a normal pressure system; it is primarily composed of light oil, with crude oil viscosities ranging from 1.03 to 3.96 mPa·s, except for Shinan 4... J 2s The oil reservoir has a salinity of 8651.9 mg / L and a water type of NaHCO3. Other oil reservoirs have salinity above 20000 mg / L and formation water of CaCl2 type.

[0044] In the laboratory study of low-permeability layer protection technology, to simulate real formation conditions, the following heterogeneous matrix channel models were designed with permeabilities of 50mD, 300mD, and 1500mD. After the model design was completed, rock samples of each permeability were selected, cut, and then assembled according to the model proportions. This embodiment achieves the protection of the low-permeability layer through Method 1: Method 1: Low-permeability layer protection method based on a combination of temporary plugging agent and unplugging agent, namely, the method of injecting 0.2PV temporary plugging agent + 0.8PV gel profile control agent followed by unplugging.

[0045] (1) Screening and static performance evaluation of unblocking agents First, the static evaluation of the unblocking effects of different types of unblocking agents on gel profile control agents and temporary plugging agents was conducted using bottle testing. Subsequently, dynamic evaluation was carried out through core experiments.

[0046] ① Compatibility evaluation of ammonium persulfate At 80℃, prepare two sets of ammonium persulfate solutions with a mass concentration of 2%~6% using ten test tubes. Add gelling agent and temporary plugging agent to each solution, and read the volume of gelling agent and temporary plugging agent every half hour. Figure 2 The final unblocking effects of gel profile control agents and temporary plugging agents at different concentrations of ammonium persulfate are presented. Figure 2It can be seen that ammonium persulfate has a good unblocking effect on gel profile control agents, with a preferred concentration of 5%. However, ammonium persulfate has a poor unblocking effect on temporary plugging agents, and subsequent agglomerates cannot be degraded.

[0047] ② Suitability evaluation of acetic acid depolymerization agent At 80℃, prepare two sets of 8%-12% depolymerization agent solutions using ten test tubes, and add gel profile control agent and temporary plugging agent respectively. Read the volume of gel profile control agent and temporary plugging agent every half hour. Figure 3 The final unblocking effects of gel profile control agents and temporary plugging agents at different concentrations of depolymerizing agents are presented. Figure 3 It can be seen that, compared to ammonium persulfate, the depolymerizing agent has a poorer declogging effect on gel profile control agents. Compared to ammonium persulfate, the depolymerizing agent has a better declogging effect on temporary plugging agents, with a preferred concentration of 12%.

[0048] ③ Compatibility evaluation of ammonium persulfate and depolymerizing agent combination The previous study investigated the de-clogging effects of a single de-clogging agent on gel profile control agents and temporary plugging agents. The subsequent study investigated the de-clogging effects of mixed solutions of ammonium persulfate and depolymerizing agent at different concentration ratios on gel profile control agents and temporary plugging agents.

[0049] At 80℃, prepare two sets of solutions using fourteen test tubes. Figure 3 Different ratios of depolymerizing agent and ammonium persulfate composite solutions were shown. Gel profile control agent and temporary plugging agent were added to each solution, and the volumes of gel profile control agent and temporary plugging agent were read every half hour. Figure 4 The final unblocking effects of gel profile control agents and temporary plugging agents in compound solutions of different concentrations are presented. Figure 4 It can be seen that for gel profile control agents, the optimal unblocking compound concentration is depolymerizer: ammonium persulfate = 0:10. For temporary plugging agents, the optimal unblocking compound concentration is depolymerizer: ammonium persulfate = 2:8.

[0050] (2) Evaluation of the protective performance of low-permeability layers based on the combination of temporary plugging agent and unplugging agent ① Blocking experiment Using artificial cores from the target stratum, the permeability was first measured by vacuum saturation with water. Then, heavy water was injected, and T2 analysis was used to observe the leakage along the high-permeability layer during water flooding. Next, a temporary plugging agent prepared with 0.2 PV of heavy water and a polymer-phenolic gel system prepared with 0.8 PV of heavy water were injected at a rate of 0.5 mL / min at an experimental temperature of 73℃. T2 analysis was performed using NMR. After 3 days of curing, a second water flooding was performed, this time using heavy water flooding. The injection and plugging of the gel were observed using NMR T2 signals. Finally, a 0.5 PV composite unblocking agent was used for unblocking treatment, maintained at a constant temperature for 1 day, followed by a second (heavy) water flooding. The plugging performance of the gel system after unblocking was measured. At this point, the protection performance of the low-permeability layer during water flooding using the gel profile control agent based on the unblocking agent was analyzed using NMR T2 spectra.

[0051] Figure 5 The protective performance of low-permeability layers using artificial cores from the target formation after combined plugging and unplugging with temporary plugging agents and gel profile control agents is presented. For high-water-cut cores, the plugging rate was 93% before unplugging and 41% after unplugging. The permeability recovery rate of the contaminated core after unplugging reached 88.33%. Compared with the protection process using a single unplugging agent, the combined approach of temporary plugging agent and unplugging agent provides better protection for low-permeability layers.

[0052] Figure 6 The changes in T2 spectra before and after plugging with a combination of temporary plugging agent and gel profile control agent using artificial cores from the target formation are presented. During the injection of the temporary plugging agent and gel profile control agent, both primarily penetrate the high-permeability layer, with a small amount penetrating the medium- and low-permeability layers. Before unplugging, secondary waterflooding mainly occurs through the medium- and low-permeability layers, with a slight increase in pressure during the secondary waterflooding process. Figure 7 The changes in T2 spectra after temporary plugging and gel profile control using artificial cores from the target stratigraphic level are presented. After unplugging, the gel profile control agent mainly flows through low-permeability layers, thus removing contamination from the low-permeability layer (end face).

[0053] ② Oil displacement experiment Using artificial cores from the target stratum, the system was first saturated with water under vacuum to determine permeability, then saturated with oil to determine oil saturation. T2 analysis was used to observe the oil content and distribution in each layer of the core after oil saturation. Subsequently, heavy water flooding was performed, with real-time measurement of injection pressure and oil-water flow rate changes at the outlet. T2 analysis was used to observe the oil content and distribution in each layer of the core after water flooding, analyzing the leakage along high-permeability layers and changes in residual oil. Next, a temporary plugging agent prepared with 0.2 PV heavy water and a polymer-phenolic gel system prepared with 0.8 PV heavy water were injected at a rate of 0.5 mL / min at an experimental temperature of 73℃. T2 analysis was performed using NMR. After 3 days of curing, a second water flooding was performed, this time using heavy water flooding, to observe the gel injection and plugging status using NMR T2 signals. Finally, a 0.5 PV composite unblocking agent was used for unblocking treatment, maintained at a constant temperature for 1 day, followed by a second (heavy) water flooding, and the unblocking status of the gel system was measured. At this time, the low-permeability layer protection performance and oil displacement effect of gel profile control agent based on unblocking agent were also analyzed by using nuclear magnetic resonance T2 spectrum.

[0054] Figure 8 The changes in oil recovery after using artificial cores from the target formation for plugging and displacement with temporary plugging agents and gel profilers are presented. For oil-bearing cores after waterflooding, the waterflooding recovery rate was 45.5%, and the recovery rate after injecting temporary plugging agents and gel profilers was 45.5%. Using a low-permeability layer protection process combining temporary plugging agents, gel profilers, and unplugging agents, the recovery rate reached 60.02%, and subsequent waterflooding could still produce a small amount of oil. Figure 9The changes in T2 signal after plugging with temporary plugging agents and gel profilers using artificial cores from the target formation are presented. Compared with gel injection alone, injecting temporary plugging agents as pre-plugs can better initiate residual oil in medium and low permeability formations.

[0055] Example 2 Building upon previous low-permeability layer protection techniques, this study further optimizes the design of the combination of profile control agent bulk slugs to achieve high-strength sealing of the target layer while minimizing damage to low-permeability layers. This research utilizes three different methods to design the combination of profile control agent bulk slugs.

[0056] Method 1: Experimental temperature 73℃, inject 1PV gel profile control agent (without temporary plugging agent) at a rate of 0.5mL / min.

[0057] Method 2: The experimental temperature was 73℃, and 0.2PV of temporary plugging agent + 0.8PV of gel profile control agent were injected at a rate of 0.5mL / min.

[0058] Method 3: The experimental temperature was 73℃. 0.2PV temporary plugging agent + 0.8PV gel profile control agent + 0.2PV temporary plugging agent + 0.8PV gel profile control agent were injected at a rate of 0.5mL / min.

[0059] The analysis of the profile control effect of the main slug combination of heterogeneous core profile control agent within the layer was conducted using artificial cores from the target layer. First, the cores were saturated with water under vacuum, and their permeability was measured. Then, heavy water was injected, and T2 analysis was used to observe the leakage along the high-permeability layer during water flooding. Next, three cores were injected with 1 PV gel profile control agent (mixed with heavy water), 0.2 PV temporary plugging agent + 0.8 PV gel profile control agent, and 0.2 PV temporary plugging agent + 0.8 PV gel profile control agent + 0.2 PV temporary plugging agent + 0.8 PV gel profile control agent, respectively. The injection rate was 0.5 mL / min, and the experimental temperature was 73℃. T2 analysis was performed using NMR. After 3 days of curing, a second water flooding was performed, this time using heavy water flooding, to observe the injection and sealing of the gel using NMR T2 signals. Finally, a 0.5 PV composite unblocking agent was used for unblocking treatment, which was carried out at a constant temperature for 1 day, followed by a second (heavy) water flooding, and the sealing performance of the gel system after unblocking was measured. At this point, the profile control effect based on different profile control agent bulk slug combinations was also analyzed using nuclear magnetic resonance T2 spectra.

[0060] Figure 10 , Figure 11 , Figure 12Displacement pressure curves for slugs with different profile control agent combinations are presented. The figures also show that polymer gelling solutions have better injectability, while temporary plugging agents have poorer injectability. Injecting a temporary plugging agent followed by a polymer gelling solution causes a rapid increase in injection pressure. The combination of temporary plugging agent and gelling profile control agent exhibits the strongest sealing performance, followed by pure gelling profile control agent (without temporary plugging agent), and the combination of temporary plugging agent, gelling profile control agent, temporary plugging agent, and gelling profile control agent exhibits the weakest sealing performance.

[0061] Table 1 presents the unplugged plugging rate, plugging rate, and permeability recovery rate under three different profile control agent slug combination designs. The plugging rate was 91.2% with pure gel profile control agent (without temporary plugging agent), 93% with temporary plugging agent plus gel profile control agent, and 90.3% with temporary plugging agent plus gel profile control agent plus temporary plugging agent plus gel profile control agent. The comparison shows that the slug combination using temporary plugging agent plus gel profile control agent provides the strongest plugging performance on the target layer.

[0062] Table 1. Permeability Recovery of Three Combined Design Methods

[0063] Figure 13 , Figure 14 , Figure 15 The NMR dynamic curves of slugs with different profile control agent combinations are presented. The results show that slugs with the same combination of profile control agents mainly enter the high-permeability layer. The figures also show that after unplugging Method 1 (single gel slug), the secondary waterflooding mainly enters the medium-permeability layer. After unplugging Method 2 (a combination of temporary plugging agent and gel slug), the secondary waterflooding mainly enters the low-permeability layer. After unplugging Method 3 (a two-stage combination of temporary plugging agent and gel slug), both the medium-permeability and low-permeability layers are entered during the secondary waterflooding, expanding the waterflooding sweep area.

[0064] Analysis of the Profile Control Effect of Parallel Core Combinations of Profile Control Agents and Main Slugs in Heterogeneous Interlayer Cores: Based on previous experiments with different profile control agent main slugs in heterogeneous cores within single-tube layers, this study further optimizes the design of profile control agent main slug combinations through parallel core experiments in heterogeneous interlayer cores. The aim is to achieve high-strength sealing of the target layer while minimizing damage to low-permeability layers. This study implements the design of profile control agent main slug combinations using three different methods.

[0065] Method 1: Parallel core samples 100 / 300 / 1500-1 and 100 / 300 / 1000-1 were used at an experimental temperature of 73℃. 2PV gel profile control agent (without temporary plugging agent) was injected at a rate of 1mL / min.

[0066] Method 2: Parallel core samples 100 / 300 / 1500-2 and 100 / 300 / 1000-2 were used. The experimental temperature was 73℃. 0.4PV temporary plugging agent + 1.6PV gel profile control agent were injected at a rate of 1mL / min.

[0067] Method 3: Parallel cores 100 / 300 / 1500-3 and 100 / 300 / 1000-3 were used. The experimental temperature was 73℃. 0.4PV temporary plugging agent + 1.6PV gel profile control agent + 0.4PV temporary plugging agent + 1.6PV gel profile control agent were injected at a rate of 1mL / min.

[0068] Using artificial cores from the target strata, the permeability was first measured by vacuum saturation with water, followed by heavy water injection. T2 analysis was then performed to observe the leakage along high-permeability layers during water flooding. Next, two cores from the target strata were connected in parallel, and profile control agents were injected using the three methods described above, at an injection rate of 1 mL / min at an experimental temperature of 73℃. T2 analysis was performed using NMR. After a 3-day curing period, a second water flooding was performed, this time using heavy water flooding, to observe the injection and sealing of the gel using NMR T2 signals. Finally, a 0.5 PV composite unblocking agent was used for unblocking treatment, maintained at a constant temperature for 1 day, followed by a second (heavy) water flooding. The sealing effect of the gel system after unblocking was measured. At this point, NMR T2 spectra were again used to analyze the profile control effect based on different profile control agent main block plug combinations in interlayer heterogeneous cores.

[0069] Figure 16 , Figure 17 , Figure 18 The parallel flow rates at different stages after three different combinations of profile control agents and main slugs in heterogeneous interlayer cores are presented. As shown in the figure, the flow rate ratio for secondary waterflooding in Method 1 is 0.8:0.2, for Method 2 it is 0.85:0.15, and for Method 1 it is 0.7:0.3. When injecting gel profile control agent, the flow rate ratio is 0.6:0.4. After one unplugging, the flow rate ratio is 0.45:0.55. After two unpluggings, the flow rate ratio is 0.8:0.2. When injecting temporary plugging agent and gel profile control agent, the flow rate ratio is 0.6:0.4. After one unplugging, the flow rate ratio is 0.8:0.2. After two unpluggings, the flow rate ratio is 0.85:0.15. When injecting two rounds of temporary plugging agent and gel profile control agent, the flow rate ratio is 0.6:0.4. After one unplugging, the flow rate ratio is 0.9:0.1. After the secondary unblocking, the flow ratio is 0.7:0.3.

[0070] Example 3 Building upon the previous optimization of low-permeability layer protection technology and profile control agent slug combination design, this study further optimizes the injection rate of the combined slug to achieve high-strength sealing of the target layer while minimizing damage to the low-permeability layer. This research utilizes three different methods to design the injection rate of the profile control agent combined slug.

[0071] Method 1: At an experimental temperature of 73℃, inject 0.2 PV temporary plugging agent + 0.8 PV gel profile control agent + 0.2 PV temporary plugging agent + 0.8 PV gel profile control agent at a rate of 0.2 mL / min.

[0072] Method 2: The experimental temperature was 73℃. 0.2PV temporary plugging agent + 0.8PV gel profile control agent + 0.2PV temporary plugging agent + 0.8PV gel profile control agent were injected at a rate of 0.5mL / min.

[0073] Method 3: At an experimental temperature of 73℃, inject 0.2PV temporary plugging agent + 0.8PV gel profile control agent + 0.2PV temporary plugging agent + 0.8PV gel profile control agent at a rate of 5mL / min.

[0074] (1) Analysis of the profile control effect of different injection rates of profile control agent combination slug Artificial cores from the target stratum were first vacuum-saturated with water to determine permeability. Then, heavy water was injected, and T2 analysis was used to observe the leakage along the high-permeability layer during water flooding. Next, three cores were injected with 0.2 PV temporary plugging agent + 0.8 PV gel profile control agent + 0.2 PV temporary plugging agent + 0.8 PV gel profile control agent, respectively, at injection rates of 0.2 mL / min, 0.5 mL / min, and 5 mL / min, at an experimental temperature of 73℃. T2 analysis was performed using NMR. After 3 days of curing, a second water flooding was performed, this time using heavy water flooding, to observe the injection and plugging of the gel using NMR T2 signals. Finally, a 0.5 PV composite unplugging agent was used for unplugging treatment, maintained at a constant temperature for 1 day, followed by a second (heavy) water flooding, and the plugging effect of the gel system after unplugging was measured. At this point, NMR T2 spectra were again used to analyze the profile control effect of the profile control agent combination slugs at different injection rates. The experimental results are as follows: Figures 19 to 21 As shown.

[0075] Figure 22 , Figure 23 , Figure 24 Displacement pressure curves for the profile control agent combination slugs at different injection rates are presented. As shown in the figure, when the injection rate is 0.2 mL / min, the injection pressure reaches 20 MPa when the fourth slug is injected. When the injection rate is 0.5 mL / min, the injection pressure reaches 20 MPa when the second slug is injected. When the injection rate is 5 mL / min, the injection pressure rises rapidly, making further injection difficult. Table 2 shows the unblocking and plugging rates of the profile control agent combination slugs at three different injection rates. Table 2 shows that at the three injection rates, the unblocking and plugging rate is 64.2% at an injection rate of 0.2 mL / min, 24.2% at an injection rate of 0.5 mL / min, and 67.7% at an injection rate of 5 mL / min.

[0076] Table 2 Experimental parameters for three injection rates

[0077] Figure 25 , Figure 26 , Figure 27 The NMR dynamics curves of the profiling agent combination slug at different injection rates are presented. Under different injection rates, the secondary waterflooding after unblocking all targeted the medium- and low-permeability layers. Comparison showed that when the injection rate was 0.2 mL / min, the injection pressure was lower, but the degree of mobilization of the medium- and low-permeability layers was greater. The figure also shows that at an injection rate of 0.2 mL / min, the secondary waterflooding mainly targeted the medium- and low-permeability layers, with the strongest mobilization ability towards the medium-permeability layer. At an injection rate of 0.5 mL / min, the secondary waterflooding mainly targeted the medium- and low-permeability layers, with the weakest mobilization ability towards the medium-permeability layer. At an injection rate of 5 mL / min, the secondary waterflooding mainly targeted the medium- and low-permeability layers, with a relatively strong mobilization ability towards the medium-permeability layer.

[0078] Example 4 Building upon previous work on low-permeability layer protection technology, profile control agent slug combination design, and slug injection rate optimization, this study further optimizes the design of sealing and displacement slugs to achieve high-strength sealing of the target layer while minimizing damage to low-permeability layers. This research utilizes three different methods to design sealing and displacement slugs.

[0079] Method 1: At an experimental temperature of 73℃, inject 0.2 PV temporary plugging agent + 0.8 PV gel profile control agent + 0.2 PV temporary plugging agent + 0.8 PV gel profile control agent at a rate of 0.5 mL / min. (Without displacement slug) Method 2: The experimental temperature was 73℃. 0.2PV temporary plugging agent + 0.8PV gel profile control agent + 0.2PV temporary plugging agent + 0.8PV gel profile control agent + 0.2PV temporary plugging agent (BPPG) were injected at a rate of 0.5mL / min.

[0080] Method 3: At an experimental temperature of 73℃, inject 0.2PV temporary plugging agent + 0.8PV gel profile control agent + 0.2PV temporary plugging agent + 0.8PV gel profile control agent + 0.2PV temporary plugging agent (DPPG) at a rate of 5mL / min.

[0081] (1) Analysis of the profile adjustment effect of using sealing slugs and displacement slugs Using artificial cores from the target stratum, the permeability was first measured by vacuum saturation with water, followed by the injection of heavy water. T2 analysis was then performed to observe the water-drive flow along the high-permeability layer. Next, three cores were injected with the following solutions: 0.2 PV temporary plugging agent + 0.8 PV gel profile control agent + 0.2 PV temporary plugging agent + 0.8 PV gel profile control agent (without a sealing plug); 0.2 PV temporary plugging agent + 0.8 PV gel profile control agent + 0.2 PV temporary plugging agent + 0.8 PV gel profile control agent + 0.2 PV temporary plugging agent (BPPG); and 0.2 PV temporary plugging agent + 0.8 PV gel profile control agent + 0.2 PV temporary plugging agent + 0.8 PV gel profile control agent + 0.2 PV temporary plugging agent (DPPG). The injection rate was 0.5 mL / min, and the experimental temperature was 73℃. T2 analysis was performed using NMR. Three days after coagulation, a second water flooding was performed, this time using heavy water flooding, to observe the gel injection and plugging status using NMR T2 signals. Finally, a 0.5PV composite unblocking agent was used for unblocking treatment, with a treatment time of one day at a constant temperature, followed by a second (heavy) water flooding, and the plugging status of the gel system after unblocking was measured. At this time, NMR T2 spectra were also used to analyze the profile modification effect based on different sealing slugs and displacement slugs. Experimental results are as follows: Figures 28 to 30 As shown in the figure, the slug combination using DPPG sealing exhibits the best injection performance and unblocking effect in the target layer. It is worth noting that the injection pressure using BPPG sealing is too high, making it suitable for highly heterogeneous reservoirs. Table 3 presents the unblocking and plugging rates under different sealing and displacement slug designs. Table 3 shows that the unblocking and plugging rates vary under different sealing and displacement slug designs: the plugging rate without sealing is 24.2%, the plugging rate using BPPG sealing is 42.2%, and the plugging rate using DPPG sealing is 25%.

[0082] Figure 28 , Figure 29 , Figure 30 The NMR dynamics curves of different sealing and displacement slugs are presented. Slugs with different profile control agent combinations primarily penetrate the high-permeability layer. The figures also show that in Method 1 (without displacement slugs), secondary waterflooding expands the swept area of ​​medium- and low-permeability zones. In Method 2 (with BPPG displacement slugs), secondary waterflooding primarily penetrates the medium-permeability layer. In Method 3 (with DPPG displacement slugs), secondary waterflooding penetrates even further into the medium-permeability layer than in Method 2.

[0084] Example 5 In the Shi 204 and Shi 4 well areas of the Shinan Oilfield, 20 wells underwent profile control measures. After the measures, the overall increase in injection pressure in the modified areas was controlled within 2 MPa, water injection met the requirements, pressure drop curves showed good sealing performance, and overall reservoir streamlines showed a 45% increase in planar sweep efficiency. The reservoir water cut decreased from 74.0% to 68.0%, achieving a daily oil production increase of 30 tons / day, with a cumulative increase of 5860 tons (see appendix). Figure 31 The predicted final recovery rate is 22.35%, higher than the development plan's 18.89%, indicating a significant improvement in the production situation.

[0085] In summary, the water injection well profile control method based on protecting low-permeability layers provided by this invention has the characteristics of simple synthesis process, no by-products, high viscosity, high shear resistance and high fluidity, thereby playing the role of high-permeability plugging and medium-low permeability oil displacement, providing technical support for the stable production and increase of light oil in the Shinan Oilfield.

[0086] The above description is merely a preferred embodiment of the present invention and is illustrative in nature, not intended to limit the scope of the invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the invention should fall within the protection scope defined by the claims.

Claims

1. A method for profile control of injection wells based on protecting low-permeability layers, characterized in that, include: The first stage of plugging involves temporarily sealing the medium- and low-permeability layers using a temporary plugging agent solution. The second stage plug utilizes a gel profile control agent to seal the hyperpermeable layer; the gel profile control agent includes a polymer, a crosslinking agent, and additives. The third stage plug utilizes a displacement slug to migrate the previously injected high-permeability layer system to the deeper part of the reservoir, achieving deep profile control; the displacement slug is the same as the first stage plug. The fourth stage involves using a plugging agent solution to unblock the low-permeability layer.

2. The method for profile control of injection wells based on the protection of low-permeability layers according to claim 1, characterized in that: The temporary plugging agent solution includes one or more of CQKL-1 type pre-crosslinked gel particles and SAK-3 (Ⅱ) type pre-crosslinked gel particles.

3. The method for profile control of injection wells based on the protection of low-permeability layers according to claim 2, characterized in that: In the temporary plugging agent solution, the mass concentration of the CQKL-1 type pre-crosslinked gel particles is 0.3~0.5%, and the mass concentration of the SAK-3(Ⅱ) type pre-crosslinked gel particles is 0.3~0.5%.

4. The method for profile control of injection wells based on the protection of low-permeability layers according to claim 1, characterized in that: The gel modifier, by mass percentage, consists of 0.4-0.6% polymer, 0.4-0.6% crosslinking agent, 0.3-0.5% additives, and the balance being water.

5. The method for profile control of injection wells based on the protection of low-permeability layers according to claim 1 or 4, characterized in that: The polymer includes anionic polyacrylamide and / or its derivatives; The crosslinking agent includes phenol, formaldehyde, phenolic prepolymer and / or its derivatives; The adjuvant is thiourea.

6. The method for profile control of injection wells based on the protection of low-permeability layers according to claim 1 or 4, characterized in that: The polymer is one or more of the following: urea-based anionic polyacrylamide, benzyl imidazole ionic liquid-modified anionic polyacrylamide, and crown ether grafted modified anionic polyacrylamide. The crosslinking agent is composed of one or more of phenol, formaldehyde, phenolic prepolymer, and hexamethylenetetramine. The adjuvant is thiourea.

7. The method for profile control of injection wells based on the protection of low-permeability layers according to claim 6, characterized in that: The urea-based anionic polyacrylamide is composed of one or more of ditert-butyl dicarbonate, o-nitrophenyl isocyanate, hydrazine hydrate, trifluoroacetic acid, and di(N-succinimide) sebacate, and has a triple helix structure. The benzylimidazolium ionic liquid-modified anionic polyacrylamide is prepared by a Friedel-Crafts alkylation reaction between benzylimidazolium ionic liquid and polyacrylamide. The crown ether grafted modified anionic polyacrylamide is composed of one or more of dibenzo-18-crown-6, 4-formyldibenzo-18-crown-6, polyvinyl alcohol, and polyacrylamide, and has a core-shell structure.

8. The method for profile control of injection wells based on the protection of low-permeability layers according to claim 7, characterized in that: The benzylimidazolium ionic liquid modified anionic polyacrylamide is composed of one or more of 1-butyl-3-methylimidazolium bromide ionic liquid, 1-vinyl-3-(pentafluorobenzyl)imidazolium bromide ionic liquid, polyacrylamide, benzoic acid ester, and triphenylmethane, and has a tubular structure.

9. The method for profile control of injection wells based on the protection of low-permeability layers according to claim 1, characterized in that: In the third stage plug, the displacement plug is the same as the first stage plug, that is, the displacement solution is one or more of BPPG and DPPG.

10. The method for profile control of injection wells based on the protection of low-permeability layers according to claim 9, characterized in that: The displacement solution contains 0.3-0.5% BPPG and 0.3-0.5% DPPG by mass.

11. The method for profile control of injection wells based on the protection of low-permeability layers according to claim 1, characterized in that: The unblocking agent is one or more of ammonium persulfate and acetic acid depolymerizing agent.

12. The method for profile control of injection wells based on the protection of low-permeability layers according to claim 11, characterized in that: The unblocking agent solution contains acetic acid depolymerizing agent at a mass concentration of 8-12% and ammonium persulfate at a mass concentration of 35-48%.

13. An application of the method for profile control of injection wells based on the protection of low-permeability layers as described in any one of claims 1-12, characterized in that: This water injection well profile adjustment method is suitable for heterogeneous oil reservoirs with a permeability variation coefficient greater than 0.5.

Images