A modified starch adhesive plugging agent, a composite regulating and driving system and its application

Abstract

The present application relates to a modified starch glue blocking agent, a composite profile control and flooding system and application thereof, and belongs to the technical field of profile control and flooding of high-temperature and low-permeability reservoirs. The modified starch glue blocking agent is made of the following raw materials in percentage by mass: 4-8% of hydroxypropyl modified cassava starch, 4-8% of acrylic acid, 0.1-0.5% of a crosslinking agent, 0.01-0.05% of dibenzoyl peroxide, and the rest of water; the crosslinking agent is N,N'-methylene bisacrylamide. The modified starch glue blocking agent has good injectivity and temperature resistance, can be resistant to temperatures above 120 DEG C, has controllable gel strength and time, has selective plugging capacity, and can effectively plug the channeling channel. The present application also provides a composite profile control and flooding system, which first blocks the high-permeability channel, forces the subsequent injected nano oil displacement agent to flow to the low-permeability layer, and finally realizes the combination of deep profile control and flooding of high-temperature and low-permeability reservoirs, improves the oil recovery, and realizes the economic and efficient development of high-temperature and low-permeability reservoirs.

Description

Technical Field

[0001] This invention relates to a modified starch adhesive plugging agent, a composite regulation and displacement system and its application, belonging to the field of regulation and displacement technology for high-temperature and low-permeability reservoirs. Background Technology

[0002] Conventional oil reservoirs, after long-term development, have entered a stage of high water cut and high recovery, resulting in poor economic returns. Unconventional reservoirs, such as those with low permeability, possess enormous development potential and are gradually becoming the focus of global oil and gas exploration and development. However, low-permeability reservoirs have small matrix pore throats and severe heterogeneity. During water injection development, these reservoirs are prone to forming dominant channels, leading to leakage and low water drive sweep efficiency, resulting in a large amount of residual oil remaining in the reservoir and poor development outcomes. Reservoir heterogeneity is generally divided into intra-layer and inter-layer heterogeneity. Oil reservoirs typically consist of multiple oil layers. Due to the large differences in permeability between these layers—ranging from several times, tens of times, or even hundreds of times—during water injection development, injected water rapidly surges along the wells with good connectivity, quickly entering production wells and rapidly increasing the water cut, sometimes even causing water flooding and production shutdown. Meanwhile, the crude oil in the low-permeability layers remains intact underground. This is what is commonly referred to in oilfield development as inter-layer heterogeneity causing inter-layer contradictions. Similarly, even within a single oil reservoir, there exist relatively low-permeability and high-permeability channels, known as intra-layer heterogeneity. Injected water can escape along the high-permeability channels, rendering a large amount of crude oil in the low-permeability channels unusable. Therefore, improving reservoir heterogeneity is an effective method to enhance oil recovery. Common profile control and plugging agents, such as polymers, gels, colloids, and granules, are effective at improving reservoir heterogeneity. However, polymers and conventional gel-based agents are prone to degradation and failure in high-temperature reservoirs, leading to a decrease in gel strength and failure to meet plugging requirements. Furthermore, in low-permeability reservoirs, they face challenges such as difficult injection, easy degradation after shearing, and a tendency to cause reservoir blockage. Although polymer microsphere-based plugging agents can be effectively injected into low-permeability reservoirs, they also suffer from problems such as poor high-temperature resistance and short effective operating distance. Therefore, a high-temperature resistant deep profile control and plugging system is urgently needed for high-temperature, low-permeability reservoirs.

[0003] Injecting plugging agents into heterogeneous reservoirs can effectively improve the sweep efficiency of subsequent waterflooding, but it cannot improve the oil displacement efficiency. Nano-displacement technology is one of the most promising technologies for future oil and gas development. Nanomaterials, with their small size, large specific surface area, and high interfacial activity, have shown great application potential in low-permeability reservoirs. Nano-displacement systems achieve efficient oil displacement in low-permeability reservoirs through wedge-shaped permeation, thereby improving oil recovery. Common nano-displacement materials mainly include metal oxide (iron oxide, alumina, etc.) particles, organic particles (carbon nanotubes), and inorganic particles (silicon dioxide). Among them, nano-SiO2 particles are widely used, but they exhibit poor dispersion stability and are prone to agglomeration and flocculation at high temperatures. Furthermore, the spherical nanoparticles, primarily composed of nano-SiO2, interact with the oil-water interface in a point-to-surface manner, resulting in a small effective contact area, high concentrations required for effective action, and uncontrollable costs, further limiting their application in oilfields. Moreover, in low-permeability heterogeneous reservoirs, nano-displacement agents are prone to escape along dominant channels, leading to ineffective or inefficient circulation. Therefore, before injection, plugging operations should be carried out to improve reservoir heterogeneity and control runoff channels.

[0004] In summary, to achieve efficient development of high-temperature, low-permeability reservoirs, the first step should be to inject a regulating and plugging system to block dominant channels and improve reservoir heterogeneity. However, injecting only a single regulating and plugging agent cannot improve the efficiency of subsequent waterflooding. Therefore, it is necessary to further inject a low-cost, high-temperature resistant nano-displacement system with high oil displacement capabilities to achieve a combination of regulating and displacement for economical and efficient development. Currently, the aforementioned regulating and plugging systems face the problem of poor high-temperature resistance, severe cross-contamination when using nano-displacement systems alone, limited oil displacement effect, and inability to effectively control usage costs. Summary of the Invention

[0005] The first objective of this invention is to provide a modified starch adhesive plugging agent to solve the problem that the existing plugging system is not resistant to high temperatures, resulting in a decrease in gel strength and failure to meet the plugging requirements.

[0006] The second objective of this invention is to provide a composite regulation and displacement system for high-temperature, low-permeability reservoirs, in order to solve the problem that the oil displacement effect is limited when using a single regulation and displacement system in high-temperature, low-permeability reservoirs in the prior art.

[0007] The third objective of this invention is to provide an application of a composite moderating and driving system for high-temperature and low-permeability reservoirs, in order to solve the problem that the oil displacement effect is limited when using a single moderating and driving system in high-temperature and low-permeability reservoirs in the prior art.

[0008] To achieve the above objectives, the technical solution of the modified starch adhesive blockage remedy in this invention is as follows:

[0009] A modified starch adhesive blockage accelerator, by mass percentage, is made from the following raw materials: 4-8% hydroxypropyl modified cassava starch, 4-8% acrylic acid, 0.1-0.5% crosslinking agent, 0.01-0.05% benzoyl peroxide, and the balance being water.

[0010] The beneficial effects of the above technical solution are as follows: The modified starch adhesive plugging agent of the present invention uses modified starch and acrylic acid as the main raw materials, and reacts to generate the modified starch adhesive plugging agent in the presence of a crosslinking agent and an initiator. The modified starch adhesive plugging agent of the present invention has good injection performance and temperature resistance, and can withstand temperatures above 120°C. The gelation time and strength are controllable, and it can effectively block escape channels and improve water drive sweep efficiency. Secondly, the modified starch adhesive plugging agent of the present invention is a pure viscous fluid before gelation, and has obvious selective plugging ability. Compared with polymers, gels, and other plugging agents, the modified starch adhesive only blocks the dominant channels and does not block secondary channels, which can significantly improve the sweep efficiency.

[0011] As a further improvement, the crosslinking agent is N,N′-methylenebisacrylamide.

[0012] To achieve the above objectives, the technical solution of the composite regulation and displacement system for high-temperature, low-permeability reservoirs in this invention is as follows:

[0013] A composite regulation and displacement system for high-temperature, low-permeability oil reservoirs includes the aforementioned modified starch adhesive plugging agent and nano-displacement agent.

[0014] The beneficial effects of the above technical solution are as follows: The composite regulation and displacement system for high-temperature, low-permeability reservoirs of the present invention includes a high-temperature resistant modified starch adhesive plugging agent, which can block dominant channels and improve reservoir heterogeneity. However, the modified starch adhesive plugging agent cannot effectively improve oil displacement efficiency. Therefore, the composite regulation and displacement system includes a nano-displacement agent. The modified starch adhesive system stabilizes and gels in high-temperature reservoirs, blocking escape channels and forcing the nano-displacement agent to flow to low-permeability layers, activating the remaining oil in the low-permeability layers, and ultimately achieving a combination of regulation and displacement in high-temperature, low-permeability reservoirs, effectively improving oil displacement efficiency and sweep efficiency, and significantly increasing oil recovery rate.

[0015] As a further improvement, the active ingredient of the nano-oil displacement agent is MoS2 nanosheets.

[0016] The beneficial effects of the above technical solution are as follows: MoS2 nanosheets, as a highly efficient oil displacement agent, are resistant to high temperatures, can exert wedge-shaped penetration, peel off the oil film, and significantly improve the oil displacement efficiency.

[0017] As a further improvement, the MoS2 nanosheets are present in a nano-oil displacement agent at a mass concentration of 0.005–0.01 wt%.

[0018] To achieve the above objectives, the technical solution of the composite regulation and displacement system for high-temperature and low-permeability reservoirs in this invention is as follows:

[0019] Application of a composite regulation and drive system for high-temperature and low-permeability reservoirs.

[0020] The beneficial effects of the above technical solution are as follows: The composite regulation and displacement system for high-temperature, low-permeability reservoirs of the present invention includes a modified starch-based plugging agent and a nano-displacement agent. The modified starch-based plugging agent, as a plugging agent, has good injectability and temperature resistance, can withstand temperatures above 120℃, and its gelation time and strength are controllable. It can effectively block escape channels and improve waterflood sweep efficiency, but it cannot effectively improve oil displacement efficiency. The nano-displacement agent, as a highly efficient oil displacement agent, is resistant to high temperatures and can exert wedge-shaped penetration, stripping oil films and significantly improving oil displacement efficiency. However, due to its low viscosity, its improvement in sweep efficiency is limited. Therefore, the present invention uses a combination of a modified starch-based plugging agent and a nano-displacement agent. The modified starch-based plugging agent stably gels in high-temperature reservoirs, blocking escape channels and forcing the nano-displacement agent to flow to low-permeability layers, activating the remaining oil in the low-permeability layers, ultimately achieving a combination of regulation and displacement in high-temperature, low-permeability reservoirs, effectively improving oil displacement efficiency and sweep efficiency, and significantly improving oil recovery.

[0021] As a further improvement, the modified starch adhesive is injected into a high-temperature, low-permeability reservoir, and the nano-displacement agent is injected after the adhesive has gelled.

[0022] Specifically, in field applications, a certain amount of modified starch adhesive is first injected as a plugging agent. After the starch adhesive solution solidifies into a gel, a nano-displacement agent is injected. Once the modified starch adhesive solidifies, it blocks the escape channels, improves sweep efficiency, and forces the nano-displacement agent to flow into low-permeability channels, thereby improving oil displacement efficiency. This achieves efficient regulation and displacement of low-permeability heterogeneous reservoirs and improves oil recovery.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] This invention proposes a modified starch-based plugging agent that overcomes the shortcomings of traditional plugging agents, such as inability to be injected into low-permeability reservoirs, short effective range, easy well blockage, and poor shear and high-temperature resistance. It also addresses the inability of ordinary starch gel to gel at high temperatures (above 100°C). The modified starch-based plugging agent of this invention can withstand temperatures above 120°C and gels at high temperatures (110°C–140°C), with controllable gelation time and strength. Before gelation, the starch gel solution is a pure viscous fluid with significant selective flow capability, blocking only dominant channels and not secondary channels. This allows it to be injected into deep formations for deep reservoir sealing, overcoming the disadvantages of conventional plugging agents that easily cause complete blockage in the near-wellbore zone.

[0025] Furthermore, this invention proposes a composite modulating and displacing system for high-temperature, low-permeability reservoirs, which can effectively improve the oil recovery rate of such reservoirs. Its key feature is the injection of a modified starch-based plugging agent, which solidifies into a gel at reservoir temperatures above 120°C, blocking high-permeability channels, improving sweep efficiency, and forcing subsequently injected nano-displacing agents to divert to low-permeability channels, thereby maximizing oil displacement efficiency and achieving a combination of modulating and displacing. This effectively controls the leakage of subsequently injected water or nano-displacing agents along high-permeability channels, significantly improving the oil displacement effect of the nano-displacing system and substantially increasing the oil recovery rate of low-permeability, high-temperature reservoirs. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of different strength codes in the Sydansk gel coding method used to evaluate gel strength in this invention (where AI represents the gradual increase in gel strength);

[0027] Figure 2 The images show the state of the starch adhesive blockage modifiers in Example 1 and Comparative Examples 1-3 after gelation in Experimental Example 1 of the present invention (wherein, from left to right, they are the blockage modifiers of Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3, respectively).

[0028] Figure 3 The modified starch adhesive blockage modifiers in Example 1, Comparative Example 4 and Comparative Example 5 of Experiment 2 of the present invention are in their gelled state (wherein, from left to right, they are the blockage modifiers of Example 1, Comparative Example 4 and Comparative Example 5 respectively).

[0029] Figure 4 The modified starch adhesive blockage modifiers in Examples 1-3 of Experiment 3 of the present invention are in their gelled state (wherein, from left to right, they are the modified starch adhesive blockage modifiers of Examples 1, 2 and 3, respectively).

[0030] Figure 5 The curves showing the changes in injection pressure, water cut, and recovery rate of the composite displacement system in Experimental Example 5 of this invention are shown.

[0031] Figure 6 The curves show the flow rates of the high-permeability and low-permeability layers in the composite displacement system during the displacement process in Experimental Example 5 of this invention. Detailed Implementation

[0032] This invention addresses the shortcomings of traditional plugging agents in low-permeability reservoirs, such as inability to be injected, short effective range, easy well blockage, and poor shear and high-temperature resistance. Using hydroxypropyl-modified cassava starch and acrylic acid as main raw materials, and in the presence of an initiator and crosslinking agent, a modified starch adhesive plugging agent with high temperature resistance and controllable gelation time and strength is prepared.

[0033] Based on the modified starch-based plugging agent, this invention further provides a composite regulation and displacement system for high-temperature, low-permeability reservoirs. The modified starch-based plugging agent blocks high-permeability channels, improving sweep efficiency and forcing the subsequently injected nano-displacement agent system to redirect to low-permeability channels, thereby maximizing its oil displacement capacity and improving overall oil recovery efficiency, achieving a combination of regulation and displacement. This effectively controls the leakage of subsequently injected water or nano-displacement agents along high-permeability channels, significantly improving the oil displacement effect of the nano-displacement system and substantially increasing the oil recovery rate in low-permeability, high-temperature reservoirs.

[0034] The present invention will be further described below with reference to specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments. The equipment and raw materials used are all commercially available or commonly used in the art. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0035] Unless otherwise specified, the operations described in the following embodiments are conventional operations in the art.

[0036] Unless otherwise specified, the raw materials used in the following embodiments are all conventional commercial products in the art.

[0037] The hydroxypropyl-modified cassava starch used in the following examples and comparative examples was: α-starch (petroleum) adjuvant (ash content 73.5%, fineness 93%, pH value 6.2, viscosity (5% starch solution) 1500-2000 mPa·s), purchased from Beijing Xingbao Hongye Industry and Trade Co., Ltd.; the hydroxypropyl-modified corn starch was S97300-500g, purchased from Shanghai Jizhi Biochemical Technology Co., Ltd.

[0038] The nano-black card oil displacement agent used in the following examples is model SX-36, purchased from Henan Dancheng Shunxing Petroleum Additives Co., Ltd., and the active ingredient in the nano-black card oil displacement agent is MoS2 nanosheets.

[0039] I. Specific Embodiments of the Modified Starch Adhesive Blocking Agent of the Present Invention

[0040] Example 1

[0041] The modified starch adhesive blockage maker of this embodiment is made from the following raw materials by weight percentage: 4% modified starch, 4% acrylic acid, 0.1% crosslinking agent, 0.01% initiator, and the balance being water; the modified starch is hydroxypropyl-modified cassava starch; the initiator is benzoyl peroxide (BPO); and the crosslinking agent is N,N′-methylenebisacrylamide. The specific preparation method is as follows:

[0042] Add 4g of hydroxypropyl modified cassava starch to 91.89g of formation water and stir to dissolve. Then add 4g of acrylic acid and continue stirring to dissolve. Slowly add 0.1g of N,N′-methylenebisacrylamide and stir to dissolve. Then add 0.01g of BPO and stir to dissolve to obtain modified starch adhesive plugging agent 1.

[0043] Example 2

[0044] The modified starch adhesive blockage maker of this embodiment is made from the following raw materials by mass percentage: 4% modified starch, 4% acrylic acid, 0.5% crosslinking agent, 0.05% initiator, and the balance being water; the modified starch is hydroxypropyl-modified cassava starch; the initiator is benzoyl peroxide (BPO); and the crosslinking agent is N,N′-methylenebisacrylamide. The specific preparation method is as follows:

[0045] Add 4g of hydroxypropyl modified cassava starch to 91.45g of formation water and stir to dissolve. Then add 4g of acrylic acid and continue stirring to dissolve. Slowly add 0.5g of N,N′-methylenebisacrylamide and stir to dissolve. Then add 0.05g of BPO and stir to dissolve to obtain modified starch glue plugging agent 2.

[0046] Example 3

[0047] The modified starch adhesive blockage maker of this embodiment is made from the following raw materials by mass percentage: 8% modified starch, 8% acrylic acid, 0.1% crosslinking agent, 0.01% initiator, and the balance being water; the modified starch is hydroxypropyl-modified cassava starch; the initiator is benzoyl peroxide (BPO); and the crosslinking agent is N,N′-methylenebisacrylamide. The specific preparation method is as follows:

[0048] Add 8g of hydroxypropyl-modified cassava starch to 83.89g of formation water and stir to dissolve. Then add 8g of acrylic acid and continue stirring to dissolve. Slowly add 0.1g of N,N′-methylenebisacrylamide and stir to dissolve. Finally, add 0.01g of BPO and stir to dissolve to obtain modified starch adhesive plugging agent 3.

[0049] II. Specific Embodiments of the Composite Regulated Drive System for High-Temperature, Low-Permeability Oil Reservoirs of the Present Invention

[0050] Example 4

[0051] The high-temperature, low-permeability reservoir composite regulation and displacement system of this embodiment includes the modified starch glue plugging agent 1 of Example 1 and the nano oil displacement agent; the nano oil displacement agent is a nano black card oil displacement agent, and the effective component of the nano black card oil displacement agent is MoS2 nanosheets; the mass concentration of the MoS2 nanosheets in the nano black card oil displacement agent is 0.005wt%.

[0052] Example 5

[0053] The high-temperature, low-permeability reservoir composite regulation and displacement system of this embodiment includes the modified starch glue plugging agent 2 of Example 2 and the nano oil displacement agent; the nano oil displacement agent is a nano black card oil displacement agent, and the effective component of the nano black card oil displacement agent is MoS2 nanosheets; the mass concentration of the MoS2 nanosheets in the nano black card oil displacement agent is 0.005wt%.

[0054] Example 6

[0055] The composite regulation and displacement system for high-temperature, low-permeability reservoirs in this embodiment includes the modified starch glue plugging agent 3 of Example 3 and the nano-displacement agent; the nano-displacement agent is a nano-black card oil displacement agent, and the effective component of the nano-black card oil displacement agent is MoS2 nanosheets; the mass concentration of the MoS2 nanosheets in the nano-black card oil displacement agent is 0.005wt%.

[0056] III. Comparative Example

[0057] Comparative Example 1

[0058] The corn starch adhesive blockage modifier of this comparative example, by mass percentage, is made from the following raw materials: 4% corn starch, 4% acrylic acid, 0.1% crosslinking agent, 0.01% initiator, and the balance being water; the corn starch is unmodified corn starch; the initiator is benzoyl peroxide (BPO); and the crosslinking agent is N,N′-methylenebisacrylamide. The specific preparation method is as follows:

[0059] Add 4g of corn starch to 91.89g of formation water and stir to dissolve. Then add 4g of acrylic acid and continue stirring to dissolve. Slowly add 0.1g of N,N′-methylenebisacrylamide and stir to dissolve. Finally, add 0.01g of BPO and stir to dissolve to obtain corn starch adhesive blockage modifier.

[0060] Comparative Example 2

[0061] The cassava starch adhesive blockage modifier of this comparative example, by mass percentage, is made from the following raw materials: 4% cassava starch, 4% acrylic acid, 0.1% crosslinking agent, 0.01% initiator, and the balance being water; the cassava starch is unmodified cassava starch; the initiator is benzoyl peroxide (BPO); and the crosslinking agent is N,N′-methylenebisacrylamide. The specific preparation method is as follows:

[0062] Add 4g of cassava starch to 91.89g of formation water and stir to dissolve. Then add 4g of acrylic acid and continue stirring to dissolve. Slowly add 0.1g of N,N′-methylenebisacrylamide and stir to dissolve. Finally, add 0.01g of BPO and stir to dissolve to obtain cassava starch glue blockage modifier.

[0063] Comparative Example 3

[0064] The modified starch adhesive blockage agent 4 in this comparative example, by mass percentage, is made from the following raw materials: 4% modified corn starch, 4% acrylic acid, 0.1% crosslinking agent, 0.01% initiator, and the balance being water; the modified corn starch is hydroxypropyl-modified corn starch; the initiator is benzoyl peroxide (BPO); and the crosslinking agent is N,N′-methylenebisacrylamide. The specific preparation method is as follows:

[0065] Add 4g of modified corn starch to 91.89g of formation water and stir to dissolve. Then add 4g of acrylic acid and continue stirring to dissolve. Slowly add 0.1g of N,N′-methylenebisacrylamide and stir to dissolve. Then add 0.01g of BPO and stir to dissolve to obtain modified starch adhesive plugging agent 4.

[0066] Comparative Example 4

[0067] The modified starch adhesive blockage agent 5 in this comparative example, by mass percentage, is made from the following raw materials: 4% modified starch, 4% acrylic acid, 0.1% crosslinking agent, 0.01% initiator, and the balance being water; the modified starch is hydroxypropyl-modified cassava starch; the initiator is potassium persulfate; and the crosslinking agent is N,N′-methylenebisacrylamide. The specific preparation method is as follows:

[0068] 4g of hydroxypropyl-modified cassava starch was added to 91.89g of formation water and stirred until dissolved. Then, 4g of acrylic acid was added and stirred until dissolved. Then, 0.1g of N,N′-methylenebisacrylamide was slowly added and stirred until dissolved. Finally, 0.01g of potassium persulfate was added and stirred until dissolved to obtain modified starch glue blockage agent 5.

[0069] Comparative Example 5

[0070] The modified starch adhesive blockage agent 6 in this comparative example, by mass percentage, is made from the following raw materials: 4% modified starch, 4% acrylamide, 0.1% crosslinking agent, 0.01% initiator, and the balance being water; the modified starch is hydroxypropyl-modified cassava starch; the initiator is potassium persulfate; and the crosslinking agent is N,N′-methylenebisacrylamide. The specific preparation method is as follows:

[0071] Add 4g of hydroxypropyl-modified cassava starch to 91.89g of formation water and stir to dissolve. Then add 4g of acrylamide and continue stirring to dissolve. Slowly add 0.1g of N,N′-methylenebisacrylamide and stir to dissolve. Finally, add 0.01g of potassium persulfate and stir to dissolve to obtain modified starch glue plugging agent 6.

[0072] IV. Experimental Examples

[0073] Experiment 1: Screening and Parameter Evaluation of Starch

[0074] This experimental example uses the Sydansk gel coding method (see the diagram of the evaluation criteria). Figure 1 The gelation time and strength of the starch adhesive blockage remedies prepared in Example 1 and Comparative Examples 1-3 were evaluated. The prepared starch adhesives were placed in a high-temperature constant temperature chamber at 120°C, and the gelation time and strength were recorded. The experimental results are shown in Table 1 and [Table data missing]. Figure 2 Experimental results show that at a high temperature of 120℃, only the modified starch adhesive and blockage regulator 1 can achieve a gel strength of Grade I, while the corn starch adhesive, cassava starch adhesive, and blockage regulator are only Grades C, D, and E, respectively. Therefore, modified cassava starch was selected as the main agent.

[0075] Table 1 Gelation time and gel strength of modified starch adhesive

[0076]

[0077] Experimental Example 2: Screening and Parameter Evaluation of Initiators

[0078] This experiment used the Sydansk gel coding method to evaluate the gelation time and strength of the modified starch adhesive blockage eliminators prepared in Example 1 and Comparative Examples 4 and 5. The prepared modified starch adhesive blockage eliminators were placed in a high-temperature constant temperature chamber at 120℃, and the gelation time and gelation strength were recorded. The experimental results are shown in Table 2 and [Table data missing]. Figure 3 Experimental results showed that the modified starch adhesive used as an initiator had the highest gel strength, reaching Grade I; while the modified starch adhesive used as an initiator only reached Grade G. Therefore, BPO was selected as the initiator for the modified starch adhesive. Moreover, when the initiator was the same (both were potassium persulfate), the modified starch adhesive achieved a higher gel strength (Grade G) when acrylic acid was chosen as the monomer, compared to acrylamide.

[0079] Table 2 Gelation time and gel strength of modified starch adhesive

[0080]

[0081] Example 3: Evaluation of Parameters of Modified Starch Adhesive Blocking Agent

[0082] This experiment used the Sydansk gel coding method to evaluate the gelation time and strength of the modified starch adhesive blockage eliminators prepared in Examples 1-3. The modified starch adhesives prepared in Examples 1-3 were placed in a high-temperature constant temperature chamber at 120°C, and the gelation time and strength were recorded. The experimental results are shown in Table 3 and [Table data missing]. Figure 4 Experimental results show that the modified starch adhesives under different formulations can all achieve Grade I gelation performance at a high temperature of 120℃, and the gelation time can be controlled by changing the component content.

[0083] Table 3. Gelation time and gel strength of modified starch adhesive blockage inhibitors

[0084]

[0085] Experimental Example 4: Evaluation of the sealing performance of modified starch adhesive plugging agent

[0086] This experiment evaluates the plugging performance of the modified starch adhesive plugging agents prepared in Examples 1-3.

[0087] Sand-filled pipe models with permeability of 500mD, 1000mD, 1500mD, and 2000mD were fabricated as required. Vacuum was applied, and the formation was saturated with formation water. A first water flooding was performed in a 120℃ constant temperature chamber at an injection rate of 0.3 mL / min until the injection pressure at the inlet stabilized, and the pressure value P1 was recorded. 0.2 PV of high-temperature resistant modified starch adhesive was injected at an injection rate of 0.3 mL / min and allowed to stand for 12 hours to allow for gelation. A second water flooding was performed at an injection rate of 0.3 mL / min until the injection pressure at the inlet stabilized, and the pressure value P2 was recorded. The plugging rate η was calculated as η = (P2 - P1) / P2.

[0088] Table 4 shows the experimental results for sand-filled pipes with different permeabilities. The results indicate that the modified starch adhesive can effectively block water channeling at a high temperature of 120℃, with a blocking rate exceeding 90%. The experimental process demonstrates that the modified starch adhesive has good injectability, did not cause blockage at the inlet of the sand-filled pipe, and can smoothly penetrate deep into the pipe, where it solidifies into an adhesive, thus blocking the water channeling.

[0089] Table 4. Experimental results of sand-filled pipe plugging with different permeabilities

[0090]

[0091] Example 5: Application of a composite modulating and driving system in high-temperature, low-permeability reservoirs

[0092] The application of the composite moderating and driving system in high-temperature, low-permeability reservoirs in this experimental example is implemented as follows:

[0093] 100mD and 500mD cores were connected in parallel to simulate a heterogeneous reservoir. Vacuum was pumped, and the reservoir was saturated with formation water and crude oil. In a 120℃ constant temperature chamber, water flooding was performed once until the water cut at the outlet was 98%. 0.2PV of modified starch glue plugging agent 1 from Example 1 was injected and allowed to stand for 12 hours to form a gel. 0.3PV of nano black card oil displacement agent was injected, and subsequent water flooding was carried out until the water cut at the outlet was 98%. The recovery rate and diversion rate of high-permeability and low-permeability cores were recorded during the experiment.

[0094] Changes in injection pressure, water cut, recovery rate, and diversion rate of high-permeability and low-permeability layers during the displacement process of the composite displacement system are as follows: Figure 5 and Figure 6 As shown, the primary waterflood recovery rates of low-permeability and high-permeability cores were 32.63% and 54.65%, respectively. After sequential injection into the composite system, the recovery rates of low-permeability and high-permeability cores increased by 6.79% and 5.61%, respectively, ultimately reaching 39.42% and 60.26%. Furthermore, the diversion rate of the low-permeability layer significantly increased from 7.3% to 94%, indicating that the modified starch adhesive can effectively block the high-permeability water channel, forcing the nano-black card oil displacement agent to flow into the low-permeability layer. This, in turn, activates the remaining oil through the wedge-shaped permeability of the nano-black card, thereby improving the recovery rate and diversion rate of the low-permeability layer.

[0095] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the embodiments of the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A modified starch gelling fluid loss control agent characterized by: The modified starch glue blocking agent is made of the following raw materials in percentage by mass: 4-8% of hydroxypropyl modified cassava starch, 4-8% of acrylic acid, 0.1-0.5% of crosslinking agent, 0.01-0.05% of dibenzoyl peroxide, and the rest is water; the crosslinking agent is N,N'-methylene bisacrylamide.

2. A composite profile control and flooding system for high-temperature and low-permeability oil reservoirs, characterized in that: The modified starch glue blocking agent and the nano oil displacement agent.

3. The composite profile control and flooding system for high-temperature and low-permeability oil reservoirs according to claim 2, characterized in that: The effective component of the nano oil displacement agent is MoS2 nanosheet.

4. The composite profile control and flooding system for high-temperature and low-permeability oil reservoirs according to claim 3, characterized in that: The mass concentration of the MoS2 nanosheet in the nano oil displacement agent is 0.005-0.01 wt%.

5. The application of the composite profile control and flooding system for high-temperature and low-permeability oil reservoirs in high-temperature and low-permeability oil reservoirs according to any one of claims 2-4.

6. The use of the composite profile control and flooding system for high-temperature and low-permeability oil reservoirs according to claim 5, characterized in that: The modified starch glue blocking agent is injected into the high-temperature and low-permeability oil reservoir, and the nano oil displacement agent is injected after the gelation.

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