A method for plugging micro-nano cracks by graphene to optimize oil and gas exploitation

Abstract

This invention relates to the field of oil and gas field development technology, and particularly to a method for optimizing oil and gas extraction by using graphene to seal micro- and nano-sized fractures. The technical solution includes the following steps: geological assessment and channel establishment, identifying high-temperature geothermal layers adjacent to the target oil reservoir, and establishing fracture channels connecting the geothermal layers and the oil reservoir; selective fracture sealing, preparing graphene-based sealing materials and injecting them into the fracture channels to selectively seal some fractures to form a thermal insulation layer and reduce heat loss; geothermal circulation and oil displacement, injecting fluids into the geothermal layers through injection wells. This invention innovatively and deeply integrates geothermal development and oil and gas extraction. Through graphene sealing technology and systematic well network design, it constructs an efficient, economical, and environmentally friendly method for enhancing oil recovery, not only improving oil and gas production and thermal energy utilization efficiency, but also achieving carbon sequestration while saving energy and reducing consumption.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development technology, and in particular to a method for optimizing oil and gas extraction by using graphene to seal micro-nano fractures. Background Technology

[0002] With the increasing depletion of conventional oil and gas resources, enhanced oil and gas recovery (EOR) technologies have become a key support for maintaining stable production in oil and gas fields. Currently, commonly used EOR technologies in the industry mainly include waterflooding, chemical flooding, gas miscible flooding, and thermal recovery. Among these, thermal recovery technology, with its core advantages of reducing crude oil viscosity and improving mobility ratio, is widely used in the extraction of heavy oil and high-pour-point oil. However, traditional thermal recovery methods (such as steam flooding and hot water flooding) consume large amounts of fossil fuels such as gas and oil to generate high-temperature steam or hot water, resulting in significant problems of high energy density and large carbon emissions. Furthermore, the deployment and operation costs of steam generation equipment are significantly increased due to space constraints on offshore oilfield platforms, leading to poor techno-economic efficiency.

[0003] In recent years, geothermal energy, as a clean and renewable new energy source, has gradually attracted attention in the field of oil and gas field development. However, current technologies largely limit the utilization of geothermal energy to single scenarios, such as directly heating crude oil from geothermal wells, providing heating sources for oilfield surface gathering and transportation facilities, or using it solely for geothermal power generation, failing to achieve deep synergy with the oil and gas extraction process. This type of application has three core limitations: first, low geothermal utilization efficiency, with heat loss rates as high as 30%-50% during transmission due to formation heterogeneity, fractures, and leakage; second, poor system integration, with geothermal energy extraction, oil and gas production, and fluid processing operating independently, failing to form an integrated recycling system; and third, inability to achieve thermal energy recycling, with heated geothermal fluids being directly discharged after a single use, leading to energy waste and failing to fully realize the potential of geothermal energy in enhancing oil and gas recovery.

[0004] In addition, while existing gas-driven oil recovery technologies (such as carbon dioxide flooding) can improve oil recovery and achieve environmental protection synergy by improving crude oil mobility and achieving carbon sequestration, the injected carbon dioxide usually needs to be heated to ensure oil recovery efficiency. The heating process relies on external fossil fuel heat sources, which not only increases operating costs but also generates additional carbon emissions, contradicting the "dual carbon" goal and the need for low-cost development.

[0005] In summary, overcoming the bottlenecks in the synergy between geothermal energy and oil and gas extraction, and solving problems such as high energy consumption, low geothermal energy utilization efficiency, and poor system integration in traditional thermal oil recovery, to construct an efficient, economical, and environmentally friendly integrated enhanced oil recovery technology system has become a key technical challenge urgently needing to be addressed in the oil and gas field development field. Therefore, this application proposes a method for optimizing oil and gas extraction by using graphene to seal micro-nano fractures. Summary of the Invention

[0006] The purpose of this invention is to address the problems of high energy consumption, low efficiency of geothermal energy utilization, and poor system integration in the background technology, and to propose a method for optimizing oil and gas extraction by using graphene to seal micro-nano cracks.

[0007] The technical solution of this invention: A method for optimizing oil and gas extraction by using graphene to seal micro-nano cracks, comprising the following steps:

[0008] S1. Geological assessment and channel establishment: Identify the high-temperature geothermal layer adjacent to the target oil reservoir and establish a fracture channel connecting the geothermal layer and the oil reservoir.

[0009] S2. Selective crack sealing: Prepare graphene-based sealing material and inject it into the crack channel to selectively seal some cracks, thereby forming a thermal insulation layer and reducing heat loss.

[0010] S3. Geothermal circulation and oil displacement: Fluid is injected into the geothermal layer through injection wells. The fluid is heated by the geothermal system to form a high-temperature fluid, which flows into the target oil reservoir through sealed fracture channels, heating the crude oil and driving its flow.

[0011] S4. Fluid Lifting and Treatment: Fluid lifting is achieved through a production well with a dual-channel structure, which includes:

[0012] The production tubing located in the production well and the production well casing surrounding the production tubing;

[0013] The inner pipe is located inside the production tubing. The bottom of the inner pipe is directly connected to the target geothermal reservoir through a perforated section. High-temperature geothermal fluid is directly drawn in through this channel and independently lifted to the ground.

[0014] The annular channel is a ring-shaped space formed by the outer wall of the production tubing string and the inner wall of the production well casing. The bottom of the annular channel is connected to the oil and gas reservoir through a packer, and oil and natural gas flow directly into the annular channel after flowing out of the production layer.

[0015] The inner channel lifts geothermal fluids, while the annular channel extracts oil and gas fluids.

[0016] S5. Waste heat utilization and gas reinjection: recover the waste heat of the lifted geothermal fluid and reinject a portion of the separated gas back into the formation.

[0017] Optionally, in S1, the temperature of the high-temperature geothermal layer is ≥150℃, and the distribution range, reservoir thickness, fracture development density, and orientation of geothermal resources are determined by seismic exploration, well logging, and core analysis techniques.

[0018] Optionally, in S1, the process for establishing fracture channels is hydraulic fracturing or acid fracturing; when hydraulic fracturing is used, the fracturing fluid is a guar gum-based fracturing fluid, with 0.3-0.5% by mass of a flow aid and 0.1-0.2% by mass of an anti-swelling agent added, and the flow rate is 3-5 m³ / s. 3 / min, the fracturing pressure is 1.2-1.5 times the in-situ stress of the reservoir; when using acid fracturing, the acid is a mixture of 15-20% hydrochloric acid and 5-8% hydrofluoric acid by mass fraction, the acid volume is calculated at 80-100L per meter of fracture length, and the construction pressure does not exceed 90% of the reservoir fracturing pressure.

[0019] Optionally, in step S2, the step of preparing the graphene-based sealing material includes:

[0020] (1) Preparation of graphene oxide: Take 2 parts by mass of graphite powder, add 50-60 parts by volume of 98% concentrated sulfuric acid and 6-12 parts by mass of potassium permanganate in sequence under ice bath conditions, stir evenly and then heat to 40-45℃ and react for 1-3 hours; after the reaction is completed, add 50-60 parts by volume of water and react at 90-100℃ for 0.5-1 hours; finally add 2-5 parts by volume of 30% hydrogen peroxide, sonicate for 1-3 hours and freeze dry to obtain graphene oxide.

[0021] (2) Graphene aerogel synthesis: Graphene oxide is dispersed in deionized water to prepare a graphene oxide slurry with a solid content of 5-8% and a viscosity of 1000-15000 cP. The pH of the slurry is adjusted to 5.0-7.0 with 0.1 mol / L sodium hydroxide solution. The slurry is placed in a high-pressure reactor and reacted at 180-200℃ for 6-12 hours to form a hydrogel. The hydrogel is dried at a temperature of -50~0℃ and a vacuum of 1.3~13 Pa for 24-100 hours to obtain graphene aerogel.

[0022] (3) Preparation of sealing material: Graphene aerogel is crushed into nanoparticles of 100-500nm, deionized water and sodium hexametaphosphate dispersant of 0.2-0.4% by mass are added, and after stirring evenly, a sealing agent suspension of 0.5-2.0% by mass is formed, which is the graphene-based sealing material.

[0023] Optionally, in step S2, the graphene-based sealing material undergoes surface modification, and the modification step includes the following steps:

[0024] Take 1-3 parts by mass of graphene oxide and disperse it in N,N-dimethylformamide. Add 0.21-0.9 parts by mass of sodium ethoxide in a constant temperature water bath at 60-80℃. After stirring for 1 hour, add 0.6-2.7 parts by mass of allyl chloride and continue to react for 6-10 hours. After centrifugation, wash with ethanol 3-5 times to obtain the intermediate.

[0025] Take 1-2 parts by weight of the intermediate and disperse it in deionized water, add 0.04-0.12 parts by weight of silane coupling agent and 2-6 parts by weight of the first monomer, wherein the first monomer is a mixture of methacryloyloxyethyltrimethylammonium chloride and 2-acrylamide-2-methylpropanesulfonic acid in a molar ratio of 1:1.

[0026] After purging with nitrogen for 30 minutes to remove oxygen, 0.01-0.03 parts by mass of ammonium persulfate initiator are added, and the reaction is carried out at 60°C for 4-8 hours. After centrifugation and freeze-drying, the modified graphene-based sealing material is obtained.

[0027] Optionally, in step S2, the graphene-based sealing material is injected in stages: the first stage involves injecting a pre-treatment solution of clean water at a flow rate of 2-3 m³. 3 The injection rate is 1.5-2 times the wellbore volume; the second stage involves injecting a plugging agent suspension at a rate of 1-2 m³ / min. 3 The injection rate is 1.1-1.3 times the reservoir pore pressure, and the injection volume is calculated based on the fracture pore volume. The sealing agent forms a sealing layer with a thickness of ≥5mm in high-permeability fractures with a permeability ≥100mD. The third stage involves injecting a water displacement fluid at a discharge rate of 2-3m³ / min. 3 / min, the injection volume is the sum of the wellbore and near-wellbore zone volumes.

[0028] Optionally, in step S3, the injected fluid is low-temperature clean water or low-temperature carbon dioxide fluid; when injecting clean water, the water temperature is 20-40℃, and the injection pressure is 0.5-1.0MPa higher than the geothermal layer pressure and lower than the crack reopening pressure; when injecting carbon dioxide fluid, supercritical carbon dioxide with a temperature ≥31.1℃ and a pressure ≥7.38MPa is used, and the injection rate is 0.5-1.0t / h; after being heated in the geothermal layer, the fluid forms a high-temperature fluid with a temperature of 150-300℃, and the high-temperature fluid flow rate is 0.3-0.8m / s.

[0029] Optionally, in S4, the production well with the dual-channel structure meets the following requirements: the inner channel is made of Cr13 stainless steel with a diameter of 2-4 inches, and the inner wall is coated with polytetrafluoroethylene for corrosion resistance, with a temperature range of -20~350℃ and a pressure rating of ≥35MPa; the annular channel is the annular space between the inner channel and the production well casing, the casing is made of N80 steel with a diameter of 4-8 inches, and the annular channel is equipped with a spiral gas-liquid separation component with a gas-liquid separation efficiency of ≥95%, and the liquid water content in the produced oil and gas mixture is ≤10% and the gas purity is ≥90%.

[0030] Optionally, in step S5, a shell-and-tube heat exchanger is used to recover waste heat. The shell side of the heat exchanger is supplied with geothermal fluid at a temperature of 150-300℃, and the tube side is supplied with cold water or heat transfer oil. When cold water is supplied to the tube side, the inlet temperature is 20-30℃ and the outlet temperature is 80-100℃. When heat transfer oil is supplied to the tube side, the inlet temperature is 30-40℃ and the outlet temperature is 120-150℃. The heat transfer oil is connected to an organic Rankine cycle power generation system, and the waste heat recovery efficiency is ≥70%.

[0031] Optionally, in step S5, the gas reinjected into the formation is purified carbon dioxide, and the purification step includes the following steps:

[0032] The oil and gas mixture extracted from S4 is separated into crude carbon dioxide gas by a three-phase separator, then dehydrated by molecular sieve to a water content ≤10ppm, desulfurized by activated carbon to a sulfur content ≤5ppm, and purified by membrane separation to a carbon dioxide purity ≥99.5%.

[0033] The reinjection process uses a high-pressure injection pump with an injection pressure of 1.2-1.5 times the reservoir pressure and an injection rate of 0.3-0.6 t / h. The reinjection formation is a formation with a porosity ≥15% and a permeability ≥50 mD below the target reservoir.

[0034] Compared with the prior art, this application includes at least one of the following beneficial technical effects:

[0035] This invention utilizes in-situ geothermal heating of injected fluids, completely replacing traditional gas or oil boilers and significantly reducing fuel consumption and direct operating costs during oil and gas extraction. By efficiently heating the reservoir with geothermal fluids, the viscosity of crude oil is significantly reduced, improving the mobility ratio and effectively driving crude oil flow, thereby enhancing the ultimate recovery rate. By eliminating fossil fuel combustion, CO2 emissions are reduced at the source; simultaneously, some of the CO2 separated during extraction is reinjected into the formation, achieving carbon sequestration and resulting in significant environmental benefits.

[0036] Utilizing the superior thermal insulation properties of graphene-based materials, highly permeable fractures are selectively sealed, effectively preventing unnecessary losses of geothermal energy during transmission and ensuring that heat is concentrated and directed to the target oil reservoir. The dual-channel production well structure achieves efficient separation and lifting of geothermal fluids and oil / gas flows, and recovers residual heat at the surface, resulting in high overall energy utilization efficiency.

[0037] In summary, this invention innovatively and deeply integrates geothermal development with oil and gas extraction. Through graphene plugging technology and systematic well network design, it constructs an efficient, economical, and environmentally friendly method for enhancing oil recovery. This not only improves oil and gas production and thermal energy utilization efficiency, but also achieves carbon sequestration while saving energy and reducing consumption. Attached Figure Description

[0038] Figure 1XRD patterns of different samples;

[0039] Figure 2 This is a scanning electron microscope image of graphene oxide grafted with PVP.

[0040] Figure 3 The figures show the contact angle test results of graphene oxide grafted with PVP of different molecular weights. From top to bottom, the figures show the contact angle test results of graphene oxide grafted with PVP of molecular weights of 10,000, 40,000, and 58,000.

[0041] Figure 4 These are the FT-IR spectra of different samples. Detailed Implementation

[0042] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0043] This invention proposes a method for optimizing oil and gas extraction by using graphene to seal micro- and nano-cracks. The method is described in detail below.

[0044] S1. Geological Assessment and Fracturing Channel Establishment: Identify the high-temperature geothermal layer adjacent to the target reservoir and establish a fracture channel connecting the geothermal layer and the reservoir. The temperature of the high-temperature geothermal layer is ≥150℃, and the distribution range of geothermal resources, reservoir thickness, fracture development density, and orientation are determined through seismic exploration, well logging, and core analysis. The fracture channel establishment process is hydraulic fracturing or acid fracturing. When using hydraulic fracturing, the fracturing fluid is guar gum-based, with 0.3-0.5% flow aid and 0.1-0.2% anti-swelling agent added by mass. The flow rate is 3-5 m³ / min, and the fracturing pressure is 1.2-1.5 times the in-situ reservoir stress. When using acid fracturing, the acid solution is a mixture of 15-20% hydrochloric acid and 5-8% hydrofluoric acid by mass. The acid solution volume is calculated at 80-100 L per meter of fracture length, and the fracturing pressure does not exceed 90% of the reservoir fracturing pressure.

[0045] S2. Selective crack sealing: Graphene-based sealing materials are prepared and injected into crack channels to selectively seal some cracks, forming a thermal insulation layer and reducing heat loss.

[0046] In S2, the steps for preparing graphene-based plugging materials include:

[0047] (1) Preparation of graphene oxide: Take 2 parts by mass of graphite powder, add 50-60 parts by volume of 98% concentrated sulfuric acid and 6-12 parts by mass of potassium permanganate in sequence under ice bath conditions, stir evenly and then heat to 40-45℃ and react for 1-3 hours; after the reaction is completed, add 50-60 parts by volume of water and react at 90-100℃ for 0.5-1 hours; finally add 2-5 parts by volume of 30% hydrogen peroxide, sonicate for 1-3 hours and freeze dry to obtain graphene oxide.

[0048] (2) Graphene aerogel synthesis: Graphene oxide is dispersed in deionized water to prepare a graphene oxide slurry with a solid content of 5-8% and a viscosity of 1000-15000 cP. The pH of the slurry is adjusted to 5.0-7.0 with 0.1 mol / L sodium hydroxide solution. The slurry is placed in a high-pressure reactor and reacted at 180-200℃ for 6-12 hours to form a hydrogel. The hydrogel is dried at a temperature of -50~0℃ and a vacuum of 1.3~13 Pa for 24-100 hours to obtain graphene aerogel.

[0049] (3) Preparation of sealing material: Graphene aerogel is crushed into nanoparticles of 100-500nm, deionized water and sodium hexametaphosphate dispersant of 0.2-0.4% by mass are added, and after stirring evenly, a sealing agent suspension of 0.5-2.0% by mass is formed, which is the graphene-based sealing material.

[0050] In S2, the graphene-based sealing material undergoes surface modification. The modification steps include the following:

[0051] Take 1-3 parts by mass of graphene oxide and disperse it in N,N-dimethylformamide. Add 0.21-0.9 parts by mass of sodium ethoxide in a constant temperature water bath at 60-80℃. After stirring for 1 hour, add 0.6-2.7 parts by mass of allyl chloride and continue to react for 6-10 hours. After centrifugation, wash with ethanol 3-5 times to obtain the intermediate.

[0052] Take 1-2 parts by weight of the intermediate and disperse it in deionized water, add 0.04-0.12 parts by weight of silane coupling agent and 2-6 parts by weight of the first monomer, wherein the first monomer is a mixture of methacryloyloxyethyltrimethylammonium chloride and 2-acrylamide-2-methylpropanesulfonic acid in a molar ratio of 1:1;

[0053] After purging with nitrogen for 30 minutes to remove oxygen, 0.01-0.03 parts by mass of ammonium persulfate initiator are added, and the reaction is carried out at 60°C for 4-8 hours. After centrifugation and freeze-drying, the modified graphene-based sealing material is obtained.

[0054] In S2, the graphene-based sealing material is injected using a segmented injection method:

[0055] The first stage involves injecting pre-flue water at a flow rate of 2-3 m³ / h.3 / min, the injection volume is 1.5-2 times the wellbore volume;

[0056] The second stage involves injecting a suspension of sealing agent at a flow rate of 1-2 m³. 3 / min, the injection pressure is 1.1-1.3 times the reservoir pore pressure, the injection volume is calculated based on the fracture pore volume, and the plugging agent forms a plugging layer with a thickness of ≥5mm in high-permeability fractures with a permeability ≥100mD;

[0057] The third stage involves injecting a water displacement solution at a displacement of 2-3 m³. 3 / min, the injection volume is the sum of the wellbore and near-wellbore zone volumes.

[0058] S3. Geothermal circulation and oil displacement: Fluid is injected into the geothermal layer through injection wells. After being heated by the geothermal system, the fluid becomes a high-temperature fluid and flows into the target oil reservoir through sealed fracture channels, heating the crude oil and driving its flow. The injected fluid is low-temperature clean water or low-temperature carbon dioxide fluid. When injecting clean water, the water temperature is 20-40℃, and the injection pressure is 0.5-1.0MPa higher than the geothermal layer pressure and lower than the fracture reopening pressure. When injecting carbon dioxide fluid, supercritical carbon dioxide with a temperature ≥31.1℃ and a pressure ≥7.38MPa is used, with an injection rate of 0.5-1.0t / h. After being heated by the geothermal layer, the fluid becomes a high-temperature fluid with a temperature of 150-300℃ and a flow velocity of 0.3-0.8m / s.

[0059] S4. Fluid Lifting and Treatment: Fluid lifting is achieved through a production well with a dual-channel structure, which includes:

[0060] The production tubing located in the production well and the production well casing surrounding the production tubing;

[0061] The inner pipe is located inside the production tubing. The bottom of the inner pipe is directly connected to the target geothermal reservoir through a perforated section. High-temperature geothermal fluid is directly drawn in through this channel and independently lifted to the ground.

[0062] The annular channel is a ring-shaped space formed by the outer wall of the production tubing string and the inner wall of the production well casing. The bottom of the annular channel is connected to the oil and gas reservoir through a packer, and oil and natural gas flow directly into the annular channel after flowing out of the production layer.

[0063] The inner channel lifts geothermal fluids, while the annular channel extracts oil and gas fluids. The dual-channel production well meets the following requirements: the inner channel is made of Cr13 stainless steel with a diameter of 2-4 inches, and the inner wall is coated with PTFE for corrosion resistance, with a temperature range of -20~350℃ and a pressure rating of ≥35MPa; the annular channel is the annular space between the inner channel and the production well casing, the casing is made of N80 steel with a diameter of 4-8 inches, and the annular channel is equipped with a spiral gas-liquid separation component with a gas-liquid separation efficiency of ≥95%, and the extracted oil and gas mixture has a liquid water content of ≤10% and a gas purity of ≥90%.

[0064] S5. Waste Heat Utilization and Gas Reinjection: The waste heat from the lifted geothermal fluid is recovered, and a portion of the separated gas is reinjected into the formation. Waste heat recovery utilizes a shell-and-tube heat exchanger. Geothermal fluid at 150-300℃ is introduced into the shell side, while cold water or thermal oil is introduced into the tube side. When cold water is introduced into the tube side, the inlet temperature is 20-30℃ and the outlet temperature is 80-100℃. When thermal oil is introduced into the tube side, the inlet temperature is 30-40℃ and the outlet temperature is 120-150℃, and the thermal oil is connected to an organic Rankine cycle power generation system.

[0065] In S5, the gas reinjected into the formation is purified carbon dioxide. The purification process includes the following steps:

[0066] The oil and gas mixture extracted from S4 is separated into crude carbon dioxide gas by a three-phase separator, then dehydrated by molecular sieve to a water content ≤10ppm, desulfurized by activated carbon to a sulfur content ≤5ppm, and purified by membrane separation to a carbon dioxide purity ≥99.5%.

[0067] The reinjection process uses a high-pressure injection pump with an injection pressure of 1.2-1.5 times the reservoir pressure and an injection rate of 0.3-0.6 t / h. The reinjection formation is a formation with a porosity ≥15% and a permeability ≥50 mD below the target reservoir.

[0068] Example 1:

[0069] This embodiment focuses on a certain onshore heavy oil reservoir (crude oil viscosity 5000 mPa・s / 50℃), and uses the method of the present invention for geothermal energy assisted extraction. The following is a detailed description.

[0070] 1. Geological assessment and access point establishment

[0071] Using seismic exploration, well logging, and core analysis techniques, a high-temperature geothermal layer with a temperature of 180℃ (reservoir thickness 30m, fracture density 8 fractures / m, trending in the same direction as the main seepage direction of the reservoir) was identified 2000m below the target reservoir. Hydraulic fracturing was employed to establish a fracture channel connecting the geothermal layer and the reservoir. A guar gum-based fracturing fluid was selected, with 0.4% (w / w) of a flow aid (fluorocarbon surfactant) and 0.15% (w / w) of a swelling inhibitor (potassium chloride). The flow rate was controlled at 4m³ / h. 3 The fracture pressure was set at 1.3 times the reservoir in-situ stress (50MPa) (i.e., 65MPa) per minute, ultimately forming a fracture channel with a length of 80m and a width of 5mm.

[0072] 2. Selective crack sealing

[0073] 2.1 Preparation of graphene-based plugging materials

[0074] (1) Preparation of graphene oxide: Take 2 parts by mass of flake graphite powder and place it in a 500mL ice bath reactor. Slowly add 55 parts by volume of 98% concentrated sulfuric acid and stir for 30 minutes. Then add 9 parts by mass of potassium permanganate in batches (control the temperature not to exceed 20℃). After the addition is complete, raise the temperature to 42℃ and react for 2 hours. Then slowly add 55 parts by volume of deionized water and raise the temperature to 95℃ and react for 0.8 hours. Finally, add 3.5 parts by volume of 30% hydrogen peroxide. After the solution changes from brown to bright yellow, sonicate for 2 hours and place it in a -40℃ freeze dryer to dry for 48 hours to obtain graphene oxide powder. (2) Graphene aerogel synthesis: The above-mentioned graphene oxide powder was dispersed in deionized water to prepare a graphene oxide slurry with a solid content of 6.5% and a viscosity of 8000 cP. The pH of the slurry was adjusted to 6.0 with 0.1 mol / L sodium hydroxide solution. The slurry was transferred to a 1000 mL high-pressure reactor and reacted at 190 °C for 9 hours to form a three-dimensional network structure hydrogel. The hydrogel was placed in a freeze dryer and dried at -30 °C and 5 Pa vacuum for 72 hours to obtain a porous graphene aerogel. (3) Blocking material preparation: The graphene aerogel was pulverized into 300 nm nanoparticles using an air jet mill. Deionized water and 0.3% sodium hexametaphosphate dispersant were added. The mixture was stirred for 1 hour using a high-speed stirrer (3000 r / min) to form a blocking agent suspension with a mass fraction of 1.2%.

[0075] 2.2 Injection of Graphene-based plugging materials

[0076] The sealing agent suspension was pumped into the fracture channel using a segmented injection method: the first segment injected a pre-treatment solution of clean water at a flow rate of 2.5 m³ / s. 3 / min, injection volume is the wellbore volume (8m³) 3 1.8 times (i.e., 14.4m)3 The first stage involves cleaning the wellbore and clearing the injection channels; the second stage involves injecting a plugging agent suspension at a rate of 1.5 m³ / min, with the injection pressure set at 1.2 times the reservoir pore pressure (18 MPa) (i.e., 21.6 MPa), based on the fracture pore volume (12 m³ / min). 3 The calculated injection volume is 12m. 3 This ensures that the sealing agent forms a 6mm thick, tightly sealed layer in the high-permeability fracture with a permeability of 120mD; the third stage involves injecting a water displacement solution at a discharge rate of 2.5m³. 3 / min, the injection volume is the sum of the wellbore and near-wellbore zone volumes (10m³). 3 This pushes the sealing agent completely into the target crack area.

[0077] 3. Geothermal circulation and oil displacement

[0078] Low-temperature clean water (30℃) is injected into the high-temperature geothermal layer through an injection well, with the injection pressure set at 20MPa (18MPa and 2MPa higher than the geothermal layer pressure, and 28MPa lower than the fracture reopening pressure). After exchanging heat with the high-temperature rock layer in the geothermal layer, the clean water forms a high-temperature fluid with a temperature of 220℃. The high-temperature fluid flows into the target oil reservoir through the sealed fracture channel at a flow rate of 0.5m / s. After making full contact with the crude oil, the temperature of the crude oil is raised from 50℃ to 120℃, the viscosity of the crude oil is reduced to 500mPa・s, the mobility is significantly improved, and it flows towards the production well.

[0079] 4. Fluid Lifting and Treatment

[0080] The production well adopts a dual-channel structure: the inner channel is made of Cr13 stainless steel with a diameter of 3 inches and the inner wall is coated with polytetrafluoroethylene anti-corrosion coating, with a temperature range of -20~350℃ and a pressure rating of 40MPa, and is used to lift geothermal fluids with a lifting temperature of 220℃; the annular channel is the annular space between the inner channel and the N80 steel casing (6 inches in diameter). The channel is equipped with a spiral gas-liquid separation component with a gas-liquid separation efficiency of 96%, and the produced oil and gas mixture has a liquid water content of 8% and a gas purity of 92%.

[0081] 5. Waste heat utilization and gas reinjection

[0082] 5.1 Waste Heat Recovery

[0083] A shell-and-tube heat exchanger is installed on the ground. The shell side of the heat exchanger is filled with geothermal fluid at a temperature of 220°C, which is lifted from the production well, and the tube side is filled with cold water (inlet temperature 25°C). After heat exchange, the cold water outlet temperature is 90°C, which is used for heating the oilfield's surface gathering and transportation station. The waste heat recovery efficiency reaches 72%.

[0084] 5.2 Gas Separation, Purification, and Reinjection

[0085] The oil and gas mixture produced in S4 is separated into crude carbon dioxide gas (85% purity) by a three-phase separator. The crude carbon dioxide gas is then dehydrated by molecular sieve (water content reduced to 8 ppm), desulfurized by activated carbon (sulfur content reduced to 4 ppm), and purified by membrane separation (purity increased to 99.6%). The purified carbon dioxide is then reinjected into the storage formation (porosity 18%, permeability 60 mD) below the target reservoir using a high-pressure injection pump. The injection pressure is set to 1.3 times the storage formation pressure (25 MPa) (i.e., 32.5 MPa), and the injection rate is 0.45 t / h, which achieves carbon sequestration while assisting in driving the remaining crude oil in the reservoir.

[0086] Through field application, this embodiment has shown that the crude oil recovery rate is 8 percentage points higher than that of traditional thermal recovery technology, carbon emissions are reduced by 40%, and geothermal energy utilization efficiency reaches 68%, resulting in significant economic and environmental benefits.

[0087] The following are the test results of the graphene-based sealing material prepared in this embodiment.

[0088] like Figure 1 The polyvinylpyrrolidone (PVP) grafted samples showed no significant shift in the main peak position at low angles (0–10°) compared to standard graphene oxide (PDF #44-0558), indicating that the grafting process did not disrupt the basic crystal structure of graphene oxide at this location. PVP-58000 and PVP-40000 exhibited strong and sharp diffraction peaks at 10°, indicating high crystallinity. The PVP-40000 peak was narrower, suggesting larger crystal size or fewer defects; the PVP-58000 peak was slightly wider, possibly indicating the presence of fine defects or smaller grains. The PVP-10000 peak at the same position was significantly weaker and broader, indicating low crystallinity, an imperfect crystal structure, and shorter molecular chains that are difficult to arrange in an orderly manner. In the high-angle region, all samples showed weak diffraction peaks, possibly originating from other crystal planes or small amounts of impurities, but the low intensity suggests that these crystal planes have low orientation or low content. It is clear that the molecular weight of PVP directly affects the crystallization behavior of the grafted sample. High molecular weight (40,000, 58,000) is conducive to maintaining or forming an ordered crystal structure, while low molecular weight (10,000) leads to a significant decrease in crystallinity. Grafting does not change the original main peak structure of graphene oxide, but it may introduce local defects or size differences.

[0089] like Figure 2 As shown, graphene oxide typically exhibits a sheet-like structure, while PVP grafting results in edge wrinkles and deformation, indicating a change in surface tension due to molecular bonding. PVP uniformly coats the sheet surface in a particle form, significantly improving dispersibility, with no obvious agglomeration observed.

[0090] like Figure 3As shown, with the molecular weight increasing from 10,000 to 40,000 and 58,000, the material surface exhibits a hydrophilic-to-hydrophobic transition. The left and right contact angles of the PVP sample grafted with graphene oxide at a molecular weight of 10,000 were 48.9° and 44.5°, respectively, showing a difference of approximately 4.4°, indicating uneven surface wetting and incomplete modification. The left and right contact angles of the PVP-40,000 sample were both 41.5°, exhibiting complete symmetry, indicating uniform surface coverage and enhanced hydrophilicity. The left and right contact angles of the PVP-58,000 sample were further symmetrical and reached a high of 113.9°, showing significant hydrophobic properties. This may be due to the coverage method of the high molecular weight PVP chains leading to a decrease in surface energy and changes in microstructure. In summary, increasing the molecular weight not only improved the grafting uniformity but also significantly regulated the wetting behavior of the material surface transitioning from hydrophilic to hydrophobic.

[0091] like Figure 4 As shown, infrared spectroscopy analysis indicates that all samples are within 1650 cm⁻¹. -1 and 1230 cm -1 The presence of distinct C=O and CN stretching vibration peaks near the surface confirms that PVP of different molecular weights has been successfully grafted onto graphene oxide. The grafting degree is positively correlated with molecular weight: PVP-58000 exhibits the highest characteristic peak intensity, indicating the largest grafting amount and strongest interaction; PVP-40000 has a moderate peak intensity; while the corresponding peak of PVP-10000 is significantly weaker, suggesting that its lower grafting amount or shorter molecular chain limits its effective interaction. Furthermore, at 3400 cm⁻¹... -1 The broad OH peaks in the vicinity indicate that the material surface is rich in hydroxyl groups. These results suggest that increasing the molecular weight of PVP helps improve grafting efficiency and the degree of surface modification, providing a basis for further control of material dispersibility and mechanical properties.

[0092] Example 2:

[0093] This embodiment focuses on a marine medium-high pour point oil reservoir (crude oil pour point 35℃), and uses the method of this invention for extraction. The key parameters and steps that differ from those in Embodiment 1 are as follows:

[0094] 1. Geological assessment and access point establishment

[0095] The temperature of the high-temperature geothermal layer is 160℃. Acid fracturing is used to establish the fracture channel: the acid is a mixture of 18% hydrochloric acid and 6.5% hydrofluoric acid by mass. Based on the designed fracture length of 60m, the acid consumption is calculated to be 4800L (60m×80L / m). The construction pressure is controlled at 85% of the reservoir fracturing pressure (45MPa) (i.e., 38.25MPa).

[0096] 2. Selective crack sealing

[0097] Surface modification of graphene-based sealing materials: 2 parts by mass of graphene oxide were dispersed in N,N-dimethylformamide. 0.5 parts by mass of sodium ethoxide were added in a constant temperature water bath at 70℃. After stirring for 1 hour, 1.8 parts by mass of allyl chloride were added, and the reaction continued for 8 hours. After centrifugation, the mixture was washed 4 times with ethanol to obtain an intermediate. 1.5 parts by mass of the intermediate were dispersed in deionized water. 0.08 parts by mass of silane coupling agent and 4 parts by mass of the first monomer (a mixture of methacryloyloxyethyltrimethylammonium chloride and 2-acrylamido-2-methylpropanesulfonic acid, molar ratio 1:1) were added. After purging with nitrogen for 30 minutes to remove oxygen, 0.02 parts by mass of ammonium persulfate initiator were added. The reaction was carried out at 60℃ for 6 hours. After centrifugation and freeze-drying, the modified graphene-based sealing material was obtained, which showed a 40% increase in adhesion strength in cracks compared to the unmodified material.

[0098] 3. Geothermal circulation and oil displacement

[0099] The injected fluid is supercritical carbon dioxide (temperature 32℃, pressure 7.5MPa), with an injection rate of 0.8t / h. After being heated in the geothermal layer, the supercritical carbon dioxide forms a high-temperature fluid with a temperature of 180℃ and a flow rate of 0.6m / s. When it comes into contact with crude oil, it lowers the freezing point of the crude oil to below 20℃, thus enabling the crude oil to flow smoothly.

[0100] 4. Waste heat utilization and gas reinjection

[0101] During waste heat recovery, heat transfer oil is introduced into the tube side of the shell-and-tube heat exchanger at an inlet temperature of 35°C. After heat exchange, the outlet temperature of the heat transfer oil is 135°C, which is then connected to the organic Rankine cycle power generation system, generating up to 120kW. The carbon dioxide reinjection rate is 0.5t / h, the porosity of the reinjected formation is 16%, the permeability is 55mD, and the carbon sequestration rate reaches 92%.

[0102] This embodiment is applicable to scenarios where space is limited on offshore platforms. It eliminates the need to deploy large-scale steam generators, reduces equipment investment costs by 35%, and increases crude oil recovery by 6 percentage points, meeting the needs of efficient and environmentally friendly development of offshore oil and gas fields.

[0103] The above specific embodiments are merely several optional embodiments of the present invention. Based on the technical solutions of the present invention and the relevant teachings of the above embodiments, those skilled in the art can make various alternative improvements and combinations to the above specific embodiments.

Claims

1. A method for optimizing oil and gas extraction by using graphene to seal micro- and nano-sized cracks, characterized in that, Includes the following steps: S1. Geological assessment and channel establishment: Identify the high-temperature geothermal layer adjacent to the target oil reservoir and establish a fracture channel connecting the geothermal layer and the oil reservoir. S2. Selective crack sealing: Prepare graphene-based sealing material and inject it into the crack channel to selectively seal some cracks, thereby forming a thermal insulation layer and reducing heat loss. S3. Geothermal circulation and oil displacement: Fluid is injected into the geothermal layer through injection wells. The fluid is heated by the geothermal system to form a high-temperature fluid, which flows into the target oil reservoir through sealed fracture channels, heating the crude oil and driving its flow. S4. Fluid Lifting and Treatment: Fluid lifting is achieved through a production well with a dual-channel structure, which includes: The production tubing located in the production well and the production well casing surrounding the production tubing; The inner pipe is located inside the production tubing. The bottom of the inner pipe is directly connected to the target geothermal reservoir through a perforated section. High-temperature geothermal fluid is directly drawn in through this channel and independently lifted to the ground. The annular channel is a ring-shaped space formed by the outer wall of the production tubing string and the inner wall of the production well casing. The bottom of the annular channel is connected to the oil and gas reservoir through a packer, and oil and natural gas flow directly into the annular channel after flowing out of the production layer. The inner channel lifts geothermal fluids, while the annular channel extracts oil and gas fluids. S5. Waste heat utilization and gas reinjection: recover the waste heat of the lifted geothermal fluid and reinject a portion of the separated gas back into the formation.

2. The method for optimizing oil and gas extraction by using graphene to seal micro-nano cracks according to claim 1, characterized in that, In S1, the temperature of the high-temperature geothermal layer is ≥150℃, and the distribution range, reservoir thickness, fracture development density, and orientation of geothermal resources are determined by seismic exploration, well logging, and core analysis techniques.

3. The method for optimizing oil and gas extraction by using graphene to seal micro-nano cracks according to claim 1, characterized in that, In S1, the process for establishing fracture channels is hydraulic fracturing or acid fracturing; when hydraulic fracturing is used, the fracturing fluid is guar gum-based fracturing fluid, with 0.3-0.5% by mass of a flow aid and 0.1-0.2% by mass of an anti-swelling agent added, and the flow rate is 3-5 m³ / s. 3 / min, the fracturing pressure is 1.2-1.5 times the in-situ stress of the reservoir; when using acid fracturing, the acid is a mixture of 15-20% hydrochloric acid and 5-8% hydrofluoric acid by mass fraction, the acid volume is calculated at 80-100L per meter of fracture length, and the construction pressure does not exceed 90% of the reservoir fracturing pressure.

4. The method for optimizing oil and gas extraction by using graphene to seal micro-nano cracks according to claim 1, characterized in that, In step S2, the step of preparing the graphene-based sealing material includes: (1) Preparation of graphene oxide: Take 2 parts by mass of graphite powder, add 50-60 parts by volume of 98% concentrated sulfuric acid and 6-12 parts by mass of potassium permanganate in sequence under ice bath conditions, stir evenly and then heat to 40-45℃ and react for 1-3 hours; after the reaction is completed, add 50-60 parts by volume of water and react at 90-100℃ for 0.5-1 hours; finally add 2-5 parts by volume of 30% hydrogen peroxide, sonicate for 1-3 hours and freeze dry to obtain graphene oxide. (2) Graphene aerogel synthesis: Graphene oxide is dispersed in deionized water to prepare a graphene oxide slurry with a solid content of 5-8% and a viscosity of 1000-15000 cP. The pH of the slurry is adjusted to 5.0-7.0 with 0.1 mol / L sodium hydroxide solution. The slurry is placed in a high-pressure reactor and reacted at 180-200℃ for 6-12 hours to form a hydrogel. The hydrogel is dried at a temperature of -50~0℃ and a vacuum of 1.3~13 Pa for 24-100 hours to obtain graphene aerogel. (3) Preparation of sealing material: Graphene aerogel is crushed into nanoparticles of 100-500nm, deionized water and sodium hexametaphosphate dispersant of 0.2-0.4% by mass are added, and after stirring evenly, a sealing agent suspension of 0.5-2.0% by mass is formed, which is the graphene-based sealing material.

5. A method for optimizing oil and gas extraction by using graphene to seal micro-nano cracks according to claim 4, characterized in that, In step S2, the graphene-based sealing material is injected in a segmented manner: The first stage involves injecting pre-flue water at a flow rate of 2-3 m³ / h. 3 / min, the injection volume is 1.5-2 times the wellbore volume; The second stage involves injecting a suspension of sealing agent at a flow rate of 1-2 m³. 3 / min, the injection pressure is 1.1-1.3 times the reservoir pore pressure, the injection volume is calculated based on the fracture pore volume, and the plugging agent forms a plugging layer with a thickness of ≥5mm in high-permeability fractures with a permeability ≥100mD; The third stage involves injecting a water displacement solution at a displacement of 2-3 m³. 3 / min, the injection volume is the sum of the wellbore and near-wellbore zone volumes.

6. The method for optimizing oil and gas extraction by using graphene to seal micro-nano cracks according to claim 1, characterized in that, In step S3, the injected fluid is either low-temperature clean water or low-temperature carbon dioxide fluid. When injecting clean water, the water temperature is 20-40℃, and the injection pressure is 0.5-1.0 MPa higher than the geothermal layer pressure and lower than the crack reopening pressure. When injecting carbon dioxide fluid, supercritical carbon dioxide with a temperature ≥31.1℃ and a pressure ≥7.38 MPa is used, and the injection rate is 0.5-1.0 t / h. After being heated in the geothermal layer, the fluid forms a high-temperature fluid with a temperature of 150-300℃, and the high-temperature fluid flow rate is 0.3-0.8 m / s.

7. The method for optimizing oil and gas extraction by using graphene to seal micro-nano cracks according to claim 1, characterized in that, In S4, the production well with a dual-channel structure meets the following requirements: the inner channel is made of Cr13 stainless steel with a diameter of 2-4 inches, and the inner wall is coated with polytetrafluoroethylene for corrosion resistance, with a temperature range of -20~350℃ and a pressure rating of ≥35MPa; the annular channel is the annular space between the inner channel and the production well casing, the casing is made of N80 steel with a diameter of 4-8 inches, and the annular channel is equipped with a spiral gas-liquid separation component with a gas-liquid separation efficiency of ≥95%, and the liquid water content in the produced oil and gas mixture is ≤10% and the gas purity is ≥90%.

8. A method for optimizing oil and gas extraction by using graphene to seal micro-nano cracks according to claim 1, characterized in that, In S5, waste heat recovery is achieved using a shell-and-tube heat exchanger. The shell side of the heat exchanger is supplied with geothermal fluid at a temperature of 150-300°C, while the tube side is supplied with cold water or heat transfer oil. When cold water is supplied to the tube side, the inlet temperature is 20-30°C and the outlet temperature is 80-100°C. When heat transfer oil is supplied to the tube side, the inlet temperature is 30-40°C and the outlet temperature is 120-150°C. The heat transfer oil is connected to an organic Rankine cycle power generation system.

9. A method for optimizing oil and gas extraction by using graphene to seal micro-nano cracks according to claim 1, characterized in that, In step S5, the gas reinjected into the formation is purified carbon dioxide, and the purification step includes the following steps: The oil and gas mixture extracted from S4 is separated into crude carbon dioxide gas by a three-phase separator, then dehydrated by molecular sieve to a water content ≤10ppm, desulfurized by activated carbon to a sulfur content ≤5ppm, and purified by membrane separation to a carbon dioxide purity ≥99.5%. The reinjection process uses a high-pressure injection pump with an injection pressure of 1.2-1.5 times the reservoir pressure and an injection rate of 0.3-0.6 t / h. The reinjection formation is a formation with a porosity ≥15% and a permeability ≥50 mD below the target reservoir.

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