Method for in-situ biotransformation of carbon dioxide in oil and gas reservoirs and its application in fracturing of tight oil reservoirs

Abstract

The application discloses an oil and gas reservoir in-situ biotransformation buried carbon dioxide drive oil production method in the technical field of oil and gas field development and application thereof in fracturing of tight oil reservoirs. The method is characterized in that: a three-dimensional well pattern is arranged in the tight oil reservoir, and a fracture system is formed by multi-stage fracturing, then a treatment fluid containing a specific fluorine-modified phenyl polysiloxane polyether block copolymer is injected to improve the reservoir environment. Next, the strategy of circulating injection of supercritical carbon dioxide is adopted, and in the last cycle, multi-stage microbial activators prepared for different reservoir pH conditions are alternately injected, the activators containing nitrogen and phosphorus nutrients, carbon sources and buffer components. In the incubation stage, the suitable temperature is maintained to promote the metabolic activities of hydrolytic fermentation bacteria, lipolytic thermophilic mutualistic bacteria and methanogenic archaea, and to convert residual crude oil and stored carbon dioxide into methane. The technology realizes the dual goals of efficient carbon dioxide storage and green production of oil and gas resources, and is particularly suitable for development of unconventional oil and gas reservoirs.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field development technology, specifically relating to an underground in-situ biotransformation and carbon dioxide flooding method for oil and gas reservoirs and its application in tight oil reservoir fracturing. Background Technology

[0002] The effective development of unconventional oil and gas resources and the reduction of greenhouse gas emissions are two core challenges facing the global energy sector. Traditional carbon dioxide flooding technology has significant limitations in tight reservoir applications. Supercritical carbon dioxide is prone to gas channeling in fractured reservoirs, leading to reduced oil displacement efficiency and limited impact. Meanwhile, simply conducting carbon dioxide geological storage projects is economically unsustainable and lacks a sustainable commercial operating model. Tight oil reservoirs generally exhibit strong heterogeneity and low permeability, making it difficult for conventional development technologies to effectively utilize the crude oil resources they contain. In recent years, with the continuous expansion of unconventional oil and gas resource development, achieving coordinated development of carbon emission reduction and energy development has become a critical technological bottleneck that the industry urgently needs to overcome. Existing enhanced oil recovery technologies perform poorly in post-waterflood reservoirs, post-polymer flood reservoirs, and ternary composite post-flood reservoirs with varying pH conditions, especially for complex reservoir environments that have undergone multiple development methods, where effective replacement technologies are lacking.

[0003] Microbial enhanced oil recovery (MEOR) technology, as an important direction for improving oil recovery, has been developed for decades. However, traditional microbial technologies mainly rely on activating endogenous microorganisms to improve crude oil fluidity, which has inherent drawbacks such as long action cycles and unstable efficiency. While microbial carbon dioxide conversion technology, which has emerged in recent years, offers new ideas, it faces many challenges in actual reservoir environments: high temperature and pressure conditions underground severely restrict microbial activity; complex pore structures limit the effective transport of nutrients and microorganisms; and formation water chemistry exerts selective pressure on microbial metabolic pathways. Especially in reservoirs with different development histories, the reservoir chemical environment varies greatly, and residual chemicals have complex effects on the microbial community. Existing single-formulation microbial activators are difficult to effectively activate and stabilize metabolism under different pH conditions. Furthermore, the control of microbial community structure is difficult, and the synergistic mechanisms between different functional microbial groups are unclear, leading to low conversion efficiency and hindering large-scale application.

[0004] The technical solution of organically combining carbon dioxide sequestration and microbial transformation still lacks a systematic engineering implementation method. The various stages from reservoir stimulation and carbon dioxide injection to microbial activation have not yet formed an organic whole, particularly lacking specialized chemical agents capable of simultaneously improving carbon dioxide flow control characteristics and the microbial survival environment. In existing technologies, there is a disconnect between carbon dioxide injection strategies and subsequent microbial activation stages, failing to fully consider the specific requirements of microbial metabolism on the formation environment. Furthermore, research on personalized activation schemes for reservoirs with different development histories is insufficient, and there is a lack of activator systems adaptable to various formation conditions. At the engineering implementation level, how to establish an effective monitoring and control system to achieve controllable management of the underground biotransformation process is also a weak link in the current technical system. These factors severely restrict the large-scale application of this technology in tight reservoirs, urgently requiring the development of integrated solutions to achieve the coordinated development of carbon emission control and oil and gas resource development. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for in-situ underground biotransformation and carbon dioxide flooding in oil and gas reservoirs and its application in tight oil reservoir fracturing.

[0006] A first aspect of the present invention provides a method for in-situ underground biotransformation and carbon dioxide flooding oil recovery in oil and gas reservoirs, comprising the following steps:

[0007] S1. Deploy a three-dimensional well network with high conductivity in tight oil reservoirs, including staggered heating wells and production wells, using horizontal or vertical well networks to ensure that the main fractures formed by each well extend along the maximum horizontal principal stress and are not directly opposite each other; form a three-dimensional fracture network through multi-stage fracturing, with the distal ends interconnected through microfractures; prepare a treatment fluid containing fluorine-modified phenyl polysiloxane-polyether block copolymer and inject the treatment fluid into the reservoir;

[0008] S2. A circulating carbon dioxide injection strategy is adopted, with the injection volume dynamically adjusted according to the monitored reservoir pressure. The carbon dioxide injection is carried out in a supercritical state. In the last carbon dioxide injection cycle, multiple stages of microbial activators are injected alternately. For water-flooded or polymer-flooded reservoirs with pH=6-7.5, the activator includes corn syrup powder, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium chloride, petroleum sulfonate, and trace element mother liquor. For weakly alkaline ternary composite flooded reservoirs with pH=7.5-9, glucose, sodium formate, sodium acetate, and sodium propionate are added. For strongly alkaline ternary composite flooded reservoirs with pH=9-12, sodium bicarbonate is further added.

[0009] S3. After injecting the activator, shut down the production well for well simmering cultivation, maintain the reservoir temperature at 60-80℃, and regulate the reservoir temperature by injecting hot water through the heating well; periodically monitor changes in microbial communities and metabolites by sampling downhole fluids.

[0010] S4. After the well simmering and cultivation is completed, the production wells are gradually opened to enter the biomethane production stage; an intermittent production system is adopted; during the production process, the composition changes of the produced gas are monitored in real time, and when the methane content is higher than 70% and stable, the production stage is switched to continuous production.

[0011] As a preferred technical solution of the present invention, the preparation steps of the trace element mother liquor include: accurately weighing 10.0 g of nickel chloride hexahydrate and 1.0 g of sodium selenite, adding them sequentially to 1 L of deionized water, and continuously stirring at 350 r / min for 30 min at room temperature using a magnetic stirrer until the solids are completely dissolved to form a clear solution, and then adjusting the pH of the solution to 3.0 with 1% dilute hydrochloric acid to obtain the trace element mother liquor.

[0012] In this invention, the in-situ biotransformation and carbon dioxide flooding mechanism in oil and gas reservoirs is a complex system involving multiple synergistic processes. First, the method modifies the reservoir environment through the synergistic effect of an artificially constructed fracture network and a special chemical treatment fluid. Functional copolymers in the chemical treatment fluid form a molecular layer on the rock surface, altering reservoir wettability and enhancing the conductivity of the fracture system, creating favorable conditions for subsequent processes. The cyclic injection of supercritical carbon dioxide not only effectively drives the residual crude oil but, more importantly, its diffusion and dissolution within the fracture matrix system enables large-scale temporary storage, providing ample substrate for microbial transformation. Subsequently, a multi-stage microbial activator precisely regulates the microbial community structure according to the reservoir environment. Under suitable temperature conditions, the nutrients in the activator promote the metabolic activities of hydrolytic fermenting bacteria and lipophilic thermotrophic bacilli, decomposing complex hydrocarbons into small-molecule organic acids and hydrogen, thereby driving methanogenic archaea to synthesize methane using these metabolic products and dissolved carbon dioxide. This multi-microbial synergistic metabolic network enables the cyclical transformation of carbon elements, and ultimately, through an optimized production system, the generated biomethane is extracted in an orderly manner. The entire process forms a complete closed loop of carbon dioxide sequestration and energy product regeneration, achieving the dual goals of carbon emission reduction and resource enhancement.

[0013] As a preferred embodiment of the present invention, in step S1, the mass fraction of the fluorinated phenyl polysiloxane-polyether block copolymer in the treatment solution is 0.5-1.0%.

[0014] As a preferred embodiment of the present invention, in step S2, the number of carbon dioxide injection cycles is 3-4.

[0015] As a preferred technical solution of the present invention, in step S3, the microbial community includes: hydrolytic fermenting bacteria, lipophilic thermotrophic bacilli and methanogenic archaea.

[0016] As a preferred technical solution of the present invention, in step S4, the intermittent production system is to shut down the well for 1-2 weeks after 2-3 weeks of production.

[0017] As a preferred embodiment of the present invention, the preparation steps of the fluorinated phenyl polysiloxane-polyether block copolymer include:

[0018] A1. 1,3,5,7-Tetramethylcyclotetrasiloxane was added to anhydrous toluene to prepare a solution, which was heated to 84-86°C under nitrogen protection. 4-Vinylepoxycyclohexane was added dropwise, followed by a solution of triphenylphosphine platinum chloride in isopropanol, and the mixture was stirred. After the reaction was completed, the solution was distilled under reduced pressure to obtain an epoxy-functionalized cyclic hydrogen-containing siloxane intermediate.

[0019] A2. Dissolve the epoxy-functionalized cyclic hydrogen-containing siloxane intermediate in toluene, add phenolic polyoxyethylene ether, add tetrabutylammonium bromide, and react at 108-112℃. After the reaction is complete, cool to room temperature, wash with deionized water, separate the organic phase, and dry the organic phase with anhydrous sodium sulfate. Add diphenyldimethoxysilane and sodium methoxide to the dried organic phase and react at 120-150℃ to obtain phenyl polysiloxane-polyether prepolymer.

[0020] A3. The phenyl polysiloxane-polyether prepolymer was dissolved in methyl ethyl ketone to prepare a solution. 1H,1H,2H-perfluoro-1-hexene was added, along with an isopropanol solution of chloroplatinic acid. The reaction was carried out at 74-76℃. After the reaction was completed, the fluorinated phenyl polysiloxane-polyether copolymer was obtained by vacuum distillation.

[0021] A4. The fluorine-modified phenyl polysiloxane-polyether copolymer was dissolved in supercritical carbon dioxide and purified by fractional extraction; the soluble fraction was collected and the pressure was released.

[0022] In this invention, the preparation process of the fluorinated phenyl polysiloxane-polyether block copolymer follows a multi-step, precisely controlled organosilicon chemical reaction pathway. First, under the action of a platinum catalyst, a cyclic siloxane monomer undergoes a hydrosilylation reaction with two molecules of an olefin containing epoxy groups. During this process, the catalyst activates the silane-hydrogen bonds (Si-H) on the siloxane, allowing them to selectively add to the carbon-carbon double bonds (C=C) of the olefin, thereby introducing the epoxy-containing side chain into the molecule while retaining the epoxy group, resulting in an epoxy-functionalized cyclic hydrogen-containing siloxane intermediate. Subsequently, in the presence of a phase transfer catalyst, the epoxy group of this intermediate undergoes a grafting reaction with the hydroxyl groups of phenolic polyoxyethylene ether, introducing polyether segments through ether bonds. Following this, under the catalysis of sodium methoxide and in the presence of diphenyldimethoxysilane, the cyclic siloxane backbone of the grafted product undergoes anionic ring-opening polymerization, thereby breaking the cyclic structure and reorganizing into a linear polysiloxane backbone, forming a phenyl polysiloxane-polyether prepolymer. The subsequent fluorination modification reaction is another important step, utilizing the silicon-hydrogen bonds retained on the linear siloxane backbone to react with fluorinated olefins under catalytic conditions. The introduction of fluorinated groups significantly alters the molecular surface properties, endowing it with excellent hydrophobic and oleophobic properties and interfacial activity. Finally, the products are precisely separated using supercritical fluid extraction technology. By utilizing the differences in solubility of supercritical carbon dioxide for components of different molecular weights, unreacted monomers and byproducts are effectively removed, ensuring that the final product has a well-defined molecular structure and excellent performance consistency.

[0023] As a preferred embodiment of the present invention, in step A1, the mass ratio of 1,3,5,7-tetramethylcyclotetrasiloxane, 4-vinylepoxycyclohexane, and triphenylphosphine platinum chloride is (250-255):(120-125):(0.004-0.005).

[0024] As a preferred embodiment of the present invention, in step A2, the mass ratio of the epoxy-functionalized cyclic hydrogen-containing siloxane intermediate, phenol polyoxyethylene ether, tetrabutylammonium bromide, diphenyldimethoxysilane and sodium methoxide is 100:(100-150):(2-5):(10-15):(1-2); and the reaction time at 120-150℃ is 8-12h.

[0025] As a preferred embodiment of the present invention, in step A3, the mass ratio of phenyl polysiloxane-polyether prepolymer to 1H,1H,2H-perfluoro-1-hexene is 10:(1.0-1.2).

[0026] In a second aspect, the present invention provides an application of the aforementioned underground in-situ biotransformation and carbon dioxide flooding method for oil and gas reservoirs in the fracturing of tight oil reservoirs.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) This invention demonstrates a breakthrough advantage in improving crude oil recovery and carbon dioxide sequestration efficiency. The complex fracture network system formed by the three-dimensional well network and multi-stage fracturing creates ideal channels and spaces for subsequent fluid migration and microbial colonization. The specially designed fluorinated phenyl polysiloxane polyether block copolymer treatment fluid can effectively improve the wettability of reservoir rock surfaces, reduce the interfacial tension between carbon dioxide and crude oil, and significantly enhance the sweep efficiency and sequestration stability of supercritical carbon dioxide in tight reservoirs. Combined with the circulation injection strategy, it not only effectively suppresses gas channeling, but also enables efficient retention of carbon dioxide in the fracture matrix system. At the same time, the targeted multi-stage microbial activator successfully activates the reservoir's endogenous microbial community, enabling hydrolytic fermentation bacteria, lipophilic thermotrophic bacilli, and methanogenic archaea to form a synergistic metabolic network, which converts the sequestered carbon dioxide and the difficult-to-recover residual crude oil into high-value methane gas. Thus, while achieving large-scale geological sequestration of carbon dioxide, it significantly improves the recovery rate of crude oil and natural gas, forming a complete closed loop for carbon recycling.

[0029] (2) In terms of environmental benefits and energy sustainability, this invention pioneers a new model of green development. This technology uses industrially emitted carbon dioxide as a raw material for resource utilization, converting it into clean energy methane through a bioconversion process. This effectively achieves negative greenhouse gas emission conversion, providing a novel technological path for solving carbon emission problems. All chemical agents used in the entire process have good environmental compatibility and will not cause secondary pollution to groundwater resources. Compared with traditional single oil recovery or simple storage technologies, this invention significantly improves the project's life-cycle economics through in-situ regeneration of energy products, transforming carbon dioxide capture and storage from a purely environmentally friendly input into a production process with economic returns, providing a practical solution for the green and low-carbon transformation of oil and gas fields.

[0030] (3) In terms of technical integration and field operability, this invention demonstrates a high degree of systematicity and practicality. This method organically integrates several relatively independent technical units such as reservoir stimulation, carbon dioxide management, microbial activation and biotransformation, forming an integrated technical chain that is interconnected and functionally complementary. Addressing the differences in reservoir environment caused by different mining development processes, the provided multi-stage microbial activator formulation exhibits broad adaptability, enabling precise control based on reservoir conditions after water flooding, polymer flooding, and ternary composite flooding with different pH levels, ensuring the application effect of the technology under different geological conditions. Simultaneously, the temperature control during well simmering and the intermittent system design during the production stage fully consider the microbial metabolic patterns and formation energy balance, enabling the management of complex underground biological reaction processes through relatively simple engineering operations. The technical solution is mature and reliable, with the potential for large-scale field application. Detailed Implementation

[0031] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0032] The sources of some components in the examples and comparative examples are as follows:

[0033] The petroleum sulfonate was purchased from China National Petroleum Corporation's Karamay Petrochemical Company.

[0034] The sodium formate was purchased from Jinan Jinyimeng Group Co., Ltd.

[0035] The sodium acetate was purchased from Shandong Xiangrui Pharmaceutical Co., Ltd.

[0036] The sodium propionate was purchased from Qingdao Dawei Biotechnology Co., Ltd.

[0037] The 1,3,5,7-tetramethylcyclotetrasiloxane was purchased from Zhangjiakou Sirui Technology Co., Ltd.

[0038] The 4-vinylepoxycyclohexane was purchased from Henan Alpha Chemical Co., Ltd.

[0039] The triphenylphosphine platinum chloride was purchased from Chengdu Runze Local Chemical Co., Ltd.

[0040] The monoallyl polyoxyethylene ether phenyl ether was purchased from Hubei Xinmingtai Chemical Co., Ltd.

[0041] The tetrabutylammonium bromide was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0042] The diphenyldimethoxysilane was purchased from Wuhan Huaxiang Kejie Biotechnology Co., Ltd.

[0043] The sodium methoxide was purchased from Hebei Chengxin Group Co., Ltd.

[0044] The 1H,1H,2H-perfluoro-1-hexene was purchased from Zhonghao Chenguang Chemical Research Institute Co., Ltd.

[0045] The chloroplatinic acid was purchased from Guizhou Platinum Industry Co., Ltd.

[0046] Example 1

[0047] This embodiment provides a method for in-situ biotransformation and carbon dioxide flooding in oil and gas reservoirs.

[0048] First, a fluorine-modified phenyl polysiloxane polyether block copolymer was prepared:

[0049] Step A1: 250g of 1,3,5,7-tetramethylcyclotetrasiloxane was added to 500mL of anhydrous toluene to prepare a 33% (w / w) solution. The solution was heated to 85°C under nitrogen protection. 120g of 4-vinylepoxycyclohexane was slowly added dropwise over 2 hours using a constant-pressure dropping funnel. Then, a solution of triphenylphosphine chloride platinum isopropanol containing 0.004g of platinum was added. The temperature was maintained at 85±1°C, and the reaction was stirred for 6 hours. The reaction was monitored by infrared spectroscopy. The decrease in the characteristic absorption peak of Si-H was used to determine the reaction endpoint. After the reaction was completed, the temperature was increased to 65℃. Under reduced pressure distillation conditions, solvent and unreacted monomers were removed to obtain epoxy-functionalized cyclic hydrogen-containing siloxane intermediates.

[0050] Step A2: Dissolve 100g of epoxy-functionalized cyclic hydrogen-containing siloxane intermediate in 200mL of toluene, add 130g of phenol polyoxyethylene ether and 2.0g of tetrabutylammonium bromide, and react at 110℃ for 12h. After the reaction is complete, cool to room temperature, wash with deionized water, separate the organic phase, and dry the organic phase with anhydrous sodium sulfate. Add 12g of diphenyldimethoxysilane and 1.5g of sodium methoxide to the dried organic phase, and react at 130℃ for 10h to obtain phenyl polysiloxane-polyether prepolymer.

[0051] In step A3, 10g of phenyl polysiloxane-polyether prepolymer was dissolved in 30mL of methyl ethyl ketone to prepare a 25% (w / w) solution. 1.0g of 1H,1H,2H-perfluoro-1-hexene was added, along with a solution of isopropanol chloroplatinic acid containing 0.0003g of platinum. The reaction was carried out at 75°C for 8 hours. After the reaction was completed, the solvent was removed by vacuum distillation at 60°C and -0.092MPa to obtain the crude product of fluorine-modified phenyl polysiloxane polyether copolymer.

[0052] Step A4: The crude product is loaded into a supercritical extraction vessel and purified by fractional extraction for 2 hours at a temperature of 60℃, a pressure of 25MPa, and a supercritical carbon dioxide flow rate of 10L / h. The soluble fraction is collected, and after depressurization, 8.5g of high-purity fluorine-modified phenyl polysiloxane polyether copolymer is obtained. The product is a pale yellow transparent viscous liquid.

[0053] Implement the oil recovery method: Step S1, deploy a three-dimensional well network consisting of 3 horizontal wells and 6 vertical wells in a tight oil reservoir at a depth of 2500m, form a complex fracture network system through 25 stages of multi-stage fracturing, prepare 1000kg of treatment fluid containing 0.5% by mass of fluorine-modified phenyl polysiloxane polyether block copolymer, and inject it into the reservoir at a discharge rate of 12m³ / min.

[0054] Step S2 involves a circulating carbon dioxide injection strategy, with three cycles of injection. Each cycle injects 150t of liquid carbon dioxide over a period of 5 days, followed by a 12-day well-closing period. In the final cycle, a multi-stage microbial activator is injected alternately. For a waterflood reservoir with a pH of 7.0, the activator consists of 50kg corn syrup powder, 5kg sodium dihydrogen phosphate, 5kg disodium hydrogen phosphate, 7kg ammonium chloride, 0.1kg petroleum sulfonate, and 1kg trace element mother liquor.

[0055] Step S3: Close the production well for well simmering cultivation, maintain the reservoir temperature at 70°C, and inject 80°C hot water through the injection well to adjust the temperature. Monitor the changes in the microbial community every 30 days by sampling the downhole fluid.

[0056] Step S4: After 120 days of well simmering and cultivation, the production well is gradually opened. An intermittent production system is adopted, with the well shut down for one week after two weeks of production. When the methane content reaches 75% and stabilizes for 5 days, the production will switch to the continuous production stage.

[0057] Example 2

[0058] This embodiment provides a method for in-situ biotransformation and carbon dioxide flooding in oil and gas reservoirs.

[0059] First, a fluorine-modified phenyl polysiloxane polyether block copolymer was prepared:

[0060] Step A1: 253g of 1,3,5,7-tetramethylcyclotetrasiloxane was added to 480mL of anhydrous toluene to prepare a 34% solution. The solution was heated to 85°C under nitrogen protection. 123g of 4-vinylepoxycyclohexane was slowly added dropwise over 2.5h using a constant-pressure dropping funnel. Then, a solution of triphenylphosphine chloride platinum isopropanol containing 0.0045g of platinum was added. The temperature was maintained at 85±1°C, and the reaction was stirred for 6.5h. The reaction was monitored by infrared spectroscopy at 2160cm⁻¹. -1 The decrease in the characteristic absorption peak of Si-H was used to determine the reaction endpoint. After the reaction was completed, the solvent and unreacted monomers were removed by vacuum distillation at 65℃ and -0.095MPa to obtain epoxy-functionalized cyclic hydrogen-containing siloxane intermediates.

[0061] Step A2: Dissolve 100g of epoxy-functionalized cyclic hydrogen-containing siloxane intermediate in 220mL of toluene, add 138g of phenolic polyoxyethylene ether, add 3.0g of tetrabutylammonium bromide, and react at 110℃ for 13h. After the reaction is completed, cool to room temperature, wash with deionized water, separate the organic phase, and dry the organic phase with anhydrous sodium sulfate. Add 14g of diphenyldimethoxysilane and 1.8g of sodium methoxide to the dried organic phase, and react at 135℃ for 11h to obtain phenyl polysiloxane-polyether prepolymer.

[0062] In step A3, 10g of phenyl polysiloxane-polyether prepolymer was dissolved in 35mL of methyl ethyl ketone to prepare a 22% (w / w) solution. 1.1g of 1H,1H,2H-perfluoro-1-hexene was added, along with a chloroplatinic acid isopropanol solution containing 0.00035g of platinum. The reaction was carried out at 75°C for 8.5h. After the reaction was completed, the solvent was removed by vacuum distillation at 60°C and -0.092MPa to obtain the crude product of fluorine-modified phenyl polysiloxane polyether copolymer.

[0063] Step A4: The crude product is loaded into a supercritical extraction vessel and purified by fractional extraction for 2.5 h at a temperature of 65℃, a pressure of 28MPa, and a supercritical carbon dioxide flow rate of 12L / h. The soluble fraction is collected and after depressurization, 8.6 g of high-purity fluorine-modified phenyl polysiloxane polyether copolymer is obtained. The product is a pale yellow transparent viscous liquid.

[0064] Implement the oil recovery method: Step S1, deploy a three-dimensional well network consisting of 4 horizontal wells and 8 vertical wells in a tight oil reservoir at a depth of 2600m, form a complex fracture network system through 28 stages of multi-stage fracturing, prepare 1200kg of treatment fluid containing 0.8% by mass of fluorine-modified phenyl polysiloxane polyether block copolymer, and inject it into the reservoir at a discharge rate of 15m³ / min.

[0065] Step S2 involves a circulating carbon dioxide injection strategy, with four cycles of injection. Each cycle injects 180t of liquid carbon dioxide over a period of 6 days, followed by a 14-day well-closing period. In the final cycle, a multi-stage microbial activator is injected alternately. For a weakly alkaline ternary composite post-flood reservoir with a pH of 8.2, the activator consists of 60kg corn syrup powder, 6kg sodium dihydrogen phosphate, 6kg disodium hydrogen phosphate, 8kg ammonium chloride, 0.12kg petroleum sulfonate, and 1.2kg trace element mother liquor, with additional additions of 2kg glucose, 0.1kg sodium formate, 0.1kg sodium acetate, and 0.1kg sodium propionate.

[0066] Step S3: Close the production well for well simmering cultivation, maintain the reservoir temperature at 75°C, and inject 85°C hot water through the injection well to adjust the temperature. Monitor the changes in the microbial community every 35 days by sampling the downhole fluid.

[0067] Step S4: After 150 days of well simmering and cultivation, the production well is gradually opened. An intermittent production system is adopted, with 3 weeks of production followed by 2 weeks of well shut-off. When the methane content reaches 78% and stabilizes for 6 days, the production is switched to the continuous production stage.

[0068] Example 3

[0069] This embodiment provides a method for in-situ biotransformation and carbon dioxide flooding in oil and gas reservoirs.

[0070] First, a fluorine-modified phenyl polysiloxane polyether block copolymer was prepared:

[0071] Step A1: 255g of 1,3,5,7-tetramethylcyclotetrasiloxane was added to 460mL of anhydrous toluene to prepare a 36% solution. The solution was heated to 85°C under nitrogen protection. 125g of 4-vinylepoxycyclohexane was slowly added dropwise over 3 hours using a constant-pressure dropping funnel. Then, a solution of triphenylphosphine chloride platinum isopropanol containing 0.005g of platinum was added. The temperature was maintained at 85±1°C with stirring for 7 hours. The reaction was monitored by infrared spectroscopy at 2160 cm⁻¹. -1 The decrease in the characteristic absorption peak of Si-H was used to determine the reaction endpoint. After the reaction was completed, the solvent and unreacted monomers were removed by vacuum distillation at 65℃ and -0.095MPa to obtain epoxy-functionalized cyclic hydrogen-containing siloxane intermediates.

[0072] Step A2: Dissolve 100g of epoxy-functionalized cyclic hydrogen-containing siloxane intermediate in 240mL of toluene, add 145g of phenolic polyoxyethylene ether and 4.0g of tetrabutylammonium bromide, and react at 110℃ for 14h. After the reaction is complete, cool to room temperature, wash with deionized water, separate the organic phase, and dry the organic phase with anhydrous sodium sulfate. Add 15g of diphenyldimethoxysilane and 2.0g of sodium methoxide to the dried organic phase, and react at 140℃ for 9h to obtain phenyl polysiloxane-polyether prepolymer.

[0073] In step A3, 10g of phenyl polysiloxane-polyether prepolymer was dissolved in 40mL of methyl ethyl ketone to prepare a 20% (w / w) solution. 1.2g of 1H,1H,2H-perfluoro-1-hexene was added, along with a solution of isopropanol chloroplatinic acid containing 0.0004g of platinum. The reaction was carried out at 75°C for 9h. After the reaction was completed, the solvent was removed by vacuum distillation at 60°C and -0.092MPa to obtain the crude product of fluorine-modified phenyl polysiloxane polyether copolymer.

[0074] Step A4: The crude product is loaded into a supercritical extraction vessel and purified by fractional extraction for 3 hours at a temperature of 70℃, a pressure of 30MPa, and a supercritical carbon dioxide flow rate of 15L / h. The soluble fraction is collected, and after depressurization, 8.8g of high-purity fluorine-modified phenyl polysiloxane polyether copolymer is obtained. The product is a pale yellow transparent viscous liquid.

[0075] Implement the oil recovery method: Step S1, deploy a three-dimensional well network consisting of 5 horizontal wells and 10 vertical wells in a tight oil reservoir at a depth of 2800m, form a complex fracture network system through 32 stages of multi-stage fracturing, prepare 1500kg of treatment fluid containing 1.0% by mass of fluorine-modified phenyl polysiloxane polyether block copolymer, and inject it into the reservoir at a discharge rate of 18m³ / min.

[0076] Step S2 involves a circulating carbon dioxide injection strategy, with four cycles of injection. Each cycle injects 200t of liquid carbon dioxide over a period of 7 days, followed by a 15-day well-closing period. In the final cycle, a multi-stage microbial activator is injected alternately. For a strongly alkaline ternary composite post-flood reservoir with a pH of 10.5, the activator consists of 70kg corn syrup powder, 7kg sodium dihydrogen phosphate, 7kg disodium hydrogen phosphate, 9kg ammonium chloride, 0.15kg petroleum sulfonate, and 1.5kg trace element mother liquor. Additionally, 3kg glucose, 0.15kg sodium formate, 0.15kg sodium acetate, and 0.15kg sodium propionate are added, along with 4kg sodium bicarbonate.

[0077] Step S3: Close the production well for well simmering cultivation, maintain the reservoir temperature at 80°C, and inject 90°C hot water through the injection well to regulate the temperature. Monitor the changes in the microbial community every 40 days by sampling the downhole fluid.

[0078] Step S4: After 180 days of simmering cultivation, the production well is gradually opened. An intermittent production system is adopted, with the well shut down for one week after three weeks of production. When the methane content reaches 80% and stabilizes for 7 days, the production will switch to the continuous production stage.

[0079] Comparative Example 1

[0080] The difference between this comparative example and Example 1 is that this comparative example provides a comparative method. Except for the absence of fluorine-modified phenyl polysiloxane polyether block copolymer treatment solution, the remaining steps are exactly the same as in Example 1. In step S1, only 1000 kg of base solution without the modified compound is injected. The operating parameters for steps S2 to S4 are consistent with those in Example 1.

[0081] Comparative Example 2

[0082] The difference between this comparative example and Example 1 is that this comparative example provides a comparative method in which the fluorination modification step is omitted in the preparation of the modified compound. Steps A1 and A2 are the same as in Example 1, except that 1H,1H,2H-perfluoro-1-hexene is not added in step A3, and the unfluorinated phenyl polysiloxane polyether prepolymer is obtained directly. The unfluorinated modified compound is used to prepare the treatment fluid in step S1, and the remaining oil recovery steps are exactly the same as in Example 1.

[0083] Comparative Example 3

[0084] The difference between this comparative example and Example 1 is that the comparative example provides a comparative method in which the polyether grafting step is omitted during the preparation of the modified compound. Step A1 is the same as in Example 1. In step A2, monoallyl polyoxyethylene ether phenyl ether is not added; instead, an epoxy-terminated hydrogen-containing siloxane intermediate is directly reacted with diphenyldimethoxysilane to obtain an ungrafted polyether siloxane prepolymer. In step S1, the ungrafted polyether compound is used to prepare the treatment fluid; the remaining oil recovery steps are exactly the same as in Example 1.

[0085] The underground in-situ bioconversion and carbon dioxide flooding oil recovery methods for oil and gas reservoirs provided in the above embodiments and comparative examples were tested according to national and industry standards. The test methods are as follows: The performance test of the present invention was carried out in a high-temperature and high-pressure reactor system simulating tight oil reservoir conditions. The reactor volume was 10L, the working pressure range was 0-50MPa, and the temperature control range was 20-150℃. The test samples were prepared according to the methods of Examples 1-3 and Comparative Examples 1-3, and each sample was tested three times and the average value was taken. The specific test process is as follows:

[0086] 500g of dense core and 200mL of crude oil sample were loaded into a reactor. Treatment fluid and activator were injected according to the parameters specified in the examples and comparative examples, maintaining the set temperature and pressure conditions. During the test, gas samples were collected every 24 hours, and their composition, particularly methane and carbon dioxide content, was analyzed using gas chromatography. Liquid samples were collected every 72 hours to measure crude oil viscosity and composition changes. Carbon dioxide sequestration rate was calculated using the mass balance method, comparing the difference between the injected and produced carbon dioxide. Methane yield was determined by the ratio of cumulative methane production to the theoretical maximum methane production. Oil recovery rate was calculated by the ratio of produced oil to original oil volume. Microbial community changes were analyzed using 16S rRNA gene sequencing, focusing on the relative abundance changes of hydrolytic fermenting bacteria, lipophilic thermotrophic bacilli, and methanogenic archaea. All tests were conducted for 180 days to ensure complete biotransformation process data were obtained.

[0087] The performance test data above are shown in Table 1.

[0088] Table 1 Performance Test Results

[0089] Carbon dioxide sequestration rate / % 78.5 82.3 85.6 45.2 62.1 58.7 Methane yield / % 76.8 79.4 83.2 22.5 48.3 41.6 Oil recovery rate increased by % 28.3 31.7 35.2 12.4 18.9 16.3 Final crude oil viscosity reduction rate / % 68.5 72.3 76.8 25.6 45.2 38.7 Relative abundance of methanogenic archaea / % 35.2 38.7 42.5 8.3 18.6 15.4 Relative abundance of hydrolytic fermentation bacteria / % 28.7 31.2 33.8 12.5 19.3 16.8 relative abundance of lipophilic thermotrophic bacilli / % 25.4 27.9 30.5 9.8 16.2 13.7

[0090] As can be seen from the above, Embodiments 1-3 of the present invention effectively solve the key technical problems pointed out in the background art by adopting a complete fluorine-modified phenyl polysiloxane-polyether block copolymer and its supporting process.

[0091] Specifically, the carbon dioxide sequestration rates of Examples 1-3 reached 78.5-85.6%, which is a significant improvement compared to 45.2% of Comparative Example 1. This demonstrates that the modified compound effectively improves the flow control characteristics of supercritical carbon dioxide in tight reservoirs and solves the problems of easy gas channeling and low sequestration efficiency in traditional carbon dioxide flooding.

[0092] Regarding microbial conversion efficiency, the methane yield of Examples 1-3 reached 76.8-83.2%, and the methane content could be increased to over 70% in just 72-85 days. In contrast, Comparative Example 1 failed to reach this level even after 180 days. This indicates that the favorable microbial environment created by the modified compound significantly accelerated the biological metabolic process.

[0093] Regarding enhanced oil recovery, Examples 1-3 increased crude oil recovery by 28.3-35.2%, significantly higher than the 12.4% of Comparative Example 1, demonstrating that this technology can effectively utilize crude oil from tight reservoirs that are difficult to extract using traditional techniques. Comparative Example 2, lacking fluorine modification, showed a decrease of approximately 20% in carbon dioxide sequestration and methane yield compared to the examples, proving that fluorine groups play a crucial role in enhancing interfacial activity and compound stability. Comparative Example 3, lacking polyether segment grafting, had a lower relative abundance of microbial communities than the examples, indicating that polyether segments are indispensable for improving biocompatibility and nutrient transfer efficiency. The relative abundance of methanogenic archaea reached 35.2-42.5%, significantly higher than the 8.3-18.6% of the comparative examples, confirming that this technology system can effectively activate and maintain the efficient operation of functional microbial communities, achieving the dual goals of efficient carbon dioxide sequestration and in-situ conversion of energy products.

Claims

1. A method for in-situ underground biotransformation and carbon dioxide flooding oil recovery in oil and gas reservoirs, characterized in that, Includes the following steps: S1. Deploy a three-dimensional well network with high conductivity in tight oil reservoirs, including staggered heating wells and production wells, using horizontal or vertical well networks to ensure that the main fractures formed by each well extend along the maximum horizontal principal stress and are not directly opposite each other; form a three-dimensional fracture network through multi-stage fracturing, with the distal ends interconnected through microfractures; prepare a treatment fluid containing fluorine-modified phenyl polysiloxane-polyether block copolymer and inject the treatment fluid into the reservoir; S2. A circulating carbon dioxide injection strategy is adopted, with the injection volume dynamically adjusted according to the monitored reservoir pressure. The carbon dioxide injection is carried out in a supercritical state. In the last carbon dioxide injection cycle, multiple stages of microbial activators are injected alternately. For water-flooded or polymer-flooded reservoirs with pH=6-7.5, the activator includes corn syrup powder, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium chloride, petroleum sulfonate, and trace element mother liquor. For weakly alkaline ternary composite flooded reservoirs with pH=7.5-9, glucose, sodium formate, sodium acetate, and sodium propionate are added. For strongly alkaline ternary composite flooded reservoirs with pH=9-12, sodium bicarbonate is further added. S3. After injecting the activator, shut down the production well for well simmering cultivation, maintain the reservoir temperature at 60-80℃, and regulate the reservoir temperature by injecting hot water through the heating well; periodically monitor changes in microbial communities and metabolites by sampling downhole fluids. S4. After the well simmering and cultivation is completed, the production wells are gradually opened to enter the biomethane production stage; an intermittent production system is adopted; during the production process, the composition changes of the produced gas are monitored in real time, and when the methane content is higher than 70% and stable, the production stage is switched to continuous production.

2. The method for underground in-situ biotransformation and carbon dioxide flooding oil recovery in oil and gas reservoirs according to claim 1, characterized in that, In step S1, the mass fraction of the fluorinated phenyl polysiloxane-polyether block copolymer in the treatment solution is 0.5-1.0%.

3. The method for underground in-situ biotransformation and carbon dioxide flooding oil recovery in oil and gas reservoirs according to claim 1, characterized in that, In step S2, the carbon dioxide injection cycle is repeated 3-4 times.

4. The method for underground in-situ biotransformation and carbon dioxide flooding oil recovery in oil and gas reservoirs according to claim 1, characterized in that, In step S3, the microbial community includes: hydrolytic fermenting bacteria, lipophilic thermotrophic bacilli, and methanogenic archaea.

5. The method for in-situ underground biotransformation and carbon dioxide flooding oil recovery in oil and gas reservoirs according to claim 1, characterized in that, In step S4, the intermittent production system involves producing for 2-3 weeks and then shutting down the well for 1-2 weeks.

6. The method for underground in-situ biotransformation and carbon dioxide flooding oil recovery in oil and gas reservoirs according to any one of claims 1-5, characterized in that, The preparation steps of the fluorinated phenyl polysiloxane-polyether block copolymer include: A1. 1,3,5,7-Tetramethylcyclotetrasiloxane was added to anhydrous toluene to prepare a solution, which was heated to 84-86°C under nitrogen protection. 4-Vinylepoxycyclohexane was added dropwise, followed by a solution of triphenylphosphine platinum chloride in isopropanol, and the mixture was stirred. After the reaction was completed, the solution was distilled under reduced pressure to obtain an epoxy-functionalized cyclic hydrogen-containing siloxane intermediate. A2. Dissolve the epoxy-functionalized cyclic hydrogen-containing siloxane intermediate in toluene, add phenolic polyoxyethylene ether, add tetrabutylammonium bromide, and react at 108-112℃. After the reaction is complete, cool to room temperature, wash with deionized water, separate the organic phase, and dry the organic phase with anhydrous sodium sulfate. Add diphenyldimethoxysilane and sodium methoxide to the dried organic phase and react at 120-150℃ to obtain phenyl polysiloxane-polyether prepolymer. A3. The phenyl polysiloxane-polyether prepolymer was dissolved in methyl ethyl ketone to prepare a solution. 1H,1H,2H-perfluoro-1-hexene was added, along with an isopropanol solution of chloroplatinic acid. The reaction was carried out at 74-76℃. After the reaction was completed, the fluorinated phenyl polysiloxane-polyether copolymer was obtained by vacuum distillation. A4. The fluorine-modified phenyl polysiloxane-polyether copolymer was dissolved in supercritical carbon dioxide and purified by fractional extraction; the soluble fraction was collected and the pressure was released.

7. The method for underground in-situ biotransformation and carbon dioxide flooding oil recovery in oil and gas reservoirs according to claim 6, characterized in that, In step A1, the mass ratio of 1,3,5,7-tetramethylcyclotetrasiloxane, 4-vinylepoxycyclohexane, and triphenylphosphine platinum chloride is (250-255):(120-125):(0.004-0.005).

8. The method for in-situ underground biotransformation and carbon dioxide flooding oil recovery in oil and gas reservoirs according to claim 6, characterized in that, In step A2, the mass ratio of the epoxy-functionalized cyclic hydrogen-containing siloxane intermediate, phenol polyoxyethylene ether, tetrabutylammonium bromide, diphenyldimethoxysilane, and sodium methoxide is 100:(100-150):(2-5):(10-15):(1-2); the reaction time is 8-12 h at 120-150 °C.

9. The method for in-situ underground biotransformation and carbon dioxide flooding oil recovery in oil and gas reservoirs according to claim 6, characterized in that, In step A3, the mass ratio of phenyl polysiloxane-polyether prepolymer to 1H,1H,2H-perfluoro-1-hexene is 10:(1.0-1.2).

10. An application of the underground in-situ biotransformation and carbon dioxide flooding method for oil and gas reservoirs according to any one of claims 1-9, characterized in that, Application of the underground in-situ biotransformation and carbon dioxide flooding method for oil and gas reservoirs in tight oil reservoir fracturing.