Injection well fluids and methods of making and use thereof

Abstract

The application provides an injection well fluid and a preparation method and application thereof, the injection well fluid comprising a solvent and graphene oxide, the pH of the injection well fluid being 3-6; in the injection well fluid, the mass concentration of the graphene oxide is 0.2 mg / mL-5 mg / mL. The injection well fluid strengthens the acidification effect under the operation condition of high temperature and high pressure, and further significantly improves the overall flow conductivity of the hot dry rock reservoir and the heat exchange efficiency and development stability of the EGS system.

Description

Technical Field

[0001] This invention relates to the field of hot dry rock development technology, and in particular to an injection well fluid, its preparation method, and its application. Background Technology

[0002] Currently, the development of hot dry rock mainly adopts enhanced geothermal systems (EGS), the core of which is to inject fluids into the reservoir through injection wells to create fractures. In existing technologies, neutral water, as the mainstream injection fluid, has a cost advantage, but its neutral nature results in a slow reaction rate between the fluid and reservoir minerals, making it difficult to effectively dissolve mineral components and expand pore space. This leads to persistently high fracturing initiation pressure and hindered fracture propagation, seriously affecting the stimulation efficiency of geothermal reservoirs.

[0003] To improve acidizing effects, some studies have attempted to use strong acidic fluids. However, excessive acidizing can trigger violent reactions in the matrix minerals, producing a large amount of secondary precipitates that clog pores. At the same time, the corrosion risk to equipment and environmental hazards of strong acids cannot be ignored, resulting in a decrease in reservoir permeability instead of an increase, and a significant reduction in fracturing efficiency and economics.

[0004] Therefore, the existing injection well fluid acidizing stimulation capabilities used in hot dry rock development are insufficient, and the actual reservoir stimulation application results are unsatisfactory. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide an injection well fluid that, by constructing a weakly acidic fluid system with a pH value of 3-6 and compounding it with a specific mass concentration of graphene oxide, can gently and efficiently dissolve mineral components in hot dry rock reservoirs, significantly improving the acidizing effect of the injection well fluid on the reservoir under high temperature and high pressure operating conditions.

[0006] The present invention also provides a method for preparing injection well fluid, which is simple to operate, has easily adjustable process parameters, and can stably prepare the above-mentioned qualified injection well fluid.

[0007] This invention also provides a method for mining hot dry rock based on injection well fluid. By relying on optimized special injection well fluid and matching on-site mining construction technology, it is possible to complete the uniform acid dissolution of fractures at all scales in hot dry rock reservoirs, thereby comprehensively improving the overall effect of geothermal reservoir stimulation.

[0008] In a first aspect, the present invention provides an injection well fluid comprising a solvent and graphene oxide, wherein the pH of the injection well fluid is 3 to 6; and wherein the mass concentration of the graphene oxide in the injection well fluid is 0.2 mg / mL to 5 mg / mL.

[0009] Furthermore, the Dv50 particle size of the graphene oxide is 0.5 μm to 5 μm.

[0010] Furthermore, the injected well fluid also includes a dispersant;

[0011] Preferably, the mass concentration of the dispersant in the injected well fluid is 0.05 mg / mL to 2 mg / mL.

[0012] In a second aspect, the present invention provides a method for preparing the injection well fluid described in the first aspect, comprising the following steps:

[0013] 1) Graphite, a strong oxidant, and water are mixed once, and the solid is separated to obtain the graphene oxide.

[0014] 2) The solvent and the graphene oxide are mixed a second time to obtain the injection well fluid.

[0015] Further, in step 1), the mass ratio of the strong oxidant to graphite is (2~4):1;

[0016] Preferably, the strong oxidizing agent includes potassium permanganate.

[0017] Furthermore, the separation of solids includes centrifugation, wherein the centrifugation speed is 6000 r / min to 10000 r / min.

[0018] Thirdly, the present invention provides a method for mining hot dry rock, comprising the following steps:

[0019] a) In a hot dry rock injection well, a completion string is first run in and cemented, and then a production string is coaxially run in inside the completion string, so that an annular space is formed between the completion string and the production string.

[0020] b) Use water to perform a single hydraulic fracturing treatment on the dry, hot rock to create fractures;

[0021] c) The injection well fluid described in the first aspect is subjected to secondary fracturing treatment to form a fracturing network.

[0022] Furthermore, after the formation of the fracture network, the injection well fluid is continuously injected.

[0023] Furthermore, the secondary fracturing process includes the following steps: pressurizing and injecting the injection well fluid into the annular space to form the fracturing network.

[0024] Furthermore, the pressure in the annular space is 15MPa~25MPa;

[0025] And / or, the injection flow rate of the pressurized injection treatment is 5m. 3 / h~10m 3 / h.

[0026] The injection well fluid provided by this invention employs a weakly acidic system with a pH of 3-6. This overcomes the shortcomings of pure water fluids, such as slow mineral dissolution rates and weak reservoir stimulation, while avoiding the problems of excessive reactions in strongly acidic fluids that generate large amounts of precipitation that clog pores and corrode downhole equipment, thus achieving mild and controllable acidizing stimulation. The addition of graphene oxide at a mass concentration of 0.2 mg / mL to 5 mg / mL optimizes the fluid's permeability and transport characteristics, helps expand reservoir pores and fracture space, reduces fracturing initiation pressure, promotes smooth fracture propagation, and significantly improves the stimulation efficiency of hot dry rock reservoirs. Through the synergistic effect of pH and graphene oxide concentration, the acidizing effect of this injection well fluid is synergistically enhanced. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the accompanying drawings used in the description of the embodiments of the present invention or related technologies are briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 A schematic diagram of the process flow of the injection well fluid provided for one specific implementation. Detailed Implementation

[0029] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Enhanced geothermal systems (EGS) are the mainstream deep geothermal development technology. They mainly involve artificially fracturing the reservoir to create a fracture network and relying on the annular fluid of the injection well to exchange heat with the high-temperature rock mass, thereby achieving efficient extraction of geothermal resources. The performance of the working fluid in the annular fluid of the injection well directly determines the effect of reservoir acidizing and fracturing.

[0031] Hot dry rock reservoirs generally possess characteristics of high density, low permeability, and high hardness. Efficient reservoir stimulation requires fluid acidification to dissolve minerals, widen fractures, and reduce initiation pressure. Currently, the annular fluids used in the industry have significant technical shortcomings: when using neutral fluids such as water, the system lacks acidification activity, resulting in an extremely low reaction rate with reservoir minerals. This fails to effectively dissolve the rock mass and widen fractures, leading to high fracturing initiation pressure, hindered fracture propagation, and extremely poor reservoir stimulation. While traditional strong acidic fluids have strong acidification capabilities, the intense and uncontrollable acidic reaction can cause excessive dissolution of the rock matrix, generating large amounts of secondary precipitates that clog pores and fractures, thus reducing reservoir permeability. Furthermore, strong acids can corrode downhole equipment and pose environmental hazards.

[0032] In summary, existing fluid systems cannot solve the technical challenges of efficient acidification in weakly acidic environments, and struggle to simultaneously meet the multiple requirements of mild acidification, reservoir protection, and efficient fracture creation, severely restricting the quality and economic viability of hot dry rock reservoir stimulation. Therefore, developing a novel injection well annulus fluid that can stably maintain a weakly acidic environment, possess excellent acidification and dissolution effects, and protect the reservoir while avoiding blockage and corrosion problems is the core technological breakthrough for current hot dry rock EGS development.

[0033] In a first aspect, the present invention provides an injection well fluid comprising a solvent and graphene oxide, wherein the pH of the injection well fluid is 3 to 6; and the mass concentration of graphene oxide in the injection well fluid is 0.2 mg / mL to 5 mg / mL.

[0034] For example, the pH of the injected well fluid is any value or a range of any two of the following: 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6.

[0035] For example, the mass concentration of graphene oxide is any value or a range of any two of the following: 0.2 mg / mL, 0.4 mg / mL, 0.6 mg / mL, 0.8 mg / mL, 1.0 mg / mL, 1.2 mg / mL, 1.4 mg / mL, 1.6 mg / mL, 1.8 mg / mL, 2 mg / mL, 2.2 mg / mL, 2.4 mg / mL, 2.6 mg / mL, 2.8 mg / mL, 3 mg / mL, 3.2 mg / mL, 3.4 mg / mL, 3.6 mg / mL, 3.8 mg / mL, 4 mg / mL, 4.2 mg / mL, 4.4 mg / mL, 4.6 mg / mL, 4.8 mg / mL, 5 mg / mL.

[0036] In this invention, the injection well fluid provided serves as a novel annular water system. Through the synergistic effect of a weakly acidic environment and the mass concentration of graphene oxide, the injection well fluid, after being injected into a hot dry rock reservoir, can chemically react with readily soluble minerals within the reservoir, achieving reservoir acidizing and thus effectively reducing fracturing initiation pressure. Simultaneously, it enhances the fluid's pressure support, drag reduction, and temporary plugging diversion capabilities, allowing acidizing and fracturing to work together efficiently, ultimately significantly improving the acidizing effect of the injection well fluid.

[0037] Specifically, by controlling the mass concentration of graphene oxide within the range of 0.2 mg / mL to 5 mg / mL, and by ensuring that the surface of graphene oxide is rich in oxygen-containing active functional groups such as carboxyl and hydroxyl groups, the injection well fluid can be stably maintained in a weakly acidic range of pH 3 to 6. This effectively enhances the interfacial reaction activity between the fluid and reservoir minerals, enabling the fluid to achieve uniform and sufficient acidification and dissolution of fractures across all scales within the hot dry rock reservoir, thereby strengthening the overall acidification and stimulation effect of the injection well fluid.

[0038] Meanwhile, the injection well fluid of the present invention can further improve the reservoir conductivity and the heat exchange efficiency of the EGS system.

[0039] It should be noted that the specific method for testing the acidizing effect of the injected well fluid includes the following steps: preparing a simulated hot dry rock core, an injected well fluid sample, and acidizing reaction monitoring equipment; ensuring full contact between the injected well fluid and the simulated hot dry rock core, controlling the contact time and temperature to simulate the reaction environment in actual mining; observing and recording the dissolution roughness of the surface of the simulated hot dry rock core, and detecting the amount of easily soluble minerals dissolved in the fluid; comparing the changes in surface roughness and permeability of the simulated hot dry rock core before and after contact, as well as the sufficiency of the fluid reaction, to determine the acidizing effect.

[0040] In some embodiments, the solvents mentioned above include, but are not limited to, water.

[0041] In some embodiments, the Dv50 particle size of graphene oxide is 0.5 μm to 5 μm.

[0042] In the above embodiments, the Dv50 particle size of graphene oxide is controlled within the range of 0.5μm to 5μm, which can be adapted to different scales of pore and fracture structures in hot dry rock reservoirs. It can not only smoothly penetrate into micro-fractures to complete deep dissolution, but also form appropriate bridging at large fractures to regulate the fluid flow distribution, promote the uniform action of acidic components on the reservoir rock mass, improve the uniformity of mineral dissolution, and further enhance the acidizing effect of the injected well fluid.

[0043] For example, the Dv50 particle size of graphene oxide is any value or a range of any two of the following: 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm.

[0044] It should be noted that the method for measuring the Dv50 particle size of graphene oxide in this invention includes the following steps:

[0045] 1) Take an appropriate amount of graphene oxide as a test sample and place it in an ultrasonic disperser. Disperse it ultrasonically for 10 min to 30 min at a power of 200W to 300W to ensure that the graphene oxide particles are fully dispersed and there is no obvious agglomeration, thus obtaining the dispersion to be tested; 2) Use a laser particle size analyzer to test the particle size distribution of the above dispersion to be tested. The test environment temperature is 20℃ to 25℃, and the volume particle size distribution curve is obtained; 3) Read the peak particle size corresponding to the characteristic particle size peak, which is the Dv50 particle size of graphene oxide.

[0046] In some implementations, the injected well fluid also includes a dispersant.

[0047] In the above embodiments, the injected well fluid also includes a dispersant, which can effectively reduce the interfacial tension of graphene oxide, ensure that graphene oxide can exist stably in an independent dispersed state and be uniformly transported to fractures of all scales in the hot dry rock reservoir, provide a stable dispersion system guarantee for uniform acidizing and dissolving, pressure support, drag reduction and temporary plugging diversion of fractures of all scales, and further improve the acidizing effect of the injected well fluid.

[0048] To further promote the oxidation of graphene oxide and enhance the acidizing effect of the injected well fluid, in some preferred embodiments, the dispersant includes, but is not limited to, sodium dodecylbenzenesulfonate and / or zwitterionic surfactants.

[0049] In some preferred embodiments, the zwitterionic surfactants include, but are not limited to, alkyl dimethyl betaine and / or alkyl dimethyl sulfoethyl betaine.

[0050] In some implementations, the mass concentration of the dispersant in the injected well fluid is 0.05 mg / mL to 2 mg / mL.

[0051] In the above embodiments, the mass concentration of the dispersant is controlled within the range of 0.05 mg / mL to 2 mg / mL. This ensures that the graphene oxide is fully dispersed, does not agglomerate or settle, and avoids the effect of excessive dispersant on the acidity of the system and the acidizing reaction efficiency. This allows the graphene oxide to act stably and uniformly on the fractures of all scales, thereby further improving the acidizing effect of the injected well fluid.

[0052] For example, the mass concentration of the dispersant is any value or a range of any combination of 0.05 mg / mL, 0.1 mg / mL, 0.15 mg / mL, 2 mg / mL, etc.

[0053] In a second aspect, the present invention provides a method for preparing injection well fluid according to the first aspect, comprising the following steps:

[0054] 1) Graphite, a strong oxidant, and water are mixed once, and the solid is separated to obtain graphene oxide;

[0055] 2) The solvent and graphene oxide are mixed twice to obtain the injection well fluid.

[0056] In this invention, the above preparation method has simple process steps, controllable parameters, and easy operation. It can accurately achieve uniform compounding of graphene oxide of three particle sizes and stable control of the pH value of the system, effectively avoid the agglomeration of graphene oxide, and stably produce weakly acidic injection well fluid with uniform performance and good dispersibility. This provides a stable material basis for the injection well fluid to perform acidification and dissolution, thereby ensuring the acidification effect of the injection well fluid.

[0057] Figure 1 This is a schematic diagram of the process flow of the injection well fluid provided for a specific embodiment of the present invention.

[0058] This invention does not limit the form of graphite; by way of example and not limitation, the form of graphite includes, but is not limited to, graphite powder.

[0059] In some example embodiments, the mixing process in step 1) specifically includes the following steps: mixing graphite and a strong oxidant, stirring at 150 r / min to 200 r / min for 1 h to 2 h, and heating to 30 °C to 40 °C to obtain an oxidized graphite reaction solution; adding water to the oxidized graphite reaction solution until the reaction solution no longer produces bubbles, terminating the reaction to obtain a solid-liquid mixture.

[0060] Separating the solid from the above solid-liquid mixture yields graphene oxide. The strong oxidizing properties of a strong oxidizing agent are used to perform oxidative etching and interlayer exfoliation on the graphite sheets. The process of separating the solid includes solvent washing to remove residual strong oxidizing agents and water-soluble byproducts; the solvent includes, but is not limited to, water.

[0061] For example, the stirring speed is any value or a range of any two of the following: 150 r / min, 160 r / min, 170 r / min, 180 r / min, 190 r / min, 200 r / min.

[0062] For example, the stirring time is any value or a range of any two of the following: 1h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h, 2h.

[0063] For example, the heating temperature is any value or a range of any two of the following: 30°C, 32°C, 34°C, 36°C, 38°C, 40°C, etc.

[0064] In some embodiments, the mass ratio of strong oxidant to graphite is (2~4):1.

[0065] In the above embodiments, the mass ratio of strong oxidant to graphite is limited to (2~4):1, which can improve the grafting density and uniformity of acidic functional groups such as carboxyl and hydroxyl groups on the surface of graphene oxide, enhance its hydrophilicity and dispersion stability in high mineralization systems, and precisely control the oxidation degree and size distribution of graphene oxide sheets, regulate the acidity of graphene oxide, adjust the pH of the injection well fluid, and further improve the acidification effect of the injection well fluid.

[0066] For example, the mass ratio of strong oxidant to graphite is any value or a range of any two of the following: 2:1, 2.5:1, 3:1, 3.5:1, 4:1, etc.

[0067] In some preferred embodiments, the strong oxidizing agent includes, but is not limited to, potassium permanganate.

[0068] In the above embodiments, potassium permanganate is used as a strong oxidant, which can fully oxidize graphite to prepare highly active graphene oxide, enrich oxygen-containing functional groups on the surface, enhance the weak acidity of the system, and further improve the acidizing effect of the injected well fluid.

[0069] In some embodiments, the separation of solids includes centrifugation at a speed of 6000 r / min to 10000 r / min.

[0070] In step 1), the solid separation involves centrifuging the mixture obtained after the first mixing process, discarding the supernatant, and collecting the precipitate, which is graphene oxide. The above embodiment limits the centrifugation speed to 6000 r / min to 10000 r / min, which can efficiently purify graphene oxide, remove impurity components, ensure its surface activity, and further improve the acidizing effect of the injected well fluid.

[0071] For example, the rotational speed for separating solids is any value or a range of any two of the following: 6000 r / min, 6200 r / min, 6400 r / min, 6600 r / min, 6800 r / min, 7000 r / min, 7200 r / min, 7400 r / min, 7600 r / min, 7800 r / min, 8000 r / min, 8200 r / min, 8400 r / min, 8600 r / min, 8800 r / min, 9000 r / min, 9200 r / min, 9400 r / min, 9600 r / min, 9800 r / min, 10000 r / min.

[0072] In some implementations, the centrifugation time is 30 to 40 minutes.

[0073] For example, the centrifugation time is any value or a range of any two of the following: 30 min, 31 min, 32 min, 33 min, 34 min, 35 min, 36 min, 37 min, 38 min, 39 min, 40 min.

[0074] In some implementations, the secondary mixing process in step 2) includes ultrasonic treatment.

[0075] In some preferred embodiments, the power of the secondary ultrasonic treatment is 200W~300W, and the time is 10min~15min.

[0076] In the above embodiments, the power and time of ultrasonic treatment are controlled within the range of 200W~300W and 10min~15min, respectively, which can ensure that graphene oxide is fully dispersed in the weakly acidic system without agglomeration and sedimentation, making the fluid system uniform and stable, thereby further improving the acidization effect of the injection well fluid.

[0077] For example, the power of the ultrasonic treatment is any value or a range of any two of the following: 200W, 210W, 220W, 230W, 240W, 250W, 260W, 270W, 280W, 290W, 300W.

[0078] For example, the ultrasonic treatment time is any value or a range of any two of the following: 10 min, 10.5 min, 11 min, 11.5 min, 12 min, 12.5 min, 13 min, 13.5 min, 14 min, 14.5 min, 15 min.

[0079] In some embodiments, step 2) further includes mixing the dispersant with the solvent and graphene oxide.

[0080] In some embodiments, the dispersant includes, but is not limited to, sodium dodecylbenzenesulfonate and / or zwitterionic surfactants.

[0081] In some implementations, the solvent in step 2) includes, but is not limited to, water.

[0082] Thirdly, the present invention provides a method for mining hot dry rock, comprising the following steps:

[0083] a) In hot dry rock injection wells, first run in the completion string and cement it, then run in the production string coaxially inside the completion string, so that an annular space is formed between the completion string and the production string.

[0084] b) Use water to perform a single hydraulic fracturing treatment on the dry, hot rock to create fractures;

[0085] c) The injection well fluid from the first aspect is subjected to secondary fracturing treatment to form a fracturing network.

[0086] In this invention, an annular space is first constructed between the completion tubing and the production tubing of the injection well, providing a stable spatial foundation for the injection of injection well fluid, pressure transmission, and annular action. Water is first used for primary fracturing to form basic fractures, providing an initial channel for the subsequent seepage and action of the injection well fluid. Then, the injection well fluid of this invention is used for secondary fracturing. The weakly acidic properties of the fluid allow for the gentle dissolution and widening of easily soluble minerals around the fractures formed in the primary fracturing. Simultaneously, graphene oxide guides the orderly expansion of fractures to form a connected fracture network. Based on the existing main mining process, this invention improves the stability and effectiveness of hot dry rock mining, further optimizing the effects of fracturing and reservoir acidizing.

[0087] In addition, graphene oxide has excellent thermal conductivity, which can absorb the high temperature around the wellbore through circulation, reduce the temperature of downhole equipment, extend equipment life, and improve sealing effect. At the same time, using the injection well fluid from the first aspect to fill the annulus space can form a stable liquid column pressure, balance the formation pressure, prevent formation fluid backflow, and ensure construction safety.

[0088] In this invention, the method of single-stage fracturing is not limited; however, by way of example and not limitation, the method of single-stage fracturing includes the following steps:

[0089] S1. Liquid preparation: Prepare clean water at 0℃~4℃;

[0090] S2. Use water at 0℃~4℃ to fracturing to form microcracks along the direction of maximum principal stress;

[0091] S3. Multi-stage temporary plugging fracturing forms transverse microcracks; water is injected to carry high-temperature resistant temporary plugging agent into the crack, and the increased net pressure inside the crack by the large displacement and the three-stage temporary plugging agent causes the microcracks to turn, forming transverse microcracks; the high-temperature resistant temporary plugging agent is powdered ceramic with a particle size range of 140 mesh to 200 mesh.

[0092] S4. After the temporary plugging fracturing is completed, the fracture in step b) above is obtained.

[0093] In some implementations, after the fracturing network is formed, continuous injection of injection well fluid is also included.

[0094] The fracture network contains minerals within its pores. The injected well fluid within the annular space undergoes an acidification reaction with these minerals. Because the injected well fluid is weakly acidic, the acidification reaction is mild and controllable, effectively preventing excessive acidification that could lead to secondary precipitation, preventing fracture blockage, slowly dissolving readily soluble minerals, expanding fracture width, improving fracture connectivity, and enhancing reservoir conductivity. This ensures that the injected well fluid fully penetrates the deep micro- and nano-pores and fractures of various scales within the fracture network, continuously achieving acidification, pressure support, and temporary plugging and diversion, thereby further improving the acidification effect of the injected well fluid.

[0095] In some implementations, secondary fracturing includes the following process: pressurizing and injecting the injection well fluid into the annular space to form a fracturing network.

[0096] Secondary fracturing ensures that the injected well fluid fully penetrates into the basic fractures formed by the primary fracturing. Relying on the weakly acidic properties of the injected well fluid, it uniformly acidifies and dissolves the easily soluble minerals around the fractures, widening the fractures. At the same time, with the pressure support of graphene oxide, it guides the fractures to extend in an orderly manner and connect with each other, forming a uniform and well-connected fracture network. This ensures efficient synergy between acidizing and fracturing, thereby further improving the acidizing effect of the injected well fluid and enhancing the stability and effectiveness of the hot dry rock mining process.

[0097] In some implementations, the pressure in the annular space is 15 MPa to 25 MPa.

[0098] In the above implementation method, the pressure in the annular space is controlled within the range of 15MPa to 25MPa. This pressure range is suitable for the actual working conditions of hot dry rock reservoirs. It can not only ensure that the fluid can smoothly penetrate into the fracture, but also stably promote the extension and development of fractures, give full play to the acidizing and support enhancement effects of the fluid, further improve the overall quality of reservoir stimulation, and enhance the acidizing effect of the injected well fluid.

[0099] For example, the pressure in the annular space is any value or a range of any two of the following: 15 MPa, 15.5 MPa, 16 MPa, 16.5 MPa, 17 MPa, 17.5 MPa, 18 MPa, 18.5 MPa, 19 MPa, 19.5 MPa, 20 MPa, 20.5 MPa, 21 MPa, 21.5 MPa, 22 MPa, 22.5 MPa, 23 MPa, 23.5 MPa, 24 MPa, 24.5 MPa, 25 MPa.

[0100] In some implementations, the injection flow rate for pressurized injection treatment is 5 m / s. 3 / h~10m 3 / h.

[0101] In the above implementation method, the flow rate of pressurized injection is controlled at 5m. 3 / h~10m 3 Within a range of / h, the injection process can be guaranteed to be stable, the fluid can uniformly fill the annular space and fully contact the reservoir, ensuring sufficient acidizing reaction and uniform fracturing, thereby further improving the acidizing effect of the injected well fluid and improving the stability and effectiveness of the hot dry rock mining process.

[0102] For example, the injection flow rate for pressurized injection treatment is 5m. 3 / h, 5.5 m 3 / h、6 m 3 / h, 6.5 m 3 / h、7 m 3 / h, 7.5 m 3 / h、8 m 3 / h, 8.5 m 3 / h、9 m 3 / h, 9.5 m 3 / h, 10m 3 Any value in / h or a range of any two of them.

[0103] It should be noted that the above injection method specifically includes, but is not limited to, the following steps: pressurizing the prepared weakly acidic graphene oxide nanofluid (i.e., the injection well fluid) through an injection device at a rate of 5m... 3 / h~10m 3The fluid is pumped at an injection rate of / h into the annular space between the completion string and the production string of the hot dry rock injection well. After ensuring that the fluid fills the annulus evenly, it enters the hot dry rock reservoir through the perforated section of the wellbore. The fluid is then injected into the injection well after the fracture network is formed. The weak acidity of the fluid can have a mild chemical reaction with the easily soluble minerals such as feldspar and calcite on the surface of the hot dry rock mass, dissolving some of the surface minerals, reducing the rock mass hardness and the fracturing initiation pressure, making the fracturing process easier to implement. At the same time, it helps to control the direction of fracture extension and promotes the formation of a complex fracture network.

[0104] To further understand the present invention, the technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0105] The present invention will be further described below with reference to specific embodiments. The graphite used is Sinopharm reagent SUP14030U.

[0106] Unless otherwise specified, all reagents involved in the embodiments of this invention are commercially available products and can be obtained through commercial channels.

[0107] Example 1

[0108] This embodiment prepares an injection well fluid, including the following steps:

[0109] S1. Graphite and strong oxidant KMnO4 were mixed (mass ratio of strong oxidant to graphite was 3:1), stirred at 175 r / min for 1.5 h, and heated to 35 °C to obtain a graphite oxide reaction solution. Water was added to the graphite oxide reaction solution until no more bubbles were produced, at which point the reaction was terminated to obtain a solid-liquid mixture. The above solid-liquid mixture was centrifuged at 8000 r / min for 30 min to obtain a solid, which was washed three times with deionized water to obtain graphene oxide. The Dv50 particle size of the graphene oxide was measured using a laser particle size analyzer, and the results are shown in Table 1.

[0110] S2. The dispersant sodium dodecylbenzenesulfonate (SDBS), water, and the prepared graphene oxide were subjected to a secondary mixing treatment (250W ultrasonic treatment for 12.5 min) to obtain the injection well fluid. The pH value of the injection well fluid was measured using a pH meter (Leici PHS-3C), and the results are shown in Table 1. The mass concentration of the dispersant in the injection well fluid was 0.125 mg / mL, and the mass concentration of graphene oxide was 2.6 mg / mL.

[0111] Table 1

[0112]

[0113] Example 2

[0114] It is basically the same as Example 1, except that the mass concentration of graphene oxide in the injected well fluid is 0.2 mg / mL.

[0115] Example 3

[0116] It is basically the same as Example 1, except that the mass concentration of graphene oxide in the injected well fluid is 5 mg / mL.

[0117] Example 4

[0118] It is basically the same as Example 1, except that the mass ratio of strong oxidant to graphite is 2:1.

[0119] Example 5

[0120] It is basically the same as Example 1, except that the mass ratio of strong oxidant to graphite is 4:1.

[0121] Example 6

[0122] It is basically the same as Example 1, except that the mass concentration of the dispersant in the injected well fluid is 0.05 mg / mL.

[0123] Example 7

[0124] It is basically the same as Example 1, except that the mass concentration of the dispersant in the injected well fluid is 2 mg / mL.

[0125] Example 8

[0126] It is basically the same as Example 1, except that the centrifugation speed is 10000 r / min.

[0127] Example 9

[0128] It is basically the same as Example 1, except that the centrifugation speed is 6000 r / min.

[0129] Example 10

[0130] It is basically the same as Example 1, except that the mass concentration of graphene oxide in the injected well fluid is 0.5 mg / mL.

[0131] Example 11

[0132] It is basically the same as Example 1, except that the mass concentration of graphene oxide in the injected well fluid is 1 mg / mL.

[0133] Comparative Example 1

[0134] Sodium dodecylbenzenesulfonate (SDBS) and water were mixed and ultrasonically dispersed (250W, 12.5min) to obtain a mixture. The pH of the mixture was adjusted to 4.5 using sodium hydroxide solution and hydrochloric acid solution to obtain the injection well fluid, in which the mass concentration of SDBS was 0.125mg / ml.

[0135] Test case

[0136] The acidizing effect of the injection well fluid was tested: the test samples were the 0.5 mg / ml injection well fluid prepared in Example 10 and the 1 mg / ml injection well fluid prepared in Example 11; granite H1 and carbonate rock T1 as shown in Table 2 were selected as experimental cores.

[0137] Table 2

[0138]

[0139] The acidizing experiment employed a reactor to simulate the environmental conditions of the injected well fluid operating underground in hot, dry rock. The reactor's maximum operating pressure was 25 MPa, and its maximum operating temperature was 300℃. An electromagnetic stirrer was installed at the top of the reactor to continuously agitate the fluid, ensuring a more uniform temperature distribution and preventing localized temperature deviations from interfering with the experimental results. Nitrogen (N2) was used as the pressurizing medium to deliver N2 into the reactor.

[0140] Experimental procedure:

[0141] 1) Place the experimental core into the reaction vessel and fill the reaction vessel with the injection well fluid sample, so that the experimental core is completely immersed in the injection well fluid sample; introduce nitrogen into the reaction vessel until the pressure inside the reaction vessel is 20MPa, heat the temperature inside the reaction vessel to 200℃, and after the temperature and pressure inside the reaction vessel are balanced, use a white light interferometer to measure the arithmetic mean height Sa and root mean square height Sq of the surface roughness of the experimental core, and record it as the surface roughness of 0 days;

[0142] 2) The experimental conditions inside the reactor were maintained at 20 MPa and 200℃ for 70 days of acidification. During this period, a fish tank pump was used every 7 days to pump cooling water into the cooling pipes of the reactor to lower the reactor temperature to room temperature. After that, the experimental core was removed, and the arithmetic mean height Sa and root mean square height Sq of the surface roughness of the experimental core were measured using a white light interferometer. The results are shown in Table 3.

[0143] After each measurement, the experimental core was placed back into the reactor to restore the experimental conditions of 20 MPa and 200 °C, and the acidification experiment was continued.

[0144] Table 3:

[0145]

[0146] As shown in Tables 1 and 3, the injection well fluids prepared in Examples 10 and 11 of this invention exhibit uniform and precise graphene oxide Dv50 particle size distribution, and the system pH value is stably maintained in the weakly acidic range of 3-6. Under simulated operating conditions, this fluid can effectively improve the surface roughness of the simulated dry hot rock core, fully demonstrating its excellent acidification and dissolution capabilities. It can efficiently dissolve the mineral components inside the reservoir, laying a solid foundation for the development and expansion of fractures in the dry hot rock reservoir and improving the efficiency of geothermal extraction.

[0147] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An injection well fluid, characterized in that, The fluid includes a solvent and graphene oxide, and the pH of the injection well fluid is 3 to 6; the mass concentration of the graphene oxide in the injection well fluid is 0.2 mg / mL to 5 mg / mL.

2. The injection well fluid according to claim 1, characterized in that, The Dv50 particle size of the graphene oxide is 0.5μm~5μm.

3. The injection well fluid according to claim 1 or 2, characterized in that, The injection well fluid also includes a dispersant; Preferably, the mass concentration of the dispersant in the injected well fluid is 0.05 mg / mL to 2 mg / mL.

4. A method for preparing injection well fluid as described in any one of claims 1-3, characterized in that, Includes the following steps: 1) Graphite, a strong oxidant, and water are mixed once, and the solid is separated to obtain the graphene oxide. 2) The solvent and the graphene oxide are mixed a second time to obtain the injection well fluid.

5. The method for preparing injection well fluid according to claim 4, characterized in that, In step 1), the mass ratio of the strong oxidant to graphite is (2~4):1; Preferably, the strong oxidizing agent includes potassium permanganate.

6. The method for preparing injection well fluid according to claim 4, characterized in that, The separation of solids includes centrifugation, wherein the centrifugation speed is 6000 r / min to 10000 r / min.

7. A method for mining hot dry rock, characterized in that, Includes the following steps: a) In a hot dry rock injection well, a completion string is first run in and cemented, and then a production string is coaxially run in inside the completion string, so that an annular space is formed between the completion string and the production string. b) Use water to perform a single hydraulic fracturing treatment on the dry, hot rock to create fractures; c) The injection well fluid as described in any one of claims 1-3 is subjected to secondary fracturing to form a fracturing network.

8. The method for mining hot dry rock according to claim 7, characterized in that, After the formation of the fracture network, the injection well fluid is continuously injected.

9. The method for mining hot dry rock according to claim 7 or 8, characterized in that, The secondary fracturing process includes the following steps: pressurizing and injecting the fluid from the injection well into the annular space to form the fracturing network.

10. The method for mining hot dry rock according to claim 9, characterized in that, The pressure in the annular space is 15MPa~25MPa; And / or, the injection flow rate of the pressurized injection treatment is 5m. 3 / h~10m 3 / h.

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