A method for flexible reservoir formation of hot dry rock geothermal reservoir and application thereof

Abstract

The application discloses a dry hot rock heat reservoir flexible storage forming method and application, and the storage forming method comprises the following steps: (1) reservoir evaluation and fracturing construction parameter optimization; (2) low-displacement injection of low-temperature liquid capable of generating a thermal damage effect on the storage rock mass; (3) variable-displacement cyclic injection of slickwater; (4) multi-slug injection of an alkaline chemical stimulating agent in the process of the variable-displacement cyclic injection of the slickwater in step (3); and (5) intermittent construction of non-uniform liquid injection units. The storage forming method can form a fracture network system with a large heat exchange volume and no dominant main fracture in a high-temperature rock mass through fracturing, improve heat exchange efficiency, greatly reduce construction pressure and the duration of high construction pressure and the risk of inducing earthquakes, and guarantee construction safety, and plays an important technical supporting role for the development and utilization of dry hot rock resources.

Description

Technical Field

[0001] This invention relates to the technical field of hot dry rock fracturing, and more specifically, to a flexible reservoir creation method and application for hot dry rock reservoirs. Background Technology

[0002] Hot dry rock is a type of high-temperature rock mass buried deep underground (3-10 km), with extremely poor permeability, no fluid or only a small amount of fluid, and a temperature exceeding 180°C. The thermal energy it contains can be used for power generation and heating, representing a clean energy source with enormous potential. Hot dry rock is primarily composed of granite, which is extremely hard and has very poor physical properties. Its thermal energy cannot be directly utilized; it must be fracturing, i.e., artificial reservoir creation. This involves forming a massive, interconnected network of fractures within the high-temperature rock mass, then injecting water into these fracture networks to exchange heat and bring the thermal energy to the surface for power generation, heating, and other uses. Previously, hot dry rock fracturing for reservoir creation mainly employed medium to large displacement, large-scale fluid volume, and continuous, uninterrupted fracturing operations using clean water, with a constant displacement of 3-6 m³ / h. 3 / min, construction fluid volume 20000~30000m 3 This high-intensity fracturing method, for hot dry rock masses in high-temperature hard strata, not only involves high construction pressure, small modification volume, long main fractures, and low heat exchange efficiency, but also often causes earthquakes of magnitude 1 to 3, or even 5, during construction, which seriously affects construction safety and the safety of life and property of surrounding residents, leading to the failure or termination of hot dry rock development and utilization projects. It has become a major factor restricting the large-scale commercial development of hot dry rock resources worldwide.

[0003] Chinese Patent Publication No. CN103790564A discloses a laboratory simulation device for high-pressure fracturing and extraction of hot dry rock. The device includes a fracturing fluid injection system, a proppant injection system, a high-pressure gas booster injection system, a fracturing body, an annular pressure application system, and high-pressure pipe valves. The proppant injection system includes indirect proppant injection and solidification; the high-pressure gas booster injection system includes gas boosting and indirect gas injection. This patent is only an experimental simulation device and does not involve reservoir formation processes.

[0004] Chinese Patent Publication No. CN103790580A discloses a laboratory simulation system for in-situ heat exchange during fracturing in hot dry rock. The system includes fracturing fluid injection, a fracturing body, an annular pressure application system, and high-pressure pipe valves. The fracturing body includes a sample fracturing chamber and a sample annular pressure cavity. The fracturing chamber includes a three-dimensional fixed support and a three-dimensional hydraulic system. The three-dimensional hydraulic system includes a hydraulic sliding cavity and a hydraulic movable plug. The sample annular pressure cavity includes an annular pressure cavity steel plate and a rubber inner sleeve, with a cavity between the sleeve and the steel plate. Injected fluid achieves pressure encapsulation. Both fracturing fluid injection and annular pressure application are achieved through high-pressure pipelines and high-pressure control components. This patent pertains to underground heat exchange simulation experimental devices and does not involve reservoir creation processes.

[0005] Chinese Patent Publication No. CN105696996A, entitled "A Method for Constructing an Artificial Geothermal Reservoir in Hot Dry Rock," discloses a technical solution for constructing an artificial geothermal reservoir by using supercritical carbon dioxide fracturing along weak surfaces or interlayers formed by igneous facies to generate a main fracture, followed by high-volume hydraulic fracturing within the main fracture to generate secondary fracturing. The hot dry rock mass undergoes volumetric or cluster fracturing under cyclic fracturing to achieve this process. This patent addresses a method for constructing an artificial geothermal reservoir in hot dry rock, which utilizes supercritical carbon dioxide to create fractures, followed by high-volume hydraulic fracturing to generate secondary fracturing.

[0006] In summary, the above methods involve high construction pressure and risks, poor construction safety, and small-scale thermal storage retrofitting. Therefore, there is a need to develop a safer construction method that can accommodate larger-scale thermal storage retrofitting. Summary of the Invention

[0007] To address the problems in existing technologies, this invention proposes a flexible reservoir creation method and its application for hot dry rock reservoirs. This invention employs an innovative process approach, utilizing the thermal damage effect of low-temperature liquids such as liquid nitrogen on the high-temperature rock mass to create micro-fractures and reduce fracturing pressure. Then, it uses a low-volume, high-frequency, multi-cycle injection method with slickwater to induce fatigue damage, and a slug-type injection of alkaline chemical stimulants to dissolve some quartz minerals and reduce rock strength, thereby lowering construction pressure. Instead of continuous construction, the entire process is divided into several non-uniform injection units, with intermittent construction based on varying construction pressures. This avoids prolonged periods of high construction pressure that could reach the critical stress state for fracture and strike-slip, inducing strong earthquakes. The combination of these methods not only allows for the formation of a fracture network system with a large heat exchange volume and no dominant main fracture in the high-temperature rock mass, improving heat exchange efficiency, but also significantly reduces construction pressure, the duration of high construction pressure, and the risk of earthquakes, ensuring construction safety. This will play a crucial technical supporting role in the development and utilization of hot dry rock resources.

[0008] One objective of this invention is to provide a flexible reservoir creation method for hot dry rock reservoirs, the method comprising the following steps:

[0009] (1) Reservoir evaluation and optimization of fracturing operation parameters;

[0010] (2) Low-volume injection of low-temperature liquids that can produce thermal damage effects on reservoir-forming rock masses;

[0011] (3) Variable displacement circulating injection of slickwater;

[0012] (4) During the process of injecting slickwater in the variable displacement circulation in step (3), alkaline chemical stimulants are injected through the multi-segment plug;

[0013] (5) Intermittent construction of non-uniform injection units.

[0014] Preferably,

[0015] Step (2), the low displacement is 0.5m 3 / min~1.0m 3 / min, total injection volume is 500-1000m³ 3 ; and / or,

[0016] The cryogenic liquid is selected from liquid nitrogen.

[0017] Preferably,

[0018] Step (5),

[0019] Non-uniform injection unit intermittent construction involves dividing the designed amount of fluid to be injected into the formation into multiple injection units with different injection volumes. Each injection unit has a construction time interval and pressure drop.

[0020] More preferably, each injection unit uses variable displacement circulating injection of slickwater, and during the variable displacement circulating injection of slickwater, a mixture of alkaline chemical stimulant and acidic chemical stimulant is injected through multiple plugs;

[0021] In further optimization step (3) or step (5),

[0022] Variable displacement cyclic injection is a cyclic injection method in which the injection cycle is from low displacement to high displacement and then from high displacement to low displacement.

[0023] Preferably,

[0024] Step (3),

[0025] The viscosity of slippery water is 2–3 mPa·s; and / or,

[0026] Step (4),

[0027] The alkaline chemical stimulant is selected from a strong alkaline solution, preferably sodium hydroxide solution; the viscosity is 1–1.1 mPa·s; and / or,

[0028] Step (5),

[0029] The viscosity of slippery water is 3–5 mPa·s; and / or,

[0030] The alkaline chemical stimulant is selected from a strong alkaline solution, preferably from a sodium hydroxide solution; the acidic chemical stimulant is preferably selected from an acidic solution, preferably from a diethylenetriaminepentaacetic acid solution; more preferably, the viscosity of the mixture of the alkaline chemical stimulant and the acidic chemical stimulant is 1 to 1.12 mPa·s; even more preferably, the pH value of the mixture of the alkaline chemical stimulant and the acidic chemical stimulant is 11 to 13.

[0031] In step (5), the purpose of adding diethylenetriaminepentaacetic acid solution is because the alkalinity of the alkaline chemical stimulant is too strong and it causes too much dissolution of the rock skeleton. The acidic chemical stimulant is added to neutralize part of the alkalinity.

[0032] Preferably,

[0033] Step (3),

[0034] Variable displacement circulating injection uses a displacement starting from 0.5m. 3 / min increased to 1.5m 3 / min then reduced to 0.5m 3 / min represents a cyclic injection, with the displacement varying by 0.5m per cycle. 3 / min~1.0m 3 / min;

[0035] More preferably, the slickwater is injected in a pulse, with an interval of 20 to 30 seconds between each change in displacement.

[0036] Further optimization of the variable displacement circulation cycle, the number of cycles is 5 to 8; the total injection volume of slickwater is 15,000 to 20,000 m³. 3 .

[0037] Preferably,

[0038] Step (4),

[0039] Slippery water is injected at a rate of 2000-3000m³. 3 One injection of an alkaline chemical stimulant septum; the number of septum injections is 5 to 10.

[0040] More preferably, the amount of alkaline chemical stimulant injected once via septum is 10–50 mg. 3 ,

[0041] The optimal displacement of the alkaline chemical stimulant is 1.5 m³. 3 / min~2.0m 3 / min.

[0042] Preferably,

[0043] Step (5): Inject slickwater intermittently in three units; preferably, stop the pump after the first unit of injection is completed, and start the second unit of injection after the pressure drops to 50-70% of the construction pressure; stop the pump after the second unit of injection is completed, and start the third unit of injection after the pressure drops to 40-60% of the construction pressure.

[0044] In this invention, when fracturing hot dry rock, the construction pressure can be adjusted according to the properties of the hot dry rock, and the preferred construction pressure is 55-78 MPa.

[0045] The preferred injection volume of the first unit slickwater is 7000–9000 m³. 3 ; and / or,

[0046] The preferred injection volume of the second unit slickwater is 5000–7000 m³. 3 ; and / or,

[0047] The preferred injection volume of the slickwater in the third unit is 3000–4000 m³. 3 .

[0048] Preferably,

[0049] Step (5),

[0050] The first unit of water injection begins at a depth of 0.5m. 3 / min increased to 2.0m 3 / min then reduced to 0.5m 3 / min represents a cyclic injection, with the displacement varying by 0.5m per cycle. 3 / min~1.0m 3 / min; and / or,

[0051] The second unit's slickwater injection method begins with a 0.5m depth. 3 / min increased to 2.5m 3 / min then reduced to 0.5m 3 / min represents a cyclic injection, with the displacement varying by 0.5m per cycle. 3 / min~1.0m 3 / min; and / or,

[0052] The third unit's slickwater injection method starts from 0.5m. 3 / min increased to 5.5m 3 / min then reduced to 0.5m 3 / min represents a cyclic injection, with the displacement varying by 0.5m per cycle. 3 / min~1.0m 3 / min;

[0053] Preferably, the number of cycles for the first unit is 4 to 6; and / or,

[0054] Preferably, the second unit cycles 3 to 5 times; and / or,

[0055] The preferred number of cycles for the third unit is 2 to 4.

[0056] Preferably,

[0057] In step (5), when the first, second, and third units inject slickwater using variable displacement circulation, the slickwater is injected via pulse.

[0058] Preferably, the first unit injects slickwater, with a 40-60 second interval between each change in discharge rate; and / or,

[0059] Preferably, the second unit injects slickwater, with a 60-90 second interval between each change in discharge rate; and / or,

[0060] The preferred method is to inject slickwater in the third unit, with an interval of 90 to 120 seconds between each change in discharge volume.

[0061] Preferably,

[0062] Step (5), during the variable displacement circulation injection of slickwater in the first, second, and third units, every 1500-2000 m³ of water is injected. 3 A mixture of alkaline and acidic chemical stimulants was injected into the plug.

[0063] The preferred first unit has an injection volume of 2000m³ of slickwater. 3 4000m 3 6000m 3 7000~9000m 3 At any point within the slug, a mixture of alkaline and acidic chemical stimulants is injected once; and / or,

[0064] The preferred second unit has an injection volume of 2000m³ of slickwater. 3 4000m 3 5000~7000m 3 At any point within the slug, a mixture of alkaline and acidic chemical stimulants is injected once; and / or,

[0065] The preferred third unit has an injection volume of 2000m³ of slickwater. 3 3000~4000m 3 At any point within the slug, a mixture of alkaline and acidic chemical stimulants is injected once.

[0066] Preferably,

[0067] The displacement during the first slug injection is 1.5–2.0 m³. 3 / min; the preferred injection volume for each slug is 10-20m. 3 ; and / or,

[0068] The displacement during the second unit slug injection is 2.0–2.5 m³.3 / min; the preferred injection volume for each slug is 20-30m³. 3 ; and / or,

[0069] The displacement during the third unit slug injection is 3.0–3.5 m³. 3 / min; the preferred injection volume for each slug is 30-50m³. 3 .

[0070] The second objective of this invention is to provide the application of the flexible reservoir creation method described in the first objective of this invention in the development of rock formation energy, preferably in the development of hot dry rock energy, and more preferably in the development of hot dry rock thermal energy.

[0071] The formation of the fracture network during reservoir formation in this invention mainly occurs through the following processes:

[0072] (1) Injecting cryogenic fluids to form microfractures near the wellbore. At low flow rates, injecting cryogenic fluids such as liquid nitrogen causes thermal damage effects between the injected cryogenic fluid and the high-temperature formation, which in turn forces a large number of microfractures to form near the wellbore.

[0073] (2) High-frequency, multi-cycle injection of slickwater (i.e., variable displacement injection of slickwater) expands microfractures and forms a fracture system. Slickwater is pumped in a cycle with a time interval of 20 to 30 seconds, changing the construction displacement and the displacement from low to high and then from high to low, to expand microfractures in the formation and form a microfracture system.

[0074] (3) During the variable displacement circulation injection of slickwater, alkaline chemical stimulants are injected through multiple slugs. During the process of slickwater expanding the cracks, alkaline chemical stimulants are injected through multiple slugs to dissolve some quartz minerals, reduce rock strength and construction pressure.

[0075] (4) Intermittent construction of non-uniform injection units. The designed amount of liquid to be injected into the formation is divided into multiple injection units, each with a different amount of liquid. After the liquid volume of one unit is completed, the next unit is constructed according to the pressure situation until the required huge fracture volume is formed in the formation.

[0076] As can be seen, this invention utilizes the thermal damage effect of low-volume injection of liquid nitrogen and high-temperature rock mass to generate a large number of microfractures near the well, reducing the fracturing pressure; high-frequency, multi-cycle injection of slickwater and the injection of alkaline chemical stimulants through multiple plugs during the slickwater injection process reduce rock strength and construction pressure, expanding microfractures to form an interconnected microfracture system; the intermittent construction of the non-uniform injection unit significantly reduces the duration of high construction pressure and the risk of induced earthquakes, ensuring construction safety.

[0077] In summary, the flexible modification method of the present invention, which involves injecting liquid nitrogen at small displacement, injecting slickwater at high frequency through circulation, injecting alkaline chemical stimulants through slug injection, and intermittent construction using non-uniform injection units, can effectively ensure the modification volume and construction safety.

[0078] Compared with the prior art, the present invention has at least the following advantages:

[0079] (1) This invention is designed for high-temperature dry hot rock formations with hard rock and extremely poor physical properties. It can form a massive interconnected fracture network system with no dominant main fracture, with a transformation volume of more than 10 million cubic meters, high heat exchange efficiency, large water flow and high temperature.

[0080] (2) This invention can significantly reduce the fracture pressure, construction pressure and duration of high construction pressure in high-temperature dry hot rock formations with hard rock and poor physical properties, thereby reducing the risk of inducing high-intensity earthquakes with an earthquake magnitude of less than 2, ensuring construction safety. Attached Figure Description

[0081] Figure 1 A schematic diagram of the original strata of the hot dry rock reservoir;

[0082] Figure 2 A schematic diagram of microfractures formed by thermal damage effects in hot dry rock reservoirs;

[0083] Figure 3 A schematic diagram of a fracture network without dominant master fractures formed by flexible reservoir creation in hot dry rock reservoirs. Detailed Implementation

[0084] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0085] All raw materials used in this invention can be purchased directly from existing technologies or prepared directly using existing technologies.

[0086] Example 1

[0087] A dry hot rock vertical well, with a reservoir stimulation depth of 3500 meters, was stimulated using the flexible fracturing method proposed in this invention. The process is as follows:

[0088] (1) Material preparation, reservoir evaluation and optimization of fracturing construction parameters;

[0089] Based on the use of fracture propagation simulation software such as FracMan or Meyer, the open-hole fracturing parameters of granite vertical wells are determined through simulation optimization using conventional procedures.

[0090] Prepare liquid nitrogen, alkaline chemical stimulants, acidic chemical stimulants, slickwater, fracturing truck assembly, surface manifold, liquid tanks, and process flow according to the fracturing design requirements of a certain hot dry rock well; a schematic diagram of the original formation of the hot dry rock reservoir is shown below. Figure 1 As shown;

[0091] (2) Low-flow-rate liquid nitrogen injection: using a flow rate of 0.5m 3 Injecting liquid nitrogen at a rate of / min to 500m³ 3 Numerous microfractures are generated near the wellbore, and their structure is illustrated as follows: Figure 2 As shown;

[0092] (3) Variable displacement circulating injection of slickwater: The viscosity of the slickwater is 3 mPa·s; the variable displacement circulating injection uses a displacement starting from 0.5 m... 3 / min increased to 1.5m 3 / min then reduced to 0.5m 3 / min represents a cyclic injection, with the displacement changing by 0.5m each time. 3 / min; slickwater is injected via pulses, with a 30-second interval between each change in flow rate; the cycle count is 8 times; the total injection volume of slickwater is 20000m³. 3 .

[0093] (4) During the variable displacement circulating injection of slickwater, an alkaline chemical stimulant is injected via a multi-stage plug: the alkaline chemical stimulant is selected from sodium hydroxide solution; the viscosity is 1.1 mPa·s; the injection rate is 2000 m³ / s. 3 One injection of alkaline chemical stimulant into the slug; the number of slug injections should be 10; the amount of alkaline chemical stimulant injected in each slug injection should be 10 mg. 3 The emission rate of the alkaline chemical stimulant is 1.5m³. 3 / min.

[0094] (5) Intermittent construction of non-uniform injection units: The designed remaining liquid volume is divided into three units for intermittent injection of slickwater; after the first unit injection is completed, the pump is stopped, and the second unit injection is carried out after the pressure drops to 70% of the construction pressure of 60MPa; after the second unit injection is completed, the pump is stopped, and the third unit injection is carried out after the pressure drops to 60% of the construction pressure of 60MPa; the injection volume of slickwater in the first unit is 9000m³. 3 The injection volume of the second unit's slickwater is 7000m³. 3 The injection volume of the slickwater in the third unit is 4000m³. 3 .

[0095] The first unit of water injection begins at a depth of 0.5m. 3 / min increased to 2.0m 3 / min then reduced to 0.5m3 / min represents a cyclic injection, with each injection cycle involving a displacement change of 1.0m. 3 / min; The first unit has 6 iterations;

[0096] The second unit's slickwater injection method begins with a 0.5m depth. 3 / min increased to 2.5m 3 / min then reduced to 0.5m 3 / min represents a cyclic injection, with each injection cycle involving a displacement change of 1.0m. 3 / min; the second unit has 5 iterations;

[0097] The third unit's slickwater injection method starts from 0.5m. 3 / min increased to 5.5m 3 / min then reduced to 0.5m 3 / min represents a cyclic injection, with each injection cycle involving a displacement change of 1.0m. 3 / min; the third unit has 4 iterations.

[0098] When injecting slickwater in the first, second, and third units with variable displacement, the slickwater is injected via pulses. In the first unit, there is a 60-second interval between each displacement change; in the second unit, there is a 90-second interval; and in the third unit, there is a 120-second interval.

[0099] The first unit achieved an injection volume of 2000m³ of slickwater. 3 4000m 3 6000m 3 9000m 3 At each of these four injection points, a mixture of alkaline and acidic chemical stimulants was injected via slug injection; the displacement during the first slug injection was 1.5 m³. 3 / min; the injection volume of each slug is 10m. 3 ;

[0100] The second unit achieved a liquid injection volume of 2000m³ in the slickwater. 3 4000m 3 7000m 3 During the injection at these three points, a mixture of alkaline and acidic chemical stimulants was injected into each slug injection; the displacement during the second slug injection was 2.0 m³. 3 / min; the injection volume of each slug is 20m. 3 ;

[0101] The third unit achieved an injection volume of 2000m³ of slickwater. 3 4000m 3 During the injection of the first two units, a mixture of alkaline and acidic chemical stimulants was injected into each unit via slug injection; the displacement during the third unit slug injection was 3.0 m³. 3 / min; the injection volume of each slug is 30m. 3 .

[0102] The mixture of the alkaline chemical stimulant sodium hydroxide solution and the acidic chemical stimulant diethylenetriaminepentaacetic acid solution injected into Unit 1, Unit 2, and Unit 3 has a pH of 8 and a viscosity of 1 mPa·s.

[0103] The aforementioned flexible reservoir formation method can create a massive, interconnected fracture network system without dominant primary fractures, as illustrated in the diagram below. Figure 3 As shown, the renovation volume is 14 million cubic meters, with high heat exchange efficiency, a water output flow rate of 26 l / s and a temperature of 124℃, and no earthquakes of magnitude 2 or above were caused during the construction process.

[0104] Example 2

[0105] A dry hot rock vertical well, with a reservoir stimulation depth of 4000 meters, was stimulated using the flexible fracturing method proposed in this invention. The schematic process is as follows:

[0106] (1) Material preparation, reservoir evaluation and optimization of fracturing construction parameters;

[0107] Based on the use of fracture propagation simulation software such as FracMan or Meyer, the open-hole fracturing parameters of granite vertical wells are determined through simulation optimization using conventional procedures.

[0108] Prepare liquid nitrogen, alkaline chemical stimulants, acidic chemical stimulants, slickwater, fracturing truck sets, surface manifolds, liquid tanks, processes, etc., according to the fracturing design requirements of a certain dry hot rock well;

[0109] (2) Low-flow-rate liquid nitrogen injection: using a flow rate of 1.0 m³ / h 3 Injecting 1000m³ of liquid nitrogen at a displacement of / min 3 This generates a large number of microfractures near the wellbore;

[0110] (3) Variable displacement circulating injection of slickwater: The viscosity of the slickwater is 2 mPa·s; the variable displacement circulating injection uses a displacement starting from 0.5 m... 3 / min increased to 1.5m 3 / min then reduced to 0.5m 3 / min represents a cyclic injection, with each injection cycle involving a displacement change of 1.0m. 3 / min; slickwater is injected via pulses, with a 20-second interval between each change in flow rate; the cycle count is 5 times; the total injected slickwater volume is 15000m³. 3 .

[0111] (4) During the variable displacement circulating injection of slickwater, an alkaline chemical stimulant is injected via a multi-stage plug: the alkaline chemical stimulant is selected from sodium hydroxide solution; the viscosity is 1 mPa·s; and the injection rate is 3000 m³ / s. 3 One injection of alkaline chemical stimulant into the slug; the number of slug injections should be 5; the amount of alkaline chemical stimulant injected in each slug injection should be 50 mg. 3 The emission rate of the alkaline chemical stimulant is 2.0 m³. 3 / min.

[0112] (5) Intermittent construction of non-uniform injection units: The designed remaining liquid volume is divided into three units for intermittent injection of slickwater; after the first unit injection is completed, the pump is stopped, and the second unit injection is carried out after the pressure drops to 50% of the construction pressure of 67MPa; after the second unit injection is completed, the pump is stopped, and the third unit injection is carried out after the pressure drops to 40% of the construction pressure; the injection volume of slickwater in the first unit is 7000m³. 3 The injection volume of the second unit's slickwater is 5000m³. 3 The injection volume of the slickwater in the third unit is 3000m³. 3 .

[0113] The first unit of water injection begins at a depth of 0.5m. 3 / min increased to 2.0m 3 / min then reduced to 0.5m 3 / min represents a cyclic injection, with the displacement changing by 0.5m each time. 3 / min; The first unit has 4 iterations;

[0114] The second unit's slickwater injection method begins with a 0.5m depth. 3 / min increased to 2.5m 3 / min then reduced to 0.5m 3 / min represents a cyclic injection, with the displacement changing by 0.5m each time. 3 / min; the second unit has 3 iterations;

[0115] The third unit's slickwater injection method starts from 0.5m. 3 / min increased to 5.5m 3 / min then reduced to 0.5m 3 / min represents a cyclic injection, with the displacement changing by 0.5m each time. 3 / min; the third unit has 2 iterations.

[0116] When injecting slickwater in the first, second, and third units with variable displacement, the slickwater is injected via pulses. In the first unit, there is a 40-second interval between each displacement change; in the second unit, there is a 60-second interval; and in the third unit, there is a 90-second interval.

[0117] The first unit achieved an injection volume of 2000m³ of slickwater. 3 4000m 3 6000m 3 7000m 3 At each of these four injection points, a mixture of alkaline and acidic chemical stimulants was injected via slug injection; the displacement during the first slug injection was 2.0 m³. 3 / min; the injection volume of each slug is 20m. 3 ;

[0118] The second unit achieved a liquid injection volume of 2000m³ in the slickwater. 3 4000m 3 5000m 3 At each of these three injection points, a mixture of alkaline and acidic chemical stimulants was injected via slug injection; the displacement during the second slug injection was 2.5 m³. 3 / min; the injection volume of each slug is 30m. 3 ;

[0119] The third unit achieved an injection volume of 2000m³ of slickwater. 3 4000m 3 During the injection of the first two units, a mixture of alkaline and acidic chemical stimulants was injected into each unit via slug injection; the displacement during the third unit slug injection was 3.5 m³. 3 / min; the injection volume of each slug is 50m. 3 .

[0120] The mixture of alkaline chemical stimulant sodium hydroxide solution and acidic chemical stimulant diethylenetriaminepentaacetic acid solution injected into Unit 1, Unit 2, and Unit 3 has a pH of 10 and a viscosity of 1.12 mPa·s.

[0121] The aforementioned flexible reservoir construction method can form a massive interconnected fracture network system without dominant main fractures, with a modified volume of 12.6 million cubic meters. It has high heat exchange efficiency, a produced water flow rate of 211 / s, and a temperature of 115℃. No earthquakes of magnitude 2 or above were triggered during the construction process.

[0122] Example 3

[0123] A dry hot rock vertical well, with a reservoir stimulation depth of 4460 meters, was stimulated using the flexible fracturing method proposed in this invention. The process is as follows:

[0124] (1) Material preparation, reservoir evaluation and optimization of fracturing construction parameters;

[0125] Using fracture propagation simulation software such as FracMan or Meyer, the open-hole fracturing parameters for carbonate rock vertical wells are determined through simulation optimization based on conventional procedures.

[0126] Prepare liquid nitrogen, alkaline chemical stimulants, acidic chemical stimulants, slickwater, fracturing truck sets, surface manifolds, liquid tanks, processes, etc., according to the fracturing design requirements of a certain dry hot rock well;

[0127] (2) Low-flow-rate liquid nitrogen injection: using a flow rate of 0.7 m³ / h 3 Injecting liquid nitrogen at a rate of / min to 800m³ 3 This generates a large number of microfractures near the wellbore;

[0128] (3) Variable displacement circulating injection of slickwater: The viscosity of the slickwater is 2.5 mPa·s; the variable displacement circulating injection uses a displacement starting from 0.5 m... 3 / min increased to 1.5m 3 / min then reduced to 0.5m 3 / min represents a cyclic injection, with the displacement changing by 0.5m each time. 3 / min; slickwater is injected via pulse, with a 25-second interval between each change in discharge rate, and the cycle is repeated 6 times; the total injection volume of slickwater is 17500m³. 3 .

[0129] (4) During the variable displacement circulating injection of slickwater, an alkaline chemical stimulant is injected via a multi-stage plug: the alkaline chemical stimulant is selected from sodium hydroxide solution; the viscosity is 1.1 mPa·s; the slickwater is injected at a rate of 2500 m³ / s. 3 One injection of alkaline chemical stimulant into the slug; the number of slug injections should be 7; the amount of alkaline chemical stimulant injected in each slug injection should be 40 mg. 3 The emission rate of the alkaline chemical stimulant is 1.6 m³. 3 / min.

[0130] (5) Intermittent construction of non-uniform injection units: The designed remaining liquid volume is divided into three units for intermittent injection of slickwater; after the first unit of injection is completed, the pump is stopped, and the second unit of injection is carried out after the pressure drops to 60% of the construction pressure of 76MPa; after the second unit of injection is completed, the pump is stopped, and the third unit of injection is carried out after the pressure drops to 50% of the construction pressure; the injection volume of slickwater in the first unit is 8000m³. 3 The injection volume of the second unit's slickwater is 6000m³. 3 The injection volume of the slickwater in the third unit is 3500m³. 3 .

[0131] The first unit of water injection begins at a depth of 0.5m. 3 / min increased to 2.0m 3 / min then reduced to 0.5m 3 / min represents a cyclic injection, with the displacement changing by 0.5m each time. 3 / min; The first unit has 5 iterations;

[0132] The second unit's slickwater injection method begins with a 0.5m depth. 3 / min increased to 2.5m 3 / min then reduced to 0.5m 3 / min represents a cyclic injection, with the displacement changing by 0.5m each time. 3 / min; the second unit has 4 iterations;

[0133] The third unit's slickwater injection method starts from 0.5m. 3 / min increased to 5.5m 3 / min then reduced to 0.5m 3 / min represents a cyclic injection, with the displacement changing by 0.5m each time. 3 / min; the third unit has 3 iterations.

[0134] When injecting slickwater in the first, second, and third units with variable displacement, the slickwater is injected via pulses. In the first unit, there is a 50-second interval between each displacement change; in the second unit, there is a 70-second interval; and in the third unit, there is a 100-second interval.

[0135] The first unit achieved an injection volume of 2000m³ of slickwater. 3 4000m 3 6000m 3 8000m 3At each of these four injection points, a mixture of alkaline and acidic chemical stimulants was injected via slug injection; the displacement during the first slug injection was 1.6 m³. 3 / min; the injection volume of each slug is 15m. 3 ;

[0136] The second unit achieved a liquid injection volume of 2000m³ in the slickwater. 3 4000m 3 6000m 3 At each of the three injection points, a mixture of alkaline and acidic chemical stimulants was injected via slug injection; the displacement during the second slug injection was 2.3 m³. 3 / min; the injection volume of each slug is 25m. 3 ;

[0137] The third unit achieved an injection volume of 2000m³ of slickwater. 3 3500m 3 During the injection of the first two units, a mixture of alkaline and acidic chemical stimulants was injected into each unit via slug injection; the displacement during the third unit slug injection was 3.2 m³. 3 / min; the injection volume of each slug is 35m. 3 .

[0138] The mixture of the alkaline chemical stimulant sodium hydroxide solution and the acidic chemical stimulant diethylenetriaminepentaacetic acid solution injected into Units 1, 2, and 3 has a pH of 9 and a viscosity of 1.1 mPa·s.

[0139] The above-mentioned flexible reservoir construction method can form a massive interconnected fracture network system without dominant main fractures, with a modified volume of 12.1 million cubic meters. It has high heat exchange efficiency, with a produced water flow rate of 19 l / s and a temperature of 117℃. No earthquakes of magnitude 2 or above were triggered during the construction process.

[0140] Comparative Example 1

[0141] A dry hot rock vertical well, with a reservoir stimulation depth of 3500 meters and a distance of 500 meters from Example 1, was subjected to conventional fracturing methods. The process is as follows:

[0142] (1) Material preparation, reservoir evaluation and optimization of fracturing construction parameters;

[0143] Based on the use of fracture propagation simulation software such as FracMan or Meyer, the open-hole fracturing parameters of granite vertical wells are determined through simulation optimization using conventional procedures.

[0144] Prepare the clean water, fracturing truck set, surface manifold, liquid tank, process flow, etc. according to the fracturing design requirements of hot dry rock wells;

[0145] (2) Inject clean water at a constant flow rate: Use a flow rate of 3.0 m³ / h 3 Continuous injection of clean water 20000m³ / min 3 Construction pressure 75-78 MPa;

[0146] (3) Crack monitoring showed that a main northeast-trending crack was formed, with a modification volume of 8.5 million cubic meters. Seven earthquakes of magnitude 2-3 occurred during the construction process. The post-pressure produced water flow rate was 12 l / s and the temperature was 91℃.

Claims

1. A flexible reservoir creation method for dry hot rock reservoirs, the reservoir creation method comprising the following steps: (1) Reservoir evaluation and optimization of fracturing operation parameters; (2) Low-volume injection of low-temperature liquids that can produce thermal damage effects on reservoir-forming rock masses; (3) Variable displacement circulating injection of slickwater; (4) During the process of injecting slickwater in the variable displacement circulation in step (3), an alkaline chemical stimulant is injected through the multi-stage plug; (5) Intermittent construction of non-uniform injection units; Intermittent construction of non-uniform injection units is to divide the designed amount of liquid to be injected into the formation into multiple injection units with different injection volumes. There is a construction time interval and pressure drop between each injection unit. Each injection unit uses variable displacement circulation to inject slickwater, and during the variable displacement circulation injection of slickwater, a mixture of alkaline chemical stimulant and acidic chemical stimulant is injected through multiple plugs. In step (3) or step (5), Variable displacement cyclic injection is a cyclic injection method in which the injection cycle is from low displacement to high displacement and then from high displacement to low displacement.

2. The flexible reservoir creation method for dry hot rock reservoirs as described in claim 1, characterized in that: Step (2), the low discharge rate is 0.5 m³ / min to 1.0 m³ / min, and the total injected liquid volume is 500 to 1000 m³ / min. 3 ; and / or, The cryogenic liquid is selected from liquid nitrogen.

3. The flexible reservoir creation method for dry hot rock reservoirs as described in claim 1, characterized in that: Step (3), The viscosity of slippery water is 2–3 mPa·s; and / or, Step (4), The alkaline chemical stimulant is selected from a strong alkaline solution; with a viscosity of 1–1.1 mPa·s; and / or, Step (5), The viscosity of slippery water is 3–5 mPa·s; and / or, Alkaline chemical stimulants are selected from strong alkaline solutions; acidic chemical stimulants are selected from acidic solutions.

4. The flexible reservoir creation method for dry hot rock reservoirs as described in claim 3, characterized in that: Step (4), The alkaline chemical stimulant is selected from sodium hydroxide solution; and / or, Step (5), The alkaline chemical stimulant is selected from sodium hydroxide solution; the acidic chemical stimulant is selected from diethylenetriaminepentaacetic acid solution.

5. The flexible reservoir creation method for dry hot rock reservoirs as described in claim 4, characterized in that: The viscosity of the mixture of alkaline and acidic chemical stimulants is 1–1.12 mPa·s.

6. The flexible reservoir creation method for dry hot rock reservoirs as described in claim 5, characterized in that: The pH value of the mixture of alkaline and acidic chemical stimulants is 11–13.

7. The flexible reservoir creation method for dry hot rock reservoirs as described in claim 1, characterized in that: Step (3), variable displacement circulation injection is adopted, starting with a displacement of 0.5m 3 / min increased to 1.5m 3 / min then reduced to 0.5m 3 / min represents a cyclic injection, with each injection volume varying by 0.5 m³. 3 / min~1.0 m 3 / min.

8. The flexible reservoir creation method for dry hot rock reservoirs as described in claim 7, characterized in that: Step (3) involves injecting slickwater via pulses, with a 20-30 second interval between each change in discharge rate.

9. The flexible reservoir creation method for dry hot rock reservoirs as described in claim 8, characterized in that: Step (3), the number of cycles is 5 to 8; the total volume of slickwater injected is 15,000 to 20,000 m³. 3 .

10. The flexible reservoir creation method for dry hot rock reservoirs as described in claim 7, characterized in that: Step (4), Slippery water is injected at a rate of 2000-3000m³. 3 One injection of an alkaline chemical stimulant septum is performed; the septum is repeated 5 to 10 times.

11. The flexible reservoir creation method for dry hot rock reservoirs as described in claim 10, characterized in that: The amount of alkaline chemical stimulant injected once via slug injection is 10–50 mg. 3 .

12. The flexible reservoir creation method for dry hot rock reservoirs as described in claim 11, characterized in that: The emission rate of the alkaline chemical stimulant is 1.5 m³. 3 / min~2.0m 3 / min.

13. The flexible reservoir creation method for dry hot rock reservoirs as described in claim 1, characterized in that: Step (5), The process is carried out intermittently in three units. After the first unit of injection is completed, the pump is stopped and the second unit of injection is carried out after the pressure drops to 50-70% of the construction pressure. After the second unit of injection is completed, the pump is stopped and the third unit of injection is carried out after the pressure drops to 40-60% of the construction pressure.

14. The flexible reservoir creation method for dry hot rock reservoirs as described in claim 13, characterized in that: Step (5), The injection volume of the first unit's slickwater is 7000-9000 m³. 3 ; and / or, The injection volume of the second unit's slickwater is 5000-7000m³. 3 ; and / or, The injection volume of the third unit's slickwater is 3000-4000m³. 3 .

15. The flexible reservoir creation method for dry hot rock reservoirs as described in claim 13, characterized in that: Step (5), The first unit of water injection begins at a depth of 0.5 m. 3 / min increased to 2.0 m 3 / min then reduced to 0.5m 3 / min represents a cyclic injection, with each injection volume varying by 0.5 m³. 3 / min~1.0 m 3 / min; and / or, The second unit's slickwater injection method begins with a 0.5 m... 3 / min increased to 2.5 m 3 / min then reduced to 0.5m 3 / min represents a cyclic injection, with each injection volume varying by 0.5 m³. 3 / min~1.0 m 3 / min; and / or, The third unit's slickwater injection method begins with a 0.5 m depth. 3 / min increased to 5.5 m 3 / min then reduced to 0.5m 3 / min represents a cyclic injection, with each injection volume varying by 0.5 m³. 3 / min~1.0 m 3 / min.

16. The flexible reservoir creation method for dry hot rock reservoirs as described in claim 15, characterized in that: The first unit repeats 4 to 6 times; and / or, The second unit repeats 3 to 5 times; and / or, The third unit repeats 2 to 4 times.

17. The flexible reservoir creation method for dry hot rock reservoirs as described in claim 16, characterized in that: Step (5), When the first, second, and third units inject slickwater in a variable displacement cycle, the slickwater is injected via pulse.

18. The flexible reservoir creation method for dry hot rock reservoirs as described in claim 17, characterized in that: The first unit injects slickwater, with a 40-60 second interval between each change in displacement; and / or, The second unit injects slickwater, with a 60-90 second interval between each change in displacement; and / or, The third unit injects slick water, and each time the displacement changes, there is an interval of 90 to 120 seconds between the previous displacement and the next displacement.

19. The flexible reservoir creation method for dry hot rock reservoirs as described in claim 17, characterized in that: Step (5), during the variable displacement circulation injection of slickwater in the first, second, and third units, every 1500-2000 m³ of water is injected. 3 A slug containing a mixture of alkaline and acidic chemical stimulants was injected.

20. The flexible reservoir creation method for dry hot rock reservoirs as described in claim 19, characterized in that: The first unit achieved an injection volume of 2000m³ of slickwater. 3 4000m 3 6000m 3 7000~9000m 3 At any point within the slug, a mixture of alkaline and acidic chemical stimulants is injected once; and / or, The second unit achieved a liquid injection volume of 2000m³ in the slickwater. 3 4000m 3 5000~7000m 3 At any point within the slug, a mixture of alkaline and acidic chemical stimulants is injected once; and / or, The third unit achieved an injection volume of 2000m³ of slickwater. 3 3000~4000m 3 At any point within the slug, a mixture of alkaline and acidic chemical stimulants is injected once.

21. The flexible reservoir creation method for dry hot rock reservoirs as described in claim 19, characterized in that: The displacement during the injection of the first slug is 1.5–2.0 m³. 3 / min and / or, The displacement during the second unit slug injection is 2.0–2.5 m³. 3 / min; and / or, The displacement during the third unit slug injection is 3.0–3.5 m³. 3 / min.

22. The flexible reservoir creation method for dry hot rock reservoirs as described in claim 20, characterized in that: During the first slug injection, the injection volume of each slug is 10-20m³. 3 ; and / or, During the second slug injection, the injection volume of each slug is 20-30m³. 3 ; and / or, During the third slug injection, the injection volume of each slug is 30-50m³. 3 .

23. The application of a flexible reservoir-building method as described in any one of claims 1 to 22 in rock formation energy development.

24. The application as described in claim 23, characterized in that: The application of the flexible reservoir creation method in the development of hot dry rock energy.

25. The application as described in claim 24, characterized in that: The flexible reservoir creation method described above is applied in the development of hot dry rock thermal energy.

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