Proppant heat-conducting property evaluation device and method for closed circulating heat collection

Abstract

The invention provides a device and a method for evaluating the heat-conducting property of a propping agent for closed circulation heat collection, and the device comprises a heat-conducting property evaluation chamber, a fractured rock mass, a fracturing fluid and propping agent inlet, a fracturing fluid and propping agent outlet, a heating sheet and a stress loading device, the fractured rock mass is located in the heat-conducting property evaluation chamber, and the fracturing fluid and propping agent inlet is located in the fracturing fluid and propping agent outlet; the plurality of fracturing fluid and proppant inlets and the plurality of fracturing fluid and proppant outlets are correspondingly connected with cracks in the crack-containing rock mass, and the heating sheet is located on one side, where the crack-containing rock mass is placed, in the heat-conducting property evaluation chamber and provides a heat source for testing the heat-conducting property after the proppant is laid. And the stress loading device is positioned in the heat-conducting property evaluation chamber in the direction vertical to the crack surface, and is used for providing closing stress for crack closing. According to the method, the migration rule of the heat-conducting proppant in the crack and the influence rule of each influence factor on the improvement of the heat-conducting property of the rock mass after the heat-conducting proppant is filled are mastered, and the optimal reservoir fracturing transformation scheme of the closed circulation geothermal system is provided.

Description

Technical Field

[0001] The invention relates to the technical field of closed-cycle heat extraction, and in particular to a device and method for evaluating thermal conductivity of a proppant used for closed-cycle heat extraction. Background Art

[0002] In view of a series of problems such as fluid leakage and pipeline corrosion in open-cycle geothermal systems, closed-cycle geothermal systems are increasingly receiving attention from oil and gas development companies. Utilizing existing abandoned or low-yield wells and high-temperature abandoned oil and gas reservoirs to extract geothermal energy and provide heating for surrounding workstations and residential areas can effectively realize the effective utilization of abandoned oil and gas well resources in oil fields.

[0003] In the existing closed-loop heat extraction applications (including single-well coaxial heat extraction, U-shaped well heat extraction, and gravity heat pipe heat extraction), there is a problem of rapid temperature decay of the output fluid. Existing field experimental results show that when single-well coaxial heat exchange is used, the initial output fluid temperature is 49°C, and the output fluid temperature drops below 40°C after 20 days of heat extraction. The problem of rapid temperature decay of the output fluid also occurred in the U-shaped well field experiment. For gravity heat pipe heat extraction, due to its higher heat extraction efficiency, the temperature decay will be more serious. Analysis of the reasons shows that after a period of development, the reservoir temperature field is difficult to recover after the heat around the wellbore is extracted. Therefore, a method is proposed to improve the heat transfer effect from the reservoir to the wellbore by transforming the reservoir in the heat extraction section of the wellbore and filling the fracturing fracture with thermal conductive proppant.

[0004] In the Chinese patent application with application number: CN201611064653.1, a simulation experimental device for an enhanced geothermal system and a method for testing the heat extraction rate of the reservoir of the enhanced geothermal system using the same are involved. The simulation experimental device includes: a heat exchange chamber, the heat exchange chamber forms a closed chamber; one side of the heat exchange chamber has an inlet connected to the chamber, and the other side of the heat exchange chamber is located at the outlet connected to the chamber; a rock sample group, the rock sample group is composed of nxnx2 rock blocks, the nxnx2 rock blocks are arranged in an nxnx2 arrangement and placed in the chamber; the rock blocks are cube structures with a side length of 295mm-300mm; proppant; waterproof sealing plug; electric heating plate; liquid collecting tank. This invention solves the technical problem of how to test the heat extraction efficiency and stable production time of the enhanced geothermal system under different reservoir transformation methods. The invention focuses on providing a method for enhancing the heat extraction rate of geothermal systems. The invention does not take into account the migration process of the proppant within the fracture during the fracturing process, and also ignores the impact of geostress on fracture closure and the distribution morphology of the proppant within the fracture.

[0005] In the Chinese patent application with application number: CN202310192650.X, a visualization experimental device and experimental method for proppant migration and diversion are involved, which relates to the technical field of rock formation proppant experimental equipment and methods, including: a containing mechanism for containing a rock sample, the rock sample having multiple pores; a pressurizing mechanism connected to the containing mechanism for applying pressure to the rock sample and the pores; a heating mechanism connected to the containing mechanism for increasing the temperature of the rock sample; a fluid injection mechanism connected to the containing mechanism for injecting fluid into the pores; a proppant injection mechanism connected to the containing mechanism for injecting proppant into the pores; a data acquisition mechanism for acquiring movement information of the proppant and the fluid in the pores. The visualization experimental device and experimental method for proppant migration and diversion provided by the invention can simulate the proppant migration and diversion effects under real formations, and can provide visualization data. Although the rock samples can be subjected to temperature loading in this experiment, the entire chamber is loaded according to the temperature conditions of the rock test environment (the patent of this invention focuses on analyzing the relationship between the fracturing proppant laying process and its rules and the thermal conductivity of the rock after the proppant is laid).

[0006] In the Chinese patent application with application number: CN202111282078.3, a shale oil fracturing and extraction device and method are involved, which belongs to the field of petroleum engineering. The device includes: an electrically conductive and heat-conductive layer, which is arranged in the fracture area formed during the fracturing process; a heating device, which is arranged in the heating well; two electrodes, which are respectively arranged in the production well and the heating well, and the two electrodes are connected by an electrode cable. The innovation of this invention is that the heating of the electrode and the heating device and the conductive self-heating of the reservoir proppant work simultaneously, so as to achieve simultaneous heating of the formation and the fracturing fractures. The formation heating temperature is increased from 15°C to 30°C per month. It takes 8 to 10 months to heat the temperature to 250-300°C, and the heating efficiency is increased by about 2 times; the oil production of a single well is increased from 3.2 to 8.0m 3 / d increased to 15~20.0m 3 / d, the production increased by 3 to 5 times. The invention provides a method for improving the development effect of shale oil by adding conductive and thermal proppants to the fractures, but the patent ignores the study of the quantitative relationship between the injection fracture morphology and the improvement of thermal conductivity.

[0007] However, the optimization of thermal conductive proppants, the migration and placement of thermal conductive proppants in fracturing cracks, the type of thermal conductive proppants, the concentration of thermal conductive proppants, the crack closure pressure, etc., are not clear, and there is no relevant research at home and abroad. Therefore, it is necessary to explore the migration law of thermal conductive proppants in fractures and the influence of thermal conductive proppants on the thermal conductivity of rock mass after filling in the reservoir transformation process of closed-loop geothermal system, and then propose the best closed-loop geothermal system reservoir fracturing transformation plan. To this end, we invented a new proppant thermal conductivity evaluation device and method for closed-loop heat recovery. Summary of the invention

[0008] The purpose of the present invention is to provide a device and method for evaluating the thermal conductivity of a proppant for closed-cycle heat recovery, which provides technical support for the feasibility and production capacity prediction of a closed-cycle geothermal system based on filling thermal conductive materials in fractures after reservoir transformation.

[0009] The object of the present invention can be achieved through the following technical measures: a proppant thermal conductivity evaluation device for closed-cycle heat recovery, the proppant thermal conductivity evaluation device for closed-cycle heat recovery comprising a thermal conductivity evaluation chamber, a rock mass containing fractures, a fracturing fluid and proppant inlet, a fracturing fluid and proppant outlet, a heating plate and a stress loading device, the rock mass containing fractures is located in the thermal conductivity evaluation chamber, the fracturing fluid and proppant inlet and the fracturing fluid and proppant outlet are both provided with a plurality of proppant inlets and a plurality of proppant outlets, which are connected correspondingly to the fractures in the rock mass containing fractures, the heating plate is located on one side of the thermal conductivity evaluation chamber where the rock mass containing fractures is placed, and provides a heat source for thermal conductivity testing after proppant laying, and the stress loading device is located in the thermal conductivity evaluation chamber in a direction perpendicular to the fracture surface, and provides closing stress for fracture closure.

[0010] The purpose of the present invention can also be achieved by the following technical measures:

[0011] The proppant thermal conductivity evaluation device for closed-cycle heat recovery also includes a thermal conductivity evaluation chamber shell, which is located at the outer layer of the thermal conductivity evaluation chamber.

[0012] The heating plates are multiple and are fixed on the wall surface of the thermal conductivity evaluation chamber by screw threads.

[0013] The proppant thermal conductivity evaluation device for closed-cycle heat recovery also includes a plurality of temperature sensors, which are arranged through openings on the surface opposite to the heating plate. The connecting wires of the temperature sensors pass through the wall of the thermal conductivity evaluation chamber and are fastened and sealed by threaded sealing rings.

[0014] The proppant thermal conductivity evaluation device for closed-cycle heat recovery also includes a thermal insulation layer, which is located around the fractured rock mass to isolate the fractured rock mass from heat exchange with the outside world.

[0015] The stress loading device is implemented by a hydraulic sealing rubber sleeve, which has a pressing effect on the heat conductive material filled in the crack.

[0016] The proppant is injected into the fractures of the fractured rock mass through the fracturing fluid and proppant inlet and the fracturing fluid and proppant outlet, and the proppant settles and accumulates in the fractures.

[0017] The object of the present invention can also be achieved by the following technical measures: a method for evaluating the thermal conductivity of a proppant for closed-cycle heat recovery, the method for evaluating the thermal conductivity of a proppant for closed-cycle heat recovery adopts a device for evaluating the thermal conductivity of a proppant for closed-cycle heat recovery, comprising:

[0018] Step 1, preparing a rock mass containing fractures;

[0019] Step 2, placing the fractured rock mass into a thermal conductivity evaluation chamber;

[0020] Step 3: determining the fracture closure pressure according to the simulated geostress conditions of the thermal reservoir, and applying geostress to the fractured rock mass through a stress loading device;

[0021] Step 4: prepare the fracturing fluid and thermal conductive proppant required for the experiment;

[0022] Step 5, injecting a thermal conductive proppant into the fractured rock mass through the fracturing fluid and proppant injection port;

[0023] Step 6, turn on the heating plate to monitor the temperature change of the wall surface of the fractured rock mass;

[0024] Step 7: Turn off the heating plate and record the laying status of the thermal conductive proppant in the cracks of the fractured rock mass.

[0025] The purpose of the present invention can also be achieved by the following technical measures:

[0026] In step 1, the rock mass containing fractures can be obtained by rock sample cutting or rock sample splitting.

[0027] The method for evaluating thermal conductivity of proppant for closed-cycle heat recovery also includes, after step 2, closing the upper sealing cover of the thermal conductivity evaluation chamber, wherein the upper sealing cover of the thermal conductivity evaluation chamber is sealed with temperature-resistant rubber.

[0028] In step 4, the required fracturing fluid and proppant inlet and outlet are opened or closed according to the actual number of fractures in the fractured rock mass, and the fracturing fluid and thermal conductive proppant required for the experiment are prepared. The fracturing fluid includes clean water, scraped glue fracturing fluid, and slippery water fracturing fluid. The thermal conductive proppant includes metal powder, graphite powder and other high thermal conductivity powder materials.

[0029] In step 5, the injection rate of the fracturing fluid and the interval and amount of the proppant are set according to the experimental plan. After the ground stress applied to the fractured rock mass is stabilized, the thermal conductive proppant is injected into the fractured rock mass through the fracturing fluid and proppant injection ports. The fracture opens under the action of the injection pressure, and the thermal conductive proppant is also brought into the fracture. The injection of the fracturing fluid is then stopped, and the fracture closes under the action of the ground stress. The thermal conductive proppant filled in the fracture is in closer contact under the action of the compact after the fracture is closed.

[0030] In step 6, the power of the single-chip heater is set to P h , heating time is t h , the temperature changes of the wall of the fractured rock mass are monitored by temperature sensors located on two corresponding sides of the fractured rock mass.

[0031] In step 7, the heating plate is turned off, and the ground stress is unloaded after the fractured rock mass cools down. The upper sealing cover of the thermal conductivity evaluation chamber is opened, the fractured rock mass is taken out, each layer of fractures is opened, and the laying status of the thermal conductive proppant in the fractures of the fractured rock mass is recorded.

[0032] The method for evaluating the thermal conductivity of proppants for closed-loop heat recovery also includes, after step 7, step 8, changing the type of fracturing fluid, the type of thermal conductive proppant material, the injection displacement of the fracturing fluid, the interval for adding thermal conductive proppants, the amount of thermal conductive proppant added, and the ground stress conditions, and repeating steps 5-7.

[0033] The method for evaluating the thermal conductivity of proppants used for closed-loop heat recovery also includes, after step 8, step 9, analyzing the temperature distribution and evolution law obtained by the temperature sensor located on the wall of the fractured rock mass under various experimental conditions and the laying form of the thermal conductive proppant in the fracture, calculating the thermal conductivity resistance at various positions of the fractured rock mass, clarifying the influence of different factors on the laying form of the thermal conductive proppant in the fracture and the influence of different thermal conductive proppant laying forms on the thermal conductivity of the fractured rock mass, and then providing the best closed-loop geothermal system reservoir transformation plan.

[0034] In step 9, the thermal resistance of the thermal conductivity at each position in the rock mass is, by analyzing the thermal resistance of the thermal conductivity at each position in the rock mass, the influence of adding thermal conductive proppants on improving the thermal conductivity of the rock mass is clarified.

[0035] The device and method for evaluating the thermal conductivity of proppants for closed-loop heat recovery in the present invention are designed to understand the migration law of thermal conductive proppants in fractures during the closed-loop geothermal system transformation process and the influence of various influencing factors on the improvement of rock thermal conductivity after the thermal conductive proppants are filled, and then propose the best closed-loop geothermal system reservoir fracturing transformation plan. Compared with the prior art, the present invention has the following technical advantages:

[0036] 1. The migration and placement rules of thermal conductive materials in cracks under geostress conditions and the influence of various factors on the migration of thermal conductive materials in cracks can be obtained;

[0037] 2. The changing law of thermal conductivity of rock mass after filling the cracks with thermal conductive materials can be obtained, and the influence of the filling characteristics of thermal conductive materials on the improvement of thermal conductivity of rock mass can be clarified;

[0038] 3. It can provide technical support for the feasibility and capacity prediction of closed-loop geothermal systems based on filling thermal conductive materials in fractures after reservoir transformation. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a structural diagram of a specific embodiment of the proppant thermal conductivity evaluation device for closed-cycle heat recovery of the present invention;

[0040] In the figure: 1-shell of the chamber for evaluating thermal conductivity filled with proppant; 2-rock mass containing fractures; 3-insulating layer; 4-heat-conducting material filled in the fractures; 5-ground stress loading device; 6-heating plate H1; 7-heating plate H2; 8-heating plate H3; 9-heating plate H4; 10-inlet of fracturing fluid and proppant; 11-outlet of fracturing fluid and proppant; 12-temperature sensor SR1; 13-temperature sensor SL1; 14-temperature sensor SR2; 15-temperature sensor SL2; 16-temperature sensor SR3; 17-temperature sensor SL3; 18-temperature sensor SR4; 19-temperature sensor SL4; 20-temperature sensor SR5; 21-temperature sensor SL5; 22-temperature sensor SR6; 23-temperature sensor SL6; 24-temperature sensor SR7; 25-temperature sensor SL7; 26-temperature sensor SR8; 27-temperature sensor SL8. DETAILED DESCRIPTION

[0041] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0042] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations and / or combinations thereof.

[0043] The invention provides a method for evaluating the heat transfer performance of a thermal conductive proppant suitable for a closed-cycle geothermal system after reservoir transformation. The method specifically comprises: preparing a rock mass containing fractures, loading the rock mass containing fractures into a proppant-filled thermal conductivity evaluation chamber, wherein the proppant-filled thermal conductivity evaluation chamber has a fracturing fluid and proppant inlet and a fracturing fluid and proppant outlet, a heating plate is placed on one side of a rock sample in the proppant-filled thermal conductivity evaluation chamber to provide a heat source for thermal conductivity testing after proppant laying, an insulation layer is arranged around the rock sample in the proppant-filled thermal conductivity evaluation chamber, and a temperature sensor is arranged on a surface of the insulation layer opposite to the heating plate through an opening; and the proppant-filled thermal conductivity evaluation chamber has a stress loading device in a direction perpendicular to the fracture surface to provide a closing stress for the fracture closure and simultaneously play a role in pressing the thermal conductive material into a blank. By changing the type of fracturing fluid, the type of thermal conductive proppant material, the injection displacement of the fracturing fluid, the interval between adding thermal conductive proppant, the amount of thermal conductive proppant added, the ground stress conditions, etc., the temperature distribution and evolution law obtained by the temperature sensor located on the rock wall under various experimental conditions and the paving form of thermal conductive proppant in the fracture are analyzed to clarify the influence of different factors on the paving form of thermal conductive proppant in the fracture and the influence of different paving forms of thermal conductive proppant on the thermal conductivity of the rock mass. Then the best closed-loop geothermal system reservoir transformation plan is given.

[0044] The method for evaluating the thermal conductivity of a proppant for closed-cycle heat recovery of the present invention comprises the following steps:

[0045] 1. Prepare a rock sample containing fractures, wherein the rock sample containing fractures can be obtained by cutting the rock sample or splitting the rock sample;

[0046] 2. Load the rock sample into the proppant-filled thermal conductivity evaluation chamber, which has a fracturing fluid and proppant inlet and a fracturing fluid and proppant outlet. The fracturing fluid and proppant inlet and outlet are connected to the cracks in the rock sample, and the opening and closing of the inlet and outlet can be controlled by a valve according to the actual number of cracks. A heating plate is placed on one side of the rock sample in the proppant-filled thermal conductivity evaluation chamber to provide a heat source for the thermal conductivity test after the proppant is laid, and the heating plate is fixed on the chamber wall by threads. An insulation layer is arranged around the rock sample in the proppant-filled thermal conductivity evaluation chamber to isolate the rock sample from the heat exchange with the outside world. A temperature sensor is arranged through an opening on the surface opposite to the heating plate, and the temperature sensor connection line passes through the chamber wall and is tightened and sealed by a threaded sealing ring. The proppant-filled thermal conductivity evaluation chamber has a stress loading device in the vertical direction to the crack surface to provide closing stress for crack closure and play a role in pressing the thermal conductive material. The stress loading device is realized by a hydraulic sealing rubber sleeve.

[0047] 3. Close the upper sealing cover of the proppant filling thermal conductivity evaluation chamber, wherein the upper sealing cover of the thermal conductivity evaluation chamber is sealed with a temperature-resistant rubber;

[0048] 4. Determine the fracture closure pressure according to the simulated geostress conditions of the thermal reservoir, and apply geostress to the fractured rock mass through a stress loading device in a direction perpendicular to the fracture surface, wherein an insulation layer is provided between the stress loading device and the rock mass;

[0049] 5. Open or close the required fracturing fluid and proppant inlet and outlet according to the actual number of cracks in the rock sample, and prepare the fracturing fluid and thermal conductive proppant required for the experiment. The fracturing fluid includes clean water, scraped glue fracturing fluid, slippery water fracturing fluid, etc. The thermal conductive proppant includes metal powder, graphite powder and other high thermal conductivity powder materials;

[0050] 6. According to the experimental plan, the injection rate of the fracturing fluid and the interval and amount of the proppant are set, and the thermal conductive proppant is injected into the fractured rock mass through the injection port of the fracturing fluid and the proppant. The fracture opens under the action of the injection pressure, and the thermal conductive proppant is also brought into the fracture. Then the injection of the fracturing fluid is stopped, and the fracture closes under the action of the ground stress. The thermal conductive proppant filled in the fracture is in closer contact under the action of the compact after the fracture is closed;

[0051] 7. After the experiment in step 6 is completed, turn on the heating plate on one side of the rock mass, and set the power of the single heating plate to P h , heating time is t h , monitoring the temperature change of the rock wall surface by temperature sensors located on two corresponding sides of the rock mass, wherein the temperature sensors are in contact with the rock mass wall surface, and an insulation layer is arranged outside the temperature sensors;

[0052] 8. After the experiment in step 7 is completed, turn off the heat source, wait for the rock sample to cool down and unload the ground stress, open the upper sealing cover of the thermal conductivity evaluation chamber, take out the experimental rock mass, open each layer of cracks, and record the laying status of the thermal conductive proppant in the cracks;

[0053] 9. Change the fracturing fluid type, thermal conductive proppant material type, fracturing fluid injection displacement, thermal conductive proppant addition interval, thermal conductive proppant addition amount, ground stress conditions, etc., and repeat steps 6-8;

[0054] 10. Analyze the temperature distribution and evolution law obtained by the temperature sensor on the rock wall under various experimental conditions and the paving form of thermal conductive proppants in the fractures, calculate the thermal resistance of the thermal conductivity at various locations in the rock mass, clarify the influence of different factors on the paving form of thermal conductive proppants in the fractures and the influence of different paving forms of thermal conductive proppants on the thermal conductivity of the rock mass, and then give the best closed-loop geothermal system reservoir transformation plan.

[0055] The thermal resistance of thermal conductivity at various positions in the rock mass is. By analyzing the thermal resistance of thermal conductivity at various positions in the rock mass, the influence of adding thermal conductive proppants on improving the thermal conductivity of the rock mass is clarified.

[0056] like Figure 1 As shown, the fractured rock mass 2 of the proppant thermal conductivity evaluation device for closed-cycle heat recovery is located in a proppant-filled thermal conductivity evaluation chamber, and the fractures are filled with thermally conductive materials 4, which are graphite particles or metal powders.

[0057] The proppant-filled thermal conductivity evaluation chamber has a fracturing fluid and proppant inlet 10 and a fracturing fluid and proppant outlet 11. The fracturing fluid and proppant inlet and outlet are connected to the cracks in the rock sample, and the opening and closing of the inlet and outlet can be controlled by a valve according to the actual number of cracks. The function of the fracturing fluid and proppant outlet 11 is to allow the proppant and fracturing fluid to circulate continuously during the injection process. If no outlet is set, the injected proppant and fracturing fluid will be pressed in the cracks and cannot be discharged. During the cyclic injection of proppant and fracturing fluid, the proppant will settle and accumulate in the cracks.

[0058] The proppant-filled thermal conductivity evaluation chamber is provided with a heating plate 6-9 on one side of the rock sample, the number of which is the number of cracks plus one, to provide a heat source for the thermal conductivity test after the proppant is laid, and the heating plate 6-9 is fixed on the chamber wall by threads; the proppant-filled thermal conductivity evaluation chamber is provided with an insulation layer 3 around the rock sample to isolate the rock sample from the heat exchange with the outside world; temperature sensors 12-27 are provided through openings on the surface opposite to the heating plate, the number of sensors is four times the number of heating plates, the temperature sensor connection line passes through the chamber wall and is tightened and sealed by a threaded sealing ring; the proppant-filled thermal conductivity evaluation chamber is provided with a stress loading device 5 in a direction perpendicular to the crack surface to provide closing stress for the crack closure and play a role in pressing the thermal conductive material, and the stress loading device is implemented by a hydraulic sealing rubber sleeve; the above-mentioned components, except for the fracturing fluid and proppant inlet 10 and the fracturing fluid and proppant outlet 11, are all located in the shell 1 of the proppant-filled thermal conductivity evaluation chamber.

[0059] The following are several specific embodiments of the present invention.

[0060] Example 1

[0061] In a specific embodiment 1 of the present invention, a device for evaluating the thermal conductivity of proppant filling in a closed-loop geothermal system after reservoir transformation is used to analyze the effect of different mesh sizes of graphite thermal conductive materials on the thermal conductivity of rock mass.

[0062] 1. Prepare a sandstone sample containing three fractures, wherein the fractured rock sample is obtained by rock sample cutting;

[0063] 2. Load the rock sample containing fractures into the proppant-filled thermal conductivity evaluation chamber, the proppant-filled thermal conductivity evaluation chamber has a fracturing fluid and proppant inlet and a fracturing fluid and proppant outlet, the fracturing fluid and proppant inlet and outlet are connected to the fractures in the rock sample, and the opening and closing of the inlet and outlet can be controlled by a valve according to the actual number of fractures; the proppant-filled thermal conductivity evaluation chamber is provided with a heating plate on one side of the rock sample to provide a heat source for the thermal conductivity test after the proppant is laid; the proppant-filled thermal conductivity evaluation chamber is provided with an insulation layer around the rock sample to isolate the rock sample from the heat exchange with the outside, and a temperature sensor is provided on the surface of the insulation layer opposite to the heating plate through an opening; the proppant-filled thermal conductivity evaluation chamber has a stress loading device in the direction perpendicular to the fracture surface to provide closing stress for the fracture closure, and at the same time play a role in pressing the thermal conductive material into a blank;

[0064] 3. Close the upper sealing cover of the proppant filling thermal conductivity evaluation chamber, wherein the upper sealing cover of the thermal conductivity evaluation chamber is sealed with a temperature-resistant rubber;

[0065] 4. The crack closing pressure is set to Pc, and the ground stress is applied to the rock mass containing the cracks through a stress loading device in a direction perpendicular to the crack surface, and an insulation layer is provided between the stress loading device and the rock mass;

[0066] 5. Open the fracturing fluid and proppant inlets and outlets corresponding to the three fractures, and prepare the slick water fracturing fluid and graphite thermal conductive proppants of different mesh sizes (20-40 mesh, 60-80 mesh, 80-100 mesh) required for the experiment;

[0067] 6. Set the fracturing fluid injection displacement Vf and the proppant addition interval Ti and the addition amount Vi, inject the thermal conductive proppant into the fractured rock mass through the fracturing fluid and proppant injection ports, the fracture opens under the action of the injection pressure, and the thermal conductive proppant is also brought into the fracture. After a time Td, stop injecting the fracturing fluid, and the fracture closes under the action of the ground stress. The thermal conductive proppant filled in the fracture is in closer contact under the action of the compact after the fracture is closed;

[0068] 7. After the experiment in step 6 is completed, turn on the heating plate on one side of the rock mass, and set the power of the single heating plate to P h , heating time is t h The temperature change of the rock wall (the temperature at the heat source end T sl1 ,T sl2 ,T sl3 ,T sl4 ,T sl5 ,T sl6 ,T sl7 ,T sl8 ; Heat transfer end temperature T sr1 ,T sr2 ,T sr3 ,T sr4 ,T sr5 ,T sr6 ,T sr7 ,T sr8 ), the temperature sensor is in contact with the rock wall, and an insulation layer is provided outside the temperature sensor;

[0069] 8. After the experiment in step 7 is completed, turn off the heat source, wait for the rock sample to cool down and unload the ground stress, open the upper sealing cover of the thermal conductivity evaluation chamber, take out the experimental rock mass, open each layer of cracks, and record the laying status of the thermal conductive proppant in the cracks;

[0070] 9. Change the mesh size of graphite thermal conductive support agent and repeat steps 6-8;

[0071] 10. Analyze the temperature distribution and evolution law obtained by the temperature sensor located on the rock wall under different graphite thermal conductive proppant mesh sizes and the laying form of thermal conductive proppants in the cracks, calculate the thermal resistance of the thermal conductivity at various positions of the rock mass, clarify the influence of the graphite thermal conductive proppant mesh size on the laying form of thermal conductive proppants in the cracks and the influence of different thermal conductive proppant laying forms on the thermal conductivity of the rock mass.

[0072] The thermal resistance of the rock mass at each location is:

[0073]

[0074]

[0075]

[0076]

[0077]

[0078] The average thermal conductivity resistance of rock is:

[0079]

[0080] Where P h is the heating plate power; t h is the heating time of the heater; R1, R2, R2…R8 are the thermal resistances at each position; R a is the average thermal conductivity resistance of rock; T sl1 , T sl2 , T sl3 …T sl8 is the temperature of the temperature sensor at the end of the heating plate; T sr1 , T sr2 , T sr3 …T sr8 is the temperature of the temperature sensor located at the temperature receiving end.

[0081] Example 2

[0082] In a specific embodiment 2 of the present invention, a device for evaluating the thermal conductivity of proppant filling in a closed-cycle geothermal system after reservoir transformation is used to analyze the influence of different formation pressure conditions on the thermal conductivity of the rock mass after transformation.

[0083] 1. Prepare a sandstone sample containing three fractures, wherein the fractured rock sample is obtained by rock sample cutting;

[0084] 2. Load the rock sample containing fractures into the proppant-filled thermal conductivity evaluation chamber, the proppant-filled thermal conductivity evaluation chamber has a fracturing fluid and proppant inlet and a fracturing fluid and proppant outlet, the fracturing fluid and proppant inlet and outlet are connected to the fractures in the rock sample, and the opening and closing of the inlet and outlet can be controlled by a valve according to the actual number of fractures; the proppant-filled thermal conductivity evaluation chamber is provided with a heating plate on one side of the rock sample to provide a heat source for the thermal conductivity test after the proppant is laid; the proppant-filled thermal conductivity evaluation chamber is provided with an insulation layer around the rock sample to isolate the rock sample from the heat exchange with the outside, and a temperature sensor is provided on the surface of the insulation layer opposite to the heating plate through an opening; the proppant-filled thermal conductivity evaluation chamber has a stress loading device in the direction perpendicular to the fracture surface to provide closing stress for the fracture closure, and at the same time play a role in pressing the thermal conductive material into a blank;

[0085] 3. Close the upper sealing cover of the proppant filling thermal conductivity evaluation chamber, wherein the upper sealing cover of the thermal conductivity evaluation chamber is sealed with a temperature-resistant rubber;

[0086] 4. The crack closing pressure is set to Pc, and the ground stress is applied to the rock mass containing the cracks through a stress loading device in a direction perpendicular to the crack surface, and an insulation layer is provided between the stress loading device and the rock mass;

[0087] 5. Open the fracturing fluid and proppant inlets and outlets corresponding to the three fractures, and prepare the slick water fracturing fluid and graphite thermal conductive proppant of a certain mesh size (80-100 mesh) required for the experiment;

[0088] 6. Set the fracturing fluid injection displacement Vf and the proppant addition interval Ti and the addition amount Vi, inject the thermal conductive proppant into the fractured rock mass through the fracturing fluid and proppant injection ports, the fracture opens under the action of the injection pressure, and the thermal conductive proppant is also brought into the fracture. After a time Td, stop injecting the fracturing fluid, and the fracture closes under the action of the ground stress. The thermal conductive proppant filled in the fracture is in closer contact under the action of the compact after the fracture is closed;

[0089] 7. After the experiment in step 6 is completed, turn on the heating plate on one side of the rock mass, and set the power of the single heating plate to P h , heating time is t h The temperature change of the rock wall (the temperature at the heat source end T sl1 ,T sl2 ,T sl3 ,T sl4 ,T sl5 ,T sl6 ,T sl7 ,T sl8 ; Heat transfer end temperature T sr1 ,T sr2 ,T sr3 ,Tsr4 ,T sr5 ,T sr6 ,T sr7 ,T sr8 ), the temperature sensor is in contact with the rock wall, and an insulation layer is provided outside the temperature sensor;

[0090] 8. After the experiment in step 7 is completed, turn off the heat source, wait for the rock sample to cool down and unload the ground stress, open the upper sealing cover of the thermal conductivity evaluation chamber, take out the experimental rock mass, open each layer of cracks, and record the laying status of the thermal conductive proppant in the cracks;

[0091] 9. Change the crack closure pressure Pc and repeat steps 4-8;

[0092] 10. Analyze the temperature distribution and evolution law obtained by the temperature sensor located on the rock wall under different graphite thermal conductive proppant mesh sizes and the laying form of thermal conductive proppants in the cracks, calculate the thermal resistance of the thermal conductivity at various positions of the rock mass, clarify the influence of the graphite thermal conductive proppant mesh size on the laying form of thermal conductive proppants in the cracks and the influence of different thermal conductive proppant laying forms on the thermal conductivity of the rock mass.

[0093] The thermal resistance of the rock mass at each location is:

[0094]

[0095]

[0096]

[0097]

[0098]

[0099] Example 3

[0100] In a specific embodiment 3 of the present invention, a proppant filling thermal conductivity evaluation device for a closed-cycle geothermal system after reservoir transformation is used to analyze the influence of different numbers of fracturing cracks on the thermal conductivity of the transformed rock mass.

[0101] 1. Prepare sandstone samples containing 3 fractures, 4 fractures, and 5 fractures, wherein the fractured rock samples are obtained by rock sample cutting;

[0102] 2. Load the rock sample containing fractures into the proppant-filled thermal conductivity evaluation chamber, the proppant-filled thermal conductivity evaluation chamber has a fracturing fluid and proppant inlet and a fracturing fluid and proppant outlet, the fracturing fluid and proppant inlet and outlet are connected to the fractures in the rock sample, and the opening and closing of the inlet and outlet can be controlled by a valve according to the actual number of fractures; the proppant-filled thermal conductivity evaluation chamber is provided with a heating plate on one side of the rock sample to provide a heat source for the thermal conductivity test after the proppant is laid; the proppant-filled thermal conductivity evaluation chamber is provided with an insulation layer around the rock sample to isolate the rock sample from the heat exchange with the outside, and a temperature sensor is provided on the surface of the insulation layer opposite to the heating plate through an opening; the proppant-filled thermal conductivity evaluation chamber has a stress loading device in the direction perpendicular to the fracture surface to provide closing stress for the fracture closure, and at the same time play a role in pressing the thermal conductive material into a blank;

[0103] 3. Close the upper sealing cover of the proppant filling thermal conductivity evaluation chamber, wherein the upper sealing cover of the thermal conductivity evaluation chamber is sealed with a temperature-resistant rubber;

[0104] 4. The crack closing pressure is set to Pc, and the ground stress is applied to the rock mass containing the cracks through a stress loading device in a direction perpendicular to the crack surface, and an insulation layer is provided between the stress loading device and the rock mass;

[0105] 5. Open the inlet and outlet of the fracturing fluid and proppant corresponding to the crack, and prepare the slick water fracturing fluid and graphite thermal conductive proppant of a certain mesh size (80-100 mesh) required for the experiment;

[0106] 6. Set the fracturing fluid injection displacement Vf and the proppant addition interval Ti and the addition amount Vi, inject the thermal conductive proppant into the fractured rock mass through the fracturing fluid and proppant injection ports, the fracture opens under the action of the injection pressure, and the thermal conductive proppant is also brought into the fracture. After a time Td, stop injecting the fracturing fluid, and the fracture closes under the action of the ground stress. The thermal conductive proppant filled in the fracture is in closer contact under the action of the compact after the fracture is closed;

[0107] 7. After the experiment in step 6 is completed, turn on the heating plate on one side of the rock mass, and set the power of the single heating plate to P h , heating time is t h , the temperature changes of the rock wall are monitored by temperature sensors located on two corresponding sides of the rock mass (taking four cracks as an example: the temperature at the heat source end T sl1 ,T sl2 ,T sl3 ,T sl4 ,T sl5 ,T sl6 ,T sl7 ,T sl8 ,T sl9 ,T sl10 ; Heat transfer end temperature T sr1,T sr2 ,T sr3 ,T sr4 ,T sr5 ,T sr6 ,T sr7 ,T sr8 ,T sr9 ,T sr10 ), the temperature sensor is in contact with the rock wall, and an insulation layer is provided outside the temperature sensor;

[0108] 8. After the experiment in step 7 is completed, turn off the heat source, wait for the rock sample to cool down and unload the ground stress, open the upper sealing cover of the thermal conductivity evaluation chamber, take out the experimental rock mass, open each layer of cracks, and record the laying status of the thermal conductive proppant in the cracks;

[0109] 9. Replace the rock sample with a different number of cracks and repeat steps 1-8;

[0110] 10. Analyze the temperature distribution and evolution law obtained by the temperature sensor located on the rock wall under different graphite thermal conductive proppant mesh sizes and the laying form of thermal conductive proppants in the cracks, calculate the thermal resistance of the thermal conductivity at various positions of the rock mass, clarify the influence of the graphite thermal conductive proppant mesh size on the laying form of thermal conductive proppants in the cracks and the influence of different thermal conductive proppant laying forms on the thermal conductivity of the rock mass.

[0111] When there are three cracks, the thermal resistance at each position of the rock mass is:

[0112]

[0113]

[0114]

[0115]

[0116]

[0117] The average thermal conductivity resistance of rock is:

[0118]

[0119] When there are 4 cracks, the thermal resistance at each position of the rock mass is:

[0120]

[0121]

[0122]

[0123]

[0124]

[0125] The average thermal conductivity resistance of rock is:

[0126]

[0127] When there are 5 cracks, the thermal resistance at each position of the rock mass is:

[0128]

[0129]

[0130]

[0131]

[0132]

[0133] The average thermal conductivity resistance of rock is:

[0134]

[0135] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions recorded in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0136] Except for the technical features described in the specification, all other technical features are known technologies to those skilled in the art.

Claims

1. A device for evaluating the thermal conductivity of proppant for closed-cycle heat recovery, characterized in that: The proppant thermal conductivity evaluation device for closed-cycle heat recovery comprises a thermal conductivity evaluation chamber, a rock mass containing fractures, a fracturing fluid and proppant inlet, a fracturing fluid and proppant outlet, a heating plate and a stress loading device. The rock mass containing fractures is located in the thermal conductivity evaluation chamber. The fracturing fluid and proppant inlet and the fracturing fluid and proppant outlet are both provided in plurality and are connected correspondingly to fractures in the rock mass containing fractures. The heating plate is located at one side of the thermal conductivity evaluation chamber where the fractured rock mass is placed, and provides a heat source for thermal conductivity testing after proppant laying. The stress loading device is located in the thermal conductivity evaluation chamber in a direction perpendicular to the fracture surface, and provides closing stress for fracture closure.

2. The device for evaluating thermal conductivity of proppant for closed-cycle heat recovery according to claim 1, characterized in that: The proppant thermal conductivity evaluation device for closed-cycle heat recovery also includes a thermal conductivity evaluation chamber shell, which is located at the outer layer of the thermal conductivity evaluation chamber.

3. The device for evaluating thermal conductivity of proppant for closed-cycle heat recovery according to claim 1, characterized in that: There are multiple heating plates, which are fixed on the wall surface of the thermal conductivity evaluation chamber through threads.

4. The device for evaluating thermal conductivity of proppant for closed-cycle heat recovery according to claim 3, characterized in that: The proppant thermal conductivity evaluation device for closed-cycle heat recovery also includes a plurality of temperature sensors, which are arranged through openings on the surface opposite to the heating plate. The connecting wires of the temperature sensors pass through the wall of the thermal conductivity evaluation chamber and are fastened and sealed by threaded sealing rings.

5. The device for evaluating thermal conductivity of proppant for closed-cycle heat recovery according to claim 1, characterized in that: The proppant thermal conductivity evaluation device for closed-cycle heat recovery also includes a thermal insulation layer, which is located around the fractured rock mass to isolate the fractured rock mass from heat exchange with the outside world.

6. The device for evaluating thermal conductivity of proppant for closed-cycle heat recovery according to claim 1, characterized in that: The stress loading device is implemented by a hydraulic sealing rubber sleeve, which has a pressing effect on the heat conductive material filled in the crack.

7. The device for evaluating thermal conductivity of proppant for closed-cycle heat recovery according to claim 1, characterized in that: The proppant is injected into the fractures of the fractured rock mass through the fracturing fluid and proppant inlet and the fracturing fluid and proppant outlet, and the proppant settles and accumulates in the fractures.

8. A method for evaluating thermal conductivity of a proppant for closed-cycle heat recovery, characterized in that: The method for evaluating the thermal conductivity of a proppant for closed-cycle heat recovery adopts the device for evaluating the thermal conductivity of a proppant for closed-cycle heat recovery according to claim 1, comprising: Step 1, preparing a rock mass containing fractures; Step 2, placing the fractured rock mass into a thermal conductivity evaluation chamber; Step 3: determining the fracture closure pressure according to the simulated geostress conditions of the thermal reservoir, and applying geostress to the fractured rock mass through a stress loading device; Step 4: prepare the fracturing fluid and thermal conductive proppant required for the experiment; Step 5, injecting a thermal conductive proppant into the fractured rock mass through the fracturing fluid and proppant injection port; Step 6, turn on the heating plate to monitor the temperature change of the wall surface of the fractured rock mass; Step 7: Turn off the heating plate and record the laying status of the thermal conductive proppant in the cracks of the fractured rock mass.

9. The method for evaluating thermal conductivity of proppant for closed-cycle heat recovery according to claim 8, characterized in that: In step 1, the rock mass containing fractures can be obtained by rock sample cutting or rock sample splitting.

10. The method for evaluating thermal conductivity of proppant for closed-cycle heat recovery according to claim 8, characterized in that: The method for evaluating thermal conductivity of proppant for closed-cycle heat recovery also includes, after step 2, closing the upper sealing cover of the thermal conductivity evaluation chamber, wherein the upper sealing cover of the thermal conductivity evaluation chamber is sealed with temperature-resistant rubber.

11. The method for evaluating thermal conductivity of proppant for closed-cycle heat recovery according to claim 8, characterized in that: In step 4, the required fracturing fluid and proppant inlet and outlet are opened or closed according to the actual number of fractures in the fractured rock mass, and the fracturing fluid and thermal conductive proppant required for the experiment are prepared. The fracturing fluid includes clean water, scraped glue fracturing fluid, and slippery water fracturing fluid. The thermal conductive proppant includes metal powder, graphite powder and other high thermal conductivity powder materials.

12. The method for evaluating thermal conductivity of proppant for closed-cycle heat recovery according to claim 8, characterized in that: In step 5, the injection rate of the fracturing fluid and the interval and amount of the proppant are set according to the experimental plan. After the ground stress applied to the fractured rock mass is stabilized, the thermal conductive proppant is injected into the fractured rock mass through the fracturing fluid and proppant injection ports. The fracture opens under the action of the injection pressure, and the thermal conductive proppant is also brought into the fracture. The injection of the fracturing fluid is then stopped, and the fracture closes under the action of the ground stress. The thermal conductive proppant filled in the fracture is in closer contact under the action of the compact after the fracture is closed.

13. The method for evaluating thermal conductivity of proppant for closed-cycle heat recovery according to claim 8, characterized in that: In step 6, the power of the single-chip heater is set to P h , heating time is t h , the wall temperature changes of the fractured rock mass are monitored by temperature sensors located on two corresponding sides of the fractured rock mass.

14. The method for evaluating thermal conductivity of proppant for closed-cycle heat recovery according to claim 8, characterized in that: In step 7, the heating plate is turned off, and the ground stress is unloaded after the fractured rock mass cools down. The upper sealing cover of the thermal conductivity evaluation chamber is opened, the fractured rock mass is taken out, each layer of fractures is opened, and the laying status of the thermal conductive proppant in the fractures of the fractured rock mass is recorded.

15. The method for evaluating thermal conductivity of proppant for closed-cycle heat recovery according to claim 8, characterized in that: The method for evaluating the thermal conductivity of proppants for closed-loop heat recovery also includes, after step 7, step 8, changing the type of fracturing fluid, the type of thermal conductive proppant material, the injection displacement of the fracturing fluid, the interval for adding thermal conductive proppants, the amount of thermal conductive proppant added, and the ground stress conditions, and repeating steps 5-7.

16. The method for evaluating thermal conductivity of proppant for closed cycle heat recovery according to claim 15, characterized in that: The method for evaluating the thermal conductivity of proppants used for closed-loop heat recovery also includes, after step 8, step 9, analyzing the temperature distribution and evolution law obtained by the temperature sensor located on the wall of the fractured rock mass under various experimental conditions and the laying form of the thermal conductive proppant in the fracture, calculating the thermal conductivity resistance at various positions of the fractured rock mass, clarifying the influence of different factors on the laying form of the thermal conductive proppant in the fracture and the influence of different thermal conductive proppant laying forms on the thermal conductivity of the fractured rock mass, and then providing the best closed-loop geothermal system reservoir transformation plan.

17. The method for evaluating thermal conductivity of proppant for closed cycle heat recovery according to claim 16, characterized in that: In step 9, the thermal resistance of the thermal conductivity at each position in the rock mass is, by analyzing the thermal resistance of the thermal conductivity at each position in the rock mass, the influence of adding thermal conductive proppants on improving the thermal conductivity of the rock mass is clarified.

Images