Rock acid etching crack flow guide and heat exchange testing device and testing method

Abstract

The invention discloses a rock acid etching fracture flow guide and heat exchange testing device and a testing method, which are used for testing flow guide and heat exchange of a rock core fracture sample under an acid etching condition. The device comprises a rock core fracture sample holder for holding a rock core fracture sample, a fluid filling assembly for filling fluid into the rock core fracture sample, a pressure sensor group and a temperature sensor group, and the temperature sensor group comprises an inlet temperature sensor, an outlet temperature sensor and an outer wall temperature sensor. The temperature sensors are respectively used for measuring the temperature of a liquid inlet, a liquid outlet and an outer side wall of the rock core fracture sample. According to the method, the characteristic that the convective heat transfer process is directly carried out after acid fracturing in the actual geothermal exploitation process is considered, seamless connection of the acid liquid and the experimental fluid is achieved through the piston container, and the convective heat transfer coefficient of the complex fracture and the acid etching fracture can be measured and calculated by considering the real geometrical shape of the acid etching fracture.

Description

Technical Field

[0001] The invention belongs to the field of geothermal resource development, and specifically relates to a rock acid-etched fracture diversion and heat exchange testing device and method. Background Art

[0002] With the vigorous development of geothermal resource mining projects based on enhanced geothermal systems (EGS) technology, the cost issues in the project mining process and the demand for increased production have gradually become prominent. Therefore, acid fracturing technology has been valued as a technology to improve the ability to exploit geothermal resources. Acid fracturing is to dissolve the fracture surface into an uneven surface through the dissolution of acid. Even after stopping the pump and unloading the pressure, the fracture will not be completely closed, and the geothermal resource output can be increased by improving the fracture conductivity. Therefore, the conduction and heat exchange experiment of rock acid-etched fractures is of great significance to practical engineering.

[0003] The surface of the acid-etched fracture is uneven, and the convective heat transfer process of the fluid in it is relatively complicated. Although the conventional rock fracture conduction heat transfer experiment can simulate the convective heat transfer process of the fluid in the fracture, such as the Chinese patent publication with application number 202011254783.8 discloses a rock fracture conduction heat transfer test device and method, it can only simulate the convective heat transfer process of general fractures. However, in actual working conditions, when the acid passes through the fracture and increases the fracture opening, the fracture surface is not smooth and flat, and the heat exchange area will also change. Therefore, the test results of the conventional conduction heat transfer test device have little guiding significance for actual working conditions. Therefore, it is necessary to design a convective heat transfer coefficient test device and method for acid-etched fractures. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] The invention aims to solve the problem that the existing rock fissure flow conduction and heat exchange testing device cannot effectively simulate the rock fissure flow conduction and heat exchange in the geothermal mining process.

[0006] (II) Technical solution

[0007] In order to solve the above technical problems, the first aspect of the present invention proposes a rock acid-etched fracture conduction and heat exchange testing device, which is used to test the conduction and heat exchange of core fracture samples under acid etching conditions, including a core fracture sample clamp for clamping the core fracture sample, a fluid filling assembly for filling the core fracture sample with fluid, and a pressure sensor group, wherein the pressure sensor group is used to measure the pressure of the fluid filled into the core fracture sample at the inlet and outlet of the core fracture sample, and the testing device also includes a temperature sensor group, which includes an inlet temperature sensor, an outlet temperature sensor and an outer wall temperature sensor, which are respectively used to measure the temperatures of the liquid inlet, liquid outlet and outer wall of the core fracture sample.

[0008] According to a preferred embodiment of the present invention, the core fracture sample holder comprises an inlet pipe, an outlet pipe, an outer pipe, an elastic heating sleeve and a shell, and the core fracture sample is placed in the elastic heating sleeve; the elastic heating sleeve tightly wraps the core fracture sample and is used to heat the outer wall of the core fracture sample;

[0009] The detection ends of the inlet temperature sensor, the outlet temperature sensor and the outer wall temperature sensor are respectively fixed at the inlet, the outlet and the middle of the elastic heating sleeve, and are closely attached to the outer surface of the core fracture sample.

[0010] According to a preferred embodiment of the present invention, the fluid filling assembly includes a piston container and a pressurized fluid container, the piston container includes an inlet and an outlet, the inlet is connected to the pressurized fluid container, and the outlet is connected to the inlet pipe of the core fracture sample holder; the piston container includes a plurality of piston spaces, each piston space includes an inlet space and an outlet space separated by a piston, the inlet space is connected to the inlet of the piston container, and the outlet space is connected to the outlet of the piston container; at least one piston space is used to accommodate acid for etching the fractures of the rock fracture sample, and at least one piston space is used to accommodate experimental fluid for conducting conduction and heat exchange tests on the rock fracture sample.

[0011] Another aspect of the present invention provides a rock acid-etched fissure conduction and heat transfer testing method, which is used to test the conduction and heat transfer of a core fissure sample under acid etching to calculate the convection heat transfer coefficient of the fissure of the core fissure sample after acid etching, and comprises the following steps:

[0012] S1, obtaining a point cloud image of the fracture surface of the core fracture sample before acid etching, and calculating the roughness coefficient JRC1 of the fracture surface of the core fracture sample before acid etching;

[0013] S2. Construct the point cloud map of the crack surface with different roughness coefficients, and obtain the fitting relationship between the equivalent eddy current layer thickness d, the roughness coefficient JRC and the Reynolds number Re through numerical simulation;

[0014] S3, acid-etching the fissures of the core fissure sample, and then performing a flow conduction and heat exchange experiment on the acid-etched core fissure sample;

[0015] S4. Obtain a point cloud of the fracture surface of the core fracture sample after acid etching, and calculate the roughness coefficient JRC2, the average width y2 of the acid etching path, and the average opening a2 of the acid etching path of the fracture surface of the core fracture sample after acid etching.

[0016] S5. Calculate the convection heat transfer coefficient of the fissure of the core fissure sample after acid etching according to the following formula:

[0017]

[0018] Where h is the convective heat transfer coefficient of the fracture of the core fracture sample after acid etching, L is the length of the core fracture sample, y1 is the width of the unetched area, y2 is the width of the acid etching path, c f is the specific heat capacity of the experimental fluid, ρ f is the density of the experimental fluid, b1 is half of the laminar zone opening of the unetched area, u1 is the experimental fluid flow rate of the unetched area, b2 is half of the laminar zone opening of the etched passage, u2 is the experimental fluid flow rate of the etched passage, T1 and T2 are the inlet and outlet temperatures of the core fracture sample, respectively, K f is the thermal conductivity of the experimental fluid, T c is the outer wall temperature of the core fracture sample, h1 is the convective heat transfer coefficient of the unetched area, h2 is the convective heat transfer coefficient of the etched path, R1 is half of the equivalent core fracture sample thickness of the unetched area, R2 is half of the equivalent core fracture sample thickness of the etched path, d1 is the thickness of the equivalent eddy layer of the unetched area, d2 is the thickness of the equivalent eddy layer of the etched path, K f is the thermal conductivity of the experimental fluid.

[0019] According to a preferred embodiment of the present invention, step S5 comprises: fn (L) = T2 and substitute it into the following formula to solve the convective heat transfer coefficient h n :

[0020] Where n = 1 or 2, M is

[0021] According to a preferred embodiment of the present invention, the thickness d of the equivalent eddy current layer n and crack opening a n The ratio of Reynolds number Re and roughness coefficient JRC n The relationship is calculated by the following formula:

[0022]

[0023] Wherein, n is 1 or 2, i, j, k are the coefficients of the fitting relationship in the step S2, a1 is the crack opening of the unetched area, a2 is the crack opening of the etched path, JRC1 is the roughness coefficient of the unetched area, JRC2 is the roughness coefficient of the etched path, Re1 is the Reynolds number of the unetched area, and Re2 is the Reynolds number of the unetched area.

[0024] According to a preferred embodiment of the present invention, the Reynolds number Re n The calculation formula is:

[0025]

[0026] Where μ is the kinematic viscosity of the experimental fluid and n is 1 or 2.

[0027] (III) Beneficial effects

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The present invention takes into account the characteristics of the direct convection heat exchange process after acid fracturing in the actual geothermal exploitation process, and adopts a piston container to achieve seamless connection between acid and water as experimental fluids. The process of dissolution and diversion heat exchange can be switched at any time by loading different experimental fluids in the piston container, which is more in line with the actual geothermal exploitation process and improves work efficiency.

[0030] 2. The present invention proposes a method for calculating the convective heat transfer coefficient of acid-etched cracks by considering the real geometric shape of the acid-etched cracks, thereby realizing the measurement of the convective heat transfer coefficient of complex cracks and acid-etched cracks.

[0031] 3. The present invention measures the convective heat transfer coefficient of the acid-etched fractures under different acid concentrations, acid injection rates, and roughness coefficients of the fractures before acid etching, thereby achieving the evaluation of the heat transfer efficiency of the geothermal reservoir under acid fracturing under various conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the overall structure of the rock acid-etched fracture flow conduction and heat exchange testing device of the present invention. Figure 2 The present invention is a schematic diagram of the overall structure of a core fracture sample holder of a rock acid-etched fracture conduction and heat exchange testing device.

[0033] Figure 3 and Figure 4 They are views of the inlet pipe side and the outlet pipe side of the core fracture sample holder of the rock acid-etched fracture conduction and heat exchange testing device of the present invention.

[0034] Figure 5 The present invention is a flow chart of the rock acid-etched fracture conduction and heat exchange testing method.

[0035] Figure 6 Theoretical model used for calculating the convective heat transfer coefficient of the present invention;

[0036] Figure 7 It is a two-dimensional slice diagram of the theoretical model of the present invention.

[0037] Description of reference numerals:

[0038] Core fracture sample 1, core holder 2, piston container 3, horizontal flow pump 4, annular pressure pump 5, pressurized fluid container 6, constant temperature box 7, experimental fluid container 8, mass measuring instrument 9, inlet temperature sensor 10, outlet temperature sensor 11, outer wall temperature sensor 12, inlet pressure sensor 13, outlet pressure sensor 14; inlet pipe 2-1, outlet pipe 2-2, outer pipe 2-3, elastic heating sleeve 2-4, core holder sealing end 2-5, core holder shell 2-6, rock sealing end 2-7. DETAILED DESCRIPTION

[0039] In order to solve the above problems, the present invention proposes a rock acid-etched fissure convection heat transfer testing device and method to achieve the measurement and calculation of the rock acid-etched fissure convection heat transfer coefficient.

[0040] The rock acid-etched fracture flow conduction and heat exchange testing device of the present invention comprises a core fracture sample holder for clamping a core fracture sample, a fluid filling assembly for filling the core fracture sample with fluid, and a pressure sensor group, wherein the pressure sensor group is used to measure the pressure of the fluid filled into the core fracture sample at the inlet and outlet of the core fracture sample.

[0041] Different from the prior art, the testing device of the present invention also includes a temperature sensor group, which includes an inlet temperature sensor, an outlet temperature sensor and an outer wall temperature sensor, which are respectively used to measure the temperature of the liquid inlet, liquid outlet and outer wall of the core fracture sample.

[0042] On the other hand, in order to conduct the flow conduction and heat transfer test of the acid etching and experimental fluid, the present invention also improves the fluid filling assembly, which includes a piston container and a pressurized fluid container, the piston container includes an inlet and an outlet, the inlet is connected to the pressurized fluid container, and the outlet is connected to the inlet pipe of the core fracture sample holder. In addition, the piston container includes a plurality of piston spaces, each of which includes an inlet space and an outlet space separated by a piston, the inlet space is connected to the inlet of the piston container, and the outlet space is connected to the outlet of the piston container.

[0043] According to the present invention, at least one piston space is used to contain acid for etching the fissures of the rock fissure sample, and at least one piston space is used to contain experimental fluid for conducting a flow conduction and heat exchange test on the rock fissure sample. In this way, the present invention can conveniently implement acid etching through a testing device and convert the piston space after acid etching, thereby converting the injected fluid from acid to experimental fluid (water), which is convenient for testing.

[0044] Based on the above test device, the present invention also proposes a method for testing and calculating the convective heat transfer coefficient of the fissure of the core fracture sample. The method includes:

[0045] S1. Obtain a point cloud image of the fracture surface of the core fracture sample before acid etching, and calculate the roughness coefficient JRC1 of the fracture surface of the core fracture sample before acid etching;

[0046] S2. Construct point cloud maps of crack surfaces with different roughness coefficients, and obtain the fitting relationship between the equivalent eddy current layer thickness d, the roughness coefficient JRC and the Reynolds number Re through numerical simulation.

[0047] S3, acid-etching the fissures of the core fissure sample, and then conducting a flow conduction and heat exchange experiment on the acid-etched core fissure sample.

[0048] S4. Obtain a point cloud image of the fracture surface of the core fracture sample after acid etching, and calculate the roughness coefficient JRC2, the average width y2 of the acid etching path, and the average opening a2 of the acid etching path of the fracture surface of the core fracture sample after acid etching.

[0049] S5. Calculate the convection heat transfer coefficient of the fissures of the core fissure sample after acid etching.

[0050] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present application is not limited thereto.

[0051] Figure 1 The structure of the rock acid-etched fracture conduction and heat exchange testing device (hereinafter referred to as the device) of the present invention is shown. Figure 2 As shown, the device includes a core holder 2, a piston container 3, a horizontal flow pump 4, an annular pressure pump 5, a pressurized fluid container 6, a constant temperature box 7, an experimental fluid container 8, a mass measuring instrument 9, an inlet temperature sensor 10, an outlet temperature sensor 11, an outer wall temperature sensor 12, an inlet pressure sensor 13 and an outlet pressure sensor 14. The core holder 2 and the piston container 3 are both placed in the constant temperature box 7.

[0052] Figure 2 Schematic diagram of the overall structure of the core holder of the rock acid-etched fracture conduction and heat exchange test device of the present invention. Figure 2 As shown, the core holder 2 includes an inlet pipe 2-1, an outlet pipe 2-2, an outer pipe 2-3, an elastic heating sleeve 2-4, a core holder sealing end 2-5, a core holder shell 2-6 and a rock sealing end 2-7.

[0053] Figure 3 and Figure 4 They are views of the inlet pipe side and the outlet pipe side of the core holder of the rock acid-etched fracture conduction and heat exchange testing device of the present invention, respectively.

[0054] like Figures 2 to 4As shown, the core fracture sample 1 is placed in the elastic heating sleeve 2-4, and the elastic heating sleeve 2-4 tightly wraps the core fracture sample 1 to heat the outer wall of the core fracture sample; two rock sealing ends 2-7 are sealed and installed at both ends of the elastic heating sleeve 2-4, and the core fracture sample 1 is in seamless contact with the core sealing ends 2-7. The elastic heating sleeve 2-4 with the core fracture sample 1 and the two core sealing ends 2-7 installed is placed inside the core clamp housing 2-6; there is a gap between the outside of the elastic heating sleeve 2-4 and the inside of the core clamp housing 2-6 for the confining pressure fluid to enter; two core clamp sealing ends 2-5 are sealed and installed at both ends of the core clamp housing 2-6. An outer pipe 2-3 is opened in the middle of the core clamp housing 2-6, and the annular pressure pump 5 contains the confining pressure fluid. One end of the outer pipe 2-3 is connected to the gap between the elastic heating sleeve 2-4 and the core holder shell 2-6, and the other end is connected to the annular pressure pump 5 through a pipeline. The confining pressure fluid loaded in the annular pressure pump 5 flows into the gap between the elastic heating sleeve 2-4 and the core holder shell 2-6 through the outer pipe 2-3, and the confining pressure is adjusted by adjusting the flow rate of the inflowing confining pressure fluid.

[0055] The outlet end of the inlet pipe 2-1 passes through the core holder sealing end 2-5 and the rock body sealing end 2-7 in sequence, and the inlet end of the outlet pipe 2-2 passes through the rock body sealing end 2-7 and the core fracture sample holder sealing end 2-5 in sequence. The detection end of the inlet temperature sensor 10 is fixed at the inlet of the elastic heating sleeve 2-4, located at the inlet end of the rock body 1, and is used to measure the temperature of the inlet of the rock body 1. The detection end of the outlet temperature sensor 11 is fixed at the outlet of the elastic heating sleeve 2-4, located at the outlet end of the rock body 1, and is used to measure the temperature of the outlet of the rock body 1. The detection end of the outer wall temperature sensor 12 is fixed at the middle of the elastic heating sleeve 2-4, tightly attached to the outer surface of the rock body 1, and is used to measure the temperature of the outer wall of the rock body 1. The detection end of the inlet pressure sensor 13 is fixed at the inlet end of the inlet pipe 2-1, and the detection end of the outlet pressure sensor 14 is fixed at the outlet end of the outlet pipe 2-2.

[0056] The interior of the piston container 3 is divided into two spaces by the piston; one space is connected to the inlet of the piston container 3 and is the inlet space; the other space is connected to the outlet of the piston container 3 and is the outlet space. The outlet space contains acid or experimental fluid; the pressurized fluid container 6 contains pressurized fluid; the inlet of the horizontal flow pump 4 is connected to the pressurized fluid container 6, and the outlet is connected to the inlet of the piston container 3, which is used to flow the pressurized fluid in the pressurized fluid container 6 into the piston container 3 through the horizontal flow pump 4 to provide pressure to push the experimental fluid in the piston container 3 to flow to the cracks of the rock mass 1; the outlet of the piston container 3 is connected to the inlet end of the inlet pipe 2-1; the outlet end of the outlet pipe 2-2 is connected to the experimental fluid container 8; the experimental fluid container 8 is placed on the mass measuring instrument 9.

[0057] Preferably, the outlet end of the inlet pipe 2 - 1 contacts one end of the core fracture sample 1 after passing through the core holder sealing end 2 - 5 and the rock body sealing end 2 - 7 in sequence, and faces the fracture of the core fracture sample 1 .

[0058] Preferably, the inlet end of the outlet pipe 2-2 sequentially passes through the rock sealing end 2-7 and the core clamp sealing end 2-5 and contacts with the other end of the core fracture sample 1, and faces the fracture of the core fracture sample 1.

[0059] Preferably, the pressurized fluid, the confining pressure fluid and the experimental fluid are all water.

[0060] Preferably, the elastic heating sleeve 2-4 is located in the middle of the core holder housing 2-6.

[0061] Preferably, the outer wall temperature sensor 12 is fixed in the middle of the elastic heating sleeve 2 - 4 ; the inlet temperature sensor 10 and the outlet temperature sensor 11 are symmetrically arranged on both sides of the outer wall temperature sensor 12 .

[0062] Preferably, the piston container 3 has multiple outlet spaces (preferably 2 to 5). In this embodiment, the piston container 3 has two outlet spaces, one of which contains acid liquid, and the other of which contains experimental fluid. After the acid liquid dissolution is achieved through the piston container 3, the experiment is directly carried out with the experimental fluid.

[0063] Preferably, a resistance layer is provided in the elastic heating sleeve 2-4, and the outer wall of the core fracture sample is heated by energizing the resistance during the experiment.

[0064] Preferably, the outlet space of the piston container 3 is located above the inlet space.

[0065] Figure 5 The flowchart of the rock acid-etched fracture conduction and heat exchange test method of the present invention is as follows. Figure 5 As shown, the present invention also provides a testing method (hereinafter referred to as the method) based on the rock acid-etched fracture conduction and heat exchange testing device, and the method comprises the following steps:

[0066] S1. Obtain a point cloud image of the fracture surface of the core fracture sample before acid etching, and calculate the roughness coefficient JRC1 of the fracture surface of the core fracture sample before acid etching.

[0067] In this step, a splitting test is performed on the core sample, and a point cloud image of the fracture surface before acid etching is obtained by scanning, and the roughness coefficient JRC1 of the fracture surface before acid etching is obtained;

[0068] Preferably, in step S1, the splitting test adopts Brazilian splitting, and the core sample is split along the diameter by Brazilian splitting; the loading rate of Brazilian splitting is 1 ml / min.

[0069] Preferably, in step S1, the core sample 1 is a cylinder, and a core sample 1 with a diameter of 25 mm ± 0.05 mm and a length of more than 50 mm is selected, and the end surface flatness of the core sample 1 is ± 0.5 mm.

[0070] S2. Construct the point cloud map of the crack surface with different roughness coefficients, and obtain the fitting relationship between the equivalent eddy current layer thickness d, the roughness coefficient JRC and the Reynolds number Re through numerical simulation

[0071] In this step, point cloud images of crack surfaces with different roughness coefficients are constructed and imported into multi-field coupling simulation software for modeling. The fitting relationship between the equivalent eddy current layer thickness d and the roughness coefficient JRC and Reynolds number Re is obtained through numerical simulation.

[0072] Preferably, step S2 specifically comprises: obtaining the coordinate data of the crack surface with different roughness coefficients JRC based on Fourier transform, and constructing a numerical model through the coordinate point data based on linear interpolation, controlling different Reynolds numbers Re through different flow velocities u, and determining the eddy current size of the numerical model with different Reynolds numbers Re and roughness coefficients JRC through the eddy current judgment standard, thereby obtaining the equivalent eddy current layer thickness d, and then constructing a fitting relationship between different Reynolds numbers, roughness coefficients and equivalent eddy current layer thicknesses through these data.

[0073] Preferably, in step S2, the criteria for determining whether a vortex is a vortex are: (1) the fluid is a vortex, and the fluid whose flow direction is opposite to the inlet flow direction is a vortex; and (2) the monotonicity of the vortex changes from increasing to decreasing at the vortex boundary.

[0074] S3, acid-etching the fissures of the core fissure sample, and then conducting a flow conduction and heat exchange experiment on the acid-etched core fissure sample.

[0075] In this step, the core sample is first cleaned and fixed to obtain a core fracture sample 1 with fractures;

[0076] Preferably, step S3 specifically comprises: first cleaning the core fracture sample 1 with fractures, and then drying; then fixing a gasket between the fractures to control the fracture opening to be a1, and then nesting the heat shrink tube on the outside of the core fracture sample 1, and then splicing the split fractures together, and then heating the heat shrink tube to shrink the surface to a smooth and flat surface, and then subtracting the protruding parts at both ends of the heat shrink tube to obtain the core fracture sample 1 with fractures;

[0077] Preferably, in step S3, the cleaning process is: carried out in an ultrasonic cleaning apparatus at 30° C. to 50° C. for 3 to 5 minutes.

[0078] Preferably, in step S3, the drying process is: drying at 95-105° C. for 23-25 ​​hours, with a heating rate of 1-3° C. / min, so as to avoid thermal cracks in the core fracture sample.

[0079] Preferably, in step S3, a hot air blower is used to heat the heat shrink tube.

[0080] Preferably, in step S3, the heat shrink tube is transparent, high temperature resistant, corrosion resistant, has a diameter of 28 mm or 30 mm, and is 1 to 2 mm longer than the core fracture sample.

[0081] Next, a rock acid-etched fissure conduction and heat exchange test device is built; the obtained core fissure sample 1 with fissures is placed in the elastic heating sleeve 2-4, and the elastic heating sleeve 2-4 tightly wraps the core fissure sample 1; two rock sealing ends 2-7 are sealed and installed at both ends of the elastic heating sleeve 2-4, at this time, the core fissure sample 1 and the core sealing end 2-7 are tightly fitted with the elastic heating sleeve 2-4 and the core fissure sample 1 is in seamless contact with the core sealing end 2-7; then the core fissure sample 1 and the two core sealing ends 2-7 are installed in the elastic heating sleeve 2-4. The elastic heating sleeve 2-4 of the end head 2-7 is placed inside the core holder shell 2-6, and there is a gap between the outside of the elastic heating sleeve 2-4 and the inside of the core holder shell 2-6; then the two core holder sealing ends 2-5 are sealed and installed at both ends of the core holder shell 2-6, and then the outlet end of the inlet pipe 2-1 passes through the core holder sealing end head 2-5 and the rock sealing end head 2-7 in turn, and the inlet end of the outlet pipe 2-2 passes through the rock sealing end head 2-7 and the core holder sealing end head 2-5 in turn.

[0082] Before the experiment, check whether the confining pressure is 0; open the thermostat 7 to keep the experimental environment at room temperature, and then start the conduction heat transfer experiment to measure the convective heat transfer coefficient of the fractured rock mass after being dissolved by acid:

[0083] S3.1. Preparation of acid-etched cracks:

[0084] When a piston container 3 with two outlet spaces is used, acid is filled into the first outlet space of the piston container 3, and distilled water is filled into the second outlet space as the experimental fluid, pressurized fluid is filled into the pressurized fluid container 6, and confining pressure fluid is added into the annular pressure pump 5; then the annular pressure pump 5 is turned on to allow the confining pressure fluid to fill the gap between the elastic heating sleeve 2-4 and the core clamp shell 2-6, and the confining pressure is slowly increased to the experimental set value; then the horizontal flow pump 4 is turned on to allow the pressurized fluid to flow into the inlet space of the piston container; the outlet space valve of the piston container filled with acid is opened, and the acid is pressed by the pressurized fluid to flow into the rock fissure; the pressure difference between the inlet pressure sensor 13 and the outlet pressure sensor 14 is observed to determine the acid flow pressure difference, and when the pressure difference changes from increasing to decreasing, it indicates that acid-etched fissures have been formed in the rock, the valve of the piston container filled with acid is closed, and the valve of the piston container filled with water is opened, and the fluid is observed to flow out of the fissure, indicating that the acid in the fissure has been discharged at this time, and the valve of the piston container filled with water is closed at this time, and the experimental fluid container 8 connected to the fissure outlet is replaced;

[0085] S3.2. Conducting a flow conduction and heat transfer experiment in an acid-etched fracture: First, the outer wall of the core fracture sample is heated by the elastic heating sleeve 2-4, and the outer wall temperature T of the core fracture sample is controlled by observing the data transmitted to the computer by the outer wall temperature sensor 12. c The experimental setting value is reached; then the outlet space valve of the piston container 3 filled with distilled water is opened, and the horizontal flow pump 4 is turned on to compress the distilled water through the pressurized fluid to make it flow into the inlet pipe 2-1; the outlet temperature of the core fracture sample measured by the outlet temperature sensor 11 is observed. When the temperature does not change significantly within a few minutes (i.e., steady state), the inlet temperature sensor 10 measures the inlet temperature T1 of the core fracture sample, the outlet temperature sensor 11 measures the outlet temperature T2 of the core fracture sample, and the outer wall temperature sensor 12 measures the outer wall temperature T c , the mass m of the experimental fluid is measured by the mass measuring instrument 9 and the time △t required for the mass of the experimental fluid to decrease from 0 to m is recorded;

[0086] S4. Obtain a point cloud image of the fracture surface of the core fracture sample after acid etching, and calculate the roughness coefficient JRC2, the average width y2 of the acid etching path, and the average opening a2 of the acid etching path of the fracture surface of the core fracture sample after acid etching.

[0087] After the experiment, the core fracture sample 1 was taken out and scanned again to obtain the point cloud map of the fracture surface after acid etching. The core fracture sample 1 was taken out and the roughness coefficient JRC2, the average width y2 and the average opening a2 of the acid etching path in the fracture surface after acid etching were calculated. The area outside the acid etching path, that is, the un-acid etching area, was assumed to be evenly distributed on both sides of the acid etching path in the model, and the average width of the un-acid etching area was y1 (m).

[0088] S5. Calculate the convection heat transfer coefficient of the fissures of the core fissure sample after acid etching.

[0089] According to the data measured during the experiment, the convective heat transfer coefficient of the fractured rock mass after acid etching is calculated:

[0090] The core fracture sample 1 is used as a cylinder for the conduction heat transfer experiment. In order to calculate the convection heat transfer coefficient h, the equivalent area rectangular parallelepiped calculation model is used to replace the cylinder. The width of the equivalent core fracture sample is the diameter of the core fracture sample, and the thickness R1 of the equivalent core fracture sample is:

[0091]

[0092] In formula (1), R is the radius of the core fracture sample (m), and the model is as follows: Figure 6 As shown, the experimental fluid in the crack is divided into a laminar flow zone and an equivalent vortex layer according to the flow state. The flow pattern of the experimental fluid in the center of the crack is laminar flow, and the equivalent vortex layer is located between the crack surface and the laminar flow zone. Only the heat conduction process is considered in the equivalent vortex layer.

[0093] Based on the law of conservation of energy and Newton's law of cooling, the heat Q absorbed by the experimental fluid in the acid-etched cracks has the following relationship:

[0094]

[0095] In formula (2), Q is the heat absorbed by the experimental fluid in the laminar flow region (W), is the average temperature of the lower surface of the equivalent eddy current layer in the unetched area (K), is the average temperature of the laminar flow zone in the unetched area (K), is the average temperature of the lower surface of the equivalent eddy flow layer of the acid-etched passage (K), is the average temperature of the equivalent eddy layer of the acid-etched path (K), L is the length of the core fracture sample (m), and h is the convective heat transfer coefficient of the acid-etched fracture (W / (m 2 K), y1 is the width of the unetched area (m), y2 is the width of the etched path (m), c f is the specific heat capacity of the experimental fluid (J / (kg·K)), ρ f is the density of the experimental fluid (kg / m 3 ), b1 is half of the laminar zone opening of the unetched area (m), u1 is the experimental fluid flow rate of the unetched area (m / s), b2 is half of the laminar zone opening of the etched passage (m), u2 is the experimental fluid flow rate of the etched passage (m / s), T1 and T2 are the inlet and outlet temperatures of the core fracture sample (K);

[0096] Therefore, in order to calculate the convective heat transfer coefficient h of the acid-etched crack, it is necessary to calculate the average temperature of the experimental fluid in the equivalent eddy layer and laminar flow zone. The calculation formula is as follows:

[0097]

[0098]

[0099] In formula (3) and (4), n=1,2.

[0100] Therefore, in order to solve the convective heat transfer coefficient h of the acid-etched crack, it is necessary to solve the temperature analytical formula of the two-dimensional slice of the acid-etched crack along the flow direction. The specific solution method is as follows.

[0101] Based on the one-dimensional Fourier law, the heat transfer equation of the rock matrix and the equivalent eddy layer can be expressed as:

[0102]

[0103]

[0104] In formula (5) and formula (6), T r1 is the temperature of the core fracture sample in the unetched area (K), T r2 is the temperature of the core fracture sample in the acid-etched channel (K), n = 1,2.

[0105] On the other hand, it is assumed that there is a local thermal nonequilibrium at the interface between the equivalent eddy layer and the laminar flow region. Therefore, the heat transfer equation in the laminar flow region is:

[0106]

[0107] In formula (7), K f is the thermal conductivity of the experimental fluid (W / (m·K)), h1 is the convective heat transfer coefficient of the unetched area (W / (m 2 ·K)), h2 is the convective heat transfer coefficient of the acid etching passage (W / (m 2 K)), n = 1, 2;

[0108] Previous studies have shown that the thermal convection effect dominates the heat transfer process in the laminar flow region. Therefore, by ignoring the thermal radiation term in equation (7), a simplified heat transfer equation can be obtained:

[0109]

[0110] The boundary conditions can be expressed as:

[0111] T fn (0) = T1 (9)

[0112] T fn(∞)=T c (10)

[0113] T rn (x, b n + d n + R n )=T c (11)

[0114]

[0115] In formulas (9), (10), (11) and (12), R1 is half of the equivalent core fracture specimen thickness in the unetched area (m), R2 is half of the equivalent core fracture specimen thickness in the etched path (m), d1 is the thickness of the equivalent eddy current layer in the unetched area (m), d2 is the thickness of the equivalent eddy current layer in the etched path (m), and K f is the thermal conductivity of the experimental fluid (W / (m·K)), T c is the outer wall temperature of the core fracture sample (K), n = 1, 2;

[0116] Substituting equations (9), (10), (11) and (12) into equations (5), (6) and (8), the solution of the temperature of each layer is:

[0117]

[0118]

[0119]

[0120] In formulas (13), (14), and (15), K r is the thermal conductivity of the core fracture sample (W / (m·K)). From formula (15), we can know that in order to solve the convective heat transfer coefficient h n , we need to first solve the thickness d of the equivalent eddy current layer n

[0121] Thickness of the equivalent eddy current layer d n and crack opening a n The ratio of Reynolds number Re and roughness coefficient JRC n The relationship can be obtained through numerical simulation:

[0122]

[0123] In formula (16), i, j, and k are the coefficients of the fitting relationship, a1 is the crack opening of the unetched area (m), a2 is the crack opening of the etched path (m), JRC1 is the roughness coefficient of the unetched area, JRC2 is the roughness coefficient of the etched path, Re1 is the Reynolds number of the unetched area, Re2 is the Reynolds number of the unetched area, n = 1, 2; Reynolds number Re n The calculation formula is:

[0124]

[0125] In formula (17), μ is the kinematic viscosity of the experimental fluid (Pa·s).

[0126] To solve the experimental fluid velocity u in equation (17): n Based on Darcy's law and mass conservation, the experimental fluid flow rate u1 in the unetched area and the experimental fluid flow rate u2 in the etched passage have the following relationship:

[0127] uS=2u1y1a1+u2y2a2 (18)

[0128]

[0129] In formula (18), u is the average flow velocity of the fluid in the acid-etched fracture experiment (m / s), S is the cross-sectional area of ​​the acid-etched fracture (m 2 ), the average flow velocity u of the fluid in the acid-etched fracture experiment is:

[0130]

[0131] In formula (20), △t is the experimental time (s), m is the mass of the experimental fluid (kg); the calculation formula of the cross-sectional area S of the acid-etched crack is S = y2a2 + 2y1a1;

[0132] Substituting the calculation formula (16) of the equivalent eddy layer opening into formula (14), the analytical expression of the temperature distribution of the equivalent eddy layer is:

[0133]

[0134] T fn (L) = T2 Substitute into equation (15) to solve for the convective heat transfer coefficient h n .

[0135] After solving the temperature analytical formula of the two-dimensional slice, equation (15) and the convection heat transfer coefficient h n Substitute into equation (4) to solve Substituting equation (21) and the convective heat transfer coefficient h n Substitute into formula (3) to solve Finally, and Substituting into formula (1) can solve the convective heat transfer coefficient h of the acid-etched crack, and the calculation formula is as follows:

[0136]

[0137] As described above, the rock acid-etched fracture conduction heat transfer testing device and method of the present invention can study the convective heat transfer coefficient of the fluid in the fractured rock mass dissolved by acid liquid, which has guiding significance for the exploitation of deep geothermal resources.

[0138] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A rock acid-etched fracture flow conduction and heat exchange testing device, used for testing the flow conduction and heat exchange of a core fracture sample under acid-etching conditions, comprising a core fracture sample holder (2) for clamping the core fracture sample (1), a fluid filling assembly for filling the core fracture sample with fluid, and a pressure sensor group, wherein the pressure sensor group is used to measure the pressure of the fluid filled into the core fracture sample at the inlet and outlet of the core fracture sample, characterized in that: The testing device also includes a temperature sensor group, which includes an inlet temperature sensor (10), an outlet temperature sensor (11) and an outer wall temperature sensor (12), which are used to measure the temperatures of the liquid inlet, liquid outlet and outer wall of the core fracture sample (2) respectively.

2. The rock acid-etched fracture flow conduction and heat exchange testing device according to claim 1, characterized in that: The core fracture sample holder (2) comprises an inlet pipe (2-1), an outlet pipe (2-2), an outer pipe (2-3), an elastic heating sleeve (2-4) and a shell (2-6), and the core fracture sample (1) is placed in the elastic heating sleeve (2-4); The elastic heating sleeve (2-4) tightly wraps the core fracture sample (1) and is used to heat the outer wall of the core fracture sample (1); The detection ends of the inlet temperature sensor (10), the outlet temperature sensor (11) and the outer wall temperature sensor (12) are respectively fixed at the inlet, the outlet and the middle of the elastic heating sleeve (2-4), and are closely attached to the outer surface of the core fracture sample.

3. The rock acid-etched fracture flow conduction and heat exchange testing device according to claim 2, characterized in that: The fluid filling assembly comprises a piston container (3) and a pressurized fluid container (6), the piston container (3) comprises an inlet and an outlet, the inlet is connected to the pressurized fluid container (6), and the outlet is connected to the inlet pipe (2-1) of the core fracture sample holder (2); The piston container (3) comprises a plurality of piston spaces, each piston space comprising an inlet space and an outlet space separated by a piston, the inlet space being in communication with the inlet of the piston container (3), and the outlet space being in communication with the outlet of the piston container (3); At least one piston space is used to contain acid for etching the fissures of the rock fissure sample, and at least one piston space is used to contain experimental fluid for conducting a flow conduction and heat exchange test on the rock fissure sample.

4. A rock acid-etched fissure conduction and heat transfer testing method, used to test the conduction and heat transfer of a core fissure sample under acid etching to calculate the convection heat transfer coefficient of the fissure of the core fissure sample after acid etching, characterized in that: The steps include: S1. Obtain a point cloud image of the fracture surface of the core fracture sample before acid etching, and calculate the roughness coefficient JRC1 of the fracture surface of the core fracture sample before acid etching; S2. Construct the point cloud map of the crack surface with different roughness coefficients, and obtain the fitting relationship between the equivalent eddy current layer thickness d, the roughness coefficient JRC and the Reynolds number Re through numerical simulation; S3, acid-etching the fissures of the core fissure sample, and then performing a flow conduction and heat exchange experiment on the acid-etched core fissure sample; S4, obtaining a point cloud image of the fracture surface of the core fracture sample after acid etching, and calculating the roughness coefficient JRC2, the average width y2 of the acid etching path, and the average opening a2 of the acid etching path of the fracture surface of the core fracture sample after acid etching; S5. Calculate the convection heat transfer coefficient of the fissure of the core fissure sample after acid etching according to the following formula: Where h is the convective heat transfer coefficient of the fracture of the core fracture sample after acid etching, L is the length of the core fracture sample, y1 is the width of the unetched area, y2 is the width of the acid etching path, c f is the specific heat capacity of the experimental fluid, ρ f is the density of the experimental fluid, b1 is half of the laminar zone opening of the unetched area, u1 is the experimental fluid flow rate of the unetched area, b2 is half of the laminar zone opening of the etched passage, u2 is the experimental fluid flow rate of the etched passage, T1 and T2 are the inlet and outlet temperatures of the core fracture sample, respectively, K f is the thermal conductivity of the experimental fluid, T c is the outer wall temperature of the core fracture sample, h1 is the convective heat transfer coefficient of the unetched area, h2 is the convective heat transfer coefficient of the etched path, R1 is half of the equivalent core fracture sample thickness of the unetched area, R2 is half of the equivalent core fracture sample thickness of the etched path, d1 is the thickness of the equivalent eddy layer of the unetched area, d2 is the thickness of the equivalent eddy layer of the etched path, K f is the thermal conductivity of the experimental fluid.

5. The rock acid-etched fracture flow conduction and heat exchange testing method according to claim 4, characterized in that: The step S5 comprises: fn (L) = T2 and substitute it into the following formula to solve the convective heat transfer coefficient h n : Where n = 1 or 2, M is 6. The rock acid-etched fracture conduction and heat transfer testing method according to claim 5, characterized in that: Thickness of the equivalent eddy current layer d n and crack opening a n The ratio of Reynolds number Re and roughness coefficient JRC n The relationship is calculated by the following formula: Wherein, n is 1 or 2, i, j, k are the coefficients of the fitting relationship in the step S2, a1 is the crack opening of the unetched area, a2 is the crack opening of the etched path, JRC1 is the roughness coefficient of the unetched area, JRC2 is the roughness coefficient of the etched path, Re1 is the Reynolds number of the unetched area, and Re2 is the Reynolds number of the unetched area.

7. The rock acid-etched fracture conduction and heat transfer testing method according to claim 6, characterized in that: Reynolds number n The calculation formula is: Where μ is the kinematic viscosity of the experimental fluid and n is 1 or 2.

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