Physical simulation system and method for fracture network flow heat transfer interference under rock damage condition

Abstract

The invention discloses a physical simulation system and method for fracture network flow heat transfer interference under a rock damage condition, and relates to the technical field of rock mass mechanics and geothermal development. The method comprises the following steps: acquiring cubic rock of a deep high-temperature geothermal reservoir, fracturing and cutting a sample to form a crack, taking the rock with the crack as a detection sample, uniformly distributing pressure detection points in the crack, respectively distributing acoustic emission monitoring probes on the overlook surface and the front surface of the detection sample, heating the detection sample, injecting fluid, and detecting the pressure of the crack. Thermal interference data and acoustic emission monitoring results of the samples are obtained, the relative interference degree of inter-fracture seepage heat transfer is obtained based on the thermal interference data of the samples, main factors of inter-fracture seepage heat transfer interference formation and development are determined, and the influence of rock damage evolution on fracture flow heat transfer is obtained based on the acoustic emission monitoring results. According to the method, a basis is provided for optimizing deep geothermal reservoir fracturing transformation and dynamic mining evaluation.

Description

Technical Field

[0001] The present invention relates to the field of rock mechanics and geothermal development technology, and in particular to a physical simulation system and method for flow and heat transfer interference in a fracture network under rock damage conditions. Background Art

[0002] In deep geothermal development, interference in seepage heat transfer within a rock mass with multiple fractures directly impacts energy recovery efficiency. Existing experimental setups struggle to simultaneously simulate the seepage-heat transfer process under conditions of high geothermal temperatures (≤300°C), high geostresses (≤100 MPa), and multiple fractures. Furthermore, there is a lack of quantitative characterization methods for the degree of interference between fractures. Furthermore, traditional experiments are unable to monitor in real time the effects of fracture expansion and damage evolution on heat transfer.

[0003] Therefore, it is an urgent problem for those skilled in the art to provide a physical simulation system and method for flow and heat transfer interference in fracture networks under rock damage conditions to solve the difficulties existing in the prior art. Summary of the Invention

[0004] In view of this, the present invention provides a physical simulation system and method for flow and heat transfer interference in fracture networks under rock damage conditions, which can study the main controlling factors and their influencing laws of flow and heat transfer interference in multi-fracture systems, and thus provide a basis for optimizing deep geothermal reservoir fracturing transformation and dynamic mining evaluation.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A physical simulation system for flow and heat transfer interference in a fracture network under rock damage conditions, comprising a sample fixing module, a data acquisition module, an execution module, a communication module and a computer module;

[0007] A sample fixing module, used to fix the sample to be tested;

[0008] The data acquisition module has an input end connected to the output end of the sample fixing module and is used to collect test sample data;

[0009] An execution module, whose output terminal is connected to the input terminal of the sample fixing module, is used to execute corresponding operations;

[0010] The communication module has an output end connected to the input end of the execution module and an input end connected to the output end of the data acquisition module, for realizing data communication;

[0011] The computer module is in communication connection with the communication module and is used for analyzing the detection sample data and generating an execution signal.

[0012] Optionally, the sample fixing module includes an arc pad and two side rock plates, wherein the rock plates are sealed with epoxy resin glue.

[0013] Optionally, the data acquisition module includes a thin film pressure sensor, a temperature sensor and an acoustic emission receiver, which are used to collect sample pressure, temperature and acoustic emission monitoring results.

[0014] Optionally, the execution module includes a hydraulic cylinder, a heating control unit, a water injection unit and an acoustic emission monitoring probe, which are used to create a high-temperature and high-pressure environment for the sample and input fluid to determine the inter-slit flow interference characteristics.

[0015] A physical simulation method for flow and heat transfer interference in a fracture network under rock damage conditions, applied to any of the above-mentioned physical simulation systems for flow and heat transfer interference in a fracture network under rock damage conditions, comprises the following steps:

[0016] Sample acquisition steps: obtain cubic rocks from a deep, high-temperature geothermal reservoir, fracture and cut the samples to form cracks, and use the rocks with cracks as test samples;

[0017] Point layout steps: evenly distribute pressure detection points inside the crack, and place acoustic emission monitoring probes on the top and front surfaces of the test sample respectively;

[0018] Data acquisition step: heating the test sample and injecting fluid to obtain the thermal interference data and acoustic emission monitoring results of the sample;

[0019] Data analysis steps: Based on the thermal interference data of the samples, the relative interference degree of inter-fracture seepage heat transfer is obtained, the main factors for the formation and development of inter-fracture seepage heat transfer interference are determined, and based on the acoustic emission monitoring results, the influence of rock damage evolution on fracture flow heat transfer is obtained.

[0020] Optionally, the relative interference degree of the seepage heat transfer between the seams in the data analysis step is expressed as:

[0021]

[0022] Among them, RIF is the relative interference coefficient between the gaps; P d P is the heat output power of the inferior seam; a is the thermal output power of the dominant seam; q d and q a are the fluid flow rates at the outlet of the inferior / dominant seam respectively; T d and T a are the fluid temperatures at the outlet of the inferior / dominant seam respectively; C w is the specific heat capacity of the fluid; T in is the temperature of the fluid injected into the port.

[0023] It can be seen from the above technical solution that compared with the existing technology, the present invention provides a physical simulation system and method for flow and heat transfer interference in fracture networks under rock damage conditions, which has the following beneficial effects: 1) The present invention quantitatively analyzes the influence of fracture conductivity, rock plate thickness, damage degree and injection pressure on heat transfer interference through orthogonal experimental design, and reveals the damage evolution law based on acoustic emission monitoring; 2) The present invention can study the main controlling factors and influencing laws of flow and heat transfer interference in multi-fracture systems, and thus provide a basis for optimizing fracturing transformation and dynamic mining evaluation of deep geothermal reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0025] Figure 1 This is a block diagram of a physical simulation system for flow and heat transfer interference in a fracture network under rock damage conditions disclosed by the present invention;

[0026] Figure 2 This is a flow chart of a physical simulation method for flow and heat transfer interference in a fracture network under rock damage conditions disclosed by the present invention. DETAILED DESCRIPTION

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0028] Reference Figure 1 As shown, the present invention discloses a physical simulation system for flow and heat transfer interference in fracture networks under rock damage conditions, including a sample fixing module, a data acquisition module, an execution module, a communication module and a computer module;

[0029] A sample fixing module, used to fix the sample to be tested;

[0030] The data acquisition module has an input end connected to the output end of the sample fixing module and is used to collect test sample data;

[0031] An execution module, whose output terminal is connected to the input terminal of the sample fixing module, is used to execute corresponding operations;

[0032] The communication module has an output end connected to the input end of the execution module and an input end connected to the output end of the data acquisition module, for realizing data communication;

[0033] The computer module is in communication connection with the communication module and is used for analyzing the detection sample data and generating an execution signal.

[0034] Furthermore, the sample fixing module includes an arc pad and two side rock plates, wherein the rock plates are sealed with epoxy resin glue.

[0035] Furthermore, the data acquisition module includes a thin film pressure sensor, a temperature sensor and an acoustic emission receiver, which are used to collect sample pressure, temperature and acoustic emission monitoring results.

[0036] Furthermore, the execution module includes a hydraulic cylinder, a heating control unit, a water injection unit and an acoustic emission monitoring probe, which are used to create a high-temperature and high-pressure environment for the sample and input fluid to determine the inter-slit flow interference characteristics.

[0037] Specifically, the temperature of the test sample can be controlled to be heated to a maximum of 300°C, the pumping pressure can be adjusted within the range of 0 to 60 MPa, and the three-axis pressure can be adjusted within the range of 0 to 100 MPa to simulate the ground stress state. It is equipped with 32-channel real-time acoustic emission monitoring, and can collect signals with a frequency range of 60 to 400 kHz, which can meet the requirements of precise positioning of micro-fracture events.

[0038] A physical simulation method for flow and heat transfer interference in a fracture network under rock damage conditions, applied to a physical simulation system for flow and heat transfer interference in a fracture network under rock damage conditions as described above, with reference to Figure 2 As shown, the following steps are included:

[0039] Sample acquisition steps: obtain cubic rocks from deep high-temperature geothermal reservoirs, fracture and cut the samples to form cracks, and use the rocks with cracks as test samples;

[0040] Point layout steps: evenly distribute pressure detection points inside the crack, and place acoustic emission monitoring probes on the top and front surfaces of the test sample respectively;

[0041] Data acquisition step: heating the test sample and injecting fluid to obtain the thermal interference data and acoustic emission monitoring results of the sample;

[0042] Data analysis steps: Based on the thermal interference data of the samples, the relative interference degree of inter-fracture seepage heat transfer is obtained, the main factors for the formation and development of inter-fracture seepage heat transfer interference are determined, and based on the acoustic emission monitoring results, the influence of rock damage evolution on fracture flow heat transfer is obtained.

[0043] Furthermore, in the data acquisition step, obtaining the thermal interference data of the sample specifically includes the following steps:

[0044] Weigh the dry test sample, and weigh it again after saturating it with water to calculate the void content;

[0045] The sample is heated to 200°C and kept at this temperature for 0.5h to ensure that the test sample is heated evenly;

[0046] Inject water at a constant rate from both ends, monitor the pressure, and calculate the conductivity of the two fractures based on Darcy's law;

[0047] After saturating the damaged rock slab with water injection, single-hole injection and double-hole mining were used. The two cracks interfered with each other, and the pressure along the cracks, the fluid flow rate at the outlet, and the fluid temperature were monitored in real time until the outlet flow rate and temperature were stable and the experiment was terminated.

[0048] Fluid mixed with red ink was injected into the fractures to trace and analyze the fluid exchange between the superior and inferior fractures, and to study the correlation between the dry bond strength of the fluid flowing between the fractures and the degree of damage.

[0049] By changing the injection pressure and repeating the above steps with rock plates of different damage degrees and thicknesses, the effects of injection pressure, rock damage degree, rock plate thickness and other factors on the flow and heat transfer interference in fractures were studied.

[0050] Furthermore, obtaining the acoustic emission monitoring results specifically includes the following steps:

[0051] Sensor pasting: Paste the acoustic emission sensor on the prepared sample surface. The acoustic emission sensor usually uses a piezoelectric ceramic sensor with a frequency range of 60 to 400 kHz.

[0052] Sensor placement: Multiple sensors are evenly distributed on the rock surface to avoid interference from heat sources;

[0053] Signal acquisition: The acoustic emission signal is recorded through a preamplifier with a gain of 40 to 60 dB and an acquisition card with a sampling rate of ≥1 MHz;

[0054] Record acoustic emission parameters: record hit count, energy, amplitude, frequency, b value, etc.

[0055] Specifically, during the heating and heat exchange process of rocks, temperature changes cause local stress in rock mineral particles due to differences in thermal expansion coefficients, triggering micro-fractures and releasing elastic waves (acoustic emission signals). This principle can be used to analyze whether there is rock matrix damage in the dynamic seepage and heat exchange process between dominant and inferior fractures, leading to reservoir seepage and heat exchange.

[0056] Furthermore, the relative interference degree of seepage heat transfer between seams in the data analysis step is expressed as:

[0057]

[0058] Among them, RIF is the relative interference coefficient between the gaps; P d P is the heat output power of the inferior seam; a is the thermal output power of the dominant seam; q d and q a are the fluid flow rates at the outlet of the inferior / dominant seam respectively; T d and T a are the fluid temperatures at the outlet of the inferior / dominant seam respectively; C w is the specific heat capacity of the fluid; T in is the temperature of the fluid injected into the port.

[0059] In this embodiment, for the 300×300×300mm deep high temperature geothermal reservoir 3 A plate-shaped test specimen was prepared from a cubic fracturing specimen. When cutting the slab, the hydraulic fracture was retained as the dominant fracture. A second fracture, formed by cutting, was relatively flat and highly closed under confining pressure, serving as the inferior fracture. The longitudinal cross-sectional dimensions of the prepared physical model specimen were length × height = 300 mm × 100 mm, with the model width dependent on the thickness of the central slab. The slabs on both sides were fixed at 10 cm thick. One end of the slab had a single-port design, while the other had a double-port design. The two cracks on the single-port end were merged, while the two cracks on the double-port end were separated, facilitating independent and unified testing of the fracture properties. The test sample temperature was set at 200°C, and the three-dimensional confining pressures were set at 6 / 8 / 10 MPa. The thickness of the middle damaged rock plate is designed to have 4 levels (1.0, 2.0, 4.0, 6.0 cm); the damage degree of the middle rock plate is prefabricated to have 4 levels (damage factor D = 0.1, 0.2, 0.4, 0.6); the injection pressure is set to have 4 levels (2, 4, 6, 8 MPa), and 3 pressure monitoring points are evenly distributed along the length direction of each seam. 4 acoustic emission monitoring probes are arranged on the top and front surfaces of the test sample. This embodiment is a 3-factor 4-level experiment, so the L16 (43) orthogonal arrangement experiment is adopted. A total of 16 experiments are conducted to finally obtain the actual inferior / dominant seam outlet fluid flow rate q d and q a ; Fluid temperature at the outlet of inferior / advantageous seam T d and T a ; Real-time recording parameters of acoustic emission (AE).

[0060] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A physical simulation system for flow and heat transfer interference in fracture networks under rock damage conditions, characterized by: It includes a sample fixing module, a data acquisition module, an execution module, a communication module and a computer module; A sample fixing module, used to fix the sample to be tested; The data acquisition module has an input end connected to the output end of the sample fixing module and is used to collect test sample data; An execution module, whose output terminal is connected to the input terminal of the sample fixing module, is used to execute corresponding operations; The communication module has an output end connected to the input end of the execution module and an input end connected to the output end of the data acquisition module, for realizing data communication; The computer module is in communication connection with the communication module and is used for analyzing the detection sample data and generating an execution signal.

2. A physical simulation system for flow and heat transfer interference in fracture networks under rock damage conditions according to claim 1, characterized in that: The sample fixing module includes an arc pad and two side rock plates, wherein the rock plates are sealed with epoxy resin glue.

3. The physical simulation system for flow and heat transfer interference in fracture networks under rock damage conditions according to claim 1 is characterized in that: The data acquisition module includes a thin film pressure sensor, a temperature sensor and an acoustic emission receiver, which are used to collect sample pressure, temperature and acoustic emission monitoring results.

4. The physical simulation system for flow and heat transfer interference in fracture networks under rock damage conditions according to claim 1 is characterized in that: The execution module includes a hydraulic cylinder, a heating control unit, a water injection unit and an acoustic emission monitoring probe, which are used to create a high-temperature and high-pressure environment for the sample and inject fluid to determine the inter-slit flow interference characteristics.

5. A physical simulation method for flow and heat transfer interference in a fracture network under rock damage conditions, applied to a physical simulation system for flow and heat transfer interference in a fracture network under rock damage conditions as claimed in any one of claims 1 to 4, characterized in that: The following steps are involved: Sample acquisition steps: obtain cubic rocks from deep high-temperature geothermal reservoirs, fracture and cut the samples to form cracks, and use the rocks with cracks as test samples; Point layout steps: evenly distribute pressure detection points inside the crack, and place acoustic emission monitoring probes on the top and front surfaces of the test sample respectively; Data acquisition step: heating the test sample and injecting fluid to obtain the thermal interference data and acoustic emission monitoring results of the sample; Data analysis steps: Based on the thermal interference data of the samples, the relative interference degree of inter-fracture seepage heat transfer is obtained, the main factors for the formation and development of inter-fracture seepage heat transfer interference are determined, and based on the acoustic emission monitoring results, the influence of rock damage evolution on fracture flow heat transfer is obtained.

6. The physical simulation method for flow and heat transfer interference in fracture networks under rock damage conditions according to claim 5 is characterized in that: The relative interference degree of seepage heat transfer between seams in the data analysis step is expressed as: Among them, RIF is the relative interference coefficient between the gaps; P d P is the heat output power of the inferior seam; a is the thermal output power of the dominant seam; q d and q a are the fluid flow rates at the outlet of the inferior / dominant seam respectively; T d and T a are the fluid temperatures at the outlet of the inferior / dominant seam respectively; C w is the specific heat capacity of the fluid; T in is the temperature of the fluid injected into the port.

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