Experimental method for three-dimensional heat transfer characteristic of kg-grade rock core

Abstract

The invention provides a kg-level rock core three-dimensional heat transfer characteristic experiment method. The method comprises the following steps: S001, collecting kg-level shale in a test area through geological drilling; s002, a high-temperature strain gauge is fixed to the side wall of the kg-level shale; s003, kg-grade shale is put into a stress chamber, and high-temperature concrete is poured into the stress chamber for solidification and fixation; s004, transversely penetrating a fixed heating rod into the middle of the kg-level shale, and setting a temperature controller to detect the temperature of the heating rod; s005, a plurality of thermocouples are arranged in the directions of the upper side and the lower side of the heating rod in the kg-level shale at equal intervals; s006, electrically connecting leads of the heating rod, the temperature controller and the plurality of thermocouples with a plurality of signal ends of an electric control cabinet, and connecting the electric control cabinet with a computer signal; and S007, loading constant stress on the upper part of the kg-grade shale, heating the kg-grade shale, monitoring the temperatures of the thermocouples at different positions in real time, recording the temperatures of the heating rod and the thermocouples at different positions in the experiment process, and calculating the thermal conductivity of the kg-grade shale under different grading temperature conditions.

Description

Technical Field

[0001] The invention belongs to the technical field of in-situ exploitation of medium- and low-maturity shale oil, and specifically relates to a kg-level core three-dimensional heat transfer characteristic experimental method. Background Art

[0002] In recent years, for low-middle maturity shale oil, Sinopec has drilled 15 wells in Jiyang and Qianjiang, using horizontal wells + multi-stage volume fracturing technology, but has not obtained industrial oil flow; PetroChina has drilled many wells in Songliao, Ordos, Bohai Bay and other basins using existing technologies, but has not achieved commercial breakthroughs. Therefore, in order to explore the exploitation methods of low-middle maturity shale oil, the in-situ conversion technology of shale oil is proposed, which uses artificial electric heating to convert the unconverted organic matter into oil and gas resources. The thermal conductivity of rock refers to the energy passed per unit time when the temperature difference is 1℃ / m along the direction of heat flow transfer inside the rock when heat conduction occurs inside the rock, which indicates the size of the heat energy transfer capacity inside the rock. Therefore, by simulating the formation conditions and carrying out large-scale kg-level shale in-situ electrical heat conduction experiments, the measured parameters have practical engineering application value and can be truly used to guide the development of in-situ heating engineering of shale. At present, indoor experiments are still the most commonly used method to determine the thermal conductivity of rocks. Commonly used steady-state methods include guarded hot plate method (GHP), heat flow meter method (HFM), water flow plate method (WFP), and circular tube method; transient test methods include transient hot wire method (THW), transient hot zone method (THS), transient thermal bridge method (THB), transient thermal probe method (THP), transient plane heat source method (TPS), hot wire method (HWM), laser flash method (LFM), etc. The above are all conventional rock thermophysical parameter test schemes. The rock samples used are all mm-level, and stress loading cannot be performed on rock specimens. It is difficult to simulate the actual temperature and stress environment of rocks underground. Summary of the invention

[0003] In view of this, an object of the present invention is to provide a kg-level core three-dimensional heat transfer characteristics experimental method for overcoming the above problems or at least partially solving or alleviating the above problems.

[0004] The present invention proposes a kg-level core three-dimensional heat transfer characteristic experimental method, comprising the following steps:

[0005] S001: Collect kg-level shale as experimental samples through geological drilling in the test area;

[0006] S002: Fixing high temperature strain gauges on the side wall of kg-grade shale;

[0007] S003: Place kg-level shale into the stress chamber, and pour high-temperature concrete into the stress chamber for solidification and fixation;

[0008] S004: insert a fixed heating rod horizontally into the middle of the kg-grade shale, and set a temperature controller to detect the temperature of the heating rod;

[0009] S005: Multiple thermocouples are arranged equidistantly in the upper and lower sides of the heating rod in the kg-grade shale;

[0010] S006: electrically connect the leads of the heating rod, the temperature controller and multiple thermocouples to multiple signal terminals of the power control cabinet, and connect the power control cabinet to the computer signal;

[0011] S007: A constant stress is applied to the upper part of kg-grade shale by a hydraulic loader, and the heating rod is controlled by an empty electrical cabinet to heat the kg-grade shale. The temperature of thermocouples at different positions is monitored in real time. The temperature of the heating rod and thermocouples at different positions during the experiment is recorded by a computer, and the thermal conductivity of kg-grade shale under different graded temperature conditions is calculated.

[0012] Optionally, in step S003, the stress chamber is a cubic steel trough with an open upper end.

[0013] Optionally, in step S003, before pouring high-temperature concrete into the stress chamber, reserved holes are drilled on the side wall of the stress chamber according to the relative positions of the heating rod, the temperature controller and multiple thermocouples, and embedded pipes are respectively inserted into the reserved holes.

[0014] Optionally, in step S004, the embedded pipes at the heating rod position and the temperature controller position are taken out, and then heating holes and temperature control holes are drilled for kg-grade shale through the reserved holes, the heating rod is inserted into the heating hole and fixed, and the temperature controller is inserted into the temperature control hole and fixed.

[0015] Optionally, in step S005, the embedded pipes at the positions of the thermocouples are taken out, and then detection holes are drilled for the kg-grade shale through the reserved holes, and the thermocouples are inserted into the detection holes and fixed.

[0016] Optionally, in step S007, the temperatures of the heating rod and thermocouples at different positions during the experiment are recorded, the temperature data of the entire heat transfer process is extracted, the evolution law of the temperature recorded by each thermocouple over time is obtained, and the change law of the temperature gradient over time is obtained according to the actual position of the thermocouple. Finally, according to the steady-state heat transfer theory, the effective thermal conductivity between the relative positions of kg-level shale under different heating temperature conditions is calculated.

[0017] Beneficial effects of the present invention:

[0018] The three-dimensional heat transfer characteristic experimental method of kg-level core of the present invention simulates the ground stress condition corresponding to the buried depth of the reservoir by stress loading, so that it satisfies the heat transfer process of shale under in-situ stress conditions, monitors the temperature of thermocouples at different positions in real time through the power control cabinet, and controls the heating temperature of the heating rod by adjusting the output power. The temperature of the heating rod and the thermocouples at different positions during the experiment is displayed and recorded in real time by a computer. The temperature data collected during the entire heat transfer process is extracted, and the evolution law of the temperature recorded by each thermocouple over time can be obtained. At the same time, according to the actual position of the temperature sensor, the change law of the temperature gradient over time is obtained. Finally, according to the steady-state heat transfer theory, the effective thermal conductivity between the relative position distances in kg-level shale under different heating temperature conditions is calculated. The present invention breaks through the limitation of mm-level small specimens and cannot be stress loaded, can truly simulate the temperature and stress environment of the rock mass underground, and the measured rock thermal conductivity data has high reliability, which can be directly applied to the engineering practice of guiding the in-situ electrical heating of shale. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural diagram of the kg-level core three-dimensional heat transfer characteristics experimental method of the present invention;

[0020] Figure 2 It is a physical model of steady-state heat conduction of shale cylinder wall.

[0021] In the above figure: 1 high temperature strain gauge; 2 heating rod; 3 electric thermocouple; 4 high temperature concrete; 5 temperature controller; 6 kg grade shale; 7 pressure plate; 8 stress chamber; 9 control cabinet; 10 computer.

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. DETAILED DESCRIPTION

[0023] Now, an experiment is conducted according to an embodiment. Figure 1 ,

[0024] Step S001: Collect kg-level shale 6 as an experimental sample through geological drilling in the test area. The diameter of the rock sample is 100 mm and the length is 400 mm. The center point of the kg-level shale 6 is selected as the heating position. Six temperature detection positions are set at intervals of 60 mm on both sides of the upper and lower sides with the heating position as the center;

[0025] S002: A high temperature strain gauge 1 is fixed on the side wall of the kg-grade shale 6. The high temperature strain gauge 1 is arranged on the opposite side of the temperature detection position on the kg-grade shale 6 to measure strain, i.e., the tiny mechanical changes of the kg-grade shale 6 under the action of external force. The high temperature strain gauge 1 adopts a glass fiber substrate and can withstand high temperatures of 400-450°C.

[0026] S003: Place kg-grade shale 6 into the stress chamber 8, and pour high-temperature concrete 4 into the stress chamber 8 for solidification and fixation; first, place kg-grade shale 6 in the center of the stress chamber 8, and then slowly pour the pre-prepared high-temperature concrete 4 into the stress chamber 8, smooth the upper surface, so that the high-temperature concrete 4 tightly wraps the kg-grade shale 6 and is tightly consolidated with the stress chamber 8, and continuously waters and maintains for three weeks to ensure that the high-temperature concrete 4 does not crack; the high-temperature concrete 4 uses heat-resistant high-temperature concrete, and the maximum heat-resistant temperature is 1200°C.

[0027] S004: Insert the fixed heating rod 2 horizontally into the middle of the kg-grade shale 6, and set the temperature controller 5 to detect the temperature of the heating rod 2; drill the installation hole for the kg-grade shale 6 according to the selected heating position and temperature control position, insert the heating rod 2 into the installation hole at the heating position, insert the thermostat 5 into the hole at the temperature control position, seal the gap in the installation hole with high-temperature sealing material, and finally tighten it with bolts.

[0028] S005: Multiple thermocouples 3 are equidistantly arranged in the kg-grade shale 6 in the directions of the upper and lower sides of the heating rod 2; mounting holes are drilled in the kg-grade shale 6 according to the selected multiple temperature detection positions, and thermocouples 3 are respectively inserted into the mounting holes of the multiple temperature detection positions, and the gaps in each mounting hole are sealed by high-temperature sealing materials, and finally fastened with bolts.

[0029] S006: Electrically connect the leads of the heating rod 2, the temperature controller 5 and the multiple thermocouples 3 to the multiple signal terminals of the power control cabinet 9, and connect the power control cabinet 9 to the computer 10 signal; the power control cabinet 9 can be used to supply power and heat the heating rod 2, and the temperature of the heating rod 2 and the temperatures of multiple detection positions on the kg-grade shale 6 can be detected by the temperature controller 5 and the multiple thermocouples 3.

[0030] S007: A constant stress is applied to the upper part of the kg-grade shale 6 by the hydraulic loader 11, and the kg-grade shale 6 is heated by the heating rod 2. The temperature of the thermocouples 3 at different positions is monitored in real time. The temperature of the heating rod 2 and the thermocouples 3 at different positions during the experiment are recorded by the computer 10, and the thermal conductivity of the kg-grade shale under different graded temperature conditions is calculated. The purpose is to simulate the ground stress conditions corresponding to the reservoir burial depth so that it can meet the heat transfer process of the shale under the in-situ stress conditions. The experimental loading stress applies a load to the shale specimen according to the formation pressure at the sampling depth. The stress of the hydraulic loader 11 and the corresponding high-temperature strain gauge 1 are used to automatically collect data to obtain the stress-deformation relationship curve of the whole process;

[0031] Place a pressure plate 7 on the upper end of the kg-grade shale 6, and then use the hydraulic loader 11 to load constant stress. By adjusting the output power of the power control cabinet 9, first stabilize the temperature of the heating rod 2 at 200°C, and synchronously monitor the temperature change of thermocouples 3 at different distances over time. When the temperature of all thermocouples 3 stabilizes to a certain value, the steady-state heat transfer process is achieved, and the "temperature-time" data of different positions of the kg-grade shale 6 are obtained. Continue to heat up, set the temperature of the heating rod 2 to 300°C, and repeat the above experimental process. Subsequently, continue to set the temperature of the heating rod 2 to 400°C, 500°C, and 600°C (the temperature can be set according to the test conditions) to complete the graded heating test process. The thermal conductivity of the kg-grade shale 6 under stress and no stress conditions under different graded temperature conditions can be calculated.

[0032] Direct heating: Similarly, first adjust the output power of the power control cabinet 9 to stabilize the temperature of the heating rod 2 at 200°C, and simultaneously monitor the temperature change process of the thermocouple 3 at different distances over time. When the temperature of the thermocouple 3 stabilizes to a certain value, the steady-state heat transfer process is achieved, and the "temperature-time" data of the kg-level shale 6 at different positions is obtained. Then stop heating, cool the kg-level shale 6 to room temperature, and record the temperature data during the cooling process. Then set the temperature of the heating rod 2 to 300°C, 400°C, 500°C and 600°C in turn, repeat the heating and cooling process of the above experiment, and complete the direct heating test process at different temperatures. Calculate the thermal conductivity of the kg-level shale 6 under stress and no stress under different direct heating conditions.

[0033] In step S003, the stress chamber 8 is a cubic steel trough with an open top, a thickness of 20 mm, a width of 300 mm, and a height of 600 mm.

[0034] In step S003, before pouring high-temperature concrete 4 into the stress chamber 8, reserved holes are drilled on the side wall of the stress chamber 8 according to the relative positions of the heating rod 2, the temperature controller 5 and the plurality of thermocouples 3, and embedded pipes are respectively inserted into the reserved holes.

[0035] When pouring the high temperature concrete 4, the embedded pipe is taken out after the high temperature concrete 4 solidifies, and the embedded hole will be left at the embedded pipe, so the experimenter can avoid drilling holes on the high temperature concrete 4.

[0036] In step S004, the embedded pipes at the positions of the heating rod 2 and the temperature controller 5 are taken out, and then heating holes and temperature control holes are drilled in the kg-grade shale 6 through the reserved holes. The heating rod 2 is inserted into the heating hole and fixed, and the temperature controller 5 is inserted into the temperature control hole and fixed.

[0037] After the embedded pipe passes through the reserved hole, it is pressed against the side wall of the kg-grade shale 6. After the high-temperature concrete 4 solidifies, the embedded pipe is taken out, and then a heating hole and a temperature control hole are drilled on the side wall of the kg-grade shale 6 after passing through the reserved hole with an electric drill. Then, the heating rod 2 and the temperature controller 5 are respectively inserted into the heating hole and the temperature control hole, and then the heating hole, the temperature control hole and the gap in the reserved hole are sealed with a high-temperature sealing material, and finally fastened with bolts.

[0038] In step S005, the embedded pipes at the positions of the thermocouples 3 are taken out, and then detection holes are drilled into the kg-grade shale 6 through the reserved holes, and the thermocouples 3 are inserted into the detection holes and fixed.

[0039] After the embedded pipe passes through the reserved hole, it is pressed against the side wall of the kg-grade shale 6. After the high-temperature concrete 4 solidifies, the embedded pipe is taken out, and then an electric drill is used to drill a detection hole on the side wall of the kg-grade shale 6 after passing through the reserved hole. Then, the thermocouple 3 is inserted into the detection hole respectively, and then the gap between the detection hole and the reserved hole is sealed with a high-temperature sealing material, and finally fastened with bolts.

[0040] In step S007, the temperatures of the heating rod 2 and the thermocouples 3 at different positions during the experiment are recorded, the temperature data of the entire heat transfer process is extracted, the evolution law of the temperature recorded by each thermocouple 3 over time is obtained, and the change law of the temperature gradient over time is obtained according to the actual position of the thermocouple 3. Finally, according to the steady-state heat transfer theory, the effective thermal conductivity between the relative positions of the kg-level shale 6 under different heating temperature conditions is calculated.

[0041] The steady-state heat transfer calculation formula is as follows:

[0042] Based on the steady-state thermal conduction model of the cylinder wall and the stable temperatures at different positions in the shale specimen, the effective thermal conductivity of the shale at different temperatures is calculated.

[0043] exist Figure 2 In the equation, r1 is the radius of the heating rod; t1 is the measured surface temperature of the heating rod; t2 is the measured temperature of the shale at a distance of r2 from the center of the heating rod; and L is the length of the heating rod. In the steady-state heat conduction through the cylindrical wall model, the heat flux density at different radii is inversely proportional to the radius. However, the heat flux Φ through the entire cylindrical wall is a constant and does not vary with the radius. The cylindrical wall heat conduction model is:

[0044]

[0045] Where: Ф is the heat flux of the entire cylinder wall, that is, the output power of the heating rod at different temperatures t1, W; λ is the effective thermal conductivity, W / (m·k). Then the effective thermal conductivity λ in the shale r1~r2 region is:

[0046]

[0047] The effective thermal conductivity of shale at different temperatures can be calculated using the above formula.

[0048] By extracting the temperature data collected during the entire heat transfer process, the evolution law of the temperature recorded by each thermocouple 3 over time can be obtained. At the same time, according to the actual position of the thermocouple 3, the change law of the temperature gradient over time is obtained. Finally, according to the steady-state heat transfer theory, the "effective thermal conductivity" between the relative position distances within the kg-level shale 6 under different heating temperature conditions is calculated. The comprehensive "anisotropic heat transfer law and thermal parameters" can be directly applied to the engineering practice of in-situ electrical heating of shale.

[0049] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims. The components and structures not described in detail in this embodiment are well-known components and common structures or common means in the industry, and are not described here one by one.

Claims

1. A kg-level core three-dimensional heat transfer characteristics experimental method, characterized in that: The following steps are involved: S001: Collect kg-level shale (6) as experimental samples through geological drilling in the test area; S002: Fixing a high temperature strain gauge (1) on the side wall of kg-grade shale (6); S003: placing kg-level shale (6) into a stress chamber (8), and pouring high-temperature concrete (4) into the stress chamber (8) for solidification and fixation; S004: inserting a fixed heating rod (2) transversely into the middle of the kg-grade shale (6), and setting a temperature controller (5) to detect the temperature of the heating rod (2); S005: a plurality of thermocouples (3) are arranged at equal intervals in the upper and lower sides of the heating rod (2) in the kg-grade shale (6); S006: electrically connecting the leads of the heating rod (2), the temperature controller (5) and the plurality of thermocouples (3) to the plurality of signal terminals of the power control cabinet (9), and connecting the power control cabinet (9) to the computer (10) by signal; S007: A constant stress is applied to the upper part of the kg-grade shale (6) by a hydraulic loader (11), and the kg-grade shale (6) is heated by a heating rod (2). The temperature of the thermocouples (3) at different positions is monitored in real time. The temperature of the heating rod (2) and the thermocouples (3) at different positions during the experiment are recorded by a computer (10), and the thermal conductivity of the kg-grade shale under different graded temperature conditions is calculated.

2. The kg-level core three-dimensional heat transfer characteristics experimental method according to claim 1 is characterized in that: In step S003, the stress chamber (8) is a cubic steel trough with an open upper end.

3. The kg-level core three-dimensional heat transfer characteristics experimental method according to claim 1 is characterized in that: In step S003, before pouring high-temperature concrete (4) into the stress chamber (8), reserved holes are drilled on the side wall of the stress chamber (8) according to the relative positions of the heating rod (2), the temperature controller (5) and the plurality of thermocouples (3), and embedded pipes are respectively inserted into the reserved holes.

4. The kg-level core three-dimensional heat transfer characteristics experimental method according to claim 3 is characterized in that: In step S004, the embedded pipes at the positions of the heating rod (2) and the temperature controller (5) are taken out, and then the heating holes and temperature control holes are drilled into the kg-grade shale (6) through the reserved holes, the heating rod (2) is inserted into the heating hole and fixed, and the temperature controller (5) is inserted into the temperature control hole and fixed.

5. The kg-level core three-dimensional heat transfer characteristics experimental method according to claim 4 is characterized in that: In step S005, the embedded pipes at the positions of the respective thermocouples (3) are taken out, and then detection holes are drilled into the kg-grade shale (6) through the respective reserved holes, and the respective thermocouples (3) are inserted into the respective detection holes and fixed.

6. The kg-level core three-dimensional heat transfer characteristics experimental method according to claim 1 is characterized in that: In step S007, the temperatures of the heating rod (2) and the thermocouples (3) at different positions during the experiment are recorded, the temperature data of the entire heat transfer process is extracted, the evolution law of the temperature recorded by each thermocouple (3) over time is obtained, and the change law of the temperature gradient over time is obtained according to the actual position of the thermocouple (3). Finally, according to the steady-state heat transfer theory, the effective thermal conductivity between the relative positions of the kg-level shale (6) under different heating temperature conditions is calculated.

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