WO2017152473A1

WO2017152473A1 - System and method for testing thermophysical properties of rock under high pressure condition

Info

Publication number: WO2017152473A1
Application number: PCT/CN2016/079687
Authority: WO
Inventors: 杨小秋; 林为人; 多田井修; 徐子英; 施小斌
Original assignee: 中国科学院南海海洋研究所
Priority date: 2016-03-08
Filing date: 2016-04-19
Publication date: 2017-09-14
Also published as: CN105784756A; JP2018518686A; JP6473524B2; CN105784756B

Abstract

A system for testing thermophysical properties of rock under a high pressure condition, comprising two pressure resistant tanks (1, 2), a high-pressure pump (3), a temperature monitoring module (8), and a confining pressure monitoring module (9). The high-pressure pump (3) is connected to a first cavity (11) by means of a first connection pipe (5) on which a first bleeder valve (51) and a first pressure sensor (52) are mounted; a rock sample (4) is mounted in a second cavity (21); temperature sensors (61, 62, 63) are respectively mounted on the center and the outer surface of the rock sample (4) and in the second cavity (21); the first cavity (11) is connected to the second cavity (21) by means of a second connection pipe (7) on which a second bleeder valve (71) and a second pressure sensor (72) are mounted. Also disclosed is a method for testing thermophysical properties of rock under a high pressure condition. Without the use of an electrical heating heat source, the system and method can implement instantaneous loading of the rock sample (4) by quickly opening a second bleeder valve (71), and thermophysical property parameters of the rock sample (4) under a high pressure condition are obtained by means of an established finite element numerical inversion model and in combination with a global optimization method.

Description

Rock thermal property test system and method under high pressure conditions

Technical field

The invention relates to a rock thermal property testing system under high pressure conditions, and belongs to the technical field of rock thermal property testing.

Background technique

The thermal properties of the inner rock layer of the earth are the most basic physical parameters in the thermal structure, thermal evolution and geodynamics of the Earth. Under different temperature and pressure conditions, there are differences in thermal properties of rocks. Therefore, it is very important to carry out in-depth research on thermal properties of rock under different confining pressure conditions.

At present, the existing thermal property testing methods and systems for high-pressure conditions are assembled in a pressure-resistant tank by pre-assembling the thermal property test probe (including the heating source and the temperature sensor) with the rock sample. Start the pressure pump, add the pressure inside the pressure tank to the predetermined pressure, and maintain it for a period of time. After the temperature of the whole system reaches equilibrium, turn on the thermal property test system for electric heating, and monitor the internal temperature change of the rock to complete Thermal properties test under different confining pressure conditions.

The above existing test methods and systems must actively perform electrical heating (such as passing a constant current through the heating wire) as a "heat source" for transient thermal property testing. Therefore, the heating source and the temperature sensor must be placed inside the rock at the same time, making the test system relatively complicated. Moreover, the thermophysical parameter test has a particularly high temperature requirement for ambient temperature, and during the thermal property test under laboratory conditions, the test system is usually in direct contact with air, and it is difficult to test in a relatively constant temperature environment. Because the fluctuation of the ambient temperature is difficult to control, the test results are often greatly affected.

This test method and technique requires active electrical heating (such as passing a constant current through the heating wire) as a "heat source" for transient thermal properties testing.

Our experimental results show that the stress-temperature response coefficient (ΔT/Δσ) of common rock in the crust is relatively small (only 2~6mK/MPa), while the stress-temperature response coefficient of pressure transmitting medium (such as silicone oil) is as high as 138.74mK. /MPa, which is two orders of magnitude higher than the stress-temperature response coefficient of common rocks in the earth's crust. Therefore, after the confining pressure is instantaneously increased, there is a temperature difference between the rock sample and the pressure transmitting medium. Therefore, the present invention can obtain the thermal properties of rock samples under high pressure conditions by real-time monitoring of the temperature changes of the surface of the rock sample, the temperature of the central temperature and the pressure transmitting medium during the transient increase of the confining pressure in the pressure tank, combined with the finite element numerical inversion method. Parameters (thermal conductivity / thermal diffusivity / thermal diffusivitiy, and volumetric heat capacity).

Summary of the invention

In order to overcome the deficiencies of the prior art, one of the objects of the present invention is to provide a "heat source" that does not require electrical heating under high pressure conditions. The rock thermal property test system, which only places a temperature sensor in the center, surface and pressure medium of the rock sample, realizes the instantaneous loading of the rock sample by quickly opening the drain valve, and monitors the rock sample during the transient rise of the confining pressure. The temperature changes of the central and surface-level pressure-transfer media, using the established finite element numerical inversion model, combined with the global optimization method, can obtain the thermal property parameters of rock samples under high pressure conditions. Thus, the transient thermal property test of the "heat source" without electric heating is realized, which greatly simplifies the rock thermal property test system and its operating procedure under high pressure conditions.

In order to achieve the above object, the technical solution adopted by the present invention is:

A rock thermal property testing system under high pressure conditions, comprising two pressure tanks, a high pressure pump, a temperature monitoring module and a confining pressure monitoring module, wherein a first cavity and a second withstand voltage are formed in the first pressure tank Forming a second cavity in the tank, the first cavity and the second cavity are filled with a pressure transmitting medium, and the high pressure pump conveying the pressure transmitting medium to the first pressure tank passes through the first communication pipe and the first space a cavity is connected, a first drain valve and a first pressure sensor are mounted on the first communication pipe; a rock sample is installed in the second cavity, a center and an outer surface of the rock sample, and a second cavity a first temperature sensor, a second temperature sensor and a third temperature sensor are respectively installed in the pressure transmitting medium, and the first cavity and the second cavity are connected by a second communication pipe, and the second communication is a second drain valve and a second pressure sensor are mounted on the pipeline, the second cavity is also in communication with a third drain valve; the output ends of the first temperature sensor, the second temperature sensor, and the third temperature sensor are Temperature monitoring module Input terminal, the first pressure sensor and the output of the second pressure sensor are connected to an input of the confining pressure monitoring module.

The outer surface of the rock sample is provided with a rubber sleeve for encapsulating the rock sample, the upper and lower ends of which are sealed by a hard silicone.

The rock sample is cylindrical.

The pressure transmitting medium is silicone oil, and of course, it may be vegetable oil, deionized water or the like.

Another object of the present invention is to provide a rock thermal property test method under high pressure conditions without electric heating "heat source", which only places a temperature sensor in the center of the rock sample, the surface and the pressure medium in the second pressure-resistant irrigation. The instantaneous loading of the rock sample is realized by quickly opening the drain valve, and the temperature change of the pressure medium in the center and surface of the rock sample during the transient increase of the confining pressure is monitored, and the established finite element numerical inversion model is combined with the global optimization method. The thermal properties of the rock samples under high pressure conditions can be obtained. Thus, the transient thermal property test of the "heat source" without electric heating is realized, which greatly simplifies the rock thermal property test system and its operating procedure under high pressure conditions.

A rock thermal property testing method under high pressure conditions, comprising the following steps:

Step 1. The first temperature sensor and the second temperature sensor are placed on the center and the outer surface of the prepared cylindrical rock sample, and the rock sample is water-sealed by a rubber sleeve, and the hard silica gel is passed through the upper and lower ends of the rock sample. Sealed, Forming a rock sample assembly;

Step 2. The rock sample component and the third temperature sensor are placed in the second pressure tank, and the second pressure tank is filled with the pressure transmitting medium and then sealed, and the first drain valve and the first pressure sensor are installed. a communication pipe connecting the high pressure pump and the first pressure tank, connecting the second communication pipe with the second drain valve and the second pressure sensor to the first pressure tank and the second pressure tank, on the second pressure tank Installing a third drain valve, then connecting the first temperature sensor, the second temperature sensor, and the third temperature sensor to the temperature monitoring module, and connecting the first pressure sensor and the second pressure sensor to the confining pressure monitoring module to assemble the rock heat Physical property test system; open temperature monitoring module and confining pressure monitoring module to start temperature and confining pressure monitoring;

Step 3, only opening the first drain valve, closing the second drain valve and the third drain valve, opening the high pressure pump, raising the confining pressure in the first pressure tank to a predetermined pressure;

Step 4: Instant loading: When the whole set of rock thermal property testing system is in balance, the first drain valve is closed, the third drain valve is kept closed, and the second drain valve is quickly opened, thereby realizing instantaneous supercharging of the second pressure tank;

Step 5: According to the temperature change of the first temperature sensor, the second temperature sensor and the third temperature sensor monitored by the temperature monitoring module and the confining pressure change of the second pressure sensor monitored by the confining pressure monitoring module in real time, through the finite element numerical model, The thermal properties of the rock samples under arbitrary confining pressure were obtained by inversion.

The step 5 includes the following steps:

Step 51: taking a center of the cylindrical rock sample as a dot, and establishing a finite element numerical model based on the heat conduction differential equation in a cylindrical coordinate system formed by the radial and axial directions of the cylindrical rock sample;

Step 52: Let the thermal conductivity and volumetric heat capacity of the rock sample be λ and (ρc), respectively, and the thermal conductivity and volumetric heat capacity of the common rock in the crust are 0.5-6.0 W·m ^-1 ·K ^-1 , respectively. 0.5 × 10 ⁶ ~ 5.0 × 10 ⁶ J · m ^-3 · K ^-1 , for the solution area

In both parameters, λ and (ρc) are equally divided into m equal parts to obtain the initial (m+1)×(m+1) mesh nodes (λ _i ,(ρc) _j ), where i,j =1, 2, 3, ..., m;

Step 53: Input each mesh node (λ _i , (ρc) _j ) into the established finite element numerical model to monitor the temperature change T02(t) and pressure transmission of the rock sample surface in real time during rapid loading. The medium temperature change T03(t) is used as the boundary condition. When the simulation calculates (λ, (ρc)) = (λ _i , (ρc) _j ), the temperature change at the center of the rock sample is recorded as

Step 54: Calculating the finite element numerical model by using a least squares method

Linear fit to the temperature change T01(t) measured at the rock sample center:

Solving the fitted straight line slope K _i,j and the correlation coefficient R _i,j , wherein the correlation coefficient is calculated as follows

Step 55, defining an objective function is

F(λ _i ,(ρc) _j )=1.0-(R _i,j ) ² (4)

And solving the objective function value F(λ _i ,(ρc) _j ) at each grid point;

Where: n is the total number of samples, t _k is the time of the kth sampling, and T01(t _k ) is the temperature change collected by the first temperature sensor at the time t _k after the instantaneous loading, 1≤k≤n;

Step 56: Find a grid point with the smallest objective function value.

in case

ε is the threshold set to determine whether the solution requirement is met, then accept

The thermal conductivity and volumetric heat capacity (λ, (ρc)) of the rock sample required to be solved, otherwise

The centered neighborhood is the solution area, the grid is encrypted, and the process returns to step 53 until it is satisfied.

So far, the thermal conductivity and volumetric heat capacity of the rock sample are solved.

Step 57, finally according to the relationship between thermal conductivity λ, volumetric heat capacity (ρc) and thermal diffusivity κ

The thermal diffusivity of the rock sample was calculated.

In the step 51, the heat conduction differential equation under the cylindrical coordinate system is expressed as

Its initial condition is

T(r,z,0)=0, r≤r ₀ ,|z|≤z ₀₂ ) (7)

The boundary conditions are determined by the surface temperature change T02(t) of the sample and the temperature change T03(t) of the pressure medium monitored by the rock thermal property test system.

Where γ is the temperature response coefficient of the adiabatic stress change of various media, and A is due to the change of confining pressure

The heat source corresponding to the temperature change, r ₀ is the radius of the rock sample, z ₀₁ is the vertical distance from the top or bottom surface of the cylindrical rock sample to the cylindrical surface of the rock sample, and z ₀₂ is the top surface of the cylindrical rock sample component after packaging Or the vertical distance from the bottom surface to the cylindrical surface of the rock sample center.

The measured temperature change T01(t) of the rock sample center, the rock sample surface temperature change T02(t) and the pressure transfer medium temperature change T03(t) are the temperature difference between the measured temperature and the instantaneous loading at each moment, namely:

T01(t)=T ₁ (t)-T ₁ (0)

T02(t)=T ₂ (t)-T ₂ (0)

T03(t)=T ₃ (t)-T ₃ (0)

Where T ₁ (t), T ₂ (t), and T ₃ (t) are the measured temperatures of the first temperature sensor, the second temperature sensor, and the third temperature sensor at time t after the instantaneous loading, respectively, and are measured by step 5. , T ₁ (0), T ₂ (0), and T ₃ (0) are measured temperatures of the first temperature sensor, the second temperature sensor, and the third temperature sensor before the instantaneous loading, respectively, and are measured by the step 2. The confining pressure change is the same as the principle, that is, the difference between the measured value of the pressure sensor in step 5 and the measured value in step 2.

When the temperatures measured by the first temperature sensor, the second temperature sensor, and the third temperature sensor are both stable, the temperature of the entire set of rock thermal property testing systems is balanced.

The invention opens the valve between the two pressure-resistant tanks (the internal confining pressure is different, the rock sample is placed in the second pressure-resistant tank with a lower confining pressure), so that the second pressure-resistant tank with a lower confining pressure is The confining pressure instantly rises. Our experimental results show that the stress-temperature response coefficient (ΔT/Δσ) of common rocks in the crust is relatively small (only 2~6mK/MPa), while the pressure transmitting medium (such as silicone oil, vegetable oil, deionized water and other pressure transmitting media) The stress-temperature response coefficient is two orders of magnitude higher than the common rock in the crust (for example, the stress-temperature response coefficient of silicone oil is as high as 138.74 mK/MPa). Therefore, after the confining pressure is instantaneously increased, the temperature difference between the rock sample and the pressure transmitting medium is obtained. The real-time monitoring of the pressure of the Confining pressure, the center of the rock sample, the surface and the temperature change of the pressure medium in the second pressure-resistant medium, combined with the finite element numerical inversion method, can obtain the heat of the rock sample under high pressure conditions. Physical parameters (thermal conductivity / thermal diffusivity / thermal diffusivitiy, and volumetric heat capacity). The main advantage is that there is no need to electrically heat the “heat source”, and only one temperature sensor is placed in the center of the rock sample, the surface and the pressure medium in the second pressure-resistant filling, for monitoring the center of the rock sample during the transient rise of the confining pressure. The temperature variation of the pressure medium in the surface pressure-resistant second pressure-resistant medium can be obtained by using the finite element numerical inversion model and the global optimization method to obtain the thermal property parameters of the rock sample under high pressure conditions. Thus, the transient thermal property test of the "heat source" without electric heating is realized, which greatly simplifies the rock thermal property test system and its operating procedure under high pressure conditions.

DRAWINGS

1 is a schematic structural view of a temperature response test system for adiabatic stress variation of underwater rock according to the present invention;

Figure 2 is a finite element numerical model under a two-dimensional cylindrical coordinate system;

Figure 3 shows the temperature response curve during the transient loading of sandstone L28 in the Longmenshan fault zone;

Figure 4 shows the temperature response curve during the RJS transient loading of Rajasthan sandstone in India;

Figure 5 is a comparison of the measured results of the center temperature of the sandstone L28 rock sample in the Longmenshan fault zone with the finite element numerical model simulation results;

Figure 6 is a comparison of the measured results of the RJS rock sample center temperature and the finite element numerical model simulation results of the Rajasthan sandstone in India.

Wherein, 1, a first pressure tank; 11, a first cavity; 2, a second pressure tank; 21, a second cavity; 22, a third drain valve; 3, a high pressure pump; 4, a rock sample; , hard hard silicone; 42, hard silicone; 43, rubber sleeve; 5, first connecting pipe; 51, first drain valve; 52, first pressure sensor; 61, first temperature sensor; 62, second Temperature sensor; 63, third temperature sensor; 7, second communication pipe; 71, second drain valve; 72, second pressure sensor; 8, temperature monitoring module; 9, confining pressure monitoring module;

detailed description

The content of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

Example

Please refer to FIG. 1 , a rock thermal property test system under high pressure conditions, comprising two pressure tanks (first pressure tank 1 and second pressure tank 2 respectively), high pressure pump 3, temperature monitoring module. 8 and a confining pressure monitoring module 9, wherein a first cavity 11 (filled with a pressure transmitting medium, such as silicone oil, vegetable oil, deionized water, etc.) is formed in the first pressure tank 1, and a second pressure tank 2 is formed therein. a second cavity 21 (filled with a pressure transmitting medium), a high pressure pump 3 for conveying a pressure transmitting medium to the first pressure tank 1 is connected to the first cavity 11 through a first communication pipe 5, on the first communication pipe 5 A first drain valve 51 and a first pressure sensor 52 are mounted; a rock sample assembly is mounted in the second cavity 21 (the cylindrical rock sample assembly includes a cylindrical rock sample 4 and a center and a surface thereof are respectively disposed first The temperature sensor 61 and the second temperature sensor 62 then place the cylindrical upper hard silicone 41 and the lower hard silica gel 42 respectively and press them on the upper and lower sides of the cylindrical rock sample 4, and then the rubber sleeve 43 Hard silicone 41, cylindrical rock sample 4 and lower hard silicone 42 are wrapped A watertight package is realized, which is placed in the second cavity 21 disposed in the second pressure tank 2 after being packaged, and a third temperature sensor 63 is mounted in the second cavity 21, the first cavity 11 and the second cavity The cavities 21 are connected by a second communication conduit 7, A second drain valve 71 and a second pressure sensor 72 are mounted on the second communication conduit 7, and the second cavity 21 is further connected to a third drain valve 22; the first temperature sensor 61, the first The outputs of the two temperature sensors 62 and the third temperature sensor 63 are connected to the input end of the temperature monitoring module 8, and the temperature changes of the three temperature sensors are monitored in real time by the temperature monitoring module 8, the first pressure sensor 52 and the second pressure. The output end of the sensor 72 is connected to the input end of the confining pressure monitoring module 9, and the confining pressure change in the second pressure tank 2 is monitored in real time by the confining pressure monitoring module 9. The output of the temperature monitoring module 8 and the confining pressure monitoring module 9 is also connected to a processing module 10, and the temperature response coefficient of the adiabatic stress change of the rock sample can be calculated by the processing module 10. In addition, the processing module 10 can work on the high pressure pump 3. Control is performed. When the confining pressure monitoring module 9 detects that the confining pressure of the first pressure tank 1 reaches a predetermined pressure by the first pressure sensor 52, the high pressure pump 3 can be controlled to stop working by the processing module 10.

The invention relates to a method and a system for testing thermal properties of rocks under high pressure conditions. First, the high pressure pump 3 is used to raise the confining pressure in the first pressure tank 1 to a predetermined pressure (for example, 130 MPa), and after the temperature of the entire system reaches equilibrium, Then, the second drain valve 71 between the first pressure tank 1 and the second pressure tank 2 is manually opened quickly, so that the confining pressure in the second pressure tank 2 is instantaneously increased within 1 to 2 seconds due to the rock sample and The stress-dependent temperature response coefficients of pressure-transmitting media (such as silicone oil) differ by two orders of magnitude, so there is a temperature difference between the rock sample and the pressure-transmitting medium. By monitoring the temperature change of the center and surface of the rock sample during the transient increase of confining pressure and the pressure medium in the second pressure-resistant filling, the finite element numerical inversion model established by our combination and the global optimization method can be used to obtain the high pressure condition. Thermal properties of rock samples. Thus, the transient thermal property test of the "heat source" without electric heating is realized, which greatly simplifies the rock thermal property test system and its operating procedure under high pressure conditions.

The finite element numerical model and method for thermal property parameter inversion are as follows:

1) Heat conduction differential equation

Since the rock sample in the test system is prepared in a cylindrical shape, for convenience of calculation, the first temperature sensor 61 is located at the center of the rock sample, and the second temperature sensor 62 and the first temperature sensor 61 are located on the same radial circle of the rock sample. Therefore, the heat conduction differential equation under the corresponding cylindrical coordinate system (2drz) can be expressed as

Its initial condition is

T(r,z,0)=0, r≤25mm,|z|≤65mm), (11)

The boundary conditions are constrained by the sample surface temperature change T02(t) monitored by the test system and the pressure medium temperature change T03(t) as follows.

Where λ, ρc are the thermal conductivity and volumetric heat capacity of various media, respectively, and γ is the adiabatic pressure derivative of temperature of various media, A is Heat source term driven by change rate of confining pressure

According to this heat conduction differential equation, a finite element numerical model is established in the cylindrical coordinate system (2drz), as shown in Fig. 2.

Step 2. The thermal conductivity and volumetric heat capacity of the rock sample are λ, (ρc), respectively. The thermal conductivity and volumetric heat capacity of the common rock in the crust are respectively in the range of 0.5-6.0W·m ^-1 ·K ^{-1 .} 0.5×10 ⁶ ～5.0×10 ⁶ J·m ^-3 ·K ^-1 , in order to broaden the adaptability of the inversion method, the solution area of the thermal property parameter of the rock can be appropriately increased again.

Where λ, (ρc) are equally divided into m equal parts, the initial (m+1) × (m+1) mesh nodes (λ _i , (ρc) _j ) are obtained, where i, j=1 , 2, 3, ..., m;

Step 3, and input each grid node (λ _i , (ρc) _j ) into the established PT-FE finite element numerical model to monitor the temperature change of the surface of the rock sample obtained in real time during the fast loading process T02(t) And the temperature change T03(t) of the pressure transmitting medium (such as silicone oil) as the boundary condition (Fig. 2), and the temperature change at the center of the rock sample when the simulation calculates (λ, (ρc)) = (λ _i , (ρc) _j ) , as

Step 4: Calculating the above finite element numerical model by using the least squares method

Linear fit to the measured temperature change T01 at the rock sample center:

Step 5. Define the objective function as

F(λ _i ,(ρc) _j )=1.0-(R _i,j ) ² (16)

And solving the objective function value F(λ _i ,(ρc) _j ) at each grid point, i, j=1, 2, 3, ..., m;

Step 6. Find the grid point with the smallest objective function value.

in case

Accepted to determine if the threshold is set to meet the solution requirements)

The centered neighborhood is the solution area, encrypt the mesh, and return to step 3 until it is satisfied.

Step 7. Finally, according to the relationship between thermal conductivity, volumetric heat capacity and thermal diffusivity, κ = λ / (ρc), the thermal diffusivity of the rock sample can be calculated. At this point, the thermal property parameters of the rock under a confining pressure are solved.

The steps of the rock thermal property test method under the high pressure condition of the invention are as follows:

First step: The first temperature sensor 61 and the second temperature sensor 62 are placed on the center and outer surface of the prepared cylindrical rock sample 4, and the rock sample 4 is hermetically sealed with a rubber sleeve to form a rock sample assembly.

Second step: The rock sample assembly and the third temperature sensor 63 are placed in the second pressure tank 2 and sealed. At the same time, the first communication pipe 5 to which the first drain valve 51 and the first pressure sensor 52 are mounted is connected to the high pressure pump 3 and the first pressure tank 1, and the second drain valve 71 and the second pressure sensor 72 are installed. The communication pipe 7 connects the first pressure tank 1 and the second pressure tank 2, and the third pressure relief tank 2 is mounted with a third drain valve 22, and then the first temperature sensor 61, the second temperature sensor 62, and the third temperature The sensor 63 is connected to the temperature monitoring module 8, and connects the first pressure sensor 52 and the second pressure sensor 72 to the confining pressure monitoring module 9, thereby assembling to form a rock thermal property testing system; opening the temperature monitoring module 8 and the confining pressure monitoring module 9, Start temperature and confining pressure monitoring.

The third step: opening only the first drain valve 51, closing the second drain valve 71 and the third drain valve 22, opening the high pressure pump 3, and raising the confining pressure in the first pressure tank 1 to a predetermined pressure.

The fourth step: after 3 to 6 hours, the temperature of the whole system tends to be balanced, the first drain valve 51 is closed, and the third drain valve 22 is kept closed, and the second drain valve 71 is quickly opened, thereby realizing the second pressure tank. 2 instant boost.

Through the above operation, the instantaneous loading of rock samples, and the temperature and confining pressure changes in this process are monitored and recorded in real time, and the finite element numerical model and method of inversion of the above established thermal property parameters are used, that is, inversion Obtain the thermophysical parameters of the rock sample under a confining pressure.

It should be noted that the above is a thermal property test by means of instantaneous loading of the rock sample. In fact, after the fourth step, the third drain can be opened after the first drain valve 51 and the second drain valve 71 are closed. Valve 22, making the second resistant The instantaneous decompression of the pressure tank 2 can realize the instantaneous unloading, and the temperature and confining pressure changes before and after the instantaneous unloading can also invert the thermal property parameters of the rock sample under a certain confining pressure.

Figure 3 and Figure 4 show the temperature response curves of the Longmenshan fault zone sandstone L28 and the Indian Rajasthan sandstone RJS during transient loading. Table 1 shows the thermal property parameters obtained by testing the sandstone samples of L28 and RJS under the confining pressure of 15.31MPa and 13.61MPa respectively:

Table 1 Thermal property inversion results of the Longmenshan fault zone sandstone (L28) and the Indian Rajasthan sandstone (RJS)

The measured results of the center temperature of the L28 and RJS rock samples and the finite element numerical simulation results are shown in Figures 5 and 6. The method and system provided by the present invention can be used not only for testing the thermal property parameters of rocks under high pressure conditions, but also greatly simplifying The original test system and its operating procedures.

While the invention has been described by way of specific embodiments, the embodiments of the invention In addition, various modifications may be made to the invention without departing from the scope of the invention. Therefore, the invention is not limited to the specific embodiments disclosed, but all the embodiments falling within the scope of the appended claims.

Claims

A rock thermal property testing system under high pressure conditions, characterized in that it comprises two pressure tanks, a high pressure pump, a temperature monitoring module and a confining pressure monitoring module, wherein a first cavity is formed in the first pressure tank, a second cavity is formed in the second pressure tank, wherein the first cavity and the second cavity are filled with a pressure transmitting medium, and the high pressure pump that transmits the pressure transmitting medium to the first pressure tank passes through the first communication pipe. Connected to the first cavity, a first drain valve and a first pressure sensor are mounted on the first communication pipe; a rock sample is installed in the second cavity, a center and an outer surface of the rock sample, and a first temperature sensor, a second temperature sensor and a third temperature sensor are respectively installed in the pressure transmitting medium of the second cavity, and the first cavity and the second cavity are connected by a second communication pipe. a second drain pipe and a second pressure sensor are mounted on the second communication pipe, and the second cavity is further connected to a third drain valve; the first temperature sensor, the second temperature sensor, and the third temperature sensor Outputs are Monitoring module connected to the input, the first pressure sensor and the output of the second pressure sensor are connected to an input of the confining pressure monitoring module.
The rock thermal property testing system under high pressure conditions according to claim 1, wherein the outer surface of the rock sample is provided with a rubber sleeve for water-sealing the rock sample, and upper and lower ends of the rock sample. They are sealed by hard silicone.
The rock thermal property testing system under high pressure conditions according to claim 1, wherein the rock sample is cylindrical.
The rock thermal property testing system under high pressure conditions according to claim 1, wherein the pressure transmitting medium is silicone oil.
A method for testing thermal properties of rocks under high pressure conditions, characterized in that it comprises the following steps:

Step 1. The first temperature sensor and the second temperature sensor are placed on the center and the outer surface of the prepared cylindrical rock sample, and the rock sample is water-sealed by a rubber sleeve, and the hard silica gel is passed through the upper and lower ends of the rock sample. Sealing to form a rock sample assembly;

Step 2. The rock sample component and the third temperature sensor are placed in the second pressure tank, and the second pressure tank is filled with the pressure transmitting medium, and then the second pressure tank is sealed, and the first drain valve and the first drain valve are installed. a first communication pipe of the first pressure sensor is connected to the high pressure pump and the first pressure tank, and the second communication pipe with the second drain valve and the second pressure sensor is connected to the first pressure tank and the second pressure tank, a third drain valve is mounted on the second pressure tank, and then the first temperature sensor, the second temperature sensor, and the third temperature sensor are connected to the temperature monitoring module, and the first pressure sensor and the second pressure sensor are connected to the confining pressure monitoring module. , thereby assembling to form a rock thermal property test system; opening a temperature monitoring module and a confining pressure monitoring module to start temperature and confining pressure monitoring;

Step 3, only opening the first drain valve, closing the second drain valve and the third drain valve, opening the high pressure pump, raising the confining pressure in the first pressure tank to a predetermined pressure;

Step 4: Instant loading: When the whole set of rock thermal property testing system is in balance, the first drain valve is closed, the third drain valve is kept closed, and the second drain valve is quickly opened, thereby realizing instantaneous supercharging of the second pressure tank;

Step 5: According to the temperature change of the first temperature sensor, the second temperature sensor and the third temperature sensor monitored by the temperature monitoring module and the confining pressure change of the second pressure sensor monitored by the confining pressure monitoring module in real time, through the finite element numerical model, The thermal properties of the rock samples under arbitrary confining pressure were obtained by inversion.
The method for testing thermal properties of rock under high pressure conditions according to claim 5, wherein said step 5 comprises the following steps:

Step 51: taking a center of the cylindrical rock sample as a dot, and establishing a finite element numerical model based on the heat conduction differential equation in a cylindrical coordinate system formed by the radial and axial directions of the cylindrical rock sample;

Step 52: Let the thermal conductivity and volumetric heat capacity of the rock sample be λ and (ρc), respectively, and the thermal conductivity and volumetric heat capacity of the common rock in the crust are 0.5-6.0 W·m -1 ·K -1 , respectively. 0.5 × 10 6 ~ 5.0 × 10 6 J · m -3 · K -1 , for the solution area

In both parameters, λ and (ρc) are equally divided into m equal parts to obtain the initial (m+1)×(m+1) mesh nodes (λ i ,(ρc) j ), where i,j =1, 2, 3, ..., m;

Step 53: Input each mesh node (λ i , (ρc) j ) into the established finite element numerical model to monitor the temperature change T02(t) and pressure transmission of the rock sample surface in real time during rapid loading. The medium temperature change T03(t) is used as the boundary condition. When the simulation calculates (λ, (ρc)) = (λ i , (ρc) j ), the temperature change at the center of the rock sample is recorded as

Step 54: Calculating the finite element numerical model by using a least squares method
Linear fit to the measured temperature change T01(t) at the rock sample center:

Solving the fitted straight line slope K i,j and the correlation coefficient R i,j , wherein the correlation coefficient is calculated as follows

Where: n is the total number of samples, t k is the time of the kth sampling, and T01(t k ) is the temperature change collected by the first temperature sensor at the time t k after the instantaneous loading, 1≤k≤n;

Step 55, defining an objective function is

F(λ i ,(ρc) j )=1.0-(R i,j ) 2 (4)

And solving the objective function value F(λ i ,(ρc) j ) at each grid point;

Step 56: Find a grid point with the smallest objective function value.
in case
ε is the threshold set to determine whether the solution requirement is met, then accept
The thermal conductivity and volumetric heat capacity (λ, (ρc)) of the rock sample required to be solved, otherwise
The centered neighborhood is the solution area, the grid is encrypted, and the process returns to step 53 until it is satisfied.
So far, the thermal conductivity and volumetric heat capacity of the rock sample are solved.

Step 57, finally according to the relationship between thermal conductivity λ, volumetric heat capacity (ρc) and thermal diffusivity κ
The thermal diffusivity of the rock sample was calculated.
The method for testing thermal properties of rock under high pressure conditions according to claim 6, wherein in the step 51, the differential equation of heat conduction under the cylindrical coordinate system is expressed as

Its initial condition is

T(r,z,0)=0, r≤r 0 ,|z|≤z 02 ) (7)

The boundary conditions are determined by the surface temperature change T02(t) of the sample and the temperature change T03(t) of the pressure medium monitored by the rock thermal property test system.

Where γ is the temperature response coefficient of the adiabatic stress change of various media, and A is due to the change of confining pressure
The heat source corresponding to the temperature change, r 0 is the radius of the rock sample, z 01 is the vertical distance from the top or bottom surface of the cylindrical rock sample to the cylindrical surface of the rock sample, and z 02 is the top surface of the cylindrical rock sample component after packaging Or the vertical distance from the bottom surface to the cylindrical surface of the rock sample center.
The method for testing thermal properties of rock under high pressure conditions according to claim 7, characterized in that the measured temperature change T01(t) of the rock sample center, the surface temperature change of the rock sample T02(t) and the pressure change of the pressure medium T03 (t) and the rock sample is the temperature difference between the measured temperature and the instantaneous loading at each moment, namely:

T01(t)=T 1 (t)-T 1 (0)

T02(t)=T 2 (t)-T 2 (0)

T03(t)=T 3 (t)-T 3 (0)

Among them, T 1 (t)T, T 2 (t)T, and T 3 (t)T are the measured values of the first temperature sensor, the second temperature sensor, and the third temperature sensor respectively after the moment t loading. Temperature, measured by step 5, T 1 (0), T 2 (0), T 3 (0) are the measured temperatures of the first temperature sensor, the second temperature sensor and the third temperature sensor before the instantaneous loading, respectively. 2 measured.
The method for testing thermal properties of rock under high pressure conditions according to claim 5, wherein when the temperatures measured by the first temperature sensor, the second temperature sensor and the third temperature sensor are both stable, the temperature of the whole set of thermal properties of the rock is tested. Achieve balance.