CN117233198A - Method and system for testing convective heat transfer coefficient inside dry-heat rock cracks - Google Patents
Method and system for testing convective heat transfer coefficient inside dry-heat rock cracks Download PDFInfo
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Abstract
The invention discloses a method and a system for testing the internal convective heat transfer coefficient of a dry-heat rock fracture, wherein the method comprises the following steps: collecting a dry heat rock sample of a current area to be researched, and manufacturing an experimental rock sample with cracks; injecting a heating working medium into a crack of the experimental rock sample, heating the current experimental rock sample to a preset target temperature, and stopping heating when the temperature is uniform; measuring temperature change data of an outer wall surface of an experimental rock sample in a transient cooling process and temperature change data of a heating working medium inlet and outlet; and constructing a heat conduction positive problem model related to the current transient heat conduction process, and obtaining a heat convection coefficient by solving the positive problem model according to the outer wall surface temperature change data and the working medium inlet and outlet temperature change data. According to the method, on the premise of avoiding direct measurement of the temperature of the wall surface inside the crack, the accurate prediction of the heat convection performance of the smooth crack and the rough crack of the dry hot rock under the high-temperature and high-pressure environment is realized.
Description
Technical Field
The invention belongs to the technical field of development of hot dry rock, and particularly relates to a method and a system for testing the internal convective heat transfer coefficient of a hot dry rock crack.
Background
The dry hot rock is a hot rock mass buried at 3-10 km from the surface, the rock temperature is 150-650 ℃, water or steam is hardly contained in the rock stratum, and the porosity and permeability are extremely low. When the heat energy of the dry and hot rock is extracted, a reservoir with low permeability is usually transformed by technical means such as hydraulic fracturing, a heat exchange channel in the reservoir is constructed, and heat for power generation and other purposes is extracted from the reservoir by utilizing a heat collecting working medium. Therefore, the convection heat exchange coefficient of the heat collecting working medium in the dry heat rock cracks is tested, and the method is a basis for researching the flow heat exchange rule of the heat collecting working medium in the rock cracks.
At present, the temperature of the outer wall surface of a cylindrical rock sample and the fluid temperature at the inlet and outlet positions of a crack on the sample are measured under a steady state condition by constructing a high-temperature and high-pressure environment of dry-hot rock, and then the average convective heat transfer coefficient in the crack of the rock is obtained by utilizing Newton's law of cooling. Or the heat-flow-force coupling characteristic of water flowing through the granite single rough crack is utilized, namely: the average convective heat transfer coefficient of water flowing through the rough cracks is calculated by measuring the temperature of water at the inlet and outlet positions of the cracks and the temperature of the outer wall surface of the rock and then utilizing Newton's law of cooling and energy conservation relation. In the process of realizing the invention, the inventor finds that the two ways further need to measure the wall temperature in the accurate crack, and the corresponding average heat convection coefficient can be calculated, but the wall temperature in the rock crack is difficult to accurately measure aiming at the high-temperature and high-pressure environment where the dry-heated rock is positioned. In addition, in the prior art, the temperature of the wall surface in the rock crack is directly measured by using a thermocouple, and the convective heat transfer coefficient of supercritical carbon dioxide with severe physical property change in the crack is obtained by combining a numerical simulation method through a transient experiment, but the temperature measurement in a narrow space of the crack is measured by using the thermocouple in a high-temperature and high-pressure environment, so that the operation difficulty is high, the numerical simulation is combined, more assumption is made, and the error of the convective heat transfer coefficient finally obtained by calculation is larger.
Disclosure of Invention
In order to solve the above problems, the present invention provides a method for testing the convective heat transfer coefficient inside a dry-hot rock fracture, comprising: collecting a dry heat rock sample of a current area to be researched, and manufacturing an experimental rock sample with cracks; injecting a heating working medium into the crack of the experimental rock sample, heating the current experimental rock sample to a preset target temperature, and stopping heating when the temperature is uniform; measuring temperature change data of an outer wall surface of the experimental rock sample in a transient cooling process and temperature change data of a heating working medium inlet and outlet; and constructing a heat conduction positive problem model related to the current transient heat conduction process, and obtaining a convection heat transfer coefficient by solving the positive problem model according to the outer wall surface temperature change data and the working medium inlet and outlet temperature change data.
Preferably, in the process of making the experimental rock sample, it comprises: polishing the dry-heated rock sample to obtain a cylindrical sample or a plurality of cuboid samples with smooth and flat surfaces; the plurality of rectangular parallelepiped samples are configured as a first experimental rock sample having a smooth crack, or the cylindrical sample is configured as a second experimental rock sample having a rough crack, wherein the first experimental rock sample is formed by stacking two rectangular parallelepiped samples and a mica strip disposed between the two rectangular parallelepiped samples, and the second experimental rock sample is formed by performing a brazilian disk split test on the cylindrical sample.
Preferably, before heating the current laboratory rock sample to the preset target temperature, the method further comprises: a plurality of temperature measuring points are respectively configured for the outer wall surface of the experimental rock sample and the inlet and the outlet of the heat collecting working medium, wherein the outer wall surface is a first side surface and a second side surface which are symmetrical about the extending direction of the crack and are positioned on the side wall of the experimental rock sample, when the temperature measuring points are configured for the first side surface, a plurality of temperature measuring points are uniformly arranged on the intersecting line of the first side surface and a first plane, and the first plane is a plane which is perpendicular to the extending direction of the crack and intersects with the central axis of the experimental rock sample; and when the temperature measuring point is configured for the second side surface, setting the temperature measuring point at a midpoint on an intersection line of the second side surface and the first plane.
Preferably, the temperature uniformity state satisfies the following condition: each temperature measuring point on the experimental rock sample reaches the preset target temperature; the temperature difference between the temperature measuring points does not exceed a preset temperature difference threshold value; and the temperature change of each temperature measuring point does not exceed the preset temperature difference threshold value within the appointed time period.
Preferably, the experimental rock sample is heated by adopting an oil bath heating mode, the experimental rock sample has the same confining pressure as the heat collecting environment of the current area to be researched, and the confining pressure is kept stable by adjusting the oil bath pressure in real time.
Preferably, the method further comprises: measuring the thermal physical property parameter of the thermal working medium of the experimental rock sample in the transient cooling process, and obtaining the correlation between the thermal physical property parameter and the convective heat transfer coefficient; and designating a plurality of oil bath pressure parameters, and respectively obtaining the convective heat transfer coefficient and the thermal property parameter corresponding to each oil bath pressure parameter, thereby obtaining the correlation between the thermal property parameter and the convective heat transfer coefficient under different confining pressure conditions, and further obtaining the correlation between the confining pressure and the convective heat transfer coefficient.
Preferably, the heat conduction positive problem model is represented by the following expression:
wherein, the initial conditions are:
the adiabatic boundary conditions of the outer wall surface of the experimental rock sample are as follows:
the thermal insulation boundary conditions of the end face of the experimental rock sample are as follows:
the crack wall facing flow heat exchange boundary conditions of the experimental rock sample are as follows:
wherein ρ represents the density of the dry-hot rock sample, C P The specific heat capacity of the experimental rock sample is represented by T, the temperature of the central section of the experimental rock sample is represented by T, the time is represented by T, the heat conductivity coefficient is represented by k, x, y and z respectively represent the coordinates of each position on the central section of the experimental rock sample, T (x, y and T) represents the temperature of a certain position on the central section of the experimental rock sample at the T moment, T i The initial temperature of the experimental rock sample in the transient cooling process is represented by H, the height of a cuboid sample forming the experimental rock sample is represented by L, the length of the cuboid sample or a cylinder sample forming the experimental rock sample is represented by r, the radius of the cylinder sample forming the experimental rock sample is represented by H (T), the convective heat transfer coefficient is represented by T f,m And (t) represents the average temperature of the heat collecting working medium in the crack, wherein the average temperature of the heat collecting working medium is the arithmetic average value of the temperatures at the inlet and the outlet of the heat collecting working medium in the crack.
Preferably, in the step of calculating the convective heat transfer coefficient, it includes: selecting an initial variable to be solved and constructing an objective function; based on the initial value of the variable to be solved, solving the objective function according to the outer wall surface temperature change data and the working medium inlet and outlet temperature change data to obtain a target value; judging whether the target value meets the iteration termination condition, if yes, obtaining a final solution value, based on the final solution value, obtaining an estimated value of a variable to be solved corresponding to the current target value as the convection heat transfer coefficient, and if not, adjusting the search direction and the search step length, thereby determining a new solution value until the iteration termination condition is met.
Preferably, the objective function is expressed by the following expression:
wherein J (R) represents a target value, R represents a variable to be solved, T n,m,mea Representing the measured temperatures of M temperature measuring points of the end face of the experimental rock sample at N time points, T n,m,cal (R) represents a temperature obtained by solving the positive problem model using the estimated value of the variable R to be solved.
Preferably, in the process of adjusting the search direction and the search step length, the method includes: and constructing a sensitivity coefficient equation about the variable to be solved, calculating gradient values of conjugate coefficients and objective functions by using the sensitivity coefficient equation, and determining a search direction and a search step length according to the conjugate coefficients and the gradient values.
In another aspect, the present invention also provides a system for testing the convective heat transfer coefficient inside a dry-hot rock fracture, the system comprising: an experimental rock sample fixture for clamping and fixing an experimental rock sample with cracks, which is acquired from a dry hot rock sample in a current area to be studied and is manufactured; the heating device is used for injecting a heating working medium into the crack of the experimental rock sample, then heating the current experimental rock sample to a preset target temperature, and stopping heating when the temperature is uniform; the data acquisition device is connected with the heating device and is used for measuring the temperature change data of the outer wall surface of the experimental rock sample in the transient cooling process and the temperature change data of the inlet and outlet of the heating working medium in the crack; the data processing device is used for constructing a heat conduction positive problem model related to the current transient heat conduction process, and obtaining a heat convection coefficient by solving the positive problem model according to the outer wall surface temperature change data and the working medium inlet and outlet temperature change data.
Preferably, the heating device comprises a container formed by a heat insulation material and a heating element, and is used for heating and applying confining pressure to the experimental rock sample through a heating medium, wherein the experimental rock sample fixture is arranged in the container, the heating medium is filled between the experimental rock sample fixture and the outer wall of the container, and the heating medium is heat conducting oil.
Preferably, the heating device further comprises: a heating control unit for heating the experimental rock sample according to the preset target temperature; and a pressure-applying control unit for applying a confining pressure to the experimental rock sample according to a preset target confining pressure, wherein the pressure-applying control unit comprises a pressure control device, wherein the pressure control device is used for adjusting the pressure of the heating medium in the container when the experimental rock sample reaches the preset target confining pressure so that the current experimental rock sample keeps the confining pressure stable.
Preferably, the system further comprises: a plurality of temperature measuring units configured at the inlet of the heating working medium; a plurality of temperature measuring units configured at the outlet of the heating working medium; a plurality of temperature measuring units disposed on an outer wall surface of the experimental rock sample, wherein the plurality of temperature measuring units disposed on the outer wall surface include: the first side faces are symmetrical to the outer wall face in terms of the extending direction of the cracks and are positioned on one of the side walls of the experimental rock sample, and the first plane is a plane perpendicular to the extending direction of the cracks and intersecting with the central axis of the experimental rock sample; and the temperature measuring unit is arranged at the middle point on the intersection line of the second side surface and the first plane, and the second side surface is the other side surface which is symmetrical to the outer wall surface about the crack extending direction and is positioned on the side wall of the experimental rock sample.
Preferably, the system further comprises: the rock sample sleeve is used for wrapping an experimental rock sample fixture clamping an experimental rock sample, and the rock sample sleeve adopts a high-temperature-resistant silica gel sleeve or a red copper sleeve; and the cooling device is used for communicating with the heating device when the temperature of the experimental rock sample reaches the preset target temperature so as to cool the experimental rock sample.
Preferably, the plurality of temperature measuring units adopt T-shaped thermocouples, wherein the T-shaped thermocouples are led out from the inside of the experimental rock sample fixture and are connected with the data acquisition device.
One or more embodiments of the above-described solution may have the following advantages or benefits compared to the prior art:
the invention provides a method and a system for testing the internal convective heat transfer coefficient of a dry-heat rock fracture. The method is characterized in that a transient heat collection experiment is carried out on an experimental rock sample from a current area to be researched, and the temperature of the outer wall surface of the experimental rock sample is measured. Thereafter, a thermal conductivity positive problem model is constructed for the current transient thermal conductivity process. And finally, solving a heat conduction positive problem model by utilizing the measured temperature data and combining a data processing method of a heat conduction inverse problem to obtain a heat convection coefficient. According to the method, on the premise of avoiding direct measurement of the temperature of the wall surface inside the crack, the accurate prediction of the heat convection performance of the smooth crack and the rough crack of the dry hot rock under the high-temperature and high-pressure environment is realized. Meanwhile, the invention also realizes that the correlation between the convective heat transfer coefficient in the rock crack and the thermal physical property of the heat collecting working medium is obtained through one transient experiment under the confining pressure condition corresponding to the current transient experiment.
Additional features and advantages of the application will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the application. The objectives and other advantages of the application will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Drawings
The accompanying drawings are included to provide a further understanding of the application, and are incorporated in and constitute a part of this specification, illustrate the application and together with the embodiments of the application, serve to explain the application, without limitation to the application. In the drawings:
fig. 1 is a step diagram of a method for testing the convective heat transfer coefficient inside a dry-heat rock fracture according to an embodiment of the present application.
Fig. 2 is a schematic diagram of a thermal conductivity positive problem model of a method for testing convective heat transfer coefficients inside a dry thermal rock fracture according to an embodiment of the present application.
Fig. 3 is a schematic diagram of a correlation between a convective heat transfer coefficient and a flow rate of a thermal recovery medium according to a method for testing a convective heat transfer coefficient in a dry-thermal rock fracture according to an embodiment of the present application.
FIG. 4 is a schematic diagram of a system for testing the convective heat transfer coefficient inside a dry-thermal rock fracture according to an embodiment of the present application.
Fig. 5 is a diagram illustrating an exemplary distribution of temperature measurement units on a first experimental rock sample of a system for testing convective heat transfer coefficients inside a dry-thermal rock fracture according to an embodiment of the present application.
Fig. 6 is a diagram showing an exemplary distribution of temperature measuring units on a second experimental rock sample of the system for testing convective heat transfer coefficients inside a dry-heat rock fracture according to an embodiment of the present application.
In the present application, all of the figures are schematic drawings which are intended to illustrate the principles of the application only and are not to scale.
Wherein the list of reference numerals is as follows:
100: experimental rock sample fixture
101: rock sample sleeve
102: crack of experimental rock sample
200: heating device
201: thermal insulation cotton
202: annular heating belt
203: heating control unit
204: pressure application control unit
205: main way ball valve
206: bypass ball valve
207: back pressure valve
208: plunger pump
209: flowmeter for measuring flow rate
300: data acquisition device
400: cooling device
401: cooling circulation pump
402: heat exchanger
500: gas cylinders or tanks
600: liquid storage tank
700: pressure stabilizing tank
Detailed Description
The following will describe embodiments of the present application in detail with reference to the drawings and examples, thereby solving the technical problems by applying technical means to the present application, and realizing the technical effects can be fully understood and implemented accordingly. It should be noted that, as long as no conflict is formed, each embodiment of the present application and each feature of each embodiment may be combined with each other, and the formed technical solutions are all within the protection scope of the present application.
Additionally, the steps illustrated in the flowcharts of the figures may be performed in a computer system such as a set of computer executable instructions, and although a logical order is illustrated in the flowcharts, in some cases the steps illustrated or described may be performed in an order other than that herein.
The dry hot rock is a hot rock mass buried at 3-10 km from the surface, the rock temperature is 150-650 ℃, water or steam is hardly contained in the rock stratum, and the porosity and permeability are extremely low. When the heat energy of the dry and hot rock is extracted, a reservoir with low permeability is usually transformed by technical means such as hydraulic fracturing, a heat exchange channel in the reservoir is constructed, and heat for power generation and other purposes is extracted from the reservoir by utilizing a heat collecting working medium. Therefore, the convection heat exchange coefficient of the heat collecting working medium in the dry heat rock cracks is tested, and the method is a basis for researching the flow heat exchange rule of the heat collecting working medium in the rock cracks.
At present, the temperature of the outer wall surface of a cylindrical rock sample and the fluid temperature at the inlet and outlet positions of a crack on the sample are measured under a steady state condition by constructing a high-temperature and high-pressure environment of dry-hot rock, and then the average convective heat transfer coefficient in the crack of the rock is obtained by utilizing Newton's law of cooling. Or the heat-flow-force coupling characteristic of water flowing through the granite single rough crack is utilized, namely: the average convective heat transfer coefficient of water flowing through the rough cracks is calculated by measuring the temperature of water at the inlet and outlet positions of the cracks and the temperature of the outer wall surface of the rock and then utilizing Newton's law of cooling and energy conservation relation. In the process of realizing the invention, the inventor finds that the two ways further need to measure the wall temperature in the accurate crack, and the corresponding average heat convection coefficient can be calculated, but the wall temperature in the rock crack is difficult to accurately measure aiming at the high-temperature and high-pressure environment where the dry-heated rock is positioned. In addition, in the prior art, the temperature of the wall surface in the rock crack is directly measured by using a thermocouple, and the convective heat transfer coefficient of supercritical carbon dioxide with severe physical property change in the crack is obtained by combining a numerical simulation method through a transient experiment, but the temperature measurement in a narrow space of the crack is measured by using the thermocouple in a high-temperature and high-pressure environment, so that the operation difficulty is high, the numerical simulation is combined, more assumption is made, and the error of the convective heat transfer coefficient finally obtained by calculation is larger.
Therefore, in order to solve the above problems, the embodiment of the invention provides a method for testing the convective heat transfer coefficient inside a dry-hot rock fracture. According to the method, a transient heat collection experiment is carried out on an experimental rock sample from a current area to be researched, the temperature of the outer wall surface of the experimental rock sample is measured, then a heat conduction positive problem model related to a current transient heat conduction process is constructed, and finally, the heat conduction positive problem model is solved by utilizing measured temperature data and combining a data processing method of a heat conduction inverse problem, so that a convection heat exchange coefficient is obtained. The method realizes the accurate prediction of the convective heat transfer performance of the smooth crack and the rough crack of the dry hot rock under the high-temperature and high-pressure environment under the premise of avoiding the direct measurement of the temperature of the wall surface inside the crack. Meanwhile, the invention also realizes that the correlation between the convective heat transfer coefficient in the rock crack and the thermal physical property of the heat collecting working medium is obtained through one transient experiment under the confining pressure condition corresponding to the current transient experiment. In addition, the invention provides basic parameters for the system design and the operation regulation of the system of the hot extraction of the hot dry rock by realizing the test of the convection heat exchange coefficient of the heat-collecting working medium in the hot dry rock crack. The invention has important significance for the development and utilization of deep geothermal resources.
Example 1
Fig. 1 is a step diagram of a method for testing the convective heat transfer coefficient inside a dry-heat rock fracture according to an embodiment of the present application. The individual steps of the method are described below with reference to fig. 1 and.
As shown in fig. 1, in step S110, a dry heat rock sample of a current region to be studied is collected, and an experimental rock sample having a crack is produced. In the embodiment of the application, aiming at a dry hot rock reservoir of a current area to be researched, a dry hot rock sample collected at a field open-air position or a downhole position is used as a dry hot rock sample, and then an experimental rock sample with cracks is manufactured by using the currently collected dry hot rock sample.
Next, a method for producing an experimental rock sample in the embodiment of the present application will be described in detail. First, the dry-hot rock sample collected in step S110 is subjected to polishing treatment, so that the current dry-hot rock sample is processed into a sample with a regular shape and a smooth and flat surface, namely: the method comprises the steps of polishing a current dry-heated rock sample into a cylindrical sample or a plurality of cuboid samples with smooth and flat surfaces, wherein the sizes of all the cuboid samples are the same, the length of each cuboid sample is recorded as L, the width is recorded as D, the height is recorded as H, the sizes of the cuboid samples meet L/D not less than 1, D/H not less than 2, the lengths of the cylindrical samples are recorded as L, the diameters are recorded as D, and the sizes of the cylindrical samples meet L/D not less than 1.
A plurality of rectangular parallelepiped samples were used to make experimental rock samples with smooth cracks, and cylindrical samples were used to make experimental rock samples with rough cracks. The present embodiment constructs a plurality of rectangular parallelepiped samples as a first experimental rock sample having a smooth crack, which is formed by stacking two rectangular parallelepiped samples and a mica strip arranged between the two rectangular parallelepiped samples, or constructs a cylindrical sample as a second experimental rock sample having a rough crack, which is formed by performing a brazilian disk split test on the cylindrical sample. Specifically, the cuboid sample is suitable for a smooth crack flow-guiding heat exchange experiment. In the process of manufacturing the first experimental rock sample, the smooth crack on the first experimental rock sample is formed by stacking two cuboid samples with smooth and flat cut surfaces and mica strips arranged between the two cuboid samples, wherein the cut surfaces are planes comprising two long and wide edges in the cuboid samples, and the mica strips are arranged at the edges of the cut surfaces. Thus, two rectangular parallelepiped samples were stacked with mica strips at the edges of the cut surface, i.e., to form a smooth fracture with a certain opening, whereby a first experimental rock sample was obtained. The cylindrical sample is suitable for the rough crack flow-guiding heat exchange experiment. In the process of manufacturing the second experimental rock sample, rough cracks on the second experimental rock sample were formed based on the brazilian disk split test. The cylindrical sample was placed between two bending splints of a tester for carrying out a brazilian disk split test, so that the load of the tester acted on the cylindrical sample through 2 wire filler strips attached to the upper and lower ends of the cylindrical sample, thereby forming a rock crack having a rough surface and a certain tortuosity on the cylindrical sample, thereby obtaining a second experimental rock sample.
In another embodiment of the application, the cylindrical sample is also used to make an experimental rock sample with smooth fissures using the bottom surface of the cylindrical sample as a cut surface in a similar manner as the experimental rock sample constructed with respect to the rectangular parallelepiped sample. The method for manufacturing the experimental rock sample with the smooth fracture is not particularly limited, and can be selected by a person skilled in the art according to actual processing conditions.
After the experimental rock sample is manufactured, in step S120, a heating medium is injected into a crack of the experimental rock sample, and then the current experimental rock sample is heated to a preset target temperature and stops heating when a temperature uniformity state is reached. The application tests the convection heat transfer coefficient inside the dry heat rock cracks by exploring the flow heat transfer characteristics in the heat collecting working medium cracks. Specifically, the heat collecting working medium is injected into the crack of the experimental rock sample, after the injection is finished, the experimental rock sample and the heat collecting working medium in the experimental rock sample are heated to a preset target temperature to simulate the high-temperature environment of the dry hot rock in the reservoir, and when the temperature of the current experimental rock sample reaches the preset target temperature and is in a uniform temperature state, the heating is stopped. In the embodiment of the application, after the injection of the heat collecting working medium is finished, the heat collecting working medium does not flow any more until the transient cooling process is started, and the heat collecting working medium starts to flow.
Furthermore, the experimental rock sample is heated in an oil bath heating mode, the experimental rock sample has the confining pressure the same as the heat collecting environment of the current area to be researched, and the confining pressure is kept stable by adjusting the oil bath pressure in real time. Specifically, the experimental rock sample is heated through the oil bath, a certain confining pressure is applied to the experimental rock sample, and the oil bath pressure is adjusted in real time in the heating process, so that the oil bath pressure is always kept at a set pressure threshold value, and stable confining pressure is obtained.
Before the experimental rock sample is heated to the preset target temperature, the application also provides a plurality of temperature measuring points for measuring the temperature state change of the experimental rock sample for the outer wall surface of the experimental rock sample (the first experimental rock sample or the second experimental rock sample) and the inlet and outlet positions of the heat collecting working medium, wherein the outer wall surface is a first side surface and a second side surface which are symmetrical about the extending direction of the crack and are positioned on the outer side wall surface of the experimental rock sample. A plane perpendicular to the extending direction of the crack and intersecting with the central axis of the experimental rock sample is recorded as a first plane, and when the temperature measuring points are configured for the first side surface, a plurality of temperature measuring points are uniformly arranged on the intersecting line of the first side surface and the first plane according to preset intervals; when the temperature measuring point is configured for the second side surface, the temperature measuring point is arranged at the midpoint on the intersection line of the second side surface and the first plane. In the embodiment of the application, the temperature measuring points arranged at the inlet and outlet positions of the heat collecting working medium in the crack on the experimental rock sample are used for measuring the fluid temperature of the heat collecting working medium in real time.
In the embodiment of the application, the temperature uniformity state satisfies the following conditions: each temperature measuring point positioned on the outer wall surface of the experimental rock sample and at the inlet and outlet positions of the heat collecting working medium reaches a preset target temperature, the temperature difference between the temperature measuring points does not exceed a preset temperature difference threshold value, and the temperature change of each temperature measuring point does not exceed the preset temperature difference threshold value in a specified time period. In a specific embodiment of the application, each temperature measuring point on the experimental rock sample reaches a preset target temperature, the temperature difference between the temperature measuring points does not exceed a preset temperature difference threshold value of 0.2 ℃, and the temperature state when the temperature change of each temperature measuring point per se does not exceed the preset temperature difference threshold value of 0.2 ℃ within 20min is taken as a temperature uniformity state.
Further, in step S130, the temperature change data of the outer wall surface of the experimental rock sample during transient cooling and the temperature change data of the inlet and outlet of the heating working medium are measured. After the current experimental rock sample reaches a temperature uniform state, the flow and pressure of the heat collecting working medium flowing through the crack in the transient cooling process are adjusted, so that the heat collecting working medium in the crack can flow stably according to the adjusted flow and pressure after the transient cooling process starts. And then, measuring the temperature change data of the outer wall surface of the experimental rock sample in the transient cooling process and the temperature change data of the inlet and outlet positions of the heating working medium according to the transient cooling process of the experimental rock sample.
After obtaining the corresponding temperature change data of the experimental rock sample, in step S140, a heat conduction positive problem model related to the current transient heat conduction process is constructed, and the convective heat transfer coefficient is obtained by solving the positive problem model according to the temperature change data of the outer wall surface and the temperature change data of the inlet and outlet of the working medium. The heat conduction positive problem model is determined by establishing an energy control equation and a solution condition of a transient cooling process of a cuboid sample or a cylinder sample. Fig. 2 is a schematic diagram of a thermal conductivity positive problem model of a method for testing convective heat transfer coefficients inside a dry thermal rock fracture according to an embodiment of the present application. In a specific embodiment of the application, a heat conduction positive problem model is determined through a two-dimensional section (refer to fig. 2) positioned at the center of a cuboid sample, and a convective heat transfer coefficient is obtained by solving the positive problem model according to temperature change data of the outer wall surface and temperature change data of a working medium inlet and outlet of an experimental rock sample made of the cuboid sample.
Specifically, the heat conduction positive problem model is expressed by the following expression:
wherein, the initial conditions are:
the adiabatic boundary conditions of the outer wall surface of the experimental rock sample are as follows:
the thermal insulation boundary conditions of the end face of the experimental rock sample are as follows:
the crack wall facing flow heat exchange boundary conditions of the experimental rock sample are as follows:
Wherein ρ represents the density of the dry-hot rock sample, C P The specific heat capacity of the experimental rock sample is represented by T, the temperature of the central section of the experimental rock sample is represented by T, the time is represented by T, the heat conductivity coefficient is represented by k, x, y and z respectively represent the coordinates of each position on the central section of the experimental rock sample, T (x, y and T) represents the temperature of a certain position on the central section of the experimental rock sample at the T moment, T i The initial temperature of the experimental rock sample in the transient cooling process is represented by H, the height of a cuboid sample forming the experimental rock sample is represented by L, the length of the cuboid sample or a cylinder sample forming the experimental rock sample is represented by r, the radius of the cylinder sample forming the experimental rock sample is represented by H (T), the convective heat transfer coefficient is represented by T f,m And (t) represents the average temperature of the heat collecting working medium in the crack, wherein the average temperature of the heat collecting working medium is the arithmetic average value of the temperatures at the inlet and the outlet of the heat collecting working medium in the crack.
Further, in this example, the dimensions of a rectangular or cylindrical sample used to make an experimental rock sample were measured a plurality of times using a vernier caliper, and the sample dimensions were determined by taking an average value. The sample mass was then measured using an analytical balance. Finally, the density of the current sample is calculated according to the quality and the size of the sample. In addition, the embodiment also adopts a differential scanning calorimeter to measure the specific heat capacity of the sample at different temperatures in real time, adopts a thermal parameter analyzer to measure the heat conductivity coefficient of the sample at different temperatures in real time, and finally fits the measured data of the specific heat capacity and the heat conductivity coefficient into a relational expression related to temperature, so that the heat conduction positive problem model is solved according to the corresponding relational expression by combining the outer wall surface temperature change data and the working medium inlet and outlet temperature change data measured in the step S130.
When solving the heat conduction positive problem model, firstly, selecting an initial variable to be solved and constructing an objective function; and then, solving an objective function based on the initial value of the variable to be solved according to the outer wall surface temperature change data and the working medium inlet and outlet temperature change data to obtain a target value. And judging whether the target value meets the iteration termination condition, if so, obtaining a final solution value, and based on the final solution value, obtaining an estimated value of a variable to be solved corresponding to the current target value as a heat convection coefficient, and if not, adjusting the search direction and the search step length to determine a new solution value until the iteration termination condition is met.
Specifically, the objective function is expressed by the following expression:
wherein J (R) represents a target value, R represents a variable to be solved, T n,m,mea Representing the measured temperatures of M temperature measuring points of the end face of the experimental rock sample at N time points, T n,m,cal (R) represents a temperature obtained by solving the positive problem model using the estimated value of the variable R to be solved.
Next, a process of solving the heat conduction positive problem model will be described in detail.
Firstly, an initial variable R= { h (t) } to be solved is selected, wherein the convective heat transfer coefficient h (t) is related to time t, and the variable R to be solved is a series of convective heat transfer coefficients related to time. In the initial iteration stage, an estimated value of a variable to be solved is selected as an initial value, the constructed objective function is solved by combining the outer wall surface temperature change data and the working medium inlet and outlet temperature change data, a corresponding target value is obtained, and the estimated value of the variable to be solved corresponding to the current target value is used as a solution value of a heat conduction positive problem, so that a convection heat transfer coefficient is obtained. If the target value obtained by current calculation does not meet the iteration termination condition, updating the estimated value of the variable to be solved by adjusting the search direction and the search step length until the variable to be solved meets the iteration termination condition, and taking the latest estimated value of the variable to be solved as the solution value of the heat conduction positive problem, thereby obtaining the heat convection coefficient.
In the embodiment of the application, ifIt is determined that an iteration termination condition (i.e., iteration convergence) is reached and the iteration is ended, where epsilon represents the convergence condition. Otherwise, if the target value obtained by current calculation does not meet the iteration termination condition, constructing a sensitivity coefficient equation about the variable to be solved, and then calculating a conjugate coefficient and a gradient value of the objective function by using the Li Yongmin-degree coefficient equation, and further determining a search direction and a search step length according to the conjugate coefficient and the gradient value. Accordingly, the application continuously obtains the new variable to be solved by determining the searching direction and the searching step length until the latest estimated value of the variable to be solved is determined after the iteration termination condition is met. Specifically, the implementation carries out sensitivity analysis by establishing a sensitivity coefficient equation and a solution condition about variables to be solved, and obtains partial derivatives of temperature pairs of each temperature measuring point.
The control equation and the solution condition of the sensitivity coefficient equation are as follows:
and then, adopting a conjugate gradient method to adjust the searching direction and the searching step length to find the latest numerical value of the variable to be solved when the target value reaches the minimum value. Li Yongmin the gradient values of conjugate coefficients and objective functions are calculated by the coefficient equation, and then the search direction and the search step length are determined according to the conjugate coefficients and the gradient values. Wherein the conjugate coefficient is calculated using the following expression:
Wherein r is b Represents the conjugate coefficient of the light-emitting diode,gradient value representing the objective function, < >>Representing the gradient value of the variable to be solved by temperature, R b Representing the variable to be solved determined in step b, R b-1 And b represents the variable to be solved determined in the step b-1, and b represents the iteration step number.
Next, gradient values of the objective function are calculated using the following expression:
wherein M represents the number of temperature measuring points, N represents the number of transient test time points, and h N The convective heat transfer coefficient corresponding to the Nth transient test time point is represented, l represents the sequence number of the transient test time point, T n，m，cal (R b ) Representing the temperature, T, obtained by solving the positive problem model using the estimated value of the variable R to be solved determined in step b n，m，cal A temperature measurement representing a temperature measurement point.
After obtaining the gradient value of the objective function, the search direction is determined using the following expression:
wherein d b Representing the search direction determined in step b, d b-1 Indicating the search direction determined in step b-1.
Further, the sensitivity coefficient equation is expressed by the following expression:
wherein,representing the gradient values of the variable to be solved for by temperature.
Next, a search step is determined by solving a sensitivity coefficient equation, wherein the search step is determined using the following expression:
Wherein beta is b Representing the search step size determined in step b.
After the search direction and the search step length are determined, updating parameters to be solved according to the current search direction and the search step length, and obtaining newly generated parameters to be solved:
R b+1 ＝R b -β b d b (18)
wherein R is b+1 Representing the variable to be solved determined in the step b+1.
And substituting the newly generated parameter to be solved into the heat conduction positive problem for loop calculation until the objective function meets the iteration termination condition.
Further, the application also measures the thermophysical parameter of the thermal working medium in the transient cooling process of the experimental rock sample, and obtains the correlation between the thermophysical parameter and the convective heat transfer coefficient. In an embodiment of the present application, the thermophysical parameters include: the characteristic parameters of the thermal physical properties such as the thermal conductivity, the dynamic viscosity, the specific heat capacity and the like of the heat collecting working medium under the same temperature and pressure condition, and the dimensionless parameter Reynolds number of the flow condition of the heat collecting working medium, the flow parameter and the pressure parameter of the heat collecting working medium. Based on the thermal physical property parameters of the thermal working medium of the experimental rock sample measured in the step S130 in the transient cooling process, the correlation between each parameter in the thermal physical property parameters and the convective heat transfer coefficient is calculated. Further, the application also designates a plurality of oil bath pressure parameters, so as to form different confining pressures aiming at experimental rock samples, and then respectively obtains the convective heat transfer coefficient and the thermal property parameter corresponding to each oil bath pressure parameter, so as to obtain the correlation between the thermal property parameter and the convective heat transfer coefficient under different confining pressure conditions, and further obtain the correlation between the confining pressure and the convective heat transfer coefficient.
The application realizes the simulation of the high-temperature and high-pressure environment of the reservoir where the dry-hot rock is located by using the high-temperature resistant oil bath, and obtains the convective heat transfer coefficient in the rock cracks under certain confining pressure based on the data inversion model established by the unsteady state multiple volume heat conduction inverse problem. Meanwhile, the confining pressure is indirectly adjusted by adjusting the oil bath pressure parameters, and experiments are repeated aiming at different oil bath pressure parameters, so that the influence rule of the confining pressure on the convective heat transfer coefficient in the crack is obtained.
Example two
Based on the method for testing the internal convective heat transfer coefficient of the dry-thermal rock fracture according to the first embodiment, the embodiment of the application further provides a system for testing the internal convective heat transfer coefficient of the dry-thermal rock fracture (hereinafter referred to as a "convective heat transfer coefficient testing system"). FIG. 4 is a schematic diagram of a system for testing the convective heat transfer coefficient inside a dry-thermal rock fracture according to an embodiment of the present application. The structure and function of the system for testing the convective heat transfer coefficient inside the hot dry rock fracture are described in detail below in connection with the embodiments of the present application.
As shown in fig. 4, the convective heat transfer test system includes at least: experimental rock sample fixture 100, heating device 200, data acquisition device 300, and data processing device (not shown). Wherein, experimental rock sample fixture 100 includes: a holder for holding and fixing an experimental rock sample having a slit 102, which is collected and manufactured from a dry hot rock sample in a current region to be studied, in the heating device 200. And the heating device is used for injecting a heating working medium into the crack 102 of the experimental rock sample, then heating the current experimental rock sample to a preset target temperature and stopping heating when the temperature is uniform. The data acquisition device 300 comprises a data acquisition device, wherein the data acquisition device is connected with the heating device 200 and is used for measuring temperature change data of the outer wall surface of the experimental rock sample in the transient cooling process and temperature change data of the inlet and outlet of the heat-collecting working medium in the crack. The data processing device is used for constructing a heat conduction positive problem model related to the current transient heat conduction process, and obtaining a heat convection coefficient by solving the positive problem model according to the outer wall surface temperature change data and the working medium inlet and outlet temperature change data measured by the data acquisition device 300.
Next, the convective heat transfer test system further comprises: the rock sample sleeve 101, the rock sample sleeve 101 is used for wrapping the experimental rock sample fixture 100 holding the experimental rock sample. Specifically, the holder holding the experimental rock sample is fitted into the rock sample sleeve 101, effectively isolating the experimental rock sample from the heating medium in the heating device 200. In the embodiment of the present application, the rock sample sleeve 101 preferably adopts a high temperature resistant silica gel sleeve or a red copper sleeve which can be closely attached to the experimental rock sample so as to achieve the sealing effect.
The heating device 200 includes: a container composed of a thermal insulation material and a heating element. The heating device 200 is used for heating and applying confining pressure to an experimental rock sample by means of a heating medium. Wherein, the experimental rock sample fixture 100 is arranged in the container, and a heating medium is filled between the experimental rock sample fixture 100 and the outer wall of the container. In the embodiment of the present application, the heating medium preferably adopts heat conduction oil, and the heating apparatus 200 preferably adopts a high-temperature autoclave equipped with heat-insulating cotton 201 and an endless heating belt 202 as a container.
Further, the heating device 200 further includes: a heating control unit 203 and a pressing control unit 204. A heating control unit 203 for heating the experimental rock sample by heating the heating medium according to a preset target temperature. And a pressure-applying control unit 204 for applying a confining pressure to the experimental rock sample by pressurizing the heating medium according to a preset target confining pressure, wherein the pressure-applying control unit 204 comprises a pressure control device, wherein the pressure control device is used for adjusting the pressure of the heating medium in the container when the experimental rock sample reaches the preset target confining pressure, so that the current experimental rock sample keeps the confining pressure stable. In the embodiment of the present application, the heating control unit 203 preferably employs a temperature controller, and the pressurizing control unit 204 preferably employs an oil bath pressurizing pump. In the process of applying confining pressure to the experimental rock sample, the main path ball valve 205 is closed, the bypass ball valve 206 is opened, and the pressurizing pressure is set for the oil bath pressurizing pump, so that confining pressure is applied to the experimental rock sample through the oil bath in the container. In the process of heating the experimental rock sample, the temperature controller is opened to set the temperature, then the oil bath is heated according to the set temperature, and in the heating process, the oil bath is always kept at the set pressure by the automatic control system of the oil pump.
In the process of applying confining pressure to the experimental rock sample by the pressure applying control unit 204, the pressure applying control unit 204 applies confining pressure to the experimental rock sample in the heating device 200 by extracting an appropriate amount of oil bath in the liquid storage tank 600 according to a preset target confining pressure, and stabilizes the oil bath in transmission in the process of extracting the oil bath by the pressure stabilizing tank 700.
Next, the back pressure valve 207 is adjusted, the plunger pump 208 is opened to adjust the flow and pressure of the heat collecting working medium, so that the heat collecting working medium in the system can flow stably according to the adjusted flow and pressure in the transient cooling process, the main path ball valve 205 is opened after the adjustment is finished, the bypass ball valve 206 is closed, the flow parameters in the thermal physical parameters of the heat collecting working medium in the transient cooling process of the experimental rock sample are collected through the flow meter 209, and the outer wall surface temperature change data and the temperature change data of the heat collecting working medium inlet and outlet are collected through the data collecting device 300.
The convection heat transfer test system according to the embodiment of the application further comprises: a plurality of temperature measuring units configured at the inlet of the heating working medium; a plurality of temperature measuring units configured at the outlet of the heating working medium; and a plurality of temperature measuring units arranged on the outer wall surface of the experimental rock sample. Specifically, the plurality of temperature measuring units 106 are respectively arranged at an inlet of the heating working medium on the experimental rock sample, an outlet of the heating working medium on the experimental rock sample and an outer wall surface of the experimental rock sample. The temperature measuring unit 106 in this embodiment employs a thermocouple.
Fig. 5 is a diagram illustrating an exemplary distribution of temperature measurement units on a first experimental rock sample of a system for testing convective heat transfer coefficients inside a dry-thermal rock fracture according to an embodiment of the present application. Fig. 6 is a diagram showing an exemplary distribution of temperature measuring units on a second experimental rock sample of the system for testing convective heat transfer coefficients inside a dry-heat rock fracture according to an embodiment of the present application. Referring to fig. 5 and 6, thermocouples are disposed on the outer wall surface of the experimental rock sample, and the inlet and outlet of the heating medium.
Next, the plurality of temperature measuring units 106 disposed on the outer wall surface include: the first side face is one side face of the outer wall face which is symmetrical with respect to the extending direction of the crack and is positioned on the side wall of the experimental rock sample, and the first plane is a plane which is perpendicular to the extending direction of the crack and is intersected with the central axis of the experimental rock sample; and the temperature measuring unit is arranged at the middle point on the intersection line of the second side surface and the first plane, and the second side surface is the other side surface which is symmetrical to the outer wall surface about the crack extending direction and is positioned on the side wall of the experimental rock sample. The method comprises the steps of firstly determining a first side surface which is symmetrical to the extending direction of a crack in an outer wall surface and is positioned on the side wall of an experimental rock sample, and a first plane which is perpendicular to the extending direction of the crack and is intersected with the central axis of the experimental rock sample, and then uniformly configuring a plurality of thermocouples on the intersection line of the first side surface and the first plane; and determining a second side surface which is symmetrical about the crack extending direction in the outer wall surface and is positioned on the side wall of the experimental rock sample, and then arranging a thermocouple at the midpoint on the intersection line of the second side surface and the first plane.
The thermocouples in the plurality of temperature measuring units of the present application are preferably T-type thermocouples, wherein the T-type thermocouples are led out from the inside of the experimental rock sample fixture 100 and are connected with the data acquisition device 300.
The convection heat transfer test system according to the embodiment of the application further comprises: cooling device 400. The cooling device 400 is used for communicating with the heating device 200 to cool the experimental rock sample inside the container of the heating device 200 when the temperature of the experimental rock sample reaches a preset target temperature. In an embodiment of the present application, the cooling apparatus 400 preferably employs a combination of a cooling circulation pump 401 and a heat exchanger 402. The cooling device 400 cools the oil bath and the experimental rock sample in the heating device 200 using the cooling substance stored in the gas cylinder or the water tank 500 when the preset target temperature of the experimental rock sample is reached and the temperature uniformity state is thus formed, thereby forming a transient cooling condition.
Example III
The method for testing the convective heat transfer coefficient in the crack is described in detail below by taking an experimental rock sample made of granite core in a certain area as an example.
The granite core collected in the field is processed into a regular cylindrical sample serving as an experimental rock sample, wherein the diameter of the cylindrical sample is 50mm, and the length of the cylindrical sample is 50mm. And then polishing the surface of the cylindrical sample smoothly, and measuring the surface of the cylindrical sample for multiple times by adopting a vernier caliper with the precision of 0.02mm to obtain an average value to determine the diameter D and the length L of the sample. Then, the mass of the sample was measured using an analytical balance having an accuracy of 0.1 mg. Finally, calculating the density of the granite core to 2650kg/m according to the size and the mass of the sample 3 。
Next, 5T-type thermocouples were uniformly arranged in the axial direction at the positions 5mm, 15mm, 25mm, 35mm and 45mm from the left end face of the inlet at the first side of the experimental rock sample, one thermocouple was arranged at the position 25mm from the left end face of the inlet at the second side facing the first side, and 1 temperature measuring point was arranged at each of the center points of the inlet and outlet of the crack to measure the fluid temperature of the heating medium, thereby verifying the uniformity of the temperature state. Wherein, the diameter of the single bare wire of the thermocouple is 0.127mm, and the temperature measurement error is calibrated to +/-0.15 ℃. The thermocouple wire is led out from the clamp holder, the experimental rock sample and the clamp holder are together put into a red copper sleeve with the wall thickness of 0.5mm, and the red copper sleeve and the clamp holder are put into an autoclave filled with high-temperature-resistant oil bath and fixed.
After the experimental rock sample is fixed, the main path ball valve is closed, the bypass ball valve is opened, the pressure of the oil bath pressurizing pump is set, certain confining pressure is applied to the experimental rock sample through the oil bath, the temperature controller is opened after the pressure is applied, the temperature is set, and the oil bath is heated. During the heating process, the automatic control system of the oil pump enables the oil bath to be always kept at the set pressure.
When the measured temperature of the experimental rock sample is close to the set temperature of the heater, the wall temperature of the rock sample to be tested changes by not more than 0.2 ℃ within 20min, the temperature difference of each temperature measuring point is consistent and not more than 0.2 ℃, the current experimental rock sample is considered to be in a uniform temperature state, and at the moment, the heating is stopped and the temperature data of each temperature measuring point in the transient cooling process are acquired. In the embodiment of the application, a multifunctional precise voltage/thermocouple measuring instrument (Ametek EX 1048A) is adopted for collecting the transient temperature signals, the measuring frequency is 200Hz, and the high-precision measurement of the temperature signals can be realized rapidly.
After the current experimental rock sample reaches a temperature uniform state, the backpressure valve is regulated, the plunger pump is opened, the flow and the pressure of the heat collecting working medium injected into the crack are regulated, the heat collecting working medium in the crack can stably flow according to the regulated flow and the regulated pressure in the transient cooling process, the main path ball valve is opened after the regulation is finished, the bypass ball valve is closed, and meanwhile, the experimental rock sample is stopped being heated. Then, aiming at the transient cooling process of the experimental rock sample, the temperature data of each temperature measuring point is measured, and simultaneously, the change of thermophysical parameters such as the flow of the heat collecting working medium in the transient cooling process is recorded. And then, adjusting the pressure of the oil bath and the fluid flow of the heating working medium, repeating the transient cooling process of the experimental rock sample for a plurality of times, and recording the temperature change data of the outer wall surface of the experimental rock sample and the temperature change data of the inlet and outlet positions of the heating working medium in the transient cooling process corresponding to different working conditions under the flow conditions of different confining pressures and different heating working mediums.
Next, for different working conditions, measuring the specific heat capacity of the experimental rock sample at different temperatures in real time by using a differential scanning calorimeter, and measuring the heat conductivity coefficient of the experimental rock sample at different temperatures in real time by using a thermal parameter analyzer, thereby fitting the measured data of the specific heat capacity into a temperature-related relation of c=777.72+1.61.t-0.0012.t 2 And fitting the measured data of the thermal conductivity to a temperature-dependent relation k=2.50-0.0009·t. According to the relational expressions, the heat conduction positive problem model is solved by combining the temperature change data of the outer wall surface of the experimental rock sample and the temperature change data of the inlet and outlet positions of the heat collecting working medium. Finally, according to a data processing manner similar to that of the embodiment, the convective heat transfer coefficient is calculated, and a correlation between the convective heat transfer coefficient in the current experimental rock sample crack and the flow rate of the heat collecting working medium is further obtained as shown in fig. 3 (fig. 3 is a schematic diagram of the correlation between the convective heat transfer coefficient of the method for testing the convective heat transfer coefficient in the dry heat rock crack and the flow rate of the heat collecting working medium according to the embodiment of the application).
The application provides a method for testing the internal convective heat transfer coefficient of a dry-heat rock fracture. The method is characterized in that a transient heat collection experiment is carried out on an experimental rock sample from a current area to be researched, and the temperature of the outer wall surface of the experimental rock sample is measured. Thereafter, a thermal conductivity positive problem model is constructed for the current transient thermal conductivity process. And finally, solving a heat conduction positive problem model by utilizing the measured temperature data and combining a data processing method of a heat conduction inverse problem to obtain a heat convection coefficient. According to the method, on the premise of avoiding direct measurement of the temperature of the wall surface inside the crack, the accurate prediction of the heat convection performance of the smooth crack and the rough crack of the dry hot rock under the high-temperature and high-pressure environment is realized. Meanwhile, the application also realizes that the correlation between the convective heat transfer coefficient in the rock crack and the thermal physical property of the heat collecting working medium is obtained through one transient experiment under the confining pressure condition corresponding to the current transient experiment. The application overcomes the defects that the existing experimental device and the existing experimental method cannot accurately measure the wall temperature of the rock fracture under the conditions of high temperature and high pressure, the steady-state experiment is time-consuming, the single experiment data is less, and the like, and simplifies the experimental operation, shortens the experiment time-consuming and reduces the experiment test workload while ensuring the experiment test precision.
The present invention is not limited to the above-mentioned embodiments, and any changes or substitutions that can be easily understood by those skilled in the art within the scope of the present invention are intended to be included in the scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.
Of course, the present invention is capable of other various embodiments and its several details are capable of modification and variation in light of the present invention, as will be apparent to those skilled in the art, without departing from the spirit and scope of the invention as defined in the appended claims.
It will be appreciated by those skilled in the art that the modules or steps of the invention described above may be implemented in a general purpose computing device, they may be centralized on a single computing device, or distributed over a network of computing devices, or they may alternatively be implemented in program code executable by computing devices, such that they may be stored in a memory device and executed by computing devices, or they may be separately fabricated as individual integrated circuit modules, or multiple modules or steps within them may be fabricated as a single integrated circuit module. Thus, the present invention is not limited to any specific combination of hardware and software.
Although the embodiments of the present invention are described above, the embodiments are only used for facilitating understanding of the present invention, and are not intended to limit the present invention. Any person skilled in the art can make any modification and variation in form and detail without departing from the spirit and scope of the present disclosure, but the scope of the present disclosure is still subject to the scope of the appended claims.
Claims (16)
1. A method for testing the convective heat transfer coefficient inside a dry-heated rock fracture, comprising:
collecting a dry heat rock sample of a current area to be researched, and manufacturing an experimental rock sample with cracks;
injecting a heating working medium into the crack of the experimental rock sample, heating the current experimental rock sample to a preset target temperature, and stopping heating when the temperature is uniform;
measuring temperature change data of an outer wall surface of the experimental rock sample in a transient cooling process and temperature change data of a heating working medium inlet and outlet;
and constructing a heat conduction positive problem model related to the current transient heat conduction process, and obtaining a convection heat transfer coefficient by solving the positive problem model according to the outer wall surface temperature change data and the working medium inlet and outlet temperature change data.
2. The method of claim 1, wherein during the making of the experimental rock sample, comprising:
polishing the dry-heated rock sample to obtain a cylindrical sample or a plurality of cuboid samples with smooth and flat surfaces;
the plurality of rectangular parallelepiped samples are configured as a first experimental rock sample having a smooth crack, or the cylindrical sample is configured as a second experimental rock sample having a rough crack, wherein the first experimental rock sample is formed by stacking two rectangular parallelepiped samples and a mica strip disposed between the two rectangular parallelepiped samples, and the second experimental rock sample is formed by performing a brazilian disk split test on the cylindrical sample.
3. The method according to claim 1 or 2, wherein prior to heating the current laboratory rock sample to the preset target temperature, the method further comprises:
a plurality of temperature measuring points are respectively configured for the outer wall surface of the experimental rock sample, and the inlet and the outlet of the heat collecting working medium, wherein the outer wall surface is a first side surface and a second side surface which are symmetrical relative to the extending direction of the crack and are positioned on the side wall of the experimental rock sample, and the first side surface and the second side surface are arranged on the side wall of the experimental rock sample,
when the temperature measuring points are configured for the first side surface, a plurality of temperature measuring points are uniformly arranged on an intersecting line of the first side surface and a first plane, wherein the first plane is a plane which is perpendicular to the extending direction of the crack and intersects with the central axis of the experimental rock sample; and
When the temperature measuring point is configured for the second side surface, the temperature measuring point is arranged at the midpoint on the intersecting line of the second side surface and the first plane.
4. A method according to claim 3, wherein the temperature uniformity condition satisfies the following condition:
each temperature measuring point on the experimental rock sample reaches the preset target temperature;
the temperature difference between the temperature measuring points does not exceed a preset temperature difference threshold value; and
and the temperature change of each temperature measuring point does not exceed the preset temperature difference threshold value within the specified time period.
5. The method according to any one of claims 1 to 4, wherein the experimental rock sample is heated by means of oil bath heating, and the experimental rock sample has the same confining pressure as the heat collecting environment of the current area to be studied, and the confining pressure is kept stable by adjusting the oil bath pressure in real time.
6. The method of claim 5, wherein the method further comprises:
measuring the thermal physical property parameter of the thermal working medium of the experimental rock sample in the transient cooling process, and obtaining the correlation between the thermal physical property parameter and the convective heat transfer coefficient; and
designating a plurality of oil bath pressure parameters, and respectively obtaining the convection heat exchange coefficient and the thermal property parameter corresponding to each oil bath pressure parameter, thereby obtaining the correlation between the thermal property parameter and the convection heat exchange coefficient under different confining pressure conditions, and further obtaining the correlation between the confining pressure and the convection heat exchange coefficient.
7. The method of any one of claims 1-6, wherein the thermally conductive positive problem model is represented using the following expression:
wherein, the initial conditions are:
the adiabatic boundary conditions of the outer wall surface of the experimental rock sample are as follows:
the thermal insulation boundary conditions of the end face of the experimental rock sample are as follows:
the crack wall facing flow heat exchange boundary conditions of the experimental rock sample are as follows:
wherein ρ represents the density of the dry-hot rock sample, C P The specific heat capacity of the experimental rock sample is represented by T, the temperature of the central section of the experimental rock sample is represented by T, the time is represented by T, the heat conductivity coefficient is represented by k, x, y and z respectively represent the coordinates of each position on the central section of the experimental rock sample, T (x, y and T) represents the temperature of a certain position on the central section of the experimental rock sample at the T moment, T i The initial temperature of the experimental rock sample in the transient cooling process is represented by H, the height of a cuboid sample forming the experimental rock sample is represented by L, the length of the cuboid sample or a cylinder sample forming the experimental rock sample is represented by r, the radius of the cylinder sample forming the experimental rock sample is represented by H (T), the convective heat transfer coefficient is represented by T f,m And (t) represents the average temperature of the heat collecting working medium in the crack, wherein the average temperature of the heat collecting working medium is the arithmetic average value of the temperatures at the inlet and the outlet of the heat collecting working medium in the crack.
8. The method according to any one of claims 1 to 7, characterized in that in the step of calculating the convective heat transfer coefficient, it comprises:
selecting an initial variable to be solved and constructing an objective function;
based on the initial value of the variable to be solved, solving the objective function according to the outer wall surface temperature change data and the working medium inlet and outlet temperature change data to obtain a target value;
judging whether the target value meets the iteration termination condition, if yes, obtaining a final solution value, based on the final solution value, obtaining an estimated value of a variable to be solved corresponding to the current target value as the convection heat transfer coefficient, and if not, adjusting the search direction and the search step length, thereby determining a new solution value until the iteration termination condition is met.
9. The method of claim 8, wherein the objective function is represented by the following expression:
wherein J (R) represents a target value, R represents a variable to be solved, T n,m,mea Representing the measured temperatures of M temperature measuring points of the end face of the experimental rock sample at N time points, T n,m,cal (R) represents a temperature obtained by solving the positive problem model using the estimated value of the variable R to be solved.
10. The method according to claim 8 or 9, characterized in that in adjusting the search direction and the search step size, it comprises:
And constructing a sensitivity coefficient equation about the variable to be solved, calculating gradient values of conjugate coefficients and objective functions by using the sensitivity coefficient equation, and determining a search direction and a search step length according to the conjugate coefficients and the gradient values.
11. A system for testing the convective heat transfer coefficient inside a hot dry rock fracture, characterized in that it is adapted to perform the method according to any one of claims 1 to 10, the system comprising:
an experimental rock sample fixture for clamping and fixing an experimental rock sample with cracks, which is acquired from a dry hot rock sample in a current area to be studied and is manufactured;
the heating device is used for injecting a heating working medium into the crack of the experimental rock sample, then heating the current experimental rock sample to a preset target temperature, and stopping heating when the temperature is uniform;
the data acquisition device is connected with the heating device and is used for measuring the temperature change data of the outer wall surface of the experimental rock sample in the transient cooling process and the temperature change data of the inlet and outlet of the heating working medium in the crack;
the data processing device is used for constructing a heat conduction positive problem model related to the current transient heat conduction process, and obtaining a heat convection coefficient by solving the positive problem model according to the outer wall surface temperature change data and the working medium inlet and outlet temperature change data.
12. The system of claim 11, wherein the system further comprises a controller configured to control the controller,
the heating device comprises a container formed by a heat insulation material and a heating element and is used for heating and applying confining pressure to the experimental rock sample through a heating medium, wherein the experimental rock sample fixture is arranged in the container, the heating medium is filled between the experimental rock sample fixture and the outer wall of the container, and the heating medium is heat conduction oil.
13. The system of claim 12, wherein the heating device further comprises:
a heating control unit for heating the experimental rock sample according to the preset target temperature; and
a pressure-applying control unit for applying a confining pressure to the experimental rock sample according to a preset target confining pressure, wherein the pressure-applying control unit comprises a pressure control device, wherein,
and the pressure control device is used for adjusting the pressure of the heating medium in the container when the experimental rock sample reaches the preset target confining pressure so that the current experimental rock sample keeps stable confining pressure.
14. The system according to claim 12 or 13, characterized in that the system further comprises:
a plurality of temperature measuring units configured at the inlet of the heating working medium;
A plurality of temperature measuring units configured at the outlet of the heating working medium;
a plurality of temperature measuring units disposed on an outer wall surface of the experimental rock sample, wherein the plurality of temperature measuring units disposed on the outer wall surface include:
the first side faces are symmetrical to the outer wall face in terms of the extending direction of the cracks and are positioned on one of the side walls of the experimental rock sample, and the first plane is a plane perpendicular to the extending direction of the cracks and intersecting with the central axis of the experimental rock sample; and
the temperature measuring unit is arranged at the middle point on the intersection line of the second side face and the first plane, and the second side face is the other side face, which is symmetrical to the outer wall face in the extending direction of the crack and is positioned on the side wall of the experimental rock sample.
15. The system according to any one of claims 12 to 14, wherein the system further comprises:
the rock sample sleeve is used for wrapping an experimental rock sample fixture clamping an experimental rock sample, and the rock sample sleeve adopts a high-temperature-resistant silica gel sleeve or a red copper sleeve;
and the cooling device is used for communicating with the heating device when the temperature of the experimental rock sample reaches the preset target temperature so as to cool the experimental rock sample.
16. The system of claim 14, wherein the system further comprises a controller configured to control the controller,
the temperature measuring units adopt T-shaped thermocouples, wherein the T-shaped thermocouples are outwards led out from the inside of the experimental rock sample fixture and are connected with the data acquisition device.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN118171571A (en) * | 2024-03-12 | 2024-06-11 | 中国石油大学(北京) | Intelligent inversion method, device, equipment and storage medium for geothermal reservoir fracture network characteristics |
| CN118687807A (en) * | 2024-08-23 | 2024-09-24 | 中国航空工业集团公司沈阳空气动力研究所 | A non-contact measurement method and device for convective heat transfer distribution on a model surface in a wind tunnel |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN118171571A (en) * | 2024-03-12 | 2024-06-11 | 中国石油大学(北京) | Intelligent inversion method, device, equipment and storage medium for geothermal reservoir fracture network characteristics |
| CN118171571B (en) * | 2024-03-12 | 2024-09-17 | 中国石油大学(北京) | Geothermal reservoir stratum fracture network characteristic intelligent inversion method, device, equipment and storage medium |
| CN118687807A (en) * | 2024-08-23 | 2024-09-24 | 中国航空工业集团公司沈阳空气动力研究所 | A non-contact measurement method and device for convective heat transfer distribution on a model surface in a wind tunnel |
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