CN110057740A - High temperature and pressure coal petrography supercritical carbon dioxide pressure break-creep-seepage tests method - Google Patents

Abstract

High temperature and high pressure coal rock supercritical carbon dioxide fracturing-creep-seepage test method, supercritical carbon dioxide fluid fracturing test of coal rock under high temperature and high pressure, and real-time monitoring and recording of supercritical carbon dioxide temperature and pressure during supercritical carbon dioxide fracturing As well as the characteristics of crack initiation and expansion, real-time monitoring and recording of the axial and radial deformation of the coal rock sample, it can ensure the direct and effective measurement before and after fracturing without unloading the stress of the coal rock sample. The CH ₄ permeability of coal rock, and the measurement of the CH ₄ permeability of the coal rock after fracturing under the action of creep can be realized. The measuring method of the invention has high precision, is intuitive, and has a high degree of automation, and the device used has a simple structure.

Description

High temperature and high pressure coal rock supercritical carbon dioxide fracturing-creep-seepage test method

technical field

The invention relates to a supercritical carbon dioxide fracturing-creep-seepage test method for coal rock under high temperature and high pressure. The fracturing medium is supercritical carbon dioxide, which belongs to the field of rock mechanics and engineering technology. Specifically, in the exploitation of deep coalbed methane, supercritical carbon dioxide is used as the fracturing medium to fracturing coal samples, and the temperature and pressure of supercritical carbon dioxide in the process of supercritical carbon dioxide fracturing are monitored and recorded in real time. At the same time, the axial and radial deformation of the coal and rock samples were monitored and recorded in real time. Change law of permeability of cracked coal samples under creep.

technical background

The hydraulic pressure of the coal seam can achieve a wide range of coal and rock pressure relief, increase the permeability of the coal and rock mass, so as to achieve the effect of improving the coal seam gas drainage rate and releasing the gas pressure. However, due to the complex physical and mechanical properties of the coal seam and the heterogeneity Strong, with the characteristics of water sensitivity, strong adsorption and low permeability, therefore, the fracturing effect is not ideal. In the hydraulic fracturing activities in coal seams, the most commonly used fracturing fluid is water. During the fracturing process, there are disadvantages such as high filtration loss, clogging of coal powder, and large water volume, which affect the fracturing construction effect. Therefore, the use of gas as the fracturing fluid for fracturing has a good development prospect.

As a greenhouse gas, carbon dioxide can be used as fracturing fluid for fracturing coal seams, which is conducive to reducing the carbon dioxide content in the atmosphere and reducing the greenhouse effect. When the temperature and pressure of carbon dioxide are greater than 31.10 °C and 7.38 MPa at the same time, carbon dioxide will reach the supercritical state. Supercritical carbon dioxide has gas-like diffusivity and liquid dissolving ability and density, as well as low surface tension, low viscosity, good permeability and fluidity. Therefore, it can be used as a fracturing fluid instead of clear water. Supercritical carbon dioxide fracturing is a new type of fracturing technology that uses supercritical carbon dioxide as fracturing fluid. Compared with conventional fracturing fluids, supercritical carbon dioxide has no damage to the reservoir and is easy to flow back. Therefore, its It has great advantages in fracturing stimulation of unconventional reservoirs. However, at present, it is not clear about supercritical carbon dioxide fracturing coal and rock mass, and there are few experimental devices that can realize supercritical carbon dioxide fracturing coal and rock mass.

In the field of oil and gas exploitation, fracturing devices and methods have achieved a number of achievements. Among them, the invention patents related to true triaxial fracturing methods and devices mainly include: CN 103821487 A, CN 102621000 B, CN 103883301 A, CN103728184 A, CN 103993867 A, CN 103592186 A, CN 104655495 A. The existing true triaxial fracturing simulation test device and method can realize hydraulic fracturing and other gas fracturing tests under the simulated deep buried formation temperature and stress conditions, but it is difficult for the true triaxial fracturing device to directly measure the fracturing Gas permeability of square specimens. However, for the existing triaxial fracturing device (cylindrical sample), such as CN 105510142 A, it is difficult to directly measure the permeability of the sample before and after fracturing without unloading the stress of the sample, and it is difficult to achieve Under the conditions of high temperature (300°C) and high pressure (70MPa), the acoustic emission technology is used to accurately and reliably monitor the crack initiation and propagation characteristics of the sample during the fracturing process, and observe, analyze and master the formation and propagation of cracks. mechanism. Therefore, in order to better simulate the occurrence conditions of deep underground rocks, the supercritical carbon dioxide fracturing test was carried out. At the same time, the gas permeability of coal samples before and after fracturing can be directly measured without unloading the stress conditions of the samples. And to measure the gas permeability of the fracturing coal and rock samples under long-term action, it is necessary to carry out important innovations in the test equipment and methods.

SUMMARY OF THE INVENTION

The invention provides a supercritical carbon dioxide fracturing-creep-seepage test method for coal rock under high temperature and high pressure, the purpose of which is to realize the supercritical carbon dioxide fluid fracturing experiment of coal rock under high temperature and high pressure, and to monitor and record supercritical carbon dioxide in real time The temperature and pressure changes of supercritical carbon dioxide and the characteristics of crack initiation and expansion during the fracturing process, and at the same time monitor and record the axial and radial deformation of the coal sample in real time, and can ensure that the stress of the coal sample is not unloaded. The CH ₄ permeability of coal samples before and after fracturing can be measured under the same conditions, and the CH ₄ permeability of coal samples after fracturing under creep can be measured.

A high temperature and high pressure coal rock supercritical carbon dioxide fracturing-creep-seepage test device is characterized in that the test device can load high stress and high temperature conditions on the coal rock sample, and the size of the coal rock sample is Ф50×100mm, The axial pressure and confining pressure of the coal rock sample can reach 70MPa, and the temperature of the coal rock sample can reach 300°C, which can simulate the geological environment where the mineral burial depth reaches 2500m.

The test device consists of a triaxial pressure chamber, an axial pressure and confining pressure loading system, a temperature rise and temperature control system, a supercritical carbon dioxide generator system, an acoustic emission monitoring system, a pressure-deformation monitoring system, and a permeability measurement system.

The triaxial pressure chamber provides an environment for simulating the stress state and temperature of the formation for the coal and rock samples.

The triaxial pressure chamber includes a triaxial pressure chamber cylinder (16), a perforated plate b (3), a perforated plate a (2), a left pressure head (4), a right pressure head (5), an axial hydraulic piston ( 10), the axial pressure cavity (9), the axial pressure cavity fixing device (8), the rubber sleeve (22), the tapered sleeve b (18), the tapered sleeve a (23), the first fixing device (24), the first Two fixing devices (25).

The triaxial pressure chamber cylinder (16) has an axially penetrating triaxial pressure chamber cavity (21), and the axial pressure cavity fixing device (8) is coaxially placed with the triaxial pressure chamber cavity (21), A confining pressure inlet (20), a confining pressure outlet (15) and a temperature measuring inlet (19) are sequentially arranged on the side wall of the triaxial pressure chamber cylinder (16).

The taper sleeve a (23) and the taper sleeve b (18) are respectively arranged on the periphery of the two indenters.

The cavity between the rubber sleeve (22) and the triaxial pressure chamber cylinder (16) forms a triaxial pressure chamber cavity (21).

The front end of the taper sleeve a (23) and the taper sleeve b (18) are tapered, which can ensure a good sealing effect between the taper sleeves a, b and the rubber sleeve, and between the triaxial pressure chamber cylinder (16) Sealing is achieved by an O-ring; the first fixing device (24) is connected to the triaxial pressure chamber cylinder (16), and the axial pressure chamber fixing device (8) is connected to the triaxial pressure chamber cylinder (16) and is fixed Purpose of taper sleeve a (23) and taper sleeve b (18);

The second fixing device (25) is connected to the first fixing device (24), lightly touches the left end face of the left indenter (4), and squeezes the perforated plate a (2) to ensure that the perforated plate a (2) is in contact with the coal rock. The left end face of the specimen (1) is in contact. A right indenter (5) with an end face diameter of 50mm is placed on the left end of the axial hydraulic piston (10), and then passes through the porous plate b (3) to contact the right end of the coal rock sample; the axial pressure constant current and constant pressure pump ( 34) Inject water into the axial pressure cavity (9) to push the axial hydraulic piston (10) for loading.

The surfaces of the left indenter (4) and the right indenter (5) are provided with three reserved holes (7) for acoustic emission probes (see Figure 5 and Figure 6). The distribution is uneven to ensure that any four probes are not in the same spatial plane, so as to realize the accurate and reliable acquisition of the spatial position of the damage point by acoustic emission monitoring.

The left pressure head (4) and the right pressure head (5) are both provided with a water inlet (44) of a circulating water cooling device and a water outlet (45) of the circulating water cooling device, so as to realize the cooling of the left and right pressure heads under high temperature test conditions, Ensure the working temperature of the acoustic emission probe.

The left pressure head (4) is provided with a central hole (46), and the stainless steel high pressure pipeline can pass through the central hole to enter the coal rock sample (1) to realize the supercritical carbon dioxide fracturing test. It is sealed to ensure that the gas does not flow out of the gap between the stainless steel high-pressure pipeline and the central hole during the fracturing test and the permeability measurement test.

The lower part of the left indenter (4) is provided with a circular hole (6), which is connected to the measuring cylinder (28) through the valve V8 to ensure that in the measurement of permeability, after closing the valve V1, the gas only flows out from the left end face of the coal rock sample , and pass into the measuring cylinder through the round hole (6) to prevent the gas flowing out of the central hole or the stainless steel high-pressure pipeline from interfering with the results of the permeability measurement.

The axial pressure and confining pressure loading system includes an axial pressure constant current and constant pressure pump (34), a confining pressure constant current and constant pressure pump (36), a valve V9, a valve V10, an axial pressure cooling device (42) and a confining pressure cooling device The device (41), the axial pressure and confining pressure cooling device uses circulating water to cool the stainless steel high-pressure pipeline to ensure the normal operation of the pump under high temperature conditions (above 60°C).

The axial pressure constant current and constant pressure pump (34) is connected to the axial pressure cooling device (42) through the valve V10, and is connected to the axial pressure cavity (9) to realize axial pressure loading; the confining pressure constant current and constant pressure pump (36) , connected to the confining pressure cooling device (41) through the valve V9, and finally connected to the triaxial pressure chamber cavity (21) to realize the loading of the confining pressure; the axial pressure and confining pressure loading system adopts constant current and constant pressure water pump, and The pressure value is monitored by the pressure sensor, and the flow rate is automatically controlled to meet the constant pressure condition.

It is further explained that the above-mentioned axial pressure and confining pressure loading system can ensure that during the fracturing process, the axial pressure and confining pressure are always kept constant.

The temperature rise and temperature control system includes a heating jacket (17), a temperature measurement inlet (19) and a heating device (35).

The heating jacket (17) is wrapped outside the cylinder of the triaxial pressure chamber, and is connected to the heating device (35), so as to achieve the purpose of heating the coal and rock sample (1), and detect the coal and rock sample (1) through the temperature measuring inlet (19). ) temperature, the real-time monitoring and control of the temperature is carried out by the heating device (35).

The supercritical carbon dioxide generator system consists of a _CO2 gas cylinder (39), a fracturing pump (38), a preheater (37), a valve V2, a valve V4, a valve V5, a four-way valve (30), a first It is composed of a temperature sensor (31), a first pressure sensor (29) and a thermally insulated stainless steel high-pressure pipeline.

The _CH4 gas cylinder is used to provide the gas source, and the fracturing pump (38) increases the pressure of carbon dioxide in a constant flow mode, and injects it into the interior of the coal sample (1) until the fracturing test is successful;

The preheater (37) heats the CO ₂ gas to keep the CO ₂ in a supercritical state during the fracturing process; the heat preservation stainless steel high-pressure pipeline is mainly to ensure the constant temperature of the supercritical carbon dioxide coming out of the preheater.

To further illustrate, a four-way valve (30) is connected to the front end of the preheater (37), and the four-way valve (30) is respectively connected to the first temperature sensor (31) and the first pressure sensor (29), through the valve V1, and the pressure The fracturing inlet (26) is connected; the four-way valve (30) is required to be as close as possible to the fracturing inlet (26) to ensure accurate monitoring of the pressure and temperature changes of carbon dioxide during the fracturing process.

The acoustic emission monitoring system uses an acoustic emission instrument to monitor the crack initiation and propagation characteristics of cracks in the process of supercritical carbon dioxide fracturing coal and rock samples, so as to realize crack positioning and real-time tracking, and the left pressure in the triaxial pressure chamber. The thickness of the head (4) and the right indenter (5) is relatively thin, and three reserved holes for acoustic emission probes are set on the left end face of the left indenter and the right end face of the right indenter (see Figures 5 and 6). Ensure accurate and stable detection and transmission of acoustic emission signals; during installation, pay attention to make the spatial distribution of the probes as different as possible, and ensure that any four probes are not in the same spatial plane, so as to realize the spatial position of the damage point by acoustic emission monitoring. Accurate and reliable collection.

The pressure-deformation monitoring system (43) mainly includes a pressure-temperature acquisition device, an axial deformation acquisition device and a radial displacement acquisition device. 32), a first temperature sensor (31), a second temperature sensor (33), an LVDT displacement sensor (13), an axial pressure constant current and constant pressure pump (34), a confining pressure constant current and constant pressure pump (36), and a fracturing The pump (38) is connected with the multi-channel data acquisition card and connected to the computer to realize real-time acquisition of pressure, flow rate, temperature and deformation.

The pressure-temperature acquisition device is obtained by combining the fracturing pump (38), the first pressure sensor (29), the second pressure sensor (32), the first temperature sensor (31), the second temperature sensor (33) ) is connected to the multi-channel data acquisition card and connected to the computer to automatically measure and record the temperature and pressure values measured by various temperature and pressure sensors during the experiment, and record the flow and pressure of the fracturing pump.

The axial deformation acquisition device includes an LVDT displacement sensor fixing bracket (11), an LVDT displacement sensor (13) (see FIG. 1) and a multi-channel data acquisition card, and the LVDT displacement sensor fixing bracket (11) is fixed in the axial pressure cavity. On the fixing device (8), the LVDT displacement sensor (13) is symmetrically installed on both sides of the axial pressure hydraulic piston (10), and the bottom ends of the LVDT displacement sensor abut against the right end face of the axial pressure hydraulic piston (10) respectively, and ensure the displacement of the LVDT The axes of the sensor (13), the axial pressure hydraulic piston (10) and the triaxial pressure chamber cylinder (16) are parallel to each other.

As a further explanation, under high temperature conditions, the LVDT displacement sensor will not be suitable for work. Therefore, a circulating water cooling device (12) is added to the outside of the axial pressure hydraulic piston (10) to cool down, so as to ensure that the temperature at the location of the LVDT displacement sensor is maintained. at room temperature.

The radial deformation acquisition device includes a multi-channel data acquisition card, and the radial deformation of the coal rock sample during the fracturing process is measured by collecting and recording the volume change of the fluid in the confining pressure constant current and constant pressure pump. The specific method is as follows: Assuming that the length of the coal sample is L ₀ mm and the diameter is d ₀ mm, when t ₀ =0, the cumulative flow of the confining pressure constant current and constant pressure pump is V ₀ ml, and the reading of the LVDT displacement sensor is a ₀ mm; At t ₁ , the cumulative flow of the confining pressure constant current and constant pressure pump is V ₁ ml, the reading of the LVDT displacement sensor is a ₁ mm, and the compression amount Δ L (axial deformation) of the coal rock sample length is

Then the radial diameter d ₁ of the coal rock sample is

The radial strain of the coal-rock sample at this time t ₁ is

As a further explanation, under high temperature conditions, the axial pressure cooling device (42) and the confining pressure cooling device (41) are respectively set in front of the axial pressure and confining pressure constant current and constant pressure pump (see Figure 1) to ensure constant axial pressure and confining pressure. The temperature of the constant pressure pump is basically kept at room temperature to ensure that the two can work normally.

As a further illustration, at normal temperature, water can be used as the loading medium for axial pressure and confining pressure, while under high temperature conditions, silicone oil can be used as the loading medium for axial pressure and confining pressure.

The permeability measurement system consists of CH ₄ gas cylinder (40), fracturing pump (38), preheater (37), graduated cylinder (28), second pressure sensor (32), valves V3, V4, V7, V8 and thermal insulation stainless steel High pressure pipeline composition. _CH4 from _CH4 cylinder (40) enters fracturing pump (38) through valve V3, fracturing pump (38) injects _CH4 gas in constant flow mode, through valve V4, connected to preheater (38), through Valve V7 to the osmotic pressure inlet (14); the function of the preheater (38) is to heat the CH ₄ gas to ensure that it reaches the same temperature as the coal rock sample, and can accurately measure the CH ₄ permeability under different temperatures; At the left end of the coal rock sample, close the valve V1 so that CH ₄ only flows out from the circular hole (6), and the CH ₄ gas is collected through the graduated cylinder (28). Therefore, it is possible to accurately measure the CH ₄ permeability of the coal and rock samples before and after fracturing without unloading the coal and rock samples _.

As a further illustration, the gas used to measure the permeability of the coal and rock samples before and after fracturing is not limited to CH ₄ , and can be nitrogen, supercritical carbon dioxide or inert gas.

As a further scheme of the present invention:

Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention can realize the fracturing test of simulated deep (high temperature and high pressure conditions) coal rock under the action of supercritical carbon dioxide, and monitor the supercritical carbon dioxide (fracturing) during the fracturing process. The pressure and temperature changes of the fracturing fluid) and the crack initiation and propagation characteristics of the fracture during the fracturing process, and at the same time, the axial and radial deformation mechanisms of the coal rock during the fracturing process can be monitored, so that a more comprehensive analysis of supercritical carbon dioxide The crack initiation, propagation mechanism and deformation mechanism of fracturing coal are studied and analyzed.

Compared with the prior art, the present invention has the beneficial effects that: after the supercritical carbon dioxide fracturing the coal rock sample, the present invention can directly conduct the _CH4 seepage experiment on the coal rock without unloading the coal rock sample, In this way, the damage of the coal and rock samples caused by the loading and unloading history can be avoided, and the unavoidable damage to the coal and rock samples caused by human beings during the unloading and reloading process can be avoided. After the fracturing test, the coal and rock samples before and after fracturing can be obtained. The CH ₄ permeability of the samples can be obtained, and the evolution law of the CH ₄ permeability of the fracturing coal samples under long-term action can be obtained. The beneficial effects of gas extraction.

Compared with the prior art, the rubber sleeve of the sealing device of the coal and rock samples can withstand high temperature (300°C) and is resistant to corrosion, which can realize the function of sealing carbon dioxide for a long time during the fracturing process, and prevent part of the carbon dioxide from penetrating through the rubber sleeve. into the triaxial pressure chamber cavity, affecting the experimental results.

Description of drawings

Fig. 1 is the structural representation of the test device in the present invention;

Fig. 2 is the structural sectional view of perforated plate a;

Figure 3 is a structural cross-sectional view of a left indenter;

Fig. 4 is the structural representation of the processed coal rock sample;

Fig. 5 is the left end face structure schematic diagram of the left pressure head;

Fig. 6 is the right end face structure schematic diagram of the right pressure head;

Labels in the figure: 1—coal rock sample; 2—perforated plate a; 3—perforated plate b; 4—left indenter; 5—right indenter; 6—round hole; 7—sound Reserved hole for transmitting probe; 8--axial pressure cavity fixing device; 9--axial pressure cavity; 10--axial hydraulic piston; 11--LVDT displacement sensor fixing bracket; 12--circulating water cooling device; 13 - LVDT displacement sensor; 14 - osmotic pressure inlet; 15 - confining pressure outlet; 16 - triaxial pressure chamber cylinder; 17 - heating jacket; 18 - taper jacket b; 19 - temperature measuring inlet; 20——Confining pressure inlet; 21——Triaxial pressure chamber cavity; 22——Rubber sleeve; 23——Taper sleeve a; 24——First fixing device; 25——Second fixing device; 26——Pressure 27 - osmotic pressure outlet; 28 - measuring cylinder; 29 - first pressure sensor; 30 - four-way valve; 31 - first temperature sensor; 32 - second pressure sensor; 33 - first pressure sensor Two temperature sensors; 34 - axial pressure constant current and constant pressure pump; 35 - heating device; 36 - confining pressure constant current and constant pressure pump; 37 - preheater; 38 - fracturing pump; 39 - - CO ₂ cylinder; 40 - CH ₄ cylinder; 41 - confining pressure cooling device; 42 - axial pressure cooling device; 43 - pressure-deformation monitoring system; 44 - water inlet of circulating water cooling device; 45 - - water outlet of circulating water cooling device; 46 - center hole.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Embodiment: Coal rock supercritical carbon dioxide fracturing-creep-seepage test device under high temperature and high pressure is characterized in that the device can load high stress and high temperature conditions on the coal rock sample, and the size of the coal rock sample can be Ф50×100mm , The axial pressure and confining pressure of the coal rock sample can reach 70MPa, and the temperature of the coal rock sample can reach 300°C, which can simulate the geological environment where the mineral burial depth reaches 2500m.

The test device consists of a triaxial pressure chamber, an axial and confining pressure loading system, a heating and temperature control system, a supercritical carbon dioxide generator system, an acoustic emission monitoring system, a pressure-deformation monitoring system, and a permeability measurement system.

The triaxial pressure chamber is an important part of the device, which provides a formation stress and temperature environment for the coal and rock samples.

The triaxial pressure chamber includes a triaxial pressure chamber cylinder (16), a perforated plate b (3), a perforated plate a (2), a left pressure head (4), a right pressure head (5), an axial hydraulic piston ( 10), the axial pressure cavity (9), the axial pressure cavity fixing device (8), the rubber sleeve (22), the tapered sleeve b (18), the tapered sleeve a (23), the first fixing device (24), the first Two fixing devices (25).

The triaxial pressure chamber cylinder (16) has a triaxial pressure chamber cavity (21) axially passing through, and the axial pressure cavity fixing device (8) is coaxial with the triaxial pressure chamber cavity (21), and the three A confining pressure inlet (20), a temperature measuring inlet (19) and a confining pressure outlet (15) are sequentially arranged on the side wall of the axial pressure chamber cylinder (16).

The taper sleeve a (23) and the taper sleeve b (18) are respectively arranged on the periphery of the two indenters.

The cavity between the rubber sleeve (22) and the triaxial pressure chamber cylinder (16) forms a triaxial pressure chamber cavity (21).

The front end of the taper sleeve a (23) and the taper sleeve b (18) are tapered, which can ensure a good sealing effect between the taper sleeve a, b and the rubber sleeve. The taper sleeve a (23) and the taper sleeve b (18) ) are sealed with the triaxial pressure chamber cylinder (16) through an O-ring; the first fixing device (24) is connected with the triaxial pressure chamber cylinder (16), and the axial pressure chamber fixing device (8) is connected to The triaxial pressure chamber cylinder (16) is connected, and the purpose of fixing the taper sleeve a (23) and the taper sleeve b (18) is achieved;

The second fixing device (25) is connected to the first fixing device (24), lightly touches the left end face of the left indenter (4), and squeezes the perforated plate a (2) to ensure that the perforated plate a (2) is in contact with the coal rock. The left end face of the specimen (1) is in contact. A right indenter (5) with an end face diameter of 50mm is placed on the left end of the axial hydraulic piston (10), and then passes through the perforated plate b (3) to contact the right end of the coal rock sample; inject water through an axial pressure constant current and constant pressure pump into the axial pressure cavity (9), thereby pushing the axial hydraulic piston (10) for loading.

The axial pressure and confining pressure loading system includes an axial pressure constant current and constant pressure pump (34), a confining pressure constant current and constant pressure pump (36), a valve V9, a valve V10, an axial pressure cooling device (42), a confining pressure cooling device The device (41), the axial pressure and confining pressure cooling device adopts the circulating water method to cool the pipeline to ensure the normal operation of the pump under the high temperature condition above 60°C; the axial pressure constant current and constant pressure pump (34), through The valve V10 is connected to the axial pressure cooling device (42) and connected to the axial pressure cavity (9) to realize axial pressure loading; the confining pressure constant current and constant pressure pump (36) is connected to the confining pressure cooling device through the valve V9 (41), and finally connected to the triaxial pressure chamber cavity (21) to realize the loading of the confining pressure.

The temperature rise and temperature control system includes a heating jacket (17), a temperature sensor (19), a heating device (35), the heating jacket (17) is wrapped outside the cavity of the triaxial pressure chamber, and the heating jacket (17) is connected to the heating device (35), the purpose of heating the coal rock sample (1), and detecting the temperature of the coal rock sample (1) through the temperature measuring inlet (19), and the real-time monitoring and control of the temperature by the heating device (35).

The supercritical carbon dioxide generator system is composed of a _CO2 gas cylinder (39), a fracturing pump (38), a preheater (37) and a thermally insulated stainless steel high-pressure pipeline. The CH ₄ gas cylinder is used to provide the gas source; the fracturing pump (38) increases the pressure of CO ₂ in a constant flow mode and injects it into the interior of the coal rock sample (1) until the fracturing test is successful; the preheater ( 37) The carbon dioxide gas is heated to keep the carbon dioxide in a supercritical state during the fracturing process; the heat preservation stainless steel high-pressure pipeline is mainly to ensure the constant temperature of the supercritical carbon dioxide coming out of the preheater.

The acoustic emission monitoring system adopts an acoustic emission instrument, and the function of the acoustic emission monitoring system is to monitor the crack initiation and propagation characteristics of the cracks in the process of fracturing the coal and rock samples with supercritical carbon dioxide, so as to realize the positioning and real-time tracking of the cracks, and the triaxial pressure. The thickness of the left indenter (4) and the right indenter (5) in the chamber is relatively thin, and three acoustic emission probes are respectively set on the left end face of the left indenter and the right end face of the right indenter (see Figures 5 and 6). ), to ensure accurate and stable detection and transmission of acoustic emission signals; during installation, pay attention to make the spatial distribution of the probes as different as possible, to ensure that any four probes are not in the same spatial plane, so as to achieve acoustic emission monitoring and damage points. Accurate and reliable spatial location acquisition.

The pressure-deformation monitoring system includes a pressure-temperature acquisition device, an axial deformation acquisition device, and a radial displacement acquisition device, a first pressure sensor (29), a second pressure sensor (32), and a first temperature sensor (31) , the second temperature sensor (33), the LVDT displacement sensor (13), the axial pressure constant current and constant pressure pump (36), the confining pressure constant current and constant pressure pump (34), the fracturing pump (38) and the multi-channel collection box. Connect and connect to the computer to realize real-time acquisition of pressure, flow, temperature and deformation.

The permeability measurement system consists of CH ₄ gas cylinder (40), fracturing pump (38), preheater (37), graduated cylinder (28), valve V3, valve V4, valve V7, valve V8, and insulated stainless steel high-pressure pipeline.

_CH4 from _CH4 gas cylinder (40) enters fracturing pump (38) through valve V3, and fracturing pump (38) injects _CH4 gas in constant flow mode; _CH4 is connected to preheater (38) through valve V4; CH ₄ passes through the valve V7 to the osmotic pressure inlet (14); the function of the preheater (38) is to heat the CH ₄ gas to ensure that the CH ₄ gas reaches the same temperature as the coal sample, and accurately measure the CH ₄ under the action of different temperatures At the left end of the coal rock sample, close the valve V1 to make CH ₄ flow out from the circular hole (6), and complete the collection of CH ₄ gas through the graduated cylinder (28). After calculation, the CH ₄ permeability of coal and rock samples can be obtained under the conditions of temperature and stress, so as to accurately measure the CH ₄ permeability of coal and rock samples before and after fracturing without unloading the coal and rock samples.

The high temperature and high pressure coal rock supercritical carbon dioxide fracturing-creep-seepage test device of the invention can accurately measure the _CH4 permeability of the coal rock sample before and after supercritical carbon dioxide fracturing without unloading the coal rock sample stress.

The supercritical carbon dioxide fracturing measurement method, the specific operation steps are as follows:

1. Process the coal rock sample into a cylindrical coal rock sample with a diameter of 50 mm and a length of 100 mm; drill a hole in the axis of the coal rock sample with a diameter of 5 mm and a depth of 60 mm; After drying, insert the stainless steel high-pressure pipeline into the drilled hole, and use epoxy resin glue to pour the gap between the stainless steel high-pressure pipeline and the wall of the drilled hole; leave it for 24 hours;

2. Pass the stainless steel high pressure pipeline through the center hole of the perforated plate a (2) of the test device and the left pressure head (4), and fasten the stainless steel high pressure pipeline and the left pressure head (4) through the ferrule; and put it into the chamber of the triaxial pressure chamber, and install the second fixing device (25) to make it lightly against the left indenter (4); then, install the perforated plates b (3), The right indenter (5) and the axial pressure cavity fixing device (8) are tightened, and the axial pressure cavity fixing device (8) and the second fixing device (25) are screwed, so that the left indenter (4) and the left porous plate (2) ), the coal rock sample (1), the perforated plate b (3) and the right indenter (5) are in close contact with each other;

3. Turn on the heating and temperature control system, set the temperature to a given temperature (25°C-300°C), and set a certain heating rate (5°C/min-40°C/min), after reaching the given temperature , after 4 hours of heat preservation, the temperature of the coal rock sample can be considered to reach a given temperature;

4. Turn on the axial pressure and confining pressure constant current and constant pressure pumps, open the valves V10 and V9, and pass the axial pressure cooling device (42) and the confining pressure cooling device (41), respectively, to pass the loading medium (water or silicone oil) through the pump. into the axial pressure chamber and the triaxial pressure chamber, so that the axial pressure and the confining pressure reach the set values σ ₁ and σ ₃ MPa respectively, and keep them constant.

5. The measurement of the CH4 permeability k ₁ of the coal rock sample before fracturing, the specific steps are as follows: The gas in the _CH4 gas cylinder (40) passes through the valve V3, and is passed into the fracturing pump (38), and the osmotic pressure is set as Given the pressure P ₀ MPa, and keep P ₀ MPa constant, open the valve V4, pass the gas into the preheater, set the same temperature as the coal sample (25°C-300°C), and then open the valve V7, _CH4 gas is introduced into the osmotic pressure inlet (14) through the second pressure sensor (32); close the valve V1, and a circular hole (6) is provided at the lower position of the left pressure head (4), stainless steel high pressure The pipeline is connected to the round hole (6), open the valve V8, and pass it into the measuring cylinder (28), using the drainage gas collection method to measure the gas volume in the measuring cylinder per unit time, and after the gas volume is stable, it is calculated from this value. The CH ₄ permeability of the coal sample under the conditions of temperature, axial pressure and confining pressure is recorded as k ₁ ;

6. Close the valves V3 and V7, and empty the gas in the preheater and fracturing pump, and evacuate the CH ₄ gas inside the coal sample by vacuuming;

7. Turn on the pressure-deformation monitoring system, collect the axial deformation of the coal rock sample through the axial deformation collection device; collect the radial deformation during fracturing through the radial displacement collection device, and collect the confining pressure constant current and constant pressure pump through the collected The volume change of the fluid in the medium is used to measure the radial deformation of the coal rock sample;

The specific method for measuring _radial deformation is as follows: Assuming that the original length of the coal rock sample is L ₀ mm and the diameter is d ₀ mm _; The reading of the LVDT displacement sensor is a ₀ mm; at t ₁ , the cumulative flow of the confining pressure constant current and constant pressure pump is V ₁ ml, the reading of the LVDT displacement sensor is a ₁ mm, and the compression amount Δ L ( Axial deformation) is

Then the diameter d ₁ of the deformed rock coal sample is

Then the radial strain of the coal rock sample at this moment is

As a further illustration, the constant current and constant pressure pump does not work well under high temperature conditions. Therefore, a cooling device can be added in front of the constant current and constant pressure pump, and cooling is carried out by means of water circulation, so that the constant current and constant pressure pump can be cooled. The temperature is kept at a constant temperature (see Figure 1); as a further illustration, under high temperature conditions, silicone oil can be used as the medium for loading axial pressure and confining pressure; as a further explanation, under high temperature conditions, the LVDT displacement sensor will not work. Therefore, a cooling water circulation device (12) is added to the outside of the axial pressure hydraulic piston to reduce the temperature to ensure that the temperature at the location of the LVDT displacement sensor is maintained at the indoor temperature;

8. Turn on the acoustic emission monitoring system to monitor the crack initiation, expansion and closure characteristics of coal during the fracturing process;

9. Open the carbon dioxide gas cylinder, open the valve V2, start the fracturing pump, open the valve V4, and use the constant flow mode to inject carbon dioxide into the preheater at a constant flow rate, and set the preheater temperature. Heating is carried out to make it reach a supercritical state, and then it is connected to a four-way valve (30) through the valve V5 and a high-pressure stainless steel heat preservation pipe, and the four-way valve is respectively connected to the temperature sensor (31) and the pressure sensor (29), and connected The valve V1 passes through the fracturing inlet (26) and is connected to the inside of the sample, and then, in a constant flow mode, the fracturing pump continuously injects supercritical carbon dioxide into the coal sample until the fracturing is successful;

It is further explained that the above-mentioned four-way valve can ensure accurate measurement of the temperature and pressure changes of supercritical carbon dioxide during the fracturing process, so as to better judge the supercritical phase state change of the supercritical carbon dioxide during the fracturing process;

10. Close valve V2 and valve V3, vent the supercritical carbon dioxide gas in the preheater and fracturing pump, and repeat step (5) to obtain the CH ₄ gas permeability k ₂ of the coal rock sample after fracturing;

11. Keep the axial pressure, confining pressure, and temperature set for the coal rock sample unchanged, set 6 hours as the time gradient, repeat step 5, measure the CH ₄ permeability of the coal rock sample after fracturing at different times, In this way, the evolution law of CH ₄ permeability of coal and rock samples after supercritical carbon dioxide fracturing under the action of creep can be obtained. Evolution law of axial deformation and radial deformation of rock sample under creep action;

12. When the experiment is over, turn off the power and put all the devices back in their original condition.

The foregoing specification illustrates and describes preferred embodiments of the present invention, and as previously stated, it should be understood that the present invention is not limited to the form disclosed herein, and should not be construed as an exclusion of other embodiments, but may be used in a variety of other Combinations, modifications and environments are possible within the scope of the inventive concepts described herein, from the above teachings or from skill or knowledge in the relevant fields. However, modifications and changes made by those skilled in the art do not depart from the spirit and scope of the present invention, and should all fall within the protection scope of the appended claims of the present invention.

Claims (7)

1. coal petrography supercritical carbon dioxide pressure break-creep-seepage tests method under high temperature and pressure, it is characterized in that including following steps It is rapid:

(1) coal petrography sample is processed into diameter is 50 mm, and length is the cylindrical body coal petrography sample of 100mm；In the axis of coal petrography sample Heart drilling, the diameter of drilling are 5mm, depth 60mm；The drilling for cleaning coal petrography sample, after to be dried, by stainless steel high-voltage tube In line insertion drilling, and the gap of stainless steel high pressure line and the wall of a borehole is poured using epoxide-resin glue；It is small to place 24 When；

(2) stainless steel high pressure line is passed through to the porous plate a(2 of experimental rig), the centre bore of left pressure head (4), and stainless steel High pressure line and left pressure head (4) are tightly fixed by cutting ferrule；Later, it is put into triaxial cell's cavity together, installation second is solid Determine device (25), it is made gently to resist left pressure head (4)；Then, porous plate b(3 is successively installed on the right side of the triaxial cell), it is right Pressure head (5) and axis pressure cavity are fixed device (8), screw axis pressure cavity fixed device (8), second fixed device (25), so that Left pressure head (4), left porous plate (2), coal petrography sample (1), porous plate b(3) and right pressure head (5) tightly contact；

(3) heating temperature-controlling system to be opened, and temperature is set as 25 °C -300 °C, the setting rate of heat addition is 5 °C/min-40 °C/ Min, after reaching given temperature, after heat preservation 4 hours；

(4) axis pressure, confining pressure constant current constant voltage pump are opened, and opens valve V10, V9, and cooling device (42) are pressed by axis respectively, are enclosed It presses cooling device (41), loaded medium is each led into axis pressure cavity, in triaxial cell's cavity, makes axis pressure, confining pressure difference Reach setting value σ₁、σ₃MPa, and keep constant；

(5) coal petrography sample CH before pressure break₄Permeability k₁Measuring process it is as follows: CH₄Gas in gas cylinder (40) passes through valve V₃, lead to Enter in fracturing pump (38), setting osmotic pressure is given pressureP ₀ MPa, and keepP ₀MPa is constant, valve V4 is opened, gas Body is passed into preheater, and it is 25 °C -300 °C that temperature identical with coal petrography sample, which is arranged, then opens valve V7, CH₄Gas It is passed into osmotic pressure entrance (14) by pressure sensor 2(32)；Valve V1 is closed, is set in the position on the lower side of left pressure head (4) There are a circular hole (6), stainless steel high pressure line and circular hole (6) connection, opens valve V8, be passed into graduated cylinder (28), using row Water gas collection method, the gas volume in cooling water of units of measurement time in graduated cylinder calculate the coal by the value after gas volume is stablized CH of the rock sample under the conditions of temperature, axis pressure, confining pressure₄Permeability is denoted as k₁；

(6) valve V3 and V7 are closed, and empties the gas in preheater and fracturing pump, by the way of vacuumizing, empties coal petrography CH inside sample₄Gas；

(7) it opens pressure-deformation and monitors system, the deformation of coal petrography sample axial direction is acquired by axial deformation acquisition device；Pass through Radial displacement acquisition device acquires radial deformation in fracturing process, is become by the volume of fluid in the confining pressure constant current constant voltage pump of acquisition Change the radial deformation for measuring coal petrography sample；

Measuring radial deformation, the specific method is as follows: assuming that the original length of coal petrography sample isL ₀Mm, diameter ared ₀mm；?t ₀= When 0, the integrated flux of confining pressure constant current constant voltage pump isV ₀The reading of ml, LVDT displacement sensor isa ₀ mm；?t ₁When, confining pressure constant current The integrated flux of constant pressure pump isV ₁Ml, LVDT displacement sensor are reada ₁ Mm, the decrement of coal petrography specimen lengthLFor

The diameter of coal petrography sample after then deformingd ₁For

The then radial strain of the coal petrography sample at the moment is

(8) acoustic emission monitoring system is opened, crack initiation, extension and the closing characteristics of coal petrography sample in fracturing process are monitored；

(9) dioxide bottle is opened, opens valve V2, and start fracturing pump, valve V4 is opened, with constant flow dioxy Change carbon to be injected into preheater, and set preheater temperature, carbon dioxide is heated, carbon dioxide is made to reach supercritical state State, carbon dioxide are passed through temperature sensor (31) and pressure sensing by valve V5, heat preservation stainless steel high-voltage tube, four-way valve (30) Device (29), and it is passed through valve V1, it passes through pressure break entrance (26), is passed into inside coal petrography sample, fracturing pump is constantly by constant current Supercritical carbon dioxide injects inside coal petrography sample, until pressure break success；

(10) valve V2, V3 are closed, the supercritical carbon dioxide gas being vented in preheater and fracturing pump is repeated step (5), obtained The CH of coal petrography sample after to pressure break₄Gas permeability k₂；

(11) axis pressure set by coal petrography sample, confining pressure, temperature-resistant is kept, setting 6 hours are time gradient, step 5 is repeated, Post-fracturing coal petrography sample is measured in the CH of different moments₄Permeability so just obtains coal petrography after supercritical carbon dioxide pressure break CH of the sample under creep effect₄The Evolution of permeability；Meanwhile it being acquired by axial deformation acquisition device and radial deformation The Evolution of axial deformation and radial deformation of the post-fracturing coal petrography sample under creep effect also can be obtained in device.

2. high temperature and pressure coal petrography supercritical carbon dioxide pressure break-creep-seepage tests method according to claim 1, It is characterized in that test temperature can achieve 300 °C, axis pressure, confining pressure can achieve 70MPa.

3. coal petrography supercritical carbon dioxide pressure break-creep-seepage tests method under high temperature and pressure according to claim 1, It is characterized in the experimental rig, it is characterized in that by triaxial cell, axis pressure and confining pressure loading system, heating temperature-controlling system, surpassing and facing Boundary's carbon-dioxide generator system, acoustic emission monitoring system, pressure-deformation monitoring system, permeability measurement systems composition；It is described Triaxial cell includes triaxial cell's cylinder (16), porous plate b(3), porous plate a(2), left pressure head (4), right pressure head (5), axis To hydraulic piston (10), axis pressure cavity (9), axis pressure cavity fixed device (8), rubber sleeve (22), coning sleeve b(18), coning sleeve a (23), first fixed device (24), second fixed device (25)；Triaxial cell's cylinder (16) have axially through Triaxial cell's cavity (21), axis press cavity fixed device (8) and triaxial cell's cavity (21) coaxially, triaxial cell's cylinder (16) side wall is disposed with confining pressure entrance (20), confining pressure outlet (15) and thermometric entrance (19)；Coning sleeve a(23) and taper Set b(18) it is separately positioned on two pressure head peripheries；Cavity between rubber sleeve (22) and triaxial cell's cylinder (16) forms three Axis pressure chamber cavity (21)；Coning sleeve a(23) and coning sleeve b(18) front end is tapered, guarantee coning sleeve a, coning sleeve b and rubber Sealed between set, coning sleeve a(23) and coning sleeve b(18) sealed between triaxial cell's cylinder (16) by O-ring；The One fixed device (24) are connect with triaxial cell's cylinder (16), and axis presses cavity fixed device (8) and triaxial cell's cylinder (16) connect, to realize fixed coning sleeve a(23) and coning sleeve b(18) purpose；Second fixed device (25) connection first is solid Determine device (24), second fixed device (25) are against left pressure head (4) left side and squeeze porous plate a(2), guarantee porous plate a(2) With the left end face contact of coal petrography sample (1)；Place the right pressure that an end face diameter is 50mm in the left end of axial hydraulic piston (10) Porous plate b(3 is arranged on the left of right pressure head (5) in head (5)), porous plate b(3) it offsets with the right end of coal petrography sample；Constant current is pressed by axis Constant pressure pump is filled to axis and presses cavity (9) inner, so that axial hydraulic piston (10) be pushed to be loaded；

The described axis pressure and confining pressure loading system include axis pressure constant current constant voltage pump (34), confining pressure constant current constant voltage pump (36), valve V9, Valve V10, axis press cooling device (42), confining pressure cooling device (41), and axis pressure constant current constant voltage pump (34) is linked by valve V10 Axis presses cooling device (42), and is connected in axis pressure cavity (9) and realizes axis pressure load；Confining pressure constant current constant voltage pump (36) passes through valve V9 is connected to confining pressure cooling device (41), and accesses in triaxial cell's cavity (21), realizes the load of confining pressure；

The heating temperature-controlling system includes heating mantle (17), heating device (35), the first temperature sensor (33), heating mantle (17) It is wrapped in outside the cavity of triaxial cell and connects heating device (35), the first temperature sensor (33) is inserted into thermometric entrance (19) The temperature for carrying out detection coal petrography sample (1) carries out the real-time control of temperature by heating device (35)；

The supercritical carbon dioxide generator system, by CO₂Gas cylinder (39), fracturing pump (38), preheater (37) and heat preservation Stainless steel high pressure line composition, is connected with valve V4, fracturing pump (38) and CO between preheater (37) and fracturing pump (38)₂Gas cylinder (39) valve V2 is connected between；

Pressure-deformation monitoring system (43) includes pressure-temperature acquisition device, axial deformation acquisition device, radial position Move acquisition device；

The pressure-temperature acquisition device includes computer, first pressure sensor (29), second pressure sensor (32), and One pressure sensor (29), second pressure sensor (32), the first temperature sensor (31), second temperature sensor (33), LVDT displacement sensor (13), axis pressure constant current constant voltage pump (34), confining pressure constant current constant voltage pump (36), fracturing pump (38) pass through multichannel Data collecting card is connected in computer, is surveyed for each temperature and pressure sensor in automatic measurement, record experimentation Temperature and pressure value, and record the flow and pressure of fracturing pump；

The axial deformation acquisition device includes LVDT displacement transducer fixed support (11) and LVDT displacement sensor (13) And multi-channel data acquisition board, LVDT displacement transducer fixed support (11) are fixed on axis pressure cavity fixed device (8), LVDT displacement sensor (13) is symmetrically mounted at the two sides of axis pressure hydraulic piston (10), and LVDT displacement sensor bottom end is supported respectively Hydraulic piston (10) right side is pressed in axis, and guarantees LVDT displacement sensor (13), axis pressure hydraulic piston (10) and three axis pressures The axis of power room cylinder (16) is parallel to each other；

The radial displacement acquisition device, pressure-temperature acquisition device include first pressure sensor (29), second pressure sensing Device (32), the first temperature sensor (31), second temperature sensor (33), LVDT displacement sensor (13), axis press constant current constant voltage Pump (36), confining pressure constant current constant voltage pump (34), fracturing pump (38) are connected with multichannel collecting box, and are linked into computer, realize pressure Power, flow, temperature and the real-time acquisition of deformation；Permeability measurement systems are by CH₄Gas cylinder (40), fracturing pump (38), preheater (37), graduated cylinder (28), valve V3, valve V4, valve V7, valve V8 and heat preservation stainless steel high pressure line composition；

CH₄Gas cylinder (40) passes through valve V3 connection fracturing pump (38), CH₄Gas cylinder (40) passes through valve V4 connection preheater (38)； CH₄Gas cylinder (40) passes through valve V7 to osmotic pressure entrance (14).

4. high temperature and pressure coal petrography supercritical carbon dioxide pressure break-creep-seepage tests method according to claim 2, The left pressure head (4) in triaxial cell described in being characterized in that is equipped with centre bore (46), and stainless steel high pressure line passes through centre bore Into coal petrography sample (1), supercritical carbon dioxide crushing test is realized, while stainless steel high pressure line passes through cutting ferrule and left pressure head It is sealed, when guaranteeing that crushing test and permeability survey are tested, gas is not from the gap of stainless steel high pressure line and centre bore Place's outflow.

5. high temperature and pressure coal petrography supercritical carbon dioxide pressure break-creep-seepage tests method according to claim 3, The lower part of the left pressure head (4) in triaxial cell described in being characterized in that is equipped with circular hole (6), passes through valve V8 and graduated cylinder (28) phase Even, it is ensured that in the measurement of coal petrography sample permeability, after closing valve V1, gas is flowed out from the left side of coal petrography sample, is passed through Circular hole (6) is passed into graduated cylinder.

6. high temperature and pressure coal petrography supercritical carbon dioxide pressure break-creep-seepage tests method according to claim 3, It is characterized in that three acoustic emission probe preformed holes, left pressure head is respectively set in the left side of left pressure head, the right side of right pressure head (4), right pressure head (5) is provided with circulating water cooling device water inlet (44) and circulating water cooling device water outlet (45), realizes The cooling of left and right pressure head under the conditions of hot test, guarantees the operating temperature of acoustic emission probe.

7. high temperature and pressure coal petrography supercritical carbon dioxide pressure break-creep-seepage tests method according to claim 3, It is characterized in that four-way valve (30) is respectively connected to the first temperature sensor (31) and first pressure sensor (29), with pressure break entrance phase Even, it is ensured that temperature, the pressure change of the supercritical carbon dioxide in fracturing process at the same position are accurately measured, with Just more accurately judge the phase-state change of supercritical carbon dioxide in fracturing process.