Stress loading device and method

Abstract

The invention relates to the technical field of oil and gas drilling, and discloses a stress loading device and method.The stress loading device comprises a gas source used for providing experimental gas; the core holder is provided with an inlet and an outlet, and the inlet is connected with a gas source; the confining pressure pump is communicated with the core holder through a first pipeline, and the confining pressure pump is used for applying confining pressure; the back pressure valve is provided with a first port, a second port and a discharge port, the first port is communicated with the outlet, the second port is communicated with the confining pressure pump through a connecting pipeline, the discharge port is opened under the condition that the confining pressure pump is closed, the first port is provided with a first switch, and the first switch is opened under the condition that the confining pressure pump is opened; according to the stress loading device and method, loading of the preset effective stress can be completed, hole seam deformation can be effectively avoided in the whole loading process, and then the accuracy of subsequent shale core experiment results is effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas drilling, in particular to a stress loading device and method. Background Art

[0002] In core experiments, in order to make the core pore structure during the experiment reflect the actual underground situation, it is necessary to apply a preset effective stress to the experimental core. The preset effective stress is equivalent to the effective stress at the location where the experimental core is prepared. Therefore, whether the method of applying the preset effective stress can truly restore the actual pore and fracture morphology characteristics of the reservoir is particularly important for the accuracy of the core experiment results.

[0003] When applying preset effective stress to the experimental core in conventional methods, confining pressure is usually applied to the experimental core first, and then pore pressure is applied to the experimental core. The difference between the confining pressure and the pore pressure is the effective stress. This method is more suitable for rocks with simple mineral composition and mainly elastic deformation, and their pore characteristics can be better restored to the true form under the preset effective stress conditions.

[0004] Compared with other types of oil and gas reservoirs, shale reservoirs have low porosity and permeability, more complex pore structure and multi-scale characteristics, high clay mineral content and rich organic matter in shale. These rock components are more susceptible to plastic deformation than other minerals, and once pore deformation occurs, it is difficult to recover to the initial state. Therefore, for shale cores, when applying preset effective stress according to conventional methods, confining pressure will be applied to the shale cores first, and the confining pressure will be much greater than the preset effective stress. When applying confining pressure, it is very easy to cause excessive deformation of the pores and fractures of the shale cores, and it is difficult to recover to the true shape under the preset effective stress conditions. Therefore, conventional effective stress loading methods are not suitable for shale cores. Once the pores and fractures of shale cores are excessively deformed, it will have a greater adverse effect on the results of subsequent core experiments. Summary of the invention

[0005] The purpose of the present invention is to provide a stress loading device and method, which can complete the loading of preset effective stress and effectively avoid pore deformation during the entire loading process, thereby effectively improving the accuracy of subsequent shale core experimental results.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A first aspect provides a stress loading device, comprising: a gas source for providing experimental gas; a core holder, provided with an inlet and an outlet, the inlet being connected to the gas source; a confining pressure pump, connected to the core holder through a first pipeline, the confining pressure pump being used to apply confining pressure; a back pressure valve, provided with a first port, a second port and a discharge port, the first port being connected to the outlet, the second port being connected to the confining pressure pump through a connecting pipeline, the discharge port being opened when the confining pressure pump is closed, the first port being provided with a first switch, the first switch being opened when the confining pressure pump is turned on.

[0008] The stress loading device of the present invention, through the structural design between the confining pressure pump and the back pressure valve, can realize the synchronous application of confining pressure and pore pressure to the shale core after the core clamp is in a relatively sealed state, thereby keeping the shale core in a zero value state or a state close to zero value, and can complete the loading of the preset effective stress. The entire loading process can effectively avoid pore deformation of the shale core, thereby effectively improving the accuracy of subsequent shale core experimental results.

[0009] In some optional embodiments, one end of the connecting pipe is connected to the first pipe, and the other end is connected to the second port.

[0010] In some optional embodiments, the connecting pipeline includes a first connecting section and a second connecting section, one end of the first connecting section is connected to the confining pressure pump, and the second connecting section is connected to the first connecting section and the back pressure valve.

[0011] In some optional embodiments, the stress loading device further includes a second switch installed in the first connecting section, the second switch is arranged between the second connecting section and the confining pressure pump, and the second switch is opened when the confining pressure pump is turned on.

[0012] In some optional embodiments, the discharge port is disposed at the other end of the first connecting segment, and the stress loading device further includes a third switch disposed on the first connecting segment, and the third switch is disposed between the discharge port and the second connecting segment.

[0013] In some optional embodiments, the discharge port is provided on the connecting pipe, and the stress loading device further comprises a first container, and the first container is connected to the discharge port.

[0014] In some optional embodiments, the stress loading device further includes a one-way valve and a second container, and the outlet is connected to the second container through the one-way valve.

[0015] In some optional embodiments, the stress loading device includes a booster pump, and the inlet is connected to the booster pump.

[0016] In some optional embodiments, the gas source, the booster pump, the confining pressure pump and the back pressure valve are respectively provided with pressure gauges, and the gas source is provided with a pressure reducing valve.

[0017] In some optional embodiments, the stress loading device includes a constant temperature chamber, and all components are placed in the constant temperature chamber.

[0018] A second aspect provides a stress loading method, which is applied to a stress loading device, wherein the stress loading device comprises: a gas source, a core holder, a confining pressure pump and a back pressure valve, wherein the gas source is used to provide experimental gas; the core holder is provided with an inlet and an outlet, wherein the inlet is connected to the gas source; the confining pressure pump is connected to the core holder through a first pipeline, and the confining pressure pump is used to apply confining pressure; the back pressure valve is provided with a first port, a second port and a discharge port, wherein the first port is connected to the outlet, the second port is connected to the confining pressure pump through a connecting pipeline, and the first port is provided with a first switch;

[0019] The stress loading method comprises:

[0020] Preparatory steps: Obtain the average stress and formation pore pressure of the overlying formation;

[0021] Pressurizing step: controlling the gas source to pass the experimental gas into the core holder so that the experimental gas can pass through the core and be discharged from the outlet;

[0022] Under the condition that the pressure of the experimental gas is greater than or equal to the average stress of the overlying formation, the confining pressure pump and the first switch are controlled to be turned on;

[0023] Stress loading step: controlling the confining pressure pump to close under the condition that the applied pressure of the confining pressure pump is greater than or equal to the average stress of the overlying formation;

[0024] regulating the pressure at the inlet and / or controlling the opening of the discharge port;

[0025] Under the condition that the pore pressure of the core is less than or equal to the pore pressure of the formation, the discharge port is controlled to be closed and / or the regulation of the pressure at the inlet is stopped.

[0026] In some optional embodiments, the stress loading device further includes a constant temperature chamber, and the preparation step includes: obtaining the reservoir temperature in advance, and setting the temperature of the constant temperature chamber to be the same as the reservoir temperature.

[0027] In some optional embodiments, the connecting pipeline includes a first connecting section and a second connecting section, one end of the first connecting section is connected to the confining pressure pump, the other end of the first connecting section is provided with the discharge port, and the second connecting section is connected to the first connecting section and the back pressure valve; the stress loading device also includes a second switch and a third switch installed in the first connecting section, the second switch is provided between the second connecting section and the confining pressure pump, and the third switch is provided between the discharge port and the second connecting section;

[0028] The pressurizing step specifically includes: when controlling the gas source to pass the experimental gas, closing the first switch, when the experimental gas is equal to the average stress of the overlying formation, opening the confining pressure pump, the first switch and the second switch, and closing the third switch.

[0029] In some optional embodiments, the stress loading step specifically includes: when the applied pressure of the confining pressure pump is equal to the average stress of the overlying formation, closing the confining pressure pump and the second switch, and opening the third switch; when the pore pressure of the core is equal to the formation pore pressure, closing the third switch.

[0030] In some optional embodiments, after completing the stress loading step, the pressure at the inlet continues to be adjusted and / or the discharge port is controlled to be opened to simulate the change of pore pressure during the gas well production process.

[0031] The stress loading method provided in the second aspect has the same beneficial effects as the stress loading device provided in the first aspect, which will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following is a brief introduction to the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0033] Figure 1 is a schematic structural diagram of the stress loading device described in the embodiment;

[0034] Markings in the figure: 100-stress loading device, 110-gas source, 111-pressure reducing valve, 112-gas source switch, 120-core holder, 121-inlet, 122-outlet, 123-core holder tube, 130-confining pressure pump, 131-confining pressure pump switch, 140-first pipeline, 150-back pressure valve, 151-first port, 152-second port, 153-discharge port, 154-first switch, 160-connecting pipeline, 161-first connecting section, 162-second connecting section, 163-second switch, 164-third switch, 170-first container, 180-second container, 181-check valve, 190-boosting pump, 191-boosting pump switch, 192-pressure gauge, 193-constant temperature chamber, 200-shale core. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] In shale core experiments, since shale is rich in organic matter and clay minerals, has low porosity and permeability, is prone to plastic deformation, and based on the characteristic that pore deformation is difficult to recover to the initial state once it occurs, higher requirements are put forward for stress loading devices and methods, including: 1) being able to simulate the in-situ effective stress of the reservoir, which is the effective stress at the location where the shale core is prepared; 2) being able to avoid excessive deformation of the rock pore structure due to excessive effective stress, thereby adversely affecting the experimental results; 3) being able to be used for indoor experimental porosity, permeability and other parameter tests; 4) being simple and convenient to operate the experiment; In order to meet the above requirements, the present invention proposes a stress loading device and method, which aims to avoid the effective stress of the shale core being higher than the rated value for pore deformation before the shale core reaches the preset effective stress, thereby effectively ensuring the accuracy of the shale-related experimental results.

[0037] The present application is described below with reference to the accompanying drawings and specific embodiments:

[0038] Example

[0039] like Figure 1 FIG. 1 is a schematic diagram of the structure of a stress loading device 100 according to an embodiment of the present invention. The stress loading device 100 includes:

[0040] A gas source 110, for providing experimental gas;

[0041] The core holder 120 is provided with an inlet 121 and an outlet 122, and the inlet 121 is connected to the gas source 110;

[0042] A confining pressure pump 130 is connected to the core holder 120 through a first pipe 140, and the confining pressure pump 130 is used to apply confining pressure;

[0043] The back pressure valve 150 is provided with a first port 151, a second port 152 and a discharge port 153. The first port 151 is connected to the outlet 122, and the second port 152 is connected to the confining pressure pump 130 through a connecting pipe 160. The discharge port 153 is opened when the confining pressure pump 130 is closed. The first port 151 is provided with a first switch 154, and the first switch 154 is opened when the confining pressure pump 130 is turned on.

[0044] If, according to the conventional effective stress loading method, confining pressure is first applied to the shale core 200, the effective stress of the core will be equal to the confining pressure and gradually increase with it, and then pore pressure is applied to the shale core 200, the effective stress of the core will gradually decrease with the increase of pore pressure until the preset effective stress is reached. In this regard, in the process of first applying the confining pressure, the effective stress generated on the shale core 200 will be too large. When it exceeds the preset effective stress and reaches a certain threshold, that is, the effective stress exceeds the rated value, pore deformation will occur or is very likely to occur. The rated value is a pressure value determined according to the composition of the shale reservoir. Based on the characteristics of the shale reservoir, the generated pore deformation is difficult to recover, which leads to a decrease in the accuracy of the experimental results.

[0045] The gas source 110 can select a device that can provide experimental gas at a certain pressure. The core holder 120 can select a conventional Hasler type core holder. The two sides of the core holder 120 are core holder tubes 123. The shale core 200 used for the experiment will be placed in the core holder 120. Due to the structural design of the core holder 120, when the core holder tube 123 is not subjected to a certain pressure, that is, when the core holder tube 123 is not tightly abutted against the shale core 200, there are gaps on both sides of the core holder 120 and a relatively sealed state cannot be formed, and it is difficult to form pore pressure on the shale core 200. Therefore, conventional operations generally require the loading of the confining pressure to be completed first, and then the pore pressure is applied.

[0046] After the confining pressure pump 130 is connected to the core holder 120 cylinder through the first pipe 140, the confining pressure can be applied to the shale core 200 by pressurizing the core holder 120 cylinder. The confining pressure pump 130 usually uses oil as a pressure medium to perform pressure operation. The back pressure valve 150 is a common control valve and generally has two upper and lower ports. The second port 152 is connected to the confining pressure pump 130. After the first port 151 is connected to the core holder 120, the confining pressure pump 130 applies confining pressure to the core holder 120. At the same time, pressure is applied to the back pressure valve 150 to form back pressure. When the confining pressure reaches a certain pressure value, the two sides of the core holder 120 are in a relatively sealed state, that is, the core holder tube 123 and the shale core 200 are pressed against each other without any gap. The back pressure valve 150 will directly affect the pressure in the core holder 120, so that the shale core 200 is subjected to a pore pressure equivalent to the back pressure. In addition, the pressure required for the core holder 120 to form a relatively sealed state will be much smaller than the pressure that causes pore deformation of the shale core 200.

[0047] The stress loading device 100 of the present invention, through the structural design between the confining pressure pump 130 and the back pressure valve 150, can realize the synchronous application of confining pressure and pore pressure to the shale core 200 after the core holder 120 is in a relatively sealed state, thereby keeping the shale core 200 in a zero value state or a state close to zero value, and before the core holder 120 forms a relatively sealed state, the required loaded confining pressure will also be much smaller than the rated value of pore deformation. Therefore, during the whole process of loading the confining pressure to the preset value, the effective stress of the shale core 200 will not exceed the rated value of pore deformation. Subsequently, the pore pressure can be smoothly reduced to complete the loading of the preset effective stress. The whole loading process can effectively avoid pore deformation of the shale core 200, thereby effectively improving the accuracy of subsequent shale core 200 experimental results.

[0048] In addition, based on the same principle, it is not difficult to conclude that the stress loading device 100 of the present invention is also suitable for conducting corresponding experiments on other types of cores, and can also control the range of effective stress changes in core experiments on other cores, and is not limited to the application of shale cores 200.

[0049] In some optional embodiments, one end of the connecting pipe 160 is connected to the first pipe 140, and the other end is connected to the second port 152; the back pressure valve 150 is connected to the confining pressure pump 130 through the connecting pipe 160, and the connecting pipe 160 and the first pipe 140 can be selected to be disconnected from each other. For example, the confining pressure pump 130 has two pressurized output ports 122, and the two output ports 122 are respectively connected to the first pipe 140 and the connecting pipe 160, so that the confining pressure pump 130 can simultaneously apply confining pressure and pore pressure to the shale core 200. It is also possible to select to connect the connecting pipe 160 and the first pipe 140 to form a three-way pipe structure, which is convenient for using one output port 122 of the conventional confining pressure pump 130 to achieve a simultaneous increase in the confining pressure and the pore pressure, and is more conducive to controlling the synchronization of the growth of the confining pressure and the pore pressure.

[0050] In some optional embodiments, the connecting pipe 160 includes a first connecting section 161 and a second connecting section 162 , one end of the first connecting section 161 is connected to the confining pressure pump 130 , and the second connecting section 162 is connected to the first connecting section 161 and the back pressure valve 150 .

[0051] In some optional embodiments, the stress loading device 100 further includes a second switch 163 installed on the first connecting section 161 , and the second switch 163 is disposed between the second connecting section 162 and the confining pressure pump 130 , and the second switch 163 is opened when the confining pressure pump 130 is turned on.

[0052] In order to facilitate the synchronous increase of the confining pressure and the pore pressure, a structural form in which the connecting pipe 160 and the first pipe 140 are interconnected is selected. Accordingly, a second switch 163 can be installed on the connecting pipe 160 to control the connection or isolation state of the first pipe 140 and the back pressure valve 150. In the process of synchronous increase of the confining pressure and the pore pressure, the connection state of the first pipe 140 and the back pressure valve 150 is maintained. In the process of reducing the pore pressure to form effective stress, that is, when the confining pressure pump 130 is closed and preparation is made to reduce the pore pressure, it is necessary to maintain the isolation state of the first pipe 140 and the back pressure valve 150 to avoid mutual interference with the confining pressure when the pore pressure is reduced, so as to achieve single regulation of the pore pressure.

[0053] In some optional embodiments, a discharge port 153 is disposed at the other end of the first connecting section 161 , and the stress loading device 100 further includes a third switch 164 disposed on the first connecting section 161 , and the third switch 164 is disposed between the discharge port 153 and the second connecting section 162 .

[0054] The discharge port 153 is used to discharge the pressure medium in the back pressure valve 150, thereby achieving the reduction of the back pressure in the back pressure valve 150. The discharge port 153 can be directly opened on the back pressure valve 150, or it can be indirectly set by using the second port 152 of the back pressure valve 150 through a pipeline. Furthermore, since the second port 152 is connected with the confining pressure pump 130 through the connecting pipe 160, the discharge port 153 can also be directly set by using the connecting pipe 160, that is, the connecting pipe 160 is designed to be in the form of a three-way pipe, and the three ports are respectively connected with the first pipe 140, the second port 152, and the discharge port 153. At this time, the discharge port 153 can not only discharge the pressure medium in the back pressure valve 150, but also discharge the pressure medium in the first pipe 140. Then, the first pipe 140 does not need to be separately provided with a discharge port 153 to adjust the confining pressure, thereby simplifying the structure of the whole device.

[0055] In some optional embodiments, a discharge port 153 is provided on the connecting pipe 160, and the stress loading device 100 further includes a first container 170, which is connected to the discharge port 153; the first container 170 is used to accommodate the pressure medium discharged from the discharge port 153, so as to facilitate the recycling of the pressure medium and avoid waste and environmental pollution.

[0056] In some optional embodiments, the stress loading device 100 also includes a one-way valve 181 and a second container 180, and the outlet 122 is connected to the second container 180 through the one-way valve 181; the second container 180 is used to accommodate the experimental gas discharged from the outlet 122, which is convenient for the recycling of the experimental gas and also increases the safety of the experiment. The one-way valve 181 enables the second container 180 to receive the experimental gas, and the pressure in the second container 180 has no effect on the core clamp 120, thereby ensuring that the entire experimental process is not hindered during the process of receiving the experimental gas.

[0057] In some optional embodiments, the stress loading device 100 includes a booster pump 190, and the inlet 121 is connected to the booster pump 190; the gas source 110 can usually provide experimental gas of a certain pressure. If the pressure range required for the experimental process is large, the experimental gas is assisted in pressurizing by the booster pump 190, which makes it easier to reach the required pressure level of the experimental gas. At the same time, it can also reduce the equipment requirements for the gas source 110, and it is also convenient to adjust the pressure at the inlet 121 when reducing the pore pressure.

[0058] In some optional embodiments, the gas source 110, the booster pump 190, the confining pressure pump 130 and the back pressure valve 150 are respectively provided with pressure gauges 192, and the gas source 110 is provided with a pressure reducing valve 111; the multiple pressure gauges 192 are convenient for monitoring the pressure values ​​at various positions of the entire device, thereby meeting the control requirements of various operations during the experiment, and the pressure reducing valve 111 can keep the pressure of the outlet 122 of the gas source 110 stable, so that the experimental gas provided by the gas source 110 meets the use requirements, and is also convenient for subsequent auxiliary participation in the process of reducing the pore pressure.

[0059] In some optional embodiments, the stress loading device 100 includes a constant temperature chamber 193, and all components are placed in the constant temperature chamber 193; the constant temperature chamber 193 can be optionally added to simulate the reservoir temperature of the location where the sampled rock is located during the experiment, thereby ensuring that the test results of the experiment are more reliable and improving the accuracy of obtaining experimental parameters.

[0060] Based on the convenience of production and processing and the needs of specific working conditions, certain combinations are made in various optional implementation methods, such as Figure 1 As shown, specifically, a pressure reducing valve 111 is provided at the outlet 122 of the gas source 110, a gas source switch 112 is installed on a pipeline near the outlet 122 of the gas source 110, the gas source 110 is connected to the inlet 121 of the core holder 120 through a pipeline, and a booster pump 190 is additionally provided between the gas source 110 and the inlet 121, and a booster pump switch 191 is installed on a pipeline near the outlet 122 of the booster pump 190;

[0061] The side of the core holder 120 is a core holder tube 123. The core holder 120 can hold the shale core 200. The outlet 122 of the core holder 120 is connected to the second container 180 through a pipeline. A one-way valve 181 is installed on the pipeline near the second container 180. At the same time, the outlet 122 of the core holder 120 is also connected to the first port 151 of the back pressure valve 150 through a pipeline, and a first switch 154 is installed on the pipeline near the first port 151. The first switch 154 is selected as a control valve, which can control the switch of the communication state between the back pressure valve 150 and the outlet 122, and will not affect the communication state between the outlet 122 and the second container 180.

[0062] The confining pressure pump 130 is connected to the core holder 120 through the first pipe 140. Specifically, the first pipe 140 is connected to the core holder barrel 123, so that the confining pressure pump 130 applies pressure to the core holder barrel 123, and then the core holder barrel 123 applies confining pressure to the shale core 200. A confining pressure pump switch 131 is installed on the first pipe 140 near the confining pressure pump 130.

[0063] according to Figure 1As shown in the positional relationship, the upper port of the back-pressure valve 150 is the first port 151, and the lower port of the back-pressure valve 150 is the second port 152. The back-pressure valve 150 is connected to the confining pressure pump 130 through a connecting pipe 160. The connecting pipe 160 is divided into a first connecting section 161 and a second connecting section 162. One end of the first connecting section 161 is connected to the first pipe 140, and then indirectly connected to the confining pressure pump 130. The other end of the first connecting section 161 serves as a discharge port 153 of the back-pressure valve 150, and one end of the second connecting section 162 is connected to the second port 152. The other end of the second connecting section 162 is connected to the first connecting section 161 and is located between the first pipe 140 and the discharge port 153. That is, the discharge port 153 of the back-pressure valve 150 is a port extending from the second through hole through the pipe. A second switch 163 and a third switch 164 are also installed on the connecting section 161, and the second switch 163 is located between the first pipeline 140 and the second connecting section 162, and the second switch 163 can change the connection state between the first pipeline 140 and the second connecting section 162. The third switch 164 is located between the second connecting section 162 and the discharge port 153, and the third switch 164 can change the switch of the discharge port 153, thereby further controlling the discharge of the pressure medium in the back pressure valve 150, and controlling the discharge of the pressure medium in the first pipeline 140 and the connecting pipeline 160. The discharge port 153 is connected to the first container 170. Finally, a pressure gauge 192 is installed on the pipelines close to the gas source 110, the booster pump 190, the inlet 121, the confining pressure pump 130, and the second port 152, respectively.

[0064] A stress loading method of the present invention is applied to a stress loading device 100, which includes: a gas source 110, a core holder 120, a confining pressure pump 130 and a back pressure valve 150, wherein the gas source 110 is used to provide experimental gas; the core holder 120 is provided with an inlet 121 and an outlet 122, wherein the inlet 121 is connected to the gas source 110; the confining pressure pump 130 is connected to the core holder 120 through a first pipeline 140, and the confining pressure pump 130 is used to apply confining pressure; the back pressure valve 150 is provided with a first port 151, a second port 152 and a discharge port 153, wherein the first port 151 is connected to the outlet 122, the second port 152 is connected to the confining pressure pump 130 through a connecting pipeline 160, and the first port 151 is provided with a first switch 154;

[0065] Stress loading methods include:

[0066] Preparatory steps: Obtain the average stress and formation pore pressure of the overlying formation;

[0067] Pressurizing step: controlling the gas source 110 to pass the experimental gas into the core holder 120, so that the experimental gas can pass through the core and be discharged from the outlet 122;

[0068] Under the condition that the pressure of the experimental gas is greater than or equal to the average stress of the overlying formation, the confining pressure pump 130 and the first switch 154 are controlled to be turned on;

[0069] Stress loading step: controlling the confining pressure pump 130 to be closed under the condition that the applied pressure of the confining pressure pump 130 is greater than or equal to the average stress of the overlying formation;

[0070] Regulating the pressure at the inlet 121 and / or controlling the opening of the exhaust port 153;

[0071] Under the condition that the pore pressure of the core is less than or equal to the pore pressure of the formation, the drain port 153 is controlled to be closed and / or the regulation of the pressure at the inlet 121 is stopped.

[0072] In some optional embodiments, the connecting pipe 160 includes a first connecting section 161 and a second connecting section 162, one end of the first connecting section 161 is connected to the confining pressure pump 130, the other end of the first connecting section 161 is provided with a discharge port 153, and the second connecting section 162 is connected to the first connecting section 161 and the back pressure valve 150; the stress loading device 100 also includes a second switch 163 and a third switch 164 installed in the first connecting section 161, the second switch 163 is provided between the second connecting section 162 and the confining pressure pump 130, and the third switch 164 is provided between the discharge port 153 and the second connecting section 162;

[0073] The pressurizing step specifically includes: when the gas source 110 is controlled to pass the experimental gas, the first switch 154 is closed; when the experimental gas is equal to the average stress of the overlying formation, the confining pressure pump 130, the first switch 154 and the second switch 163 are opened, and the third switch 164 is closed.

[0074] In some optional embodiments, the stress loading step specifically includes: when the applied pressure of the confining pressure pump 130 is equal to the average stress of the overlying formation, closing the confining pressure pump 130 and the second switch 163, and opening the third switch 164; when the pore pressure of the core is equal to the pore pressure of the formation, closing the third switch 164.

[0075] In some optional embodiments, after the stress loading step is completed, the pressure at the inlet 121 is continuously adjusted and / or the discharge port 153 is controlled to be opened to simulate the change of pore pressure during the gas well production process.

[0076] After the effective stress loading of the shale core 200 is completed, the device can be further used to simulate the production process of a shale gas well. By utilizing the design of the components of the device, the simulated operation is simple and the simulation is good, which further improves the practicability of the device.

[0077] In some optional embodiments, the stress loading device 100 further includes a constant temperature chamber 193 , and the preparation step includes obtaining the reservoir temperature in advance and setting the temperature of the constant temperature chamber 193 to be the same as the reservoir temperature.

[0078] If there is a difference between the ambient temperature during the experiment and the reservoir temperature at the sampling location, it may cause a large error in the results of some experimental parameters. Therefore, depending on the experimental parameters to be obtained, the reservoir temperature can be selectively simulated during the experiment, thereby further improving the accuracy of the experimental results and ensuring that the various parameters of the experimental test are more reliable.

[0079] Based on the requirements of specific working conditions, certain combinations are made in various optional implementations, specifically using Figure 1 The stress loading device 100 under the specific working condition is carried out according to the following steps:

[0080] Step S10, select a certain block and an area parallel to the bedding plane as a sampling point, obtain the average stress of the overlying stratum, the formation pore pressure and the reservoir temperature of the sampling point, prepare the shale core 200 according to the SYT5358-2010 rock sample preparation method, and then put the shale core 200 into a 60°C oven, take out and weigh the shale core 200 every 24 hours until the mass change between two adjacent times is less than 1.0%, then it is considered that the shale core 200 is fully dried, dry, seal and cool, measure the mass, length and diameter of the columnar shale core 200, and dry, seal and preserve.

[0081] Step S20, place the shale core 200 into the core holder 120, set the temperature of the constant temperature chamber 193 to be the same as the reservoir temperature, and proceed to the next step after the ambient temperature in the constant temperature chamber 193 and the gas phase and liquid phase temperatures of each device are stable.

[0082] Step S30, turn on the gas source switch 112 and the booster pump switch 191, turn on the gas source 110 to supply the experimental gas, and use the booster pump 190 to pressurize the experimental gas, so that the pressure of the experimental gas gradually increases to be equal to the average stress of the overlying formation, and the experimental gas passes through the core clamp 120 through the inlet 121 and the outlet 122, and continues to flow into the second container 180 through the control valve and the one-way valve 181. In this step, since the experimental gas directly flows into the second container 180 after passing through the core clamp 120, and the gas pressure in the second container 180 is blocked by the one-way valve 181 and will not affect the core clamp 120, the shale core 200 in the core clamp 120 will not generate pore pressure accordingly.

[0083] Step S40, open the first switch 154, that is, operate the control valve so that the outlet 122 and the back pressure valve 150 are connected to each other, and the outlet 122 and the second container 180 are still connected, open the second switch 163 and the confining pressure pump switch 131, and close the third switch 164 at the same time, so that the confining pressure pump 130 and the back pressure valve 150 are connected to each other, and the confining pressure pump 130 and the first container 170 are isolated from each other, start the confining pressure pump 130, and apply pressure to the core holder 120 cylinder and the back pressure valve 150 synchronously, and the pressure applied by the confining pressure pump 130 gradually increases to be equal to the average stress of the overlying formation;

[0084] The pressure on the core holder 120 tube will become the confining pressure applied to the shale core 200, and when the core holder 120 tube is subjected to a certain pressure, it will gradually press against the shale core 200, and the core holder 120 will form a relatively sealed state, so that the experimental gas in the core holder 120 will not leak from the core holder 120 tube. After that, the pressure on the back pressure valve 150 will become the pore pressure applied to the shale core 200. As the pressure applied by the confining pressure pump 130 gradually increases, the confining pressure and pore pressure on the shale core 200 will also gradually increase, and the confining pressure and pore pressure can keep increasing synchronously.

[0085] Therefore, during the process of applying pressure by the confining pressure pump 130, before the pore pressure is generated in the shale core 200, the effective stress of the shale core 200 will be equal to the confining pressure. However, since the pressure required for the core holder 120 to form a relatively sealed state will be much smaller than the rated value corresponding to the pore deformation, that is, the effective stress of the shale core 200 will not exceed the rated value, after the pore pressure is generated in the shale core 200, the effective stress of the shale core 200 can be kept at zero or close to zero, and thus can To fully ensure that the effective stress on the shale core 200 does not exceed the rated value and cause pore deformation, the pressure applied by the confining pressure pump 130 will eventually increase to be equal to the average stress of the overlying formation. Therefore, the core clamp 120 tube will eventually apply a confining pressure equal to the average stress of the overlying formation to the shale core 200. At the same time, a back pressure equal to the average stress of the overlying formation is applied to the back pressure valve 150 through the confining pressure pump 130, and the pore pressure of the shale core 200 will eventually increase gradually to be equal to the average stress of the overlying formation.

[0086] Step S50, close the second switch 163, so that the core holder 120 cylinder and the back pressure valve 150 are isolated from each other, so that the confining pressure and pore pressure of the shale core 200 will not affect each other, close the confining pressure pump switch 131, ensure that the confining pressure pump 130 will not affect the subsequent experimental process, wait for the pressure of the experimental gas in the core holder 120 to be equal to the back pressure in the back pressure valve 150, and no longer change, ensure that the pressure conversion process of the back pressure valve 150 is fully completed and remains stable, so that the pore pressure and confining pressure of the shale core 200 are also equal to the average stress of the overlying formation and remain stable, and the effective stress of the shale core 200 is correspondingly stably maintained at zero.

[0087] Step S60, adjusting the pressure at the inlet 121 end, for example, the experimental gas pressure at the inlet 121 can be reduced by controlling the booster pump 190, or by operating the pressure reducing valve 111 of the gas source 110 and other adjustment methods, and at the same time opening the third switch 164, so that the back pressure valve 150 is connected to the first container 170, and the pressure medium filled into the back pressure valve 150 by the confining pressure pump 130 is gradually discharged into the first container 170, thereby reducing the back pressure in the back pressure valve 150, and in the process of reducing the pressure and back pressure at the inlet 121 at the same time, the back pressure is kept slightly lower than the pressure at the inlet 121, thereby ensuring that the experimental gas can flow out from the outlet 122, and the pressure and back pressure at the inlet 121 are gradually reduced until the pore pressure of the shale core 200 is reduced to be equal to the formation pore pressure, and the loading of the effective stress on the shale core 200 is completed;

[0088] The loading of effective stress is achieved by reducing the pore pressure of the shale core 200, that is, after the confining pressure and the pore pressure are equal to the average stress of the overlying formation, the pore pressure is reduced, and the difference between the confining pressure and the pore pressure corresponds to the loaded effective stress, which is in line with the actual mining conditions of shale gas wells. The generation of effective stress is formed by the reduction of pore pressure during the mining process. In the experimental process, the pore pressure can be reduced by using this device in many ways. Since the pore pressure = (pressure at the inlet 121 end + back pressure) / 2 during the pressure reduction process, the pore pressure can be reduced by only reducing the pressure at the inlet 121. At this time, the pressure at the inlet 121 will be lower. If there is a back pressure, the experimental gas will flow in the opposite direction from the outlet 122 to the inlet 121. Accordingly, a container can be connected to the inlet 121 to receive the experimental gas, or the pore pressure can be reduced by reducing the back pressure alone. The pore pressure can also be reduced by simultaneously reducing the pressure at the inlet 121 and the back pressure as in this step. The three methods can be flexibly selected. In addition, when the pressure and the back pressure at the inlet 121 are reduced simultaneously in this step, the back pressure will be controlled to be slightly lower than the pressure at the inlet 121. This is to control the flow direction of the experimental gas, so that the second container 180 can be directly used to receive the experimental gas, thereby eliminating the need to set up other additional containers.

[0089] Step S70, referring to step S60, continuously adjusting the pressure at the inlet 121 and / or the pressure in the back pressure valve 150 to simulate the change of pore pressure during the production process of the shale gas well;

[0090] By flexibly adjusting the pressure and back pressure at the inlet 121, efficient regulation of the pore pressure in the shale core 200 can be achieved. Therefore, the device can well simulate the production process of shale gas wells, that is, as shale gas is continuously produced, the formation pressure will continue to decay, thereby obtaining reliable experimental test results.

[0091] In the effective stress loading experiment process of the related art, the core pore pressure value is often higher than the confining pressure value due to experimental operation errors, which leads to damage to the rubber sleeve in the core holder 120. The stress loading device 100 of the present invention realizes the loading of the confining pressure and the pore pressure at the same time through the confining pressure pump 130, which can effectively avoid the erroneous operation of the pore pressure being higher than the confining pressure during the experimental operation, thereby avoiding the occurrence of the phenomenon of damage to the rubber sleeve in the core holder 120.

[0092] The stress loading device 100 and method of the present invention can first introduce the experimental gas into the core holder 120, and then load the confining pressure. By setting a second container 180 with a one-way valve 181 at the outlet 122, it is ensured that before the confining pressure is applied to the core, the core holder 120 serves as a flow channel for the experimental gas. The experimental gas quickly flows into the second container 180 through the core holder 120, which can avoid the situation where the pore pressure will be higher than the confining pressure during the entire process of completing the effective stress loading.

[0093] In the effective stress loading experiment process of the related technology, the pore pressure is applied after the confining pressure is loaded, which will generate an effective stress higher than the preset value, which is very likely to cause excessive deformation of the pores and fractures of the shale core 200, and it is difficult to restore the pore and fracture shape corresponding to the preset effective stress;

[0094] The device sets a back pressure valve 150 connected to the confining pressure pump 130 at the outlet 122 of the core clamp 120, and sets back pressure to the back pressure valve 150 through the confining pressure pump 130. As the back pressure increases, the experimental gas forms pore pressure in the shale core 200, which can avoid deformation of the shale pore structure caused by excessive effective stress and improve the accuracy of the experimental results.

[0095] In the effective stress loading experiment of related technologies, the process is usually simulated by changing the confining pressure, without considering the influence of pore pressure on the experimental results;

[0096] The device controls the pore pressure by adjusting the back pressure of the back pressure valve 150, and can quickly and realistically simulate the in situ effective stress conditions of the shale reservoir. By flexibly adjusting the pressure at the inlet 121 end and the back pressure in the back pressure valve 150, the shale pore structure of the actual underground situation can be realistically simulated.

[0097] The experimental gas used in the experiment can be recovered into the second container 180, and the oil used by the confining pressure pump 130 and the oil in the back pressure valve 150 can be recovered into the first container 170, thereby avoiding environmental pollution and waste of experimental gas, realizing the recycling and reuse of experimental gas and oil, and also increasing the safety of the experiment. The experimental operation is simple and convenient, meeting the current requirements of green, energy-saving and environmental protection, and has a good application prospect.

[0098] In the description of this specification, reference is made to the terms "one embodiment", "some embodiments", "illustration", etc. It should be noted that all directional indications in the embodiments of the present invention are only used to explain the relative position relationship, movement status, etc. between various components in a certain specific posture. If the specific posture changes, the directional indication will also change accordingly.

[0099] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0100] In addition, in the present invention, descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0101] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification.

Claims

1. A stress loading device, It is characterized in that include: A gas source (110), used for providing experimental gas; A core holder (120) is provided with an inlet (121) and an outlet (122), wherein the inlet (121) is connected to the gas source (110); a confining pressure pump (130), connected to the core holder (120) via a first pipeline (140), the confining pressure pump (130) being used to apply confining pressure; The back pressure valve (150) is provided with a first port (151), a second port (152) and a discharge port (153); the first port (151) is connected to the outlet (122); the second port (152) is connected to the confining pressure pump (130) through a connecting pipe (160); the discharge port (153) is opened when the confining pressure pump (130) is closed; the first port (151) is provided with a first switch (154); the first switch (154) is opened when the confining pressure pump (130) is turned on.

2. The stress loading device according to claim 1, It is characterized in that One end of the connecting pipe (160) is in communication with the first pipe (140), and the other end is in communication with the second opening (152).

3. The stress loading device according to claim 1, It is characterized in that The connecting pipeline (160) comprises a first connecting section (161) and a second connecting section (162), one end of the first connecting section (161) is connected to the confining pressure pump (130), and the second connecting section (162) is connected to the first connecting section (161) and the back pressure valve (150).

4. The stress loading device according to claim 3, It is characterized in that The stress loading device (100) further comprises a second switch (163) installed on the first connecting section (161), wherein the second switch (163) is arranged between the second connecting section (162) and the confining pressure pump (130), and the second switch (163) is opened when the confining pressure pump (130) is turned on.

5. The stress loading device according to claim 3, It is characterized in that The discharge port (153) is arranged at the other end of the first connecting section (161), and the stress loading device (100) further comprises a third switch (164) arranged on the first connecting section (161), and the third switch (164) is arranged between the discharge port (153) and the second connecting section (162).

6. The stress loading device (100) according to claim 1, It is characterized in that The discharge port (153) is arranged on the connecting pipe (160), and the stress loading device (100) further comprises a first container (170), wherein the first container (170) is in communication with the discharge port (153).

7. A stress loading method, It is characterized in that The invention is applied to a stress loading device (100), wherein the stress loading device (100) comprises: a gas source (110), a core holder (120), a confining pressure pump (130) and a back pressure valve (150), wherein the gas source (110) is used to provide experimental gas; the core holder (120) is provided with an inlet (121) and an outlet (122), wherein the inlet (121) is connected to the gas source (110); the confining pressure pump (130) is connected to the gas source (110) through a first pipeline (140); ) is connected to the core holder (120), the confining pressure pump (130) is used to apply confining pressure; the back pressure valve (150) is provided with a first port (151), a second port (152) and a discharge port (153), the first port (151) is connected to the outlet (122), the second port (152) is connected to the confining pressure pump (130) through a connecting pipe (160), and the first port (151) is provided with a first switch (154); The stress loading method comprises: Preparatory steps: Obtain the average stress and formation pore pressure of the overlying formation; A pressure application step: controlling the gas source (110) to pass the experimental gas into the core holder (120) so that the experimental gas can pass through the core and be discharged from the outlet (122); Under the condition that the pressure of the experimental gas is greater than or equal to the average stress of the overlying formation, the confining pressure pump (130) and the first switch (154) are controlled to be turned on; Stress loading step: controlling the confining pressure pump (130) to close under the condition that the applied pressure of the confining pressure pump (130) is greater than or equal to the average stress of the overlying formation; regulating the pressure at the inlet (121) and / or controlling the opening of the discharge port (153); Under the condition that the pore pressure of the core is less than or equal to the pore pressure of the formation, the discharge port (153) is controlled to be closed and / or the regulation of the pressure at the inlet (121) is stopped.

8. The stress loading method according to claim 7, It is characterized in that The connecting pipe (160) comprises a first connecting section (161) and a second connecting section (162), one end of the first connecting section (161) is connected to the confining pressure pump (130), the other end of the first connecting section (161) is provided with the discharge port (153), and the second connecting section (162) is connected to the first connecting section (161) and the back pressure valve (150); the stress loading device (100) further comprises a second switch (163) and a third switch (164) installed on the first connecting section (161), the second switch (163) is provided between the second connecting section (162) and the confining pressure pump (130), and the third switch (164) is provided between the discharge port (153) and the second connecting section (162); The pressurizing step specifically includes: when controlling the gas source (110) to pass the experimental gas, closing the first switch (154); when the experimental gas is equal to the average stress of the overlying formation, opening the confining pressure pump (130), the first switch (154) and the second switch (163), and closing the third switch (164).

9. The stress loading method according to claim 8, It is characterized in that The stress loading step specifically includes: when the applied pressure of the confining pressure pump (130) is equal to the average stress of the overlying formation, closing the confining pressure pump (130) and the second switch (163), and opening the third switch (164); when the pore pressure of the core is equal to the pore pressure of the formation, closing the third switch (164).

10. The stress loading method according to claim 7, It is characterized in that After completing the stress loading step, the pressure at the inlet (121) is continuously adjusted and / or the discharge port (153) is controlled to be open, so as to simulate the change of pore pressure during the production process of the gas well.

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