CN106644734A - True tri-axial hydraulic fracture test machine and test method - Google Patents

Abstract

The invention relates to a true triaxial hydraulic fracturing test machine, which includes a confining pressure system, an injection system and a true triaxial test frame. The injection system includes a fracturing fluid container I, a fracturing fluid container II and a piston container. A stirring mechanism is installed in the liquid container II. The test method includes the following steps: inject clean water and additives into the fracturing fluid container II according to a certain proportion, start the stirring mechanism to stir; use pressure to inject the fracturing solution into the upper cavity of the piston plate in the piston container; pass three high-pressure The advection pump applies confining pressure to the three axial directions of the downhole core at the same time; through constant pressure and constant speed plunger pump I and/or constant pressure and constant speed plunger pump II, drains water into the cavity below the piston plate in the piston container; fracturing The solution is injected into the downhole core to start fracturing. After fracturing, the downhole core is taken out to observe the fracture expansion. The technical scheme of the invention is simple and easy to understand, convenient to operate, can realize the unified control of the confining pressure system and the injection system, and is convenient to replace the fracturing fluid.

Description

True triaxial hydraulic fracturing testing machine and its testing method

technical field

The invention belongs to the technical field of oil and gas reservoir development, and in particular relates to a true triaxial hydraulic fracturing test machine and a test method thereof.

Background technique

During the development of oil and gas reservoirs, due to the low-permeability geological characteristics of the reservoirs, the migration of oil and gas is hindered. At this time, hydraulic fracturing has become an important means for the efficient development of such reservoirs. Through hydraulic fracturing, a complex large-scale fracture network with high conductivity can be formed, thereby increasing the drainage area of oil and gas and reducing the flow resistance of oil and gas in the reservoir. Therefore, indoor physical simulation experiments are carried out to study the crack initiation and expansion behavior of fractures. is of great significance. The true three-axis experimental device in the prior art is mainly composed of a true three-axis experimental frame, a three-axis hydraulic pressure stabilizer, an oil-water separator, an MTS pressurization and controller, a data acquisition and processing system, etc. , operability, safety and maintenance and other aspects of deficiencies. On the one hand, the triaxial confining pressure device for simulating the stress state of the formation rock and the injection device for simulating the fracturing process are controlled by two independent systems, which cannot be coordinated and controlled on the same platform. , the lack of unified monitoring measures, which not only increases the operating procedures, affects the efficiency of the experiment, but also brings certain safety hazards; on the other hand, the hydraulic pressure source with triaxial confining pressure is pressurized in the form of a plunger pump During the operation, the pressurization rate cannot be effectively controlled, resulting in excessive triaxial pressure difference of the rock mass, causing crushing and deformation, and affecting the experimental results; in addition, the disassembly and assembly of the oil-water separator is not easy to operate, and there are certain difficulties in replacing the fracturing fluid .

As the scope of oil and gas reservoir research continues to deepen, the existing equipment can no longer meet the requirements of experimental parameters. There are many control lines and high-pressure pipelines connected between equipment, which bring certain safety hazards and are not easy to maintain. Therefore, there is an urgent need to develop a new type of true triaxial hydraulic fracturing test machine and its test method, in order to improve the operability and safety of the experiment, and simulate the fracturing process of downhole rock as realistically as possible.

Contents of the invention

In order to solve the problems existing in the prior art, the present invention provides a true triaxial hydraulic fracturing testing machine, comprising a confining pressure system, an injection system and a true triaxial test frame, the confining pressure system and the injection system are connected with the The true triaxial test frame is connected, and the downhole core is placed in the true triaxial test frame; the injection system and the confining pressure system are connected with a computer, and the injection system includes a fracturing fluid container I and a fracturing fluid container II and a piston container, a stirring mechanism is installed in the fracturing fluid container II, and the stirring mechanism is connected with a computer.

The fracturing fluid container and the injection container (that is, the piston container) of the true triaxial hydraulic fracturing testing machine of the present invention are designed separately, so that it is convenient to replace the fracturing fluid. When it is necessary to replace the fracturing fluid, you only need to operate in the fracturing fluid container, open the drain valve at the lower end of the fracturing fluid container to discharge the fracturing fluid in the container, and then inject new one into the opening at the upper end of the container. The fracturing fluid can be used, or the container can be cleaned first, and then new fracturing fluid can be injected. In the prior art, the fracturing fluid container and injection container are realized by one device (oil-water separator). When the fracturing fluid needs to be replaced, the oil-water separator is disassembled, the water and oil in the container are poured out, and then manually Or use tools to push the piston in the container to the bottom of the container, and then inject new fracturing fluid into the upper cavity of the piston, which is difficult to operate, and the container is not easy to clean, and the oil-water separator must be disassembled every time the fracturing fluid is replaced , After several times of disassembly, it will lead to poor sealing of the oil-water separator and loose connection of components, which will also lead to a decrease in the accuracy of the injected liquid and an unstable fracturing state.

Preferably, the upper end of the fracturing fluid container I is connected to the high-pressure gas cylinder through a pipeline, and a switch valve I is installed on the pipeline; the lower end of the fracturing fluid container I is connected to the upper end of the piston container through a pipeline, and a switch valve is installed on the pipeline. Valve II.

In any of the above schemes, it is preferred that a discharge valve I is provided at the bottom of the fracturing fluid container I.

In any of the above schemes, preferably, the upper end of the fracturing fluid container II is connected to the high-pressure gas cylinder through a pipeline, and the switch valve III is installed on the pipeline; the lower end of the fracturing fluid container II is connected to the upper end of the piston container through the pipeline. Connect, install on-off valve IV on the pipeline.

In any of the above schemes, it is preferred that a discharge valve II is provided at the bottom of the fracturing fluid container II.

In any of the above solutions, it is preferred that a piston piece that can move up and down is arranged in the piston container.

In any of the above schemes, preferably, the upper end of the piston container is connected to the downhole core through a pipeline; the lower end of the piston container is connected to a water tank through a pipeline.

In any of the above schemes, preferably, the water tank is respectively connected to the constant pressure and constant speed plunger pump I and the constant pressure and constant speed plunger pump II through pipelines.

In any of the above schemes, preferably, the constant pressure and constant speed plunger pump I and the constant pressure and constant speed plunger pump II are connected to a computer.

In any of the above solutions, preferably, the confining pressure system includes a high-pressure advection pump I, a high-pressure advection pump II and a high-pressure advection pump III, and the three pump bodies are all connected to a computer.

In any of the above schemes, preferably, the high-pressure advection pump I is connected to the front and rear surfaces of the downhole core through a pipeline, and a back pressure valve I is installed on the pipeline; the high-pressure advection pump II is connected to the downhole core through a pipeline. The left and right sides of the core are connected, and a back pressure valve II is installed on the pipeline; the high-pressure advection pump III is connected to the upper and lower sides of the downhole core through a pipeline, and a back pressure valve III is installed on the pipeline. When the generated confining pressure exceeds the set value, the back pressure valve will automatically open to relieve the pressure to the set value.

The present invention also provides a true triaxial hydraulic fracturing test method, using any of the above true triaxial hydraulic fracturing test machines, which comprises the following steps in sequence:

Step 1: Close all on-off valves and drain valves, inject fracturing fluid water into the fracturing fluid container I, first open the on-off valve I and on-off valve II, and then open the high-pressure gas cylinder, at this time the fracturing fluid water enters the piston In the cavity above the piston plate in the container;

Step 2: After all the fracturing fluid clear water enters the piston container, first close the high-pressure gas cylinder, and then close the switch valve Ⅰ and switch valve Ⅱ;

Step 3: Set the confining pressure value according to the test requirements, and apply confining pressure to the three axial directions of the downhole core at the same time through the high-pressure advection pump I, high-pressure advection pump II and high-pressure advection pump III;

Step 4: Start the constant pressure and constant speed plunger pump Ⅰ and the constant pressure and constant speed plunger pump Ⅱ. If the water in the cavity of the two plunger pumps is not full, the two plunger pumps will be filled from the water tank through the pipeline respectively. If the water in the cavity of the two plunger pumps is full, the fracturing operation will be performed directly;

Step 5: Set the displacement according to the test requirements. When the displacement is less than or equal to 50ml/min, only the constant pressure and constant speed plunger pump I drains water into the cavity below the piston plate in the piston container. At this time, the constant pressure and constant speed plunger pump II In the standby state, when all the water in the constant pressure and constant speed plunger pump Ⅰ is drained, the constant pressure and constant speed plunger pump Ⅱ starts to drain water into the cavity below the piston plate in the piston container, at this time the constant pressure and constant speed plunger Pump I absorbs water from the water tank; when the displacement is greater than 50ml/min, the constant pressure and constant speed plunger pump I and the constant pressure and constant speed plunger pump II discharge water into the cavity below the piston plate in the piston container at the same time;

Step 6: As the constant pressure and constant speed plunger pump I and/or the constant pressure and constant speed plunger pump II work, inject clean fracturing fluid into the downhole core, and observe the changes of inlet pressure and time displayed on the computer at the same time Relational curve, when the inlet pressure drops to a low point and is in a stable state, it is judged that the fracturing process is over, and the data recorded by the computer is saved;

Step 7: Turn off the constant pressure and constant speed piston pump I and the constant pressure and constant speed piston pump II, and make sure that the inlet pressure is zero, and at the same time make sure that the inner chamber pressure of the two plunger pumps is zero, if the inner chamber pressure is not zero, it is necessary to restart the corresponding plunger pump, and then stop it at the moment of starting to make the inner cavity pressure become zero; open the back pressure valve I, back pressure valve II and back pressure valve III at the same time, and unload the three axial axes of the downhole core. confining pressure on

Step 8: Take out the downhole core from the true triaxial test frame, and observe the fracture expansion.

Preferably, in step 3, the triaxial confining pressure is applied to the downhole core, the X direction is the horizontal maximum principal stress, the Y direction is the horizontal minimum principal stress, and the Z direction is the vertical stress, wherein the confining pressure in the X direction is greater than that in the Y direction Confining pressure.

Preferably in any of the above solutions, in step five, the setting range of the displacement is 0-100ml/min.

The present invention also provides a true triaxial hydraulic fracturing test method, using any of the above true triaxial hydraulic fracturing test machines, which comprises the following steps in sequence:

Step 1: Close all switch valves and drain valves, inject clean water and additives into the fracturing fluid container II in a certain proportion, set the stirring time, and start the stirring mechanism to stir to form a uniform fracturing solution;

Step 2: Open the on-off valve III and the on-off valve IV first, and then open the high-pressure gas cylinder. At this time, the fracturing solution enters the cavity above the piston plate in the piston container;

Step 3: After all the fracturing solution enters the piston container, first close the high-pressure gas cylinder, and then close the switch valve III and switch valve IV;

Step 4: Set the confining pressure value according to the test requirements, and apply confining pressure to the three axial directions of the downhole core at the same time through the high-pressure advection pump I, the high-pressure advection pump II and the high-pressure advection pump III;

Step 5: Start the constant pressure and constant speed plunger pump Ⅰ and the constant pressure and constant speed plunger pump Ⅱ. If the water in the cavity of the two plunger pumps is not full, the two plunger pumps will suck up the water from the water tank through the pipeline respectively. If the water in the cavity of the two plunger pumps is full, the fracturing operation will be performed directly;

Step 6: Set the displacement according to the test requirements. When the displacement is less than or equal to 50ml/min, only the constant pressure and constant speed plunger pump I drains water into the cavity below the piston plate in the piston container. At this time, the constant pressure and constant speed plunger pump II In the standby state, when all the water in the constant pressure and constant speed plunger pump Ⅰ is drained, the constant pressure and constant speed plunger pump Ⅱ starts to drain water into the cavity below the piston plate in the piston container, at this time the constant pressure and constant speed plunger Pump I absorbs water from the water tank; when the displacement is greater than 50ml/min, the constant pressure and constant speed plunger pump I and the constant pressure and constant speed plunger pump II discharge water into the cavity below the piston plate in the piston container at the same time;

Step 7: As the constant pressure and constant speed plunger pump Ⅰ and/or constant pressure and constant speed plunger pump Ⅱ are drained, the fracturing solution is injected into the downhole core, and the relationship between the inlet pressure and time displayed on the computer is observed at the same time When the inlet pressure drops to a low point and is in a stable state, it is judged that the fracturing process is over and the data recorded by the computer is saved;

Step 8: Turn off the constant pressure and constant speed plunger pump Ⅰ and constant pressure and constant speed plunger pump Ⅱ, and make sure that the inlet pressure is zero, and at the same time make sure that the inner chamber pressure of the two plunger pumps is zero, if the inner chamber pressure is not zero, it is necessary to restart the corresponding plunger pump, and then stop it at the moment of starting to make the inner cavity pressure become zero; open the back pressure valve I, back pressure valve II and back pressure valve III at the same time, and unload the three axial axes of the downhole core. confining pressure on

Step 9: Take out the downhole core from the true triaxial test frame, and observe the fracture expansion.

Preferably, in step one, the stirring time is at least 20 minutes.

In any of the above schemes, it is preferred that in step 4, a triaxial confining pressure is applied to the downhole core, the X direction is the horizontal maximum principal stress, the Y direction is the horizontal minimum principal stress, and the Z direction is the vertical stress, wherein The confining pressure is greater than the confining pressure in the Y direction.

In any of the above schemes, preferably, in step 6, the displacement setting range is 0-100ml/min.

The clean water and additives in step 1 can be replaced with fracturing fluid and proppant. The fracturing fluid and proppant are injected into the fracturing fluid container II according to a certain ratio, the stirring time is set, and the stirring mechanism is started to stir to form a uniform sand-carrying fracturing fluid. Since the particle size of the sand is between 100-3000 μm, which is much larger than that of clear water or other fracturing solutions, the size of the pipeline connecting the fracturing fluid container II and the piston container, and between the piston container and the downhole core should be large enough. It can ensure the smooth injection of sand-carrying fracturing fluid into the downhole core. When it is necessary to inject sand-carrying fracturing fluid for testing, it is only necessary to replace the pipeline between the piston container and the downhole core with a larger-sized pipeline, and there is no need to replace other pipelines or the fracturing fluid container, thus saving It saves time and cost, and avoids the clogging of pipelines by sand particles, which can ensure the smooth progress of sand fracturing tests. In addition, use the corresponding fracturing fluid container and pipeline according to the type of fracturing fluid injected (such as fracturing fluid water or sand-carrying fracturing fluid), which is easy to clean, and you only need to clean the corresponding fracturing fluid container and pipeline after use .

In order to overcome the defects of the prior art such as inconsistent triaxial pressurization efficiency, lack of a unified operating platform, cumbersome operating procedures, and difficult replacement of fracturing fluid, the present invention collects The four aspects of the control system and the control system have been improved and innovated, which greatly simplifies the structure of the true triaxial hydraulic fracturing test machine, and greatly improves the overall operability of the test machine while ensuring safety.

In the true triaxial hydraulic fracturing testing machine of the present invention, its confining pressure system is composed of three separate pressure systems, each system can be pressurized simultaneously or step by step, and the confining pressure on three sides can be both equal pressure and Differential pressure exists. Each individual confining pressure system consists of a silicone oil container, an advection pump, a back pressure valve, and pipelines. Confining pressure medium adopts silicone oil, because silicone oil has excellent heat resistance, electrical insulation, weather resistance, hydrophobicity, physiological inertness and small surface tension, in addition, it has a low viscosity-temperature coefficient and high compression resistance , so silicone oil as a pressurized medium has the characteristics of high efficiency, good safety performance, and no interference. The high-pressure infusion pump adopts a double-piston reciprocating pump, one is the main suction plunger, and the other is the auxiliary plunger. The high-efficiency and precise infusion pump system controlled by the computer can ensure high infusion accuracy under various conditions of use. and good repeatability indicators. The injection system consists of a piston container, an injection medium container, a fracturing fluid stirring container and a push injection system. The piston container is made of stainless steel, with a rated safety pressure of 100MPa and a volume of 1.5L; the piston container is divided into upper and lower chambers by the piston plate, the upper chamber is filled with fracturing fluid, and the lower chamber is injected with liquid. The injection medium container is made of stainless steel with a rated safety pressure of 2MPa and a volume of 2L. The container has a solution blending tank with a scale of 500ml. Different fracturing fluids are blended in the blending tank according to the experimental requirements. After the blending is completed, open the valve below the blending tank and inject into the container, and then close the valve of the solution blending tank. Turn on the high-pressure gas cylinder or air compression pump, and use the air pressure to press the injection medium into the piston container. The fracturing fluid mixing vessel is made of stainless steel, with a rated safety pressure of 2MPa and a volume of 2L. It is equipped with a motor stirring mechanism and the speed can be adjusted. There is a proppant injection port and a liquid injection port on the fracturing fluid mixing container. According to the test ratio, water and additives are injected, and the stirring mechanism is controlled by a computer to adjust to the required speed and stirring time. After stirring evenly, the fracturing fluid is injected into the piston by air pressure. inside the container. The booster system consists of a double-cylinder constant-pressure constant-speed plunger pump and a booster liquid container. The pressure of the twin-cylinder constant pressure and constant speed plunger pump is 100MPa, the flow rate is 0-100ml/min, and the precision is 0.01ml/min. The characteristic of the plunger pump is that the start, stop, flow, etc. are all automatically controlled by computer programs. The system is compact in design, convenient and completely closed, and uses imported servo motors with programmable controllers and intelligent display screens to precisely control the advance, retreat, speed regulation, and pressure regulation of the plunger pump, and uses animation demonstration to indicate the plunger pump The operating status and faults, the curve shows the real-time changes of liquid flow rate, flow rate and pressure, and has a simple and convenient man-machine interface. The double-cylinder constant-pressure constant-speed plunger pump can work independently with a single cylinder, or it can work uninterruptedly in conjunction with the two cylinders. Single-cylinder and double-cylinder work have three working modes of constant pressure, constant current and tracking to meet the needs of different operations and tests. In terms of safety system, the testing machine of the present invention is a high-pressure device. In order to ensure the safety of the test, a safety valve is equipped at the inlet of the confining pressure system and the injection system. The safety valve has high sensitivity, convenient operation, safety and reliability. When the confining pressure or When the injection pressure exceeds the safety set value, the safety valve will automatically open to release the pressure, and at the same time set the upper limit pressure value on the computer. When the pressure exceeds the set value, the computer will issue an order to automatically stop the pump to ensure the safety of the pipeline and operators . In terms of computer acquisition and control systems, the data acquisition system can collect real-time values such as pressure, temperature, flow, and constant-speed constant-pressure plunger pump pressure. In order to ensure measurement accuracy and control reliability, the C168H digital acquisition control card is used to realize digital acquisition and transmission. The software runs under Windows7/XP environment, and has functions of gas parameter conversion and data analysis. The test operation process is displayed on the interface, which can realize man-machine dialogue. After the operator sets the parameters, the test machine can work alone, and the computer can automatically collect all values such as pressure and flow rate. The data collected by the computer can be processed to generate raw data reports, analysis reports and graphs, and at the same time generate database files for backup and query.

Description of drawings

Fig. 1 is a schematic structural view of a preferred embodiment of a true triaxial hydraulic fracturing testing machine according to the present invention;

Fig. 2 is a schematic structural view of the injection system according to the embodiment shown in Fig. 1 of the true triaxial hydraulic fracturing testing machine of the present invention;

Fig. 3 is a schematic structural diagram of the confining pressure system of the embodiment shown in Fig. 1 of the true triaxial hydraulic fracturing testing machine according to the present invention.

Notes in the figure: 1-confining pressure system, 101-high pressure advection pump Ⅰ, 102-high pressure advection pump Ⅱ, 103-high pressure advection pump Ⅲ, 104-back pressure valve Ⅰ, 105-back pressure valve Ⅱ, 106-back pressure valve III;

2-injection system, 201-fracturing fluid container Ⅰ, 202-fracturing fluid container Ⅱ, 203-piston container, 204-stirring mechanism, 205-high pressure gas cylinder, 206-on-off valve Ⅰ, 207-on-off valve Ⅱ, 208 - Drain valve Ⅰ, 209-Switch valve Ⅲ, 210-Switch valve Ⅳ, 211-Drain valve Ⅱ, 212-Piston piece, 213-Sink, 214-Constant pressure and constant speed plunger pump Ⅰ, 215-Constant pressure and constant Speed plunger pump II;

3-true triaxial test frame, 4-downhole core, 5-computer.

detailed description

In order to further understand the content of the present invention, the present invention will be described in detail below in conjunction with specific examples.

Embodiment one:

As shown in Figure 1, according to an embodiment of the true triaxial hydraulic fracturing testing machine of the present invention, it comprises a confining pressure system 1, an injection system 2 and a true triaxial test frame 3, the confining pressure system 1 and the The injection system 2 is connected with the true triaxial test frame 3, and the downhole core 4 is placed in the true triaxial test frame 3; the injection system 2 and the confining pressure system 1 are connected with a computer 5, and the injection system 2 It includes a fracturing fluid container I 201 , a fracturing fluid container II 202 and a piston container 203 . The fracturing fluid container II 202 is equipped with a stirring mechanism 204 connected to the computer 5 .

The fracturing fluid container and the injection container (that is, the piston container) of the true triaxial hydraulic fracturing testing machine of this embodiment are designed separately, which facilitates replacement of fracturing fluid. When it is necessary to replace the fracturing fluid, you only need to operate in the fracturing fluid container, open the drain valve at the lower end of the fracturing fluid container to discharge the fracturing fluid in the container, and then inject new one into the opening at the upper end of the container. The fracturing fluid can be used, or the container can be cleaned first, and then new fracturing fluid can be injected. In the prior art, the fracturing fluid container and injection container are realized by one device (oil-water separator). When the fracturing fluid needs to be replaced, the oil-water separator is disassembled, the water and oil in the container are poured out, and then manually Or use tools to push the piston in the container to the bottom of the container, and then inject new fracturing fluid into the upper cavity of the piston, which is difficult to operate, and the container is not easy to clean, and the oil-water separator must be disassembled every time the fracturing fluid is replaced , After several times of disassembly, it will lead to poor sealing of the oil-water separator and loose connection of components, which will also lead to a decrease in the accuracy of the injected liquid and an unstable fracturing state.

As shown in Figure 2, the upper end of the fracturing fluid container I201 is connected to a high-pressure gas cylinder 205 through a pipeline, and a switch valve I206 is installed on the pipeline; the lower end of the fracturing fluid container I201 is connected to the upper end of the piston container 203 through a pipeline, On-off valve II 207 is installed on the pipeline. The bottom of the fracturing fluid container I201 is provided with a discharge valve I208. The upper end of the fracturing fluid container II 202 is connected to the high-pressure gas cylinder 205 through a pipeline, and an on-off valve III 209 is installed on the pipeline; the lower end of the fracturing fluid container II 202 is connected to the upper end of the piston container 203 through a pipeline, and an on-off valve IV 210 is installed on the pipeline. . A discharge valve II 211 is set at the bottom of the fracturing fluid container II 202 . The piston container 203 is provided with a piston piece 212 that can move up and down; the upper end of the piston container 203 is connected to the downhole core 4 through a pipeline, and the lower end is connected to the water tank 213 through a pipeline. The water tank 213 is respectively connected to the constant pressure and constant speed plunger pump I 214 and the constant pressure and constant speed plunger pump II 215 through pipelines. The constant pressure and constant speed plunger pump I 214 and the constant pressure and constant speed plunger pump II 215 are connected to the computer 5 .

As shown in FIG. 3 , the confining pressure system 1 includes a high-pressure advection pump I 101 , a high-pressure advection pump II 102 and a high-pressure advection pump III 103 , and all three pump bodies are connected to the computer 5 . The high-pressure advection pump I101 is connected to the front and rear surfaces of the downhole core 4 through a pipeline, and a back pressure valve I104 is installed on the pipeline; the high-pressure advection pump II102 is connected to the left and right surfaces of the downhole core 4 through a pipeline, A back pressure valve II105 is installed on the pipeline; the high-pressure advection pump III103 is connected to the upper and lower surfaces of the downhole core 4 through a pipeline, and a back pressure valve III106 is installed on the pipeline. When the generated confining pressure exceeds the set value, the back pressure valve will automatically open to relieve the pressure to the set value.

According to the true triaxial hydraulic fracturing test method of the present invention, using the true triaxial hydraulic fracturing testing machine of the present embodiment, it comprises the following steps in sequence:

Step 1: Close all on-off valves and drain valves, inject fracturing fluid water into the fracturing fluid container I, first open the on-off valve I and on-off valve II, and then open the high-pressure gas cylinder, at this time the fracturing fluid water enters the piston In the cavity above the piston plate in the container;

Step 2: After all the fracturing fluid clear water enters the piston container, first close the high-pressure gas cylinder, and then close the switch valve Ⅰ and switch valve Ⅱ;

Step 3: Set the confining pressure value according to the test requirements, and apply confining pressure to the three axial directions of the downhole core at the same time through the high-pressure advection pump I, high-pressure advection pump II and high-pressure advection pump III;

Step 4: Start the constant pressure and constant speed plunger pump Ⅰ and the constant pressure and constant speed plunger pump Ⅱ. If the water in the cavity of the two plunger pumps is not full, the two plunger pumps will be filled from the water tank through the pipeline respectively. If the water in the cavity of the two plunger pumps is full, the fracturing operation will be performed directly;

Step 5: Set the displacement according to the test requirements. When the displacement is less than or equal to 50ml/min, only the constant pressure and constant speed plunger pump I drains water into the cavity below the piston plate in the piston container. At this time, the constant pressure and constant speed plunger pump II In the standby state, when all the water in the constant pressure and constant speed plunger pump Ⅰ is drained, the constant pressure and constant speed plunger pump Ⅱ starts to drain water into the cavity below the piston plate in the piston container, at this time the constant pressure and constant speed plunger Pump I absorbs water from the water tank; when the displacement is greater than 50ml/min, the constant pressure and constant speed plunger pump I and the constant pressure and constant speed plunger pump II discharge water into the cavity below the piston plate in the piston container at the same time;

Step 6: As the constant pressure and constant speed plunger pump I and/or the constant pressure and constant speed plunger pump II work, inject clean fracturing fluid into the downhole core, and observe the changes of inlet pressure and time displayed on the computer at the same time Relational curve, when the inlet pressure drops to a low point and is in a stable state, it is judged that the fracturing process is over, and the data recorded by the computer is saved;

Step 7: Turn off the constant pressure and constant speed piston pump I and the constant pressure and constant speed piston pump II, and make sure that the inlet pressure is zero, and at the same time make sure that the inner chamber pressure of the two plunger pumps is zero, if the inner chamber pressure is not zero, it is necessary to restart the corresponding plunger pump, and then stop it at the moment of starting to make the inner cavity pressure become zero; open the back pressure valve I, back pressure valve II and back pressure valve III at the same time, and unload the three axial axes of the downhole core. confining pressure on

Step 8: Take out the downhole core from the true triaxial test frame, and observe the fracture expansion.

In step 3, triaxial confining pressure is applied to the downhole core, the X direction is the horizontal maximum principal stress, the Y direction is the horizontal minimum principal stress, and the Z direction is the vertical stress, wherein the confining pressure in the X direction is greater than the confining pressure in the Y direction. In Step 5, the displacement setting range is 0-100ml/min.

In the true triaxial hydraulic fracturing testing machine of this embodiment, its confining pressure system is composed of three separate pressure systems, each system can be pressurized simultaneously or step by step, and the confining pressure on three sides can be both equal pressure and pressure. Differential pressure can exist. Each individual confining pressure system consists of a silicone oil container, an advection pump, a back pressure valve, and pipelines. Confining pressure medium adopts silicone oil, because silicone oil has excellent heat resistance, electrical insulation, weather resistance, hydrophobicity, physiological inertness and small surface tension, in addition, it has a low viscosity-temperature coefficient and high compression resistance , so silicone oil as a pressurized medium has the characteristics of high efficiency, good safety performance, and no interference. The high-pressure infusion pump adopts a double-piston reciprocating pump, one is the main suction plunger, and the other is the auxiliary plunger. The high-efficiency and precise infusion pump system controlled by the computer can ensure high infusion accuracy under various conditions of use. and good repeatability indicators. The injection system consists of a piston container, an injection medium container, a fracturing fluid stirring container and a push injection system. The piston container is made of stainless steel, with a rated safety pressure of 100MPa and a volume of 1.5L; the piston container is divided into upper and lower chambers by the piston plate, the upper chamber is filled with fracturing fluid, and the lower chamber is injected with liquid. The injection medium container is made of stainless steel with a rated safety pressure of 2MPa and a volume of 2L. The container has a solution blending tank with a scale of 500ml. Different fracturing fluids are blended in the blending tank according to the experimental requirements. After the blending is completed, open the valve below the blending tank and inject into the container, and then close the valve of the solution blending tank. Turn on the high-pressure gas cylinder or air compression pump, and use the air pressure to press the injection medium into the piston container. The fracturing fluid mixing vessel is made of stainless steel, with a rated safety pressure of 2MPa and a volume of 2L. It is equipped with a motor stirring mechanism and the speed can be adjusted. There is a proppant injection port and a liquid injection port on the fracturing fluid mixing container. According to the test ratio, water and additives are injected, and the stirring mechanism is controlled by a computer to adjust to the required speed and stirring time. After stirring evenly, the fracturing fluid is injected into the piston by air pressure. inside the container. The booster system consists of a double-cylinder constant-pressure constant-speed plunger pump and a booster liquid container. The pressure of the twin-cylinder constant pressure and constant speed plunger pump is 100MPa, the flow rate is 0-100ml/min, and the precision is 0.01ml/min. The characteristic of the plunger pump is that the start, stop, flow, etc. are all automatically controlled by computer programs. The system is compact in design, convenient and completely closed, and uses imported servo motors with programmable controllers and intelligent display screens to precisely control the advance, retreat, speed regulation, and pressure regulation of the plunger pump, and uses animation demonstration to indicate the plunger pump The operating status and faults, the curve shows the real-time changes of liquid flow rate, flow rate and pressure, and has a simple and convenient man-machine interface. The double-cylinder constant-pressure constant-speed plunger pump can work independently with a single cylinder, or it can work uninterruptedly in conjunction with the two cylinders. Single-cylinder and double-cylinder work have three working modes of constant pressure, constant current and tracking to meet the needs of different operations and tests. In terms of safety system, the testing machine in this embodiment is a high-pressure device. In order to ensure the safety of the test, a safety valve is installed at the inlet of the confining pressure system and the injection system. The safety valve has high sensitivity, convenient operation, safety and reliability. When the confining pressure Or when the injection pressure exceeds the safety set value, the safety valve will automatically open to release the pressure, and at the same time set the upper limit pressure value on the computer. When the pressure exceeds the set value, the computer will issue an order to automatically stop the pump to ensure the safety of the pipeline and the operator. Safety. In terms of computer acquisition and control systems, the data acquisition system can collect real-time values such as pressure, temperature, flow, and constant-speed constant-pressure plunger pump pressure. In order to ensure measurement accuracy and control reliability, the C168H digital acquisition control card is used to realize digital acquisition and transmission. The software runs under Windows7/XP environment, and has functions of gas parameter conversion and data analysis. The test operation process is displayed on the interface, which can realize man-machine dialogue. After the operator sets the parameters, the test machine can work alone, and the computer can automatically collect all values such as pressure and flow rate. The data collected by the computer can be processed to generate raw data reports, analysis reports and graphs, and at the same time generate database files for backup and query.

Embodiment two:

According to another embodiment of the true triaxial hydraulic fracturing testing machine of the present invention, its structure, connection relationship between components, working principle and beneficial effects are all the same as those of the first embodiment. Using the testing machine of this embodiment to carry out another embodiment of the true triaxial hydraulic fracturing test method, it includes the following steps in sequence:

Step 1: Close all switch valves and drain valves, inject clean water and additives into the fracturing fluid container II in a certain proportion, set the stirring time, and start the stirring mechanism to stir to form a uniform fracturing solution;

Step 2: Open the on-off valve III and the on-off valve IV first, and then open the high-pressure gas cylinder. At this time, the fracturing solution enters the cavity above the piston plate in the piston container;

Step 3: After all the fracturing solution enters the piston container, first close the high-pressure gas cylinder, and then close the switch valve III and switch valve IV;

Step 4: Set the confining pressure value according to the test requirements, and apply confining pressure to the three axial directions of the downhole core at the same time through the high-pressure advection pump I, the high-pressure advection pump II and the high-pressure advection pump III;

Step 5: Start the constant pressure and constant speed plunger pump Ⅰ and the constant pressure and constant speed plunger pump Ⅱ. If the water in the cavity of the two plunger pumps is not full, the two plunger pumps will suck up the water from the water tank through the pipeline respectively. If the water in the cavity of the two plunger pumps is full, the fracturing operation will be performed directly;

Step 6: Set the displacement according to the test requirements. When the displacement is less than or equal to 50ml/min, only the constant pressure and constant speed plunger pump I drains water into the cavity below the piston plate in the piston container. At this time, the constant pressure and constant speed plunger pump II In the standby state, when all the water in the constant pressure and constant speed plunger pump Ⅰ is drained, the constant pressure and constant speed plunger pump Ⅱ starts to drain water into the cavity below the piston plate in the piston container, at this time the constant pressure and constant speed plunger Pump I absorbs water from the water tank; when the displacement is greater than 50ml/min, the constant pressure and constant speed plunger pump I and the constant pressure and constant speed plunger pump II discharge water into the cavity below the piston plate in the piston container at the same time;

Step 7: As the constant pressure and constant speed plunger pump Ⅰ and/or constant pressure and constant speed plunger pump Ⅱ are drained, the fracturing solution is injected into the downhole core, and the relationship between the inlet pressure and time displayed on the computer is observed at the same time When the inlet pressure drops to a low point and is in a stable state, it is judged that the fracturing process is over and the data recorded by the computer is saved;

Step 8: Turn off the constant pressure and constant speed plunger pump Ⅰ and constant pressure and constant speed plunger pump Ⅱ, and make sure that the inlet pressure is zero, and at the same time make sure that the inner chamber pressure of the two plunger pumps is zero, if the inner chamber pressure is not zero, it is necessary to restart the corresponding plunger pump, and then stop it at the moment of starting to make the inner cavity pressure become zero; open the back pressure valve I, back pressure valve II and back pressure valve III at the same time, and unload the three axial axes of the downhole core. confining pressure on

Step 9: Take out the downhole core from the true triaxial test frame, and observe the fracture expansion.

In step 1, the stirring time is at least 20 minutes. In step 4, triaxial confining pressure is applied to the downhole core, the X direction is the horizontal maximum principal stress, the Y direction is the horizontal minimum principal stress, and the Z direction is the vertical stress, wherein the confining pressure in the X direction is greater than the confining pressure in the Y direction. In Step 6, the displacement setting range is 0-100ml/min.

Embodiment three:

According to another embodiment of the true triaxial hydraulic fracturing testing machine of the present invention, its structure, connection relationship between various components, working principle and beneficial effects are the same as those of Embodiment 2, the difference is: the fracturing fluid container The size of the pipeline connected between II and the piston container, and between the piston container and the downhole core should be large enough to ensure the smooth injection of sand-carrying fracturing fluid into the downhole core.

Using the testing machine of this embodiment to carry out another embodiment of the true triaxial hydraulic fracturing test method, the process steps are the same as in the second embodiment, except that the clear water and additives in step one are replaced with fracturing fluid and proppant . The fracturing fluid and proppant are injected into the fracturing fluid container II according to a certain ratio, the stirring time is set, and the stirring mechanism is started to stir to form a uniform sand-carrying fracturing fluid. Since the particle size of the sand is between 100-3000 μm, which is much larger than that of clear water or other fracturing solutions, the size of the pipeline connecting the fracturing fluid container II and the piston container, and between the piston container and the downhole core should be large enough. It can ensure the smooth injection of sand-carrying fracturing fluid into the downhole core. When it is necessary to inject sand-carrying fracturing fluid for testing, it is only necessary to replace the pipeline between the piston container and the downhole core with a larger-sized pipeline, and there is no need to replace other pipelines or the fracturing fluid container, thus saving It saves time and cost, and avoids the clogging of pipelines by sand particles, which can ensure the smooth progress of sand fracturing tests.

It is not difficult for those skilled in the art to understand that the true triaxial hydraulic fracturing testing machine and its test method of the present invention include any combination of the summary of the invention and the specific embodiments of the description of the present invention described above and the various parts shown in the accompanying drawings, and are limited to In order to keep the description concise, the space does not describe each scheme formed by these combinations one by one. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. A true triaxial hydraulic fracturing testing machine, comprising a confining pressure system, an injection system and a true triaxial test frame, the confining pressure system and the injection system are connected with the true triaxial test frame, the true triaxial test frame Downhole cores are placed in the triaxial test frame, and the feature is that: the injection system and the confining pressure system are connected to a computer, the injection system includes fracturing fluid container I, fracturing fluid container II and a piston container, and the pressure A stirring mechanism is installed in the split liquid container II, and the stirring mechanism is connected with a computer. 2. The true triaxial hydraulic fracturing testing machine according to claim 1, characterized in that: the upper end of the fracturing fluid container I is connected to the high-pressure gas cylinder through a pipeline, and a switching valve I is installed on the pipeline; The lower end of the liquid container I is connected to the upper end of the piston container through a pipeline, and a switching valve II is installed on the pipeline. 3. The true triaxial hydraulic fracturing testing machine according to claim 2, characterized in that: the bottom of the fracturing fluid container I is provided with a discharge valve I. 4. The true triaxial hydraulic fracturing testing machine according to claim 1, characterized in that: the upper end of the fracturing fluid container II is connected to the high-pressure gas cylinder through a pipeline, and a switching valve III is installed on the pipeline; The lower end of the liquid container II is connected to the upper end of the piston container through a pipeline, and a switch valve IV is installed on the pipeline. 5. The true triaxial hydraulic fracturing testing machine according to claim 4, characterized in that: the bottom of the fracturing fluid container II is provided with a discharge valve II. 6. The true triaxial hydraulic fracturing testing machine according to claim 1, characterized in that: a piston piece that can move up and down is arranged in the piston container. 7. The true triaxial hydraulic fracturing testing machine according to claim 6, characterized in that: the upper end of the piston container is connected to the downhole core through a pipeline; the lower end of the piston container is connected to a water tank through a pipeline. 8. The true triaxial hydraulic fracturing testing machine according to claim 7, wherein the water tank is respectively connected to the constant pressure and constant speed plunger pump I and the constant pressure and constant speed plunger pump II through pipelines. 9. A true triaxial hydraulic fracturing test method uses the true triaxial hydraulic fracturing testing machine described in any one of claims 1-8, which comprises the following steps in sequence: Step 1: Close all on-off valves and drain valves, inject fracturing fluid water into the fracturing fluid container I, first open the on-off valve I and on-off valve II, and then open the high-pressure gas cylinder, at this time the fracturing fluid water enters the piston In the cavity above the piston plate in the container; Step 2: After all the fracturing fluid clear water enters the piston container, first close the high-pressure gas cylinder, and then close the switch valve Ⅰ and switch valve Ⅱ; Step 3: Set the confining pressure value according to the test requirements, and apply confining pressure to the three axial directions of the downhole core at the same time through the high-pressure advection pump I, high-pressure advection pump II and high-pressure advection pump III; Step 4: Start the constant pressure and constant speed plunger pump Ⅰ and the constant pressure and constant speed plunger pump Ⅱ. If the water in the cavity of the two plunger pumps is not full, the two plunger pumps will be filled from the water tank through the pipeline respectively. If the water in the cavity of the two plunger pumps is full, the fracturing operation will be performed directly; Step 5: Set the displacement according to the test requirements. When the displacement is less than or equal to 50ml/min, only the constant pressure and constant speed plunger pump I drains water into the cavity below the piston plate in the piston container. At this time, the constant pressure and constant speed plunger pump II In the standby state, when all the water in the constant pressure and constant speed plunger pump Ⅰ is drained, the constant pressure and constant speed plunger pump Ⅱ starts to drain water into the cavity below the piston plate in the piston container, at this time the constant pressure and constant speed plunger Pump I absorbs water from the water tank; when the displacement is greater than 50ml/min, the constant pressure and constant speed plunger pump I and the constant pressure and constant speed plunger pump II discharge water into the cavity below the piston plate in the piston container at the same time; Step 6: As the constant pressure and constant speed plunger pump I and/or the constant pressure and constant speed plunger pump II work, inject clean fracturing fluid into the downhole core, and observe the changes of inlet pressure and time displayed on the computer at the same time Relational curve, when the inlet pressure drops to a low point and is in a stable state, it is judged that the fracturing process is over, and the data recorded by the computer is saved; Step 7: Turn off the constant pressure and constant speed piston pump I and the constant pressure and constant speed piston pump II, and make sure that the inlet pressure is zero, and at the same time make sure that the inner chamber pressure of the two plunger pumps is zero, if the inner chamber pressure is not zero, it is necessary to restart the corresponding plunger pump, and then stop it at the moment of starting to make the inner cavity pressure become zero; open the back pressure valve I, back pressure valve II and back pressure valve III at the same time, and unload the three axial axes of the downhole core. confining pressure on Step 8: Take out the downhole core from the true triaxial test frame, and observe the fracture expansion. 10. A true triaxial hydraulic fracturing testing method, using the true triaxial hydraulic fracturing testing machine according to any one of claims 1-8, which comprises the following steps in sequence: Step 1: Close all switch valves and drain valves, inject clean water and additives into the fracturing fluid container II in a certain proportion, set the stirring time, and start the stirring mechanism to stir to form a uniform fracturing solution; Step 2: Open the on-off valve III and the on-off valve IV first, and then open the high-pressure gas cylinder. At this time, the fracturing solution enters the cavity above the piston plate in the piston container; Step 3: After all the fracturing solution enters the piston container, first close the high-pressure gas cylinder, and then close the switch valve III and switch valve IV; Step 4: Set the confining pressure value according to the test requirements, and apply confining pressure to the three axial directions of the downhole core at the same time through the high-pressure advection pump I, the high-pressure advection pump II and the high-pressure advection pump III; Step 5: Start the constant pressure and constant speed plunger pump Ⅰ and the constant pressure and constant speed plunger pump Ⅱ. If the water in the cavity of the two plunger pumps is not full, the two plunger pumps will suck up the water from the water tank through the pipeline respectively. If the water in the cavity of the two plunger pumps is full, the fracturing operation will be performed directly; Step 6: Set the displacement according to the test requirements. When the displacement is less than or equal to 50ml/min, only the constant pressure and constant speed plunger pump I drains water into the cavity below the piston plate in the piston container. At this time, the constant pressure and constant speed plunger pump II In the standby state, when all the water in the constant pressure and constant speed plunger pump Ⅰ is drained, the constant pressure and constant speed plunger pump Ⅱ starts to drain water into the cavity below the piston plate in the piston container, at this time the constant pressure and constant speed plunger Pump I absorbs water from the water tank; when the displacement is greater than 50ml/min, the constant pressure and constant speed plunger pump I and the constant pressure and constant speed plunger pump II discharge water into the cavity below the piston plate in the piston container at the same time; Step 7: As the constant pressure and constant speed plunger pump Ⅰ and/or constant pressure and constant speed plunger pump Ⅱ are drained, the fracturing solution is injected into the downhole core, and the relationship between the inlet pressure and time displayed on the computer is observed at the same time When the inlet pressure drops to a low point and is in a stable state, it is judged that the fracturing process is over and the data recorded by the computer is saved; Step 8: Turn off the constant pressure and constant speed plunger pump Ⅰ and constant pressure and constant speed plunger pump Ⅱ, and make sure that the inlet pressure is zero, and at the same time make sure that the inner chamber pressure of the two plunger pumps is zero, if the inner chamber pressure is not zero, it is necessary to restart the corresponding plunger pump, and then stop it at the moment of starting to make the inner cavity pressure become zero; open the back pressure valve I, back pressure valve II and back pressure valve III at the same time, and unload the three axial axes of the downhole core. confining pressure on Step 9: Take out the downhole core from the true triaxial test frame, and observe the fracture expansion.