CN106501488B - True triaxial sand fracturing test machine and its test method - Google Patents

Abstract

The invention relates to a true three-axis sand fracturing test machine, which includes a confining pressure system and an injection system. The injection system includes a fracturing fluid container I, a fracturing fluid container II and a piston container. Two pistons are arranged in the piston container. sheet bezel. The test method includes the following steps: stirring in the fracturing fluid container II to form a sand-carrying fracturing fluid, injecting the pre-fracturing fluid into the fracturing fluid container I; The liquid is injected into the middle cavity and the upper cavity of the piston container; the water is drained into the lower cavity of the piston container through the constant pressure constant speed plunger pump I and/or the constant pressure constant speed plunger pump II; the pre-fracturing fluid, The sand-carrying fracturing fluid and replacement fracturing fluid are injected into the downhole cores for fracturing in sequence. After fracturing, the downhole cores are 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 sand fracturing test machine and its test method

technical field

The invention belongs to the technical field of oil and gas reservoir development, and in particular relates to a true triaxial sanding 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, sand fracturing has become an important means for the efficient development of such reservoirs. Sand fracturing can form a complex large-scale fracture network with high conductivity, 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 initiation and expansion of fractures. Behavior is very important. The fracturing site often adopts sand fracturing method, calculates the volume of fracturing fluid required according to the required fracture scale and supporting fracture length, and injects it into the reservoir in sequence according to the proportion of pre-fluid, sand-carrying fluid, and replacement fluid internal. The existing technology of indoor test true triaxial experimental device is mainly composed of true triaxial experimental frame, triaxial hydraulic pressure stabilizer, oil-water separator, MTS booster and controller, data acquisition and processing system, etc. Only a single-action fracturing fluid can be injected into the rock, which cannot truly simulate the on-site fracturing process, and there are deficiencies in pressurization stability, experimental efficiency, operability, safety, and maintenance. 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 .

With the continuous deepening of the scope of oil and gas reservoir research, the existing equipment can no longer meet the requirements of the experiment, and the role of fracturing fluid is single, which is inconsistent with the real process on site. There are many control lines and high-pressure pipelines connected between fracturing equipment, which bring certain safety hazards and are not easy to maintain. Therefore, it is urgent to develop a new type of true triaxial sand fracturing test machine and its test method, which can truly simulate on-site sand fracturing, so as to improve the operability and safety of the experiment, and simulate the fracturing of downhole rock as realistically as possible. process.

Contents of the invention

In order to solve the problems existing in the prior art, the present invention provides a true triaxial sanding fracturing test machine, including a confining pressure system, an injection system and a true triaxial test frame, the confining pressure system and the injection system are compatible with The true triaxial test frame is connected, and downhole cores are placed in the true triaxial test frame; the injection system and the confining pressure system are connected to a computer, and the injection system includes a fracturing fluid container I, a fracturing fluid container II and the piston container. A stirring mechanism is installed in the fracturing fluid container II, and the stirring mechanism is connected to a computer. Piston sheet baffles I and piston sheet baffles II are arranged in the piston container. The two piston sheet baffles Open in the middle.

The fracturing fluid container and the injection container (that is, the piston container) of the true triaxial sand fracturing testing machine of the present invention 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.

Preferably, the upper end of the fracturing fluid container I is connected to the high-pressure gas cylinder through a pipeline, and an on-off valve I is installed on the pipeline; the lower end of the fracturing fluid container I is connected to the middle cavity of the piston container through a pipeline, and the pipeline is Install switch 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 part of the piston container through the pipeline. The cavity is connected, and the switching valve IV is installed 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 schemes, preferably, the piston plate baffle I and the piston plate baffle II divide the piston container into three cavities.

In any of the above schemes, it is preferred that piston piece I and piston piece II are arranged in the piston container, and the two piston pieces can move up and down.

In any of the above solutions, preferably, the piston plate I is above the piston plate baffle plate I, and the piston plate II is above the piston plate baffle plate II.

In any of the above schemes, preferably, the upper cavity of the piston container is connected to the downhole core through a pipeline, and a switching valve V is installed on the pipeline; the middle cavity of the piston container is connected to the downhole core through a pipeline , the switch valve VI is installed on the pipeline; the lower cavity of the piston container is connected with the water tank through the 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 sand fracturing test method, using any of the above true triaxial sand fracturing test machines, which comprises the following steps in sequence:

Step 1: Close all on-off valves and drain valves, inject fracturing fluid and proppant into fracturing fluid container II at a certain ratio, set the stirring time, and start the stirring mechanism to stir to form a uniform sand-carrying pressure. Fracture fluid: first open the switch valve III and switch valve IV, and then open the high-pressure gas cylinder, at this time, the sand-carrying fracturing fluid enters the upper cavity of the piston container; after all the sand-carrying fracturing fluid enters, first close the high-pressure gas cylinder, Then close the on-off valve III and the on-off valve IV;

Step 2: Inject the pre-fracturing fluid into the fracturing fluid container I, first open the switch valve I and the switch valve II, and then open the high-pressure gas cylinder, at this time the pre-fracturing fluid enters the middle cavity of the piston container; After all the fracturing fluid enters, first close the high-pressure gas cylinder, and then close the on-off valve I and on-off 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: Open the switch valve Ⅵ, and 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 pass through the pipeline Suction full water from the water tank respectively, and then carry out fracturing operation; if the water in the inner cavity of the two plunger pumps is full, directly carry out fracturing operation;

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 lower cavity of the piston container, and the constant pressure and constant speed plunger pump II is on standby. , 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 lower chamber of the piston container, and 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 drain water into the lower cavity of 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 to drain water, the pre-fracturing fluid is injected into the downhole core, and the injection volume of the current pre-fracturing fluid meets the test requirements When the on-off valve VI is closed, the on-off valve V is opened at the same time. At this time, the sand-carrying fracturing fluid is injected into the downhole core. , at this time, the replacement fracturing fluid displaces the sand-carrying fracturing fluid in the pipeline, and is finally injected into the downhole core;

Step 7: Following the drainage of constant pressure and constant speed plunger pump I and/or constant pressure and constant speed plunger pump II, pre-fracturing fluid, sand-carrying fracturing fluid and replacement fracturing fluid are injected into the downhole rock in sequence At the same time, observe the relationship curve of inlet pressure and time displayed on the computer. 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, the piston container has a volume of 2000ml.

In any of the above schemes, preferably, the total volume of pre-fracturing fluid, sand-carrying fracturing fluid and replacement fracturing fluid injected into the downhole core is 500-800ml.

In any of the above schemes, preferably, the pre-fracturing fluid, sand-carrying fracturing fluid and displacement fracturing fluid injected into the downhole core are respectively 40%, 50% and 10% of the total volume.

The pre-fracturing fluid does not contain proppant, and is used to depress the bottom layer of the downhole core, extend and expand fractures, prepare sufficient sand filling space for the fracture, and wait for the arrival of proppant; when preparing sand-carrying fracturing fluid, it can Different fracturing fluid systems are selected for further expansion of fractures due to the characteristics of accumulation and process requirements; the replacement fracturing fluid is the pre-fracturing fluid, but the functions of the two are different. Transport and place proppant to form proppant-filled fractures with design-required conductivity and geometric shape, and replace all the sand-carrying fracturing fluid in the wellbore into reservoir fractures to avoid sand sinking at the bottom of the well or sand stuck downhole tool.

In the true triaxial sand fracturing test of the present invention, the upper cavity of the piston container is used to inject sand-carrying fracturing fluid, and its volume is 500ml; the middle cavity of the piston container is used to inject pre-fracturing fluid, which The volume is 1000ml; the lower cavity of the piston container is used to inject water, and its volume is 500ml. The sand-carrying fracturing fluid injected each time must be 500ml, that is, the upper cavity of the piston container is filled, and the volume of pre-fracturing fluid injected is at least equal to the pre-fracturing fluid, sand-carrying fracturing fluid and displacement pressure. The total amount of lysate. There are two reasons: (1) The pre-fracturing fluid is injected first, and the pre-fracturing fluid is injected into the downhole core from the upper right of the cavity in the middle of the piston container (that is, the lower right of the piston plate baffle plate I). The rising volume of II is the volume of the injected pre-fracturing fluid; then the sand-carrying fracturing fluid is injected, and at this time, piston plate I and piston plate II rise simultaneously (the two piston plates are regarded as a whole), and the rising The volume of the sand-carrying fracturing fluid is the volume of the injected sand-carrying fracturing fluid; the replacement fracturing fluid is injected at the end, at this time, the constant pressure and constant speed plunger pump I and the constant pressure and constant speed plunger pump II push the piston plate II upward, and the rising The volume is the volume of the displaced fracturing fluid. During the whole process, the piston plate II is rising upwards, and the rising volume is the sum of the pre-fracturing fluid, sand-carrying fracturing fluid and replacement fracturing fluid, because during the whole fracturing process, the liquid will There is a certain compression, so the pre-fracturing fluid injected into the cavity in the middle of the piston container is at least the sum of the three. (2) Fill the upper cavity of the piston container with sand-carrying fracturing fluid, that is, inject 500ml. If it is not filled, then when the sand-carrying fracturing fluid is displaced, the first thing that will be squeezed out is the upper cavity. air, and then start to inject sand-carrying fracturing fluid. At this time, the pre-fracturing fluid consumed is the sum of the volumes of sand-carrying fracturing fluid and air, and the pre-fracturing fluid added to the middle cavity is equal to the pre-pressure The sum of fracturing fluid, sand-carrying fracturing fluid and replacement fracturing fluid, air may lead to insufficient injection of pre-fracturing fluid.

In any of the above schemes, preferably, in step 2, the stirring time is at least 20 min.

In any of the above schemes, preferably, in step 3, 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.

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

In any of the above schemes, it is preferred that the replacement fracturing fluid is a pre-fracturing fluid whose function is to displace the sand-carrying fracturing fluid in the pipeline into the core.

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 sand fracturing tester 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 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 2000ml; the piston container is divided into three cavities by two piston plates, the upper cavity and the middle cavity are injected with fracturing fluid, and the lower cavity is injected 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 1000ml. 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, and water and proppant are injected according to the test ratio, and the stirring mechanism is controlled by a computer to adjust to the required rotation speed and stirring time, and the fracturing fluid is injected by air pressure after stirring evenly. Inside the piston 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 according to a preferred embodiment structural representation of true triaxial sand fracturing testing machine of 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 sand fracturing tester of the present invention;

Fig. 3 is a schematic diagram of the internal structure of the piston container according to the embodiment shown in Fig. 1 of the true three-axis sand-filled fracturing tester of the present invention;

Fig. 4 is a schematic structural diagram of the confining pressure system of the embodiment shown in Fig. 1 of the true triaxial sand-filled fracturing tester 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-Switch valve Ⅴ, 213-Switch valve Ⅵ, 214-Piston baffle Ⅰ, 215-Piston baffle Plate II, 216-piston sheet I, 217-piston sheet II, 218-upper cavity of piston container, 219-middle cavity of piston container, 220-lower cavity of piston container, 221-water tank, 222-constant pressure Constant speed plunger pump Ⅰ, 223-constant pressure constant speed plunger pump Ⅱ;

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

Detailed ways

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 sand 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 fracturing fluid container I 201, fracturing fluid container II 202 and piston container 203. A stirring mechanism 204 is installed in the fracturing fluid container II 202, and the stirring mechanism 204 is connected to the computer 5. A piston plate is arranged in the piston container 203. The baffle plate I 214 and the piston plate baffle plate II 215 have openings in the middle of the two piston plate baffle plates.

The fracturing fluid container and the injection container (ie, the piston container) of the true triaxial sand fracturing tester in this embodiment are designed separately, which facilitates replacement of 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.

As shown in Figures 2 and 3, the upper end of the fracturing fluid container I201 is connected to the 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 middle of the piston container through the pipeline The cavity 219 is connected, and the switch 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 a switch valve III 209 is installed on the pipeline; the lower end of the fracturing fluid container II 202 is connected to the upper cavity 218 of the piston container through a pipeline, and a switch is installed on the pipeline. Valve IV 210. A discharge valve II 211 is set at the bottom of the fracturing fluid container II 202 . The upper cavity 218 of the piston container is connected with the downhole rock core 4 through a pipeline, and an on-off valve V 212 is installed on the pipeline; the middle cavity 219 of the piston container is connected with the downhole core 4 through a pipeline, and an on-off valve is installed on the pipeline VI 213; the lower cavity 220 of the piston container is connected to the water tank 221 through a pipeline. The water tank 221 is respectively connected to the constant pressure and constant speed plunger pump I 222 and the constant pressure and constant speed plunger pump II 223 through pipelines. The constant pressure and constant speed plunger pump I 222 and the constant pressure and constant speed plunger pump II 223 are connected to the computer 5 .

As shown in FIG. 3 , the piston plate I 214 and the piston plate II 215 divide the piston container 203 into three chambers. The piston container 203 is provided with a piston piece I 216 and a piston piece II 217, and the two piston pieces can move up and down. The piston plate I 216 is above the piston plate baffle plate I 214 , and the piston plate II 217 is above the piston plate baffle plate II 215 .

As shown in FIG. 4 , 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 the three pump bodies are all 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 an embodiment of the true triaxial sand fracturing test method of the present invention, using the true triaxial sand fracturing test machine of this embodiment, it comprises the following steps in sequence:

Step 1: Close all on-off valves and drain valves, inject fracturing fluid and proppant into fracturing fluid container II at a certain ratio, set the stirring time, and start the stirring mechanism to stir to form a uniform sand-carrying pressure. Fracture fluid: first open the switch valve III and switch valve IV, and then open the high-pressure gas cylinder, at this time, the sand-carrying fracturing fluid enters the upper cavity of the piston container; after all the sand-carrying fracturing fluid enters, first close the high-pressure gas cylinder, Then close the on-off valve III and the on-off valve IV;

Step 2: Inject the pre-fracturing fluid into the fracturing fluid container I, first open the switch valve I and the switch valve II, and then open the high-pressure gas cylinder, at this time the pre-fracturing fluid enters the middle cavity of the piston container; After all the fracturing fluid enters, first close the high-pressure gas cylinder, and then close the on-off valve I and on-off 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: Open the switch valve Ⅵ, and 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 pass through the pipeline Suction full water from the water tank respectively, and then carry out fracturing operation; if the water in the inner cavity of the two plunger pumps is full, directly carry out fracturing operation;

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 lower cavity of the piston container, and the constant pressure and constant speed plunger pump II is on standby. , 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 lower chamber of the piston container, and 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 drain water into the lower cavity of 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 to drain water, the pre-fracturing fluid is injected into the downhole core, and the injection volume of the current pre-fracturing fluid meets the test requirements When the on-off valve VI is closed, the on-off valve V is opened at the same time. At this time, the sand-carrying fracturing fluid is injected into the downhole core. , at this time, the replacement fracturing fluid displaces the sand-carrying fracturing fluid in the pipeline, and is finally injected into the downhole core;

Step 7: Following the drainage of constant pressure and constant speed plunger pump I and/or constant pressure and constant speed plunger pump II, pre-fracturing fluid, sand-carrying fracturing fluid and replacement fracturing fluid are injected into the downhole rock in sequence At the same time, observe the relationship curve of inlet pressure and time displayed on the computer. 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.

The volume of the piston container is 2000ml, and the volumes of its upper cavity, middle cavity and lower cavity are respectively 500ml, 1000ml and 500ml. The total volume of pre-fracturing fluid, sand-carrying fracturing fluid and replacement fracturing fluid injected into the downhole core is 500ml, of which the total volume of pre-fracturing fluid, sand-carrying fracturing fluid and replacement fracturing fluid is respectively 40%, 50% and 10% of the fracturing fluid, that is, the injected pre-fracturing fluid is 200ml, the sand-carrying fracturing fluid is 250ml, and the replacement fracturing fluid is 50ml. The replacement fracturing fluid is a pre-fracturing fluid whose function is to displace the sand-carrying fracturing fluid in the pipeline into the core.

The pre-fracturing fluid does not contain proppant, and is used to depress the bottom layer of the downhole core, extend and expand fractures, prepare sufficient sand filling space for the fracture, and wait for the arrival of proppant; when preparing sand-carrying fracturing fluid, it can Different fracturing fluid systems are selected for further expansion of fractures due to the characteristics of accumulation and process requirements; the replacement fracturing fluid is the pre-fracturing fluid, but the functions of the two are different. Transport and place proppant to form proppant-filled fractures with design-required conductivity and geometric shape, and replace all the sand-carrying fracturing fluid in the wellbore into reservoir fractures to avoid sand sinking at the bottom of the well or sand stuck downhole tool.

In the true triaxial sand fracturing test of this embodiment, the upper cavity of the piston container is used to inject sand-carrying fracturing fluid with a volume of 500ml; the middle cavity of the piston container is used to inject pre-fracturing fluid. Its volume is 1000ml; the lower cavity of the piston container is used for injecting water, and its volume is 500ml. The sand-carrying fracturing fluid injected each time must be 500ml, that is, the upper cavity of the piston container is filled, and the volume of pre-fracturing fluid injected is at least equal to the pre-fracturing fluid, sand-carrying fracturing fluid and displacement pressure. The total amount of lysate.

In step 2, the stirring time is at least 20 minutes. 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 2000ml; the piston container is divided into three cavities by two piston plates, the upper cavity and the middle cavity are injected with fracturing fluid, and the lower cavity is injected 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 1000ml. 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, and water and proppant are injected according to the test ratio, and the stirring mechanism is controlled by a computer to adjust to the required rotation speed and stirring time, and the fracturing fluid is injected by air pressure after stirring evenly. Inside the piston 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.

Embodiment two:

According to another embodiment of the true triaxial sand fracturing test method of the present invention, the true triaxial sand fracturing test machine used is the same as that of the first embodiment, the test procedure is the same as that of the first embodiment, and the test parameters are different . In this example, the total volume of the pre-fracturing fluid, sand-carrying fracturing fluid and replacement fracturing fluid injected into the downhole core is 800ml, of which the pre-fracturing fluid, sand-carrying fracturing fluid and replacement fracturing fluid The fluids are 40%, 50% and 10% of the total volume respectively, that is, the injected pre-fracturing fluid is 320ml, the sand-carrying fracturing fluid is 400ml, and the replacement fracturing fluid is 80ml.

Embodiment three:

According to another embodiment of the true triaxial sand fracturing test method of the present invention, the true triaxial sand fracturing test machine used is the same as that of the first embodiment, the test procedure is the same as that of the first embodiment, and the test parameters are different . In this example, the total volume of the pre-fracturing fluid, sand-carrying fracturing fluid and replacement fracturing fluid injected into the downhole core is 600ml, of which the pre-fracturing fluid, sand-carrying fracturing fluid and replacement fracturing fluid The fluids are 40%, 50% and 10% of the total volume respectively, that is, the injected pre-fracturing fluid is 240ml, the sand-carrying fracturing fluid is 300ml, and the replacement fracturing fluid is 60ml.

It is not difficult for those skilled in the art to understand that the true triaxial sand fracturing test machine and its test method of the present invention include any combination of the summary of the invention and the specific implementation of the description of the present invention described above and the various parts shown in the accompanying drawings, Due to space limitation and to make the description concise, the schemes formed by these combinations are not described 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 (17)

1. A true triaxial sand 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 Downhole cores are placed in the true triaxial test frame, and the feature is that: the injection system and the confining pressure system are connected to a computer, and 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 fracturing fluid container II, the stirring mechanism is connected to the computer, the piston plate baffle plate I and the piston plate baffle plate II are arranged in the piston container, and the middle parts of the two piston plate baffle plates are both open; The upper end of the fracturing fluid container I is connected to the high-pressure gas cylinder through a pipeline, and the on-off valve I is installed on the pipeline; the lower end of the fracturing fluid container I is connected to the middle cavity of the piston container through a pipeline, and the on-off valve II is installed on the pipeline. ; The upper end of the fracturing fluid container II is connected to the high-pressure gas cylinder through a pipeline, and an on-off valve III is installed on the pipeline; the lower end of the fracturing fluid container II is connected to the upper cavity of the piston container through a pipeline, and an on-off valve IV is installed on the pipeline. ; The piston baffle I and the piston baffle II divide the piston container into three cavities; the upper cavity of the piston container is connected to the downhole core through a pipeline, and a switching valve V is installed on the pipeline The middle cavity of the piston container is connected with the downhole core through a pipeline, and a switch valve VI is installed on the pipeline; the lower cavity of the piston container is connected with a water tank through a pipeline. 2. The true triaxial sand fracturing testing machine according to claim 1, characterized in that: the bottom of the fracturing fluid container I is provided with a discharge valve I. 3. The true triaxial sand fracturing testing machine according to claim 2, characterized in that: the bottom of the fracturing fluid container II is provided with a drain valve II. 4. The true triaxial sand-filled fracturing testing machine according to claim 3, characterized in that: piston plate I and piston plate II are arranged in the piston container, and the two piston plates can move up and down. 5. The true triaxial sand-filled fracturing testing machine according to claim 4, characterized in that: the piston plate I is above the piston plate baffle plate I, and the piston plate II is above the piston plate baffle plate above plate II. 6. The true triaxial sanding fracturing testing machine according to claim 5, characterized in that 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. 7. The true triaxial sanding fracturing testing machine according to claim 6, characterized in that: the constant pressure and constant speed plunger pump I and the constant pressure and constant speed plunger pump II are connected to a computer. 8. The true triaxial sand fracturing testing machine according to claim 7, characterized in that: the confining pressure system includes high-pressure advection pump I, high-pressure advection pump II and high-pressure advection pump III, and the three pump bodies are all connected to computer connection. 9. The true triaxial sanding fracturing testing machine according to claim 8, characterized in that: 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 left and right sides of the downhole core through a pipeline, 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 the pipeline Install the back pressure valve III on it. 10. A true triaxial sand fracturing test method, using the true triaxial sand fracturing test machine according to claim 9, which comprises the following steps in sequence: Step 1: Close all on-off valves and drain valves, inject fracturing fluid and proppant into fracturing fluid container II at a certain ratio, set the stirring time, and start the stirring mechanism to stir to form a uniform sand-carrying pressure. Fracture fluid: first open the switch valve III and switch valve IV, and then open the high-pressure gas cylinder, at this time, the sand-carrying fracturing fluid enters the upper cavity of the piston container; after all the sand-carrying fracturing fluid enters, first close the high-pressure gas cylinder, Then close the on-off valve III and the on-off valve IV; Step 2: Inject the pre-fracturing fluid into the fracturing fluid container I, first open the switch valve I and the switch valve II, and then open the high-pressure gas cylinder, at this time the pre-fracturing fluid enters the middle cavity of the piston container; After all the fracturing fluid enters, first close the high-pressure gas cylinder, and then close the on-off valve I and on-off 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: Open the switch valve Ⅵ, and 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 pass through the pipeline Suction full water from the water tank respectively, and then carry out fracturing operation; if the water in the inner cavity of the two plunger pumps is full, directly carry out fracturing operation; 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 lower cavity of the piston container, and the constant pressure and constant speed plunger pump II is on standby. , 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 lower chamber of the piston container, and 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 drain water into the lower cavity of 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 to drain water, the pre-fracturing fluid is injected into the downhole core, and the injection volume of the current pre-fracturing fluid meets the test requirements When the on-off valve VI is closed, the on-off valve V is opened at the same time. At this time, the sand-carrying fracturing fluid is injected into the downhole core. , at this time, the replacement fracturing fluid displaces the sand-carrying fracturing fluid in the pipeline, and is finally injected into the downhole core; Step 7: Following the drainage of constant pressure and constant speed plunger pump I and/or constant pressure and constant speed plunger pump II, pre-fracturing fluid, sand-carrying fracturing fluid and replacement fracturing fluid are injected into the downhole rock in sequence At the same time, observe the relationship curve of inlet pressure and time displayed on the computer. 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. 11. The true triaxial sand fracturing test method according to claim 10, characterized in that: the volume of the piston container is 2000ml. 12. The true triaxial sanding fracturing test method according to claim 10, characterized in that: the total volume of the pre-fracturing fluid, sand-carrying fracturing fluid and displacement fracturing fluid injected into the downhole core is 500 -800ml. 13. The true triaxial sanding fracturing test method as claimed in claim 12, characterized in that: the pre-fracturing fluid, sand-carrying fracturing fluid and displacement fracturing fluid injected into the downhole core are respectively 1/4 of the total volume 40%, 50%, and 10%. 14. The true triaxial sand fracturing test method according to claim 10, characterized in that: in step 2, the stirring time is at least 20 minutes. 15. The true triaxial sanding fracturing test method according to claim 10, characterized in that: in step 3, a triaxial confining pressure is applied to the downhole core, the X direction is the horizontal maximum principal stress, and the Y direction is the horizontal minimum principal stress. Stress, the Z direction is the vertical stress, and the confining pressure in the X direction is greater than the confining pressure in the Y direction. 16. The true triaxial sand fracturing test method according to claim 10, characterized in that: in step 5, the displacement setting range is 0-100ml/min. 17. The true triaxial sand fracturing test method according to any one of claims 10-16, characterized in that: the replacement fracturing fluid is a pre-fracturing fluid whose function is to transfer the The sand-carrying fracturing fluid is displaced into the core.