CN103993867A - Experimental device and method for simulating shale gas-pressure pressing crack process - Google Patents

Abstract

An experimental device and an experimental method for simulating a shale gas pressure fracturing process belong to the technical field of shale gas exploitation engineering. The invention is composed of a true triaxial loading unit and a gas pressure fracturing system unit. The true triaxial loading unit provides true triaxial stress loading. Under the true triaxial stress state, the gas pressure fracturing system unit simulates the shale gas pressure fracturing process to meet the pressure The fracturing simulation laboratory experiment requirements meet the gas pressurization, realize shale sample fracturing and crack expansion, and realize waste gas recovery; before the gas pressure fracturing experiment, the stress-strain relationship of the shale sample can be measured, and the shale test After the sample is fractured by air pressure, it can also directly measure the change of the permeability of the comparison shale sample before and after fracturing, and accurately evaluate the fracturing effect; by changing the fracturing gas in the high-pressure gas cylinder, it can help the experimenter find the most suitable Fracturing gas, and help experimenters study the cracking mechanism of shale cracks, and provide a theoretical basis for realizing fracturing stimulation.

Description

An experimental device and experimental method for simulating shale gas fracturing process

technical field

The invention belongs to the technical field of shale gas exploitation engineering, and in particular relates to an experimental device and an experimental method for simulating a shale gas pressure fracturing process.

Background technique

As a kind of unconventional natural gas, shale gas’s exploitation technology is different from that of conventional natural gas, and mainly includes hydraulic fracturing technology and gas pressure fracturing technology, among which hydraulic fracturing technology is the most mature in the United States, but hydraulic fracturing technology The technology consumes a lot of water resources, and a large amount of chemical agents need to be added to the water, which leads to the pollution of groundwater. Therefore, from the perspective of environmental protection, hydraulic fracturing technology is not environmentally friendly.

Gas fracturing technology, as the latest mining technology, has the advantages of water saving and environmental protection, and this technology has been carried out industrial experiments in Canadian shale test gas fields, and achieved ideal experimental results.

At present, in order to further study gas fracturing technology, it is essential to carry out fracturing simulation laboratory experiments, but the existing fracturing simulation laboratory experiments are all aimed at hydraulic fracturing technology, and are used for shale hydraulic fracturing. The experimental device cannot be simply transplanted or adjusted to a shale gas pressure fracturing experimental device, and some existing gas fracturing experimental devices can only meet the fracturing simulation indoor experiments under conventional triaxial conditions. At this stage, there is no shale gas pressure fracturing experiment device. The fracturing experimental device can meet the fracturing simulation indoor experiment under true triaxial conditions, but it cannot achieve the purpose of finding a suitable fracturing gas, nor can it accurately evaluate the fracturing effect.

Contents of the invention

Aiming at the problems existing in the prior art, the present invention provides an experimental device and an experimental method for simulating the gas pressure fracturing process of shale, which can satisfy gas pressurization under true triaxial stress state, and realize fracturing and cracking of shale samples Expansion, and can realize waste gas recovery, to meet the purpose of finding suitable fracturing gas.

In order to achieve the above object, the present invention adopts the following technical solutions: an experimental device for simulating the shale gas pressure fracturing process, including a true triaxial loading unit and a gas pressure fracturing system unit, and the true triaxial loading unit includes a vertical loading frame , a horizontal loading frame, a pressure chamber and a support platform, the vertical loading frame is installed on the support platform through a support cylinder, the horizontal loading frame is arranged on the support platform through a sliding guide rail, and the vertical loading frame is in phase with the horizontal loading frame Cross, the pressure chamber is arranged in the horizontal loading frame, and the shale sample is located in the pressure chamber;

The pneumatic fracturing system unit includes a high-pressure gas cylinder, a supercharger, a first high-pressure metering pump, a second high-pressure metering pump, a vacuum pump, and a waste gas collection tank. It is connected with the first high-pressure metering pump, the other channel of the supercharger is connected with the second high-pressure metering pump, one channel of the second high-pressure metering pump is connected with the shale sample, and the second channel of the second high-pressure metering pump is connected with the vacuum pump. The third path of the second high-pressure metering pump communicates with the waste gas collection tank.

A pressure regulating valve is arranged on the pipeline between the high-pressure gas cylinder and the supercharger, and a first on-off valve and a second on-off valve are sequentially arranged on the pipeline between the pressure regulating valve and the supercharger.

A third on-off valve is arranged on the pipeline between the booster and the second high-pressure metering pump.

A pressure sensor is connected to the pipeline between the second high-pressure metering pump and the shale sample, and a fourth on-off valve and a fifth on-off valve are sequentially arranged on the pipeline between the second high-pressure metering pump and the pressure sensor.

A sixth on-off valve is installed on the air inlet of the vacuum pump, a seventh on-off valve is installed on the air inlet of the exhaust gas collection tank, and on the common air intake pipeline of the shale sample, the vacuum pump and the exhaust gas collection tank An eighth switching valve is provided.

Adopt the experimental method of the experimental device of described simulating shale gas pressure fracturing process, comprise the steps:

Step 1: Before the experiment, the center hole is drilled and processed on the shale sample, and the center hole passes through the geometric center of the shale sample;

Step 2: Clamp the shale sample and the pressure pad. The pressure pad on the side of the central hole of the shale sample has been processed with an air guide hole in advance, and the center hole is connected to the outside through the air guide hole; Seal the clamped shale sample and the pressure pad, and install the volume change measurement sensor after the sealing is completed to form the sample assembly;

Step 3: Send the sample assembly into the pressure chamber, first connect the data transmission line of the volume change measurement sensor to the corresponding data port in the pressure chamber, and then connect the gas pressure fracturing system unit to the central hole of the shale sample. The pressure chamber is closed in time, filled with oil and pressurized, and loaded with true triaxial stress in the direction of large principal stress, medium principal stress and small principal stress, and measuring the stress-strain relationship of the shale sample through the true triaxial stress loading process;

Step 4: Start the gas pressure fracturing experiment. Before the experiment, start the vacuum pump to remove the air in the pipeline and the central hole of the shale sample;

Step 5: Let the fracturing gas in the high-pressure gas cylinder enter the supercharger through the pressure regulating valve, set the pressure in the supercharger and the pipeline through the pressure regulating valve, close the high-pressure gas cylinder, and then increase the pressure through the first high-pressure metering pump pressure in the pipeline;

Step 6: Close the gas outlet of the supercharger, adjust the air pressure rate in the pipeline through the second high-pressure metering pump, and at the same time collect the flow and pressure data of the injected fracturing gas through the second high-pressure metering pump until the pressure of the second high-pressure metering pump appears The sudden drop and volume change measurement sensor has a sudden change in value, the shale sample has completed the initial fracturing, and the pressure sensor is used to record the fracturing pressure in the pipeline during the initial fracturing process;

Step 7: Observe the flow consumption value of the fracturing gas in the pipeline through the second high-pressure metering pump until the flow rate of the fracturing gas is continuously consumed. At this time, the shale sample completes the extended fracturing and the fracturing process ends;

Step 8: Collect the residual gas in the shale sample and the pipeline through the exhaust gas collection tank. At this time, the air fracturing system unit is ready for the next air fracturing experiment.

Beneficial effects of the present invention:

The invention can simulate the gas pressure fracturing process of shale under the true triaxial stress state, meets the requirements of the gas pressure fracturing simulation indoor experiment, meets the gas pressurization, realizes the fracturing and crack expansion of shale samples, and can realize the waste gas Recovery; before the gas fracturing experiment, the stress-strain relationship of the shale sample can be measured. After the shale sample is fractured by the gas pressure, the change of the permeability of the shale sample before and after the fracturing can also be directly measured and accurately evaluated. Fracturing effect: By replacing the fracturing gas in the high-pressure gas cylinder, it can help experimenters find the most suitable fracturing gas, and help experimenters study the cracking mechanism of shale cracks, and provide a theoretical basis for realizing fracturing stimulation.

Description of drawings

Fig. 1 is a schematic structural diagram of a true triaxial loading unit in an embodiment of the present invention;

Fig. 2 is a schematic diagram of the unit pipeline connection of the gas pressure fracturing system in the embodiment of the present invention;

Fig. 3 is the schematic diagram of the clamping of the shale sample and the pressure pad in the embodiment;

Fig. 4 is a schematic diagram of the sample assembly after the shale sample and the pressure pad are installed with the volumetric measurement sensor in the embodiment;

In the figure, 1-vertical loading frame, 2-horizontal loading frame, 3-pressure chamber, 4-support platform, 5-support oil cylinder, 6-sliding guide rail, 7-shale sample, 8-high pressure cylinder, 9 -supercharger, 10-first high-pressure metering pump, 11-second high-pressure metering pump, 12-vacuum pump, 13-exhaust gas collection tank, 14-pressure regulating valve, 15-pressure sensor, 16-first switch valve, 17 -the second switching valve, 18-the third switching valve, 19-the fourth switching valve, 20-the fifth switching valve, 21-the sixth switching valve, 22-the seventh switching valve, 23-the eighth switching valve, 24- Center hole, 25-air guide hole, 26-large principal stress volume change sensor, 27-medium principal stress volume change sensor, 28-small principal stress volume change sensor.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

As shown in Figures 1 and 2, an experimental device for simulating the shale gas fracturing process includes a true triaxial loading unit and a gas fracturing system unit. The true triaxial loading unit includes a vertical loading frame 1, a horizontal loading Frame 2, pressure chamber 3 and support platform 4, the vertical loading frame 1 is installed on the support platform 4 through the support cylinder 5, the horizontal loading frame 2 is arranged on the support platform 4 through the sliding guide rail 6, and the vertical loading frame 1 is orthogonal to the horizontal loading frame 2, the pressure chamber 3 is set in the horizontal loading frame 2, and the shale sample 7 is located in the pressure chamber 3;

The air pressure fracturing system unit includes a high-pressure gas cylinder 8, a supercharger 9, a first high-pressure metering pump 10, a second high-pressure metering pump 11, a vacuum pump 12, and a waste gas collection tank 13. The high-pressure gas cylinder 8 and the supercharger 9 phases are connected, one of the supercharger 9 is connected with the first high-pressure metering pump 10, the other road of the supercharger 9 is connected with the second high-pressure metering pump 11, and the other way of the second high-pressure metering pump 11 is connected with the shale sample 7 , the second path of the second high-pressure metering pump 11 communicates with the vacuum pump 12 , and the third path of the second high-pressure metering pump 11 communicates with the waste gas collection tank 13 .

A pressure regulating valve 14 is arranged on the pipeline between the high-pressure gas cylinder 8 and the supercharger 9, and a first on-off valve 16 and a second switching valve 16 are sequentially arranged on the pipeline between the pressure regulating valve 14 and the supercharger 9. On-off valve 17, the effect of the first on-off valve 16 is to control the opening and closing of the high-pressure gas cylinder 8, and the effect of the second on-off valve 17 is to control the opening and closing of the air inlet of the supercharger 9.

A third switch valve 18 is arranged on the pipeline between the booster 9 and the second high-pressure metering pump 11 , and the function of the third switch valve 18 is to control the opening and closing of the gas outlet of the booster 9 .

A pressure sensor 15 is connected to the pipeline between the second high-pressure metering pump 11 and the shale sample 7, and a fourth on-off valve 19 is sequentially arranged on the pipeline between the second high-pressure metering pump 11 and the pressure sensor 15 And the fifth on-off valve 20, the fourth on-off valve 19 and the fifth on-off valve 20 are used to control the opening and closing of the pipeline.

The sixth on-off valve 21 is installed on the air inlet of the vacuum pump 12, the seventh on-off valve 22 is installed on the air inlet of the waste gas collection tank 13, and the shale sample 7 is connected with the vacuum pump 12 and the waste gas collection. The eighth on-off valve 23 is arranged on the public intake pipeline of the tank 13, the function of the sixth on-off valve 21 is to control the opening and closing of the air inlet of the vacuum pump 12, and the function of the seventh on-off valve 22 is to control the opening and closing of the air inlet of the waste gas collection tank 13. Opening and closing, the effect of the eighth on-off valve 23 is to close the pressure in the pipeline when the shale sample 7 is fractured.

According to the experimental requirements, there are three options for the size of the shale sample 7, which are 50×50×100mm, 75×75×150mm and 100×100×200mm. Sample 7 is taken as an example. The fracturing gas in the high-pressure gas cylinder 8 has been determined before the experiment. The conventional fracturing gas can be selected from nitrogen, carbon dioxide, helium, methane or mixed gases, etc., and can also be a new type of gas used for searching. In this embodiment, the fracturing gas The crack gas is nitrogen as an example. In this embodiment, the working pressure range of the fracturing gas is 0-100 MPa, the major principal stress applied by the true triaxial loading unit is 300 MPa, the intermediate principal stress is 300 MPa, and the minor principal stress is 100 MPa.

Adopt the experimental method of the experimental device of described simulating shale gas pressure fracturing process, comprise the steps:

Step 1: Before the experiment, drill and process a center hole on the shale sample 7, which is used to simulate horizontal drilling. The center hole passes through the geometric center of the shale sample 7. The hole depth is 100mm;

Step 2: Clamp the shale sample 7 and the pressure pad. The pressure pad on the side of the central hole 24 of the shale sample 7 has been processed with an air guide hole 25 in advance, and the central hole 24 passes through the air guide hole 25 It is connected with the outside, as shown in Fig. 3; then the clamped shale sample 7 and the pressure pad are sealed, and after the sealing is completed, the large principal stress volume change measurement sensor 26, the medium principal stress body deformation measurement sensor 26, and the medium principal stress body Variable measurement sensor 27 and small principal stress volumetric deformation measurement sensor 28 constitute a sample assembly at this moment, specifically as shown in Figure 4;

Step 3: Send the sample assembly into the pressure chamber 3, first connect the data transmission lines of the large, medium and small volume change measurement sensors to the corresponding data ports in the pressure chamber 3, and then connect the gas pressure fracturing system unit to the shale The central hole 24 of the sample 7 is connected. At this time, the pressure chamber 3 is closed, oil-filled and pressurized, and the true triaxial stress in the direction of the large principal stress, medium principal stress and small principal stress is loaded, and measured through the true triaxial stress loading process The stress-strain relationship of shale sample 7;

Step 4: Start the gas pressure fracturing experiment. Before the experiment, the first on-off valve 16, the second on-off valve 17 and the seventh on-off valve 22 are closed, and the other on-off valves are opened, and the vacuum pump 12 is started to remove the shale samples in the pipeline 7 the air in the central hole 24;

Step 5: The first on-off valve 16 and the second on-off valve 17 are opened, the fracturing gas in the high-pressure gas cylinder 8 enters the supercharger 9 through the pressure regulating valve 14, and the supercharger 9 and the pipeline are set through the pressure regulating valve 14 The pressure in the pipeline is 10MPa, the first on-off valve 16 and the second on-off valve 17 are closed, and then the pressure in the pipeline is increased through the first high-pressure metering pump 10, and the pressure is increased to within the range of 30-50MPa;

Step 6: The third on-off valve 18 is closed, the air outlet of the supercharger 9 is closed, and the air pressure rate in the pipeline is adjusted through the second high-pressure metering pump 11. The air pressure rate ranges from 0.01 to 5 MPa/min. The high-pressure metering pump 11 collects the flow rate and pressure data of the injected fracturing gas until the second high-pressure metering pump 11 experiences a sudden pressure drop and a sudden change in the value of the volume change measurement sensor. The shale sample 7 completes the initial fracturing, and at the same time passes through the pressure sensor 15 Record the fracturing pressure in the pipeline during the initial fracturing process;

Step 7: Observe the flow consumption value of the fracturing gas in the pipeline through the second high-pressure metering pump 11 until the flow rate of the fracturing gas is continuously consumed, at which point the shale sample 7 completes the expansion fracturing, and the fracturing process ends;

Step 8: The seventh switching valve 22 is opened, and the residual gas in the shale sample 7 and the pipeline is collected through the exhaust gas collection tank 13. At this time, the gas pressure fracturing system unit is ready for the next gas pressure fracturing experiment.

If the fracturing gas used in the next gas fracturing experiment is not replaced, it is only necessary to collect the residual gas in the pipeline after the fifth on-off valve 20 .

After the shale sample 7 is fractured by gas pressure, the permeability change of the shale sample 7 before and after fracturing can be directly measured to accurately evaluate the fracturing effect and provide a theoretical basis for realizing fracturing stimulation.

According to the above gas fracturing process, changing different fracturing gases can help experimenters find the most suitable fracturing gas, and provide a theoretical basis for realizing fracturing stimulation.

The solutions in the embodiments are not intended to limit the scope of patent protection of the present invention, and all equivalent implementations or changes that do not deviate from the present invention are included in the patent scope of this case.

Claims (6)

1. An experimental device for simulating a shale gas pressure fracturing process, characterized in that: it comprises a true triaxial loading unit and a gas pressure fracturing system unit, and the true triaxial loading unit comprises a vertical loading frame, a horizontal loading frame, a pressure chamber and support platform, the vertical loading frame is installed on the support platform through the support cylinder, the horizontal loading frame is set on the support platform through sliding guide rails, the vertical loading frame is orthogonal to the horizontal loading frame, the pressure chamber Set in the horizontal loading frame, the shale sample is located in the pressure chamber; The pneumatic fracturing system unit includes a high-pressure gas cylinder, a supercharger, a first high-pressure metering pump, a second high-pressure metering pump, a vacuum pump, and a waste gas collection tank. It is connected with the first high-pressure metering pump, the other channel of the supercharger is connected with the second high-pressure metering pump, one channel of the second high-pressure metering pump is connected with the shale sample, and the second channel of the second high-pressure metering pump is connected with the vacuum pump. The third path of the second high-pressure metering pump communicates with the waste gas collection tank. 2. A kind of experimental device for simulating shale gas pressure fracturing process according to claim 1, characterized in that: a pressure regulating valve is arranged on the pipeline between the high-pressure gas cylinder and the supercharger, A first on-off valve and a second on-off valve are sequentially arranged on the pipeline between the valve and the supercharger. 3. The experimental device for simulating shale gas pressure fracturing process according to claim 1, characterized in that: a third switch valve is arranged on the pipeline between the booster and the second high-pressure metering pump. 4. A kind of experimental device for simulating shale gas pressure fracturing process according to claim 1, characterized in that: a pressure sensor is connected on the pipeline between the second high-pressure metering pump and the shale sample, A fourth on-off valve and a fifth on-off valve are sequentially arranged on the pipeline between the second high-pressure metering pump and the pressure sensor. 5. A kind of experimental device for simulating shale gas pressure fracturing process according to claim 1, characterized in that: a sixth switching valve is installed on the air inlet of the vacuum pump, and the air inlet of the waste gas collection tank The seventh on-off valve is installed on the port, and the eighth on-off valve is set on the common air intake pipeline of the shale sample, vacuum pump and waste gas collection tank. 6. adopt the experimental method of the experimental device of the simulated shale gas pressure fracturing process described in claim 1, it is characterized in that: comprise the steps: Step 1: Before the experiment, the center hole is drilled and processed on the shale sample, and the center hole passes through the geometric center of the shale sample; Step 2: Clamp the shale sample and the pressure pad. The pressure pad on the side of the central hole of the shale sample has been processed with an air guide hole in advance, and the center hole is connected to the outside through the air guide hole; Seal the clamped shale sample and the pressure pad, and install the volume change measurement sensor after the sealing is completed to form the sample assembly; Step 3: Send the sample assembly into the pressure chamber, first connect the data transmission line of the volume change measurement sensor to the corresponding data port in the pressure chamber, and then connect the gas pressure fracturing system unit to the central hole of the shale sample. The pressure chamber is closed in time, filled with oil and pressurized, and loaded with true triaxial stress in the direction of large principal stress, medium principal stress and small principal stress, and measuring the stress-strain relationship of the shale sample through the true triaxial stress loading process; Step 4: Start the gas pressure fracturing experiment. Before the experiment, start the vacuum pump to remove the air in the pipeline and the central hole of the shale sample; Step 5: Let the fracturing gas in the high-pressure gas cylinder enter the supercharger through the pressure regulating valve, set the pressure in the supercharger and the pipeline through the pressure regulating valve, close the high-pressure gas cylinder, and then increase the pressure through the first high-pressure metering pump pressure in the pipeline; Step 6: Close the gas outlet of the supercharger, adjust the air pressure rate in the pipeline through the second high-pressure metering pump, and at the same time collect the flow and pressure data of injected fracturing gas through the second high-pressure metering pump until the second high-pressure metering pump has pressure The sudden drop and volume change measurement sensor has a sudden change in value, the shale sample has completed the initial fracturing, and the pressure sensor is used to record the fracturing pressure in the pipeline during the initial fracturing process; Step 7: Observe the flow consumption value of the fracturing gas in the pipeline through the second high-pressure metering pump until the flow rate of the fracturing gas is continuously consumed. At this time, the shale sample completes the extended fracturing and the fracturing process ends; Step 8: Collect the residual gas in the shale sample and the pipeline through the exhaust gas collection tank. At this time, the air fracturing system unit is ready for the next air fracturing experiment.