CN106353197B - High-pressure multiphase flow coupled rock true triaxial test system and method - Google Patents

Abstract

The invention discloses a high-pressure multiphase flow coupling rock true triaxial test system and method, and relates to rock mechanical test technology. The system is as follows: a rock sample is arranged in the center of the confining pressure chamber, loading cushion blocks are arranged around the rock sample, the left loading cushion block and the right loading cushion block are tightly pressed by the X-direction pressing shaft, and the front loading cushion block and the rear loading cushion block are tightly pressed by the Y-direction pressing shaft; the pore carbon dioxide metering pump and the pore water metering pump are respectively connected with a computer through a controller to realize the control of fluid; the acoustic emission sensor and the LVDT displacement sensor are respectively connected with a computer, and acoustic emission acoustic signals and displacement signals are collected. The method comprises the following steps: (1) processing a rock sample; (2) sealing the rock sample; (3) the pipeline is connected; (4) checking the air tightness of the system; (5) vacuumizing; (6) pre-stress loading; (7) pore fluid loading; (8) testing; (9) finishing equipment; and (5) sorting test data. The system can acquire the mechanical and deformation parameters of the rock under the coupling condition of high-pressure carbon dioxide and water, and research the mechanical properties, deformation mechanism and the like of the rock under the coupling condition of high-pressure carbon dioxide and water.

Description

High-pressure multiphase flow coupled rock true triaxial test system and method

Technical field

The invention relates to rock mechanics testing technology, and in particular to a high-pressure multi-phase flow coupled rock true triaxial testing system and method.

Background technique

Large amounts of greenhouse gas emissions are one of the main factors affecting global climate warming. CO ₂ capture, storage and utilization technology has become one of the key technologies to reduce carbon dioxide emissions internationally. Sites such as deep underground saline aquifers, abandoned oil and gas resource mining well fields, deep seas, and unconventional oil and gas reservoirs (unconventional resources such as shale oil and gas, coalbed methane, and tight oil) are the main sites for carbon dioxide storage. In CO ₂ geological storage projects, analysis and evaluation of site mechanical stability are essential links. Underground projects such as _CO2 geological storage (CCS), unconventional oil and gas resource development, and CO2 drilling and fracturing all involve the interaction of rock, water, and CO2. In recent years, a number of two-phase fluid mechanics coupling analysis software has emerged. However, due to the lack of experimental basis and constitutive model of rock mechanical properties under the action of CO2-water two-phase fluid, numerical simulation results still cannot meet engineering needs. In order to improve the accuracy of numerical analysis and calculation, it is necessary to simulate the stress and pore fluid state of deep reservoirs, carry out true triaxial mechanical tests of sandstone consolidation and drainage under the action of two-phase flow of carbon dioxide and water, and test and analyze different fluid components and pressures. Under the influence of high-pressure multi-phase flow coupling, the mechanical properties of rocks are determined, and the methods for measuring the parameters related to the mechanical properties of rocks are explored, laying the foundation for the establishment of numerical simulation mechanical constitutive models and the determination of relevant mechanical parameters. In addition, there is a relative lack of basic experimental and theoretical research on the mechanical properties of rocks under the two-phase flow conditions of CO ₂ and water. The strength criteria, damage mechanisms and constitutive equations of rocks under the coupling effect of CO ₂ and water are key scientific issues to be solved. .

Contents of the invention

The purpose of this invention is to realize rock mechanical testing under the action of high-pressure fluid multi-phase seepage coupling, fully consider the impact of high-pressure fluid on rock mechanical properties, and provide a high-pressure multi-phase seepage coupled rock true triaxial test system and method, which can study The strength criteria, crack propagation damage evolution mechanism and constitutive relationship of rocks under the coupling action of high-pressure fluids such as CO2, N2, methane and water lay the foundation for establishing effective theoretical models and numerical simulation methods for the mechanical stability risk assessment of large-scale CO2 geological storage. Base.

The purpose of the present invention is achieved as follows:

1. High-pressure multiphase flow coupled rock true triaxial test system (referred to as the system)

Including confining pressure chamber, X-direction finale, Y-direction finale, loading pad, porous partition, Pcmax ceramic plate, O-ring, rock sample, acoustic emission sensor, computer, temperature-regulated water area, filter, pore carbon dioxide metering pump , pore water metering pump, vacuum pump, controller, displacement bracket and LVDT displacement sensor;

Its location and connection relationship are:

A rock sample is set in the center of the confining pressure chamber, and loading pads are set around the rock sample. The X-direction pressing axis presses the left and right loading pads, and the Y-direction pressing axis presses the front and rear loading pads; on the left and front The loading pad is provided with a displacement bracket, and the right and rear loading pads are provided with LVDT displacement sensors; the left and right loading pads are both equipped with fluid channels; the left loading pad is provided with a Pcmax ceramic plate, and is passed through the type The sealing ring is used for sealing; porous partitions are embedded in the left and right loading pads; an acoustic emission sensor is provided on the rear loading pad;

Apply glue to seal the upper and lower sides of the rock sample; the left and right loading pads are connected to the filter through gas pipelines;

The filter is connected to the pore carbon dioxide metering pump and the pore water metering pump respectively. The pore carbon dioxide metering pump and the pore water metering pump are jointly connected to the vacuum pump to evacuate the rock sample; the pore carbon dioxide metering pump and the pore water metering pump are respectively connected to the controller and computer. connection to achieve fluid control;

The acoustic emission sensor and LVDT displacement sensor are connected to the computer respectively to collect the acoustic emission signal and displacement signal.

2. High-pressure multiphase flow coupled rock true triaxial test method (referred to as method)

This method mainly includes the following steps:

①Rock sample processing

Process the rock to be tested into a cubic rock sample with a length × width × height = 100mm × 50mm × 50mm or 80mm × 40mm × 40mm with a flat surface;

②Rock sample sealing

Place the rock sample in the center of the left, right, front and rear loading pads and clamp it. Apply a layer of sealant evenly on the upper and lower sides of the rock sample and at the edges and corners, so that the sealant and loading pads completely wrap the rock sample, forming a Assembly; wait for the sealant to dry before testing;

③Pipeline connection

Place the assembly containing the rock sample into the middle of the confining pressure chamber, and press the X-direction and Y-direction presses against the loading pad; then connect the carbon dioxide and pore water pipelines on the loading pad to the pore carbon dioxide metering pump and pore water respectively. To connect the metering pump, the pipeline must pass through the temperature-regulated water area;

④System air tightness inspection

In the pore fluid control unit, fill the sealed rock sample with high-pressure gas. After the pressure becomes constant, close the valve and observe the pressure change. If it does not drop for a long time, the air tightness is good; otherwise, seal the sample again and Steps ③④ until the unit is well sealed;

⑤Vacuum

Turn on the vacuum pump and vacuum for 12 hours. After completion, first close the gas valve and then the vacuum pump to maintain the vacuum state inside the sealed rock sample;

⑥ Prestressed loading

Start the triaxial press loading system and apply predetermined triaxial stress to the rock sample according to the pre-test plan;

⑦Pore fluid loading

Start the pore carbon dioxide metering pump, pore water metering pump, and temperature-regulated water area. First inject high-pressure pore water and maintain the predetermined pressure. After consolidation and equilibrium, inject high-pressure pore carbon dioxide and maintain the predetermined pressure. The consolidation equilibrium time remains 24 hours;

⑧Experimental test

First, start the acoustic emission monitoring unit and displacement monitoring unit, and then control and adjust the triaxial press and pore fluid pressure according to the preset stress path to carry out multi-phase flow coupled rock true three mechanical properties tests;

⑨Organize equipment

After the test is completed, first release the high-pressure gas, then unload the stress, take out the rock samples that were damaged after the test, clean the confining pressure chamber, and close the triaxial press, acoustic emission monitoring unit and pore fluid control unit;

⑩Test data sorting

Organize and analyze experimental test data saved in the computer.

The invention has the following advantages and positive effects:

①Using servo control of the true three-axis stress system can achieve precise control of stress and displacement;

② The use of fluid metering pumps can achieve precise control and measurement of fluid pressure and rock sample saturation under complex stress conditions, and can accurately measure the transient mass, flow rate and other parameters of the fluid;

③ The specially designed loading pad based on axial translation technology can apply a variety of fluids to the rock sample to achieve a multi-phase fluid coupling simulation environment, and the highly permeable partition made of dense homogeneous rock can form a matrix suction of more than 10MPa;

④ The true triaxial stress control system and pore fluid control system can be used to simulate the real stress and pore fluid state of deep reservoir rock masses;

⑤The deformation of the sample can be accurately measured using the LVDT displacement sensor on the loading pad;

⑥The acoustic emission sensor can receive damage signals caused by the development and expansion of cracks in porous media during the loading and unloading process, and realize strong coupling research on the stress, damage and seepage of multi-phase porous media;

⑦ This system can obtain the mechanical properties and deformation mechanism research of rocks under high-pressure carbon dioxide and water coupling conditions.

In short, this invention can study the high-pressure multi-phase coupled rock mass deformation and rupture mechanism and the occurrence mechanism of geological disasters such as earthquakes induced by fault sliding that are faced by deep mining and deep burial geological engineering, and provide key experiments and experiments for engineering optimization design and safe operation. Theoretical support.

Description of the drawings

Figure 1 is a schematic structural diagram of this system (top view, cross-section);

Figure 2 is a schematic cross-sectional view of the loading pad in the X direction of this system;

Figure 3.1 is the front view of the left (right) loading pad.

Figure 3.2 is a top view of the left (right) loading pad.

Figure 3.3 is the left view of the left (right) loading pad;

Figure 4.1 is the front view of the porous separator.

Figure 4.2 is a top view of a porous separator.

Figure 4.3 is a left side view of a porous separator.

In the picture:

1—Confining pressure chamber;

2—Last axis in X direction;

3—Last axis in Y direction;

4—Load the pad,

4-1—Left loading pad, 4-2—Right loading pad, 4-3—Front loading pad, 4-4—Rear loading pad;

5—porous partition;

6—Pcmax ceramic plate;

7—O-type sealing ring;

8—rock sample;

9—Acoustic emission sensor;

10—Computer;

11—Temperature-regulated waters;

12—Filter;

13—pore carbon dioxide metering pump;

14—pore water metering pump;

15—vacuum pump;

16—Controller;

17—Displacement bracket;

18—LVDT displacement sensor.

Detailed ways

Described below in detail with reference to the drawings and examples:

1. System

1. Overall

As shown in Figures 1 and 2, this system includes a confining pressure chamber 1, an X-direction pressure axis 2, a Y-direction pressure axis 3, a loading pad 4, a porous partition 5, a Pcmax ceramic plate 6, an O-ring 7, a rock sample 8, an acoustic Emission sensor 9, computer 10, temperature-regulated water area 11, filter 12, pore carbon dioxide metering pump 13, pore water metering pump 14, vacuum pump 15, controller 16, displacement bracket 17 and LVDT displacement sensor 18;

Its location and connection relationship are:

A rock sample 8 is provided in the center of the confining chamber 1, and a loading pad 4 is provided around the rock sample 8. The X-direction axis 2 presses the left and right loading pads 4-1 and 4-2, and the Y-direction axis 3 presses the left and right loading pads 4-1 and 4-2. Press the front and rear loading pads 4-3, 4-4; a displacement bracket 17 is provided on the left and front loading pads 4-1, 4-3, and a displacement bracket 17 is provided on the right and rear loading pads 4-2, 4- LVDT displacement sensor 18 is provided on 4; the left and right loading pads 4-1 and 4-2 are both provided with fluid channels; a Pcmax ceramic plate 6 is provided in the left loading pad 4-1 and is passed through an O-ring 7 for sealing; porous partitions 5 are embedded in the left and right loading pads 4-1 and 4-2; an acoustic emission sensor 9 is provided on the rear loading pad 4-4;

Apply glue to seal the upper and lower sides of the rock sample 8; the left and right loading pads (4-1, 4-2) are connected to the filter 12 through gas pipelines;

The filter 12 is connected to the pore carbon dioxide metering pump 13 and the pore water metering pump 14 respectively. The pore carbon dioxide metering pump 13 and the pore water metering pump 14 are jointly connected to the vacuum pump 15 to evacuate the rock sample 8; the pore carbon dioxide metering pump 13 and the pore water The metering pump 14 is connected to the computer 10 through the controller 16 to realize fluid control;

The acoustic emission sensor 9 and the LVDT displacement sensor 18 are respectively connected to the computer 10 to collect acoustic emission signals and displacement signals.

2. Functional components

1) Confining pressure chamber 1

Confining pressure chamber 1 is a closed cylindrical cavity made of stainless steel with a cover;

Its function is: the chamber is filled with high-pressure oil, which can generate a maximum confining pressure of 100MPa, apply uniform stress in the Z direction to the rock sample 8, and set up gas and electrical circuit through-layer channels.

2) X direction finale 2

The X-direction finale 2 is a stainless steel cylinder;

Its function is to transmit the X-direction pressure generated by the three-axis press. The maximum loading capacity of the three-axis press in the X direction is 500t.

3) Y direction final axis 3

The final axis 3 in the Y direction is a stainless steel cylinder;

Its function is to transmit the Y-direction pressure generated by the three-axis press. The maximum loading capacity of the three-axis press in the Y direction is 250t.

4) Loading pad 4

The loading pad 4 is a stainless steel rectangular block, including left, right, front and rear loading pads 4-1, 4-2, 4-3, 4-4;

The left and right loading pads 4-1 and 4-2 are respectively provided with fluid channels. The fluid channel of the left loading pad 4-1 needs to be equipped with a Pcmax ceramic plate 6 as a water channel, and the fluid channel of the right loading pad 4-2 needs to be installed. Channels serve as gas channels.

5) Porous partition 5

The porous partition 5 is a porous stainless steel plate whose shape is adapted to the loading pad 4;

Its function is: embedded in the loading pad 4, transmitting stress and allowing fluid to pass through.

6) Pcmax ceramic plate 6

Pcmax ceramic plate 6 is a ceramic plate (or dense homogeneous rock) with high gas barrier value and high pressure;

Its function is to be water-permeable and gas-proof, and can block high-pressure gases up to 10MPa, and can effectively adjust the component pressure of gases such as pore water and pore carbon dioxide.

7) O-ring 7

O-ring is an O-type rubber ring;

Its function is to seal the connections between different components.

8) Rock sample 8

Rock sample 8 is the object to be tested.

9) Acoustic emission sensor 9

Acoustic emission sensor 9 is a sensor that collects acoustic signals;

Its function is: to collect the number of acoustic emission events during the rock fracture process.

10) Computer 10

Computer 10 is a general-purpose computer;

Its functions are: controlling the flow pump and collecting data from the acoustic emission sensor and displacement sensor.

11) Temperature-regulated waters 11

Temperature regulating water area 11 is a universal constant temperature water bath;

Its function is to maintain the fluid flowing into the rock sample at a predetermined temperature and achieve constant temperature control of the fluid.

12) Filter 12

The filter 12 is a universal device that can filter solid particles of a certain size in the fluid;

Its function is to filter impurities in the fluid and prevent the pipeline from being blocked.

13) Pore carbon dioxide metering pump 13

The pore carbon dioxide metering pump 13 adopts the D series 100DX metering pump of TELEDYNE ISCO;

Its function is to accurately control the pressure of carbon dioxide, and accurately measure parameters such as the transient mass and flow rate of carbon dioxide, and has two working modes: constant pressure and constant flow. The constant pressure working mode can adjust the pressure range from 0.06895 to 68.95MPa. The display resolution is 6.895kPa.

14) Pore water metering pump 14

The pore water metering pump 14 adopts TELEDYNE ISCO's D series 100DX metering pump;

Its function is to accurately control the pressure of water, and accurately measure parameters such as transient mass and flow of water, and has two working modes: constant pressure and constant flow. The constant pressure working mode can adjust the pressure range from 0.06895 to 68.95MPa. The display resolution is 6.895kPa.

15) Vacuum pump 15

Vacuum pump 15 is a general vacuuming equipment;

Its function is to extract the gas from the rock sample and put it in a high negative pressure state.

16) Controller 16

The controller 16 is an electronic device that is matched with TELEDYNE ISCO's D series 100DX metering pump and can complete real-time computer control commands for the metering pump and transmit information to the computer in real time;

Its function is to feed back the flow parameters of the pore carbon dioxide metering pump 13 and the pore water metering pump 14 to the computer 10 in real time and execute the commands of the computer 10 to control the pore carbon dioxide metering pump 13 and the pore water metering pump 14.

17) Displacement bracket 17

The displacement bracket 17 is a stainless steel tripod fixed on the loading pad 4;

Its function is to fix the LVDT displacement sensor 18 and convert the size change of the rock sample 8 into the distance change between the displacement brackets 17.

18) LVDT displacement sensor 18.

LVDT displacement sensor 18 is a commonly used high-precision displacement sensor;

Its function is to convert the distance between the displacement brackets 17 into electrical signals, which can be restored to displacement after processing by the computer 10, so that the dimensional deformation of the rock sample 8 can be monitored in real time.

3. Working principle of this system

This system consists of 4 parts: triaxial stress control unit, pore fluid control unit, deformation measurement unit and acoustic emission measurement unit; this system can independently and accurately control triaxial stress, CO2 fluid pore pressure, pore water pressure, and accurately measure CO2 and parameters such as transient mass and flow rate of water.

1) Triaxial stress control unit

The triaxial stress control unit composed of confining pressure chamber 1, X direction pressure axis 2, Y direction pressure axis 3 and a triaxial press provides stress support for the system and completes the mechanical properties of rock sample 8;

The triaxial stress control unit generates huge stress from the triaxial press and applies it to the rock sample 8 through the two horizontal pressing axes and loading pads in the X and Y directions. The hydraulic pump exerts pressure on the rock sample 8 by injecting hydraulic oil into the confining pressure chamber. Stress in the Z direction; the stress in the three directions can be independently loaded and servo controlled (displacement control mode and force control mode). The maximum loading capacity of the Y direction pressure is 250t, the maximum loading capacity of the X direction is 500t, and the maximum loading capacity of the Z direction is 100MPa; It can load two kinds of square rock samples 8: length × width × height = 100mm × 50mm × 50mm or 80mm × 40mm × 40mm.

2) Pore fluid control unit

It consists of loading pad 4, porous partition 5, Pcmax ceramic plate 6, O-ring 7, temperature-regulated water area 11, filter 12, pore carbon dioxide metering pump 13, pore water metering pump 14, vacuum pump 15 and controller 16 The pore fluid control unit provides a high-pressure multi-phase fluid simulation environment for rock sample 8, and can control and measure multiple fluid parameters;

The pore fluid control unit injects fluids such as carbon dioxide and water into the rock sample 8 through the fluid channel of the loading pad 4 by the pore carbon dioxide metering pump 13 and the pore water metering pump 14 to realize a simulated environment of high-pressure fluid in the rock sample 8; the pore carbon dioxide metering pump 13 and pore water metering pump 14 both use TELEDYNE ISCO's D series 100DX metering pump, which can accurately control fluid pressure and flow; the Pcmax partition embedded in the left loading pad 4-1 has a high gas resistance value and high Pressure ceramic plates or dense rocks (with stable breakthrough pressure) can effectively adjust and control the pore pressure of CO2 and water through axis translation suction control technology, which can prevent carbon dioxide gas that is much higher than the pore water pressure value from flowing into the pore water metering pump. 14Achieve fluid injection with different pressure values.

3) Deformation measurement unit

The deformation measurement unit is composed of a displacement bracket 17, an LVDT displacement sensor 18 and a computer 10, which can monitor the deformation of the rock sample 8 in the X and Y directions during the test;

The deformation measurement unit uses an LVDT displacement sensor 18 to monitor the distance changes of the displacement brackets 17 at two relative positions, and indirectly monitors the dimensional changes of the rock sample 8; the LVDT displacement sensor 18 has a range of 0-5mm and a pressure resistance of 120MPa, which can meet high confining pressures. Environmental working conditions.

4) Acoustic emission measurement unit

The acoustic emission measurement unit composed of the acoustic emission sensor 9 and the computer 10 can monitor the number of acoustic emission events during the rock fracture process and study the relationship between characteristic stress and strain.

The acoustic emission measurement unit monitors the number of acoustic emission events during the rock fracture process by acoustic emission, and the relationship between characteristic stress and strain can be obtained by analyzing the number of acoustic emission times through the computer 10 .

Claims (1)

1. A test method for a high-pressure multiphase flow coupled rock true triaxial test system, The test system includes a confining pressure chamber (1), X-direction pressure axis (2), Y-direction pressure axis (3), loading pad (4), porous partition (5), Pcmax ceramic plate (6), O-type Sealing ring (7), rock sample (8), acoustic emission sensor (9), computer (10), temperature-regulated water area (11), filter (12), pore carbon dioxide metering pump (13), pore water metering pump ( 14), vacuum pump (15), controller (16), displacement bracket (17) and LVDT displacement sensor (18); Its location and connection relationship are: A rock sample (8) is provided in the center of the confining pressure chamber (1), and loading pads (4) are provided around the rock sample (8). The X-direction pressing shaft (2) presses the left and right loading pads (4) -1, 4-2), the Y-direction pressing shaft (3) presses the front and rear loading pads (4-3, 4-4); set on the left and front loading pads (4-1, 4-3) There is a displacement bracket (17) and an LVDT displacement sensor (18) is provided on the right and rear loading pads (4-2, 4-4); both the left and right loading pads (4-1, 4-2) are provided with There is a fluid channel; a Pcmax ceramic plate (6) is provided in the left loading pad (4-1) and sealed by an O-ring (7); the left and right loading pads (4-1, 4- 2) A porous partition (5) is embedded in the top; an acoustic emission sensor (9) is provided on the rear loading pad (4-4); Apply glue to seal the upper and lower sides of the rock sample (8); the left and right loading pads (4-1, 4-2) are connected to the filter (12) through gas pipelines; The filter (12) is connected to the pore carbon dioxide metering pump (13) and the pore water metering pump (14) respectively. The pore carbon dioxide metering pump (13) and the pore water metering pump (14) are jointly connected to the vacuum pump (15) to pump the rock sample. (8) Vacuuming; the pore carbon dioxide metering pump (13) and the pore water metering pump (14) are connected through the controller (16) and the computer (10) respectively to realize the control of the fluid; The acoustic emission sensor (9) and the LVDT displacement sensor (18) are respectively connected to the computer (10) to collect acoustic emission signals and displacement signals; The Pcmax ceramic plate (6) is a ceramic plate with high gas barrier value and high pressure; it has the function of water permeability and gas isolation, can block high-pressure gas up to 10MPa, and effectively regulates the component pressure of pore water and pore carbon dioxide gas. ; It is characterized by including the following steps: ①Rock sample processing Process the rock to be tested into a cuboid rock sample with a length × width × height = 100mm × 50mm × 50mm or 80mm × 40mm × 40mm with a flat surface; ②Rock sample sealing Place the rock sample in the center of the left, right, front and rear loading pads and clamp it. Apply a layer of sealant evenly on the upper and lower sides of the rock sample and at the edges and corners, so that the sealant and loading pads completely wrap the rock sample, forming a Assembly; wait for the sealant to dry before testing; ③Pipeline connection Place the assembly containing the rock sample into the middle of the confining pressure chamber, and press the X-direction and Y-direction presses against the loading pad; then connect the carbon dioxide and pore water pipelines on the loading pad to the pore carbon dioxide metering pump and pore water respectively. To connect the metering pump, the pipeline must pass through the temperature-regulated water area; ④System air tightness inspection In the pore fluid control unit, fill the sealed rock sample with high-pressure gas. After the pressure becomes constant, close the valve and observe the pressure change. If it does not drop for a long time, the air tightness is good; otherwise, seal the sample again and Steps ③④ until the unit is well sealed; ⑤Vacuum Turn on the vacuum pump and vacuum for 12 hours. After completion, first close the gas valve and then the vacuum pump to maintain the vacuum state inside the sealed rock sample; ⑥ Prestressed loading Start the triaxial press loading system and apply predetermined triaxial stress to the rock sample according to the pre-test plan; ⑦Pore fluid loading Start the pore carbon dioxide metering pump, pore water metering pump, and temperature-regulated water area. First inject high-pressure pore water and maintain the predetermined pressure. After consolidation and equilibrium, inject high-pressure pore carbon dioxide and maintain the predetermined pressure. The consolidation equilibrium time remains 24 hours; ⑧Experimental test First, start the acoustic emission monitoring unit and displacement monitoring unit, and then control and adjust the triaxial press and pore fluid pressure according to the preset stress path to carry out multi-phase flow coupled rock true three mechanical properties tests; ⑨Organize equipment After the test is completed, first release the high-pressure gas, then unload the stress, take out the rock samples that were damaged after the test, clean the confining pressure chamber, and close the triaxial press, acoustic emission monitoring unit and pore fluid control unit; ⑩Test data sorting Organize and analyze experimental test data saved in the computer.