CN108709815B - Experimental device and method for measuring fracture toughness of rock at low temperature - Google Patents
Experimental device and method for measuring fracture toughness of rock at low temperature Download PDFInfo
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- CN108709815B CN108709815B CN201810501247.XA CN201810501247A CN108709815B CN 108709815 B CN108709815 B CN 108709815B CN 201810501247 A CN201810501247 A CN 201810501247A CN 108709815 B CN108709815 B CN 108709815B
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
- G01N3/18—Performing tests at high or low temperatures
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- G—PHYSICS
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- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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- G01N2203/0048—Hydraulic means
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
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Abstract
The invention relates to an experimental device and a method for measuring the fracture toughness of rocks at low temperature, and the technical scheme is that a self-pressurization liquid nitrogen tank penetrates through the bottom end of an experimental cavity; the fluid recovery tank is connected with the top end of the experimental cavity and is provided with a control valve; the hydraulic system penetrates through the loading equipment and the piston system to be connected with the bottom end of the experiment cavity; the other end of the hydraulic system is connected with the computer control system; the low-temperature control system is connected with the experiment cavity; one end of the hydraulic system is connected with the computer control system; the other end of the hydraulic system passes through the loading equipment and is connected with the piston system; has the advantages that: the method solves the problem of testing the fracture toughness of the rock core under the low-temperature/ultralow-temperature condition, can simulate the fracture of the rock core under the low-temperature condition more truly, and has important significance for guiding the field application of low-temperature hydraulic fracturing and the like; in addition, only through changing different lower cushion blocks, can measure other mechanical properties simultaneously, the function is various, easy operation.
Description
Technical Field
The invention relates to the field of rock mechanics, in particular to an experimental device and method for measuring fracture toughness of rock at low temperature, which are used for obtaining the fracture toughness of the rock at low temperature, and providing a basis for finely analyzing the mechanical characteristics of the rock at low temperature of a stratum and guiding drilling and production of oil gas and mine resources.
Background
In 1981, the first shale gas well in the United states was successfully fractured, and the feasibility of applying a hydraulic fracturing technology to develop shale gas was verified. However, due to the large waste of water resources caused by hydraulic fracturing, countries such as france and the like have a law to forbid the exploitation of shale gas by using a hydraulic fracturing method due to the consideration of resources and environment. In recent years, to solve the problem, domestic and foreign scholars propose a novel low-temperature anhydrous fracturing technology.
The fracture toughness of the rock under the low-temperature condition is a key parameter for judging whether the low-temperature anhydrous fracturing can form a seam network. In recent years, although people obtain rock with more accurate fracture toughness through a laboratory test method, various experimental methods and devices have a certain application range according to complicated geological conditions and rock particularity. For example, patent inventions with application numbers CN106769517A and CN106644740A disclose an experimental apparatus and method for testing fracture toughness of rock under pore pressure conditions, respectively, which can be used for studying influences of factors such as pore pressure, confining pressure and temperature on fracture toughness of rock materials, and in the process of considering temperature influence, the apparatus is mainly heated by a heating rod, that is, only high temperature conditions can be realized, but for low temperature environment of anhydrous fracturing, the apparatus cannot be realized due to different realization mechanisms. In addition, the test sample of the experimental device is a 3-point bending beam, and in view of the particularity of the rock, the rock sample of the 3-point bending beam method is difficult to prepare and clamp, so the applicability is not strong; the test piece used in the invention patent with the application number of CN07340165A is a brazilian disc test piece, but the influence of external temperature is not considered when measuring the fracture toughness of rock.
In order to meet the application requirements of low-temperature anhydrous fracturing in oil and gas exploitation, accurately obtain the fracture toughness of rocks in a low-temperature environment and analyze the mechanism of the low-temperature anhydrous fracturing, an experimental device and a method for measuring the fracture toughness of rocks, which can truly reflect a low-temperature state, need to be developed urgently.
Disclosure of Invention
The invention aims to provide an experimental device and method for measuring the fracture toughness of rocks at low temperature aiming at the defects in the prior art so as to more accurately test the fracture toughness of rocks under extreme conditions such as low temperature/ultralow temperature and the like.
The invention provides an experimental device for measuring fracture toughness of rock at low temperature, which adopts the technical scheme that: comprises a self-pressurization liquid nitrogen tank (1), a liquid nitrogen recovery tank (3), a hydraulic system (5), an experimental cavity (9), a low-temperature control system (12), a hydraulic loading system (13) and a computer control system (15),
the self-pressurization liquid nitrogen tank penetrates through the bottom end of the experiment cavity (9) through a first high-pressure heat-preservation pipeline (2);
the liquid nitrogen recovery tank (3) is connected with the top end of the experiment cavity (9) through a second high-pressure heat-preservation pipeline (4), and a control valve is arranged on the liquid nitrogen recovery tank (3);
one end of the hydraulic system (5) passes through the loading equipment (7) and the piston system (8) through a first pressure-resistant pipeline (6) and is connected with the bottom end of the experiment cavity (9); the other end of the hydraulic system (5) is connected with a computer control system (15) through a third data transmission line (16);
the low-temperature control system (12) is connected with the experiment cavity (9) through a first data transmission line (10), and one end of the first data transmission line (10) is provided with a temperature sensor;
one end of the hydraulic loading system (13) is connected with the computer control system (15) through a second data transmission line (14); the other end of the hydraulic loading system (13) passes through the loading equipment (7) through a second pressure-resistant pipeline (11) and is connected with the piston system (8);
the experimental cavity (9) comprises an upper cushion block (21), a heat shrinkable tube (22), a lower cushion block (24), a cavity shell (25), a buckle (26) and a rubber sealing ring (27), wherein the cavity shell (25) is arranged at the upper end of the piston system (8), the rock core (23) is clamped between the upper cushion block (21) and the lower cushion block (24), and the heat shrinkable tube (22) is wrapped outside the rock core (23), the lower part of the upper cushion block (21) and the upper part of the lower cushion block (24); the upper cushion block (21) penetrates through the cavity shell (25) and is installed on the outer side of the upper cushion block (21) at the upper end of the cavity shell (25) through a buckle (26).
Preferably, the lower cushion block (24) is an A-shaped lower cushion block, a circular channel with the diameter slightly smaller than that of the middle hole of the core (23) is arranged in the A-shaped lower cushion block, and an internal thread is arranged at the bottom end of the circular channel; the outer side of the bottom end of the A-shaped lower cushion block is sealed by a rubber sealing ring.
Preferably, the lower cushion block (24) is a B-type lower cushion block, a circular channel is arranged in the middle of the B-type lower cushion block, and an internal thread is arranged at the bottom end of the circular channel; the outer side of the bottom end of the B-type lower cushion block is sealed by a rubber sealing ring; the section of the upper end face of the B-type lower cushion block is provided with a groove, so that the flow of fluid on the end face of the inlet of the rock core is convenient to realize.
Preferably, the axial and radial sensors are respectively installed on the outer side of the heat shrinkable tube (22), so that different experimental conditions can be simulated.
Preferably, the core (23) adopts the standard of 50mm diameter and 25mm height, a round hole with the diameter smaller than 5mm is arranged in the center, and wing-shaped cracks with the length of 0.5mm are prefabricated on two sides of the round hole respectively.
Preferably, the computer control system (15) controls the hydraulic loading system (13) to pressurize the piston system (8), so that the upper cushion block (21) is contacted and clamped with the loading device (7), and the pressure is 2 MPa.
The invention provides an experimental method of an experimental device for measuring fracture toughness of rock at low temperature, which adopts the technical scheme that: the experimental method for measuring the fracture toughness of the rock at the low temperature by the experimental device for measuring the fracture toughness of the rock at the low temperature comprises the following specific experimental steps:
(1) preparing a core: the standard of the core is 50mm in diameter and 25mm in height, a round hole with the diameter smaller than 5mm is arranged in the center, wing-shaped cracks with the length of 0.5mm are prefabricated on two sides of the round hole respectively, and two end faces of the core are required to be completely parallel to reduce errors;
(2) placing the tested rock core in a test cavity, and placing the test cavity on a piston system;
(3) a computer control system is used for controlling a hydraulic loading system to pressurize a piston system, so that an upper cushion block is in contact with loading equipment and clamped, the pressure is 2MPa, and the upper cushion block is sealed by a buckle;
(4) opening a self-pressurization liquid nitrogen tank to enable the experiment cavity to be filled with low-temperature fluid, and simultaneously maintaining the temperature in the experiment cavity by controlling a control valve of a liquid nitrogen recovery tank;
(5) opening a low-temperature control system, and recording the temperature in the experimental cavity in real time;
(6) when the temperature is stabilized to the experiment set value, a hydraulic system is opened, a computer control system applies internal pressure to the rock core, the pressure change condition is observed, when the pressure is reduced, pressurization is stopped, and the highest pressure value P is recorded;
(7) and unloading the pressure of the hydraulic system and the hydraulic loading system, closing the self-pressurization liquid nitrogen tank, taking out the rock core, and calculating the fracture toughness of the rock at the stable temperature according to the experimental result after the experiment is finished.
The experimental method of the experimental device for measuring the fracture toughness of the rock at the low temperature, which is provided by the invention, is a method for measuring the mechanical property of the rock at the low temperature by using the experimental device for measuring the fracture toughness of the rock at the low temperature, and the experimental steps are as follows:
the experimental device for measuring the fracture toughness of the rock at low temperature is utilized, the lower cushion block is replaced by the A-type lower cushion block into the B-type lower cushion block, the axial sensor and the radial sensor are respectively installed on the outer side of the heat shrink tube, different experimental conditions can be simulated, the strength, the elastic modulus and the mechanical parameters of Poisson ratio of the rock under different confining pressure, pore pressure and low/ultra-low temperature conditions are measured, and support is provided for analyzing the mechanical behavior of the rock under the low/ultra-low temperature conditions.
Preferably, the specific experimental steps of the invention are as follows:
(1) preparing a core: the standard of the core is a cylinder with the diameter of 50mm and the height of 50mm, and two end faces of the core are required to be completely parallel to reduce errors;
(2) clamping a rock core to be tested by an upper cushion block and a B-shaped lower cushion block, wrapping the outer end of the rock core by a heat shrink tube, placing a sensor for measuring axial and radial displacement outside the heat shrink tube, placing the sensor in an experimental cavity, placing the experimental cavity on a piston system, and sealing the upper cushion block by utilizing a buckle;
(3) opening a self-pressurization liquid nitrogen tank to enable the experiment cavity to be filled with low-temperature fluid, closing a control valve of a liquid nitrogen recovery tank, and maintaining the temperature and the pressure in the experiment cavity;
(4) opening a low-temperature control system, and recording the temperature in the experimental cavity in real time;
(5) when the temperature is stabilized to the experiment set value, controlling a hydraulic system to apply pore pressure to the rock core by using a computer control system, and when the rock core is fully saturated and reaches the set pore pressure value, maintaining the set pore pressure unchanged;
(6) controlling a hydraulic loading system to pressurize a piston system by using a computer control system until the rock core is damaged, and recording axial and radial deformation of the rock core along with axial load change in the whole loading process;
(7) and unloading the pressure of the hydraulic system and the hydraulic loading system, closing the self-pressurization liquid nitrogen tank, taking out the core, and calculating relevant mechanical parameters of the core under the conditions of the temperature, the confining pressure and the pore pressure according to the experimental result after the experiment is finished.
Compared with the prior art, the invention has the following beneficial effects:
(1) the method solves the problem of testing the fracture toughness of the rock core under the low-temperature/ultralow-temperature condition, can simulate the fracture of the rock core under the low-temperature condition more truly, and has important significance for guiding the field application of low-temperature hydraulic fracturing and the like;
(2) the self-pressurization liquid nitrogen tank is adopted for realizing the low-temperature environment, the low-temperature medium can be liquid nitrogen, liquid carbon dioxide and other low-temperature fluids, the cooling safety is ensured, different low-temperature environments can be flexibly realized, and the cooling method is simple and rapid;
(3) this experimental apparatus only through changing different lower cushion, can measure the mechanical properties of rock under different confined pressure and pore pressure under the low temperature/ultra-low temperature environment simultaneously, and the function is various, easy operation, and the experiment is convenient, reduces the investment.
Drawings
FIG. 1 is a schematic diagram of an experimental apparatus for measuring fracture toughness of rock at low temperature according to the present invention;
FIG. 2 is a schematic diagram of the internal structure of the experimental chamber;
FIG. 3 is a schematic view of a type A lower pad block structure for measuring fracture toughness;
FIG. 4 is a top view of a type A lower pad;
FIG. 5 is a schematic view of a type B under-pad structure for measuring mechanical parameters;
FIG. 6 is a top view of a top portion of a type B lower block;
FIG. 7 is a top view of the entirety of the type B lower pad;
in the upper diagram, a self-pressurization liquid nitrogen tank 1, a first high-pressure heat-preservation pipeline 2, a liquid nitrogen recovery tank 3, a second high-pressure heat-preservation pipeline 4, a hydraulic system 5, a first pressure-resistant pipeline 6, a loading device 7, a piston system 8, an experiment cavity 9, a first data transmission line 10, a second pressure-resistant pipeline 11, a low-temperature control system 12, a hydraulic loading system 13, a second data transmission line 14, a computer control system 15 and a third data transmission line 16;
the device comprises an upper cushion block 21, a heat shrinkable tube 22, a core 23, a lower cushion block 24, a cavity shell 25, a buckle 26 and a rubber sealing ring 27.
Detailed Description
The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings, and it will be understood that they are described herein for the purpose of illustration and explanation and not limitation.
Example 1, referring to fig. 1 to 4, the invention provides an experimental device for measuring fracture toughness of rock at low temperature, which adopts the following technical scheme: comprises a self-pressurization liquid nitrogen tank 1, a liquid nitrogen recovery tank 3, a hydraulic system 5, an experiment cavity 9, a low-temperature control system 12, a hydraulic loading system 13 and a computer control system 15,
the self-pressurization liquid nitrogen tank penetrates through the bottom end of the experiment cavity 9 through the first high-pressure heat-preservation pipeline 2;
the liquid nitrogen recovery tank 3 is connected with the top end of the experiment cavity 9 through a second high-pressure heat preservation pipeline 4, and a control valve is arranged on the liquid nitrogen recovery tank 3;
one end of the hydraulic system 5 passes through the loading equipment 7 and the piston system 8 through the first pressure-resistant pipeline 6 and is connected with the bottom end of the experiment cavity 9; the other end of the hydraulic system 5 is connected with a computer control system 15 through a third data transmission line 16;
the low-temperature control system 12 is connected with the experiment cavity 9 through a first data transmission line 10, and one end of the first data transmission line 10 is provided with a temperature sensor;
one end of the hydraulic loading system 13 is connected with a computer control system 15 through a second data transmission line 14; the other end of the hydraulic loading system 13 passes through the loading equipment 7 through a second pressure-resistant pipeline 11 and is connected with the piston system 8;
referring to fig. 2, the experimental cavity 9 of the present invention includes an upper cushion block 21, a heat shrinkable tube 22, a lower cushion block 24, a cavity housing 25, a buckle 26, and a rubber seal ring 27, wherein the cavity housing 25 is disposed at the upper end of the piston system 8, the core 23 is sandwiched between the upper cushion block 21 and the lower cushion block 24, and the heat shrinkable tube 22 is wrapped around the core 23, the lower portion of the upper cushion block 21, and the outer portion of the upper portion of the lower cushion block 24; the upper cushion block 21 penetrates through the cavity housing 25 and is mounted on the outer side of the upper cushion block 21 at the upper end of the cavity housing 25 through a buckle 26.
Signing, wherein the lower cushion block 24 adopts an A-shaped lower cushion block, a circular channel with the diameter slightly smaller than that of the middle hole of the core 23 is arranged in the A-shaped lower cushion block, and internal threads are arranged at the bottom end of the circular channel; the outer side of the bottom end of the A-shaped lower cushion block is sealed by a rubber sealing ring.
Preferably, the core 23 adopts a standard of 50mm in diameter and 25mm in height, a circular hole with a diameter smaller than 5mm is arranged in the center, and wing-shaped cracks with a length of 0.5mm are prefabricated on two sides of the circular hole respectively.
Preferably, the computer control system 15 controls the hydraulic loading system 13 to pressurize the piston system 8, so that the upper pad 21 contacts and clamps the loading device 7, and the pressure is 2 MPa.
The invention provides an experimental method of an experimental device for measuring fracture toughness of rock at low temperature, which adopts the technical scheme that: the experimental method for measuring the fracture toughness of the rock at the low temperature by the experimental device for measuring the fracture toughness of the rock at the low temperature comprises the following specific experimental steps:
(1) preparing a core: the standard of the core is 50mm in diameter and 25mm in height, a round hole with the diameter smaller than 5mm is arranged in the center, wing-shaped cracks with the length of 0.5mm are prefabricated on two sides of the round hole respectively, and two end faces of the core are required to be completely parallel to reduce errors;
(2) placing the tested rock core 23 in the test cavity 9, and placing the test cavity 9 on the piston system 8;
(3) the computer control system 15 is used for controlling the hydraulic loading system 13 to pressurize the piston system 8, so that the upper cushion block 21 is in contact with and clamped by the loading equipment 7, the pressure is 2MPa, and the upper cushion block 21 is sealed by a buckle 26;
(4) opening the self-pressurization liquid nitrogen tank 1 to enable the experiment cavity 9 to be filled with the low-temperature fluid, and simultaneously maintaining the temperature in the experiment cavity 9 by controlling a control valve of the liquid nitrogen recovery tank 3;
(5) opening the low-temperature control system 12, and recording the temperature in the experiment cavity 9 in real time;
(6) when the temperature is stabilized to the experiment set value, the hydraulic system 5 is opened, the computer control system 15 applies internal pressure to the rock core 23, the pressure change condition is observed, when the pressure is reduced, the pressurization is stopped, and the highest pressure value P is recorded;
(7) and unloading the pressure of the hydraulic system 5 and the hydraulic loading system 13, closing the self-pressurizing liquid nitrogen tank 1, taking out the rock core 23, and calculating the fracture toughness of the rock at the stable temperature according to the experiment result after the experiment is finished.
Example 2, referring to fig. 1 to 7, the experimental method of the experimental apparatus for measuring fracture toughness of rock at low temperature according to the present invention, the method for measuring mechanical properties of rock at low temperature by using the experimental apparatus for measuring fracture toughness of rock at low temperature, comprises the following experimental steps:
by utilizing the experimental device for measuring the fracture toughness of the rock at the low temperature, the lower cushion block 24 is replaced by the A-type lower cushion block into the B-type lower cushion block, and the axial and radial sensors are respectively installed outside the heat shrink tube 22, so that different experimental conditions can be simulated, the strength, the elastic modulus and the mechanical parameters of Poisson ratio of the rock under different confining pressure, pore pressure and low/ultra-low temperature conditions can be measured, and the support is provided for analyzing the mechanical behavior of the rock under the low/ultra-low temperature conditions.
Referring to fig. 5-7, a circular channel is arranged in the middle of the B-shaped lower cushion block, and internal threads are arranged at the bottom end of the circular channel; the outer side of the bottom end of the B-type lower cushion block is sealed by a rubber sealing ring; the section of the upper end face of the B-type lower cushion block is provided with a groove, so that the flow of fluid on the end face of the inlet of the rock core is convenient to realize. When the device is used, the axial sensor and the radial sensor are respectively arranged on the outer side of the heat shrinkable tube 22, so that different experimental conditions can be simulated.
The method for measuring the mechanical property of the rock at low temperature comprises the following specific experimental steps:
(1) preparing a core: the standard of the core is a cylinder with the diameter of 50mm and the height of 50mm, and two end faces of the core are required to be completely parallel to reduce errors;
(2) clamping a core 23 of an experiment by an upper cushion block 21 and a B-shaped lower cushion block, wrapping the outer end of the core by a heat shrinkable tube 22, placing a sensor for measuring axial and radial displacement outside the heat shrinkable tube 22 in an experiment cavity 9, placing the experiment cavity 9 on a piston system 8, and sealing the upper cushion block 21 by using a buckle 26;
(3) opening the self-pressurization liquid nitrogen tank 1 to enable the experiment cavity 9 to be filled with the low-temperature fluid, closing a control valve of the liquid nitrogen recovery tank 3, and maintaining the temperature and the pressure in the experiment cavity 9;
(4) opening the low-temperature control system 12, and recording the temperature in the experiment cavity 9 in real time;
(5) when the temperature is stabilized to the experiment set value, the computer control system 15 is used for controlling the hydraulic system 5 to apply pore pressure to the rock core 23, and when the rock core 23 is fully saturated and reaches the set pore pressure value, the set pore pressure is maintained unchanged;
(6) controlling a hydraulic loading system 13 to pressurize a piston system 8 by using a computer control system 15 until a rock core 23 is damaged, and recording axial and radial deformation of the rock core 23 along with axial load change in the whole loading process;
(7) and unloading the pressure of the hydraulic system 5 and the hydraulic loading system 13, closing the self-pressurizing liquid nitrogen tank 1, taking out the core, and calculating relevant mechanical parameters of the core 23 under the conditions of the temperature, the confining pressure and the pore pressure according to the experimental result after the experiment is finished.
This experimental apparatus only through changing different lower cushion, can measure the mechanical properties of rock under different confined pressure and pore pressure under the low temperature/ultra-low temperature environment simultaneously, and the function is various, easy operation, and the experiment is convenient, reduces the investment.
The above description is only a few of the preferred embodiments of the present invention, and any person skilled in the art may modify the above-described embodiments or modify them into equivalent ones. Therefore, any simple modifications or equivalent substitutions made in accordance with the technical solution of the present invention are within the scope of the claims of the present invention.
Claims (7)
1. The utility model provides a measure experimental apparatus of rock fracture toughness under low temperature, characterized by: comprises a self-pressurization liquid nitrogen tank (1), a liquid nitrogen recovery tank (3), a hydraulic system (5), an experimental cavity (9), a low-temperature control system (12), a hydraulic loading system (13) and a computer control system (15),
the self-pressurization liquid nitrogen tank penetrates through the bottom end of the experiment cavity (9) through a first high-pressure heat-preservation pipeline (2);
the liquid nitrogen recovery tank (3) is connected with the top end of the experiment cavity (9) through a second high-pressure heat-preservation pipeline (4), and a control valve is arranged on the liquid nitrogen recovery tank (3);
one end of the hydraulic system (5) passes through the loading equipment (7) and the piston system (8) through a first pressure-resistant pipeline (6) and is connected with the bottom end of the experiment cavity (9); the other end of the hydraulic system (5) is connected with a computer control system (15) through a third data transmission line (16);
the low-temperature control system (12) is connected with the experiment cavity (9) through a first data transmission line (10), and one end of the first data transmission line (10) is provided with a temperature sensor;
one end of the hydraulic loading system (13) is connected with the computer control system (15) through a second data transmission line (14); the other end of the hydraulic loading system (13) passes through the loading equipment (7) through a second pressure-resistant pipeline (11) and is connected with the piston system (8);
the experimental cavity (9) comprises an upper cushion block (21), a heat shrinkable tube (22), a lower cushion block (24), a cavity shell (25), a buckle (26) and a rubber sealing ring (27), wherein the cavity shell (25) is arranged at the upper end of the piston system (8), the rock core (23) is clamped between the upper cushion block (21) and the lower cushion block (24), and the heat shrinkable tube (22) is wrapped outside the rock core (23), the lower part of the upper cushion block (21) and the upper part of the lower cushion block (24); the upper cushion block (21) penetrates through the cavity shell (25) and is arranged on the outer side of the upper cushion block (21) at the upper end of the cavity shell (25) through a buckle (26);
the lower cushion block (24) adopts a B-type lower cushion block, a circular channel is arranged in the middle of the B-type lower cushion block, and internal threads are arranged at the bottom end of the circular channel; the outer side of the bottom end of the B-type lower cushion block is sealed by a rubber sealing ring; the section of the upper end face of the B-type lower cushion block is provided with a groove, so that the flow of fluid on the end face of the inlet of the rock core is convenient to realize.
2. The experimental device for measuring the fracture toughness of the rock at the low temperature as claimed in claim 1, wherein: and the outer side of the heat shrinkable tube (22) is respectively provided with an axial sensor and a radial sensor, so that different experimental conditions can be simulated.
3. The experimental device for measuring the fracture toughness of the rock at the low temperature as claimed in claim 1, wherein: the core (23) adopts the standard of 50mm diameter and 25mm height, the center is provided with a round hole with the diameter smaller than 5mm, and wing-shaped cracks with the length of 0.5mm are respectively prefabricated on the two sides of the round hole.
4. The experimental device for measuring the fracture toughness of the rock at the low temperature as claimed in claim 1, wherein: and the computer control system (15) controls the hydraulic loading system (13) to pressurize the piston system (8), so that the upper cushion block (21) is in contact with and clamped by the loading equipment (7), and the pressure is 2 MPa.
5. An experimental method of the experimental device for measuring the fracture toughness of the rock at the low temperature, which is described in any one of claims 1 to 4, is characterized in that: the experimental method for measuring the fracture toughness of the rock at the low temperature by the experimental device for measuring the fracture toughness of the rock at the low temperature comprises the following specific experimental steps:
(1) preparing a core: the standard of the core is 50mm in diameter and 25mm in height, a round hole with the diameter smaller than 5mm is arranged in the center, wing-shaped cracks with the length of 0.5mm are prefabricated on two sides of the round hole respectively, and two end faces of the core are required to be completely parallel to reduce errors;
(2) placing the tested rock core (23) in the test cavity (9), and placing the test cavity (9) on the piston system (8);
(3) a computer control system (15) is used for controlling a hydraulic loading system (13) to pressurize a piston system (8), so that an upper cushion block (21) is in contact with and clamped by loading equipment (7), the pressure is 2MPa, and the upper cushion block (21) is sealed by a buckle (26);
(4) opening the self-pressurization liquid nitrogen tank (1) to enable the experiment cavity (9) to be filled with the low-temperature fluid, and simultaneously maintaining the temperature in the experiment cavity (9) by controlling a control valve of the liquid nitrogen recovery tank (3);
(5) opening the low-temperature control system (12), and recording the temperature in the experiment cavity (9) in real time;
(6) when the temperature is stabilized to the experiment set value, the hydraulic system (5) is opened, the computer control system (15) applies internal pressure to the rock core (23), the pressure change condition is observed, when the pressure is reduced, the pressurization is stopped, and the highest pressure value P is recorded;
(7) unloading the pressure of the hydraulic system (5) and the hydraulic loading system (13), closing the self-pressurizing liquid nitrogen tank (1), taking out the rock core (23), and calculating the fracture toughness of the rock at the stable temperature according to the experimental result after the experiment is finished.
6. An experimental method of the experimental device for measuring the fracture toughness of the rock at the low temperature, which is described in any one of claims 1 to 4, is characterized in that: the method for measuring the mechanical properties of the rock at the low temperature is carried out by an experimental device for measuring the fracture toughness of the rock at the low temperature, and the experimental steps are as follows:
utilize the experimental apparatus who measures rock fracture toughness nature under the low temperature, with under cushion (24) by the cushion change under the A type back under the B type to install axial and radial sensor respectively in pyrocondensation pipe (22) outside, can simulate different experimental conditions, measure the intensity of rock under different confined pressure, pore pressure and low temperature/ultra-low temperature condition, elastic modulus, the mechanical parameters of poisson's ratio, provide the support for the mechanical behavior of rock under the analysis low temperature/ultra-low temperature condition.
7. The experimental method of the experimental device for measuring the fracture toughness of the rock at the low temperature as claimed in claim 6, wherein: the specific experimental steps are as follows:
(1) preparing a core: the standard of the core is a cylinder with the diameter of 50mm and the height of 50mm, and two end faces of the core are required to be completely parallel to reduce errors;
(2) clamping an experimental core (23) by an upper cushion block (21) and a B-type lower cushion block, wrapping a heat shrinkable tube (22) at the outer end, placing a sensor for measuring axial and radial displacement outside the heat shrinkable tube (22) in an experimental cavity (9), placing the experimental cavity (9) on a piston system (8), and sealing the upper cushion block (21) by using a buckle (26);
(3) opening the self-pressurization liquid nitrogen tank (1), filling the experiment cavity (9) with low-temperature fluid, closing a control valve of the liquid nitrogen recovery tank (3) and maintaining the temperature and the pressure in the experiment cavity (9);
(4) opening the low-temperature control system (12), and recording the temperature in the experiment cavity (9) in real time;
(5) when the temperature is stabilized to an experimental set value, a computer control system (15) is used for controlling a water pressure system (5) to apply pore pressure to the rock core (23), and when the rock core (23) is fully saturated and reaches a set pore pressure value, the set pore pressure is maintained unchanged;
(6) controlling a hydraulic loading system (13) to pressurize a piston system (8) by using a computer control system (15) until a rock core (23) is damaged, and recording axial and radial deformation of the rock core (23) along with axial load change in the whole loading process;
(7) and unloading the pressure of the hydraulic system (5) and the hydraulic loading system (13), closing the self-pressurizing liquid nitrogen tank (1), taking out the rock core, and calculating relevant mechanical parameters of the rock core (23) under the conditions of the temperature, the confining pressure and the pore pressure according to the experimental result after the experiment is finished.
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| CN114428047A (en) * | 2020-09-29 | 2022-05-03 | 中国石油化工股份有限公司 | Device and method for fracturing shale by ultralow-temperature carbon dioxide through multiple rounds of huffing and puff |
| CN112414882B (en) * | 2020-10-10 | 2022-04-01 | 武汉大学 | High-temperature crystalline rock cold impact cracking experiment system and method |
| CN114184486B (en) * | 2021-12-08 | 2023-12-12 | 西南科技大学 | Rock fracture toughness measuring device and method under high-temperature and high-pressure conditions |
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