CN111948056A - Large-scale fracturing experiment system and method under different flow state carbon dioxide injection conditions - Google Patents
Large-scale fracturing experiment system and method under different flow state carbon dioxide injection conditions Download PDFInfo
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- CN111948056A CN111948056A CN201910404882.0A CN201910404882A CN111948056A CN 111948056 A CN111948056 A CN 111948056A CN 201910404882 A CN201910404882 A CN 201910404882A CN 111948056 A CN111948056 A CN 111948056A
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- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 title claims abstract description 302
- 229910002092 carbon dioxide Inorganic materials 0.000 title claims abstract description 151
- 239000001569 carbon dioxide Substances 0.000 title claims abstract description 150
- 238000002347 injection Methods 0.000 title claims abstract description 54
- 239000007924 injection Substances 0.000 title claims abstract description 54
- 238000002474 experimental method Methods 0.000 title claims abstract description 32
- 238000000034 method Methods 0.000 title claims abstract description 26
- 239000012530 fluid Substances 0.000 claims abstract description 74
- 238000005086 pumping Methods 0.000 claims abstract description 31
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 18
- 230000006835 compression Effects 0.000 claims description 10
- 238000007906 compression Methods 0.000 claims description 10
- 238000003745 diagnosis Methods 0.000 claims description 10
- 238000002360 preparation method Methods 0.000 claims description 4
- 239000000126 substance Substances 0.000 claims description 3
- 239000007788 liquid Substances 0.000 description 12
- 230000001276 controlling effect Effects 0.000 description 8
- 238000004088 simulation Methods 0.000 description 8
- 238000012360 testing method Methods 0.000 description 6
- 230000007246 mechanism Effects 0.000 description 5
- 238000011160 research Methods 0.000 description 5
- 239000011435 rock Substances 0.000 description 5
- 239000003086 colorant Substances 0.000 description 4
- 238000004043 dyeing Methods 0.000 description 4
- 238000005516 engineering process Methods 0.000 description 4
- 230000008569 process Effects 0.000 description 4
- 230000001105 regulatory effect Effects 0.000 description 4
- 229910001220 stainless steel Inorganic materials 0.000 description 4
- 239000010935 stainless steel Substances 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 230000009286 beneficial effect Effects 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000006073 displacement reaction Methods 0.000 description 2
- 230000000977 initiatory effect Effects 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- VUZPPFZMUPKLLV-UHFFFAOYSA-N methane;hydrate Chemical compound C.O VUZPPFZMUPKLLV-UHFFFAOYSA-N 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 239000011148 porous material Substances 0.000 description 2
- 238000003825 pressing Methods 0.000 description 2
- 238000005057 refrigeration Methods 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000002591 computed tomography Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 239000004576 sand Substances 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 230000000007 visual effect Effects 0.000 description 1
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- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
- G01N3/10—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces generated by pneumatic or hydraulic pressure
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Abstract
The invention discloses a large-scale fracturing experiment system and method under different fluid carbon dioxide injection conditions. The invention provides a large-scale fracturing experiment system under different fluid carbon dioxide injection conditions, which comprises a carbon dioxide gas source supply unit, a plunger pump injection unit, a triaxial stress loading unit and a main pipeline, wherein the plunger pump injection unit is connected with the carbon dioxide gas source supply unit; one end of the main pipeline is connected with the carbon dioxide gas source supply unit, and the other end of the main pipeline is connected with the triaxial stress loading unit; the main pipeline is provided with a branch pipeline, and the carbon dioxide gas source supply unit and the triaxial stress loading unit are both connected with the plunger pump injection unit through the branch pipeline; the plunger pump injection unit comprises a plunger pump and an intermediate container unit; the intermediate container unit includes a first intermediate container, a second intermediate container, and a third intermediate container; the first intermediate container is provided with a first temperature control device; the second intermediate container is equipped with a second temperature control device. The system realizes the pumping of different carbon dioxide phase states and can observe the fracture state of the pressed carbon dioxide.
Description
Technical Field
The invention relates to the technical field of hydraulic fracturing physical simulation experiments in oil and gas field development. More particularly, the invention relates to a large-scale fracturing experiment system and method under different fluid carbon dioxide injection conditions.
Background
The traditional water-based fracturing fluid has the problems of incomplete gel breaking, incomplete flowback, large retention in stratum and the like, and has serious damage to the stratum. Therefore, the carbon dioxide fracturing technology is concerned and researched, has the advantages of low damage, easy flowback and the like, and is widely applied to various reservoirs at present, particularly water-sensitive reservoirs.
On the other hand, due to the complexity of reservoir geological conditions and the unclear understanding of the seam-making mechanism under different phases of carbon dioxide, the effective implementation of the process technology is still restricted. Therefore, the understanding of the fracture initiation and extension mechanism of the carbon dioxide fracturing fracture in different phases is imperative.
In recent years, the problem of crack initiation and extension mechanism is deeply researched by developing an indoor hydraulic fracture physical simulation experiment, and the research becomes a hot point of the industrial research. The physical model experiment technology aiming at different fracturing technologies is also continuously improved and innovated. For example, application No. 201710589324.7 provides a supercritical carbon dioxide core fracturing experimental method under pore pressure saturation, which can realize supercritical carbon dioxide fracturing under the conditions of simulated formation high temperature, high stress state and pore pressure. The patent with the application number of 201610105722.2 provides a method for manufacturing a test piece for a supercritical carbon dioxide fracturing shale experiment under triaxial stress, and particularly relates to a method for manufacturing a test piece for a fracturing experiment, which can simulate the influence of different process parameters on the supercritical carbon dioxide fracturing shale effect under reservoir temperature and pressure conditions, but has the common problems that: the test piece is a cylindrical rock, the diameter of the test piece is 38mm, the length of the test piece is 2-2.5 times of the diameter, the size of the sample is very small, and the simulation of stable crack expansion cannot be realized due to the scale effect; the confining pressure applied to the sample is only pseudo-three-dimensional and is not full three-dimensional; the patent is only directed to a single supercritical carbon dioxide fluid injection simulation method, and the description of the fracturing effect, i.e., fracture morphology, is not mentioned. The patent with the application number of 201510287459.9 provides a supercritical carbon dioxide rock fracturing test system, which can realize the experimental simulation that a rock sample is fractured by supercritical carbon dioxide under the ground stress condition, and can also simulate the carbon dioxide sand carrying function; but has problems that: the sample is still cylindrical, so the applied confining pressure is pseudo-three-dimensional only, not full three-dimensional; the high-pressure plunger pump is directly connected with the gas source, and the carbon dioxide needs to be liquefied and pressurized along with the reduction of the pressure of the gas cylinder, so that the experimental efficiency is reduced, and the carbon dioxide corrodes the pump to a certain extent and is not beneficial to equipment safety; in addition, the patent does not mention the method of observing the fracture morphology after pressing. The application is 201610972423.9's patent provides a supercritical carbon dioxide fracturing simulation experiment device, and it is the full three-dimensional stress loading that goes on, has also carried out liquefaction processing in advance to carbon dioxide, nevertheless because heating system is located sample loading frame, can not realize the implementation of multiple different phase fluid and switch the pump notes, and presses back crack form and adopt visual observation method, can not realize making the accurate description of seam to carbon dioxide.
In summary, although the patents of the prior application can realize the pump injection fracturing experiment of the supercritical carbon dioxide, the sample size is small, the simulated triaxial loading cannot really realize the purpose of simulating the stable expansion of the crack, or the carbon dioxide has the problems of low phase-state conversion efficiency and incapability of performing alternate pump injection of multiple phases. In addition, the biggest problem that the observation of the carbon dioxide fracturing fracture morphology is still not effectively solved, the observation of the fracture morphology by a general physical model experiment mainly adopts two means, and a small-scale sample (within 30 cm) can adopt a CT scanning mode or perform dyeing treatment on the fracturing fluid. However, it is difficult to find a coloring agent mutually soluble with a carbon dioxide solvent in the market at present, so that the traditional way for observing the fracture morphology is not suitable for the observation of the large-scale rock fractured by the carbon dioxide pump.
Therefore, the invention provides a large-scale fracturing experiment system and method under different fluid state carbon dioxide injection conditions to solve the problems.
Disclosure of Invention
The invention aims to provide a large-scale fracturing experiment system under different fluid carbon dioxide injection conditions.
The invention also aims to provide a large-scale fracturing experiment and a post-fracturing fracture morphology diagnosis method under different fluid carbon dioxide injection conditions.
In order to achieve the purpose, the invention adopts the following technical scheme:
a large-scale fracturing experiment system under different fluid carbon dioxide injection conditions comprises a carbon dioxide gas source supply unit, a plunger pump injection unit, a triaxial stress loading unit and a main pipeline; one end of the main pipeline is connected with a carbon dioxide gas source supply unit, and the other end of the main pipeline is connected with a triaxial stress loading unit; wherein the content of the first and second substances,
a branch pipeline is arranged on the main pipeline, and the carbon dioxide gas source supply unit and the triaxial stress loading unit are both connected with the plunger pump injection unit through the branch pipeline;
the plunger pump injection unit comprises a plunger pump and an intermediate container unit;
the branch lines include a first branch line, a second branch line, and a third branch line;
the intermediate container unit includes a first intermediate container, a second intermediate container, and a third intermediate container; the first intermediate container is equipped with a first temperature control device; the second intermediate container is provided with a second temperature control device;
one end of each of the first intermediate container, the second intermediate container and the third intermediate container is connected with the main pipeline through a first branch pipeline, a second branch pipeline and a third branch pipeline respectively; and the other ends of the first intermediate container, the second intermediate container and the third intermediate container are all connected with a plunger pump.
In the invention, the carbon dioxide gas source supply unit is used for providing a carbon dioxide gas source;
the plunger pump injection unit is used for realizing stable real-time switching of pump injection of different flow state carbon dioxide and dyeing of the pressed carbon dioxide crack form; the first intermediate container, the second intermediate container and the third intermediate container are respectively used for providing liquid carbon dioxide, supercritical carbon dioxide and water-based fracturing fluid for the triaxial stress loading unit, and the plunger pump is used for pumping the fluid in the intermediate container unit into the triaxial stress loading unit;
the first temperature control device is used for regulating and controlling the temperature of the fluid in the first intermediate container;
the second temperature control device is used for regulating and controlling the temperature of the fluid in the second intermediate container;
the triaxial stress loading unit is used for containing a sample and carrying out true three-dimensional ground stress loading on the sample; the true three-dimensional ground stress includes a maximum horizontal stress, a minimum horizontal stress, and a vertical stress.
Preferably, the carbon dioxide gas source supply unit comprises a carbon dioxide gas cylinder and a condenser; one end of the condenser is connected with the carbon dioxide gas cylinder, and the other end of the condenser is connected with the middle container unit.
Preferably, a first valve is arranged between the carbon dioxide gas cylinder and the condenser.
Preferably, a second valve is arranged on the first branch pipeline; a third valve is arranged on the second branch pipeline; and a fourth valve is arranged on the third branch pipeline.
Preferably, a fifth valve is arranged between the first intermediate container and the plunger pump; a sixth valve is arranged between the second intermediate container and the plunger pump; and a seventh valve is arranged between the third intermediate container and the plunger pump.
Preferably, the plunger pumping unit further comprises an air compression device and a vacuum device; the air compression equipment and the vacuum equipment are arranged between the middle container unit and the triaxial stress loading unit.
Preferably, the vacuum equipment is a vacuum pump, and the air compression equipment is an air compressor.
Preferably, the branch lines further comprise a fourth branch line and a fifth branch line; the air compression equipment and the vacuum equipment are respectively connected with a main pipeline through a fourth branch pipeline and a fifth branch pipeline.
Preferably, an eighth valve is arranged on the fourth branch pipeline; and a ninth valve is arranged on the fifth branch pipeline.
Preferably, the triaxial stress loading unit comprises a triaxial stress loading frame and a sample placed in the triaxial stress loading frame.
Preferably, the dimensions of the triaxial stress-loading frame are not less than 1m × 1m × 1 m.
Preferably, a tenth valve is arranged at the joint of the main pipeline and the triaxial stress loading unit.
Preferably, one end of the carbon dioxide gas cylinder is provided with a pressure gauge.
Preferably, one end of each of the first intermediate container, the second intermediate container and the triaxial stress loading unit is provided with a pressure gauge and a temperature gauge.
Preferably, the first temperature control equipment controls the temperature to be in a range of-10 to 30 ℃.
Preferably, the temperature range controlled by the second temperature control device is between room temperature and 100 ℃. The room temperature in the invention is 20 DEG C
Preferably, the first temperature control device is a cryogenic bath.
Preferably, the second temperature control device is a high temperature bath.
Preferably, the displacement of the plunger pump is not more than 12L/min, the single stroke volume is not more than 3700ml, and the pumping pressure is not more than 82 Mpa.
Preferably, the volumes of the first intermediate container, the second intermediate container and the third intermediate container are each at least 3000 ml.
Preferably, the material of the first intermediate container, the second intermediate container and the third intermediate container is stainless steel 316L, at least 50MPa resistant to pressure and CO resistant2。
Preferably, the first valve to the fourth valve and the eighth valve to the tenth valve are all electromagnetic remote control pneumatic ball valves, the material is stainless steel 316L, the pressure resistance is at least 50MPa, and the CO resistance is realized2And the pump injection of the fluids in three different intermediate containers can be switched in real time.
Preferably, the fifth valve to the seventh valve are all manual valves.
The invention also provides a large-scale fracturing experiment and post-fracturing fracture morphology diagnosis method under different fluid carbon dioxide injection conditions, which uses the system and comprises the following steps:
1) sample preparation: placing a sample in a triaxial stress loading unit, and loading three-dimensional stress;
2) preparing a water-based fracturing fluid: injecting the water-based fracturing fluid into a third intermediate container;
3) preparing carbon dioxide fluid: supplying carbon dioxide fluid to the first intermediate container by using a carbon dioxide gas source supply unit, and pumping the carbon dioxide fluid in the first intermediate container into the second intermediate container by using a plunger pump; respectively controlling the temperature of the first intermediate container and the second intermediate container by using first temperature control equipment and second temperature control equipment to obtain carbon dioxide fluids in different flow states;
4) and (3) fracturing experiment stage: pumping carbon dioxide fluid in different flow states in the first intermediate container and/or the second intermediate container into the triaxial stress loading unit by using a plunger pump;
5) and (3) diagnosing the fracture morphology of the carbon dioxide fracturing: after the pumping of the carbon dioxide fluid is finished, pumping the water-based fracturing fluid in the third intermediate container into the triaxial stress loading unit by using a plunger pump; the sample was taken out and the crack morphology was observed.
Preferably, the water-based fracturing fluid in step 2) contains a coloring agent.
Preferably, the carbon dioxide fluid preparation process in step 3) specifically includes the following steps:
closing the first valve, the fifth valve, the sixth valve, the seventh valve and the eighth valve, opening the second valve, the third valve, the fourth valve, the ninth valve and the tenth valve, and starting vacuum equipment to vacuumize until the vacuum equipment finishes vacuumizing when the reading is-100 to-200 mm Hg;
closing the second valve, the third valve, the fourth valve, the ninth valve, the tenth valve and the vacuum equipment, opening the first valve, the second valve and the first temperature control equipment, controlling the temperature and the pressure of the first intermediate container, and filling the first intermediate container with liquid carbon dioxide;
and closing the first valve, opening the third valve, starting the plunger pump and the second temperature control device, pumping the liquid carbon dioxide in the first intermediate container into the second intermediate container, closing the second valve and the fifth valve, opening the sixth valve, controlling the temperature and the pressure of the second intermediate container, and keeping the carbon dioxide in the second intermediate container in a supercritical state.
Preferably, the fracturing experiment stage process in the step 4) specifically includes the following steps:
when liquid carbon dioxide is pumped, keeping the first valve, the third valve, the fourth valve, the sixth valve, the seventh valve, the eighth valve and the ninth valve closed, opening the second valve, the fifth valve and the tenth valve, starting the plunger pump, and pumping the liquid carbon dioxide in the first intermediate container into the triaxial stress loading unit;
when the carbon dioxide in the supercritical state is pumped in, the first valve, the second valve, the fourth valve, the fifth valve, the seventh valve, the eighth valve and the ninth valve are kept closed, the third valve, the sixth valve and the tenth valve are opened, the plunger pump is started, and the carbon dioxide in the supercritical state in the second intermediate container is pumped into the triaxial stress loading unit.
Preferably, the carbon dioxide fracture morphology diagnosis process in the step 5) specifically includes the following steps:
after the pumping of the carbon dioxide fluid is finished, keeping the first valve, the second valve, the third valve, the fifth valve, the sixth valve, the eighth valve and the ninth valve closed, opening the fourth valve, the seventh valve and the tenth valve, starting the plunger pump, and pumping the water-based fracturing fluid in the third intermediate container into the triaxial stress loading unit; the sample was taken out and the crack morphology was observed.
Preferably, after the water-based fracturing fluid in the third intermediate container is pumped into the triaxial stress loading unit in the step 5), the method further comprises the following steps: and the pressure drop of the triaxial stress loading unit is 0, the tenth valve is closed, the second valve, the third valve, the fourth valve and the eighth valve are opened, and the pistons of the first intermediate container, the second intermediate container and the third intermediate container are dropped to the initial positions.
The invention has the following beneficial effects:
according to the large-scale fracturing experiment system under different fluid carbon dioxide injection conditions, the plunger pump injection mode is improved, and the plurality of groups of parallel-arranged intermediate containers are added, so that stable real-time pump injection switching of different carbon dioxide phase states can be realized, and the fractured forms of the compressed carbon dioxide can be dyed and observed. Thereby providing a more effective technical means for researchers to research the carbon dioxide fracturing crack propagation mechanism;
the large-scale fracturing experiment and post-fracturing fracture morphology diagnosis method under different fluid state carbon dioxide injection conditions provided by the invention overcomes the problems that continuous stable pump injection cannot be carried out on carbon dioxide in different phase states and carbon dioxide fracturing fracture morphology diagnosis cannot be effectively carried out in the traditional fracturing simulation experiment method.
Drawings
The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.
FIG. 1 shows a schematic diagram of a large scale fracturing experimental system provided by the present invention under different fluid carbon dioxide injection conditions;
wherein, 1-a carbon dioxide gas cylinder, 4-a condenser, 19-a first intermediate container, 20-a second intermediate container, 21-a third intermediate container, 22-a first temperature control device, 23-a second temperature control device, 29-a plunger pump, 11-a pneumatic device, 12-a vacuum device, 24-a triaxial stress loading frame, 25-a sample, 3-a first valve, 7-a second valve, 8-a third valve, 15-a fourth valve, 26-a fifth valve, 27-a sixth valve, 28-a seventh valve, 9-an eighth valve, 10-a ninth valve, 16-a tenth valve, 30-a main pipeline, 31-a first branch pipeline, 32-a second branch pipeline, 33-a third branch pipeline, 34-a fourth branch pipeline, 35-fifth branch line.
Detailed Description
In order to more clearly illustrate the invention, the invention is further described below with reference to preferred embodiments and the accompanying drawings. It is to be understood by persons skilled in the art that the following detailed description is illustrative and not restrictive, and is not to be taken as limiting the scope of the invention.
The invention provides a large-scale fracturing experiment system and method under different fluid state carbon dioxide injection conditions, which not only realize stable real-time pump injection of different carbon dioxide phase states, but also realize dyeing observation of pressed carbon dioxide fracture states.
Specifically, referring to fig. 1, a large-scale fracturing experiment system under different fluid carbon dioxide injection conditions includes a carbon dioxide gas source supply unit, a plunger pump injection unit, a triaxial stress loading unit and a main pipeline 30; one end of the main pipeline 30 is connected with a carbon dioxide gas source supply unit, and the other end of the main pipeline 30 is connected with a triaxial stress loading unit; wherein the content of the first and second substances,
a branch pipeline is arranged on the main pipeline 30, and the carbon dioxide gas source supply unit and the triaxial stress loading unit are both connected with the plunger pump injection unit through the branch pipeline;
the plunger pump injection unit comprises a plunger pump 29 and an intermediate container unit;
the branch lines include a first branch line 31, a second branch line 32, and a third branch line 33;
the intermediate container unit comprises a first intermediate container 19, a second intermediate container 20 and a third intermediate container 21; said first intermediate container 19 is equipped with a first temperature control device 22; said second intermediate container 20 is equipped with a second temperature control device 23;
one end of the first intermediate container 19, the second intermediate container 20 and the third intermediate container 21 is connected with the main pipeline 30 through a first branch pipeline 31, a second branch pipeline 32 and a third branch pipeline 33 respectively; the other ends of the first intermediate container 19, the second intermediate container 20 and the third intermediate container 21 are all connected with a plunger pump 29;
the carbon dioxide gas source supply unit is used for providing a carbon dioxide gas source;
the plunger pump injection unit is used for realizing stable real-time switching of pump injection of different flow state carbon dioxide and dyeing of the pressed carbon dioxide crack form; the first intermediate container 19, the second intermediate container 20 and the third intermediate container 21 are respectively used for providing liquid carbon dioxide, supercritical carbon dioxide and water-based fracturing fluid for the triaxial stress loading unit, and the plunger pump 29 is used for pumping the fluid in the intermediate container unit into the triaxial stress loading unit;
the first temperature control device 22 is used for regulating the temperature of the fluid in the first intermediate container 19;
the second temperature control device 23 is used for regulating and controlling the temperature of the fluid in the second intermediate container 20;
the triaxial stress loading unit is used for containing a sample and carrying out true three-dimensional ground stress loading on the sample; the true three-dimensional ground stress includes a maximum horizontal stress, a minimum horizontal stress, and a vertical stress.
As a preferred embodiment of the present invention, the carbon dioxide gas source supply unit includes a carbon dioxide gas cylinder 1 and a condenser 4; one end of the condenser 4 is connected with the carbon dioxide gas bottle 1, and the other end of the condenser 4 is connected with the middle container unit. In the carbon dioxide gas cylinder 1, the full amount of carbon dioxide is generally stored at liquid state at normal temperature and high pressure, and the pressure is 7-8MPa, however, with the use of carbon dioxide, the pressure is reduced and gaseous state may exist, therefore, the condenser 4 cooperates with the first temperature control device 22 to perform primary refrigeration on the fluid flowing out from the carbon dioxide gas cylinder 1.
In order to control the outflow speed, outflow amount, etc. of the carbon dioxide fluid in the carbon dioxide gas cylinder, as a preferred embodiment of the present invention, a first valve 3 is provided between the carbon dioxide gas cylinder 1 and the condenser 4.
Furthermore, in order to more intuitively regulate and control the phase state of the carbon dioxide fluid, one end of the carbon dioxide gas cylinder 1 is provided with a pressure gauge.
In addition, in order to more conveniently realize the switching of different carbon dioxide phases, the first branch pipeline 31 is provided with a second valve 7; a third valve 8 is arranged on the second branch pipeline 32; a fourth valve 15 is arranged on the third branch pipeline 33; a fifth valve 26 is arranged between the first intermediate container 19 and the plunger pump 29; a sixth valve 27 is arranged between the second intermediate container 20 and the plunger pump 29; a seventh valve 28 is arranged between the third intermediate container 21 and the plunger pump 29.
As a preferred embodiment of the present invention, the plunger pumping unit further comprises a pneumatic device 11 and a vacuum device 12; the air compression device 11 and the vacuum device 12 are both arranged between the intermediate container unit and the triaxial stress loading unit; wherein the vacuum apparatus is used to evacuate residual air from the intermediate container unit and the pipeline; the air compression equipment is matched with a plunger pump for use, and a piston of the intermediate container which completes single pumping falls to the bottom to prepare for secondary pumping; further, the vacuum device 12 is a vacuum pump, and the air compression device 11 is an air compressor.
As a preferred embodiment of the present invention, the branch lines further include a fourth branch line 34 and a fifth branch line 35; the air compression device 11 and the vacuum device 12 are respectively connected with the main pipeline 30 through a fourth branch pipeline 34 and a fifth branch pipeline 35; further, an eighth valve 9 is arranged on the fourth branch pipeline 34; and a ninth valve 10 is arranged on the fifth branch pipeline 35.
As a preferred embodiment of the present invention, the triaxial stress loading unit includes a triaxial stress loading frame 24 and a sample 25 placed in the triaxial stress loading frame; further, the dimensions of the triaxial stress loading frame are not less than 1m × 1m × 1 m; the large-size triaxial stress loading frame can be used for loading true three-dimensional (maximum horizontal stress, minimum horizontal stress and vertical stress) ground stress of a large-size fracturing rock sample, and the maximum ground stress can reach 69MPa so as to simulate a true formation stress state; further, a tenth valve 16 is arranged at the joint of the main pipeline and the triaxial stress loading unit; one end of the triaxial stress loading unit is also provided with a pressure gauge and a thermometer, so that the temperature and the pressure of the triaxial stress loading unit are visually displayed, and the control is facilitated.
As a preferred embodiment of the present invention, in order to perform low-temperature refrigeration on the fluid flowing out of the carbon dioxide gas cylinder 1, the liquid state of the carbon dioxide is ensured by temperature conditions, the temperature range of the first temperature control device 22 is controlled to be-10 to 30 ℃, and PID temperature control is performed; in addition, in order to facilitate the temperature adjustment of the first temperature control device 22, a pressure gauge and a temperature gauge are arranged at one end of the first intermediate container 19; further, the first temperature control device is a low-temperature bath.
As a preferred embodiment of the present invention, in order to heat the fluid flowing out of the first intermediate container 19, the supercritical state of the carbon dioxide is realized by the temperature condition, the temperature range of the second temperature control device 23 is controlled to be between room temperature and 100 ℃, and PID temperature control is performed; in addition, in order to facilitate the temperature adjustment of the second temperature control device 23, a pressure gauge and a thermometer are arranged at one end of the second intermediate container 20; further, the second temperature control device is a high-temperature bath.
As a preferred embodiment of the present invention, the displacement of the plunger pump 29 is not more than 12L/min, the single stroke volume is not more than 3700ml, and the pumping pressure is not more than 82 MPa.
As a preferred embodiment of the present invention, the volumes of the first intermediate container 19, the second intermediate container 20 and the third intermediate container 21 are each at least 3000 ml; the first intermediate container 19, the second intermediate container 20 and the third intermediate container 21 are made of stainless steel 316L, and are resistant to pressure of at least 50MPa and CO2。
As a preferred embodiment of the invention, the first valve to the fourth valve and the eighth valve to the tenth valve are all electromagnetic remote control pneumatic ball valves, and the material is stainless steel 316L, and the pressure resistance is at least 50MPa, and the CO resistance is realized2And the pump injection of the fluids in three different intermediate containers can be switched in real time.
As a preferred embodiment of the present invention, the fifth valve to the seventh valve are all manual valves.
As another aspect of the present invention, the present invention further provides a method for large-scale fracturing experiments and post-fracturing fracture morphology diagnosis under different fluid carbon dioxide injection conditions, the method using the above system, comprising the steps of:
1) sample preparation: placing a sample 25 in a triaxial stress loading frame 24, and loading three-dimensional stress;
2) preparing a water-based fracturing fluid: injecting a water-based fracturing fluid containing a coloring agent into a third intermediate container 21;
3) preparing carbon dioxide fluid: closing the first valve 3, the fifth valve 26, the sixth valve 27, the seventh valve 28 and the eighth valve 9, opening the second valve 7, the third valve 8, the fourth valve 15, the ninth valve 10 and the tenth valve 16, and starting the vacuum equipment 12 to vacuumize until the vacuum equipment 12 reads-100 to-200 mm Hg;
closing the third valve 8, the fourth valve 15, the ninth valve 10, the tenth valve 16 and the vacuum device 12, opening the condenser 4, the first valve 3, the second valve 7 and the first temperature control device 22, controlling the temperature and the pressure of the first intermediate container, and filling the first intermediate container 19 with liquid carbon dioxide;
closing the first valve 3, opening the third valve 8, starting the plunger pump 29 and the second temperature control device 23, pumping the liquid carbon dioxide in the first intermediate container 19 into the second intermediate container 20, closing the second valve 7 and the fifth valve 26, opening the sixth valve 27, controlling the temperature and the pressure of the second intermediate container 20, and keeping the carbon dioxide in the second intermediate container 20 in a supercritical state;
4) and (3) fracturing experiment stage:
when liquid carbon dioxide is pumped, keeping the first valve 3, the third valve 8, the fourth valve 15, the sixth valve 27, the seventh valve 28, the eighth valve 9 and the ninth valve 10 closed, opening the second valve 7, the fifth valve 26 and the tenth valve 16, starting the plunger pump 29, and pumping the liquid carbon dioxide in the first intermediate container 19 into the triaxial stress loading frame 24;
when the carbon dioxide in the supercritical state is pumped in, keeping the first valve 3, the second valve 7, the fourth valve 15, the fifth valve 26, the seventh valve 28, the eighth valve 9 and the ninth valve 10 closed, opening the third valve 8, the sixth valve 27 and the tenth valve 16, starting the plunger pump 29, and pumping the carbon dioxide in the supercritical state in the second intermediate container 20 into the triaxial stress loading frame 24;
5) and (3) diagnosing the fracture morphology of the carbon dioxide fracturing: after pumping the carbon dioxide fluid, keeping the first valve 3, the second valve 7, the third valve 8, the fifth valve 26, the sixth valve 27, the eighth valve 9 and the ninth valve 10 closed, opening the fourth valve 15, the seventh valve 28 and the tenth valve 16, starting the plunger pump 29, and pumping the water-based fracturing fluid in the third intermediate container 21 into the triaxial stress loading frame 24; injecting the water-based fracturing fluid containing the coloring agent at a constant pressure by taking the pressure of an early carbon dioxide pumping wellhead (namely the wellhead pressure at the end of the carbon dioxide pumping at the previous stage of pumping the water-based fracturing fluid, namely 4) as a reference, stopping injecting after the designed pumping volume is finished, resetting the plunger pump 29 after the wellhead pressure is reduced to 0, closing the tenth valve 16, opening the second valve 7, the third valve 8, the fourth valve 15 and the eighth valve 9, and lowering the pistons of the first intermediate container 19, the second intermediate container 20 and the third intermediate container 21 to initial positions; the sample was taken out and the crack morphology was observed.
The large-scale fracturing experiment and post-fracturing fracture morphology diagnosis method under different fluid carbon dioxide injection conditions provided by the invention overcomes the problems that continuous stable pump injection cannot be carried out on carbon dioxide in different phases and carbon dioxide induced fracture morphology diagnosis cannot be effectively carried out in the traditional fracturing simulation experiment method; through improving plunger pump and annotating the mode, increase multiunit parallel arrangement intermediate container, not only can realize the stable real-time switch pump of different carbon dioxide looks attitude and annotate, can also dye the observation to pressing back carbon dioxide crack form to research carbon dioxide fracturing crack extension mechanism provides more effective technological means for the scientific research personnel.
It should be understood that the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention, and it will be obvious to those skilled in the art that other variations or modifications may be made on the basis of the above description, and all embodiments may not be exhaustive, and all obvious variations or modifications may be included within the scope of the present invention.
Claims (10)
1. A large-scale fracturing experiment system under different fluid carbon dioxide injection conditions is characterized by comprising a carbon dioxide gas source supply unit, a plunger pump injection unit, a triaxial stress loading unit and a main pipeline; one end of the main pipeline is connected with a carbon dioxide gas source supply unit, and the other end of the main pipeline is connected with a triaxial stress loading unit; wherein the content of the first and second substances,
a branch pipeline is arranged on the main pipeline, and the carbon dioxide gas source supply unit and the triaxial stress loading unit are both connected with the plunger pump injection unit through the branch pipeline;
the plunger pump injection unit comprises a plunger pump and an intermediate container unit;
the branch lines include a first branch line, a second branch line, and a third branch line;
the intermediate container unit includes a first intermediate container, a second intermediate container, and a third intermediate container; the first intermediate container is equipped with a first temperature control device; the second intermediate container is provided with a second temperature control device;
one end of each of the first intermediate container, the second intermediate container and the third intermediate container is connected with the main pipeline through a first branch pipeline, a second branch pipeline and a third branch pipeline respectively; and the other ends of the first intermediate container, the second intermediate container and the third intermediate container are all connected with a plunger pump.
2. The large-scale fracturing experiment system under different fluid carbon dioxide injection conditions according to claim 1, wherein the first temperature control device controls the temperature to be in a range of-10 to 30 ℃; the temperature range of the second temperature control equipment is between room temperature and 100 ℃.
3. The large-scale fracturing experimental system under different fluid carbon dioxide injection conditions of claim 1 or 2, wherein the carbon dioxide gas source supply unit comprises a carbon dioxide gas cylinder and a condenser; one end of the condenser is connected with the carbon dioxide gas cylinder, and the other end of the condenser is connected with the middle container unit.
4. The large-scale fracturing experimental system under different fluid carbon dioxide injection conditions of claim 3, wherein a first valve is arranged between the carbon dioxide gas cylinder and the condenser.
5. The large-scale fracturing experimental system under different fluid carbon dioxide injection conditions of claim 4, wherein a second valve is arranged on the first branch line; a third valve is arranged on the second branch pipeline; a fourth valve is arranged on the third branch pipeline; a fifth valve is arranged between the first intermediate container and the plunger pump; a sixth valve is arranged between the second intermediate container and the plunger pump; and a seventh valve is arranged between the third intermediate container and the plunger pump.
6. The large-scale fracturing experimental system under different fluid carbon dioxide injection conditions of claim 1 or 2, wherein the plunger pumping unit further comprises a pneumatic device and a vacuum device; the air compression equipment and the vacuum equipment are arranged between the middle container unit and the triaxial stress loading unit.
7. The large scale fracturing experiment system under different fluid carbon dioxide injection conditions of claim 6, wherein the branch lines further comprise a fourth branch line and a fifth branch line; the air compression equipment and the vacuum equipment are respectively connected with a main pipeline through a fourth branch pipeline and a fifth branch pipeline.
8. The large-scale fracturing experimental system under different fluid carbon dioxide injection conditions of claim 7, wherein an eighth valve is arranged on the fourth branch pipeline; and a ninth valve is arranged on the fifth branch pipeline.
9. The large scale fracturing experimental system under different fluid carbon dioxide injection conditions of claim 1 or 2, wherein the triaxial stress loading unit comprises a triaxial stress loading frame and a sample placed in the triaxial stress loading frame.
10. A large-scale fracturing experiment and post-fracturing fracture morphology diagnosis method under different fluid carbon dioxide injection conditions, which is characterized in that the large-scale fracturing experiment and post-fracturing fracture morphology diagnosis method uses the large-scale fracturing experiment system as claimed in any one of claims 1 to 9, and comprises the following steps:
1) sample preparation: placing a sample in a triaxial stress loading unit, and loading three-dimensional stress;
2) preparing a water-based fracturing fluid: injecting the water-based fracturing fluid into a third intermediate container;
3) preparing carbon dioxide fluid: supplying carbon dioxide fluid to the first intermediate container by using a carbon dioxide gas source supply unit, and pumping the carbon dioxide fluid in the first intermediate container into the second intermediate container by using a plunger pump; respectively controlling the temperature of the first intermediate container and the second intermediate container by using first temperature control equipment and second temperature control equipment to obtain carbon dioxide fluids in different flow states;
4) and (3) fracturing experiment stage: pumping carbon dioxide fluid in different flow states in the first intermediate container and/or the second intermediate container into the triaxial stress loading unit by using a plunger pump;
5) and (3) diagnosing the fracture morphology of the carbon dioxide fracturing: after the pumping of the carbon dioxide fluid is finished, pumping the water-based fracturing fluid in the third intermediate container into the triaxial stress loading unit by using a plunger pump; the sample was taken out and the crack morphology was observed.
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