CN111948056B - Large-scale fracturing experiment system and method under different flow carbon dioxide injection conditions - Google Patents
Large-scale fracturing experiment system and method under different flow carbon dioxide injection conditions Download PDFInfo
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- CN111948056B CN111948056B CN201910404882.0A CN201910404882A CN111948056B CN 111948056 B CN111948056 B CN 111948056B CN 201910404882 A CN201910404882 A CN 201910404882A CN 111948056 B CN111948056 B CN 111948056B
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- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 title claims abstract description 291
- 229910002092 carbon dioxide Inorganic materials 0.000 title claims abstract description 146
- 239000001569 carbon dioxide Substances 0.000 title claims abstract description 146
- 238000002347 injection Methods 0.000 title claims abstract description 39
- 239000007924 injection Substances 0.000 title claims abstract description 39
- 238000000034 method Methods 0.000 title claims abstract description 33
- 238000002474 experimental method Methods 0.000 title claims abstract description 32
- 238000005086 pumping Methods 0.000 claims abstract description 38
- 238000003825 pressing Methods 0.000 claims abstract description 6
- 239000012530 fluid Substances 0.000 claims description 49
- 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 8
- 238000002360 preparation method Methods 0.000 claims description 4
- 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 7
- 238000004043 dyeing Methods 0.000 description 5
- 230000007246 mechanism Effects 0.000 description 5
- 239000011435 rock Substances 0.000 description 5
- 239000000463 material Substances 0.000 description 4
- 230000008569 process Effects 0.000 description 4
- 238000011160 research Methods 0.000 description 4
- 229910001220 stainless steel Inorganic materials 0.000 description 4
- 239000010935 stainless steel Substances 0.000 description 4
- 239000003086 colorant Substances 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 230000001105 regulatory effect Effects 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 2
- 238000005336 cracking Methods 0.000 description 2
- 238000006073 displacement reaction Methods 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
- 239000011148 porous material Substances 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 230000009286 beneficial effect Effects 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
- 238000002309 gasification Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 230000000977 initiatory effect Effects 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000005057 refrigeration Methods 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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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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- 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
- G01N3/12—Pressure testing
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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Abstract
The invention discloses a large-scale fracturing experiment system and method under different flowing carbon dioxide injection conditions. The invention provides a large-scale fracturing experiment system under different flow-state 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 carbon dioxide gas source supply unit is connected with the plunger pump injection 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 connected with the plunger pump injection unit through the branch pipeline; the plunger pump unit comprises a plunger pump and an intermediate container unit; the intermediate container unit comprises 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 equipped with a second temperature control device. The system realizes pumping of different carbon dioxide phases and can observe the form of the carbon dioxide cracks after pressing.
Description
Technical Field
The invention relates to the technical field of hydraulic fracturing physical simulation experiments in oil and gas field development. And more particularly, to a large-scale fracturing experiment system and method under different flowing carbon dioxide injection conditions.
Background
The traditional water-based fracturing fluid has the problems of incomplete gel breaking, incomplete flowback, large retention in the stratum and the like, and serious damage to the stratum. Therefore, the carbon dioxide fracturing technology is focused and researched, has the advantages of low damage, easiness in flowback and the like, and is widely applied to various reservoirs, in particular to water-sensitive reservoirs.
On the other hand, due to the complexity of reservoir geological conditions and the ambiguous knowledge of the mechanism of the seam making under different phases of carbon dioxide, the effective implementation of the process technology is still restricted. Therefore, understanding of the mechanism of cracking and extending carbon dioxide fracturing cracks in different phases is imperative.
In recent years, intensive research on the crack initiation extension mechanism problem by developing an indoor hydraulic fracturing physical simulation experiment becomes a hot spot of industrial research. The physical model experimental technology for different fracturing processes is also continuously improved and innovated. For example, the patent of application number 201710589324.7 provides a supercritical carbon dioxide core fracturing experimental method under pore pressure saturation, which can realize supercritical carbon dioxide fracturing under simulated high-temperature and high-stress conditions of a ground layer and under conditions containing pore pressure. The patent with the application number of 201610105722.2 provides a method for manufacturing a test piece for supercritical carbon dioxide fracturing shale under triaxial stress, in particular relates to a method for manufacturing a test piece for fracturing, which can simulate the influence of different technological parameters on the effect of supercritical carbon dioxide fracturing shale under the conditions of reservoir temperature and pressure, but has the common problems that: the test piece is 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 test piece is small, and stable expansion simulation of cracks cannot be realized due to scale effect; the confining pressure applied to the sample is only quasi-three-dimensional, not full-three-dimensional; the patent is directed to a single supercritical carbon dioxide fluid injection simulation method only, and the method for describing the fracturing effect, namely the 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 experimental simulation of supercritical carbon dioxide fracturing of a rock sample under the ground stress condition, and can simulate the sand carrying function of carbon dioxide; but has the following problems: the sample is still cylindrical, so the applied confining pressure is only quasi-three-dimensional, not full-three-dimensional; the high-pressure plunger pump is directly connected with an air source, and the gasification phenomenon exists along with the reduction of the pressure of the air cylinder, so that the carbon dioxide is required to be liquefied and pressurized, the experimental efficiency is reduced, and the carbon dioxide corrodes the pump to a certain extent, so that the safety of equipment is not facilitated; in addition, the patent does not mention a method for observing the morphology of the crack after pressing. The patent applied for 201610972423.9 provides a supercritical carbon dioxide fracturing simulation experiment device, although full three-dimensional stress loading is carried out, liquefaction treatment is carried out on carbon dioxide in advance, because a heating system is positioned in a sample loading frame, the implementation of switching pumping of various different phase fluids cannot be realized, and the shape of a crack after pressing adopts an visual observation method, so that accurate description of the carbon dioxide joint making cannot be realized.
In summary, although the former patent application can realize the pumping fracturing experiment of supercritical carbon dioxide, the sample size is smaller, and the triaxial loading can not really realize the purpose of simulating the stable expansion of the fracture, or the problems that the carbon dioxide phase state conversion efficiency is low and multiple phase state alternate pumping can not be performed are existed. In addition, the largest problem, namely the observation of the carbon dioxide fracturing fracture morphology, is not solved effectively, the observation of the fracture morphology in the common object model experiment is mainly carried out by two means, and a small-scale sample (within 30 cm) can be subjected to CT scanning or dyeing treatment on fracturing fluid. However, at present, a dye which is mutually soluble with a carbon dioxide solvent is difficult to find in the market, so that the traditional method for observing the crack morphology is not suitable for observing carbon dioxide pumping fracturing large-scale rock.
Therefore, the invention provides a large-scale fracturing experiment system and method under different flowing carbon dioxide injection conditions so as to solve the problems.
Disclosure of Invention
One object of the invention is to provide a large-scale fracturing experiment system under different flowing carbon dioxide injection conditions.
The invention further aims to provide a large-scale fracturing experiment and a post-fracturing fracture morphology diagnosis method under different flow-state carbon dioxide injection conditions.
In order to achieve the above purpose, the invention adopts the following technical scheme:
a large-scale fracturing experiment system under different flowing 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 main pipeline is provided with a branch pipeline, and the carbon dioxide gas source supply unit and the triaxial stress loading unit are connected with the plunger pumping unit through branch pipelines;
the plunger pump injection unit comprises a plunger pump and an intermediate container unit;
the branch pipelines comprise a first branch pipeline, a second branch pipeline and a third branch pipeline;
the intermediate container unit comprises 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 equipped with a second temperature control device;
one end of the first intermediate container, one end of the second intermediate container and one end of the third intermediate container are 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 middle container, the second middle container and the third middle container are 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 pump injection of carbon dioxide in different flow states and dyeing 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 fluid in the intermediate container unit into the triaxial stress loading unit;
the first temperature control device is used for 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 a carbon dioxide 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 cylinder and the condenser.
Preferably, a second valve is arranged on the first branch pipe line; a third valve is arranged on the second branch pipe line; and a fourth valve is arranged on the third branch pipe line.
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; a seventh valve is arranged between the third intermediate container and the plunger pump.
Preferably, the plunger pumping unit further comprises air compression equipment and vacuum equipment; the air compression equipment and the vacuum equipment are both arranged between the middle container unit and the triaxial stress loading unit.
Preferably, the vacuum device is a vacuum pump, and the air compression device is an air compressor.
Preferably, the branch lines further comprise a fourth branch line and a fifth branch line; the air compression device and the vacuum device are connected with the main pipeline through a fourth branch pipeline and a fifth branch pipeline respectively.
Preferably, an eighth valve is arranged on the fourth branch pipe line; and a ninth valve is arranged on the fifth branch pipe line.
Preferably, the triaxial stress loading unit includes a triaxial stress loading frame and a sample placed in the triaxial stress loading frame.
Preferably, the triaxial stress loading frame has a size of not less than 1m×1m.
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 the first intermediate container, one end of the second intermediate container and one end of the triaxial stress loading unit are respectively provided with a pressure gauge and a thermometer.
Preferably, the temperature range of the first temperature control device is-10-30 ℃.
Preferably, the temperature range of the second temperature control device is between room temperature and 100 ℃. The room temperature is 20 DEG C
Preferably, the first temperature control device is a cryogenic bath.
Preferably, the second temperature control device is high Wen Yucao.
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 82Mpa.
Preferably, the first intermediate container, the second intermediate container and the third intermediate container each have a volume of at least 3000ml.
Preferably, the first intermediateThe material of the container, the second intermediate container and the third intermediate container is stainless steel 316L, and the pressure resistance is at least 50MPa and the CO resistance is at least 50MPa 2 。
Preferably, the first valve to the fourth valve and the eighth valve to the tenth valve are electromagnetic remote control pneumatic ball valves, and the material is stainless steel 316L, at least 50MPa, CO resistance 2 The real-time switching pumping of the fluid in three different intermediate containers can be realized.
Preferably, the fifth valve to the seventh valve are all manual valves.
The invention also provides a large-scale fracturing experiment and a post-fracturing fracture morphology diagnosis method under different flowing carbon dioxide injection conditions, wherein the method uses the system and comprises the following steps:
1) Sample preparation: placing the sample in a triaxial stress loading unit to load the triaxial stress;
2) Preparing a water-based fracturing fluid: injecting a water-based fracturing fluid into the third intermediate reservoir;
3) Preparing a carbon dioxide fluid: providing a 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; the temperature of the first intermediate container and the temperature of the second intermediate container are respectively controlled by using first temperature control equipment and second temperature control equipment, so that carbon dioxide fluid in different flow states is obtained;
4) Fracturing experiment stage: pumping carbon dioxide fluid in different flow states in the first intermediate container and/or the second intermediate container into a triaxial stress loading unit by using a plunger pump;
5) Diagnosing the morphology of the carbon dioxide fracturing cracks: after the pumping of the carbon dioxide fluid is finished, pumping the water-based fracturing fluid in the third intermediate container into a triaxial stress loading unit by using a plunger pump; the sample was taken out and the morphology of the crack was observed.
Preferably, the water-based fracturing fluid in step 2) contains a colorant.
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 opening the vacuum equipment to vacuumize until the vacuum equipment reads-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, and controlling the temperature and the pressure of the first intermediate container to enable the first intermediate container to be filled with liquid carbon dioxide;
closing the first valve, opening the third valve, opening the plunger pump and the second temperature control equipment, 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 comprises the following steps:
when liquid carbon dioxide is pumped in, the first valve, the third valve, the fourth valve, the sixth valve, the seventh valve, the eighth valve and the ninth valve are kept closed, the second valve, the fifth valve and the tenth valve are opened, the plunger pump is started, and the liquid carbon dioxide in the first intermediate container is pumped in the triaxial stress loading unit;
when the supercritical carbon dioxide is pumped, 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 supercritical carbon dioxide in the second intermediate container is pumped into the triaxial stress loading unit.
Preferably, the carbon dioxide fracturing fracture morphology diagnosis process in step 5) specifically includes the following steps:
after the carbon dioxide fluid is pumped, 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 a plunger pump, and pumping the water-based fracturing fluid in the third intermediate container into a triaxial stress loading unit; the sample was taken out and the morphology of the crack was observed.
Preferably, after the water-based fracturing fluid in the third intermediate container in the step 5) is pumped into the triaxial stress loading unit, the method further includes the following steps: and the pressure of the triaxial stress loading unit is reduced to 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 lowered to the initial positions.
The beneficial effects of the invention are as follows:
according to the large-scale fracturing experiment system under different flow carbon dioxide injection conditions, a plunger pump injection mode is improved, a plurality of groups of intermediate containers which are arranged in parallel are added, so that stable and real-time switching pump injection of different carbon dioxide phases can be realized, and dyeing observation can be carried out on the pressed carbon dioxide crack forms. Thereby providing more effective technical means for scientific researchers to study the carbon dioxide fracturing crack propagation mechanism;
the large-scale fracturing experiment and the method for diagnosing the fracture morphology after fracturing under the injection condition of different flow state carbon dioxide provided by the invention overcome the problems that continuous and stable pumping of different flow state carbon dioxide cannot be carried out and the fracture morphology diagnosis caused by carbon dioxide cannot be effectively carried out in the traditional fracturing simulation experiment method.
Drawings
The following describes the embodiments of the present invention in further detail with reference to the drawings.
FIG. 1 shows a schematic diagram of a large scale fracturing experiment system under different flow carbon dioxide injection conditions provided by the present invention;
the device comprises a 1-carbon dioxide gas cylinder, a 4-condenser, a 19-first intermediate container, a 20-second intermediate container, a 21-third intermediate container, a 22-first temperature control device, a 23-second temperature control device, a 29-plunger pump, a 11-air compression device, a 12-vacuum device, a 24-triaxial stress loading frame, a 25-sample, a 3-first valve, a 7-second valve, a 8-third valve, a 15-fourth valve, a 26-fifth valve, a 27-sixth valve, a 28-seventh valve, a 9-eighth valve, a 10-ninth valve, a 16-tenth valve, a 30-main pipeline, a 31-first branch pipeline, a 32-second branch pipeline, a 33-third branch pipeline, a 34-fourth branch pipeline and a 35-fifth branch pipeline.
Detailed Description
In order to more clearly illustrate the present invention, the present invention will be further described 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 that this invention is not limited to the details given herein.
In order to solve the problems that in the prior art, the sample size is small, the simulated triaxial loading can not really realize stable expansion of simulated cracks, the carbon dioxide phase conversion efficiency is low, multiple phase alternate pumping can not be performed, and the morphology observation of carbon dioxide fracturing cracks is not yet effectively solved, the invention provides a large-scale fracturing experiment system and a large-scale fracturing experiment method under different flow state carbon dioxide injection conditions, which not only realize stable and real-time switching pumping of different carbon dioxide phases, but also realize dyeing observation of the pressed carbon dioxide cracking morphology.
Specifically, with reference to fig. 1, a large-scale fracturing experiment system under different flowing 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 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,
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 connected with the plunger pumping unit through the branch pipeline;
the plunger pumping 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; the second intermediate container 20 is equipped with a second temperature control device 23;
one ends of the first intermediate container 19, the second intermediate container 20 and the third intermediate container 21 are connected to 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 pump injection of carbon dioxide in different flow states and dyeing the pressed carbon dioxide crack form; wherein 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 to 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 and controlling 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 cylinder 1, and the other end of the condenser 4 is connected with the intermediate container unit. In the carbon dioxide cylinder 1, the full amount of carbon dioxide is generally stored at a liquid state at normal temperature and high pressure, and the pressure is 7-8MPa, however, with the use of carbon dioxide, the pressure reduction may have a gaseous state, so the condenser 4 cooperates with the first temperature control device 22 to primarily refrigerate the fluid flowing out of the carbon dioxide cylinder 1.
In order to control the outflow rate, outflow amount, etc. of the carbon dioxide fluid in the carbon dioxide cylinder, as a preferred embodiment of the present invention, a first valve 3 is provided between the carbon dioxide cylinder 1 and the condenser 4.
Further, in order to more intuitively regulate and control the phase state of the carbon dioxide fluid, one end of the carbon dioxide 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; the second branch line 32 is provided with a third valve 8; the third branch pipeline 33 is provided with a fourth valve 15; 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 provided 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 an air compressing device 11 and a vacuum device 12; the air compression device 11 and the vacuum device 12 are arranged between the middle 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 the plunger pump for use, and a piston of an intermediate container which is subjected to single pumping falls to the bottom to prepare for secondary pumping; further, the vacuum device 12 is a vacuum pump, and the air compressor device 11 is an air compressor.
As a preferred embodiment of the invention, the branch lines further comprise a fourth branch line 34 and a fifth branch line 35; the air pressure device 11 and the vacuum device 12 are connected to the main line 30 via a fourth branch line 34 and a fifth branch line 35, respectively; further, the fourth branch pipeline 34 is provided with an eighth valve 9; the fifth branch line 35 is provided with a ninth valve 10.
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 triaxial stress loading frame has a size of not less than 1m×1m; 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 fractured rock sample, and the ground stress can reach 69MPa at most so as to simulate the true stratum 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 triaxial stress loading unit is convenient to control.
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 carbon dioxide is ensured by the temperature condition, the temperature range of the first temperature control device 22 is-10-30 ℃, and the PID temperature control is performed; in addition, in order to facilitate the adjustment of the temperature by the first temperature control device 22, one end of the first intermediate container 19 is provided with a pressure gauge and a temperature gauge; further, the first temperature control device is a cryogenic bath.
As a preferred embodiment of the present invention, in order to warm the fluid flowing out of the first intermediate container 19, the supercritical state of carbon dioxide is achieved by the temperature condition, and the second temperature control device 23 controls the temperature range from room temperature to 100 ℃, and PID controls the temperature; in addition, in order to facilitate the adjustment of the temperature by the second temperature control device 23, one end of the second intermediate container 20 is provided with a pressure gauge and a temperature gauge; further, the second temperature control device is high Wen Yucao.
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 82MPa.
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 3000ml; the materials of the first intermediate container 19, the second intermediate container 20 and the third intermediate container 21 are stainless steel 316L, and the pressure resistance is at least 50MPa and the CO resistance is at least 50MPa 2 。
As a preferable embodiment of the invention, the first valve to the fourth valve and the eighth valve to the tenth valve are electromagnetic remote control pneumatic ball valves, and the material is stainless steel 316L, at least pressure-resistant 50MPa and CO-resistant 2 The real-time switching pumping of the fluid in three different intermediate containers can be realized.
As a preferred embodiment of the present invention, each of the fifth to seventh valves is a manual valve.
As another aspect of the invention, the invention also provides a large-scale fracturing experiment and post-fracturing fracture morphology diagnosis method under different flow state carbon dioxide injection conditions, wherein the method uses the system and comprises the following steps:
1) Sample preparation: placing a sample 25 in a triaxial stress loading frame 24 to load three-dimensional stress;
2) Preparing a water-based fracturing fluid: injecting a water-based fracturing fluid containing a colorant into the third intermediate container 21;
3) Preparing a 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 opening 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 equipment 12, opening the condenser 4, the first valve 3, the second valve 7 and the first temperature control equipment 22, and controlling the temperature and the pressure of the first intermediate container to enable the first intermediate container 19 to be filled with liquid carbon dioxide;
closing the first valve 3, opening the third valve 8, opening 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, and controlling the temperature and the pressure of the second intermediate container 20 to keep the carbon dioxide in the second intermediate container 20 in a supercritical state;
4) Fracturing experiment stage:
when liquid carbon dioxide is pumped in, 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 are kept closed, the second valve 7, the fifth valve 26 and the tenth valve 16 are opened, the plunger pump 29 is started, and the liquid carbon dioxide in the first intermediate container 19 is pumped in the triaxial stress loading frame 24;
when pumping supercritical carbon dioxide, 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, opening the plunger pump 29, and pumping the supercritical carbon dioxide in the second intermediate container 20 into the triaxial stress loading frame 24;
5) Diagnosing the morphology of the carbon dioxide fracturing cracks: after the carbon dioxide fluid is pumped, 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, opening a 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 wellhead pressure of the previous carbon dioxide pump injection (namely, the wellhead pressure at the end of the stage 4 when the water-based fracturing fluid is pumped into the previous stage carbon dioxide pump injection) as a reference, stopping injection 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 dropping the pistons of the first intermediate container 19, the second intermediate container 20 and the third intermediate container 21 to the initial positions; the sample was taken out and the morphology of the crack was observed.
The large-scale fracturing experiment and the post-fracturing fracture morphology diagnosis method under different flowing carbon dioxide injection conditions provided by the invention overcome the problems that continuous stable pumping of different flowing carbon dioxide cannot be carried out and the morphology diagnosis of the carbon dioxide fracturing fracture cannot be effectively carried out in the traditional fracturing simulation experiment method; through improving plunger pump mode, increase the intermediate container of multiunit parallel arrangement, not only can realize the steady real-time switching pump of different carbon dioxide phase states and annotate, can also dye the observation to the carbon dioxide crack form after pressing to research personnel research carbon dioxide fracturing crack extension mechanism provides more effective technical means.
It should be understood that the foregoing examples of the present invention are provided merely for clearly illustrating the present invention and are not intended to limit the embodiments of the present invention, and that various other changes and modifications may be made therein by one skilled in the art without departing from the spirit and scope of the present invention as defined by the appended claims.
Claims (4)
1. The large-scale fracturing experiment and the method for diagnosing the crack morphology after pressing under different flowing carbon dioxide injection conditions are characterized in that a large-scale fracturing experiment system is used in the large-scale fracturing experiment and the method for diagnosing the crack morphology after pressing, and the large-scale fracturing experiment system 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 main pipeline is provided with a branch pipeline, and the carbon dioxide gas source supply unit and the triaxial stress loading unit are connected with the plunger pumping unit through branch pipelines;
the carbon dioxide gas source supply unit comprises a carbon dioxide gas cylinder and a condenser; one end of the condenser is connected with a carbon dioxide gas cylinder, and the other end of the condenser is connected with the middle container unit;
the triaxial stress loading unit comprises a triaxial stress loading frame and a sample arranged in the triaxial stress loading frame;
the plunger pump injection unit comprises a plunger pump, an intermediate container unit, air compression equipment and vacuum equipment;
the branch pipelines comprise a first branch pipeline, a second branch pipeline, a third branch pipeline, a fourth branch pipeline and a fifth branch pipeline;
the intermediate container unit comprises 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 equipped with a second temperature control device; the temperature range of the first temperature control equipment is-10-30 ℃; the temperature range of the second temperature control equipment is controlled to be between room temperature and 100 ℃;
one end of the first intermediate container, one end of the second intermediate container and one end of the third intermediate container are connected with the main pipeline through a first branch pipeline, a second branch pipeline and a third branch pipeline respectively; the other ends of the first middle container, the second middle container and the third middle container are connected with a plunger pump;
the air compression equipment and the vacuum equipment are arranged between the middle container unit and the triaxial stress loading unit;
the air compression equipment and the vacuum equipment are connected with a main pipeline through a fourth pipeline and a fifth pipeline respectively;
the method comprises the following steps:
1) Sample preparation: placing the sample in a triaxial stress loading unit to load the triaxial stress;
2) Preparing a water-based fracturing fluid: injecting a water-based fracturing fluid into the third intermediate reservoir;
3) Preparing a carbon dioxide fluid: providing a 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; the temperature of the first intermediate container and the temperature of the second intermediate container are respectively controlled by using first temperature control equipment and second temperature control equipment, so that carbon dioxide fluid in different flow states is obtained;
4) Fracturing experiment stage: pumping carbon dioxide fluid in different flow states in the first intermediate container and/or the second intermediate container into a triaxial stress loading unit by using a plunger pump;
5) Diagnosing the morphology of the carbon dioxide fracturing cracks: after the pumping of the carbon dioxide fluid is finished, pumping the water-based fracturing fluid in the third intermediate container into a triaxial stress loading unit by using a plunger pump; the sample was taken out and the morphology of the crack was observed.
2. The method for large-scale fracturing experiments and post-fracturing fracture morphology diagnosis under different flowing carbon dioxide injection conditions according to claim 1, wherein a first valve is arranged between the carbon dioxide cylinder and the condenser.
3. The method for diagnosing a large-scale fracturing experiment and a post-fracturing fracture morphology under different flow-state carbon dioxide injection conditions according to claim 1, wherein a second valve is arranged on the first branch pipe; a third valve is arranged on the second branch pipe line; a fourth valve is arranged on the third branch pipe line; 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; a seventh valve is arranged between the third intermediate container and the plunger pump.
4. The method for diagnosing a large-scale fracturing experiment and a post-fracturing fracture morphology under different flow-state carbon dioxide injection conditions according to claim 1, wherein an eighth valve is arranged on the fourth branch pipe; and a ninth valve is arranged on the fifth branch pipe line.
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