A shale reservoir supercritical carbon dioxide fracturing reconstruction system and method

Abstract

The application discloses a shale reservoir supercritical carbon dioxide fracturing reconstruction system and method, relates to the technical field of unconventional oil and gas development, and adopts supercritical carbon dioxide as a fracturing fluid to implement fracturing reconstruction on reservoir rocks, forms a three-dimensional complex fracture network after fracturing, and liquid carbon dioxide injected at high pressure can ensure entering a supercritical state under the temperature and pressure conditions of deep reservoirs. The supercritical carbon dioxide has the dual characteristics of gas and liquid, can effectively reduce the fracturing pressure of shale reservoir reconstruction and avoid the expansion and migration of water-sensitive clay minerals. Meanwhile, the diffusion coefficient of supercritical carbon dioxide is similar to that of gas, which is beneficial to improving the complexity of the fracturing fracture network, and thus can significantly improve the yield of shale oil and gas wells, and has higher safety performance.

Description

Technical Field

[0001] This invention relates to the field of unconventional oil and gas development technology, specifically to a supercritical carbon dioxide fracturing system and method for shale reservoirs. Background Technology

[0002] Volumetric fracturing is one of the key technologies for the industrial development of shale oil and gas reservoirs. Current shale volumetric fracturing primarily relies on water-based fracturing. Water-based fracturing mainly uses fracturing fluid to fracture the shale reservoir, creating new fractures in the reservoir pool and connecting natural fractures and other primary weak structural surfaces. This forms a fracture network system with high conductivity, allowing the release of free and adsorbed gas in the shale reservoir, significantly improving the initial production and final recovery rate of shale oil and gas wells. However, water-based fracturing is ineffective for volumetric fracturing of deeply buried shale reservoirs. The main reason is the increased fracturing pressure required for fracturing deep reservoirs. Furthermore, the increased geostress in deep reservoirs leads to increased plasticity of the rock material, making it difficult for hydraulic fracturing to penetrate the reservoir rock and form a main fracture of sufficient height. This makes it difficult to form a complex three-dimensional fracture network and achieve effective fracturing volume. Therefore, the increase in oil and gas production after reservoir fracturing is limited, making it difficult to achieve large-scale economic benefits. Therefore, conventional water-based fracturing and hydraulic fracturing techniques for shale reservoir stimulation cannot meet the needs of industrial-scale development of deeply buried shale oil and gas reservoirs. Summary of the Invention

[0003] The purpose of this invention is to address the shortcomings of conventional water-based fracturing and hydraulic fracturing techniques for shale reservoir stimulation, which cannot meet the needs of industrial development of deep-buried shale oil and gas reservoirs. This invention provides a supercritical carbon dioxide fracturing system and method for shale reservoir stimulation. Supercritical carbon dioxide is used as the fracturing fluid to stimulate the reservoir rock, resulting in a complex three-dimensional fracture network. The high-pressure injected liquid carbon dioxide ensures it enters a supercritical state under the temperature and pressure conditions of the deep reservoir. Supercritical carbon dioxide possesses characteristics of both gas and liquid; its density is close to that of a liquid while its viscosity is similar to that of a gas. This effectively reduces the fracturing pressure in shale reservoir stimulation and prevents the expansion and migration of water-sensitive clay minerals. Furthermore, the near-gas-like diffusion coefficient of supercritical carbon dioxide helps increase the complexity of the fracturing network, thereby significantly improving the production of shale oil and gas wells. This invention overcomes the disadvantages and deficiencies of high fracturing pressure, large fracture width, short effective period, and rapid production decline in hydraulic fracturing of deep-buried shale reservoirs. It also helps prevent the expansion and migration of water-sensitive clay minerals in shale reservoirs from blocking pore throats, thus solving the aforementioned problems.

[0004] The technical solution of the present invention is as follows:

[0005] A supercritical carbon dioxide fracturing system for shale reservoirs, specifically comprising:

[0006] A carbon dioxide supply module, which provides a carbon dioxide source for supercritical carbon dioxide fracturing.

[0007] The gas-liquid separation and pressurization module separates the carbon dioxide input from the carbon dioxide supply module into gas and liquid, and pumps the liquid carbon oxide into the high-pressure carbon dioxide pumping module.

[0008] The high-pressure carbon dioxide pump module allows liquid carbon dioxide to enter the reservoir after its pressure is increased. Under the influence of temperature and pressure in the reservoir, it enters a supercritical state, causing the reservoir rock to fracture and generate a complex fracture network, thus forming oil and gas seepage channels.

[0009] Basic principles and techniques:

[0010] When the temperature of liquid carbon dioxide exceeds 31℃ and the pressure exceeds 7.38MPa, it enters the supercritical state. Supercritical carbon dioxide fluid is between gas and liquid, possessing the characteristics of both. Its density is close to that of liquid while its viscosity is close to that of gas. This reduces the fracturing pressure required for reservoir fracturing, increases the effective fracture height while reducing the fracture width, and prevents clay mineral expansion from reducing the conductivity of the reservoir matrix and fractures. It can not only effectively overcome the water sensitivity unique to shale reservoirs, but also effectively increase the complexity of the fracturing network.

[0011] When using supercritical carbon dioxide fracturing technology, liquid carbon dioxide is first supplied by the carbon dioxide supply module. After being transported by the gas-liquid separation and pressurization module, it is supplied to the high-pressure carbon dioxide pump module with pure liquid carbon dioxide. Then, after the pressure is increased by the high-pressure carbon dioxide pump module, the liquid carbon dioxide enters the reservoir through the wellhead. Under the action of the temperature and pressure of the reservoir, it enters the supercritical state, causing the reservoir rock to fracture and generate a complex fracture network and form oil and gas seepage channels.

[0012] Furthermore, it also includes: a pipeline pressure safety module, which is used to ensure that the pipeline pressure during the fracturing process is lower than the pipeline design pressure value;

[0013] If the pipeline pressure exceeds the design pressure, the pipeline pressure safety module will automatically initiate a pressure relief process until the pipeline pressure is lower than the design pressure value. During the fracturing process, the pipeline pressure should be kept below the pipeline design pressure value. If the pipeline pressure exceeds the design pressure, the pipeline pressure safety module will automatically initiate a pressure relief process until the pipeline pressure is lower than the design pressure value.

[0014] Furthermore, the carbon dioxide supply module includes:

[0015] A carbon dioxide tanker truck, which stores gaseous carbon dioxide and liquid carbon dioxide respectively; the gaseous carbon dioxide is used for pipeline cleaning and drying before and after fracturing, and the liquid carbon dioxide is used for supercritical carbon dioxide fracturing modification; that is, the carbon dioxide tanker truck stores gaseous carbon dioxide and liquid carbon dioxide respectively, and can output gaseous carbon dioxide or liquid carbon dioxide according to actual needs.

[0016] Furthermore, the gas-liquid separation and pressurization module includes: a gas-liquid separator and a carbon dioxide booster pump set;

[0017] The gas-liquid separator is used to separate the gaseous carbon dioxide mixed in with the liquid carbon dioxide output from the carbon dioxide tanker, so that the liquid carbon dioxide reaches a pure state; preferably, because even the liquid carbon dioxide directly output from the carbon dioxide tanker will contain a small amount of carbon dioxide gas, the gas-liquid separator filters out the gas in the liquid carbon dioxide, thereby purifying the liquid carbon dioxide.

[0018] The carbon dioxide booster pump unit pressurizes the purified liquid carbon dioxide and delivers it to the carbon dioxide high-pressure pump module; that is, the carbon dioxide booster pump unit plays a role in boosting and pumping.

[0019] Furthermore, the high-pressure carbon dioxide pump module includes:

[0020] The fracturing truck is equipped with a carbon dioxide booster pump unit that delivers purified liquid carbon dioxide to the fracturing truck, which then pumps it out to the reservoir at its designed displacement to carry out fracturing and fracturing. The specific structure of the fracturing truck is well known to those skilled in the art and will not be described in detail here.

[0021] Furthermore, the specific connections of the system, as well as the positional relationships between the components and valves, are given below.

[0022] Furthermore, the gaseous carbon dioxide is output through a gas phase pipeline, and a first gas phase pipeline ball valve for controlling the output of gaseous carbon dioxide is installed on the gas phase pipeline.

[0023] On the gas phase pipeline, and located at the rear end of the first gas phase pipeline ball valve, a first gas-liquid two-phase flow ball valve, a second gas-liquid two-phase flow ball valve, and a first plug valve are sequentially arranged.

[0024] The fracturing truck is connected to the wellhead via a high-pressure pipeline, and liquid carbon dioxide enters the reservoir from the wellhead through the high-pressure pipeline;

[0025] The first plug valve is connected to the high-pressure pipeline via a tee.

[0026] A second plug valve and a check valve are installed on the high-pressure pipeline at the rear end of the tee.

[0027] Furthermore, the liquid carbon dioxide is output through a liquid phase pipeline, and a first liquid phase pipeline ball valve for controlling the output of liquid carbon dioxide is installed on the liquid phase pipeline;

[0028] The gas-liquid separator is installed on the liquid phase pipeline and is located at the rear end of the ball valve of the first liquid phase pipeline;

[0029] The carbon dioxide booster pump unit is installed on the liquid phase pipeline and located at the rear end of the gas-liquid separator. A second liquid phase pipeline ball valve is installed on the liquid phase pipeline between the carbon dioxide booster pump and the fracturing truck.

[0030] Furthermore, the pipeline pressure safety module includes: a differential pressure valve, a third liquid phase pipeline ball valve, and a gas phase pipeline pressure relief valve;

[0031] The differential pressure valve is used to monitor the pressure difference between the input and output ends of the carbon dioxide booster pump set; when the pressure difference exceeds the preset value, the differential pressure valve automatically opens and releases pressure; the third liquid phase pipeline ball valve is located at the pressure release end of the differential pressure valve and is used for manual control of pressure release;

[0032] On the liquid phase pipeline, a gas phase pressure relief branch is provided between the first gas-liquid two-phase flow ball valve and the second gas-liquid two-phase flow ball valve via a tee. The gas phase pipeline pressure relief valve is installed on the gas phase pressure relief branch. When the pressure difference exceeds the preset value, the gas phase pipeline pressure relief valve automatically opens and releases pressure.

[0033] Furthermore, a four-way connector is provided on the liquid phase pipeline, and between the gas-liquid separator and the carbon dioxide booster pump group; the liquid phase pipeline is connected to the gas phase pipeline located between the first gas phase pipeline ball valve and the first gas-liquid two-phase flow ball valve through the four-way connector, and the four-way connector is also connected to the first carbon dioxide discharge branch line, and a fourth liquid phase pipeline ball valve for controlling the discharge of carbon dioxide is provided on the first carbon dioxide discharge branch line.

[0034] A third gas-liquid two-phase flow ball valve is installed on the pipeline between the four-way connector and the gas phase pipeline.

[0035] A second carbon dioxide discharge branch is provided on the gas phase pressure relief branch via a tee, and a second gas phase pipeline ball valve for controlling the discharge of carbon dioxide is provided on the second carbon dioxide discharge branch.

[0036] A method for supercritical carbon dioxide fracturing stimulation of shale reservoirs specifically includes the following steps:

[0037] Step S1: First, confirm that all valves are closed. Open the first gas phase pipeline ball valve, the first gas-liquid two-phase flow ball valve, the second gas-liquid two-phase flow ball valve, the first plug valve, and the gas phase pipeline pressure relief valve. Gaseous carbon dioxide is discharged from the carbon dioxide tanker, flows in the gas phase pipeline, and sequentially passes through the first gas phase pipeline ball valve, the first gas-liquid two-phase flow ball valve, the second gas-liquid two-phase flow ball valve, the first plug valve, and the high-pressure pipeline before entering the fracturing truck. The high-speed flow of gaseous carbon dioxide cleans and dries the hydraulic end of the fracturing truck and its pipelines.

[0038] Step S2: Close the first gas phase pipeline ball valve, and open the first liquid phase pipeline ball valve and the third gas-liquid two-phase flow ball valve; liquid carbon dioxide is discharged from the carbon dioxide tank truck, flows in the liquid phase pipeline, and enters the gas phase pipeline through the first liquid phase pipeline ball valve, the gas-liquid separator, and the third gas-liquid two-phase flow ball valve, and then enters the fracturing truck through the first gas-liquid two-phase flow ball valve, the second gas-liquid two-phase flow ball valve, the first plug valve, and the high-pressure pipeline; the high-speed flow of liquid carbon dioxide rapidly cools the hydraulic end of the fracturing truck and its pipelines;

[0039] Step S3: Close the third gas-liquid two-phase flow ball valve, the first plug valve, and the second gas-liquid two-phase flow ball valve; open the differential pressure valve, the third liquid phase pipeline ball valve, and the second liquid phase pipeline ball valve; start the carbon dioxide booster pump group to pressurize the liquid carbon dioxide separated by the gas-liquid separator; the pressurized liquid carbon dioxide enters the fracturing truck through the second liquid phase pipeline ball valve along the liquid phase pipeline; open the second plug valve and the wellhead; start the fracturing truck; the fracturing truck pumps the liquid carbon dioxide into the high-pressure pipeline at the designed displacement; then it enters the inlet through the second plug valve, thus entering the reservoir; the high-pressure liquid carbon dioxide enters the supercritical state under the temperature and pressure of the reservoir, and the reservoir is fracturing and transformed.

[0040] Step S4: After the fracturing process is completed, stop the fracturing truck and the carbon dioxide booster pump unit, then close the wellhead, open the fourth liquid phase pipeline ball valve to discharge the carbon dioxide in the liquid phase pipeline; open the first gas phase ball valve, the first gas-liquid two-phase flow ball valve, the second gas-liquid two-phase flow ball valve, and the first plug valve; gaseous carbon dioxide is discharged from the carbon dioxide tanker into the gas phase pipeline, and finally into the fracturing truck, and the hydraulic end of the fracturing truck and its pipelines are cleaned of the solid dry ice formed after the operation due to the sudden drop in temperature;

[0041] Step S5: Open the second gas phase pipeline ball valve and the fourth liquid phase pipeline ball valve to discharge the remaining carbon dioxide in the pipeline.

[0042] Compared with existing technologies, the advantages of this invention are:

[0043] 1. A supercritical carbon dioxide fracturing system and method for shale reservoirs, comprising a carbon dioxide supply module providing a carbon dioxide source for supercritical carbon dioxide fracturing; a gas-liquid separation and pressurization module separating the carbon dioxide input from the carbon dioxide supply module and pumping liquid carbon dioxide into a high-pressure carbon dioxide pumping module; and a high-pressure carbon dioxide pumping module, where the liquid carbon dioxide, after being pressurized, enters the reservoir and enters a supercritical state under the temperature and pressure of the reservoir, causing the reservoir rock to fracture and generate a complex fracture network, forming oil and gas seepage channels; it uses supercritical carbon dioxide as a fracturing fluid to fracture and transform the reservoir rock, resulting in a three-dimensional... Complex fracture networks and high-pressure injected liquid carbon dioxide can ensure entry into a supercritical state under the temperature and pressure conditions of deep reservoirs. Supercritical carbon dioxide has the dual characteristics of both gas and liquid, with a density close to that of a liquid and a viscosity close to that of a gas. It can effectively reduce the fracturing pressure of shale reservoir stimulation and avoid the expansion and migration of water-sensitive clay minerals. At the same time, the diffusion coefficient of supercritical carbon dioxide, which is close to that of a gas, is conducive to increasing the complexity of the fracture network, thereby significantly increasing the production of shale oil and gas wells. It can overcome the disadvantages and deficiencies of hydraulic fracturing in deep shale reservoirs, such as high fracturing pressure, large fracture width and short effective period after hydraulic fracturing, and rapid decline in production. It is also beneficial to prevent the expansion and migration of water-sensitive clay minerals in shale reservoirs from blocking pore throats.

[0044] 2. A supercritical carbon dioxide fracturing stimulation system and method for shale reservoirs, and a corresponding pipeline pressure safety module is designed to improve the overall safety performance of the system and ensure the safety of operators. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of a supercritical carbon dioxide fracturing system for shale reservoirs in Example 1.

[0046] Figure 2 This is a schematic diagram of a supercritical carbon dioxide fracturing system for shale reservoirs in Example 3.

[0047] Reference numerals: 1-Carbon dioxide tanker, 2-Gas phase pipeline, 3-First gas phase pipeline ball valve, 4-Liquid phase pipeline, 5-First liquid phase pipeline ball valve, 6-Gas-liquid separator, 7-Carbon dioxide booster pump set, 8-Differential pressure valve, 9-Fracturing truck, 10-Second plug valve, 11-High pressure pipeline, 13-Check valve, 14-Wellhead, 15-Gas phase pipeline pressure relief valve, 16-Fourth liquid phase pipeline ball valve, 17-First gas-liquid two-phase flow ball valve, 18-Third gas-liquid two-phase flow ball valve, 19-First plug valve, 20-Third gas phase pipeline ball valve, 21-Third liquid phase pipeline ball valve, 22-Second gas-liquid two-phase flow ball valve, 23-Second liquid phase pipeline ball valve, 24-First carbon dioxide discharge branch, 25-Second carbon dioxide discharge branch, 26-Gas phase pressure relief branch. Detailed Implementation

[0048] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0049] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0050] Example 1

[0051] Currently, conventional water-based fracturing and hydraulic fracturing techniques for shale reservoir stimulation cannot meet the needs of industrial-scale development of deeply buried shale oil and gas reservoirs.

[0052] This embodiment addresses the aforementioned problems by proposing a supercritical carbon dioxide fracturing system and method for shale reservoirs. Supercritical carbon dioxide is used as the fracturing fluid to fracture the reservoir rock, resulting in a complex three-dimensional fracture network. The high-pressure injected liquid carbon dioxide, under the temperature and pressure conditions of the deep reservoir, ensures entry into a supercritical state. Supercritical carbon dioxide possesses the dual characteristics of both gas and liquid; its density is close to that of a liquid while its viscosity is similar to that of a gas. This effectively reduces the fracturing pressure in shale reservoir stimulation and avoids the expansion and migration of water-sensitive clay minerals. Furthermore, the near-gas-like diffusion coefficient of supercritical carbon dioxide helps increase the complexity of the fracturing network, thereby significantly improving the production of shale oil and gas wells.

[0053] Please see Figure 1 A supercritical carbon dioxide fracturing system for shale reservoirs, specifically comprising:

[0054] A carbon dioxide supply module, which provides a carbon dioxide source for supercritical carbon dioxide fracturing.

[0055] The gas-liquid separation and pressurization module separates the carbon dioxide input from the carbon dioxide supply module into gas and liquid, and pumps the liquid carbon oxide into the high-pressure carbon dioxide pumping module.

[0056] The high-pressure carbon dioxide pump module allows liquid carbon dioxide to enter the reservoir after its pressure is increased. Under the influence of temperature and pressure in the reservoir, it enters a supercritical state, causing the reservoir rock to fracture and generate a complex fracture network, thus forming oil and gas seepage channels.

[0057] Basic principles and techniques:

[0058] When the temperature of liquid carbon dioxide exceeds 31℃ and the pressure exceeds 7.38MPa, it enters the supercritical state. Supercritical carbon dioxide fluid is between gas and liquid, possessing the characteristics of both. Its density is close to that of liquid while its viscosity is close to that of gas. This reduces the fracturing pressure required for reservoir fracturing, increases the effective fracture height while reducing the fracture width, and prevents clay mineral expansion from reducing the conductivity of the reservoir matrix and fractures. It can not only effectively overcome the water sensitivity unique to shale reservoirs, but also effectively increase the complexity of the fracturing network.

[0059] When using supercritical carbon dioxide fracturing technology, liquid carbon dioxide is first supplied by the carbon dioxide supply module. After being transported by the gas-liquid separation and pressurization module, it is supplied to the high-pressure carbon dioxide pump module with pure liquid carbon dioxide. Then, after the pressure is increased by the high-pressure carbon dioxide pump module, the liquid carbon dioxide enters the reservoir through wellhead 14. Under the action of reservoir temperature and pressure, it enters the supercritical state, causing the reservoir rock to fracture and generate a complex fracture network and form oil and gas seepage channels.

[0060] In this embodiment, specifically, it also includes: a pipeline pressure safety module, which is used to ensure that the pipeline pressure during the fracturing process is lower than the pipeline design pressure value;

[0061] If the pipeline pressure exceeds the design pressure, the pipeline pressure safety module will automatically initiate a pressure relief process until the pipeline pressure is lower than the design pressure value. During the fracturing process, the pipeline pressure should be kept below the pipeline design pressure value. If the pipeline pressure exceeds the design pressure, the pipeline pressure safety module will automatically initiate a pressure relief process until the pipeline pressure is lower than the design pressure value.

[0062] In this embodiment, specifically, the carbon dioxide supply module includes:

[0063] A carbon dioxide tanker 1 stores gaseous carbon dioxide and liquid carbon dioxide. The gaseous carbon dioxide is used for pipeline cleaning and drying before and after fracturing, and the liquid carbon dioxide is used for supercritical carbon dioxide fracturing modification. That is, the carbon dioxide tanker 1 stores gaseous carbon dioxide and liquid carbon dioxide, and can output gaseous carbon dioxide or liquid carbon dioxide according to actual needs.

[0064] In this embodiment, specifically, the gas-liquid separation and pressurization module includes: a gas-liquid separator 6 and a carbon dioxide booster pump group 7;

[0065] The gas-liquid separator 6 is used to separate the gaseous carbon dioxide mixed in the liquid carbon dioxide output from the carbon dioxide tanker 1, so that the liquid carbon dioxide reaches a pure state. Preferably, even the liquid carbon dioxide directly output from the carbon dioxide tanker 1 will contain a small amount of carbon dioxide gas. Therefore, the gas-liquid separator 6 filters out the gas in the liquid carbon dioxide, so that the liquid carbon dioxide is purified.

[0066] The carbon dioxide booster pump set 7 pressurizes the purified liquid carbon dioxide and delivers it to the carbon dioxide high-pressure pump module; that is, the carbon dioxide booster pump set 7 plays the role of boosting and pumping.

[0067] In this embodiment, specifically, the high-pressure carbon dioxide pump module includes:

[0068] The fracturing truck 9, wherein the carbon dioxide booster pump group 7 delivers pure liquid carbon dioxide to the fracturing truck 9, and the fracturing truck 9 pumps it out to the reservoir at the designed displacement to carry out fracturing and transformation; in detail, based on the structure of the fracturing truck 9, those skilled in the art should know it, and it will not be described in detail here.

[0069] In this embodiment, the specific connections of the system and the positional relationships between the components and valves are given below.

[0070] In this embodiment, specifically, the gaseous carbon dioxide is output through the gas phase pipeline 2, and the gas phase pipeline 2 is equipped with a first gas phase pipeline ball valve 3 for controlling the output of gaseous carbon dioxide.

[0071] On the gas phase pipeline 2, and located at the rear end of the first gas phase pipeline ball valve 3, a first gas-liquid two-phase flow ball valve 17, a second gas-liquid two-phase flow ball valve 22, and a first plug valve 19 are sequentially arranged.

[0072] The fracturing truck 9 is connected to the wellhead 14 via a high-pressure pipeline 11, and liquid carbon dioxide enters the reservoir from the wellhead 14 via the high-pressure pipeline 11.

[0073] The first plug valve 19 is connected to the high-pressure pipeline 11 via a tee;

[0074] A second plug valve 10 and a check valve 13 are installed on the high-pressure pipeline 11 and at the rear end of the tee.

[0075] In this embodiment, specifically, the liquid carbon dioxide is output through the liquid phase pipeline 4, and the liquid phase pipeline 4 is equipped with a first liquid phase pipeline ball valve 5 for controlling the output of liquid carbon dioxide.

[0076] The gas-liquid separator 6 is installed on the liquid phase pipeline 4 and is located at the rear end of the ball valve 5 of the first liquid phase pipeline;

[0077] The carbon dioxide booster pump 7 is installed on the liquid phase pipeline 4 and located at the rear end of the gas-liquid separator 6. A second liquid phase pipeline ball valve 23 is installed on the liquid phase pipeline 4 between the carbon dioxide booster pump and the fracturing truck 9.

[0078] In this embodiment, specifically, the pipeline pressure safety module includes: a differential pressure valve 8, a third liquid phase pipeline ball valve 21, and a gas phase pipeline pressure relief valve 15;

[0079] The differential pressure valve 8 is used to monitor the pressure difference between the input and output ends of the carbon dioxide booster pump group 7; when the pressure difference exceeds the preset value, the differential pressure valve 8 automatically opens and releases pressure; the third liquid phase pipeline ball valve 21 is set at the pressure release end of the differential pressure valve 8 and is used for manual control of pressure release;

[0080] A gas phase pressure relief branch line 26 is provided on the liquid phase pipeline 4, and is located between the first gas-liquid two-phase flow ball valve 17 and the second gas-liquid two-phase flow ball valve 22 via a tee. The gas phase pipeline pressure relief valve 15 is provided on the gas phase pressure relief branch line 26. When the pressure difference exceeds the preset value, the gas phase pipeline pressure relief valve 15 automatically opens and relieves pressure.

[0081] In this embodiment, specifically, a four-way connector is provided on the liquid phase pipeline 4, and between the gas-liquid separator 6 and the carbon dioxide booster pump group 7; the liquid phase pipeline 4 is connected to the gas phase pipeline 2 located between the first gas phase pipeline ball valve 3 and the first gas-liquid two-phase flow ball valve 17 through the four-way connector, and the four-way connector is also connected to the first carbon dioxide discharge branch line 24, on which a fourth liquid phase pipeline ball valve 16 for controlling the discharge of carbon dioxide is provided;

[0082] A third gas-liquid two-phase flow ball valve 18 is installed on the pipeline between the four-way connector and the gas phase pipeline 2.

[0083] A second carbon dioxide discharge branch 25 is provided on the gas phase pressure relief branch 26 via a tee, and a second gas phase pipeline ball valve 20 for controlling the discharge of carbon dioxide is provided on the second carbon dioxide discharge branch 25.

[0084] Based on the specific connection relationships of the above system, the operation process and operating principle of the carbon dioxide supply module, gas-liquid separation and pressurization module, carbon dioxide high-pressure pumping module, and pipeline pressure safety module will be further explained.

[0085] 1. Carbon dioxide supply module

[0086] Gaseous or liquid carbon dioxide is discharged from carbon dioxide tanker 1. Gaseous carbon dioxide flows along gas phase pipeline 2 via first gas phase pipeline ball valve 3 and first gas-liquid two-phase flow ball valve 17. Liquid carbon dioxide flows along liquid phase pipeline 4 via first liquid phase pipeline ball valve 5 and second liquid phase pipeline ball valve 23, providing a carbon dioxide source for supercritical carbon dioxide fracturing stimulation of shale reservoirs.

[0087] 2. Gas-liquid separation and booster module

[0088] The liquid carbon dioxide output from the carbon dioxide supply module is separated by the gas-liquid separator 6 and then enters the carbon dioxide booster pump group 7 for pressurization, providing liquid carbon dioxide for the high-pressure carbon dioxide pump into the module; the gaseous carbon dioxide after construction can be discharged along the gas phase pipeline 2 through the first gas-liquid two-phase flow ball valve 17 and the third gas phase pipeline 2 ball valve, and the liquid carbon dioxide after construction can be discharged along the liquid phase pipeline 4 through the fourth liquid phase pipeline ball valve 16.

[0089] 3. Carbon dioxide high-pressure pump module

[0090] The first plug valve 19 is closed to cut off the gaseous carbon dioxide delivery path. The liquid carbon dioxide output from the gas-liquid separation and pressurization module enters the fracturing truck 9. The fracturing truck 9 pumps out the liquid carbon dioxide at the designed displacement. The high-pressure liquid carbon dioxide enters the wellhead 14 through the tee, high-pressure pipeline 11, and second plug valve 10 to carry out fracturing and stimulation of the deep shale reservoir.

[0091] 4. Pipeline pressure safety module

[0092] The critical pressure values ​​of the gas phase pipeline pressure relief valve 15 and the differential pressure valve 8 need to be set in advance according to the pressure resistance safety values ​​of the relevant pipelines and pumps. Once the gaseous carbon dioxide in the gas phase pipeline 2 exceeds the pressure resistance safety value, the gas phase pipeline pressure relief valve 15 will be automatically activated and open to relieve pressure. The carbon dioxide booster pump group 7, which continuously supplies liquid carbon dioxide to the fracturing truck 9, will continuously increase the pressure of the liquid carbon dioxide. Once the pressure difference of the liquid carbon dioxide before and after boosting exceeds the set value of the differential pressure valve 8, the differential pressure valve 8 will automatically open and relieve pressure, and the pressure will be discharged through the third liquid phase pipeline ball valve 21 to ensure the safety of the carbon dioxide booster pump group 7 and its related pipelines.

[0093] In this embodiment, it should also be noted that among the liquid phase pipeline ball valve, gas box pipeline ball valve, and gas-liquid two-phase flow ball valve, since the gas-liquid two-phase flow ball valve passes through both liquid and gaseous carbon dioxide, its corrosion resistance and quality should be higher. It is preferable to select a valve with higher price and better quality as the gas-liquid two-phase flow ball valve.

[0094] Example 2

[0095] Example 2 proposes a method for supercritical carbon dioxide fracturing stimulation of shale reservoirs based on the supercritical carbon dioxide fracturing stimulation system in Example 1, which includes the following steps:

[0096] Step S1: First, confirm that all valves are closed. Open the first gas phase pipeline ball valve 3, the first gas-liquid two-phase flow ball valve 17, the second gas-liquid two-phase flow ball valve 22, the first plug valve 19, and the gas phase pipeline pressure relief valve 15. Gaseous carbon dioxide is discharged from the carbon dioxide tanker 1, flows in the gas phase pipeline 2, and sequentially passes through the first gas phase pipeline ball valve 3, the first gas-liquid two-phase flow ball valve 17, the second gas-liquid two-phase flow ball valve 22, the first plug valve 19, and the high-pressure pipeline 11 before entering the fracturing truck 9. The high-speed flow of gaseous carbon dioxide cleans and dries the hydraulic end and pipelines of the fracturing truck 9.

[0097] Step S2: Close the first gas phase pipeline ball valve 3, and open the first liquid phase pipeline ball valve 5 and the third gas-liquid two-phase flow ball valve 18; liquid carbon dioxide is discharged from the carbon dioxide tanker 1, flows in the liquid phase pipeline 4, and enters the gas phase pipeline 2 through the first liquid phase pipeline ball valve 5, the gas-liquid separator 6, and the third gas-liquid two-phase flow ball valve 18, and then enters the fracturing truck 9 through the first gas-liquid two-phase flow ball valve 17, the second gas-liquid two-phase flow ball valve 22, the first plug valve 19, and the high-pressure pipeline 11; the high-speed flow of liquid carbon dioxide rapidly cools the hydraulic end and pipelines of the fracturing truck 9;

[0098] Step S3: Close the third gas-liquid two-phase flow ball valve 18, the first plug valve 19, and the second gas-liquid two-phase flow ball valve 22; open the differential pressure valve 8, the third liquid phase pipeline ball valve 21, and the second liquid phase pipeline ball valve 23; start the carbon dioxide booster pump group 7 to pressurize the liquid carbon dioxide separated by the gas-liquid separator 6; the pressurized liquid carbon dioxide enters the fracturing truck 9 along the liquid phase pipeline 4 through the second liquid phase pipeline ball valve 23; open the second plug valve 10 and the wellhead 14; start the fracturing truck 9; the fracturing truck 9 pumps the liquid carbon dioxide into the high-pressure pipeline 11 at the designed displacement; then it enters the inlet through the second plug valve 10, thus entering the reservoir; the high-pressure liquid carbon dioxide enters the supercritical state under the temperature and pressure of the reservoir, and the reservoir is fracturing and modified.

[0099] Step S4: After the fracturing process is completed, stop the operation of the fracturing truck 9 and the carbon dioxide booster pump group 7, then close the wellhead 14, open the fourth liquid phase pipeline ball valve 16 to discharge the carbon dioxide in the liquid phase pipeline 4; open the first gas phase ball valve, the first gas-liquid two-phase flow ball valve 17, the second gas-liquid two-phase flow ball valve 22, and the first plug valve 19; gaseous carbon dioxide is discharged from the carbon dioxide tanker 1 into the gas phase pipeline 2, and finally into the fracturing truck 9, and the hydraulic end of the fracturing truck 9 and its pipelines are cleaned of the solid dry ice formed after the operation due to the sudden drop in temperature;

[0100] Step S5: Open the second gas phase pipeline ball valve 20 and the fourth liquid phase pipeline ball valve 16 to discharge the remaining carbon dioxide in the pipeline.

[0101] Example 3

[0102] Example 3 is a further description of Example 1. The same components will not be described again here; please refer to [link / reference needed]. Figure 1-2 In Example 1, as Figure 1 As shown, only one fracturing truck 9 and one carbon dioxide tanker 1 are provided. However, in actual use, multiple fracturing trucks 9 and multiple carbon dioxide tankers 1 are used, but their structures are basically the same. Figure 2 The diagram shows a schematic of a supercritical carbon dioxide fracturing system for shale reservoirs when there are two fracturing trucks (9) and two carbon dioxide tankers (1).

[0103] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed and specific, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the technical solution of this application, and these modifications and improvements all fall within the scope of protection of this application.

Claims

1. A supercritical carbon dioxide fracturing stimulation system for shale reservoirs, characterized in that, include: A carbon dioxide supply module, which provides a carbon dioxide source for supercritical carbon dioxide fracturing. The gas-liquid separation and pressurization module separates the carbon dioxide input from the carbon dioxide supply module into gas and liquid, and pumps the liquid carbon oxide into the high-pressure carbon dioxide pumping module. The high-pressure carbon dioxide pump module allows liquid carbon dioxide to enter the reservoir after its pressure is increased. Under the influence of temperature and pressure in the reservoir, it enters a supercritical state, causing the reservoir rock to fracture and generate a complex fracture network, thus forming oil and gas seepage channels. It also includes: a pipeline pressure safety module, which is used to ensure that the pipeline pressure during the fracturing process is lower than the pipeline design pressure value; The carbon dioxide supply module includes: A carbon dioxide tanker truck, wherein gaseous carbon dioxide and liquid carbon dioxide are stored in the tanker truck respectively; The gas-liquid separation and pressurization module includes: a gas-liquid separator and a carbon dioxide booster pump set; The high-pressure carbon dioxide pump module includes: a fracturing truck; The gaseous carbon dioxide is output through a gas phase pipeline, and a first gas phase pipeline ball valve for controlling the output of gaseous carbon dioxide is installed on the gas phase pipeline. On the gas phase pipeline, and located at the rear end of the first gas phase pipeline ball valve, a first gas-liquid two-phase flow ball valve, a second gas-liquid two-phase flow ball valve, and a first plug valve are sequentially arranged. The fracturing truck is connected to the wellhead via a high-pressure pipeline, and liquid carbon dioxide enters the reservoir from the wellhead through the high-pressure pipeline; The first plug valve is connected to the high-pressure pipeline via a tee. A second plug valve and a check valve are installed on the high-pressure pipeline at the rear end of the tee. The liquid carbon dioxide is output through a liquid phase pipeline, and a first liquid phase pipeline ball valve for controlling the output of liquid carbon dioxide is installed on the liquid phase pipeline. The gas-liquid separator is installed on the liquid phase pipeline and is located at the rear end of the ball valve of the first liquid phase pipeline; The carbon dioxide booster pump unit is installed on the liquid phase pipeline and located at the rear end of the gas-liquid separator. A second liquid phase pipeline ball valve is installed on the liquid phase pipeline between the carbon dioxide booster pump and the fracturing truck. The pipeline pressure safety module includes: a differential pressure valve, a third liquid phase pipeline ball valve, and a gas phase pipeline pressure relief valve; The differential pressure valve is used to monitor the pressure difference between the input and output ends of the carbon dioxide booster pump set; when the pressure difference exceeds the preset value, the differential pressure valve automatically opens and releases pressure; the third liquid phase pipeline ball valve is located at the pressure release end of the differential pressure valve and is used for manual control of pressure release; On the liquid phase pipeline, a gas phase pressure relief branch is provided between the first gas-liquid two-phase flow ball valve and the second gas-liquid two-phase flow ball valve via a tee. The gas phase pipeline pressure relief valve is installed on the gas phase pressure relief branch. When the pressure difference exceeds the preset value, the gas phase pipeline pressure relief valve automatically opens and releases pressure.

2. The shale reservoir supercritical carbon dioxide fracturing stimulation system according to claim 1, characterized in that, If the pipeline pressure exceeds the design pressure, the pipeline pressure safety module will automatically initiate a pressure relief process until the pipeline pressure is lower than the design pressure value.

3. The shale reservoir supercritical carbon dioxide fracturing stimulation system according to claim 2, characterized in that, The gaseous carbon dioxide is used for pipeline cleaning and drying before and after fracturing, and the liquid carbon dioxide is used for supercritical carbon dioxide fracturing modification.

4. The shale reservoir supercritical carbon dioxide fracturing stimulation system according to claim 3, characterized in that, The gas-liquid separator is used to separate the gaseous carbon dioxide mixed in with the liquid carbon dioxide output from the carbon dioxide tanker, so that the liquid carbon dioxide reaches a pure state. The carbon dioxide booster pump unit pressurizes the purified liquid carbon dioxide and delivers it to the carbon dioxide high-pressure pump module.

5. A shale reservoir supercritical carbon dioxide fracturing stimulation system according to claim 4, characterized in that, The carbon dioxide booster pump unit delivers purified liquid carbon dioxide to the fracturing truck, which then pumps it out to the reservoir at the designed displacement to carry out fracturing and modification.

6. A shale reservoir supercritical carbon dioxide fracturing stimulation system according to claim 5, characterized in that, A four-way connector is provided on the liquid phase pipeline, and between the gas-liquid separator and the carbon dioxide booster pump group; the liquid phase pipeline is connected to the gas phase pipeline between the first gas phase pipeline ball valve and the first gas-liquid two-phase flow ball valve through the four-way connector; the four-way connector is also connected to the first carbon dioxide discharge branch line, and a fourth liquid phase pipeline ball valve for controlling the discharge of carbon dioxide is provided on the first carbon dioxide discharge branch line. A third gas-liquid two-phase flow ball valve is installed on the pipeline between the four-way connector and the gas phase pipeline. A second carbon dioxide discharge branch is provided on the gas phase pressure relief branch via a tee, and a second gas phase pipeline ball valve for controlling the discharge of carbon dioxide is provided on the second carbon dioxide discharge branch.

7. A method for supercritical carbon dioxide fracturing stimulation of shale reservoirs, characterized in that, A shale reservoir supercritical carbon dioxide fracturing stimulation system according to any one of claims 1-6 includes the following steps: Step S1: First, confirm that all valves are closed. Open the first gas phase pipeline ball valve, the first gas-liquid two-phase flow ball valve, the second gas-liquid two-phase flow ball valve, the first plug valve, and the gas phase pipeline pressure relief valve. Gaseous carbon dioxide is discharged from the carbon dioxide tanker, flows in the gas phase pipeline, and sequentially passes through the first gas phase pipeline ball valve, the first gas-liquid two-phase flow ball valve, the second gas-liquid two-phase flow ball valve, the first plug valve, and the high-pressure pipeline before entering the fracturing truck. The high-speed flow of gaseous carbon dioxide cleans and dries the hydraulic end of the fracturing truck and its pipelines. Step S2: Close the first gas phase pipeline ball valve, and open the first liquid phase pipeline ball valve and the third gas-liquid two-phase flow ball valve; Liquid carbon dioxide is discharged from a carbon dioxide tanker, flows in the liquid phase pipeline, and enters the gas phase pipeline through the first liquid phase pipeline ball valve, gas-liquid separator, and third gas-liquid two-phase flow ball valve. It then enters the fracturing truck through the first gas-liquid two-phase flow ball valve, second gas-liquid two-phase flow ball valve, first plug valve, and high-pressure pipeline. The high-speed flow of liquid carbon dioxide rapidly cools the hydraulic end of the fracturing truck and its pipelines. Step S3: Close the third gas-liquid two-phase flow ball valve, the first plug valve, and the second gas-liquid two-phase flow ball valve; open the differential pressure valve, the third liquid phase pipeline ball valve, and the second liquid phase pipeline ball valve; start the carbon dioxide booster pump group to pressurize the liquid carbon dioxide separated by the gas-liquid separator; the pressurized liquid carbon dioxide enters the fracturing truck through the second liquid phase pipeline ball valve along the liquid phase pipeline; open the second plug valve and the wellhead; start the fracturing truck; the fracturing truck pumps the liquid carbon dioxide into the high-pressure pipeline at the designed displacement; then it enters the inlet through the second plug valve, thus entering the reservoir; the high-pressure liquid carbon dioxide enters the supercritical state under the temperature and pressure of the reservoir, and the reservoir is fracturing and transformed. Step S4: After the fracturing process is completed, stop the operation of the fracturing truck and the carbon dioxide booster pump set, then close the wellhead and open the ball valve of the fourth liquid phase pipeline to discharge the carbon dioxide in the liquid phase pipeline; Open the first gas phase ball valve, the first gas-liquid two-phase flow ball valve, the second gas-liquid two-phase flow ball valve, and the first plug valve; gaseous carbon dioxide is discharged from the carbon dioxide tanker into the gas phase pipeline and finally enters the fracturing truck to clean the hydraulic end of the fracturing truck and its pipelines, which form solid dry ice due to the sudden drop in temperature after construction. Step S5: Open the second gas phase pipeline ball valve and the fourth liquid phase pipeline ball valve to discharge the remaining carbon dioxide in the pipeline.

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