A liquid CO2 fracturing low-pressure manifold device and fracturing method

Abstract

The invention discloses a liquid CO 2 Fracturing low pressure manifold device and fracturing method, wherein CO 2 The tank truck, liquid manifold, booster pump, closed sand mixer truck, and fracturing pump truck are connected in sequence through pipelines and liquid valves to form a liquid pipeline, which is divided into two routes. One pipeline provides sand-carrying fluid for sand addition, and the other provides pure liquid phase. They are independent of each other and can effectively cooperate to deal with emergencies such as pipeline leakage. 2 The tank truck, liquid nitrogen pump truck, liquid nitrogen tank truck, gas phase manifold, and fracturing pump truck pipe are connected in sequence through pipelines and gas phase valves to form a gas phase pipeline. N is provided at any time according to the situation. 2 , ensuring stable fluid supply and avoiding the possibility of dry ice; when a fracturing pump truck has an empty pump, the corresponding valve can be switched to control the CO 2 Liquid and N 2 supply, realize online pumping, and finally restore its construction capacity; it can also be quickly replaced with N after the construction is completed. 2 Replace CO in all pipelines and equipment on clean ground 2 , and then release the pressure, safely and quickly.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field fracturing construction, and in particular to a liquid CO2 fracturing low-pressure manifold device and a fracturing method. Background Art

[0002] Liquid CO2 fracturing is a waterless fracturing technology that uses CO2 instead of conventional hydraulic fracturing fluid. It has many advantages that ordinary fracturing does not have, and therefore has attracted much attention.

[0003] The common connection method of the low-pressure manifold device for liquid CO2 fracturing is: several CO2 tank trucks are connected in parallel, and then connected to the CO2 booster pump truck and the closed sand mixing truck in turn to supply liquid to the fracturing pump truck. Because the liquid CO2 fracturing working fluid has the characteristics of low temperature and high pressure, the low-pressure manifold device connected in this way has the following problems: (1) As the CO2 in the CO2 tank truck is consumed, the volume of the space inside the CO2 tank truck increases, the pressure decreases, and part of the CO2 evaporates into gas to maintain the pressure balance in the CO2 tank truck. However, when the pressure of the part of the CO2 evaporated in the CO2 tank truck is less than the pressure drop caused by the lowering of the liquid level in the CO2 tank truck, the pressure in the CO2 tank truck and the liquid supply pipeline decreases. When the pressure drops to a certain level, , there is a risk of dry ice forming inside the CO2 tanker and the liquid supply pipeline, which may explode at any time; (2) In the later stage of construction, when the liquid level in the CO2 tanker drops, the construction liquid supply in the tank will be unstable, affecting the construction quality; (3) If a fracturing pump truck has an empty pump in the high-pressure area during construction, the fracturing pump truck cannot be used until the end of construction, affecting the construction quality or even making it impossible to continue construction; (4) After the construction is completed, in order to prevent dry ice from forming, the pressure needs to be released slowly, and it usually takes 4-7 days before the pipeline can be removed.

[0004] To sum up, how to solve the problem of unstable liquid supply and easy dry ice formation when the liquid level is lowered in the low-pressure liquid supply process, and how to ensure that when a fracturing pump truck has an empty pump, it can restore its construction capacity under continuous construction, and how to quickly release the pressure on the pipeline after the construction is completed, have become urgent problems to be solved by technical personnel in this field. Summary of the invention

[0005] In view of this, the present invention provides a liquid CO2 fracturing low-pressure manifold device and a fracturing method, which can not only solve the risk of easy dry ice formation and the problem of unstable liquid supply in the later stage of construction, but also ensure that when a fracturing pump truck in the high-pressure area has an empty pump, it can realize online pumping to restore its construction capacity under continuous construction. At the same time, it can also realize the rapid depressurization of the pipeline under the premise of safety after the construction is completed.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A liquid CO2 fracturing low-pressure manifold device, comprising a CO2 tanker, a first liquid phase manifold, a booster pump and a fracturing fluid supply system connected in sequence;

[0008] It also includes a liquid nitrogen tank truck, a liquid nitrogen pump truck and a first gas phase manifold connected in sequence, and a plurality of the CO2 tank trucks are all connected to the first gas phase manifold.

[0009] Preferably, the fracturing fluid supply system comprises a fracturing pump truck; the inlet of each of the fracturing pump trucks is connected to the outlet of the first gas phase manifold; one outlet of the fracturing pump truck is connected to a pressure relief valve, and the other outlet is connected to a high pressure valve.

[0010] Preferably, the fracturing fluid supply system includes: a sand-added fluid supply system and a pure liquid phase fluid supply system;

[0011] The sand adding and liquid supply system comprises a closed sand mixing vehicle, a second liquid phase manifold and a sand adding fracturing pump vehicle which are connected in sequence, and the outlet of the booster pump is connected to the inlet of the closed sand mixing vehicle;

[0012] The pure liquid phase supply system comprises a third liquid phase manifold and a pure liquid phase fracturing pump truck which are connected in sequence, and another outlet of the booster pump is connected to an inlet of the third liquid phase manifold.

[0013] Preferably, a plurality of closed sand mixing trucks in the fracturing fluid supply system are connected in parallel.

[0014] Preferably, a plurality of booster pumps are connected in parallel.

[0015] A liquid CO2 fracturing method adopts the above-mentioned liquid CO2 fracturing low-pressure manifold device; during the fracturing construction, the CO2 tank truck is supplemented with N2 through a liquid nitrogen pump truck to keep the internal pressure within a preset range.

[0016] Preferably, when a fracturing pump truck runs dry, under continuous construction conditions, the dry fracturing pump truck is shut down, and other fracturing pump trucks are used to maintain the construction; at the same time, the liquid phase valve on the inlet pipeline of the dry fracturing pump truck and the high pressure valve at the outlet are shut down, the gas phase valve on the inlet pipeline of the dry fracturing pump truck and the pressure relief valve at the outlet are opened, and N2 is replenished for the dry fracturing pump truck through a liquid nitrogen pump truck;

[0017] After replacing the medium in the empty pump fracturing pump truck with N2, close the corresponding gas phase valve, open the corresponding liquid phase valve, fill the empty pump fracturing pump truck with CO2 liquid or CO2 sand-carrying liquid medium, close the corresponding pressure relief valve, open the empty pump fracturing pump truck, and open the high-pressure valve of the empty pump fracturing pump truck.

[0018] Preferably, when leakage occurs in the sand-added liquid supply system or the pure liquid phase liquid supply system, the system with the leakage is closed and construction is continued by another system.

[0019] Preferably, in the later stage of fracturing construction, the wellhead valve is closed, the gas phase valve connected to the liquid nitrogen pump truck is opened, and then the liquid phase valve on the CO2 tank truck is closed, the bypass valve on the CO2 tank truck that communicates gas and liquid and the gas phase valve connected thereto are opened, and the pressure relief valve on the fracturing pump truck is opened, and N2 is used to gradually displace the liquid phase CO2 in the pipeline starting from the CO2 tank truck outlet pipeline. During the displacement process, the pressure in the pipeline is ensured to be greater than 75.9PSI; after all pipelines are filled with N2, the gas phase valve on the liquid nitrogen pump truck is closed to stop providing N2, the pressure is released to zero, and the construction is completed.

[0020] Preferably, during the low-pressure pipeline balancing and sweeping before fracturing construction: close all liquid phase valves, open all gas phase valves between the CO2 tanker and the liquid nitrogen pump truck, balance the pressure of all CO2 tankers with N2 provided by the liquid nitrogen pump truck, open the gas-liquid bypass valve on the CO2 tanker, open the gas phase valves on the pipeline from the CO2 tanker to the fracturing pump truck, sweep the line from the outlet of the CO2 tanker to the wellhead, clean the pipeline without residual solid particles, fill it with N2 and cool it, adjust the outlet pressure of the liquid nitrogen pump truck, and keep the pressure of all pipelines above the preset value.

[0021] It can be seen from the above technical scheme that the liquid CO2 fracturing low-pressure manifold device and fracturing method provided by the present invention can replenish N2 to each CO2 tank truck at any time according to needs through the gas phase pipeline liquid nitrogen pump truck, so as to keep the internal pressure of each CO2 tank truck constant, thereby ensuring that when the liquid level of the CO2 tank truck decreases in the later stage of construction, the liquid supply can still be guaranteed to be stable, and at the same time, the pressure of the CO2 liquid in the CO2 tank truck or pipeline will not be lower than 75.9PSI, thereby avoiding the appearance of dry ice; at the same time, if there is an emergency such as an empty pump of a single fracturing pump truck, N2 can be quickly replenished to the empty pump fracturing pump truck while ensuring the continuation of construction, and the CO2 liquid inside the fracturing pump truck can be replaced for release and spraying treatment, and the construction can be resumed after the pump is restarted; it is also possible to quickly replace the CO2 in all pipelines and equipment on the clean ground with N2 after the construction is completed, and then depressurize, which is safe and rapid. The liquid pipeline is divided into two lines, one line provides sand-carrying fluid for fracturing pump trucks, and the other line provides pure liquid for fracturing pump trucks. They are independent of each other and can effectively cooperate to deal with emergencies such as pipeline leakage. The gas pipeline can provide a certain pressure of N2 during the sweeping and spraying stages through the control of the gas valve. At the same time, it can also provide a certain pressure of N2 to the pipeline and construction equipment at any time according to needs to prevent the occurrence of dry ice and ensure construction safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 A schematic structural diagram of a liquid CO2 fracturing low-pressure manifold device provided in an embodiment of the present invention.

[0024] Among them, 1 is a CO2 tanker; 2 is the first liquid phase manifold; 3 is a booster pump; 4 is a closed sand mixing truck; 5 is a liquid phase valve; 6 is the first gas phase manifold; 7 is a gas phase valve; 8 is a liquid nitrogen pump truck; 9 is a liquid nitrogen tanker; 10 is a fracturing pump truck; 11 is the second liquid phase manifold; 12 is the third liquid phase manifold; 13 is the second gas phase manifold; 14 is a sand adding liquid supply system; 15 is a pure liquid phase liquid supply system; 16 is a pressure relief valve; 17 is a high pressure valve. DETAILED DESCRIPTION

[0025] The present invention discloses a liquid CO2 fracturing low-pressure manifold device and a fracturing method, which can not only solve the problems of unstable liquid supply and easy dry ice formation when the liquid level is reduced in the low-pressure liquid supply process, but also can realize online pumping to restore the construction capacity of a fracturing pump truck in the high-pressure area when an empty pump occurs under continuous construction, and can also safely and quickly release the pressure of the pipeline after the construction is completed.

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] The core improvement of the liquid CO2 fracturing low-pressure manifold device provided in the embodiment of the present invention is that it includes a CO2 tanker 1, a first liquid phase manifold 2, a booster pump 3 and a fracturing fluid supply system connected in sequence, which is used to achieve normal fracturing operations. Figure 1 As shown;

[0028] It also includes a liquid nitrogen tanker 9, a liquid nitrogen pump truck 8 and a first gas phase manifold 6 connected in sequence, and multiple CO2 tankers 1 are all connected to the first gas phase manifold 6. It can be understood that the connection mentioned here is through a pipeline and a corresponding liquid phase valve 5 or gas phase valve 7.

[0029] It can be seen from the above technical scheme that the liquid CO2 fracturing low-pressure manifold device provided in the embodiment of the present invention, during the fracturing construction process, opens all the gas phase valves 7 on the gas phase pipeline connected to the CO2 tanker 1, and the liquid nitrogen pump truck 8 can replenish N2 to each CO2 tanker 1 at any time as needed, so as to keep the pressure in the CO2 tanker 1 stable within a preset range (determined according to actual conditions, which can be specifically 290-350PSI here), ensuring that the CO2 tanker 1 supplies liquid steadily throughout the construction process (including when the liquid level drops in the later stage), and avoiding the occurrence of dry ice in the CO2 tanker 1 and the pipeline.

[0030] As a preferred embodiment, the fracturing fluid supply system includes a plurality of fracturing pump trucks 10; the inlet of each fracturing pump truck 10 is connected to the outlet of the first gas phase manifold 6; the outlet of the fracturing pump truck 10 includes two routes, one of which is connected to a pressure relief valve 16, and the other is connected to a high pressure valve 17. Figure 1 As shown, each fracturing pump truck 10 has a high-pressure discharge pipeline connected to a tee, one of which is connected to a high-pressure manifold and the other is connected to a blowout pipeline, and the pipelines are all connected to high-pressure valves.

[0031] With such arrangement, during the construction process, if the fracturing pump truck is empty, under continuous construction conditions, the fracturing pump truck 10 is shut down, and other fracturing pump trucks 10 are used to maintain and continue construction. At the same time, the liquid phase valve 5 on the inlet pipeline of the empty pump fracturing pump truck 10 and the high-pressure valve 17 at the outlet are shut down, and the corresponding gas phase valve 7 and the pressure relief valve 16 are opened. After the medium in the empty pump fracturing pump truck 10 is completely replaced with N2 by the liquid nitrogen pump truck 8, the corresponding gas phase valve 7 is closed, and the corresponding liquid phase valve 5 is opened to fill the fracturing pump truck 10 with CO2 liquid or CO2 sand-carrying liquid medium, and the corresponding pressure relief valve 16 is closed, and the fracturing pump truck 10 is turned on, and the high-pressure valve 17 of the fracturing pump truck 10 is opened to resume construction of the fracturing pump truck 10, thereby ensuring the continuity of the entire construction and improving the utilization efficiency of the fracturing pump truck 10.

[0032] In order to further optimize the above technical solution, the fracturing fluid supply system includes: a sand-added fluid supply system 14 and a pure liquid phase fluid supply system 15. The structure can refer to Figure 1 As shown;

[0033] The sand adding and liquid supply system 14 includes a closed sand mixing vehicle 4, a second liquid phase manifold 11 and a fracturing pump vehicle 10 for adding sand, which are connected in sequence, and the outlet of the booster pump 3 is connected to the inlet of the closed sand mixing vehicle 4;

[0034] The pure liquid phase supply system 15 includes a third liquid phase manifold 12 and a fracturing pump truck 10 for pure liquid phase, which are connected in sequence. Another outlet of the booster pump 3 is connected to the inlet of the third liquid phase manifold 12. In this way, during the construction process, when a puncture occurs somewhere in the sand supply system 14 or the pure liquid phase supply system 15, the system with the puncture is shut down and rectified and restored. During this period, the construction is continued by another system, ensuring the normal progress of the construction.

[0035] In the specific embodiment provided by this solution, in order to ensure the concentration and scale of sand addition, multiple closed sand mixing vehicles 4 can be connected in parallel. Similarly, in order to ensure the construction displacement, multiple booster pumps 3 can be connected in parallel.

[0036] The device is further described below in conjunction with specific embodiments:

[0037] A liquid CO2 fracturing low-pressure manifold device comprises a CO2 tanker 1, wherein the outlet at the bottom of each CO2 tanker 1 is connected to the inlet of a first liquid phase manifold 2 through a pipeline and a liquid phase valve 5, the outlet of the first liquid phase manifold 2 is connected to the inlet of a booster pump 3 through a pipeline and a liquid phase valve 5, one outlet of the booster pump 3 is connected to the inlet of a closed sand mixing truck 4 through a pipeline and a liquid phase valve 5, the outlet of the closed sand mixing truck 4 is connected to the inlet of a second liquid phase manifold 11 through a pipeline and a liquid phase valve 5, the second liquid phase manifold 11 is provided with a plurality of outlets, which are respectively connected to a fracturing pump truck 10, wherein the connection system from the closed sand mixing truck 4 to the fracturing pump truck 10 constitutes a sand adding liquid supply system 14; the other outlet of the booster pump 3 is connected to the inlet of a third liquid phase manifold 12, the third liquid phase manifold 12 is provided with a plurality of outlets, which are respectively connected to a fracturing pump truck, wherein the connection system from the third liquid phase manifold 12 to the fracturing pump truck constitutes a pure liquid phase liquid supply system 15. The outlet of the liquid nitrogen tank truck 9 is connected to the inlet of the liquid nitrogen pump truck 8, and the outlet of the liquid nitrogen pump truck 8 is connected to the inlet of the first gas phase manifold 6 through a connecting pipeline and a gas phase valve 7. The first gas phase manifold 6 is provided with multiple outlets, some of which are connected to the top inlet of each CO2 tank truck 1 through a connecting pipeline and a gas phase valve 7, and some of the outlets are connected to the inlet of the second gas phase manifold 13 through a connecting pipeline and a gas phase valve 7. The outlet of the second gas phase manifold 13 is connected to the inlet pipeline of each fracturing pump truck 10 through a connecting pipeline and a gas phase valve 7, and one outlet of the gas phase manifold 6 is connected to the top inlet of the closed sand mixing truck 4 through a connecting pipeline and a gas phase valve 7.

[0038] The embodiment of the present invention also provides a liquid CO2 fracturing method. The core improvement point is that the above-mentioned low-pressure manifold device is used; during the fracturing construction, the CO2 tanker 1 is supplemented with N2 by the liquid nitrogen pump truck 8 so that the internal pressure is within a preset range. The structure can refer to Figure 1 shown.

[0039] It can be seen from the above technical scheme that the liquid CO2 fracturing method provided in the embodiment of the present invention can replenish N2 to each CO2 tanker 1 at any time as needed through the gas phase pipeline liquid nitrogen pump truck 8, so as to keep the internal pressure of each CO2 tanker 1 constant, thereby ensuring that when the liquid level of the CO2 tanker 1 decreases in the later stage of construction, the liquid supply can still be guaranteed to be stable, and at the same time, the pressure of the CO2 liquid in the CO2 tanker 1 or the pipeline will not be lower than 75.9PSI, thereby avoiding the appearance of dry ice.

[0040] It is understandable that the liquid CO2 fracturing method of this scheme also includes pre-construction preparation and post-processing, such as pre-fracturing preparation, low-pressure pipeline connection, pressure test, balance and line sweeping and pumping. The method is further introduced in conjunction with specific embodiments below:

[0041] During on-site construction, the operation process is as follows:

[0042] (1) Preparation before fracturing: Keep all high and low pressure pipelines, elbows, various valves, oil tanks and joints clean and intact; clean and remove water from the valve box of the fracturing pump truck 10, check and replace the seals, and debug the lubrication system before fracturing; the number of CO2 tank trucks 1 meets the construction design liquid volume requirements and their internal pressure is guaranteed to be between 290 and 350 PSI before construction.

[0043] (2) Low-pressure pipeline connection: the connection is performed according to the low-pressure pipeline connection process described in the present invention.

[0044] (3) Low-pressure pipeline pressure test: Open all gas phase valves 7 on the pipeline connected to the CO2 tanker 1, and conduct air tightness pressure test after connecting with the first gas phase manifold 6 for balance.

[0045] (4) Balancing and sweeping low-pressure pipelines: Close all liquid valves 5, open all gas valves 7 between the CO2 tanker 1 and the liquid nitrogen pump truck 8, balance the pressure of all CO2 tankers 1 with N2 provided by the liquid nitrogen pump truck 8, open the bypass valve on the CO2 tanker 1 that connects the gas and liquid phases, and open the gas valves 7 on the pipelines from the CO2 tanker 1 to the fracturing pump truck 10 in sequence, sweep the pipelines from the outlet of the CO2 tanker 1 to the wellhead, clean the pipelines without any residual solid particles, fill them with N2 and cool them down, adjust the outlet pressure of the liquid nitrogen pump 8, and keep all pipelines at a pressure above 75.9 PSI to avoid the formation of dry ice in the pipelines during construction.

[0046] (5) Pumping: Close the gas bypass valve and all gas phase valves 7 on the CO2 tanker 1, open all liquid phase valves 5, start the fracturing pump truck 10 (first gear lock) to pump, so that the entire liquid phase pipeline is filled with liquid CO2. Whether it is full or not is determined by controlling the circulation valve and spare circulation valve of the fracturing pump truck to determine the filling condition of the hydraulic end. In addition, the quality of the pump truck's pumping is determined by the frosting condition of the hydraulic end. Each cylinder of the hydraulic end needs to be frosted.

[0047] Furthermore, the fracturing pump trucks 10 may operate the pumps one by one, or multiple fracturing pump trucks 10 may operate the pumps at the same time.

[0048] (6) Fracturing construction: Fracturing construction is carried out according to the construction procedures. During the construction process, the gas phase valve 7 on the gas phase pipeline between the CO2 tanker 1 and the liquid nitrogen pump 8 is in an open state. The CO2 tanker 1 can be replenished with N2 at any time through the liquid nitrogen pump 8 to keep the pressure in the CO2 tanker 1 stable at 290-350PSI, ensuring that the CO2 tanker 1 supplies liquid steadily during the entire construction process and avoiding the occurrence of dry ice in the CO2 tanker 1 and the pipeline.

[0049] (7) If any abnormal situation occurs during the construction process, the operation process is as follows:

[0050] S1: When the fracturing pump truck runs out of pump, under continuous construction conditions, shut down the fracturing pump truck 10, and other fracturing pump trucks 10 continue to maintain construction. At the same time, shut down the liquid phase valve 5 on the inlet pipeline of the fracturing pump truck 10, shut down the high-pressure valve 17 at the outlet of the fracturing pump truck 10, open the corresponding gas phase valve 7 and the corresponding pressure relief valve 16, and replace the medium in the fracturing pump truck 10 with N2; close the corresponding gas phase valve 7, open the corresponding liquid phase valve 5, fill the fracturing pump truck 10 with CO2 liquid or CO2 sand-carrying liquid medium, close the corresponding pressure relief valve 16, start the fracturing pump truck 10, open the high-pressure valve 17 of the fracturing pump truck 10, and resume construction of the fracturing pump truck, thereby ensuring the continuity of the entire construction and improving the utilization efficiency of the fracturing pump truck 10.

[0051] S2: If leakage occurs somewhere in the sand-added liquid supply system 14 or the pure liquid phase liquid supply system 15, the system with the leakage is shut down and repaired, and another system continues the construction during this period, thus ensuring the normal progress of the construction.

[0052] (8) Late stage of construction: close the wellhead valve, open the gas phase valve 7 connected to the liquid nitrogen pump 8, then close the liquid phase valve 5 on the CO2 tanker 1, open the bypass valve on the CO2 tanker 1 that connects the gas and liquid phases and the gas phase valve 7 connected thereto, open the pressure relief valve 16 on the fracturing pump truck 10, and gradually displace the liquid phase CO2 in the pipeline with N2 starting from the outlet pipeline of the CO2 tanker 1. During the displacement process, ensure that the pressure in the pipeline is greater than 75.9PSI; after all pipelines are filled with N2, close the gas phase valve 7 on the liquid nitrogen pump 8 to stop providing N2, release the pressure to zero, and the construction is completed. It is safe and fast to prevent the occurrence of dry ice.

[0053] In summary, the embodiment of the present invention provides a liquid CO2 fracturing low-pressure manifold device, including a CO2 tanker, a liquid phase manifold, a booster pump, a closed sand mixing truck, a liquid phase valve, a gas phase manifold, a gas phase valve, a liquid nitrogen pump truck, a liquid nitrogen tanker, a fracturing pump truck, a pressure relief valve and a high-pressure valve. Among them, the CO2 tanker, the liquid phase manifold, the booster pump, the closed sand mixing truck, and the fracturing pump truck are sequentially connected through pipelines and liquid phase valves to form a liquid phase pipeline, and the liquid phase pipeline is divided into two pipelines. One pipeline provides sand-carrying liquid for the fracturing pump truck, and the other pipeline provides pure liquid for the fracturing pump truck. They are independent of each other and can effectively cooperate to deal with emergencies such as pipeline leakage. The embodiment of the present invention also provides a liquid CO2 fracturing method using the above-mentioned manifold device, wherein the CO2 tanker, liquid nitrogen pump truck, liquid nitrogen tanker, gas manifold, and fracturing pump truck pipes are sequentially connected through pipelines and gas phase valves to form a gas phase pipeline, and the gas phase pipeline can provide N2 to the liquid phase pipeline, CO2 tanker, and fracturing pump truck at any time according to the situation, thereby ensuring the internal pressure of the on-site device and pipeline during the entire construction process and the stability of the liquid supply in the later stage of construction, and avoiding the possibility of dry ice formation; at the same time, when a certain fracturing pump truck has an empty pump, the supply of CO2 liquid and N2 can be controlled by switching the corresponding gas phase valve, liquid phase valve, pressure relief valve, and high-pressure valve, so as to realize online pumping and finally restore its construction capacity, effectively solving the problem of continuing construction when a certain fracturing pump truck has an empty pump; it is also possible to quickly replace the CO2 in all pipelines and equipment on the clean ground with N2 after the construction is completed, and then perform pressure relief treatment, which is safe and rapid.

[0054] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0055] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A liquid CO2 fracturing low-pressure manifold device, characterized in that: It comprises a CO2 tanker (1), a first liquid phase manifold (2), a booster pump (3) and a fracturing fluid supply system which are connected in sequence; It also includes a liquid nitrogen tank truck (9), a liquid nitrogen pump truck (8) and a first gas phase manifold (6) which are connected in sequence, and the plurality of CO2 tank trucks (1) are all connected to the first gas phase manifold (6); The outlet at the bottom of each CO2 tanker (1) is connected to the inlet of the first liquid manifold (2) through a pipeline and a liquid phase valve (5), and the outlet of the first liquid manifold (2) is connected to the inlet of the booster pump (3) through a pipeline and a liquid phase valve (5); The fracturing fluid supply system comprises: a sand-added fluid supply system (14) and a pure liquid phase fluid supply system (15); The sand adding and liquid supplying system (14) comprises a closed sand mixing vehicle (4), a second liquid phase manifold (11) and a sand adding fracturing pump vehicle (10) which are connected in sequence, the outlet of the booster pump (3) is connected to the inlet of the closed sand mixing vehicle (4) through a pipeline and a liquid phase valve (5), and the outlet of the closed sand mixing vehicle (4) is connected to the inlet of the second liquid phase manifold 11 through a pipeline and a liquid phase valve (5); The pure liquid phase supply system (15) comprises a third liquid phase manifold (12) and a pure liquid phase fracturing pump truck (10) which are connected in sequence, and the outlet of the booster pump (3) is connected to the inlet of the third liquid phase manifold (12) through another path; The fracturing fluid supply system comprises a plurality of fracturing pump trucks (10); the inlet of each of the fracturing pump trucks (10) is connected to the outlet of the first gas phase manifold (6); one outlet of the fracturing pump truck (10) is connected to a pressure relief valve (16) and the other outlet is connected to a high-pressure valve (17); a tee is connected to the high-pressure discharge pipeline of each of the fracturing pump trucks (10), one is connected to the high-pressure manifold, and the other is connected to the blowdown pipeline, and both pipelines are connected to high-pressure valves.

2. The liquid CO2 fracturing low-pressure manifold device according to claim 1, characterized in that: A plurality of closed sand mixing vehicles (4) in the fracturing fluid supply system are connected in parallel.

3. The liquid CO2 fracturing low-pressure manifold device according to claim 1, characterized in that: A plurality of booster pumps (3) are connected in parallel.

4. A liquid CO2 fracturing method, characterized in that: A liquid CO2 fracturing low-pressure manifold device as described in any one of claims 1 to 3 is used; during the fracturing operation, the CO2 tank truck (1) is supplemented with N2 by a liquid nitrogen pump truck (8) so that the internal pressure thereof is within a preset range; When a fracturing pump truck (10) runs dry, under continuous construction conditions, the dry fracturing pump truck (10) is shut down, and other fracturing pump trucks (10) are used to maintain and continue construction; at the same time, the liquid phase valve (5) on the inlet pipeline of the dry fracturing pump truck (10) and the high pressure valve (17) at the outlet are shut down, the gas phase valve (7) on the inlet pipeline of the dry fracturing pump truck (10) and the pressure relief valve (16) at the outlet are opened, and N2 is replenished for the dry fracturing pump truck (10) through the liquid nitrogen pump truck (8); After the medium in the empty pump fracturing pump truck (10) is completely replaced with N2, the corresponding gas phase valve (7) is closed, and the corresponding liquid phase valve (5) is opened to fill the empty pump fracturing pump truck (10) with CO2 liquid or CO2 sand-carrying liquid medium, and the corresponding pressure relief valve (16) is closed, and the empty pump fracturing pump truck (10) is opened, and the high-pressure valve (17) of the empty pump fracturing pump truck (10) is opened; When leakage occurs in the sand-added liquid supply system (14) or the pure liquid phase liquid supply system (15), the system with the leakage is closed and construction is continued by another system.

5. The liquid CO2 fracturing method according to claim 4, characterized in that: At the later stage of the fracturing construction, the wellhead valve is closed, the gas phase valve (7) connected to the liquid nitrogen pump truck (8) is opened, and then the liquid phase valve (5) on the CO2 tank truck (1) is closed, the gas-liquid bypass valve on the CO2 tank truck (1) and the gas phase valve (7) connected thereto are opened, and the pressure relief valve (16) on the fracturing pump truck (10) is opened, and N2 is gradually used to displace the liquid phase CO2 in the pipeline from the outlet pipeline of the CO2 tank truck (1), and the pressure in the pipeline is ensured to be greater than 75.9PSI during the displacement process; after all pipelines are filled with N2, the gas phase valve (7) on the liquid nitrogen pump truck (8) is closed to stop supplying N2, and the pressure is released to zero, and the construction is completed.

6. The liquid CO2 fracturing method according to claim 4, characterized in that: During the low-pressure pipeline balancing and sweeping before the fracturing operation: all liquid phase valves (5) are closed, all gas phase valves (7) between the CO2 tanker (1) and the liquid nitrogen pump truck (8) are opened, the pressure of all CO2 tankers (1) is balanced by providing N2 through the liquid nitrogen pump truck (8), the bypass valve for gas-liquid communication on the CO2 tanker (1) is opened, and the gas phase valves (7) on the pipeline are opened in sequence from the CO2 tanker (1) to the fracturing pump truck (10), and the pipeline is swept from the outlet of the CO2 tanker (1) to the wellhead, the pipeline is cleaned without any residual solid particles, and the pipeline is filled with N2 and cooled, and the outlet pressure of the liquid nitrogen pump truck (8) is adjusted to keep the pressure of all pipelines above the preset value.

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