Liquid carbon dioxide high-pressure flow distribution metering system and metering method

Abstract

The invention discloses a liquid carbon dioxide high-pressure flow distribution metering system and metering method, and belongs to the technical field of oil and gas field ground engineering operation. An outlet of the carbon dioxide injection pipeline is connected with an inlet of a carbon dioxide plunger pump; a flowmeter, a temperature transmitter and a pressure transmitter are sequentially arranged on the carbon dioxide injection pipeline; an outlet of the carbon dioxide plunger pump is connected with inlets of a plurality of injection branches arranged in parallel through high-pressure injection pipelines, and outlets of the injection branches are connected with corresponding injection well mouths respectively. A high-pressure pressure measuring point is arranged on the high-pressure injection pipeline; a branch injection pipeline stop valve, a multi-stage pressure reduction system, a pressure measuring point, a high-pressure flowmeter and a check valve are sequentially arranged on each injection branch which is arranged in parallel; the flow meter, the temperature transmitter, the pressure transmitter, the carbon dioxide plunger pump, the multi-stage pressure reduction system, the high-pressure pressure measuring point, the pressure measuring point and the high-pressure flow meter are all connected with an automatic control system.

Description

Technical Field

[0001] The invention belongs to the technical field of surface engineering operations in oil and gas fields, and in particular relates to a liquid carbon dioxide high-pressure flow distribution metering system and a metering method. Background Art

[0002] With the exploitation of low-permeability and ultra-low-permeability oil layers during oil production, how to increase formation pressure, reduce crude oil viscosity, and improve oil recovery efficiency has become a top priority in promoting the progress of oil production. In recent years, carbon dioxide injection technology has been widely used in oil field production. This technology can effectively reduce the emission of carbon dioxide into the atmosphere for underground storage, becoming a powerful tool for achieving carbon neutrality. It can also be used as a displacement fluid to increase formation pressure, reduce crude oil viscosity, improve oil recovery efficiency, and expand the affected area.

[0003] At present, when injecting carbon dioxide into underground oil layers, it is often necessary to inject carbon dioxide into multiple wells at the same time, and due to factors such as the pressure and process of each well, different rates and different injection amounts need to be used for injection. The metering and distribution device of liquid low-temperature carbon dioxide required in this operation process is lacking in the prior art. In addition, the metering error when injecting liquid carbon dioxide at different rates and different injection amounts into multiple wells at the same time using existing technical means is large. Summary of the invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a liquid carbon dioxide high-pressure flow distribution metering system and a metering method, which effectively solves the problem of simultaneously injecting liquid carbon dioxide into multiple wells at different rates and different injection volumes, and solves the phenomenon of large metering errors when injecting using existing means, reduces the frequency of pipeline and valve maintenance, and improves the injection operation efficiency.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a liquid carbon dioxide high-pressure flow distribution and metering system, comprising a carbon dioxide injection pipeline, wherein the outlet of the carbon dioxide injection pipeline is connected to the inlet of a carbon dioxide plunger pump; a flow meter, a temperature transmitter, and a pressure transmitter are sequentially arranged on the carbon dioxide injection pipeline;

[0007] The outlet of the carbon dioxide plunger pump is connected to the inlets of several injection branches arranged in parallel through a high-pressure injection pipeline, and the outlets of the injection branches are respectively connected to corresponding injection wellheads;

[0008] The high-pressure injection pipeline is provided with a high-pressure pressure measuring point; a plurality of injection branches arranged in parallel are provided with branch injection pipeline cut-off valves, multi-stage pressure reducing systems, pressure measuring points, high-pressure flow meters and check valves in sequence;

[0009] The flow meter, temperature transmitter, pressure transmitter, carbon dioxide plunger pump, multi-stage pressure reduction system, high-pressure pressure measuring point, pressure measuring point and high-pressure flow meter are all connected to an automatic control system.

[0010] In the specific implementation process, a high-pressure venting pipeline is opened on the injection branch, and a high-pressure venting valve is arranged on the high-pressure venting pipeline.

[0011] In a specific implementation process, the carbon dioxide injection pipeline is connected to a venting pipeline, and a venting valve is provided on the venting pipeline.

[0012] In the specific implementation process, a shielded pump and a stopcock are sequentially arranged on the carbon dioxide injection pipeline.

[0013] In a specific implementation process, the carbon dioxide injection pipeline is connected to a carbon dioxide return pipeline.

[0014] In the specific implementation process, a reflux stopcock is arranged on the carbon dioxide reflux pipeline.

[0015] In the specific implementation process, the carbon dioxide reflux pipeline is connected to a reflux vent pipeline; and a reflux vent valve is arranged on the reflux vent pipeline.

[0016] In a specific implementation process, the outlet of the carbon dioxide reflux pipeline is connected to the inlet of a reflux hose, and the outlet of the reflux hose is connected to the inlet of a liquid carbon dioxide storage tank.

[0017] In the specific implementation process, a high-pressure main vent valve and a safety valve are sequentially arranged on the high-pressure injection pipeline.

[0018] The present invention also provides a metering method for a liquid carbon dioxide high pressure flow distribution metering system according to any one of the above, comprising the following steps:

[0019] S1: After pre-cooling through the venting system, the canned pump is used for initial pressurization until liquid carbon dioxide is discharged; then multi-well injection is carried out, and the liquid carbon dioxide enters the carbon dioxide plunger pump through the carbon dioxide injection pipeline and is pressurized to obtain pressurized liquid carbon dioxide;

[0020] S2: The pressurized liquid carbon dioxide is diverted to several injection branches through the high-pressure injection pipeline, and then passes through the branch injection pipeline cut-off valve, multi-stage pressure reduction system, pressure measuring point, high-pressure flow meter and check valve in turn, and enters the injection wellhead;

[0021] S3: When adjusting the flow rate of each injection wellhead, open the branch injection pipeline cut-off valve on the branch to be injected, and the automatic control system obtains the temperature and pressure of the liquid carbon dioxide and the density of the liquid carbon dioxide through the temperature transmitter and the pressure transmitter, and then obtains the pressure difference based on the pressure data at the high-pressure pressure measuring point and the pressure data at the pressure measuring point on the branch to be injected;

[0022] S4: Based on the pressure difference, liquid carbon dioxide density, liquid carbon dioxide temperature and pressure, the opening of the multi-stage pressure reduction system is obtained and then adjusted to control the injection flow rate at the injection wellhead; at the same time, the frequency of the carbon dioxide plunger pump is adjusted so that the flow rate of the flow meter is the sum of the flow rates of the high-pressure flow meters on the injection branch.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention provides a liquid carbon dioxide high-pressure flow distribution and metering system, which can control the injection amount of liquid carbon dioxide on demand through an automatic control system; through an intelligent and automated control system, the input of human resources is reduced to achieve the purpose of improving quality and efficiency; multi-well information cross-management is achieved through remote transmission technology to avoid errors caused by manual transcription. The automatic control system can automatically adjust the adjustment opening of the multi-stage pressure reduction system on each branch pipe by comparing the collected branch pipe flow, pressure and preset amount of the target wellhead with the pressure measuring points set on the carbon dioxide injection pipeline, i.e., the main pipeline and the injection branch after the liquid carbon dioxide pressure and flow are stable, so as to achieve one pump for multiple injections, and the number of connected wellheads can reach more than two. The process pipeline of the present invention is simple, intelligent and highly automated. When distributing and regulating pressure and flow, the phase state is accurately controlled to avoid the formation of dry ice. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the liquid carbon dioxide high pressure flow distribution and metering system of the present invention;

[0026] Figure 2 It is a schematic diagram of the multi-flow regulation control principle of the present invention;

[0027] Among them: 1-shielded pump; 2-carbon dioxide injection pipeline; 3-venting pipeline; 4-venting valve; 5-stopcock valve; 6-carbon dioxide reflux pipeline; 7-flow meter; 8-temperature transmitter; 9-pressure transmitter; 10-carbon dioxide plunger pump; 11-multi-stage pressure reduction system; 11-1-first branch multi-stage pressure reduction system; 11-2-second branch multi-stage pressure reduction system; 12-check valve; 12-1-first branch check valve; 12-2-second branch check valve; 13-automatic control system; 14-high-pressure pressure measuring point; 15-high-pressure main venting valve; 16-safety valve; 17-pressure measuring point; 17-1-first branch check valve; 12-2-second branch check valve; 13-automatic control system; 14-high-pressure pressure measuring point; 15-high-pressure main venting valve; 16-safety valve; 17-pressure measuring point; 17-1-first branch check valve; 17-2-second branch check valve ... One branch pressure measuring point; 17-2-second branch pressure measuring point; 18-high pressure flowmeter; 18-1-first branch high pressure flowmeter; 18-2-second branch high pressure flowmeter; 19-high pressure vent valve; 19-1-first branch high pressure vent valve; 19-2-second branch high pressure vent valve; 20-injection wellhead; 20-1-first injection wellhead; 20-2-second injection wellhead; 21-return hose; 22-return vent valve; 23-return plug valve; 24-branch injection pipeline cut-off valve; 24-1-first branch injection pipeline cut-off valve; 24-2-second branch injection pipeline cut-off valve. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings 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 should fall within the scope of protection of the present invention.

[0029] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0030] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0031] See also Figure 1The present invention provides a liquid carbon dioxide high-pressure flow distribution metering system and metering method, which overcomes the shortcomings of the existing process technology and enables one injection pump to simultaneously inject liquid carbon dioxide into multiple wells with different pressures and different flow rates, effectively solving the problems of different pressures, different injection rates and different injection volumes, improving injection efficiency and reducing operating costs.

[0032] The above-mentioned liquid carbon dioxide high-pressure flow distribution and metering system includes a liquid carbon dioxide inlet valve, a shielded pump 1, a carbon dioxide injection pipeline 2, a vent pipeline 3, a vent valve 4, a plug valve 5, a carbon dioxide reflux pipeline 6, a flow meter 7, a temperature transmitter 8, a pressure transmitter 9, a carbon dioxide plunger pump 10, a multi-stage pressure reduction system 11, a check valve 12, an automatic control system 13, a high-pressure pressure measuring point 14, a high-pressure main vent valve 15, a safety valve 16, a pressure measuring point 17, a high-pressure flowmeter 18, a high-pressure vent valve 19, a reflux hose 21, a reflux vent valve 22, a reflux plug valve 23 and a branch injection pipeline cut-off valve 24.

[0033] Among them, the inlet of the carbon dioxide injection pipeline 2 is connected to the outlet of the liquid carbon dioxide storage tank, and the outlet of the carbon dioxide injection pipeline 2 is connected to the inlet of the carbon dioxide plunger pump 10; the shielded pump 1 and the vent pipeline 3, the stopcock valve 5, the flow meter 7, the temperature transmitter 8, and the pressure transmitter 9 are sequentially arranged on the carbon dioxide injection pipeline 2; among them, the vent valve 4 is arranged on the vent pipeline 3.

[0034] A branch, i.e., a carbon dioxide reflux pipeline 6, is provided on the carbon dioxide injection pipeline 2 between the stopcock 5 and the flowmeter 7. A reflux stopcock 23 is provided on the carbon dioxide reflux pipeline 6. The carbon dioxide reflux pipeline 6 is connected to a reflux venting pipeline. A reflux venting valve 22 is provided on the reflux venting pipeline. The outlet of the carbon dioxide reflux pipeline 6 is connected to the inlet of a reflux hose 21. The outlet of the reflux hose 21 is connected to the inlet of a liquid carbon dioxide storage tank.

[0035] Among them, the outlet of the carbon dioxide plunger pump 10 is connected to the inlet of several parallel injection branches through a high-pressure injection pipeline, and the outlet of the injection branch is respectively connected to the corresponding injection wellhead 20; the high-pressure pressure measuring point 14, the high-pressure total vent valve 15 and the safety valve 16 are sequentially arranged on the high-pressure injection pipeline; the branch injection pipeline cut-off valve 24, the multi-stage pressure reduction system 11, the pressure measuring point 17, the high-pressure flowmeter 18 and the check valve 12 are sequentially arranged on several parallel injection branches. High-pressure vent pipelines are opened on the injection branches, and the high-pressure vent valve 19 is arranged on the high-pressure vent pipeline.

[0036] Among them, the automatic control system 13 is connected to the flow meter 7, the temperature transmitter 8, the pressure transmitter 9, the carbon dioxide plunger pump 10, the multi-stage pressure reduction system 11, the high-pressure pressure measuring point 14, the pressure measuring point 17, and the high-pressure flow meter 18.

[0037] The venting system includes a venting pipeline 3 and a venting valve 4 arranged thereon, an exhaust valve of a carbon dioxide plunger pump 10, a high-pressure main venting valve 15, a safety valve 16, a high-pressure venting valve 19, a reflux venting valve 22 and other pipelines and valves.

[0038] The working principle of the above-mentioned liquid carbon dioxide high-pressure flow distribution and metering system is as follows: After the liquid carbon dioxide is transported to the site by a tank truck, it is transported to the liquid carbon dioxide storage tank placed on the site, and after being pressurized by the shielded pump 1, it enters the carbon dioxide injection pipeline 2, and a part of it returns to the liquid carbon dioxide storage tank through the carbon dioxide reflux pipeline 6, the reflux cock 23, and the reflux hose 21. The carbon dioxide in the carbon dioxide injection pipeline 2 enters the carbon dioxide plunger pump 10 through the cock valve 5, the flow meter 7, the pressure transmitter 9, and the temperature transmitter 8. After being pressurized by the carbon dioxide plunger pump 10, it reaches a high-pressure injection state; after the injection branch flow distribution, it passes through the branch injection pipeline cut-off valve 24, the multi-stage pressure reduction system 11, the pressure measuring point 17, the high-pressure flow meter 18, and the check valve 12 in sequence, and enters the injection wellhead 20. When multiple parallel pipelines, i.e., injection branches, repeat the process after flow distribution.

[0039] The automatic control system 13 automatically controls the injection pressure and injection volume of the liquid carbon dioxide according to the design pressure and design injection volume of the injection well, thereby realizing multiple injections with one pump.

[0040] Based on the above working principle and the metering method of the liquid carbon dioxide high pressure flow distribution metering system, the following steps are included:

[0041] S1: After emptying and precooling through the venting system, initial pressurization is performed until liquid carbon dioxide is discharged; then multi-well injection is performed, and the liquid carbon dioxide enters the carbon dioxide plunger pump 10 through the carbon dioxide injection pipeline 2 and is pressurized to obtain pressurized liquid carbon dioxide;

[0042] S2: The pressurized liquid carbon dioxide is diverted to several injection branches through the high-pressure injection pipeline, and then passes through the branch injection pipeline cut-off valve 24, the multi-stage pressure reduction system 11, the pressure measuring point 17, the high-pressure flow meter 18 and the check valve 12, and enters the injection wellhead 20;

[0043] S3: When adjusting the flow rate of each injection wellhead 20, the branch injection pipeline cut-off valve 24 on the branch to be injected is opened, and the automatic control system 13 obtains the temperature and pressure of the liquid carbon dioxide and the density of the liquid carbon dioxide through the temperature transmitter 8 and the pressure transmitter 9, and then obtains the pressure difference based on the pressure data at the high-pressure pressure measuring point 14 and the pressure data at the pressure measuring point 17 on the branch to be injected;

[0044] S4: Based on the pressure difference, liquid carbon dioxide density, liquid carbon dioxide temperature and pressure, the opening of the multi-stage decompression system 11 is obtained and then adjusted to control the injection flow rate of the injection wellhead 20; at the same time, the frequency of the carbon dioxide plunger pump 10 is adjusted so that the flow rate of the flowmeter 7 is the sum of the flow rates of the high-pressure flowmeter 18 on the branch line to be injected.

[0045] The specific steps of emptying the system for precooling and then initially pressurizing until liquid carbon dioxide is discharged are as follows:

[0046] S11: At the beginning of operation, open the reflux stopcock 23 on the reflux pipeline 6 of the carbon dioxide reflux pipeline connecting the liquid carbon dioxide storage tank and the shielded pump 1, and the stopcock 5 on the carbon dioxide injection pipeline 2 provided with the shielded pump 1, and the gaseous carbon dioxide enters the carbon dioxide reflux pipeline 6, the carbon dioxide injection pipeline 2, and the pump head cylinder of the carbon dioxide plunger pump 10 in turn, and the exhaust valve on the pump head of the carbon dioxide plunger pump 10, the vent valve 4 on the carbon dioxide injection pipeline 2, and the reflux vent valve on the carbon dioxide reflux pipeline 6 are opened in turn. 22, pre-cool the pipeline exhaust; when the temperature of the temperature transmitter 8 shows -30℃~-5℃, close the reflux vent valve 22 of the carbon dioxide reflux pipeline 6, the vent valve 4 on the carbon dioxide injection pipeline 2, and the exhaust valve on the pump head of the carbon dioxide plunger pump 10 in sequence; at the same time, open the safety valve 16 on the high-pressure injection pipeline, the branch injection pipeline cut-off valve 24 on the injection branch, and the high-pressure vent valve 19 on the side of the wellhead 20 to be injected, and pre-cool the pipeline. After the pre-cooling is completed, close the safety valve 16 and the high-pressure vent valve 19 on the side of the wellhead 20 to be injected.

[0047] S12: After the exhaust precooling is completed, the shielded pump 1 is started, and the liquid carbon dioxide is pressurized to 2.1-2.9 MPa through the shielded pump 1. The carbon dioxide injection pipeline 2 is filled with liquid carbon dioxide. The exhaust valve on the pump head of the carbon dioxide plunger pump 10, the vent valve 4 on the carbon dioxide injection pipeline 2, and the reflux vent valve 22 on the carbon dioxide reflux pipeline 6 are opened in sequence until liquid carbon dioxide is discharged from the exhaust pipeline. The reflux vent valve 22 on the carbon dioxide reflux pipeline 6, the vent valve 4 on the carbon dioxide injection pipeline 2, and the exhaust valve on the pump head of the carbon dioxide plunger pump 10 are closed in sequence. The liquid carbon dioxide plunger pump 10 is started, the safety valve 16, the branch injection pipeline shut-off valve 24, and the high-pressure vent valve 19 on the side of the wellhead 20 to be injected are opened until liquid carbon dioxide is discharged from the exhaust pipeline. The safety valve 16 and the high-pressure vent valve 19 on the side of the wellhead 20 to be injected are closed.

[0048] The above specific liquid carbon dioxide high pressure flow distribution and metering method comprises the following steps:

[0049] After the liquid carbon dioxide is pressurized by the carbon dioxide plunger pump 10, the pressure increases to 10MPa~50MPa, and passes through the multi-stage pressure reduction system 11, the pressure measuring point 17, the high-pressure flow meter 18, and the check valve 12 in sequence, and enters the injection wellhead 20.

[0050] Specifically, when multiple wells (≥2 parallel injection pipelines) are injected through several injection branches, the pressure is increased to 10MPa~50MPa after being pressurized by the carbon dioxide plunger pump 10. The liquid carbon dioxide is diverted to each injection branch through the high-pressure injection pipeline, and passes through the branch injection pipeline shut-off valve 24, the multi-stage pressure reduction system 11, the pressure measuring point 17, the high-pressure flowmeter 18, and the check valve 12 in sequence to enter the injection wellhead 20.

[0051] like Figure 2 As shown, during the injection process of multiple wells (≥2 parallel injection pipelines), the flow rate of each injection well is adjusted as follows:

[0052] Open the cut-off valve 24 of the branch injection pipeline to be injected, the automatic control system 13 collects the temperature T of liquid carbon dioxide through the temperature transmitter 8, the pressure P through the pressure transmitter 9, inquires the density ρ of liquid carbon dioxide, collects the pressure data of the high-pressure pressure measuring point 14 and the pressure data of the pressure measuring point 17 of the branch to be injected; through the pressure difference between the two, the opening of the multi-stage pressure reduction system 11 is adjusted through the automatic control system 13 to determine the injection flow rate of the injection wellhead 20. At the same time, adjust the frequency of the carbon dioxide plunger pump 10 so that the flow rate of the flowmeter 7 is the sum of the flow rates of the high-pressure flowmeter 18 on the branch to be injected.

[0053] When the flow rate of a certain injection branch changes, the pressure difference of the injection branch is adjusted, and the frequency of the carbon dioxide plunger pump 10 is adjusted in conjunction with the flow rate of the flow meter 7 so that the flow rate of the branch needs to be injected; when a certain injection branch stops injecting, the branch injection pipeline shut-off valve 24 on the injection branch is closed, and the frequency of the carbon dioxide plunger pump 10 is adjusted in conjunction with the flow rate of the flow meter 7 so that the flow rate of the branch needs to be injected; thereby achieving the purpose of accurate measurement of multiple flows with one pump.

[0054] The opening degree of the multi-stage pressure reducing system 11 is determined by the following formula:

[0055]

[0056] Among them, i is each branch; Q is the injection flow rate; ρ is the density of liquid carbon dioxide; p0 is the pressure data of the high-pressure pressure measuring point 14; pi is the pressure data of the pressure measuring point 17 on the injection branch.

[0057] Example

[0058] The present embodiment provides a liquid carbon dioxide high-pressure flow distribution and metering system, including a liquid carbon dioxide inlet valve, a shielded pump 1, a carbon dioxide injection pipeline 2, a venting pipeline 3, a venting valve 4, a plug valve 5, a carbon dioxide reflux pipeline 6, a flow meter 7, a temperature transmitter 8, a pressure transmitter 9, a carbon dioxide plunger pump 10, an automatic control system 13, a high-pressure pressure measuring point 14, a high-pressure main venting valve 15, a safety valve 16, a reflux hose 21, a reflux venting valve 22, and a reflux plug valve 23;

[0059] The system also includes three injection branches arranged in parallel, namely, a first branch, a second branch and a third branch; the first branch is sequentially provided with a first branch injection pipeline cut-off valve 24-1, a first branch multi-stage pressure reducing system 11-1, a first branch pressure measuring point 17-1, a first branch high-pressure flowmeter 18-1, a first branch check valve 12-1, a first high-pressure venting pipeline, and a first branch high-pressure venting valve 19-1 is arranged on the first high-pressure venting pipeline, and the outlet of the first branch is correspondingly connected to the first injection wellhead 20-1;

[0060] The second branch is provided with a second branch injection pipeline cut-off valve 24-2, a second branch multi-stage pressure reducing system 11-2, a second branch pressure measuring point 17-2, a second branch high-pressure flowmeter 18-2, a second branch check valve 12-2, a second high-pressure venting pipeline, and a second branch high-pressure venting valve 19-2 on the second high-pressure venting pipeline in sequence, and the outlet of the second branch is correspondingly connected to the second injection wellhead 20-2;

[0061] The third branch is provided with a branch injection pipeline cut-off valve 24, a multi-stage pressure reducing system 11, a pressure measuring point 17, a high-pressure flow meter 18, a check valve 12, a third high-pressure venting pipeline, and a high-pressure venting valve 19 in sequence, and the outlet of the third branch is correspondingly connected to the injection wellhead 20.

[0062] The above-mentioned automatic control system 13 is connected to the flow meter 7, the temperature transmitter 8, the pressure transmitter 9, the carbon dioxide plunger pump 10, the high-pressure pressure measuring point 14, the multi-stage pressure reduction system 11, the pressure measuring point 17, the high-pressure flowmeter 18, the first branch multi-stage pressure reduction system 11-1, the first branch pressure measuring point 17-1, the first branch high-pressure flowmeter 18-1, the second branch multi-stage pressure reduction system 11-2, the second branch pressure measuring point 17-2 and the second branch high-pressure flowmeter 18-2.

[0063] In multi-well injection (≥2 parallel injection pipelines), this embodiment is a three-way injection, after the liquid carbon dioxide pump 10 pressurizes, the pressure increases to 10MPa~50MPa, and the liquid carbon dioxide is divided into the first branch, the second branch and the third branch through the high-pressure injection pipeline, and passes through the branch injection pipeline cut-off valve 24, the multi-stage pressure reduction system 11, the pressure measuring point 17, the high-pressure flowmeter 18, and the check valve 12 on the third branch in sequence, and enters the injection wellhead 20, and passes through the first branch branch on the first branch in sequence. The injection pipeline shut-off valve 24-1, the first branch multi-stage pressure reducing system 11-1, the first branch pressure measuring point 17-1, the first branch high-pressure flowmeter 18-1, and the first branch check valve 12-1 enter the first injection wellhead 20-1, and at the same time, pass through the second branch injection pipeline shut-off valve 24-2 on the second branch, the second branch multi-stage pressure reducing system 11-2, the second branch pressure measuring point 17-2, the second branch high-pressure flowmeter 18-2, and the second branch check valve 12-2 in sequence to enter the second injection wellhead 20-2.

[0064] like Figure 2 As shown, during the injection process of multiple wells (≥2 parallel injection pipelines), the flow rate at each injection wellhead is adjusted as follows: In this embodiment, the first injection branch and the third injection branch are used as the branches to be injected;

[0065] Open the branch injection pipeline shut-off valve 24 and the first branch injection pipeline shut-off valve 24-1 to be injected. The automatic control system 13 collects the temperature T and pressure P of liquid carbon dioxide through the temperature transmitter 8 and the pressure transmitter 9, respectively, inquires the density ρ of liquid carbon dioxide, collects the pressure data of the high-pressure pressure measuring point 14 and the pressure measuring point 17 of the branch to be injected and the pressure measuring point 17-1 of the first branch; through the pressure difference between the two, the opening of the multi-stage decompression system 11 and the first branch multi-stage decompression system 11-1 is adjusted through the automatic control system 13 to determine the injection flow rate of the injection wellhead 20 and the first injection wellhead 20-1. At the same time, adjust the frequency of the carbon dioxide plunger pump 10 so that the flow rate of the flowmeter 7 is the sum of the high-pressure flowmeter 18 of the branch to be injected and the high-pressure flowmeter 18-1 of the first branch.

[0066] When the flow rate of the first branch changes, the pressure difference of the first branch is adjusted, and the frequency of the carbon dioxide plunger pump 10 is adjusted in conjunction with the flow rate of the flow meter 7 so that the flow rate of the flow meter 7 is the sum of the flow rates of the branches to be injected; when the injection of the first branch stops, the injection pipeline shut-off valve 24-1 of the first branch is closed, and the frequency of the carbon dioxide plunger pump 10 is adjusted in conjunction with the flow rate of the flow meter 7 so that the flow rate of the flow meter 7 is the sum of the flow rates of the branches to be injected, thereby achieving the purpose of accurate measurement of multiple flow rates with one pump.

[0067] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A liquid carbon dioxide high pressure flow distribution and metering system, characterized in that: The device comprises a carbon dioxide injection pipeline (2), wherein the outlet of the carbon dioxide injection pipeline (2) is connected to the inlet of a carbon dioxide plunger pump (10); a flow meter (7), a temperature transmitter (8), and a pressure transmitter (9) are sequentially arranged on the carbon dioxide injection pipeline (2); The outlet of the carbon dioxide plunger pump (10) is connected to the inlets of a plurality of injection branches arranged in parallel via a high-pressure injection pipeline, and the outlets of the injection branches are respectively connected to corresponding injection wellheads (20); The high-pressure injection pipeline is provided with a high-pressure pressure measuring point (14); a plurality of injection branches arranged in parallel are each provided with a branch injection pipeline cut-off valve (24), a multi-stage pressure reducing system (11), a pressure measuring point (17), a high-pressure flow meter (18) and a check valve (12) in sequence; The flow meter (7), temperature transmitter (8), pressure transmitter (9), carbon dioxide plunger pump (10), multi-stage pressure reduction system (11), high-pressure pressure measuring point (14), pressure measuring point (17) and high-pressure flow meter (18) are connected to an automatic control system (13).

2. The liquid carbon dioxide high pressure flow distribution and metering system according to claim 1, characterized in that: The injection branches are each provided with a high-pressure venting pipeline, and the high-pressure venting pipeline is provided with a high-pressure venting valve (19).

3. The liquid carbon dioxide high pressure flow distribution and metering system according to claim 1, characterized in that: The carbon dioxide injection pipeline (2) is connected to a venting pipeline (3), and a venting valve (4) is provided on the venting pipeline (3).

4. The liquid carbon dioxide high pressure flow distribution and metering system according to claim 1, characterized in that: The carbon dioxide injection pipeline (2) is provided with a shielded pump (1) and a stopcock (5) in sequence.

5. The liquid carbon dioxide high pressure flow distribution and metering system according to claim 1, characterized in that: The carbon dioxide injection pipeline (2) is connected to a carbon dioxide return pipeline (6).

6. The liquid carbon dioxide high pressure flow distribution and metering system according to claim 5, characterized in that: The carbon dioxide reflux pipeline (6) is provided with a reflux stopcock (23).

7. The liquid carbon dioxide high pressure flow distribution and metering system according to claim 5, characterized in that: The carbon dioxide reflux pipeline (6) is connected to a reflux vent pipeline; the reflux vent pipeline is provided with a reflux vent valve (22).

8. The liquid carbon dioxide high pressure flow distribution and metering system according to claim 5, characterized in that: The outlet of the carbon dioxide return pipeline (6) is connected to the inlet of a return hose (21), and the outlet of the return hose (21) is connected to the inlet of a liquid carbon dioxide storage tank.

9. The liquid carbon dioxide high pressure flow distribution and metering system according to claim 1, characterized in that: The high-pressure injection pipeline is provided with a high-pressure main vent valve (15) and a safety valve (16) in sequence.

10. A metering method for a liquid carbon dioxide high pressure flow distribution metering system according to any one of claims 1 to 9, characterized in that: The following steps are involved: S1: After evacuation and precooling, initial pressurization is performed until liquid carbon dioxide is discharged; Then, multiple well injection is performed, and the liquid carbon dioxide enters the carbon dioxide plunger pump (10) through the carbon dioxide injection pipeline (2) and is pressurized to obtain pressurized liquid carbon dioxide; S2: The pressurized liquid carbon dioxide is diverted to a plurality of injection branches through the high-pressure injection pipeline, and then passes through the branch injection pipeline cut-off valve (24), the multi-stage pressure reducing system (11), the pressure measuring point (17), the high-pressure flow meter (18) and the check valve (12) in sequence, and enters the injection wellhead (20); S3: When adjusting the flow rate of each injection wellhead (20), the branch injection pipeline cut-off valve (24) on the branch line to be injected is opened, and the automatic control system (13) obtains the temperature and pressure of the liquid carbon dioxide and the density of the liquid carbon dioxide through the temperature transmitter (8) and the pressure transmitter (9), and then obtains the pressure difference based on the pressure data at the high-pressure pressure measuring point (14) and the pressure data at the pressure measuring point (17) on the branch line to be injected; S4: Based on the pressure difference, the density of the liquid carbon dioxide, the temperature of the liquid carbon dioxide and the pressure, the opening of the multi-stage decompression system (11) is obtained and then adjusted to control the injection flow rate of the injection wellhead (20); at the same time, the frequency of the carbon dioxide plunger pump (10) is adjusted so that the flow rate of the flow meter (7) is the sum of the flow rates of the high-pressure flow meters (18) on the branch line to be injected.

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