Chemical injection system and method for deepwater underwater wellhead

Abstract

The present invention discloses a chemical agent injection system and method for a deepwater underwater wellhead. The chemical agent injection system includes a chemical agent storage tank, a high-pressure pump group, a plurality of low-pressure pump groups, and a plurality of injection pipelines connecting the oil pipes of the plurality of underwater wellheads; the high-pressure pump group and each of the low-pressure pump groups are connected in parallel between the chemical agent storage tank and a corresponding injection pipeline; before chemical agent injection, the gas column in the injection pipeline is displaced by the high-pressure pump group; after the gas column is displaced, the chemical agent in the chemical agent storage tank is injected into the oil pipe through the injection pipeline by the low-pressure pump group. The chemical agent injection system for a deepwater underwater wellhead of the present invention cooperates with a high-pressure pump group and a plurality of low-pressure pump groups. The high-pressure pump group can be used as a high-pressure displacement pump, which can complete the gas column displacement and agent injection of the plurality of underwater wellheads in the gas field, while reducing the cost investment and also reducing the difficulty of on-site operation.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas exploitation engineering, and in particular to a chemical agent injection system and method for a deepwater underwater wellhead. Background Art

[0002] In the process of exploitation of deepwater oil and gas fields, underwater production systems are generally used for exploitation. Since the formation water contains high concentrations of scale-forming ions such as calcium ions, magnesium ions, carbonate ions, and sulfate ions, and deepwater oil and gas fields are generally high-temperature and ultra-high-temperature wells, the changes in pressure, temperature or water composition destroy the original chemical balance and produce scale, thereby blocking the oil pipe and affecting the gas field production. At the same time, in order to ensure the liquidity safety of the entire production system, the influence of sea pipe hydrates must also be considered. It can be seen that in order to protect equipment and pipelines, it is very necessary to inject chemical agents (anti-scaling agents, methanol, ethylene glycol, etc.) into the development wells of deepwater gas fields.

[0003] In order to minimize the cost investment, the static liquid column pressure will be fully utilized to reduce the operating pressure of the pump when configuring the injection pump, especially for the chemical injection system below the mud surface. Since the injection depth is about several thousand meters, theoretical calculations only require the platform to be equipped with an injection pump of several MPa to inject the agent into the wellbore of tens of MPa.

[0004] Since the bottom hole injection valve is usually installed as a set with the oil pipe, it is difficult to repair. Therefore, the injection valve is equipped with multiple one-way valves to prevent gas channeling and increase the life of the injection valve. However, in the actual operation process, the injection valve has different degrees of gas channeling, resulting in the existence of gas columns in the chemical injection pipeline. When the chemical injection system is restarted, the static liquid column cannot be established normally, making it impossible to inject the chemical into the bottom of the well. In order to solve this problem, there are currently two common practices. One is to rent a high-pressure injection pump to displace the gas column in the pipeline before each startup, and restart the chemical injection system after the normal static liquid column pressure is established. The other is to no longer consider the static liquid column at the beginning of the design, and directly design the chemical injection pump as a high-pressure injection pump. The first approach increases the difficulty and risk of on-site operations, and the second approach increases the cost several times. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a chemical agent injection system and a chemical agent injection method for a deepwater underwater wellhead which are easy to operate and reduce cost investment.

[0006] The technical solution adopted by the present invention to solve the technical problem is: to provide a chemical agent injection system for a deepwater underwater wellhead, comprising a chemical agent storage tank, a high-pressure pump group, a plurality of low-pressure pump groups, and a plurality of injection pipelines connected to the oil pipes of the plurality of underwater wellheads; the high-pressure pump group and each of the low-pressure pump groups are connected in parallel between the chemical agent storage tank and a corresponding injection pipeline;

[0007] Before the chemical agent is injected, the gas column in the injection pipeline is displaced by the high-pressure pump group; after the gas column is displaced, the chemical agent in the agent storage tank is injected into the oil pipe through the injection pipeline by the low-pressure pump group.

[0008] Preferably, when the low-pressure pump group is under fault repair, the chemical agent in the agent storage tank is injected into the oil pipe through the injection pipeline by the high-pressure pump group.

[0009] Preferably, the high-pressure pump assembly comprises a high-pressure pump, a first high-pressure pipeline connected between the inlet of the high-pressure pump and the medicine storage tank, a second high-pressure pipeline connected between the outlet of the high-pressure pump and the injection pipeline, and a first isolation valve arranged on the second high-pressure pipeline;

[0010] The low-pressure pump group includes a low-pressure pump, a first low-pressure pipeline connected between an inlet of the low-pressure pump and a medicine storage tank, a second low-pressure pipeline connected between an outlet of the low-pressure pump and an injection pipeline, and a second isolation valve arranged on the second low-pressure pipeline.

[0011] Preferably, the second high-pressure pipeline has a plurality of branch pipelines, each of the branch pipelines is connected in parallel with a corresponding one of the low-pressure pump groups to the corresponding injection pipeline; and each of the branch pipelines is provided with the first isolation valve.

[0012] Preferably, the design pressure of the high-pressure pump = (injection point pressure + pipeline pressure drop) × design error coefficient;

[0013] The design pressure of the low-pressure pump = (injection point pressure - static liquid column pressure + pipeline pressure drop) × design error coefficient;

[0014] Among them, the injection point pressure refers to the agent injection point of the underwater wellhead, and the injection point pressure is the pressure in the wellbore where the agent injection point is located; the pipeline pressure drop is the pressure drop of the injection pipeline; the hydrostatic column pressure is calculated based on the density of the chemical agent and its injection depth; the design error coefficient is 1.1-1.5.

[0015] Preferably, the chemical agent injection system further comprises a pressure monitor, a flow detector, a check valve and an agent injection valve arranged on the injection pipeline; the check valve is located on one end of the agent injection valve away from the oil pipe.

[0016] Preferably, the pressure monitor comprises a first pressure monitor and a second pressure monitor; the first pressure monitor and the flow detector are located between the check valve and the agent injection valve respectively; the second pressure monitor is located on one end of the agent injection valve close to the oil pipe.

[0017] The present invention also provides a method for injecting chemicals into a deepwater underwater wellhead, using any of the chemical injection systems described above; the chemical injection method comprises the following steps:

[0018] S1, isolating the low-pressure pump group and the injection pipeline, and displacing the gas column in the injection pipeline by the high-pressure pump group;

[0019] S2. Isolate the high-pressure pump group and the injection pipeline, and inject the chemical agent in the agent storage tank into the oil pipe through the injection pipeline by the low-pressure pump group.

[0020] Preferably, in step S2, when the low-pressure pump group is under fault repair, the chemical agent in the agent storage tank is injected into the oil pipe through the injection pipeline by the high-pressure pump group.

[0021] Preferably, the design pressure of the high-pressure pump = (injection point pressure + pipeline pressure drop) × design error coefficient;

[0022] The design pressure of the low-pressure pump = (injection point pressure - static liquid column pressure + pipeline pressure drop) × design error coefficient;

[0023] Among them, the injection point pressure refers to the agent injection point of the underwater wellhead, and the injection point pressure is the pressure in the wellbore where the agent injection point is located; the pipeline pressure drop is the pressure drop of the injection pipeline; the hydrostatic column pressure is calculated based on the density of the chemical agent and its injection depth; the design error coefficient is 1.1-1.5.

[0024] The beneficial effects of the present invention are as follows: by cooperating a high-pressure pump group with a plurality of low-pressure pump groups, the high-pressure pump group can be used as a high-pressure displacement pump, which can complete the gas column displacement and agent injection of a plurality of underwater wellheads in the gas field, thereby reducing the cost investment and also reducing the difficulty of on-site operation.

[0025] In addition, the high-pressure pump group can be used to break the injection valve bursting disc at the beginning of commissioning, and can be used for gas column displacement in daily operation. At the same time, the injection flow rate of the high-pressure pump is designed to meet the injection of all wells at the same time, so the high-pressure pump can be used as a backup pump for the other low-pressure pumps. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0027] Figure 1It is a schematic diagram of the connection structure of a chemical injection system for a deepwater underwater wellhead according to an embodiment of the present invention. DETAILED DESCRIPTION

[0028] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0029] like Figure 1 As shown, a chemical agent injection system for a deepwater underwater wellhead according to an embodiment of the present invention comprises a chemical agent storage tank 10, a high-pressure pump group 20, a plurality of low-pressure pump groups 30, and a plurality of injection pipelines 40 of oil pipes 1 connecting a plurality of underwater wellheads.

[0030] Each low-pressure pump group 30 is connected to the oil pipe 1 of the underwater wellhead through an injection pipeline 40, and the high-pressure pump group 20 and each low-pressure pump group 30 are connected in parallel between the reagent storage tank 10 and a corresponding injection pipeline 40. The high-pressure pump group 20 can form multiple parallel connection relationships with multiple low-pressure pump groups 30, and each parallel connection relationship corresponds to an injection pipeline 40 and an underwater wellhead, so that the high-pressure pump group 20 can be used as a common high-pressure pump pipeline for multiple underwater wellheads to inject reagents, reducing the investment in equipment and costs.

[0031] When using the chemical injection system, the gas column in the corresponding injection pipeline 40 is displaced by the high-pressure pump group 20 before chemical injection. After the gas column is displaced, the chemical in the agent storage tank 10 is injected into the oil pipe 1 through the injection pipeline 40 by the low-pressure pump group 30. When the low-pressure pump group 30 is fault-checked, the chemical in the agent storage tank 10 is injected into the oil pipe 1 through the injection pipeline 40 by the high-pressure pump group 20. It can be seen that the high-pressure pump group 20 is not only used for gas column displacement before agent injection, but also can be used as a backup pump for the low-pressure pump group 30, which greatly reduces the number of low-pressure pumps and further reduces the cost investment.

[0032] Specifically, in the chemical agent injection system of the present invention, the high-pressure pump group 20 includes a high-pressure pump 21, a first high-pressure pipeline 22 connected between the inlet of the high-pressure pump 21 and the agent storage tank 10, a second high-pressure pipeline 23 connected between the outlet of the high-pressure pump 21 and the injection pipeline 40, and a first isolation valve 24 provided on the second high-pressure pipeline 23. The first isolation valve 24 is used to control the connection and disconnection between the high-pressure pump 21 and the injection pipeline 40.

[0033] Corresponding to the plurality of low-pressure pump groups 30, the second high-pressure pipeline 23 may have a plurality of branch pipelines 231, each branch pipeline 231 is connected in parallel with a corresponding low-pressure pump group 30 to the corresponding injection pipeline 40. In addition, each branch pipeline 231 is provided with a first isolation valve 24 to control the on-off between the high-pressure pump 21 and the corresponding injection pipeline 40.

[0034] Each low-pressure pump group 30 may include a low-pressure pump 31, a first low-pressure pipeline 32 connected between the inlet of the low-pressure pump 31 and the reagent storage tank 10, a second low-pressure pipeline 33 connected between the outlet of the low-pressure pump 31 and the injection pipeline 40, and a second isolation valve 34 disposed on the second low-pressure pipeline 33. The second low-pressure pipelines 33 of the plurality of low-pressure pump groups 30 are respectively connected in parallel with a branch pipeline 231 of the high-pressure pump group 20 to an injection pipeline 40, and each injection pipeline 40 is connected to an oil pipe 1 of an underwater wellhead.

[0035] The pressure design of the high-pressure pump group 20 and the low-pressure pump group 30 is as follows:

[0036] The design pressure of the high-pressure pump 21 = (injection point pressure + pipeline pressure drop) × design error coefficient;

[0037] The design pressure of the low-pressure pump 31 = (injection point pressure - hydrostatic column pressure + pipeline pressure drop) × design error coefficient.

[0038] Among them, in the injection point pressure, the injection point is the agent injection point of the underwater wellhead, and the injection point pressure is the pressure in the wellbore where the agent injection point is located, which can be obtained according to the wellbore pressure profile of the underwater wellhead where the agent is to be injected. The pipeline pressure drop is the pressure drop of the injection pipeline 40. The static liquid column pressure is calculated based on the density of the chemical agent and its injection depth. The design error coefficient is used to reduce the difference between theory and practice. The calculated value obtained before the multiplication coefficient is purely theoretical. In order to reduce the error between theory and practice, an error coefficient is multiplied to reduce the error between design and practical application; in the present invention, the design error coefficient can be 1.1-1.5. In addition, according to the conditions of each underwater wellhead, the design pressure of the high-pressure pump 21 and the design pressure of the low-pressure pump 31 can be respectively added with a margin of 50 bar on the basis of the above-mentioned calculated values ​​to eliminate errors, etc.

[0039] Furthermore, the chemical injection system of the present invention further comprises a pressure monitor, a flow detector 43, a check valve 44 and a chemical injection valve 45 arranged on the injection pipeline 40. The check valve 44 is located at one end of the chemical injection valve 45 away from the oil pipe 1.

[0040] The pressure monitor is used to monitor the real-time pressure; the flow detector 43 is used to monitor the injection flow; the check valve 44 is used to prevent the bottom hole pressure from flowing back; the reagent injection valve 45 is used as a reagent isolation valve to control the on-off of the injection pipeline 40.

[0041] In this embodiment, the pressure monitor includes a first pressure monitor 41 and a second pressure monitor 42. The first pressure monitor 41 and the flow detector 43 are located between the check valve 44 and the reagent injection valve 45 in sequence; the second pressure monitor 42 is located on one end of the reagent injection valve 45 close to the oil pipe 1.

[0042] The chemical agent injection system of the present invention further comprises a bottom hole injection valve 50 , and the injection pipeline 40 is connected to the oil pipe 1 via the bottom hole injection valve 50 .

[0043] refer to Figure 1 The chemical injection system is used to inject chemicals into a deepwater underwater wellhead. The chemical injection method may include the following steps:

[0044] S1. Isolate the low-pressure pump group 30 and the injection pipeline 40, and displace the gas column in the injection pipeline 40 through the high-pressure pump group 20.

[0045] According to the underwater wellhead where the chemical agent is to be injected, a high-pressure pump group 20 and a corresponding low-pressure pump group 30 are selected. The second isolation valve 34 on the low-pressure pump group 30 is closed to disconnect the low-pressure pump group 30 from the injection pipeline 40. The first isolation valve 24 on the high-pressure pump group 20 is opened to connect the chemical storage tank 10, the high-pressure pump 21 and the injection pipeline 40. The high-pressure pump 21 is started, and the high-pressure pump 21 displaces the gas column in the injection pipeline 40 with its designed pressure.

[0046] S2, isolating the high-pressure pump group 20 and the injection pipeline 40, injecting the chemical agent in the agent storage tank 10 into the oil pipe 1 through the injection pipeline 40 by the low-pressure pump group 30, thereby injecting the chemical agent into the underwater wellhead.

[0047] After the gas column displacement is completed in the above step S1, the first isolation valve 24 on the high-pressure pump group 20 is closed to disconnect the high-pressure pump 21 from the injection pipeline 40. The low-pressure pump 31 on the low-pressure pump group 30 is started to inject the chemical agent in the agent storage tank 10 into the oil pipe 1 through the injection pipeline 40 at its designed pressure.

[0048] When the low-pressure pump group 30 is under fault inspection, the faulty low-pressure pump group 30 and the injection pipeline 40 are isolated, and the high-pressure pump group 20 and the injection pipeline 40 are connected. The high-pressure pump group 20 is started, and the chemical agent in the agent storage tank 10 is injected into the oil pipe 1 through the injection pipeline 40 by the high-pressure pump group 20, ensuring the normal injection of the chemical agent.

[0049] In addition, when the chemical agent injection system of the present invention is initially put into use, the high-pressure pump 21 is first used to puncture the bursting disc on the agent injection valve 45 before normal chemical agent injection operation is performed, without the need for an external pump to puncture. When the bursting disc is punctured, the low-pressure pump group 30 and the injection pipeline 40 are isolated.

[0050] When the injection of chemical agents in the well is stopped and then restarted, if gas flows back into the injection pipeline 40, the low-pressure pump 31 cannot be injected normally. At this time, the high-pressure pump group 20 and the injection pipeline 40 can be connected first: open the first isolation valve 24, close the second isolation valve 34, and start the high-pressure pump 21. After the flow detector 43 shows a stable flow, stop the high-pressure pump 21, observe the pressure of the first pressure monitor 41 and the second pressure monitor 42, and connect the low-pressure pump group 30 and the injection pipeline 40 when the pressure drops to the same level as the operating pressure of the low-pressure pump 31: open the second isolation valve 34, close the first isolation valve 24, and start the low-pressure pump 31 to inject chemical agents into the well. At this time, the high-pressure pump 21 is used as a displacement gas column.

[0051] In the present invention, since the high-pressure pump group 20 in the chemical agent injection system can form multiple parallel relationships with multiple low-pressure pump groups 30, in the same gas field, the high-pressure pump group 20 can be connected in parallel with multiple low-pressure pump groups 30 in sequence, and gas displacement, agent injection and other operations can be performed on multiple underwater wellheads in sequence. The high-pressure pump group 20 can also be used to perform bursting piece breakdown operations on multiple underwater wellheads in sequence, which greatly reduces the configuration of the number of low-pressure pumps and reduces the cost investment.

[0052] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A chemical injection system for a deepwater underwater wellhead, characterized in that: It includes a medicine storage tank, a high-pressure pump group, a plurality of low-pressure pump groups and a plurality of injection pipelines of oil pipes connected to a plurality of underwater wellheads; the high-pressure pump group and each of the low-pressure pump groups are connected in parallel between the medicine storage tank and a corresponding injection pipeline; Before the chemical agent is injected, the gas column in the injection pipeline is displaced by the high-pressure pump group; after the gas column is displaced, the chemical agent in the agent storage tank is injected into the oil pipe through the injection pipeline by the low-pressure pump group; The high-pressure pump assembly includes a high-pressure pump, a first high-pressure pipeline connected between the inlet of the high-pressure pump and the medicine storage tank, a second high-pressure pipeline connected between the outlet of the high-pressure pump and the injection pipeline, and a first isolation valve arranged on the second high-pressure pipeline; The low-pressure pump group includes a low-pressure pump, a first low-pressure pipeline connected between an inlet of the low-pressure pump and a medicine storage tank, a second low-pressure pipeline connected between an outlet of the low-pressure pump and an injection pipeline, and a second isolation valve arranged on the second low-pressure pipeline.

2. The chemical injection system according to claim 1, characterized in that: When the low-pressure pump group is under fault repair, the chemical agent in the agent storage tank is injected into the oil pipe through the injection pipeline by the high-pressure pump group.

3. The chemical injection system according to claim 1, characterized in that: The second high-pressure pipeline has a plurality of branch pipelines, each of which is connected in parallel with a corresponding low-pressure pump group to the corresponding injection pipeline; each of the branch pipelines is provided with the first isolation valve.

4. The chemical injection system according to claim 1, characterized in that: The design pressure of the high-pressure pump = (injection point pressure + pipeline pressure drop) × design error coefficient; The design pressure of the low-pressure pump = (injection point pressure - static liquid column pressure + pipeline pressure drop) × design error coefficient; Among them, the injection point pressure refers to the agent injection point of the underwater wellhead, and the injection point pressure is the pressure in the wellbore where the agent injection point is located; the pipeline pressure drop is the pressure drop of the injection pipeline; the hydrostatic column pressure is calculated based on the density of the chemical agent and its injection depth; the design error coefficient is 1.1-1.

5.

5. The chemical injection system according to claim 1, characterized in that: The chemical agent injection system further comprises a pressure monitor, a flow detector, a check valve and an agent injection valve arranged on the injection pipeline; the check valve is located on one end of the agent injection valve away from the oil pipe.

6. The chemical injection system according to claim 5, characterized in that: The pressure monitor includes a first pressure monitor and a second pressure monitor; the first pressure monitor and the flow detector are located between the check valve and the chemical injection valve in sequence; the second pressure monitor is located on one end of the chemical injection valve close to the oil pipe.

7. A method for injecting chemicals into a deepwater underwater wellhead, characterized in that: The chemical agent injection system according to any one of claims 1 to 6 is used; the chemical agent injection method comprises the following steps: S1, isolating the low-pressure pump group and the injection pipeline, and displacing the gas column in the injection pipeline by the high-pressure pump group; S2. Isolate the high-pressure pump group and the injection pipeline, and inject the chemical agent in the agent storage tank into the oil pipe through the injection pipeline by the low-pressure pump group.

8. The method for injecting chemicals into a deep underwater wellhead according to claim 7, characterized in that: In step S2, when the low-pressure pump group is under fault repair, the chemical agent in the agent storage tank is injected into the oil pipe through the injection pipeline by the high-pressure pump group.

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