A carbon dioxide injection well thawing and plugging process

Abstract

The present invention discloses a carbon dioxide injection well thawing process, comprising: utilizing a heater (4) to release heat to melt frozen blockages in the well; utilizing chemical agents to remove dead oil in the well; and establishing a connection with the well via a buffer tank (11); the buffer tank (11) is used to release the well pressure generated by the carbon dioxide released by melting the frozen blockages and to recover the dead oil and chemical agents that are returned; and the problems of low thawing efficiency and incomplete thawing in existing electric heating and / or chemical agent thawing processes are solved.

Description

Technical Field

[0001] The invention relates to the technical field of tertiary oil recovery engineering in oil fields, in particular to a thawing and plugging process for a carbon dioxide injection well. Background Art

[0002] At present, CO2 injection wells have the problem of frozen tubing due to alternating water and gas, station transformation, and power outages, which affects the injection rate and oil recovery efficiency of the CO2 block. Frozen tubing in CO2 injection wells will make it difficult to relieve pressure in the wellbore, and the cost of lifting the tubing under pressure is high, which is a high risk.

[0003] There are two existing methods for thawing frozen oil pipes in CO2 injection wells: electric heating and chemical agents. Among them, the electric heating thawing method can only dissolve the CO2 frozen hydrate formed by the retention of CO2 in the oil pipe, and there is often dead oil attached to the inner wall of the oil pipe. The presence of this dead oil may have caused the oil pipe to be blocked or may cause secondary freezing due to the narrowing of the oil pipe channel. Obviously, since the electric heating method cannot clean the dead oil inside the oil pipe, the problem of incomplete unblocking by simple electric heating is that secondary freezing is easily caused.

[0004] The chemical agent thawing method consists of freezing point control agent, crude oil dispersant, antifreeze agent, oil washing agent, pH adjuster, gravity adjuster and thawing agent. The principle of thawing is: relying on thawing agent and crude oil dispersant to break up frozen blockages, freezing point control agent and antifreeze agent to ensure that the agent can still work under low temperature conditions, pH adjuster to adjust the pH value of the system according to the carbon dioxide produced by the melting of hydrates, and gravity adjuster to ensure that the overall density of the chemical agent is greater than 1g / cm 3 , can gradually penetrate into the bottom of the frozen blockage, increase the contact area, and the oil washing agent plays an oil washing role to clean the wellbore. The process of unblocking is to soak the chemical agent statically above the frozen blockage, and then after a long time of blocking the well, the chemical agent gradually sinks until the frozen blockage is completely dissolved; it can be seen that the construction efficiency of this method is low and the construction period is long. And when there is too much dead oil in the oil pipe, it will also hinder the contact between the chemical agent and the frozen blockage hydrate, resulting in failure of unblocking.

[0005] During the chemical thawing process, as the carbon dioxide hydrate melts, some gas is released. If the wellhead is open during the reaction, the chemical will continue to return as the hydrate dissolves and releases carbon dioxide, and the chemical cannot be allowed to remain in static contact with the frozen blockage and fully react. Therefore, the wellhead needs to be closed and pressure-held. When the pressure reaches a certain condition (generally 15MPa), the pressure is released and then the agent is replenished. The electric heating thawing process requires the placement of a heating component from the test valve and the sealing of the wellhead blowout preventer. The purpose is to prevent the carbon dioxide hydrate from melting and releasing gas as the electric heating rod works, and the carbon dioxide gas at the bottom of the well from injuring people due to the high upward return pressure at the moment of unblocking, or freezing the wellhead construction personnel due to the low temperature of the carbon dioxide gas. Therefore, both the electric heating thawing process and the chemical thawing process require the wellhead to remain closed.

[0006] If electric heating and chemical agents are used in combination to thaw plugging, the problem that may arise is that, in a closed state, electric heating will release carbon dioxide when melting carbon dioxide hydrates. As carbon dioxide accumulates, the bottom hole pressure increases. Because chemical agents need to statically soak the frozen plugging materials when thawing plugging, the increase in bottom hole pressure will affect the downward penetration of the chemical agents, making it impossible for the chemical agents to gradually sink and dissolve the frozen plugging materials, reducing the thawing efficiency of the chemical agents and affecting the final thawing effect. Therefore, the combination of electric heating and chemical agents cannot achieve the expected effect. Summary of the invention

[0007] In view of this, the present invention provides a carbon dioxide injection well thawing process to solve the problems of low thawing efficiency and incomplete thawing in the existing electric heating and / or chemical agent thawing process.

[0008] To achieve the above-mentioned purpose of the invention, the carbon dioxide injection well thawing and plugging process comprises:

[0009] Use the heater to release heat to melt the frozen blockage in the well;

[0010] removing dead oil in the well using chemical agents;

[0011] Establishing a communication relationship with the well through a buffer tank;

[0012] The buffer tank is used to release the wellbore pressure generated by the carbon dioxide released by melting the frozen blockage and to recover the dead oil and the chemical agent that are returned.

[0013] Furthermore, the chemical agent includes:

[0014] Oil cleaning agent;

[0015] The oil washing agent is used to remove the dead oil in the well.

[0016] Furthermore, the chemical agent also includes:

[0017] antifreeze;

[0018] The antifreeze agent is used to prevent secondary freezing and blocking from occurring in the well.

[0019] Furthermore, the antifreeze agent is ethylene glycol.

[0020] Furthermore, the chemical agent is pumped into the well by a pump truck.

[0021] Further, the heater is an electric heater;

[0022] The electric heater is connected to the power supply equipment on the well through a cable.

[0023] Furthermore, the heater is put into the well through a production valve.

[0024] Furthermore, the buffer tank is respectively connected to the oil pipe valve and the casing valve 7 pipelines.

[0025] Further, the buffer tank is an oil-gas-water separation buffer tank;

[0026] The oil-gas-water separation buffer tank is used to separate and recover the dead oil and the chemical agent.

[0027] Furthermore, the thawing and blocking process comprises the following steps:

[0028] Fill the well with the chemical agent, close the oil pipe valve, and after the heater releases heat for a set time, open the oil pipe valve to allow the chemical agent and the dead oil in the well to flow back to the oil-gas-water separation buffer tank;

[0029] Repeat the above steps until the frozen hydrate is completely melted.

[0030] Furthermore, the chemical separated from the oil-gas-water separation buffer tank is reused.

[0031] The present invention has the following beneficial effects:

[0032] The thawing blockage process of the present invention adopts a combination of chemical agent unblocking and electric heating unblocking, relying on the heat released by electric heating to melt the frozen hydrate, and at the same time utilizing the cleaning effect of the oil washing agent in the chemical agent on the dead oil to clean the inner wall of the oil pipe, that is, the dead oil is removed by chemical agents while the electric heating unblocks, thereby improving the thawing blockage effect of the overall thawing blockage process; in addition, a buffer tank is utilized to release the well pressure generated by the carbon dioxide released by melting the frozen hydrate and to recover the dead oil and chemicals that are returned, so that the unblocking process does not require a well-stuffing reaction, thereby shortening the construction period, improving the thawing blockage efficiency, and effectively solving the problems of low thawing blockage efficiency and / or incomplete unblocking in the existing electric heating and / or chemical agent thawing blockage processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0034] Figure 1 It is a schematic diagram of the carbon dioxide injection well thawing and plugging process according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0035] The present invention is described below based on embodiment, but it is worth noting that the present invention is not limited to these embodiments. In the detailed description of the present invention below, some specific details are described in detail. However, for the part not described in detail, those skilled in the art can also fully understand the present invention.

[0036] In addition, those skilled in the art should understand that the drawings are only provided to illustrate the purpose, features and advantages of the present invention, and the drawings are not actually drawn to scale.

[0037] At the same time, unless the context clearly requires otherwise, the words "include", "comprises" and similar words throughout the specification and claims should be interpreted as inclusive rather than exclusive or exhaustive; that is, the meaning is "including but not limited to".

[0038] Figure 1 FIG. 1 is a schematic diagram of a carbon dioxide injection well thawing process according to an embodiment of the present invention. Figure 1 As shown: The thawing process of the carbon dioxide injection well in the embodiment of the present disclosure includes: using the heater 4 to release heat to melt the frozen blockage in the well, using chemical agents to remove the dead oil in the well, establishing a connection with the well through the oil-gas-water separation buffer tank 11, and then using the oil-gas-water separation buffer tank 11 to release the well pressure generated by the melting of the frozen blockage and releasing the carbon dioxide and recovering the dead oil and the chemical agents that are returned.

[0039] The thawing and plugging process of the disclosed embodiment utilizes the buffer tank, which can, on the one hand, prevent the carbon dioxide gas released after thawing and plugging from gushing out of the wellhead, thereby avoiding the occurrence of carbon dioxide gas injuries; on the other hand, the buffer tank mainly recovers chemical agents, and the amount of gas returned is not large, and the chemical agents can be recycled and reused; on the third hand, the provision of the buffer tank can ensure that the thawing and plugging process can be carried out in the open, thereby further ensuring that chemical agent unblocking can be carried out while electric heating thawing and plugging are being carried out. Obviously, the combination of electric heating thawing and plugging by chemical agents can enhance the thawing and plugging effect and achieve the purpose of thorough thawing and plugging. Because there is no need to seal the well to meet the requirements of chemical agent thawing and plugging, the construction period can be effectively shortened and the thawing and plugging efficiency can be improved.

[0040] Preferably, the chemical agent includes an oil washing agent, which is used to remove dead oil in the well, thereby cleaning the inner wall of the oil pipe and reducing dead oil obstacles. In addition, the chemical agent also includes an antifreeze agent, which can prevent secondary freezing and blocking in the well.

[0041] The oil washing agent used in the embodiments of the present disclosure is the high-efficiency well washing fluid GXXJ produced by Shandong Binzhou Yucheng Chemical Technology Co., Ltd., and the antifreeze agent is an industrial-grade ethylene glycol antifreeze agent.

[0042] In the embodiment of the present disclosure, the chemical agent is pumped into the well by a pump truck 10; the heater 4 is an electric heater, which is preferably an insulated temperature-resistant heater; the electric heater is connected to the power supply equipment on the well by a cable, which is preferably an insulated cable; the power supply equipment includes an electric heating power system 1 and an electric heating safety system 2, and of course, the electric heating power system 1 and the electric heating safety system 2 can use conventional settings in the field, such as the electric heating power system 1 is a generator. The electric heater can be put into the well through the production valve 3.

[0043] The buffer tank 11 of the disclosed embodiment can be an oil-gas-water separation buffer tank, which is respectively connected to the oil pipe valve 6 and the casing valve 7 on the wellhead. The chemical agent separated from the oil-gas-water separation buffer tank 11 can be reused, and the separated dead oil can also be recycled.

[0044] Specifically, the process of implementing the blockage removal process disclosed in the present invention is described in detail with reference to the accompanying drawings:

[0045] a. Install the electric heating safety system 2 and the electric heating power system 1 at the wellhead, connect the water hose 12 to the oil pipe and casing to the oil-gas-water separation buffer tank 11, open the oil pipe valve 6 and the casing valve 7 to release the pressure in the oil pipe and casing;

[0046] b. Open the production valve 3, connect the insulated cable to the insulated temperature-resistant heater 4, and put it into the oil pipe to the top of the frozen section 5 of the oil pipe;

[0047] c. Open the oil pipe valve 8, use the pump truck 10 to fill the oil pipe with chemicals through the pump truck hose 9, and close the oil pipe valve 8;

[0048] d. Start the electric heating power system 1 to make the insulated temperature-resistant heater 4 work for 1 hour, release heat to melt the frozen section, and return the chemical agent in the oil pipe to the oil-gas-water separation buffer tank 11;

[0049] e. Open the oil pipe valve 8, add the chemical agent to fill the oil pipe for the second time, close the oil pipe valve 8, continue to start the electric heating power system 1, make the insulating temperature-resistant heater 4 work for 1 hour, release heat to melt the frozen blockage section 5, and return the chemical agent in the oil pipe to the oil-gas-water separation buffer tank 11;

[0050] f. Repeat the above operation until the frozen hydrate is completely melted, retract the insulated cable and the insulated temperature-resistant heater 4, close the production valve 3, remove the heating power system 1 and the electric heating safety system 2, close the oil pipe valve 6 and the casing valve 7, remove the water hose 12 and the oil-gas-water separation buffer tank 11, and resume production.

[0051] In addition, the S-1 well in the carbon dioxide injection block of a certain oil field implemented the unblocking process disclosed in the present invention. The well was frozen and blocked due to a power outage caused by an inter-station circuit failure in January 2020. The well was frozen and blocked for a total of 545 days, affecting the injection volume of more than 8,000 cubic meters and the production of more than 2,700 tons. In July 2021, the rapid thawing process was tested. After repeating the construction three times, the frozen hydrate was completely melted and production resumed.

[0052] Production data table before and after construction

[0053] time <![CDATA[Injection volume (m 3 )]]> Injection pressure (MPa) Before freezing 10 23.2 When frozen 0 0 After thawing and plugging construction 10 22.6

[0054] The data show that after the unblocking construction was carried out using the disclosed thawing and plugging process, the well was able to resume normal production, and parameters such as daily injection volume and injection pressure also returned to the levels before unblocking, and the thawing and plugging had no impact on the production system.

[0055] The above-mentioned embodiments are only embodiments of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for a person skilled in the art, without departing from the concept of the present invention, several variations, equivalent substitutions, improvements, etc. can be made, which all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the attached claims.

Claims

1. A carbon dioxide injection well thawing and plugging process, characterized in that: include: Using the heater (4) to release heat to melt the frozen blockage in the well; removing dead oil in the well using chemical agents; Establishing a communication relationship with the well via a buffer tank (11); The buffer tank (11) is used to release the wellbore pressure generated by the carbon dioxide released by melting the frozen blockage and to recover the dead oil and the chemical agent that are flowed back; The chemical agent comprises: Oil cleaning agent; The oil washing agent is used to remove the dead oil in the well.

2. The carbon dioxide injection well thawing and plugging process according to claim 1, characterized in that: The chemical agent also includes: antifreeze; The antifreeze agent is used to prevent secondary freezing and blocking from occurring in the well.

3. The carbon dioxide injection well thawing and plugging process according to claim 2, characterized in that: The antifreeze agent is ethylene glycol.

4. The carbon dioxide injection well thawing and plugging process according to any one of claims 1 to 3, characterized in that: The chemical agent is pumped into the well by a pump truck (10).

5. The carbon dioxide injection well thawing and plugging process according to claim 4, characterized in that: The heater (4) is an electric heater; The electric heater is connected to the power supply equipment on the well through a cable.

6. The carbon dioxide injection well thawing and plugging process according to claim 5, characterized in that: The heater (4) is put into the well through the production valve (3).

7. The carbon dioxide injection well thawing and plugging process according to claim 6, characterized in that: The buffer tank (11) is respectively connected to the oil pipe valve (6) and the casing valve (7) through pipelines.

8. The carbon dioxide injection well thawing and plugging process according to claim 6, characterized in that: The buffer tank (11) is an oil-gas-water separation buffer tank; The oil-gas-water separation buffer tank is used to separate and recover the dead oil and the chemical agent.

9. The carbon dioxide injection well thawing and plugging process according to claim 8, characterized in that: The steps include: Fill the well with the chemical agent, close the oil pipe valve (6), and after the heater (4) releases heat for a set time, open the oil pipe valve (6) to allow the chemical agent and the dead oil in the well to flow back to the oil-gas-water separation buffer tank; Repeat the above steps until the frozen blockage is completely melted.

10. The carbon dioxide injection well thawing and plugging process according to claim 9, characterized in that: The chemical separated from the oil-gas-water separation buffer tank is reused.

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