Oxygen control methods in fire-driven well production processes

Abstract

This invention provides an oxygen control method for the production process of fire-driven wells. The method includes: determining the critical oxygen concentration at the explosion limit of the produced gas from the fire-driven well; obtaining the produced gas from the fire-driven well; determining the oxygen concentration of the produced gas; analyzing the formation combustion state based on the oxygen concentration; and determining the oxygen control method based on the formation combustion state. This invention solves the problem of high explosion risk in existing fire-driven production processes.

Description

Technical Field

[0001] This invention relates to the field of heavy oil fire-flooding technology, and more specifically, to an oxygen control method for the production process of fire-flooding wells. Background Technology

[0002] Fire flooding is a heavy oil thermal recovery technology that involves continuously injecting air and igniting the oil reservoir to burn 10% of the difficult-to-recover heavy components, generating high-temperature upgrading, combustion flue gas, and water vapor, among other displacement effects. It is characterized by high thermal efficiency, high recovery rate, and energy conservation and environmental friendliness. The key to its successful implementation is achieving continuous and stable high-temperature combustion within the oil reservoir. Successful fire flooding projects abroad have been carried out in originally highly saturated reservoirs, with relatively balanced fire-line advancement and less difficulty in control. However, most domestic fire flooding projects are carried out in reservoirs in the later stages of steam injection. These reservoirs have problems such as widespread development of steam injection channels, enrichment of secondary water bodies from steam condensation, and large differences in oil saturation between wells. During fire-line advancement, some well groups are affected by factors such as low local oil saturation in the formation, enrichment of water bodies, and abnormal gas injection, leading to a deterioration in the combustion state of the oil reservoir, changing from high-temperature oxidation to low-temperature oxidation. Oxygen that cannot be consumed by the formation is continuously produced by the production wells, accompanied by a certain concentration of combustible gas, posing a potential explosion risk. If measures cannot be taken in time to restore the formation to a high-temperature combustion state, the production well will be forced to shut down, and the fire-driven production process will be terminated.

[0003] Currently, theoretical research on the issue of low-temperature oxidation during fire-driven processes concludes that maintaining a high air injection rate accelerates the exothermic reaction of low-temperature oxidation, increases the total heat release, and promotes a gradual increase in formation temperature, which is beneficial for the transition from low-temperature oxidation to high-temperature oxidation. However, in field applications, if oil wells undergoing low-temperature oxidation continue to maintain a high air injection rate, the concentration of oxygen and methane will exceed the explosion limits, posing a significant safety risk. Therefore, from a safety perspective, the actual field response is the opposite: reducing the air injection rate and directly shutting down wells with oxygen concentrations exceeding 5%. Ultimately, this results in difficulty in restoring high-temperature combustion, leading to low-speed gas injection, inefficient production, or even permanent well shutdown.

[0004] In other words, the existing technology for fire-driven production has a high risk of explosion. Summary of the Invention

[0005] The main objective of this invention is to provide an oxygen control method for the production process of fire-driven wells, so as to solve the problem of high explosion risk in the existing fire-driven production process.

[0006] To achieve the above objectives, according to one aspect of the present invention, an oxygen control method for a fire-driven well production process is provided, comprising: determining the critical oxygen concentration at the explosion limit of the produced gas in the fire-driven well; obtaining the produced gas from the fire-driven well; determining the oxygen concentration of the produced gas; analyzing the formation combustion state based on the oxygen concentration; and determining the oxygen control method based on the formation combustion state.

[0007] Furthermore, the formation combustion state includes a poor combustion state, a localized low-temperature oxidation state, a low-temperature oxidation state, and a low-temperature oxidation state with a significant risk of explosion.

[0008] Furthermore, in the process of analyzing the formation combustion state based on oxygen concentration and determining the oxygen control method based on the combustion state, if the oxygen concentration is greater than or equal to 1% and less than 2%, the formation combustion state is a state of deteriorated combustion.

[0009] Furthermore, in the process of analyzing the formation combustion state based on oxygen concentration and determining the oxygen control method based on the combustion state, if the oxygen concentration is greater than or equal to 2% and less than 5%, the formation combustion state is a local low-temperature oxidation state.

[0010] Furthermore, in the process of analyzing the formation combustion state based on oxygen concentration and determining the oxygen control method based on the combustion state, if the oxygen concentration is greater than or equal to 5% and less than 8%, the formation combustion state is a low-temperature oxidation state.

[0011] Furthermore, in the process of analyzing the formation combustion state based on oxygen concentration and determining the oxygen control method based on the combustion state, if the oxygen concentration is greater than or equal to 8%, the formation combustion state is a state of obvious low-temperature oxidation and has an explosion risk.

[0012] Furthermore, in determining the oxygen control method based on the formation combustion state, if the formation combustion state is in a state of deteriorated combustion, the production-injection ratio of the fire-driven well should be reduced.

[0013] Furthermore, when the formation combustion state is in a state of deterioration, the production-injection ratio of the fire-driven well is reduced to below 60% during the process of reducing the production-injection ratio.

[0014] Furthermore, in determining the oxygen control method based on the formation combustion state, if the formation combustion state is a local low-temperature oxidation state, the production-injection ratio of the fire-driven well is reduced and a chemical deoxygenator is added to the fire-driven well.

[0015] Furthermore, when the formation combustion state is a local low-temperature oxidation state, the production-injection ratio of the fire-driven well is reduced and a chemical deoxidizer is added to the fire-driven well. One of the following is selected as the chemical deoxidizer: an inorganic iron-based deoxidizer or an organic enzyme-based deoxidizer. A dose of chemical deoxidizer that can control the oxygen concentration produced to within 1% is added from the annulus of the fire-driven well.

[0016] Furthermore, in determining the oxygen control method based on the formation combustion state, when the formation combustion state is a low-temperature oxidation state, the production-injection ratio of the fire-driven well is reduced, a chemical deoxygenator is added to the fire-driven well, and high-temperature steam is injected into the annulus of the fire-driven well.

[0017] Furthermore, in the process of determining the oxygen control method based on the formation combustion state, if the formation combustion state is a low-temperature oxidation state with a clear risk of explosion, the fire-drive well should be shut down immediately, an isolation barrier from combustible gases should be established, and the well should be shut down.

[0018] Furthermore, when the formation combustion state is a low-temperature oxidation state with a clear risk of explosion, the fire-drive well should be shut down immediately. During the process of establishing an isolation barrier from combustible gases and smothering the well, the fire-drive well should be shut down. An isolation barrier from combustible gases should be established in the wellbore through well washing and pressure measures. A certain amount of steam should be injected and the well should be smothered until the oxygen concentration is less than 5%, and then the well should be opened intermittently to vent the gas.

[0019] The oxygen control method in the production process of a fire-driven well, using the technical solution of this invention, includes: determining the critical oxygen concentration at the explosion limit of the produced gas in the fire-driven well; obtaining the produced gas from the fire-driven well; determining the oxygen concentration of the produced gas; analyzing the formation combustion state based on the oxygen concentration; and determining the oxygen control method based on the formation combustion state.

[0020] By determining the critical oxygen concentration at the explosion limit of produced gas in fire-driven wells, the formation combustion state can be analyzed reasonably based on the oxygen concentration of the produced gas. Oxygen control methods can then be adjusted according to different formation combustion states to maintain the downhole oxygen concentration within a reasonable range, reducing the risk of explosion and increasing the safety and stability of the fire-driven well production process. Furthermore, using different oxygen control methods for different formation combustion states can reduce the risk of shutting in the fire-driven well, ensuring stable operation. Attached Figure Description

[0021] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0022] Figure 1 A flowchart of the oxygen control method for the fire-driven well production process of the present invention is shown. Detailed Implementation

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0024] It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0025] In this invention, unless otherwise stated, directional terms such as "upper," "lower," "top," and "bottom" are generally used in relation to the direction shown in the accompanying drawings, or in relation to the vertical, perpendicular, or gravitational direction of the component itself; similarly, for ease of understanding and description, "inner" and "outer" refer to the inner and outer contours of each component itself, but the above directional terms are not intended to limit this invention.

[0026] To address the high risk of explosion during fire-driven well production in existing technologies, this invention provides an oxygen control method for the fire-driven well production process.

[0027] like Figure 1 As shown, the oxygen control method in the production process of a fire-driven well includes: Step S10: Determine the critical oxygen concentration at the explosion limit of the produced gas in the fire-driven well; Step S20: Obtain the produced gas from the fire-driven well; Step S30: Determine the oxygen concentration of the produced gas; Step S40: Analyze the formation combustion state based on the oxygen concentration; Step S50: Determine the oxygen control method based on the formation combustion state.

[0028] By determining the critical oxygen concentration at the explosion limit of produced gas in fire-driven wells, the formation combustion state can be analyzed reasonably based on the oxygen concentration of the produced gas. Oxygen control methods can then be adjusted according to different formation combustion states to maintain the downhole oxygen concentration within a reasonable range, reducing the risk of explosion and increasing the safety and stability of the fire-driven well production process. Furthermore, using different oxygen control methods for different formation combustion states can reduce the risk of shutting in the fire-driven well, ensuring stable operation.

[0029] Specifically, formation combustion states include deteriorated combustion, localized low-temperature oxidation, low-temperature oxidation, and low-temperature oxidation with a significant risk of explosion. Fire-driven wells exhibit different formation combustion states under varying oxygen concentrations, necessitating the use of different oxygen control methods to reduce oxygen concentration within a reasonable range while minimizing the need to shut down the fire-driven well. This ensures stable operation of the well while reducing the risk of explosion.

[0030] Specifically, in the process of analyzing formation combustion state based on oxygen concentration and determining oxygen control methods based on the combustion state, if the oxygen concentration is greater than or equal to 1% and less than 2%, the formation combustion state is considered to be in a deteriorated state. An oxygen concentration between 1% and 2% indicates a deteriorated combustion state, meaning less oxygen is consumed, resulting in an oxygen concentration greater than 1%.

[0031] Specifically, in determining the oxygen control method based on the formation combustion state, if the formation combustion state is poor, the production-injection ratio of the fire-driven well should be reduced. Appropriately reducing the gas production-injection ratio involves maintaining the gas injection rate of the air injection well at a constant rate while reducing the exhaust rate of the production well. This increases the gas cavity pressure within the formation, accelerates the reaction rate between oxygen and crude oil, and ensures a continuous high-temperature combustion state in the fire-driven well.

[0032] Specifically, when the formation combustion state is poor, the production-injection ratio of the fire-drive well is reduced to below 60%. This increases the gas cavity pressure within the formation, increases the formation combustion rate under high pressure, ensures the formation is in a high-temperature combustion state, and guarantees stable operation of the fire-drive well.

[0033] Specifically, in the process of analyzing the formation combustion state based on oxygen concentration and determining the oxygen control method based on the combustion state, if the oxygen concentration is greater than or equal to 2% and less than 5%, the formation combustion state is a localized low-temperature oxidation state. In this state, the formation combustion state is worse, with excessive residual oxygen leading to an increase in oxygen concentration. Excessively high oxygen concentrations will corrode the casing and tubing, which is detrimental to their operation.

[0034] It should be noted that the low-temperature oxidation state in this application refers to the state when the temperature is less than 200°C. In the low-temperature oxidation state, the oxidation reaction rate is low and oxygen is difficult to consume. At this time, the oxygen concentration in the gas produced by the production well will continue to increase.

[0035] Specifically, in determining the oxygen control method based on the formation combustion state, if the formation combustion state is a localized low-temperature oxidation state, the production-injection ratio of the fire-driven well is reduced and a chemical oxygen scavenger is added to the fire-driven well. At this time, in addition to reducing the production-injection ratio, a chemical oxygen scavenger is added to the well to quickly remove oxygen, allowing the formation to maintain a high-temperature combustion state.

[0036] Specifically, when the formation combustion state is a localized low-temperature oxidation state, the production-injection ratio of the fire-drive well is reduced, and a chemical deoxidizer is added to the well. One type of chemical deoxidizer is selected: an inorganic-based iron-based deoxidizer or an organic-based enzyme-based deoxidizer. A dosage of chemical deoxidizer capable of controlling the produced oxygen concentration to within 1% is added from the annulus of the fire-drive well. This setup ensures that the fire-drive well remains stably in a high-temperature combustion state while reducing corrosion of the casing and tubing.

[0037] Specifically, in the process of analyzing the formation combustion state based on oxygen concentration and determining the oxygen control method based on the combustion state, if the oxygen concentration is greater than or equal to 5% and less than 8%, the formation combustion state is a low-temperature oxidation state. Under this state, oxidation of the oil casing and tubing increases further, leading to greater wear and tear on the oil casing and tubing.

[0038] Specifically, in determining the oxygen control method based on the formation combustion state, when the formation combustion state is a low-temperature oxidation state, the production-injection ratio of the fire-driven well is reduced, a chemical deoxygenator is added to the fire-driven well, and high-temperature steam is injected into the annulus of the fire-driven well. Simultaneously reducing the production-injection ratio and adding a chemical deoxygenator to the fire-driven well, while simultaneously injecting high-temperature steam into the annulus of the fire-driven well, increases the temperature of the wellbore and near-wellbore zone, further accelerating the reaction between oxygen and crude oil.

[0039] It should be noted that the high-temperature steam in this application refers to high-temperature steam with a temperature >200℃.

[0040] Specifically, in the process of analyzing the formation combustion state based on oxygen concentration and determining the oxygen control method based on the combustion state, if the oxygen concentration is greater than or equal to 8%, the formation combustion state is characterized by significant low-temperature oxidation and an explosion risk. At this point, the oxygen concentration is too high, posing a significant explosion risk to normal production of the fire-driven well.

[0041] Specifically, in determining the oxygen control method based on the formation combustion state, if the formation combustion state is a low-temperature oxidation state with a significant explosion risk, the fire-driven well should be immediately shut down, an isolation barrier from combustible gases should be established, and the well should be shut down. For oil wells with an oxygen concentration greater than 8%, indicating significant low-temperature oxidation at the fire line and a possibility of fire extinguishing, and considering the high safety risk due to approaching the explosion limit, the well should be immediately shut down. After establishing an isolation barrier from combustible gases within the wellbore through well flushing and pressure measures, a certain amount of steam should be injected and the well shut down to reduce the oxygen concentration.

[0042] Specifically, when the formation combustion state is at a low temperature and oxidation level with a significant risk of explosion, the fire-driven well should be immediately shut down. An isolation barrier from flammable gases should be established and the well should be shut down during the smoldering process. A well-washing and pressure system should be used to establish an isolation barrier from flammable gases within the wellbore. A certain amount of steam should be injected and the well should be smoldered until the oxygen concentration is less than 5%, at which point the well should be intermittently opened to release gas. This setup effectively avoids the risk of explosion from the fire-driven well, reduces the low-temperature combustion in the fire-driven well, ensures high-temperature combustion in the formation, and facilitates the resumption of production in the fire-driven oil recovery process.

[0043] This application addresses the localized low-temperature oxidation phenomenon that occurs during the commissioning of fire-driven production. It employs comprehensive oxygen control measures, such as controlling the production-injection ratio, adding chemical oxygen scavengers, and injecting high-temperature steam, to promote the transformation of low-temperature oxidation of formation oil to high-temperature oxidation, ultimately achieving stable high-temperature combustion, thereby improving the fire-driven development effect and ensuring safe production.

[0044] The following is a specific example to illustrate this:

[0045] Well Group No. 5 of a certain fire-drive project was located on a steam channel formed during previous steam injection. After ignition, it showed signs of high-temperature combustion. After 16 months of fire-drive production, the gas composition analysis of the production well on the north side of the well group showed: CO2: 8%, O2: 9.8%, N2: 74%, CH4: 5.6%. Analysis indicated that the water in the steam channel was enriched with low and fluctuating oil saturation. As the fire line advanced to a low-oil, high-water area, the heat released by localized combustion was insufficient to vaporize and displace the adjacent water, resulting in low-temperature oxidation characteristics, and the mixed gas concentration was close to the explosion limit. Based on this analysis, the production well on the north side of the well group was immediately shut down. The well was controlled with kill fluid and injected with twice the wellbore volume of clean water, followed by the injection of 200 tons of steam. After 7 days of well simmering, the O2 concentration in the mixed gas in the wellbore dropped to 3.7%, meeting the safe conditions for well opening. Production was then carried out using a self-flowing method, with the daily exhaust velocity controlled to less than 200 m³ / h by adjusting the nozzle flow rate. 3 10 kg of chemical deoxygenator was added to the annulus daily. After 10 days, the O2 concentration in the wellbore mixture dropped to 0.5%, at which point the addition of deoxygenator was stopped. After another 5 days of observation, the O2 concentration remained between 0.3% and 0.5%. The nozzle was adjusted to gradually increase the daily exhaust velocity to 500 m / s. 3 The O2 concentration was consistently below 1% during continuous monitoring. Analysis suggests that through a combination of measures, including steam injection to shut down the well, increasing the pressure in the gas chamber, and adding chemical deoxygenators, the formation successfully transitioned from low-temperature oxidation to high-temperature combustion, and the well resumed normal fire-driven production.

[0046] Obviously, the embodiments described above are merely some, not all, embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0047] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0048] It should be noted that the terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in sequences other than those illustrated or described herein.

[0049] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for controlling oxygen in the production process of fire-driven wells, characterized in that, include: Determine the critical oxygen concentration at which the produced gas of a fire-driven well reaches its explosion limit; Obtain the produced gas from fire-driven wells; Determine the oxygen concentration of the extracted gas; The formation combustion state was analyzed based on the oxygen concentration. The oxygen control method is determined based on the combustion state of the formation. The formation combustion state includes a state of deteriorated combustion, a state of localized low-temperature oxidation, a state of low-temperature oxidation, and a state of low-temperature oxidation with obvious explosion risk. In the process of analyzing the formation combustion state based on the oxygen concentration and determining the oxygen control method based on the combustion state, if the oxygen concentration is greater than or equal to 1% and less than 2%, the formation combustion state is a state of deteriorated combustion. In the process of analyzing the formation combustion state based on the oxygen concentration and determining the oxygen control method based on the combustion state, if the oxygen concentration is greater than or equal to 2% and less than 5%, the formation combustion state is a local low-temperature oxidation state. In the process of analyzing the formation combustion state based on the oxygen concentration and determining the oxygen control method based on the combustion state, if the oxygen concentration is greater than or equal to 5% and less than 8%, the formation combustion state is a low-temperature oxidation state. In the process of analyzing the formation combustion state based on the oxygen concentration and determining the oxygen control method based on the combustion state, if the oxygen concentration is greater than or equal to 8%, the formation combustion state is a state of obvious low-temperature oxidation and explosion risk. In the process of determining the oxygen control method based on the formation combustion state, if the formation combustion state is a deteriorating state, then the production-injection ratio of the fire-driven well is reduced. When the formation combustion state is a state of deteriorated combustion, the production-injection ratio of the fire-driven well is reduced to below 60% during the process of reducing the production-injection ratio. In the process of determining the oxygen control method based on the formation combustion state, if the formation combustion state is a local low-temperature oxidation state, then the production-injection ratio of the fire-driven well is reduced and a chemical deoxygenator is added to the fire-driven well. When the formation combustion state is a localized low-temperature oxidation state, the production-injection ratio of the fire-drive well is reduced and a chemical deoxidizer is added to the fire-drive well. The chemical oxygen scavenger is selected from either an inorganic matrix iron-based deoxidizer or an organic matrix enzyme-based deoxidizer. The chemical deoxygenator is added to the annulus of the fire-driven well in a dose that can control the oxygen concentration produced to within 1%.

2. The oxygen control method for the production process of fire-driven wells according to claim 1, characterized in that, In determining the oxygen control method based on the formation combustion state, if the formation combustion state is a low-temperature oxidation state, then the production-injection ratio of the fire-driven well is reduced, a chemical deoxygenator is added to the fire-driven well, and high-temperature steam is injected into the annulus of the fire-driven well.

3. The oxygen control method for the production process of fire-driven wells according to claim 1, characterized in that, In the process of determining the oxygen control method based on the formation combustion state, if the formation combustion state is a low-temperature oxidation state with obvious explosion risk, the fire drive well should be shut down immediately, an isolation barrier from combustible gases should be established, and the well should be shut down.

4. The oxygen control method for the fire-driven well production process according to claim 3, characterized in that, If the formation combustion state is a low-temperature oxidizing state with a significant risk of explosion, the fire-drive well should be immediately shut down, an isolation barrier should be established from the combustible gas, and the well should be sealed off. Close the fire-drive well; Establish an isolation barrier from combustible gases within the wellbore through well flushing and pressure measures; A certain amount of steam is injected and the well is kept closed until the oxygen concentration is less than 5%, at which point the well is opened intermittently to release the gas.

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