Oil reservoir exploitation method for improving middle and later period recovery efficiency of shale oil well group

Abstract

The invention provides an oil reservoir exploitation method for improving the recovery efficiency in the middle and later periods of shale oil well groups. The method comprises the steps that the well groups in the middle and later periods of shale oil fracturing exploitation are obtained through screening; well completion transformation is conducted on the well group; injecting a mixture of a combustion-supporting catalyst and an organic solvent into the well group; a bridge plug is put into the well group; injecting nitrogen foam into a target layer of the well group to wash the well so as to push the combustion-supporting catalyst to advance and form a slug; oxygen-enriched air is injected into the target layer of the well group, spontaneous ignition is conducted on the oil layer, and shale oil is extracted; wherein the oxygen content in the oxygen-enriched air is not less than 30%. The oil layer exploitation method is suitable for the middle and later periods of shale oil exploitation through fracturing exhaustion, the exploitation mode that oxygen-enriched air injection and combustion improver injection are combined is adopted to improve the occurrence state of shale oil, and the recovery efficiency in the middle and later periods of shale oil exploitation can be improved.

Description

Technical Field

[0001] The present application relates to the technical field of shale oil recovery, and in particular to an oil layer exploitation method for improving the recovery rate of a shale oil well group in the middle and late stages. Background Art

[0002] Shale oil generally refers to petroleum resources concentrated in organic-rich shale formations. Currently, this refers to liquid hydrocarbons that exist in free, dissolved, and adsorbed states within effective hydrocarbon-generating shale formations and can be directly accessed through drilling, fracturing, and other methods. Shale oil can be divided into two types: one, generated by organic matter in the shale at a relatively low maturity stage, forms medium- to heavy-weight oils that are relatively enriched in the shale formation, have relatively high viscosity, and exhibit poor recoverability; the other, generated by organic matter in the shale reaching a medium- to high-maturity stage, forms light oils or even condensates that are enriched in the shale formation and exhibit good recoverability.

[0003] The difficulty in developing shale oil lies in the low permeability of the reservoir. This low permeability results in poor crude oil mobility within the reservoir. Currently, shale oil is primarily developed through a depletion-based approach, involving horizontal well fracturing followed by gas or water injection. This can improve shale oil recovery to a certain extent. However, due to the relatively well-developed micro- and nano-scale pore throats in shale oil reservoirs, the permeability of the reservoir is low, resulting in low crude oil mobility and a reduced reach for gas or water injection. Conventional water injection is difficult to replenish, leading to a rapid initial decline in shale oil production. This leaves a large amount of crude oil in the reservoir unused, making further increases in crude oil recovery difficult.

[0004] Another approach to increasing the effective utilization of shale oil is through in-situ pyrolysis extraction. This involves heating the shale reservoir underground without air injection. Complex physical changes and polymer chemical reactions occur under varying temperature gradients, causing the organic matter to decompose into oil and gas, which are then extracted above ground. However, this extraction method also suffers from significant heat loss, an inability to ensure sufficient formation energy, inadequate utilization of produced gas, high costs, and low efficiency.

[0005] The current shale oil development methods all have certain shortcomings, and there is an urgent need for a technology to improve the fluidity of shale crude oil and the porosity and permeability of the reservoir to increase the recovery rate. Summary of the Invention

[0006] In order to improve the recovery rate of shale oil in the middle and late stages of production, this application proposes an oil layer production method for improving the recovery rate of shale oil well groups in the middle and late stages, and adopts the following technical solutions:

[0007] A method for producing oil layers to improve the recovery rate of a shale oil well group in the middle and late stages, comprising:

[0008] Screening out well groups in the middle and late stages of shale oil fracturing production;

[0009] Performing well completion modification on the well group;

[0010] injecting a mixture of a combustion-supporting catalyst and an organic solvent into the well group;

[0011] running a bridge plug into the well group;

[0012] Injecting nitrogen foam into the target layer of the well group to flush the well, so as to push the combustion-supporting catalyst forward and form a slug;

[0013] injecting oxygen-enriched air into the target stratum of the well group to spontaneously ignite the oil layer to produce shale oil;

[0014] The oxygen content in the oxygen-enriched air is not less than 30%.

[0015] Optionally, the oxygen content in the oxygen-enriched air is 30%-50%.

[0016] Optionally, the combustion-supporting catalyst is formed by mixing potassium permanganate, aluminum powder, magnesium powder, carbon powder and nickel chloride.

[0017] Optionally, the organic solvent is crude oil extracted from the target oil layer, and the crude oil injection volume is 45-55m 3 .

[0018] Optionally, the combustion-supporting catalyst is mixed with the organic solvent at a mass percentage of 3%.

[0019] Optionally, the screening to obtain a well group in the middle and late stages of shale oil fracturing production includes:

[0020] The well groups with burial depth ranging from 500-3000m, Ro value ranging from 0.5% to 1.0%, organic matter content greater than 10%, water saturation less than 10%, oil layer thickness ranging from 5-25m, and injection-production spacing of 75-150m were selected.

[0021] Optionally, the completion modification of the well group includes:

[0022] Lower the bellmouth, packer, safety valve and sliding sleeve into the well bottom along with the tubing in sequence;

[0023] Seal the packer so that it is sealed with the casing to form a closed space;

[0024] A wellhead sealing device is installed at the wellhead.

[0025] Optionally, the oxygen content in the oxygen-enriched air is 30%-50%.

[0026] Optionally, after injecting the separated oxygen-enriched air into the formation to spontaneously ignite the formation, the method further includes:

[0027] When variable speed injection is used and the injection speed can maintain a stable combustion front, the maximum injection speed is maintained.

[0028] Optional, according to 500m 3 / d-1000m 3 Variable speed gas injection is performed in monthly increments of / d.

[0029] Optionally, the maximum gas injection rate is calculated according to the following formula:

[0030] q M =0.24RhV R ;

[0031] Among them, q M is the maximum gas injection velocity, R is the maximum radius of the combustion front, h is the oil layer thickness, V R The amount of air required to burn oil sands.

[0032] Based on the above technical solution, the beneficial effects of this application compared with the prior art are as follows:

[0033] The oil layer extraction method disclosed in this application uses oxygen-rich air for in-situ combustion in the middle and late stages of shale oil development after fracturing and depletion, and injects a combustion-supporting catalyst to lower the reaction threshold of shale oil, allowing the crude oil to spontaneously ignite at formation temperatures. This optimizes the ignition process and technology, making ignition fast, safe, and efficient, thereby forming a stable combustion front and pushing the formation crude oil from the injection well to the production well. In-situ combustion can improve the fluidity of shale crude oil and the porosity and permeability of the reservoir, thereby increasing the fluidity of shale oil, expanding the reservoir porosity, and improving the permeability, significantly improving the effective utilization range of shale oil in the reservoir. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a flow chart of the oil layer production method in the embodiment of the present application. DETAILED DESCRIPTION

[0035] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0036] Exemplary embodiments will be described in detail herein, with examples illustrated in the accompanying drawings. In the following description, when referring to the drawings, identical numerals in different figures represent identical or similar elements, unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all possible embodiments consistent with the present disclosure. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present disclosure, as detailed in the appended claims.

[0037] In the description of this disclosure, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of this disclosure and simplify the description. They do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on this disclosure. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0038] In the description of this disclosure, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood broadly. For example, they may refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in this disclosure based on the specific circumstances.

[0039] At present, shale oil is mainly developed by first performing horizontal well volume fracturing, followed by gas or water injection, which can improve the shale oil recovery rate within a certain range. The inventors found that due to the relatively developed micro-nano-scale pore throats in shale oil reservoirs, the permeability of shale oil reservoirs is low and the mobility of crude oil is low. This reduces the scope of gas or water injection during the production process, and conventional water injection is difficult to replenish energy, resulting in a rapid decline in shale oil production in the early stage. A large amount of crude oil in the reservoir is not effectively mobilized, and it is difficult to achieve stable combustion by directly injecting air into the shale. Therefore, in order to improve the recovery rate of crude oil in the oil layer in the middle and late stages of shale oil production, the inventors conducted secondary development of the reservoir after the above-mentioned fracturing and water injection depletion development, so as to fully exploit the oil layer of the well group after the first development, and proposed a method for oil layer production to improve the recovery rate of shale oil well groups in the middle and late stages.

[0040] A method for improving the recovery rate of shale oil wells in the middle and late stages of oil layer mining, referring to Figure 1 ,include:

[0041] S1: Screen and obtain the well groups in the middle and late stages of shale oil fracturing exploitation. It should be noted that this application is applicable to shale reservoirs that have been fractured in the middle and late stages of shale oil development, that is, shale oil well groups that have undergone one-time depletion development. Specifically, when further screening this type of well group, a well group with a burial depth range of 500-3000m, a Ro value (Ro value refers to the degree of thermal evolution of organic matter in oil resources contained in shale formations dominated by shale) in the range of 0.5%-1.0%, an organic matter content greater than 10%, a water saturation less than 10%, an oil layer thickness range of 5-25m, and an injection-production well spacing of 75-150m is selected.

[0042] S2: Complete the well group. This involves sequentially lowering the bellmouth, packer, safety valve, and sliding sleeve along the tubing to the bottom of the well. Once all components are lowered, the packer is sealed, sealing the packer to the casing to create a closed space and ensuring a tight seal for subsequent gas injection. A 50MPa high-pressure wellhead is used, along with a wellhead seal to prevent backfire and two sets of valves.

[0043] Preferably, when arranging the bellmouth, packer, safety valve, and sliding sleeve, the bellmouth is lowered to 2m-5m above the bottom of the artificial well and the middle and lower part of the perforation section, the position of the packer is adjusted to 2m-5m above the overlying rock formation, the safety valve is adjusted to 10-20 meters above the packer, and the sliding sleeve is adjusted to 10m-15m above the safety valve.

[0044] S3: Injecting a mixture of a combustion-supporting catalyst and an organic solvent. Specifically, the combustion-supporting catalyst is a mixture of potassium permanganate, aluminum powder, magnesium powder, carbon powder, and nickel chloride. The combustion-supporting catalyst comprises 10-20% by weight of potassium permanganate, 60-70% by weight of aluminum powder, magnesium powder, and carbon powder, and a specific ratio of 4:3:3 of aluminum powder, magnesium powder, and carbon powder. The nickel chloride comprises 20-30% by weight.

[0045] Furthermore, the organic solvent is crude oil extracted from the target oil layer, and the crude oil injection volume is 45-55m 3 , preferably 50m 3 The combustion-supporting catalyst is mixed with the organic solvent at a mass percentage of 3%. By injecting the combustion-supporting catalyst, the reaction threshold of shale oil can be further lowered, allowing the crude oil to spontaneously combust at formation temperature without the need for an additional ignition device.

[0046] S4: Lowering a bridge plug into the well group. The bridge plug is mainly used to seal the oil and gas well group to isolate the combustion catalyst.

[0047] S5: Inject nitrogen foam into the target layer of the well group to flush the well, so as to push the combustion catalyst forward and form a slug. Specifically, the nitrogen foam injection rate is 100-120t / m 3 .

[0048] S6: Inject oxygen-enriched air into the target layer of the well group to ignite the oil layer to produce shale oil; wherein, the oxygen content in the oxygen-enriched air is not less than 30%. Specifically, air denitrification equipment and nitrogen collection equipment can be added at the injection wellhead to remove 10%-30% of the nitrogen from the air to form oxygen-enriched air. In the embodiment of the present application, the oxygen content in the oxygen-enriched air ranges from 30% to 50%, and the separated nitrogen can be collected for secondary utilization such as nitrogen flooding development. Due to the low porosity and permeability of shale oil in the formation, it burns more violently under oxygen-enriched air conditions and releases more energy, thereby making the advancement of the fire line more stable. The use of oxygen-enriched air injection for in-situ combustion solves the problem of being unable to establish a sustained and stable combustion front.

[0049] In an optional embodiment, in step S6, after the spontaneous ignition is successful, the gas injection is carried out in a variable speed manner, and when the gas injection speed can maintain a stable combustion front, the maximum gas injection speed is maintained. Specifically, the gas injection speed is adjusted once a month, according to 500m 3 / d-1000m 3 The gas injection rate is gradually increased with monthly increments of 1 / 2 / day. During this process, as the injection rate increases, the combustion front gradually expands and stabilizes, entering a stable combustion phase. This phase, as determined by wellhead pressure and flue gas composition, shows that the CO2 content in the produced gas during the stable combustion phase is above 10%, the O2 content is below 3%, and the bottomhole pressure of the producing well is half of the original reservoir pressure.

[0050] In an optional embodiment, based on the numerical simulation results, the maximum gas injection rate of the injection well is calculated according to the following formula:

[0051] q M =0.24RhV R ;

[0052] Among them, q M —Maximum gas injection velocity of injection well, m 3 / d;V R —Amount of air required to burn oil sands, m 3 / m 3 ; h—oil layer thickness, m; R—maximum radius of combustion front, m.

[0053] In an optional embodiment, the amount of air required to burn oil sands is determined by conducting indoor tests on field oil samples, and the maximum radius of the combustion front is determined by the distance the combustion front advances after injecting oxygen-enriched air.

[0054] Indoor physical model experiments have shown that injecting oxygen-enriched air and a combustion aid can reutilize shale oil reservoirs after primary depletion. The full recovery process is complete when the combustion front advances to 90% of the injection-production interval, ultimately increasing the recovery factor by 55%.

[0055] In summary, this application continuously injects oxygen-enriched air into the target formation of the well group, allowing the oxygen-enriched air to enter the pores and throats within the matrix to achieve intra-layer combustion. Self-ignition ensures safety, eliminating the need for a separate ignition device. The combined use of oxygen-enriched air injection and combustion-supporting agent technology for mining. The combustion-supporting agent catalyzes the oxygen-enriched air, lowering the oxygen content requirement. This makes self-ignition faster and more efficient, forming a stable combustion front, thereby pushing formation crude oil from the injection well to the production well, improving crude oil recovery.

[0056] First, by injecting oxygen-rich air, the temperature generated by the combustion reaction is higher, and the carbon dioxide content generated is higher. As the formation heats up, according to the theory of thermal miscibility of air injection, in the range greater than 350 degrees Celsius, the higher the temperature and the higher the carbon dioxide content, the easier it is for crude oil and carbon dioxide generated by the combustion of oxygen-rich air to mix, thereby lowering the miscibility threshold and effectively improving oil recovery efficiency.

[0057] Secondly, crude oil near the wellbore undergoes distillation and cracking, triggering chemical reactions involving various high-molecular-weight organic compounds. The resulting CO, CO₂, ethers, aldehydes, and ketones expand the volume of the crude oil within its pores, reducing viscosity and enhancing fluidity. Heavy components in the crude oil, which are less susceptible to phase change and mobility, continue to burn as residual coke deposits after distillation and cracking. The abundant oxygen in the oxygen-enriched air allows for the formation of a stable combustion front. As the combustion front advances, mass exchange between the oil and gas causes further dissolution of air and oxidation products into the pores, effectively replenishing formation energy. The simultaneous production of large amounts of carbon dioxide replenishes gas formation pressure, significantly increasing formation temperature and restoring formation energy.

[0058] Thirdly, this application improves the fluidity of shale crude oil and the porosity and permeability of the reservoir through in-situ combustion, thereby increasing the fluidity of shale oil, expanding the reservoir porosity, and improving the permeability, significantly improving the effective utilization range of shale oil in the reservoir. During the high-temperature oxidation reaction, the porosity and permeability conditions of the shale oil reservoir are greatly improved, and thermally induced microcracks are formed in the reservoir, thereby enhancing the injection capacity of oxygen-rich air and improving the occurrence state of crude oil in micro- and nano-scale pore throats that is difficult to mobilize. At the same time, due to the presence of artificially fractured cracks and matrix in the shale oil reservoir, dual medium seepage is input, oxygen-rich air burns in the cracks, and the shale oil in the matrix near the cracks expands due to heat, prompting the shale oil to seep from the matrix into the cracks, thereby producing a micro-expansion self-drive effect.

[0059] The above description includes examples of one or more embodiments. Of course, it is not possible to describe all possible combinations of components or methods for the purpose of describing the above embodiments, but it will be recognized by those skilled in the art that the various embodiments may be further combined and arranged. Therefore, the embodiments described herein are intended to cover all such changes, modifications and variations that fall within the scope of protection of the appended claims. In addition, to the extent that the term "comprising" is used in the specification or claims, the term is intended to be encompassed in a manner similar to the term "including", as explained by the use of "including" as a transitional word in the claims. In addition, any use of the term "or" in the specification of the claims is intended to mean a "non-exclusive or".

Claims

1. A method for oil layer mining to improve the recovery rate of shale oil wells in the middle and late stages, characterized in that: include: Screening out well groups in the middle and late stages of shale oil fracturing production; Performing well completion modification on the well group; injecting a mixture of a combustion-supporting catalyst and an organic solvent into the well group; running a bridge plug into the well group; Injecting nitrogen foam into the target layer of the well group to flush the well, so as to push the combustion-supporting catalyst forward and form a slug; injecting oxygen-enriched air into the target stratum of the well group to spontaneously ignite the oil layer to produce shale oil; The oxygen content in the oxygen-enriched air is not less than 30%.

2. The oil layer production method according to claim 1, characterized in that: The oxygen content in the oxygen-enriched air is 30%-50%.

3. The oil layer production method according to claim 1, characterized in that: The combustion-supporting catalyst is prepared by mixing potassium permanganate, aluminum powder, magnesium powder, carbon powder and nickel chloride.

4. The oil layer production method according to claim 1, characterized in that: The organic solvent is crude oil extracted from the target oil layer, and the crude oil injection volume is 45-55m 3 .

5. The oil layer production method according to claim 1, characterized in that: The combustion-supporting catalyst is mixed with the organic solvent at a mass percentage of 3%.

6. The oil layer production method according to claim 1, characterized in that: The screening process obtains a group of wells in the middle and late stages of shale oil fracturing production, including: The well groups with burial depth ranging from 500-3000m, Ro value ranging from 0.5% to 1.0%, organic matter content greater than 10%, water saturation less than 10%, oil layer thickness ranging from 5-25m, and injection-production spacing of 75-150m were selected.

7. The oil layer production method according to claim 1, characterized in that: The oxygen content in the oxygen-enriched air is 30%-50%.

8. The oil layer production method according to claim 1, characterized in that: After injecting oxygen-enriched air into the target layer of the well group to spontaneously ignite the oil layer, the method further includes: When variable speed injection is used and the injection speed can maintain a stable combustion front, the maximum injection speed is maintained.

9. The oil layer production method according to claim 8, characterized in that: According to 500m 3 / d-1000m 3 Variable speed gas injection is performed in monthly increments of / d.

10. The oil layer production method according to claim 8, characterized in that: The maximum gas injection rate is calculated according to the following formula: q M =0.24RhV R ; Among them, q M is the maximum gas injection velocity, R is the maximum radius of the combustion front, h is the oil layer thickness, V R The amount of air required to burn oil sands.

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