A method of cap layer modification for a salt cavern storage

Abstract

The application provides a salt cavern storage cover layer reconstruction method, which comprises the following steps: S1: hydraulically cutting off the casing of the upper stable stratum of the damaged or deformed casing, wherein the upper thick shale stable stratum forms a stratum seal as a cover layer; S2: lowering a telescopic drill bit to drill off the exposed cement ring; S3: lowering a hanging packer; S4: injecting thixotropic cement for sealing; S5: after the cement is cured, pressure test is conducted, and after the pressure test is qualified, the cement plug and the hanging packer are drilled; and S6: repairing the casing by using a casing patching method or an expandable pipe casing patching method. The salt cavern storage cover layer reconstruction method provided by the application does not reconstruct the direct roof, but reconstructs the wellbore in the upper shale stable stratum, seals the annulus, and provides favorable conditions for underground storage construction and disaster control, and has universality.

Description

Technical Field

[0001] This invention relates to the field of salt cavern storage construction technology, and more specifically, to a method for modifying the cover layer of a salt cavern storage facility. Background Technology

[0002] The main channels connecting underground storage facilities to the surface are the strata and the wellbore. Therefore, a good caprock and a wellbore with good sealing are both indispensable. Salt caverns in China generally suffer from the problem of broken salt layer tops, with cracks in the tops connecting the strata, well wall and casing annular space.

[0003] For casing damage, sealing methods such as casing patching, packer installation, or cement plugging can be used. However, the main challenges in preventing underground fluid upwelling lie in the casing-to-wellbore annulus and the formation itself. This is because a fractured roof connects the upper formation and the casing-to-wellbore annulus, creating a channel for underground fluid upwelling. Furthermore, due to direct roof fracture, the caprock's sealing function fails. Poor cementing quality in the early stages and subsequent cracks in the casing-to-wellbore annulus during production allow deep underground fluids to flow along this channel, leading to groundwater pollution and numerous problems affecting the surface environment and human life and property. This can impact the safe and high-quality operation of the reservoir, the product quality and recovery rate of production wells, and the quality of sealing abandoned wells, ultimately resulting in the failure of remediation projects.

[0004] Traditional methods mainly involve injecting cement at the wellhead or perforating the damaged section of the casing to inject cement. However, these methods are time-consuming, labor-intensive, and dangerous. Furthermore, the quality of the repair is difficult to guarantee, as the amount of cement injected into the annulus is limited and cannot guarantee that blockage will not occur. If the repair fails, it is difficult to continue construction. Summary of the Invention

[0005] This invention aims to solve at least one of the technical problems existing in the prior art, and aims to provide a method for caprock modification of salt cavern reservoirs. It utilizes a thick upper mudstone and shale stratum as a caprock to form a sealed stratum. This section of mudstone and shale, or other stable strata, is characterized by stable lithology, density, and large thickness, making it an ideal caprock. The annular space between the casing and the wellbore is then sealed through processes such as casing cutting, drilling a cement sheath, installing a packer, cementing, drilling a cement plug, and casing patching to isolate the upward flow of underground fluids, forming a sealed and stable wellbore.

[0006] Therefore, the present invention provides a method for modifying the cap layer of a salt cavern storage facility.

[0007] This invention provides a method for modifying the cap layer of a salt cavern storage facility, comprising the following steps:

[0008] S1: The casing above the damaged or deformed casing is hydraulically cut off, and the upper part of the stable stratum is a thick mudstone and shale stable stratum, which serves as a cap layer to form a formation seal.

[0009] S2: Lower the telescopic drill bit to drill away the exposed cement ring;

[0010] S3: Lower the suspended packer;

[0011] S4: Inject thixotropic cement for sealing:

[0012] S5: After the concrete has set, test the pressure. After the pressure test is passed, drill open the cement plug and the suspended packer.

[0013] S6: Repair the casing using the casing patching method or the expansion tube casing patching method.

[0014] The method for modifying the cap layer of a salt cavern storage facility according to the above-described technical solution of the present invention may also have the following additional technical features:

[0015] In the above technical solution, S2 specifically refers to:

[0016] Lower the telescopic drill bit to the exposed cement sheath section. Use the pressure of the mud pump to expand the cutting wings of the reaming drill bit to enlarge the hole. The enlarged hole diameter should not be less than the original drill bit diameter for this section. Re-adjust this section of the wellbore. After the exposed cement sheath section is enlarged, stop the enlargement, stop the pump, retract the cutting wings of the telescopic drill bit back to their original position, and then slowly pull it out of the casing.

[0017] In the above technical solution, S3 specifically refers to:

[0018] Lower the suspended packer or bridge plug to an appropriate position below the cut casing section. Depending on the actual situation, a drill-free packer can be selected. Pressurize and set the packer securely.

[0019] In the above technical solution, S4 specifically refers to:

[0020] Use a clean drill pipe to cut the casing section inside the well and inject thixotropic cement slurry. During the cement slurry injection process, pay attention to timely lifting of the drill pipe and re-inserting cement to seal the exposed section. The cement plug surface should be no less than 20m above the cut casing section.

[0021] In the above technical solution, S5 specifically refers to:

[0022] After 72 hours of curing, an internal pressure test is conducted at a pressure of 12 MPa for 30 minutes. A pressure drop of less than 0.5 MPa is considered acceptable. Drilling tools are then lowered to break open the cement plug and the suspended packer, and the well is circulated to the bottom to ensure unobstructed flow within the wellbore.

[0023] In the above technical solution, S6 specifically refers to:

[0024] The casing is repaired using either the casing patching method or the expansion tube casing patching method. A thin-walled tube is attached to the inner wall of the casing and lowered into the well to the inner wall of the damaged area. The casing and the thin-walled tube are then bonded together with an adhesive. After the adhesive has cured, the drill string is moved and the rubber sleeve is removed.

[0025] In the above technical solution, if multiple sections are damaged, the above steps can be repeated from bottom to top until the entire wellbore is sealed.

[0026] The proposed method for caprock modification of salt cavern reservoirs does not modify the direct top slab, but rather modifies the wellbore within stable strata such as shale and mudstone above it, sealing the annulus. This provides favorable conditions for underground reservoir construction and disaster management, and has universal applicability. By finding a relatively thick stable stratum such as shale and mudstone above to form a caprock, a formation seal is created. Hydraulic cutting and injection of cement or other binding materials are used for sealing. Then, techniques such as casing patching are employed to seal the annulus between the casing and the wellbore, modifying the caprock, repairing the wellbore, and creating favorable wellbore conditions, thus providing excellent conditions for underground reservoirs.

[0027] Additional aspects and advantages of the invention will become apparent in the following description or may be learned by practice of the invention. Attached Figure Description

[0028] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0029] Fig. 1 This is a schematic diagram of the damage to the top plate and casing of the salt layer;

[0030] Fig. 2 This is a schematic diagram of the step of hydraulically cutting off the casing of the stable stratum above the damaged or deformed casing in the method for modifying the cap layer of the salt cavern storage of the present invention.

[0031] Fig. 3 This is a schematic diagram of the step of injecting thixotropic cement for sealing in the capping layer modification method of the salt cavern storage of the present invention. Detailed Implementation

[0032] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0033] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0034] The following referenceFigs. 1-3 This describes a method for modifying the cap layer of a salt cavern storage facility according to some embodiments of the present invention.

[0035] Some embodiments of this application provide a method for modifying the cap layer of a salt cavern storage facility.

[0036] like Figs. 1-3 As shown, the first embodiment of the present invention proposes a method for modifying the cap layer of a salt cavern storage facility, which is implemented according to the following steps:

[0037] 1. Use hydraulic cutting to remove the casing above the damaged or deformed casing, which is in a stable formation;

[0038] In this step, a section of casing in stable formations such as mudstone and shale is cut at a certain distance above the damaged casing using a hydraulic cutter, exposing a section of cement sheath. If the casing does not fall off after being cut, it can be dislodged by lowering the drilling tool or by downhole blasting.

[0039] 2. Lower the telescopic drill bit to drill away the exposed cement ring;

[0040] In this step, the telescopic drill bit is lowered to the exposed cement sheath. The pressure from the mud pump is used to expand the cutting blades of the reaming drill bit to enlarge the hole. The enlarged diameter should not be less than the original drill bit diameter for this section of the well. The wellbore is then re-trimmed. After enlarging the exposed cement sheath section, the reaming is stopped, the pump is stopped, the telescopic drill bit's cutting blades retract back to their original position, and then the drill bit is slowly pulled out of the casing.

[0041] 3. Insert the suspended packer (bridge plug);

[0042] In this step, the suspended packer (bridge plug) is lowered to an appropriate position below the cut casing section, preferably about 5 to 10 meters. Depending on the actual situation, a drill-free packer can be selected, and the packer is pressure-set and securely fixed.

[0043] 4. Seal with thixotropic cement;

[0044] In this step, a bare drill pipe is lowered into the well to cut the casing section, and thixotropic cement slurry is injected. The slurry consists of G-grade oil well cement, calcium chloride, bentonite, etc. The main purpose is to improve the bonding quality between the cement slurry and the casing and formation. During the cement slurry injection process, attention should be paid to timely lifting of the drill pipe to avoid "flagpole insertion". The exposed section is then re-cemented and sealed. The cement plug surface should be no less than 20m above the cut casing section.

[0045] 5. After the concrete has set, perform a pressure test. Once the pressure test is passed, drill open the cement plug and the suspended packer.

[0046] In this step, after 72 hours of curing, an internal pressure test is conducted at a pressure of 12 MPa for 30 minutes. A pressure drop of less than 0.5 MPa is considered acceptable. The drilling tools are then lowered to drill through the cement plug and the suspended packer, and the well is circulated to the bottom to ensure unobstructed flow within the wellbore.

[0047] 6. Repair the casing using the casing patching method;

[0048] In this step, the casing is repaired using either the casing patching method or the expansion tube casing patching method. A thin-walled tube is attached to the inner wall of the casing. The process principle is as follows: a corrugated tube (thin-walled tube) is fitted onto a specially made high-temperature resistant rubber sleeve and lowered into the inner wall of the damaged casing in the well. The casing and the corrugated tube are then bonded together with an adhesive. After the adhesive has cured, the drill string is moved and the rubber sleeve is removed.

[0049] In addition, if multiple sections are damaged, the above process and procedures can be repeated from bottom to top until the entire wellbore is sealed.

[0050] In this specification, the illustrative expressions of the terms used do not necessarily refer to the same embodiments or examples. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0051] Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention shall be included within the scope of protection of this invention.

Claims

1. A method for modifying the cap layer of a salt cavern storage facility, characterized in that, Includes the following steps: S1: The casing above the damaged or deformed casing is hydraulically cut off, and the upper part of the stable stratum is a thick mudstone and shale stable stratum, which serves as a cap layer to form a formation seal. A section of casing in a stable mudstone and shale formation at a certain distance above the damaged casing was cut using a hydraulic cutter, exposing a section of cement ring. S2: Lower the telescopic drill bit to drill away the exposed cement ring; Lower the telescopic drill bit to the exposed cement sheath section, and use the pressure of the mud pump to expand the cutting wings of the reaming drill bit to expand the hole. The diameter of the expanded hole should not be less than the diameter of the original drill bit for this section. Re-adjust this section of the wellbore. After the exposed cement sheath section is expanded, stop the reaming, stop the pump, retract the cutting wings of the telescopic drill bit back to their original position, and then slowly pull it out of the casing. S3: Lower the suspended packer; Lower the suspended packer or bridge plug below the cut sleeve section; S4: Inject thixotropic cement for sealing: Use a bare drill pipe to cut the casing section into the well, inject thixotropic cement slurry, and then re-cement the exposed section to seal it. S5: After the cement has set, test the pressure. If the pressure test is successful, drill through the cement plug and the suspended packer, and then clear the well to the bottom to keep the wellbore unobstructed. S6: Repair the casing using the casing patching method or the expansion tube casing patching method.

2. The method for modifying the cap layer of a salt cavern storage facility according to claim 1, characterized in that, In S1: If the casing does not detach after being cut, it can be dislodged by lowering the drill string or by using downhole explosives.

3. The method for modifying the cover layer of a salt cavern storage facility according to claim 2, characterized in that, In S3: Depending on the actual situation, a drill-free packer can be selected, which is pressure-set and securely fixed.

4. The method for modifying the cap layer of a salt cavern storage facility according to claim 3, characterized in that, In S4: During the cement grouting process, attention should be paid to timely lifting of the drill rod, and the cement plug surface should be no less than 20m above the cut casing section.

5. The method for modifying the cover layer of a salt cavern storage facility according to claim 4, characterized in that, Specifically, S5 is: After 72 hours of curing, a pressure test is conducted inside the pipe at a pressure of 12 MPa for 30 minutes. A pressure drop of less than 0.5 MPa is considered acceptable. The drilling tool is then lowered to drill through the cement plug and the suspended packer.

6. The method for modifying the cover layer of a salt cavern storage facility according to claim 5, characterized in that, Specifically, S6 is: The casing is repaired using either the casing patching method or the expansion tube casing patching method. A thin-walled tube is attached to the inner wall of the casing and lowered into the well to the inner wall of the damaged area. The casing and the thin-walled tube are then bonded together with an adhesive. After the adhesive has cured, the drill string is moved and the rubber sleeve is removed.

7. The method for modifying the cap layer of a salt cavern storage facility according to claim 6, characterized in that, If multiple sections are damaged, repeat the above steps from bottom to top until the entire wellbore is sealed.

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