A construction method for converting abandoned oil and gas wells through karst caves into gas storage reservoirs

Abstract

The present application discloses a construction method for converting abandoned oil and gas wells through karst caves into gas storage facilities, which belongs to the field of natural gas storage. The method includes determining the connection position between the abandoned oil and gas wells and the karst cave reservoir based on the data of historical drilling leakage accidents of the abandoned oil and gas wells, as well as determining the upper and lower leakage layers of the karst cave reservoir; sealing the bottom of the abandoned oil and gas well until the bottom surface is flush with the bottom of the carbonate salt reservoir; accurately perforating the upper and lower leakage layers from the casing of the abandoned oil and gas well to obtain upper and lower cluster perforations; inserting a packer between the upper and lower cluster perforations of the casing, and the oil pipe of the abandoned oil and gas well passes through the packer from the wellhead and is connected to the lower cluster perforations; evaluating the gas storage capacity of the karst cave reservoir; injecting storage gas from the wellhead of the oil casing annulus, and under the gas injection pressure, the original fluid at the bottom of the karst cave reservoir is discharged from the lower cluster perforations and returned to the ground through the oil pipe. The gas storage facility converted by the present application has the advantages of low construction cost, good sealing and stability, and large effective gas storage capacity.

Description

Technical Field

[0001] The present application relates to the field of natural gas storage technology, and in particular to a construction method for converting abandoned oil and gas wells through karst caves into gas storage facilities. Background Art

[0002] As natural gas storage containers, underground gas storage facilities are crucial for strategic natural gas reserves and peak-shaving supply. Existing underground gas storage facilities primarily include depleted oil and gas reservoirs, aquifers, salt caverns, and abandoned mines.

[0003] Depleted oil reservoir gas storage can achieve the reuse of existing surface equipment, but its construction period is long and the assessment fee is high, resulting in high construction costs. Depleted gas reservoir gas storage has the advantages of high safety and reliability, high injection gas utilization rate, and short storage period, but depleted gas reservoir gas storage has high requirements for sealing and injection gas type. Aquifer gas storage has a complete structure, and drilling and completion can be completed in one go, but the exploration, research and selection of storage facilities are difficult, the risks are high, and the investment and operating costs are high. Salt cavern gas storage is formed by dissolving salt in underground salt layers with water. The gas injection time is short, but the effective storage volume for natural gas is small, drilling and completion are difficult, and the construction cost is high. Abandoned mine gas storage is relatively common, but its original wellbore is difficult to seal, there is a risk of gas leakage to the ground, and its stability is poor.

[0004] From the above, it can be seen that existing underground gas storage facilities have problems such as high construction cost, poor sealing and stability, and small effective gas storage capacity. Summary of the Invention

[0005] The embodiments of the present application provide a construction method for converting abandoned oil and gas wells through caves into gas storage facilities, which can solve the problems of existing underground gas storage facilities such as high construction cost, poor sealing and stability, and small effective gas storage capacity.

[0006] In order to achieve the above-mentioned purpose, the technical solution of the embodiment of the present invention is:

[0007] An embodiment of the present invention provides a construction method for converting an abandoned oil and gas well through a karst cave into a gas storage reservoir, comprising:

[0008] Determining the locations of the abandoned oil and gas well and the cave reservoir based on data from historical drilling loss events of the abandoned oil and gas well, and determining an upper loss layer and a lower loss layer of the cave reservoir, wherein the upper loss layer is located close to the ground, and the abandoned oil and gas well passes through a carbonate formation;

[0009] The bottom of the abandoned oil and gas well is sealed until the bottom surface is flush with the bottom of the carbonate salt reservoir;

[0010] Precisely perforating the upper leakage zone from the casing of the abandoned oil and gas well to obtain upper cluster perforations, wherein the upper cluster perforations penetrate the casing and communicate with the karst cave reservoir;

[0011] Precisely perforating from the casing toward the lower leakage zone to obtain lower cluster perforations, wherein the lower cluster perforations penetrate the casing and communicate with the cave reservoir;

[0012] A packer is placed between the upper cluster perforation and the lower cluster perforation of the casing, and the oil pipe of the abandoned oil and gas well passes through the packer from the wellhead and is connected to the lower cluster perforation;

[0013] Assessing the gas storage capacity of the cave reservoir;

[0014] Storage gas is injected from the wellhead of the oil-casing annulus between the casing and the oil pipe. Under the gas injection pressure, the original fluid at the bottom of the cave reservoir is discharged from the lower cluster perforations and returned to the ground through the oil pipe.

[0015] In a possible implementation, plugging the bottom of the abandoned oil and gas well includes:

[0016] The bottom of the abandoned oil and gas well is injected with cement slurry, and plugging is achieved after the cement slurry solidifies.

[0017] In a possible implementation, the perforating method for connecting the casing and the cave reservoir includes perforating bullet perforating or water jet perforating.

[0018] In a possible implementation, the evaluating the gas storage capacity of the cave reservoir includes:

[0019] Liquid is injected from the wellhead of the casing annulus, and the gas storage volume of the cave reservoir is calculated by constant flow injection pressure test, wherein the calculation formula is:

[0020] Where V is the volume of the cave reservoir, is the injection pressure at time t, is the injection pressure at the initial moment, c is the compressibility coefficient of the liquid, Q is the flow rate of the liquid, and t is the injection time.

[0021] In a possible implementation, the stored gas is injected from the wellhead of the casing annulus between the casing and the tubing, and under the gas injection pressure, the original fluid at the bottom of the cave reservoir is discharged from the lower cluster perforations and returned to the surface through the tubing, which includes:

[0022] The stored gas is repeatedly injected and then released from the wellhead of the oil casing annulus.

[0023] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages:

[0024] The construction method for converting abandoned oil and gas wells through caves into gas storage facilities, provided in an embodiment of the present invention, first determines the location of the abandoned oil and gas well and the cave reservoir based on historical drilling and leakage accident data of the abandoned oil and gas well, as well as the upper and lower leakage zones of the cave reservoir. The bottom of the abandoned oil and gas well is then sealed until its bottom surface is flush with the bottom of the carbonate salt reservoir. The upper cluster of perforations is then precisely perforated from the casing of the abandoned oil and gas well upward toward the leakage zone, thereby forming an upper cluster of perforations. The upper cluster of perforations penetrates the casing and connects to the cave reservoir. The lower cluster of perforations is then precisely perforated from the casing downward toward the leakage zone, thereby forming a lower cluster of perforations. The lower cluster of perforations penetrates the casing and connects to the cave reservoir. A packer is then inserted between the upper and lower cluster perforations of the casing, and the oil pipe of the abandoned oil and gas well is passed from the wellhead through the packer and connected to the lower cluster of perforations. The gas storage capacity of the cave reservoir is then assessed. Based on the assessed gas storage capacity of the cave reservoir, storage gas is finally injected from the wellhead of the oil-casing annulus between the casing and the tubing. Since the packer is located between the upper cluster perforations and the lower cluster perforations, the packer divides the oil-casing annulus into two sub-annuli. Under the injection pressure, the storage gas enters the upper sub-annulus and flows downward, and then enters the inner cavity of the cave reservoir along the upper cluster perforations. With the input of storage gas, the fluid in the cave reservoir is discharged from the lower cluster perforations to the lower sub-annulus, and then flows through the gap between the bottom end of the tubing and the bottom surface of the casing, flows into the bottom of the tubing, and is then discharged back to the ground through the tubing, thus realizing the conversion of abandoned oil and gas wells through caves into gas storage.

[0025] The embodiment of the present application utilizes existing abandoned oil and gas wells that pass through carbonate formations to reconstruct gas storage reservoirs, which is convenient and fast, has a short construction period, low construction cost, can provide a large gas storage capacity, and also has good sealing and stability. In addition, the gas storage reservoir reconstructed from abandoned oil and gas wells that pass through karst caves in the embodiment of the present application can dynamically adjust the gas injection volume and exhaust volume according to demand, and has relatively good flexibility. The construction method for reconstructing gas storage reservoirs from abandoned oil and gas wells that pass through karst caves provided in the embodiment of the present application can not only be used as a method for providing important energy reserves, but also the transformation of abandoned oil and gas wells that pass through carbonate formations can realize the effective application of geological resources, improve economic benefits, optimize resource allocation, and provide a new means for energy storage and management. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments of the present invention. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1This is a structural schematic diagram of a construction method for converting abandoned oil and gas wells in carbonate reservoirs into gas storage facilities using an embodiment of the present application.

[0028] Icons: 1-tubing; 2-casing; 3-cavity reservoir; 4-upper cluster perforation; 5-lower cluster perforation; 6-packer. DETAILED DESCRIPTION

[0029] The following will be combined with the accompanying drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0030] In the relevant description of this embodiment, the terms "including, containing, having" and the like are open-ended terms and are generally understood to mean including but not limited to. In the following description of this embodiment, the terms used in the embodiments of this application are merely for the purpose of describing specific embodiments and are not intended to limit this application. The singular forms "a," "an," and "the" used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0031] Those skilled in the art should understand that in the following description of the embodiments of this application, the order of sequence numbers does not mean the order of execution. Some or all steps can be executed in parallel or in sequence. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application. Unless otherwise specified, the technical / scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which this application belongs.

[0032] An embodiment of the present invention provides a construction method for converting an abandoned oil and gas well through a karst cave into a gas storage reservoir, comprising the following steps 1 to 8, where the numbers after the steps do not represent the order of execution.

[0033] Step 1: Based on historical data from drilling and leak-off incidents at abandoned oil and gas wells, the locations of the abandoned well and cave reservoir 3 were determined, as well as the upper and lower leak-off zones of cave reservoir 3. The upper leak-off zone is located close to the surface, as the abandoned well intersects carbonate formations. Furthermore, exploration methods such as the use of a geophone array were used to preliminarily determine the size of cave reservoir 3. This abandoned well, having experienced significant leak-offs during early drilling, is considered a potential gas storage well.

[0034] A leakage zone refers to a rock formation location where, during the drilling process, the flushing fluid (such as mud or water) is partially or completely lost due to complex formation conditions, such as cracks, caves, and loose fracture zones. This zone is a potential reservoir for a large amount of fluid. Identifying the leakage zone facilitates subsequent perforation at the corresponding location to obtain upper cluster perforations 4 or lower cluster perforations 5.

[0035] Step 2: Seal the bottom of the abandoned oil and gas well until the bottom surface is flush with the bottom of the carbonate salt reservoir.

[0036] Specifically, cement slurry is used to perfuse the bottom of the abandoned oil and gas well, and the plugging is achieved after the cement slurry solidifies. The bottom of the casing 2 is plugged with cement slurry, which has a good plugging effect, has no gaps at the bottom, and is not prone to leakage.

[0037] Step 3: The upper cluster perforations 4 are obtained by accurately perforating upward from the casing 2 of the abandoned oil and gas well to the lost layer. The upper cluster perforations 4 penetrate the casing 2 and are connected to the karst cave reservoir 3, forming the upper connection point between the casing 2 and the karst cave reservoir 3.

[0038] The perforating method for connecting the casing 2 and the karst reservoir 3 includes perforating bullet perforating or water jet perforating.

[0039] Perforating charges are explosive devices used to penetrate the casing 2 and the formation during the perforating process. Shaped charge perforating charges are the most widely used perforating charges and also offer the highest perforating efficiency. A water jet is a high-speed stream of water of varying shapes flowing out of a nozzle. The jet's velocity depends on the pressure drop across the nozzle's outlet section. A water jet is the simplest form of energy conversion and application. Typically, a power-driven pump pumps a certain amount of water through a high-pressure pipeline through a process of suction and discharge, delivering it to the nozzle with a certain amount of energy. The nozzle's aperture is much smaller than the high-pressure pipeline's diameter, so the amount of water that reaches the nozzle accelerates and condenses upon exiting the nozzle orifice, forming a jet. When the jet reaches the inner wall of the casing 2, the energy generated by its velocity is converted into impact pressure, which acts on the casing 2 to precisely perforate the upper cluster perforations 4 or the lower cluster perforations 5.

[0040] Step 4: Precisely perforate the lost layer from the casing 2 downward to obtain the lower cluster perforations 5. The lower cluster perforations 5 penetrate the casing 2 and are connected to the cave reservoir 3, forming the lower connection point between the casing 2 and the cave reservoir 3, thereby facilitating the discharge of liquid in the cave reservoir 3 from the lower cluster perforations 5.

[0041] Step 5: A packer 6 is lowered between the upper cluster hole 4 and the lower cluster hole 5 of the casing 2 , and the oil pipe 1 of the abandoned oil and gas well passes through the packer 6 from the wellhead and is connected to the lower cluster hole 5 .

[0042] Step 6: Evaluate the gas storage capacity of cave reservoir 3.

[0043] Specifically, step 6 includes: injecting liquid from the wellhead of the casing annulus between the casing 2 and the oil pipe 1, and calculating the gas storage volume of the cave reservoir 3 through a constant flow injection pressure test, wherein the calculation formula is:

[0044] Where V is the volume of the cave reservoir 3, is the injection pressure at time t, is the injection pressure at the initial moment, c is the compressibility coefficient of the liquid, Q is the flow rate of the liquid, and t is the injection time.

[0045] The method for evaluating the gas storage capacity of the cave reservoir 3 in the embodiment of the present application is simple, fast, environmentally friendly and emission-reducing, and provides a new approach for energy storage and management.

[0046] Step 7: Inject stored gas from the wellhead of the casing annulus between the casing 2 and the tubing 1. Under the gas injection pressure, the original fluid at the bottom of the cave reservoir 3 is discharged from the lower cluster perforations 5 and returned to the surface through the tubing 1.

[0047] This fluid may be the liquid originally present in the cave reservoir 3. If the gas storage capacity of the cave reservoir 3 is evaluated by constant displacement water injection, the fluid is water.

[0048] Step 8: Repeatedly inject and then release stored gas from the wellhead in the casing annulus to evaluate the stability and gas yield of the rebuilt gas storage. Stability refers to the ability to store natural gas and prevent it from leaking.

[0049] The construction method for converting an abandoned oil and gas well through a cave into a gas storage facility provided by an embodiment of the present invention first determines the location of the abandoned oil and gas well and the cave reservoir 3 based on historical drilling and leakage accident data of the abandoned oil and gas well, as well as the upper and lower leakage zones of the cave reservoir 3. The bottom of the abandoned oil and gas well is then sealed until its bottom surface is flush with the bottom of the carbonate salt reservoir. Upper cluster perforations 4 are then precisely perforated from the abandoned oil and gas well's casing 2 upward toward the leakage zone. The upper cluster perforations 4 penetrate the casing 2 and connect to the cave reservoir 3. Lower cluster perforations 5 are precisely perforated from the casing 2 downward toward the leakage zone. The lower cluster perforations 5 penetrate the casing 2 and connect to the cave reservoir 3. A packer 6 is then lowered between the upper and lower cluster perforations 4, 5, of the casing 2. The oil pipe 1 of the abandoned oil and gas well is passed from the wellhead through the packer 6 and connects to the lower cluster perforations 5. The gas storage capacity of the cave reservoir 3 is then assessed. Based on the assessed gas storage capacity of the cave reservoir 3, storage gas is finally injected from the wellhead of the oil-casing annulus between the casing 2 and the oil pipe 1. Since the packer 6 is located between the upper cluster perforations 4 and the lower cluster perforations 5, the packer 6 divides the oil-casing annulus into two sub-annuli. Under the gas injection pressure, the storage gas enters the upper sub-annulus and flows downward. It is then input into the inner cavity of the cave reservoir 3 along the upper cluster perforations 4. With the input of storage gas, the fluid in the cave reservoir 3 is discharged from the lower cluster perforations 5 to the lower sub-annulus, then flows through the gap between the bottom end of the oil pipe 1 and the bottom surface of the casing 2, flows into the bottom of the oil pipe 1, and is then discharged back to the ground through the oil pipe 1, thus realizing the conversion of abandoned oil and gas wells through the cave into a gas storage reservoir.

[0050] The embodiment of the present application utilizes existing abandoned oil and gas wells that pass through carbonate formations to reconstruct gas storage reservoirs, which is convenient and fast, has a short construction period, low construction cost, can provide a large gas storage capacity, and also has good sealing and stability. In addition, the gas storage reservoir reconstructed from abandoned oil and gas wells that pass through karst caves in the embodiment of the present application can dynamically adjust the gas injection volume and exhaust volume according to demand, and has relatively good flexibility. The construction method for reconstructing gas storage reservoirs from abandoned oil and gas wells that pass through karst caves provided in the embodiment of the present application can not only be used as a method for providing important energy reserves, but also the transformation of abandoned oil and gas wells that pass through carbonate formations can realize the effective application of geological resources, improve economic benefits, optimize resource allocation, and provide a new means for energy storage and management.

[0051] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0052] The above embodiments are intended only to illustrate the technical solutions of this application and are not intended to limit this application. Although this application has been described in detail with reference to the aforementioned embodiments, those skilled in the art will appreciate that they may modify the technical solutions described in the aforementioned embodiments or replace some or all of the technical features therein with equivalents. Such modifications or replacements do not deviate from the essence of the corresponding technical solutions within the scope of this application.

Claims

1. A construction method for converting abandoned oil and gas wells through karst caves into gas storage facilities, characterized in that: include: Determining the locations of the abandoned oil and gas well and the cave reservoir based on data from historical drilling loss events of the abandoned oil and gas well, and determining an upper loss layer and a lower loss layer of the cave reservoir, wherein the upper loss layer is located close to the ground, and the abandoned oil and gas well passes through a carbonate formation; The bottom of the abandoned oil and gas well is sealed until the bottom surface is flush with the bottom of the carbonate salt reservoir; Precisely perforating the upper leakage zone from the casing of the abandoned oil and gas well to obtain upper cluster perforations, wherein the upper cluster perforations penetrate the casing and communicate with the karst cave reservoir; Precisely perforating from the casing toward the lower leakage zone to obtain lower cluster perforations, wherein the lower cluster perforations penetrate the casing and communicate with the cave reservoir; A packer is placed between the upper cluster perforation and the lower cluster perforation of the casing, and the oil pipe of the abandoned oil and gas well passes through the packer from the wellhead and is connected to the lower cluster perforation; Assessing the gas storage capacity of the cave reservoir; Injecting stored gas from the wellhead of the oil-casing annulus between the casing and the oil pipe, under the gas injection pressure, the original fluid at the bottom of the cave reservoir is discharged from the lower cluster perforations and returned to the surface through the oil pipe; Wherein, the blocking of the bottom of the abandoned oil and gas well includes: The bottom of the abandoned oil and gas well is injected with cement slurry, and the cement slurry is solidified to achieve plugging; The evaluating the gas storage capacity of the cave reservoir comprises: Liquid is injected from the wellhead of the casing annulus, and the gas storage volume of the cave reservoir is calculated by constant flow injection pressure test, wherein the calculation formula is: , where V is the volume of the cave reservoir, is the injection pressure at time t, is the injection pressure at the initial moment, c is the compressibility coefficient of the liquid, Q is the flow rate of the liquid, and t is the injection time.

2. The construction method for converting abandoned oil and gas wells through karst caves into gas storage facilities according to claim 1 is characterized in that: The perforating method for connecting the casing and the cave reservoir includes perforating bullet perforating or water jet perforating.

3. The construction method for converting abandoned oil and gas wells through karst caves into gas storage facilities according to claim 1, characterized in that: The method includes injecting stored gas from the wellhead of the oil-casing annulus between the casing and the oil pipe, and discharging the original fluid at the bottom of the cave reservoir from the lower cluster perforations under the gas injection pressure and returning to the surface through the oil pipe, which includes: The stored gas is repeatedly injected and then released from the wellhead of the oil casing annulus.

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