Method for reinforcing the walls of a well for exploitation of marine methane hydrates using mineralized sediments

Abstract

The application discloses a method for reinforcing the well wall of a hydrate exploitation well in a sea area by using mineralization deposition, and comprises the following steps: arranging a spray hole on the pipeline of the exploitation well and extending the spray hole to the outside of the well wall; arranging a plurality of pipelines along the well wall inside the well wall for conveying branched polyethylene imine (BPEI) solution and modified nano calcium carbonate dispersion; before hydrate exploitation, conveying the reagents from an exploitation platform to a specified reinforcement depth, and spraying the two reagents from the spray hole by using a high-pressure pump at a certain time interval and pressure; the two reagents are fully reacted in the soil layer around the well wall to generate mineralization deposits and improve the strength of the soil layer; the method can be repeated according to requirements to form multiple mineralization deposits to achieve the required reinforcement strength; the method is convenient to operate, the reinforcement process is clear, and the effect is remarkable, and the method fills the blank in the field of real-time reinforcement of the well wall of a hydrate exploitation well, and helps long-term, safe and efficient exploitation of hydrate energy, and has remarkable technical advantages.

Description

Technical Field

[0001] This invention belongs to the fields of marine geotechnical engineering and energy geotechnical engineering, and relates to a method for reinforcing the well wall of a natural gas hydrate extraction well, particularly a method for reinforcing the well wall of a marine combustible ice extraction well using mineralized sedimentation, which is applicable to the problem of well wall instability reinforcement during combustible ice extraction. Background Technology

[0002] Natural gas hydrate is a clean, efficient, and promising new energy source. Resembling ice in appearance and flammable upon contact with fire, it is known as "combustible ice." Hydrate extraction is a key research area for addressing energy shortages. Natural gas hydrates are widely distributed globally; over 230 hydrate deposits have been discovered in marine and permafrost regions, demonstrating enormous resource potential and being considered the most promising clean energy source to replace conventional oil and gas in the 21st century.

[0003] Natural gas hydrates exist in the extreme environments of high pressure and low temperature on the seabed, resulting in complex reservoir characteristics that present numerous challenges to the extraction and development process. In particular, hydrate decomposition during depressurization extraction can easily lead to a series of safety issues. Changes in the characteristics of hydrate reservoirs during extraction alter the environment surrounding the wellbore. Solid hydrates, which act as cementation or support, decompose into a flowing gas-liquid mixture, reducing the reservoir's mechanical bearing capacity. Simultaneously, the water and gas produced during decomposition seep into the surrounding formation, increasing the water content of the formation around the wellbore and weakening the cementing and supporting forces between particles, making the wellbore highly susceptible to instability. Wellbore instability has become a bottleneck problem in the current extraction of natural gas hydrates, significantly restricting the safety and efficiency of extraction.

[0004] Currently, research on wellbore reinforcement for natural gas hydrate extraction is still in its early stages. Exploring a method to reinforce wellbore walls during natural gas hydrate extraction is a crucial challenge that needs to be addressed to achieve long-term, safe, and efficient extraction of hydrate energy. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for reinforcing the well walls of marine combustible ice mining wells using mineralized deposition. This method employs mineralized deposition, utilizing a branched polyethyleneimine (BPEI) solution and a modified nano-calcium carbonate dispersion to generate mineralized deposits that reinforce the soil layers surrounding the well walls. This achieves the goal of reinforcing the well walls without affecting the hydrate extraction process, filling a gap in the field of well wall instability reinforcement during hydrate extraction.

[0006] The technical solution adopted in this invention is as follows:

[0007] A method for reinforcing the wellbore of marine methane hydrate extraction wells using mineralized sedimentation, the method comprising the following steps:

[0008] Step 1: Nozzle Setup

[0009] From top to bottom, the well pipe has several nozzles extending outwards from the well wall at regular intervals along its circumference.

[0010] Step Two: Pipe Installation

[0011] Several pipes are installed inside the well wall along the well perimeter. Each pipe is installed from top to bottom and connects to the nozzles on the adjacent well wall. The upper end of the pipe is connected to the storage tank on the mining platform through a high-pressure pump. It is used to transport branched polyethyleneimine (BPEI) solution and modified nano calcium carbonate dispersion. The mining well and the pipes transporting different solutions are independent to ensure that each solution is injected, controlled and transported independently.

[0012] The production well is installed in the predetermined reservoir on site according to the pre-designed plan, and all kinds of pipe interfaces are connected.

[0013] Step 3: Reagent Preparation

[0014] Before hydrate extraction, sufficient amounts of pre-prepared BPEI solution and modified nano-calcium carbonate dispersion are stored in the storage tank of the extraction platform.

[0015] BPEI solution can be prepared by dissolving branched polyethyleneimine in deionized water. Modified nano-calcium carbonate dispersion is prepared by dissolving calcium carbonate in deionized water after fatty acid modification.

[0016] Step 4: Reagent Transfer and Injection

[0017] The reagents are transported from the mining platform to the pipeline used for transporting the reagents. At certain time intervals and pressures, two reagents are sprayed out from the nozzles and into the soil layer around the well wall. Through nozzles designed in different directions, the reagent spraying range covers the soil layer around the well wall.

[0018] Step 5: Mineralization and Consolidation

[0019] The two reagents react fully in the soil layer around the well wall to generate mineral deposits and improve the soil strength; by setting the time interval and amount of the two reagents sprayed, the mineral deposits can cover the soil layer around the well wall.

[0020] Step Six: Multiple Reinforcement

[0021] Before mining, based on the required reinforcement strength of the overlying soil layer, steps four and five are repeated after a certain interval to form multi-layered mineralized deposits to achieve the required reinforcement strength.

[0022] In the above technical solution, further, in step one, the spray hole is circular, and multiple nozzles are evenly arranged around it to spray the reinforcing agent in different directions outside the well wall, so as to achieve the purpose of having the reinforcing agent around the well wall.

[0023] Furthermore, a protective device is installed at the bottom of each nozzle to protect it. The protective device is inclined and located below the nozzle to prevent the nozzle from deforming, wearing, or becoming blocked due to friction during the contact between the nozzle and the soil layer when the well is lowered for installation.

[0024] Furthermore, in step two, the pipeline installation depth is determined based on the thickness of the overburden layer and the thickness of the natural gas hydrate reservoir obtained from engineering exploration, so that the pipeline length covers the depth of the overburden layer, and the number of pipelines is no less than three, with each pipeline evenly distributed around the well.

[0025] Furthermore, in step four: the two reagents are transported from their respective transport pipelines, and valves are installed at each nozzle. According to different nozzle depths, the opening of the corresponding valves, the pressure of the high-pressure pump, and the jet speed of the nozzle are set so that the spraying range covers the soil layer around the well wall when the reagents are sprayed.

[0026] Furthermore, in step five: after the two reagents are sprayed from the nozzle, the first reagent sprayed out remains briefly in the soil pores, and reacts after the other reagent is sprayed out, mineralizing and depositing in the soil pores. By setting the time interval and spray volume of the two reagents from the nozzle, the mineralization and deposition reinforcement strength is ensured.

[0027] Furthermore, in step six: multiple mineralization deposition reinforcements are performed according to the required reinforcement strength, the time interval between two reinforcements is greater than the time for the reagent to fully react, and the reinforcement is repeated no less than three times.

[0028] Compared with the prior art, the technical solution provided in this application, which is exemplified and not limited, has the following beneficial effects:

[0029] This invention application is applicable to the field of deep-sea energy extraction technology, and can effectively reinforce the soil layer around the well wall of the overlying soil layer, solving the problem of well wall instability in the current natural gas hydrate extraction process.

[0030] Compared with other reinforcement methods, the method of this invention is convenient to operate, has a clear reinforcement process, and has significant effects. It will fill the gap in the field of real-time reinforcement of well walls during natural gas hydrate extraction, and help the long-term, safe and efficient extraction of hydrate energy, with significant technical advantages. Attached Figure Description

[0031] Figure 1 Schematic diagram of the on-site reinforcement layout of the well wall for mining in the overburden layer;

[0032] Figure 2 This is a schematic diagram of the cross section of the mining well in this invention;

[0033] Figure 3 This is a schematic diagram of the nozzle structure in this invention;

[0034] Figure 4 This is a flowchart of the reinforcement method in this invention.

[0035] Figure 1 , Figure 2 and Figure 3 In the diagram, 1 is the storage tank; 2 is the extraction platform; 3 is the seawater layer; 4 is the extraction shaft; 5 is the reagent delivery pipeline; 6 is the nozzle; 7 is the protective device; 8 is the upper cover layer; 9 is the natural gas hydrate reservoir; 10 is the well wall; and 11 is the nozzle. Detailed Implementation

[0036] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0037] like Figure 1 As shown, the on-site mining environment includes, from top to bottom, the seawater layer 3, the bottom layer of the seabed (i.e., the overlying layer 8), and the natural gas hydrate reservoir 9.

[0038] like Figure 1 As shown, the well wall reinforcement equipment includes a storage tank 1, a mining platform 2, a mining shaft 4, a reagent delivery pipeline 5, a nozzle 6, a nozzle 11, and a wedge-shaped protective device 7.

[0039] The location of the mining platform 2 is determined based on the position of the vertical shaft 4. A storage tank 1 is installed on the mining platform 2 for the preparation and storage of reinforcement reagents. Several reagent delivery pipes 5 are evenly arranged along the vertical shaft 4, and several nozzles 6 are opened on the shaft wall 10 corresponding to each reagent delivery pipe. The nozzles 6 are connected to the reagent delivery pipes 5. To prevent excessive friction between the nozzles and the soil layer during the vertical shaft lowering process, a wedge-shaped protective device 7 is installed at the bottom of each nozzle 6. The required reagents are prepared in the storage tank 1 on the mining platform 2 and transported to the required reinforcement location through the reagent delivery pipes 5.

[0040] like Figure 3 As shown, the embodiments and implementation process of the present invention include the following steps:

[0041] Step 1: Nozzle Setup

[0042] From top to bottom, in the seabed stratum, i.e., the overburden 8, several nozzles 6 are horizontally set at 3m intervals on the well pipe, extending outwards from the well wall 10.

[0043] The nozzle 6 is circular, with four nozzles 11 evenly arranged around it for spraying the reinforcing agent in different directions outside the well wall. To prevent nozzle deformation, wear, or blockage due to friction during contact with the soil layer, a wedge-shaped protective device 7 is installed at the bottom of each nozzle to protect it. The protective device 7 is made of a high-strength material such as steel or concrete and is fixed to the well wall. Other shapes besides wedge-shaped can also be used. It is inclined and installed below the nozzle. Since the well is installed from top to bottom, the nozzle protrudes outward. The protective device can better squeeze the soil layer outward, preventing the nozzle above from directly rubbing and colliding with the soil and causing damage.

[0044] Step Two: Pipe Installation

[0045] Several reagent delivery pipes 5 are installed along the well perimeter inside the well wall 10. Each reagent delivery pipe 5 can withstand a certain pressure and is connected to the nozzles 6 opened on the adjacent well wall 10. Some of the reagent delivery pipes 5 are used to deliver branched polyethyleneimine (BPEI) solution, while the rest are used to deliver modified nano-calcium carbonate dispersion. The pipes for the two types of reagents can be installed in adjacent pairs, and the corresponding nozzles can also be installed in adjacent pairs. The close distance between the nozzles facilitates a more complete reaction between the two reagents. Figure 2 The diagram below is only a schematic representation of the nozzles; the number and distribution of nozzles can be set according to the above description or specific needs. The extraction shaft 4 and the reagent delivery pipelines 5 for transporting different solutions are independent to ensure that each solution is injected, controlled, and transported separately.

[0046] The production shaft 4 is installed in the predetermined reservoir on site according to the pre-designed plan, and all kinds of pipe interfaces are connected.

[0047] Step 3: Reagent Preparation

[0048] Before hydrate extraction, sufficient amounts of pre-prepared BPEI solution and modified nano-calcium carbonate dispersion are stored in the storage tank of the extraction platform.

[0049] BPEI solution can be prepared by dissolving branched polyethyleneimine in deionized water, with a mass concentration of 0.1%. Modified nano-calcium carbonate dispersion is prepared by dissolving calcium carbonate in deionized water after fatty acid modification, with a mass concentration of 0.4%.

[0050] The reaction formula for preparing branched polyethyleneimine (BPEI) solution:

[0051] H(NHCH2CH2)nNH2(BPEI) + H2O → H(NHCH2CH2)nNH2 solution

[0052] The reaction formula for preparing modified nano-calcium carbonate dispersion:

[0053] CnH2n + 1COOH + nano-CaCO3 + H2O → modified nano-CaCO3 dispersion

[0054] Step 4: Reagent Transfer and Injection

[0055] The reagents are transported from the mining platform 2 to the reagent delivery pipeline 5. Two reagents are then sprayed from nozzles 6 at specific time intervals and pressures using a high-pressure pump, entering the soil layer surrounding the well wall. The reagent spraying area covers the soil layer surrounding the well wall through nozzles positioned at different angles. The reagent delivery pipeline 5 only needs to cover the depth of the covering layer; its lowest point can be sealed, or valves can be installed at nozzles at different depths to control the reagent delivery to the desired depth.

[0056] Step 5: Mineralization and Consolidation

[0057] After the two reagents are sprayed from the nozzle, the first reagent remains briefly in the soil pores. A reaction occurs after the second reagent is sprayed, and the two reagents react fully in the soil layer surrounding the well wall. Under the action of the BPEI solution, calcium carbonate undergoes structural changes, forming mineralized deposits and increasing soil strength. By setting the spray time interval and spray volume of the two reagents, the mineralized deposits can cover the soil layer surrounding the well wall.

[0058] The reaction formulas for the mineralization deposition produced by the two reagents are as follows:

[0059]

[0060] Step Six: Multiple Reinforcement

[0061] Before mining, steps four and five are repeated at certain intervals to form multiple layers of mineralized deposits, based on the required reinforcement strength. The time interval between two reinforcement processes is greater than the complete reaction time of the reagents, and the reinforcement process is repeated at least three times. Experiments have verified that calcium carbonate reaches its maximum strength after 25 layers of mineralized deposits.

[0062] As can be seen from the implementation, this invention innovatively uses the reaction of BPEI solution and modified nano-calcium carbonate dispersion to reinforce the soil layer around the overburden well wall through the mineralized deposition formed therefrom. It has the advantages of clear reinforcement process and significant effect, and can solve the problems of well wall instability and collapse in the current natural gas hydrate mining process, so as to achieve the goal of safe, stable and long-term sustainable mining of natural gas hydrates in the field.

[0063] It should be noted that the embodiments of this application are preferred for implementation and are not intended to limit the application in any way. The technical features or combinations of technical features described in the embodiments of this application should not be considered isolated; they can be combined with each other to achieve better technical effects. The scope of the preferred embodiments of this application may also include other implementations, and this should be understood by those skilled in the art to which the embodiments of this application pertain.

[0064] Techniques, methods, and apparatus known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and apparatus should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limiting. Therefore, other examples of exemplary embodiments may have different values.

[0065] The accompanying drawings in this application are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of this application, and are not intended to limit the implementation of this application. Any modifications to the structure, changes in the proportional relationships, or adjustments to the size, without affecting the effects and purposes that this application can produce, should fall within the scope of the technical content disclosed in this application.

[0066] The above description is merely a description of preferred embodiments of this application and is not intended to limit the scope of this application in any way. Any changes or modifications made by those skilled in the art based on the above-disclosed technical content should be considered as equivalent and valid embodiments and fall within the scope of protection of the technical solution of this application.

Claims

1. A method for reinforcing the well walls of marine combustible ice extraction wells using mineralized sedimentation, characterized in that: The method includes the following steps: Step 1: Nozzle Setup From top to bottom, the well pipe has several nozzles at regular intervals extending outwards from the well wall. The nozzles are circular, and multiple nozzles are evenly arranged around the nozzles to spray reinforcement agents in different directions outwards from the well wall. Step Two: Pipe Installation Several delivery pipelines are installed along the well perimeter inside the well wall. Each delivery pipeline is installed from top to bottom and connects to the nozzles on the adjacent well wall. The upper end of the delivery pipeline is connected to the storage tank on the mining platform through a high-pressure pump. It is used to deliver branched polyethyleneimine solution and modified nano calcium carbonate dispersion. The mining well and the delivery pipelines for delivering different solutions are independent to ensure that each solution is injected, controlled and delivered independently. The production well is installed in the predetermined reservoir on site according to the pre-designed plan, and all kinds of pipe interfaces are connected. Step 3: Reagent Preparation Before hydrate extraction, sufficient amounts of pre-prepared branched polyethyleneimine solution and modified nano-calcium carbonate dispersion are stored in the storage tank of the extraction platform. A branched polyethyleneimine solution with a mass concentration of 0.1% can be prepared by dissolving branched polyethyleneimine in deionized water. A modified nano-calcium carbonate dispersion with a mass concentration of 0.4% is prepared by dissolving calcium carbonate in deionized water after fatty acid modification. Step 4: Reagent Transfer and Injection The reagents are transported from the mining platform to the delivery pipeline used to transport the reagents. At certain time intervals and pressures, the two reagents are sprayed out from the nozzles by a high-pressure pump and enter the soil layer around the well wall. Each nozzle is equipped with a valve, and the opening of the corresponding valve, the pressure of the high-pressure pump and the spray speed of the nozzle are set according to different nozzle depths. Step 5: Mineralization and Consolidation The first sprayed reagent remains briefly in the soil pores. After the second reagent is sprayed, a reaction occurs, and mineralization and deposition occur in the soil pores. The two reagents react fully in the soil layer around the well wall to generate mineralized deposits and improve the soil strength. By setting the spraying time interval and spraying amount of the two reagents, the mineralized deposition range covers the soil layer around the well wall. Step Six: Multiple Reinforcement Before mining, based on the required reinforcement strength of the overlying layer, steps four and five are repeated after a certain interval to form multi-layered mineralized deposits to achieve the required reinforcement strength.

2. The method for reinforcing the well wall of marine combustible ice mining wells using mineralized sedimentation according to claim 1, characterized in that: Each nozzle is equipped with a protective device at the bottom to protect it. The protective device is tilted and located below the nozzle.

3. The method for reinforcing the well wall of marine combustible ice mining wells using mineralized sedimentation according to claim 1, characterized in that: In step two, the installation depth of the transport pipeline is determined based on the thickness of the overburden layer and the thickness of the natural gas hydrate reservoir obtained from engineering exploration, so that the length of the transport pipeline covers the depth of the overburden layer, and the number of transport pipelines is no less than three, with each transport pipeline evenly distributed around the well.

4. The method for reinforcing the well wall of marine combustible ice mining wells using mineralized sedimentation according to claim 1, characterized in that: In step six: multiple mineralization deposition reinforcements are performed according to the required reinforcement strength, with the time interval between two reinforcements being greater than the time for the reagent to fully react, and the reinforcement is repeated no less than three times.

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