Formation packing type hydrate production method and device

Abstract

The present application belongs to the technical field of natural gas hydrate exploitation engineering, and discloses a stratum filling type hydrate exploitation method and device. In the stratum filling type hydrate exploitation method, firstly, a production well is drilled to the junction of a hydrate reservoir and a free gas layer; then, a filling well is drilled to the junction position of an overburden layer and the hydrate reservoir; a production pipe column is respectively lowered into the production well and the filling well, the production well exploits gaseous hydrates of the free gas layer; a perforating and fracturing tool is lowered into the filling well to perform perforating and fracturing operation on the hydrate reservoir, forming a fracturing channel in the hydrate reservoir, solid hydrates of the hydrate reservoir decompose and continuously transport to the free gas layer through the fracturing channel, continuously supplying the production well for exploitation. The present application realizes the function of continuous and stable high-efficiency gas production of the production well, and solves the problems of insufficient energy supplement and insufficient stratum stability control.

Description

Technical Field

[0001] This invention relates to the field of natural gas hydrate extraction engineering technology, and in particular to a formation filling-type hydrate extraction method and apparatus. Background Technology

[0002] Natural gas hydrates are mainly distributed in terrestrial permafrost zones with harsh engineering conditions and in seabed sediments at depths exceeding 300 meters, with over 90% located in marine areas. Based on the structural characteristics of hydrate reservoirs, they can be classified into four levels: Class I hydrate layers contain free gas-water layers below them; Class II hydrate layers contain only aquifers below them; Class III hydrate layers contain no fluid layers below them; and Class IV seabed mudstone and shale contain extremely low amounts of hydrate particles with no development value. Under current extraction technology, Class I hydrate resources represent the most valuable reservoir type, with high extraction potential, and are the target ore body type for future large-scale commercial extraction of natural gas hydrates.

[0003] In the exploitation of first-order hydrate reservoirs, the transformation of hydrates from solid to gas requires the absorption of a large amount of heat. When the formation heat is insufficient, secondary hydrate formation occurs, leading to blockage of production pipelines and affecting the efficiency and capacity of further exploitation. Conversely, under suitable hydrate exploitation conditions, the extensive decomposition of hydrates alters the mechanical properties of seabed sediments, causing localized weak points at the bottom layer due to excessive weight. This can trigger large-scale geological collapses, landslides, natural gas leaks, and other natural disasters and environmental problems. Therefore, existing hydrate reservoir exploitation processes urgently need to address the issues of insufficient formation energy replenishment and formation stability control. Summary of the Invention

[0004] The purpose of this invention is to provide a method and apparatus for extracting hydrates by filling formations, so as to solve the problems of insufficient formation energy replenishment and formation stability control.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] This invention provides a formation-filling hydrate extraction method, wherein the formation, from top to bottom, comprises an upper overburden layer, a hydrate reservoir, a free gas layer, and a lower overburden layer; the formation-filling hydrate extraction method includes the following steps:

[0007] S1, Drill a production well such that the bottom of the production well is located at the boundary between the hydrate reservoir and the free gas layer;

[0008] S2, Drill a filling well, wherein the filling well is at a safe distance from the production well, and the filling well includes a horizontal section located at the boundary between the upper overburden and the hydrate reservoir;

[0009] S3, production tubing is run into the production well and the filling well respectively, and the production well extracts the gaseous hydrates from the free gas layer;

[0010] S4. A perforating fracturing tool is inserted into the filling well to perform perforating fracturing operations on the hydrate reservoir, forming a fracturing channel in the hydrate reservoir. The solid hydrate in the hydrate reservoir decomposes and is continuously transported to the free gas layer through the fracturing channel, continuously supplying the production well for extraction.

[0011] In some embodiments, in step S3, the production well is operated using a depressurization mining method, which causes the free gas layer to form a negative pressure state.

[0012] In some embodiments, during step S4, proppant material and hot seawater are continuously injected during the perforation fracturing operation to continuously promote the decomposition of solid hydrates in the hydrate reservoir.

[0013] In some embodiments, a plurality of filling wells are provided, and the plurality of filling wells are evenly spaced around the production well.

[0014] The present invention also provides a formation-filling hydrate extraction apparatus for implementing the formation-filling hydrate extraction method; the formation-filling hydrate extraction apparatus includes:

[0015] The production well has its bottom extending directly to the boundary between the hydrate reservoir and the free gas layer;

[0016] A filling well is located at a safe distance from the production well. The filling well includes a horizontal section, which is located at the boundary between the overlying layer and the hydrate reservoir.

[0017] A perforation fracturing tool is used to perform perforation fracturing operations on the hydrate reservoir, causing the solid hydrates in the hydrate reservoir to decompose into gaseous hydrates and forming a fracturing channel in the hydrate reservoir. The gaseous hydrates are continuously transported to the free gas layer through the fracturing channel to meet the continuous production of the production well.

[0018] In some embodiments, both the production well and the filling well are provided with a cementing assembly, the cementing assembly comprising:

[0019] Cementing casing, wherein the cementing casing is disposed in the open hole trajectory of the production well and the filling well;

[0020] Cementing sheath, wherein the cementing sheath is disposed between the cementing casing and the formation;

[0021] The production string is located inside the cementing casing, and the bottom end of the production string in the production well extends into the free gas layer for hydrate extraction; the production string in the filling well is used to fix the perforation fracturing tool and inject proppant and hot seawater.

[0022] In some embodiments, the perforation fracturing tools are provided in multiples, and the multiple perforation fracturing tools are evenly spaced along the horizontal section to form multiple fracturing channels in the horizontal section.

[0023] In some embodiments, a plurality of filling wells are provided, and the plurality of filling wells are evenly spaced around the production well.

[0024] In some embodiments, two filling wells are provided, and the two filling wells are symmetrically arranged on both sides of the production well.

[0025] In some embodiments, the production well is a vertical well, the filling well is a horizontal well, and the horizontal section of the filling well extends away from the production well in a horizontal direction.

[0026] The beneficial effects of this invention are:

[0027] The formation-filling hydrate extraction method provided by this invention places the bottom of the production well at the boundary between the hydrate reservoir and the free gas layer, enabling direct extraction of gaseous hydrates from the free gas layer. As extraction time progresses, the free gas layer forms a negative pressure state. By drilling a filling well and performing perforation fracturing into the hydrate reservoir through the filling well, the solid hydrates decompose into gaseous hydrates. Under the action of negative pressure, the decomposed gaseous hydrates replenish the free gas layer, thereby achieving a continuous, stable, and efficient gas production function for the production well, solving the problems of insufficient formation energy replenishment and insufficient formation stability control. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the formation-filling hydrate extraction device provided by the present invention;

[0029] Figure 2 yes Figure 1 A magnified structural diagram of region A in the middle.

[0030] In the picture:

[0031] 1. Production well; 2. Filling well; 3. Production tubing; 4. Cementing casing; 5. Cementing sheath; 6. Hydraulic perforation cavity; 7. Fracturing channel;

[0032] a. Seawater layer; b. Upper cover layer; c. Hydrate reservoir; d. Free gas layer; e. Lower cover layer. Detailed Implementation

[0033] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0034] In the description of this invention, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0035] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0036] In the description of this embodiment, the terms "upper," "lower," "left," and "right," etc., refer to the orientation or positional relationship shown in the accompanying drawings. They are used only for ease of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. In addition, the terms "first" and "second" are used only for distinction in description and have no special meaning.

[0037] The purpose of this invention is to provide a formation-filling hydrate extraction method and apparatus for extracting natural gas hydrates. Figure 1 and Figure 2 As shown, this embodiment takes the mining of the formation below seawater layer a as an example for detailed explanation. The formation, from top to bottom, consists of the upper overburden layer b, the hydrate reservoir c, the free gas layer d, and the lower overburden layer e.

[0038] The formation-filling hydrate extraction method includes the following steps:

[0039] S1, Drill production well 1. The bottom of production well 1 is located at the boundary between hydrate reservoir c and free gas layer d.

[0040] S2, Drill filling well 2, Filling well 2 is located at a safe distance from production well 1, Filling well 2 includes a horizontal section, The horizontal section is located at the junction of the upper overburden layer b and the hydrate reservoir c;

[0041] S3, production tubing 3 is run into production well 1 and filling well 2 respectively, and production well 1 is used to extract gaseous hydrates from free gas layer d;

[0042] This step is the cementing step. First, cementing casing 4 is run into the open hole trajectories of production well 1 and filling well 2, respectively. Then, cement is injected between the cementing casing 4 and the formation to form a cementing annulus 5. Finally, a production string 3 is run into the cementing casing 4, forming an annulus between the production string 3 and the cementing casing 4. The bottom of production well 1 is located at the boundary between the hydrate reservoir c and the free gas layer d. The production string 3 protrudes from the bottom of production well 1 and extends into the free gas layer d to directly extract free gas.

[0043] S4, a perforation fracturing tool is installed in the filling well 2 to perform perforation fracturing operations on the hydrate reservoir c, forming a fracturing channel 7 in the hydrate reservoir c. The solid hydrate in the hydrate reservoir c decomposes and is continuously transported to the free gas layer d through the fracturing channel 7, continuously supplying the production well 1 for exploitation.

[0044] The formation-filling hydrate extraction method provided by this invention places the bottom of production well 1 at the boundary between hydrate reservoir c and free gas layer d, enabling direct extraction of gaseous hydrates from free gas layer d. As extraction time progresses, free gas layer d forms a negative pressure state, inducing the decomposition of gaseous hydrates from the upper hydrate reservoir c to replenish resources in free gas layer d, thereby achieving continuous and stable high-efficiency gas production from production well 1. Subsequently, filling well 2 is drilled around production well 1, and perforation fracturing is performed in filling well 2 into hydrate reservoir c, causing solid hydrates to decompose into gaseous hydrates. Under negative pressure, the decomposed gaseous hydrates continuously replenish free gas layer d, thus achieving continuous and stable high-efficiency gas production from production well 1, solving the problems of insufficient formation energy replenishment and insufficient formation stability control. It should be noted that the safety distance between filling well 2 and production well 1 is set according to the actual conditions of the extraction site and has no fixed value, meeting both extraction efficiency and safety requirements during the extraction process.

[0045] In some embodiments, in step S3, production well 1 employs a depressurization extraction method to achieve a negative pressure state in the free gas layer d. Since the free gas layer d contains abundant free methane and water, stable production can be achieved according to the actual designed rate for hydrate extraction. The depressurization extraction method is existing technology. Continuous depressurization extraction in production well 1 can maintain the negative pressure state of the free gas layer d. During depressurization extraction, it is also necessary to comprehensively consider factors such as the stability of the free gas layer d, the formation sandy characteristics and stability of the hydrate reservoir c, the amount of hydrate decomposition and flow transmission rate in the horizontal section of the filling well 2 after perforation and fracturing operations, the safety of the extraction project, and the efficiency of processing and transporting produced gaseous methane, to design reasonable depressurization extraction values, thereby maintaining the continuous, stable, efficient, and economical extraction efficiency of production well 1.

[0046] In some embodiments, during step S4, proppant material and hot seawater are continuously injected during the perforation fracturing operation to continuously promote the decomposition of solid hydrates in the hydrate reservoir c.

[0047] The proppant material is large-mesh quartz sand. During the perforation fracturing operation, hydraulic perforation holes 6 are generated in the horizontal section of the filling well 2. Propant material is filled into the hydraulic perforation holes 6 to facilitate the establishment of fracturing channels 7, which supports the formation and improves formation stability. Seawater is heated to the temperature required for the project by the storage heating equipment to obtain hot seawater. The main function of hot seawater is to promote hydrate decomposition and replenish formation energy. Using the proppant material and hot seawater, some methane hydrates can be rapidly decomposed, enhancing the fracturing effect and forming a stable fracturing channel 7 in the hydrate reservoir c to connect the horizontal section of the filling well 2 and the free gas layer d, thereby providing methane gas and water to the free gas layer d.

[0048] In some embodiments, a plurality of filling wells 2 are provided, and the plurality of filling wells 2 are evenly arranged around the production well 1 at intervals. Preferably, two filling wells 2 are provided, symmetrically arranged on both sides of the production well 1.

[0049] In this invention, the main functions of the filling well 2 include two aspects. On the one hand, by modifying the hydrate reservoir c and using methods such as injecting hot seawater, the formation energy is continuously replenished, promoting the decomposition of solid hydrates in the hydrate reservoir c into gaseous hydrates (including methane gas and water). On the other hand, the supporting material filling process is carried out on the hydrate reservoir c to control the formation stability and establish a fracturing channel 7 to realize communication between the hydrate reservoir c and the free gas layer d, thereby continuously improving the production efficiency of the production well 1.

[0050] It should be further explained that before implementing the formation-filling hydrate extraction method of this invention, the steps of extraction site selection and well construction are also included. Extraction site selection refers to exploring the internal distribution of the underlying hydrate reservoir c with free gas, and determining the location information of the bottom of the overlying layer b, the top of the hydrate reservoir c, and the top of the free gas layer, so as to determine the drilling location and depth. Well construction refers to building an offshore extraction platform to drill production well 1 and deploying a drilling and production vessel to drill filling well 2. The offshore extraction platform is equipped with gas-liquid separation and storage equipment. The hydrate extracted from production well 1 is a gas-liquid mixture. After extraction, the gas-liquid mixture is first processed through a gas-liquid separation process to separate the formation water, and then undergoes reasonable environmental protection treatment to remove harmful heavy metals before reasonable regional discharge. The pure methane gas obtained after separation is stored in a gas storage tank for storage and transportation.

[0051] This invention also provides a formation-filling hydrate extraction apparatus for realizing a formation-filling hydrate extraction method; such as Figure 1 and Figure 2 The formation-filling hydrate extraction unit includes a production well 1, a filling well 2, and a perforation fracturing tool. The bottom of the production well 1 reaches the boundary between the hydrate reservoir c and the free gas layer d. The filling well 2 is located at a safe distance from the production well 1 and includes a horizontal section located at the boundary between the overlying layer b and the hydrate reservoir c. The perforation fracturing tool is lowered into the horizontal section to perform perforation fracturing operations. The perforation fracturing tool is used to perform perforation fracturing operations on the hydrate reservoir c, causing the solid hydrates in the hydrate reservoir c to decompose into gaseous hydrates. The gaseous hydrates are continuously transported to the free gas layer d to meet the continuous extraction needs of the production well 1.

[0052] The number of filling wells 2 can be multiple, and these filling wells 2 are evenly spaced around the production well 1. In this embodiment, two filling wells 2 are provided, symmetrically arranged on both sides of the production well 1. The safe distance between the filling wells 2 and the production well 1 needs to comprehensively consider the drilling and production safety of the drilling vessel and the formation stability and recovery rate during long-term mining. The two filling wells 2 can be mined simultaneously at one time, or additional filling wells 2 can be added as needed during hydrate mining. By setting up filling wells 2, perforation and fracturing can be performed on the hydrate reservoir c around the production well 1, causing the solid hydrate in the hydrate reservoir c to decompose into gaseous hydrate. Under the negative pressure of the free gas layer d, the gaseous hydrate is transported to the free gas layer d to meet the continuous mining needs of the production well 1. It can be understood that the perforation and fracturing operation is directed towards the hydrate reservoir c, which will form hydraulic perforation holes 6 in the hydrate reservoir c, thus serving as fracturing channels 7, facilitating the directional transfer and transport of the decomposed gaseous hydrate.

[0053] In some embodiments, both production well 1 and filling well 2 are equipped with cementing assemblies, which include cementing casing 4, cementing sheath 5, and production tubing string 3. The cementing casing 4 is respectively located in the open hole trajectory of production well 1 and filling well 2, and is arranged axially through production well 1 and filling well 2. The cementing sheath 5 is located between the cementing casing 4 and the formation, and is formed by injecting cement between the formation below seawater layer a and the cementing casing 4. The production tubing string 3 is located inside the cementing casing 4, and the bottom end of the production tubing string 3 in production well 1 extends into the free gas layer d for direct extraction from the free gas layer d. The production tubing string 3 in filling well 2 is used to fix the perforation fracturing tool and inject proppant and hot seawater.

[0054] This invention utilizes a filling well (2) to modify the hydrate reservoir c. A perforation fracturing tool is installed within the filling well (2) to inject proppant material and hot seawater for perforation fracturing operations. The proppant material, made of large-sized quartz sand, serves to establish fracturing channels (7) and support the formation within the hydrate reservoir c. It connects the horizontal section of the filling well (2) with the free gas layer (d) within the hydrate reservoir c, guiding the transport of decomposed methane gas and water to the overlying free gas layer (d). The continuously filling proppant material constantly replaces the formation positions left by the decomposed solid hydrate, achieving formation stabilization without additional procedures or measures. This results in a balanced and stable state of the hydrate reservoir c, improving the stability and safety of continuous reservoir modification operations. Hot seawater can promote hydrate decomposition and continuously replenish the heat energy lost by the formation due to hydrate decomposition, thus maintaining the hydrate reservoir C in a stable state of solid hydrate decomposition. In addition, the injection of hot seawater can prevent the secondary formation of hydrates in hydrate reservoir C, maintain the flow stability of fracturing channel 7, improve the fracturing and fracture initiation effect of hydrate reservoir C, and enhance the hydrate decomposition efficiency and migration rate of hydrate reservoir C.

[0055] In some embodiments, multiple perforation fracturing tools are provided, and these tools are evenly spaced along a horizontal section. The multiple perforation fracturing tools are spaced along the horizontal section of the filling well 2, ensuring that the hydrate reservoir c area covered by the horizontal section can obtain multiple uniform fracturing channels 7. This achieves uniform support and stable exploitation of the hydrate reservoir c, which helps ensure formation stability.

[0056] In some embodiments, the production well 1 is a vertical well arranged in the vertical direction, and the filling well 2 is a horizontal well, with the horizontal section of the filling well 2 extending away from the production well 1 in the horizontal direction.

[0057] In this embodiment of the invention, production well 1 is a vertical well, directly exploiting the free gas layer d. Compared with the conventional method of exploiting hydrate reservoir c, this method has the following advantages: First, it can reduce the amount and impact of formation sand entering the production tubing 3 during production, making it less likely to cause blockage in the production tubing 3 and reduce hydrate exploitation efficiency. Moreover, since no formation sand is carried out during exploitation, it is easier to separate the exploited hydrate mixture, further improving exploitation efficiency and economy. Second, it can reduce the phenomenon of secondary hydrate formation in the production tubing 3 during production. Since the hydrate reservoir c is continuously replenished with formation energy by filling well 2, the hydrate reservoir c around production well 1 is also in a stable state of solid hydrate decomposition into gaseous hydrate. Therefore, the temperature and pressure conditions for secondary hydrate formation will not occur in the production tubing 3, and a continuous and stable hydrate exploitation efficiency can be maintained.

[0058] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art will be able to make various obvious changes, readjustments, and substitutions without departing from the scope of protection of the present invention. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for exploiting hydrates by filling formations, wherein the formations, from top to bottom, are an upper overburden (b), a hydrate reservoir (c), a free gas layer (d), and a lower overburden (e); characterized in that, The formation-filling hydrate extraction method includes the following steps: S1, Drill a production well (1) such that the bottom of the production well (1) is located at the junction of the hydrate reservoir (c) and the free gas layer (d); S2, Drill a filling well (2), the filling well (2) is at a safe distance from the production well (1), the filling well (2) includes a horizontal section, the horizontal section is located at the junction of the upper overburden (b) and the hydrate reservoir (c); S3, production tubing (3) is installed in the production well (1) and the filling well (2) respectively, and the production well (1) is used to extract gaseous hydrates from the free gas layer (d); S4, a perforation fracturing tool is inserted into the filling well (2) to perform perforation fracturing operations on the hydrate reservoir (c), forming a fracturing channel (7) in the hydrate reservoir (c). The solid hydrate in the hydrate reservoir (c) decomposes, and as the mining time progresses, the free gas layer (d) forms a negative pressure state, inducing the gaseous hydrate decomposed in the upper hydrate reservoir (c) to be continuously transported directionally to the free gas layer (d) through the fracturing channel (7) to replenish resources and continuously supply them to the production well (1) for mining.

2. The method for extracting hydrates by formation filling according to claim 1, characterized in that, In step S3, the production well (1) is operated using a depressurization mining method, which causes the free gas layer (d) to form a negative pressure state.

3. The formation-filling hydrate extraction method according to claim 1, characterized in that, In step S4, during the perforation fracturing operation, support material and hot seawater are continuously injected to continuously promote the decomposition of solid hydrates in the hydrate reservoir (c).

4. The formation-filling hydrate extraction method according to claim 1, characterized in that, The filling wells (2) are provided in multiple locations, and the multiple filling wells (2) are evenly spaced around the production well (1).

5. A formation-filling hydrate extraction apparatus, used to implement the formation-filling hydrate extraction method according to any one of claims 1-4, characterized in that, The formation-filling hydrate extraction device includes: Production well (1), the bottom of which reaches the boundary between the hydrate reservoir (c) and the free gas layer (d); A filling well (2) is located at a safe distance from the production well (1). The filling well (2) includes a horizontal section located at the junction of the upper overburden layer (b) and the hydrate reservoir (c). A perforation fracturing tool is used to perform perforation fracturing operations on the hydrate reservoir (c) to decompose the solid hydrate in the hydrate reservoir (c) into gaseous hydrate and form a fracturing channel (7) in the hydrate reservoir (c). The gaseous hydrate is continuously transported to the free gas layer (d) through the fracturing channel (7) to meet the continuous production of the production well (1).

6. The formation-filling hydrate extraction device according to claim 5, characterized in that, Both the production well (1) and the filling well (2) are equipped with cementing assemblies, which include: Cementing casing (4), wherein the cementing casing (4) is located in the open hole trajectory of the production well (1) and the filling well (2); Cementing sheath (5), wherein the cementing sheath (5) is disposed between the cementing casing (4) and the formation; The production string (3) is located inside the cementing casing (4). The bottom end of the production string (3) in the production well (1) extends into the free gas layer (d) for hydrate extraction. The production string (3) in the filling well (2) is used to fix the perforation fracturing tool and inject support material and hot seawater.

7. The formation-filling hydrate extraction device according to claim 5, characterized in that, The perforation fracturing tool is provided in multiple ways, and the multiple perforation fracturing tools are evenly spaced along the horizontal section to form multiple fracturing channels (7) in the horizontal section.

8. The formation-filling hydrate extraction device according to claim 5, characterized in that, The filling well (2) is provided in multiple locations, and the multiple filling wells (2) are evenly spaced around the production well (1).

9. The formation-filling hydrate extraction device according to claim 8, characterized in that, There are two filling wells (2), which are symmetrically arranged on both sides of the production well (1).

10. The formation-filling hydrate extraction device according to claim 5, characterized in that, The production well (1) is a vertical well, and the filling well (2) is a horizontal well. The horizontal section of the filling well (2) extends away from the production well (1) in the horizontal direction.

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