A method for reservoir reconstruction of marine natural gas hydrate directional splitting grouting

Abstract

The application discloses a reservoir reconstruction method for marine natural gas hydrate directional fracturing and grouting, and belongs to the field of marine natural gas hydrate resource development. The method is used for the unconsolidated hydrate reservoir, a hydraulic rotary jet cutting device is used to make a pre-fracture in the process of horizontal well completion, then the fracturing slurry and sand control slurry are injected in stages, and then the segmented directional fracturing and grouting of the hydrate reservoir is realized. The seepage passage is formed after the fracturing slurry is consolidated, the seepage condition of the natural gas hydrate reservoir is improved through the large-scale volume reconstruction, and the mining efficiency in the mining process is improved.

Description

A reservoir stimulation method for marine natural gas hydrates by directional fracturing grouting Technical Field

[0001] This invention belongs to the field of marine natural gas hydrate resource development, specifically, it relates to a reservoir stimulation method for directional fracturing grouting of marine natural gas hydrates. Background Technology

[0002] Natural gas hydrate is a cage-like compound formed by water and gas molecules under low temperature and high pressure. 1m 3 The decomposition of natural gas hydrates can release approximately 164 m³. 3 Natural gas. The main methods for extracting natural gas hydrates include depressurization, heating, chemical inhibitor injection, and CO2 replacement. Depressurization is an effective method for developing and utilizing marine natural gas hydrates, but due to poor reservoir permeability, the gas production from pilot production has not yet reached the standards for commercial development. Reservoir stimulation is widely used in unconventional oil and gas development. In low-permeability reservoirs, fracturing and volumetric stimulation can achieve efficient development of resources. Marine natural gas hydrates are mainly found in unconsolidated seafloor sediments, particularly in clayey silt reservoirs. These reservoirs have high clay content and low overall strength, making directional fracturing difficult and hindering large-scale reservoir stimulation. This is a significant factor hindering the commercial development of natural gas hydrates. Summary of the Invention

[0003] To address the technical challenge of low consolidation strength in marine natural gas hydrate reservoirs, which makes directional fracturing and volumetric modification difficult, this invention proposes a reservoir modification method using directional fracturing grouting for marine natural gas hydrates. This method aims to enable large-scale modification of weakly consolidated hydrate reservoirs and promote the safe and efficient development and utilization of marine natural gas hydrates.

[0004] The technical solution adopted by the present invention to achieve the above objectives is as follows: The present invention proposes a reservoir stimulation method for directional fracturing grouting of marine natural gas hydrates. It is a reservoir stimulation method for directional fracturing grouting of weakly consolidated marine natural gas hydrate reservoirs. According to the specific conditions of the burial depth, strike and dip angle of the marine natural gas hydrate reservoir, the appropriate drilling location and horizontal well completion method are selected.

[0005] After determining the well structure, suction piles are installed at the drilling location to ensure the stability and safety of the strata around the well, and surface casing is used to maintain the stability of the seabed surface strata.

[0006] When drilling horizontally into hydrate reservoirs, a hydraulic jet fracturing device is used to create pre-fractures in sections within the hydrate reservoir. The specific steps for creating pre-fractures using a hydraulic jet fracturing device include the following:

[0007] Step S1: The hydraulic jet grouting device is located inside the drill bit and advances with the drill bit in the hydrate reservoir;

[0008] Step S2: After drilling to the target position, the hydraulic jet slit cutting device remains in the original position, and the drill bit is retracted a certain distance.

[0009] Step S3: Use a hydraulic jet grouting device to hydraulically cut grooves to create pre-fractures in the hydrate reservoir;

[0010] Furthermore, after drilling is completed, coiled tubing is run into the borehole, and bridge plugs are arranged in sections within the coiled tubing. Sectional hydraulic perforation and grouting are then performed, followed by the sequential injection of fracturing slurry and sand-control slurry. The injected fracturing slurry extends along the pre-fractured areas, while the sand-control slurry fills the space between the fracturing slurry and the perforations. After solidification, the fracturing slurry forms a high-strength seepage channel with a permeability greater than 1000 mD, and the sand-control slurry solidifies to form a sand-control layer.

[0011] Furthermore, in the subsequent depressurization extraction process, the perforation serves as the extraction hole, through which the natural gas generated by the decomposition of hydrates is transported to the coiled tubing and wellhead, thus realizing depressurization extraction of marine natural gas hydrates.

[0012] In the process of creating pre-fractures in hydrate reservoirs in stages using a hydraulic jet grouting device, the drill bit is retracted 0.5m to 1m, and the hydraulic jet grouting device rotates 360° along the borehole axis to cut pre-fractures in the hydrate reservoir using water jets.

[0013] During hydraulic cutting, the angle between the central axis of the pre-fracture and the horizontal well is less than 90°, so that the hydraulic jet and the returning sand-laden fluid are not on the same straight line.

[0014] The fracturing grout is composed of fine-grained volcanic rock, fine-grained zeolite, silicate cement, polyacrylate solution, aluminum sulfate, and diethanolamine, with the maximum particle size of the fine-grained volcanic rock and fine-grained zeolite being less than 5 mm. The mass fraction ratio of each component in the fracturing grout is as follows: 30% fine-grained volcanic rock, 20% fine-grained zeolite, 30% silicate cement, 10% polyacrylate solution, 5% aluminum sulfate, and 5% diethanolamine.

[0015] The anti-sand grout is composed of gravel, silicate cement, polyacrylate solution, aluminum sulfate and diethanolamine. The maximum particle size of the gravel is less than 5 mm. The mass fraction ratio of each component of the anti-sand grout is: gravel 40%, silicate cement 40%, polyacrylate solution 10%, aluminum sulfate 5% and diethanolamine 5%.

[0016] Through the above design scheme, the present invention can bring the following beneficial effects: The segmented fracturing grouting technology of the present invention, combined with horizontal well technology, achieves directional hydrate reservoir stimulation based on hydraulic jet fracturing, overcoming the problem of difficulty in controlling the direction of fracture propagation in unconsolidated hydrate reservoirs; it utilizes fracturing pressure reduction to enhance and increase the permeability of hydrate reservoirs, and the anti-sand grout prevents wellbore blockage. Under the comprehensive reservoir stimulation mode of horizontal well technology, hydraulic jet fracturing technology, fracturing grout, and anti-sand grout system, large-scale reservoir stimulation and stable high-yield production of marine hydrate formations can be achieved. Attached Figure Description

[0017] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and are used to understand the invention. They do not constitute an improper limitation of the invention. In the drawings:

[0018] Figure 1 is a schematic diagram of hydraulic jet grouting.

[0019] Figure 2 is a schematic diagram of segmented split grouting;

[0020] The markings in the diagram are as follows: 1-Drilling vessel; 2-Suction pile; 3-Surface casing; 4-Drill rod; 5-In-hole booster; 6-Hydraulic jet grouting device; 7-High-pressure water jet pipeline; 8-Drill bit; 9-Pre-fracture; 10-Continuous tubing; 11-High-pressure grouting pipe; 12-Bridge plug; 13-Perforation; 14-Fracturing grout; 15-Anti-sand grout. Detailed Implementation

[0021] To provide a more detailed description of the technical features, objectives, and effects of the present invention, embodiments of the invention are now further described with reference to Figures 1 and 2. The contents shown in the accompanying drawings are for illustrative purposes only and do not represent the actual scale or dimensions of the methods described herein. To avoid obscuring the essence of the invention, well-known methods, processes, procedures, and components are not described in detail.

[0022] As shown in Figures 1 and 2, a reservoir stimulation method for directional fracturing grouting of marine natural gas hydrates addresses the characteristics of marine natural gas hydrate reservoirs, such as unconsolidated lithology, high clay content, and strong plasticity. A hydraulic jet fracturing device 6 is used to create pre-fractures 9 during well formation. Subsequently, fracturing grout 14 and anti-sand grout 15 are injected in stages, thereby achieving segmented directional fracturing grouting of the hydrate reservoir. The solidified body formed after the fracturing grout 14 solidifies has higher strength and permeability than the original formation. Through large-scale volumetric modification, the seepage conditions of the natural gas hydrate reservoir are improved, enhancing the extraction efficiency during the extraction process.

[0023] The specific implementation method is as follows:

[0024] As shown in Figure 1, the first step is to perform well drilling and cementing operations in the vertical section. Suction piles 2 are installed at the pre-drilled locations to ensure the stability of the formation around the vertical well section.

[0025] The second step is to run surface casing 3 into the well after completing the seabed surface drilling to cement the well, in order to ensure the well stability during drilling, fracturing grouting, and subsequent hydrate extraction.

[0026] The third step involves drilling the horizontal well section. The hydraulic jet grouting device 6 advances along with the drill bit 8. When it reaches the preset fracturing and grouting position, the hydraulic jet grouting device 6 remains in its original position, and the drill bit 8 is retracted 0.5–1 m. The hydraulic jet grouting device 6 is then activated, delivering high-pressure water through the high-pressure water jet pipeline 7. The hydraulic jet grouting device 6 rotates 360° along the borehole axis, using the water jet to cut out the pre-fracture 9. After completing the hydraulic cutting operation of this section of pre-fracture 9, the hydraulic jet grouting device 6 follows the drill bit 8 again to begin the next stage of pre-fracture 9 cutting.

[0027] During hydraulic cutting, in order to increase the effective length of the pre-crack 9, an in-hole booster 5 is used in conjunction with a booster pump on the deck of the drilling vessel 1 to increase the pressure of the water jet.

[0028] During hydraulic cutting, the angle between the central axis of the pre-fracture 9 and the horizontal well is less than 90°, so that the hydraulic jet and the returning sand-laden fluid are not on the same straight line, effectively increasing the effective range of the water jet.

[0029] The purpose of creating pre-cracks using hydraulic jets is to guide the movement of grout during subsequent fracturing grouting, thereby enabling directional modification of weakly consolidated hydrate formations.

[0030] When injecting splitting grout 14 and anti-sand grout 15, the in-hole booster 5 is used in conjunction with the booster pump on the deck of the drilling vessel 1 to ensure the grouting pressure.

[0031] As shown in Figure 2, in the fourth step, after completing the pre-fracture 9 cutting operation of the horizontal well section, the drill bit 8 and drill pipe 4 are pulled out and the coiled tubing 10 is lowered in.

[0032] In the fifth step, the first bridge plug 12 is inserted into the end of the coiled tubing 10. Using the high-pressure grouting pipe 11, a hydraulic perforation process is used to form a perforation 13 at the pre-fracture 9. Then, the fracturing grout 14 is injected. The fracturing grout 14 expands along the direction of the pre-fracture 9 to achieve fracturing grouting. Finally, the anti-sand slurry 15 is injected through the high-pressure grouting pipe 11. After the fracturing grout 14 and the anti-sand slurry 15 solidify, the subsequent pre-fractures 9 are fracturing grouting in sequence. After the fracturing grouting operation is completed, the perforation 13 serves as a gas-liquid extraction channel. The gas and liquid in the hydrate reservoir are transported to the coiled tubing 10 through the perforation 13.

[0033] It should be noted that the drilling vessel 1, suction pile 2, surface casing 3, drill rod 4, in-hole booster 5, hydraulic jet grouting device 6, high-pressure water jet pipeline 7, drill bit 8, pre-splitting, coiled tubing 10, high-pressure grouting pipe 11, and bridge plug 12 mentioned in this invention are all commonly used equipment in the existing drilling engineering field.

[0034] The fracturing grout 14 of this invention is composed of fine-grained volcanic rock, fine-grained zeolite, silicate cement, polyacrylate solution, aluminum sulfate, and diethanolamine. The fine-grained volcanic rock and fine-grained zeolite have a maximum particle size of less than 5 mm. They provide seepage channels by utilizing the porous channels of the volcanic rock and zeolite themselves and the gaps between the particles, and are the main components affecting the permeability of the fracturing grout 14 after consolidation. Silicate cement and polyacrylate solution are used as reinforcing agents and adhesives, respectively. Aluminum sulfate and diethanolamine are used as setting accelerators. The mass fraction ratio of each component is as follows: fine-grained volcanic rock 30%, fine-grained zeolite 20%, silicate cement 30%, polyacrylate solution 10%, aluminum sulfate 5%, and diethanolamine 5%.

[0035] The anti-sand slurry 15 of this invention is composed of gravel, silicate cement, polyacrylate solution, aluminum sulfate, and diethanolamine. The gravel has good gradation, with a maximum particle size of less than 5 mm, and is the main component for sand control. Silicate cement and polyacrylate solution serve as reinforcing agents and adhesives, respectively; aluminum sulfate and diethanolamine serve as setting accelerators. The mass fraction ratio of each component is as follows: gravel 40%, silicate cement 40%, polyacrylate solution 10%, aluminum sulfate 5%, and diethanolamine 5%. Unlike the splitting slurry 14, the anti-sand slurry 15 has a higher proportion of gravel, resulting in a lower overall strength after solidification compared to the splitting slurry 14. Its main function is sand control.

[0036] Marine natural gas hydrates are primarily found in incompletely consolidated clayey silt on the seabed and represent a potential clean alternative energy source. Offshore trial production experience indicates that depressurization is an economically effective method for hydrate extraction; however, low reservoir permeability is a major factor hindering the commercial development of hydrate resources. Reservoir stimulation, creating fractures and fracture networks in the original formation, is a crucial means to improve reservoir permeability and increase extraction efficiency, and also represents a major technical challenge in the development of marine natural gas hydrate resources.

[0037] In response to the characteristics of subsea hydrate reservoirs, this invention proposes a method for reservoir stimulation through directional fracturing grouting. First, during drilling, pre-fractures 9 are formed in the hydrate reservoir by hydraulic jet grouting. After running coiled tubing 10, perforations 13 are formed directionally. Then, grout is injected into the pre-fractures 9 in segments through the perforations 13, achieving directional fracturing grouting along the direction of the pre-fractures 9. After the grout is completely solidified, a high-strength, highly permeable blocky solidified body is formed, thus completing the directional stimulation of the hydrate reservoir.

[0038] The reservoir stimulation method for directional fracturing grouting of marine natural gas hydrates proposed in this invention enhances the strength of the hydrate reservoir by forming a skeleton structure after the grout solidifies, ensuring the stability of the formation during the extraction process. The highly permeable solidified body improves the seepage conditions of the hydrate reservoir, which is conducive to gas production during depressurization extraction. This method can provide technical support for the safe and efficient development of marine natural gas hydrates.

Claims

1. A method for reservoir stimulation of marine natural gas hydrates by directional fracturing grouting, the method being applied to large-scale stimulation of weakly consolidated hydrate reservoirs, characterized in that, include: When drilling horizontal wells into hydrate reservoirs, hydraulic jet fracturing devices are used to create pre-fractures in sections within the hydrate reservoirs. After pre-fractures are formed, coiled tubing is run into the borehole. Bridge plugs are arranged in sections within the coiled tubing, and perforations are formed in sections using hydraulic perforation technology. Subsequently, fracturing grout and anti-sand grout are injected sequentially. The injected fracturing grout extends along the pre-fractures, and the anti-sand grout fills the space between the fracturing grout and the perforations. After the fracturing grout solidifies, it forms a seepage channel, and after the anti-sand grout solidifies, it forms an anti-sand layer. This completes the directional fracturing and large-scale modification of the weakly consolidated hydrate reservoir. The process of creating pre-fractures in the hydrate reservoir in sections using a hydraulic jet grouting device specifically includes the following steps: Step S1: The hydraulic jet grouting device is located inside the drill bit and drills along with the drill bit; Step S2: When the preset fracturing grouting position is reached, the hydraulic jet grouting device remains in its original position, and the drill bit is retracted a predetermined distance; Step S3: Using… The hydraulic jet grouting device creates pre-fractures in the hydrate reservoir using hydraulic cutting. Step S4: After completing the hydraulic cutting of this pre-fracture section, the hydraulic jet grouting device follows the drill bit again to drill and carry out the next stage of pre-fracture cutting. During the segmented creation of pre-fractures in the hydrate reservoir using the hydraulic jet grouting device, the drill bit is retracted 0.5m to 1m, and the hydraulic jet grouting device rotates 360° along the borehole axis, using water jets to cut pre-fractures in the hydrate reservoir. During hydraulic cutting, the angle between the central axis of the pre-fracture and the horizontal well is less than 90°, so that the hydraulic jet and the returning sand-bearing fluid are not on the same straight line. The fracturing slurry is composed of fine-grained volcanic rock, fine-grained zeolite, silicate cement, polyacrylate solution, aluminum sulfate, and diethanolamine, and the maximum particle size of the fine-grained volcanic rock and fine-grained zeolite is less than 5 mm. mm; the anti-sand slurry is composed of gravel, silicate cement, polyacrylate solution, aluminum sulfate and diethanolamine, and the maximum particle size of the gravel is less than 5 mm.

2. The reservoir stimulation method for marine natural gas hydrate directional fracturing grouting according to claim 1, characterized in that, Before drilling into the hydrate reservoir using a horizontal well, the drilling location and horizontal well completion method are selected based on the depth, strike, and dip angle of the marine natural gas hydrate reservoir. After determining the well structure, suction piles are installed at the drilling location. After completing the seabed surface drilling, surface casing is run into the well for cementing.

3. The reservoir stimulation method for marine natural gas hydrate directional fracturing grouting according to claim 1, characterized in that, The mass fraction ratio of each component in the splitting grout is as follows: 30% fine-grained volcanic rock, 20% fine-grained zeolite, 30% silicate cement, 10% polyacrylate solution, 5% aluminum sulfate, and 5% diethanolamine.

4. The reservoir stimulation method for marine natural gas hydrate directional fracturing grouting according to claim 1, characterized in that, The mass fraction ratio of each component in the anti-sand mortar is as follows: gravel 40%, silicate cement 40%, polyacrylate solution 10%, aluminum sulfate 5%, and diethanolamine 5%.

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