Method for achieving multiple purposes of coal bed gas horizontal well

Abstract

The invention belongs to the technical field of coal bed gas exploitation, and particularly relates to a method for achieving multiple purposes of a coal bed gas horizontal well. Firstly, a horizontal well is constructed in a coal seam, staged fracturing is conducted to increase permeability, coal bed gas ground extraction is achieved, when the coal bed gas yield cannot reach the economic recoverable condition, coal underground gasification is conducted through the horizontal well, and finally carbon dioxide obtained after gasification separation or other output is injected for storage through underground residual coal and coal cinder gaps. Multiple purposes of the coal bed gas horizontal well are achieved; through one-well multi-stage utilization, the functions of coal bed gas extraction, coal underground gasification, carbon dioxide storage and the like are achieved step by step, and the comprehensive cost is reduced by 40% or above.

Description

Technical Field

[0001] The present invention belongs to the technical field of coalbed methane extraction, and particularly relates to a method for multi-purpose use of a single horizontal well for coalbed methane. Background Art

[0002] For deep coal seams and thin coal seams, especially deep coal seams with a permeability < 1 mD (burial depth > 800 meters) and thin coal seams with a thickness < 1.5 meters, many challenges will be faced during mining, such as greater mining difficulty, which makes the mining operation have high technical requirements and complex construction, increasing the mining cost; at the same time, the economic benefits of these two types of coal seams are often not high, and in some cases, they are not even directly exploitable, resulting in low resource utilization rate. Summary of the Invention

[0003] The present invention aims to solve the problems of greater mining difficulty, low economic benefits or direct non-exploitability of deep coal seams and thin coal seams.

[0004] The present invention provides the following technical solution: A method for multi-purpose use of a single horizontal well for coalbed methane. First, a horizontal well is constructed in the coal seam, and fracturing is carried out in sections to increase permeability to achieve surface extraction of coalbed methane. When the coalbed methane production cannot reach the economically recoverable condition, underground coal gasification is implemented using the horizontal well. Finally, carbon dioxide is injected for sequestration by utilizing the voids of residual coal and coal cinder underground, realizing the multi-purpose use of the horizontal well for coalbed methane.

[0005] Further, an L-shaped horizontal well is constructed during the surface extraction stage of coalbed methane, and a vertical well is constructed later to connect with the tail end of the L-shaped horizontal well to form a U-shaped horizontal well for underground coal gasification.

[0006] Further, the L-shaped horizontal well has a two-opening or three-opening wellbore structure, the horizontal section is cased but not cemented, and the section from the wellhead to the landing point of the horizontal section is cemented. The vertical well has a two-opening or three-opening wellbore structure, the whole well is cemented, and the coal seam section is caved and completed.

[0007] Further, after the drilling construction of the L-shaped horizontal well in the coal seam is completed, segmented perforation + large-scale fracturing is adopted to increase the permeability of the coal seam. After a progressing cavity pump is lowered into the L-shaped horizontal well or a barrel pump is lowered into the vertical well, coalbed methane is extracted on the ground, and nitrogen or carbon dioxide is injected later to displace the residual coalbed methane.

[0008] Further, the underground coal is burned under control, injected from the vertical well and produced from the L-shaped horizontal well respectively, and combustible gases are generated through the thermal and chemical effects on the coal, and available gases such as hydrogen and carbon monoxide are separated on the ground.

[0009] Furthermore, after the gasification is completed, high-strength cement is used to seal the vertical well in advance. After the carbon dioxide separated from the gasification or other outputs is captured and liquefied, it is injected into the voids of the coal seam residues deep underground through the L-shaped horizontal well, and the carbon dioxide is sealed by utilizing the permeability and sealing property of the formation.

[0010] Furthermore, after the wellhead pressure of the L-shaped horizontal well drops to atmospheric pressure, the entire well section of the L-shaped horizontal well is sealed with high-strength cement, and a cement pier is built and marked after covering the wellhead on the ground.

[0011] Furthermore, the longwall gasification technique or the controlled-retreat gas injection point gasification technique is adopted for underground coal gasification.

[0012] Furthermore, the length of the horizontal section of the L-shaped horizontal well in the coal seam is ≥800 m, and the well diameter is ≥120 mm.

[0013] Furthermore, before the carbon dioxide injection, the coal cinder layer is subjected to pickling and permeability enhancement treatment with a 5% - 10% HCl solution.

[0014] Compared with the prior art, the advantages of the present invention are as follows:

[0015] This method realizes the synergistic effect of coalbed methane development, clean energy production and carbon emission reduction, and the comprehensive economic benefit is increased by more than 30%. The biggest purpose of the multi-purpose use of the coalbed methane horizontal well is to ensure the simultaneous realization of multiple benefits such as energy, environmental protection and economy.

[0016] Surface extraction of coalbed methane can reduce the coal seam gas content. Coalbed methane is also an unconventional energy source. Surface extraction can greatly supplement the natural gas gap, generate considerable economic benefits, and reduce the greenhouse effect of methane. The coalbed methane recovery rate is increased to 40% - 50% (the traditional method < 30%);

[0017] Underground coal gasification can reduce the costs of coal mining, transportation, etc., and realize the maximization of resource utilization. The hydrogen produced by underground coal gasification is a strategic energy source, meeting the current national needs. The single-well syngas production capacity is ≥5×10 6 m 3 , the hydrogen production ratio is > 50%. A downhole temperature-pressure monitoring system is set up during the gasification stage, and nitrogen is automatically injected to extinguish the fire when the limit is exceeded. The syngas is desulfurized by a ground purification device (H2S < 10 ppm), and the CO2 capture rate is > 95%;

[0018] After the gasification is completed, underground carbon dioxide sequestration is carried out, which can effectively reduce the carbon dioxide emissions after gasification separation or other outputs, reduce the greenhouse effect, and the CO2 sequestration cost is reduced to 100 yuan / ton (the traditional geological sequestration > 200 yuan / ton);

[0019] Compared with the current horizontal wells, it can realize the function of multi - use of one well, save engineering costs, and the full - life - cycle benefits include coal - bed methane sales, hydrogen production and carbon trading subsidies, with the payback period < 5 years. Description of the Drawings

[0020] Figure 1 It is a schematic diagram of an L - shaped horizontal well;

[0021] Figure 2 It is a schematic diagram of a U - shaped horizontal well;

[0022] Figure 3 It is a schematic diagram of carbon dioxide sequestration;

[0023] Figure 4 It is a schematic diagram of the end of carbon dioxide sequestration.

[0024] In the figure: 1 - L - shaped horizontal well; 2 - ground; 3 - coal seam; 4 - vertical well; 5 - carbon dioxide; 6 - cement pier. Detailed Implementation Manner

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following - described drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0026] As Figures 1 to 4 shown: A method for multi - use of one coal - bed methane horizontal well. First, construct a horizontal well in the coal seam, and perform staged fracturing to increase permeability to realize surface extraction of coal - bed methane. When the coal - bed methane production cannot reach the economically recoverable condition, use the horizontal well to implement underground coal gasification. Adopt the long - wall gas - flow gasification technology or the controlled - retreat gas - injection point gasification technology for underground coal gasification. After gasification, finally, use the voids of the remaining underground coal and coal cinder to inject carbon dioxide separated from gasification or other produced carbon dioxide for sequestration, realizing the multi - use of the coal - bed methane horizontal well.

[0027] During the surface extraction stage of coal - bed methane, construct an L - shaped horizontal well, and later construct a vertical well to connect with the tail end of the L - shaped horizontal well to form a U - shaped horizontal well for underground coal gasification.

[0028] Construction of the L - shaped horizontal well: The horizontal section length of the L - shaped horizontal well in the coal seam is ≥800 m, and the well diameter is ≥120 mm; The L - shaped horizontal well has a two - open or three - open wellbore structure. The horizontal section is cased but not cemented, and the section from the wellhead to the landing point of the horizontal section is cemented. The vertical well has a two - open or three - open wellbore structure, and the whole well is cemented, and the coal - seam section is cavern - completed.

[0029] After the drilling construction of the L-shaped horizontal well is completed in the coal seam, staged perforation + large-scale fracturing is adopted to improve the coal seam permeability. After a progressing cavity pump is installed in the L-shaped horizontal well or a barrel pump is installed in the vertical well, coalbed methane is extracted on the ground, and nitrogen or carbon dioxide is injected later to displace the residual coalbed methane.

[0030] For coalbed methane extraction, conventional extraction processes (including drainage, pressure reduction, desorption, diffusion, seepage, gas production, etc.) are used, combined with staged perforation large-scale fracturing technology to enhance the diversion capacity. The half-length of the fracture is ≥150 m, and the proppant concentration is ≥5 kg / m 2 , the fracture conductivity is ≥30 D·cm. After installing the production equipment, coalbed methane is extracted on the ground, and nitrogen or carbon dioxide is injected later to displace the residual gas, increasing the recovery rate to over 40% and achieving the connection between extraction and gasification.

[0031] The coal underground is burned under control, injected from the vertical well and produced from the L-shaped horizontal well respectively. Combustible gases are generated through the thermal and chemical effects on the coal, and available gases such as hydrogen and carbon monoxide are separated on the ground.

[0032] By controlling the oxygen / steam injection parameters (oxygen concentration 30%-50%, temperature 800-1200 °C), using the backward gas injection point technology with a gas injection point backward rate of 0.5-1.5 m / d, the calorific value of the synthesis gas is ≥8 MJ / m 3 , the gasification efficiency is ≥70%, the proportion of H2 in the synthesis gas is ≥50%, the temperature of the coal slag layer after gasification is >200 °C, and the heat expansion effect can be used to enhance the adsorption capacity when injecting CO2, achieving the coordination of gasification and sequestration.

[0033] After gasification, high-strength cement is used to plug the vertical well in advance. After the carbon dioxide separated by gasification or other produced carbon dioxide is captured and liquefied, it is injected into the voids of the coal residues deep underground from the L-shaped horizontal well, and the carbon dioxide is sequestered using the permeability and sealing of the formation. Before injecting carbon dioxide, pickling and permeability enhancement treatment is carried out on the coal slag layer using a 5%-10% HCl solution; the sequestration capacity is ≥100,000 tons of CO2 / well, and supercritical CO2 (pressure ≥7.38 MPa) is injected from the horizontal well using the voids formed after gasification (porosity ≥15%), and the sequestration efficiency is >90%.

[0034] After the wellhead pressure of the L-shaped horizontal well drops to atmospheric pressure, the entire well section of the L-shaped horizontal well is plugged with high-strength cement. The high-strength cement uses a cement-gel composite plugging material, which is composed of nanoscale silicate cement and polymer gel in a ratio of 3:1, with a compressive strength ≥35 MPa and a permeability ≤1×10 -5 mD. The entire well section is cemented to plug the horizontal well, and after covering the wellhead on the ground, a cement pier is built and marked to ensure long-term sealing.

[0035] The present invention ingeniously utilizes horizontal wells to achieve the function of multi - purpose use of a single well, significantly improving the resource utilization efficiency and expanding the development benefits.

[0036] First, construct an L - shaped horizontal well in the target coal seam, and then carry out staged fracturing operations. By reasonably controlling the fracturing parameters and processes, the permeability of the coal seam is effectively increased, thus creating good conditions for the smooth extraction of coalbed methane and realizing the efficient surface extraction of coalbed methane. This surface extraction method not only improves the recovery rate of coalbed methane but also can timely remove the gas in the coal seam, effectively reducing the safety risks during the coal gasification process.

[0037] When the production of coalbed methane cannot meet the economically recoverable conditions, the present invention further utilizes the pre - constructed L - shaped horizontal well to implement underground coal gasification. During the production process, advanced and mature gasification technologies such as long - wall gas flow method gasification technology and controlled retreat gas injection point gasification technology can be flexibly adopted according to specific geological conditions and production requirements. These technologies can ensure the efficient and complete gasification of coal underground, convert solid coal into utilizable coal gas resources, and realize the clean and efficient utilization of coal resources.

[0038] After the completion of underground coal gasification, make full use of the voids of residual coal and coal cinder underground, and inject carbon dioxide after gasification separation or other produced carbon dioxide for sequestration. This sequestration method can not only effectively reduce the emission of carbon dioxide into the atmosphere, alleviate the greenhouse effect, but also realize the further utilization of underground space. Through the comprehensive design and efficient utilization of the L - shaped horizontal well, the multi - purpose use of a single well from coalbed methane extraction, underground coal gasification to carbon dioxide sequestration is realized, which not only improves the comprehensive utilization rate of coal resources but also brings good environmental and social benefits, providing an innovative comprehensive solution for the field of clean and efficient utilization of coal and carbon emission reduction.

[0039] Example: Deep coal seam (burial depth 1200 meters)

[0040] (1) Construct an L - shaped horizontal well and a vertical well. The horizontal section of the L - shaped horizontal well is 1000 meters long, and the screen pipe diameter is 139.7 mm;

[0041] (2) The L - shaped horizontal well adopts the extraction process of "segmented perforation + hydraulic fracturing", the half - length of the fracture is 180 meters, and the daily gas production ≥ 8000 m 3 ;

[0042] (3) When the production drops to 500 m3 / d, switch to backward gasification (the oxygen injection rate of the vertical well is 200 m 3 / h), and the proportion of H2 in the syngas produced by the L - shaped horizontal well is 55%;

[0043] (4) After coal gasification, seal the vertical well, and inject liquid CO2 into the cinder layer through the L - shaped horizontal well, with a sequestration capacity of 120,000 tons;

[0044] (5) After plugging the L-shaped horizontal well, the wellbore permeability < 1 × 10 -6 mD.

[0045] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for multi-purpose coalbed methane horizontal well, characterized by: First, construct horizontal wells in the coal seams, perform staged fracturing to increase permeability, and realize surface extraction of coalbed methane. When the coalbed methane production cannot reach economically viable conditions, use horizontal wells to implement underground coal gasification. Finally, use the gaps between underground residual coal and coal ash to inject carbon dioxide for storage, thus realizing multiple uses of one coalbed methane horizontal well.

2. The method for multi-purpose coalbed methane horizontal well according to claim 1, characterized in that: During the surface extraction stage of coalbed methane, an L-shaped horizontal well is constructed, and later a vertical well is constructed to connect with the tail end of the L-shaped horizontal well to form a U-shaped horizontal well for underground coal gasification.

3. The method for multi-purpose coalbed methane horizontal well according to claim 2, characterized in that: The L-type horizontal well has a two-opening or three-opening wellbore structure. The horizontal section is completed with casing but not cemented, and cementing is carried out from the wellhead to the landing point of the horizontal section. The vertical well has a two-opening or three-opening wellbore structure, cementing is carried out throughout the well, and the coal seam section is completed with caves.

4. The method for multi-purpose coalbed methane horizontal well according to claim 3, characterized in that: After the L-type horizontal well is drilled in the coal seam, segmented perforation + large-scale fracturing is used to improve the permeability of the coal seam. After a screw pump is lowered into the L-type horizontal well or a whole-barrel pump is lowered into the vertical well, coalbed methane is extracted from the ground, and nitrogen or carbon dioxide is injected later to displace the residual coalbed methane.

5. The method for multi-purpose coalbed methane horizontal well according to claim 4, characterized in that: The underground coal is burned in a controlled manner, injected from vertical wells and produced from L-shaped horizontal wells. Combustible gas is produced through thermal and chemical effects on the coal, and hydrogen and carbon monoxide are separated on the ground.

6. The method for multi-purpose coalbed methane horizontal well according to claim 5, characterized in that: After gasification is completed, high-strength cement is used to seal the vertical well in advance, and the carbon dioxide separated by gasification or other output is captured and liquefied. It is then injected into the residual voids of the coal seam deep underground from an L-shaped horizontal well, and the carbon dioxide is sealed by utilizing the permeability and sealing properties of the formation.

7. The method for multi-purpose coalbed methane horizontal well according to claim 6, characterized in that: After the wellhead pressure of the L-type horizontal well drops to normal pressure, high-strength cement is used to seal the entire section of the L-type horizontal well. After the wellhead is covered on the ground, cement piers are driven in and marked.

8. The method for multi-purpose coalbed methane horizontal well according to claim 1, characterized in that: Underground coal gasification is carried out using longwall airflow gasification technology or controlled retreat gas injection point gasification technology.

9. The method for multi-purpose coalbed methane horizontal well according to claim 3, characterized in that: The horizontal section length of the L-type horizontal well located in the coal seam is ≥800 meters and the well diameter is ≥120mm.

10. The method for multi-purpose coalbed methane horizontal well according to claim 6, characterized in that: Before the injection of carbon dioxide, the coal slag layer is subjected to acid washing and permeability enhancement treatment using a 5% to 10% HCl solution.

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