CN106014345B - A kind of lower part caving method exploits the pumping method for the compound old dead zone coal bed gas to be formed - Google Patents

Abstract

The invention discloses a method for extracting coalbed methane from a compound old goaf formed by mining by the lower caving method. The invention implements the extraction of coalbed methane by constructing a horizontal well 1 to 5 meters above the fissure zone of the lower old goaf; When the coalbed methane extraction volume drops to 10%~20% of Q, implement staged fracturing and re-extract coalbed methane from the old empty area. When the coalbed methane extraction volume drops to 10%~20% of Q again , inject supercritical carbon dioxide to displace coalbed methane; carry out drainage again until the extraction volume drops to 6m ³ /min and stop the extraction. This method solves the problem that the effective contact area between the drainage drilling and the old goaf reservoir is small and the extraction range is limited when the old goaf is simply extracted by ground vertical drilling; At the same time, the coalbed methane resources near the upper old empty area are extracted together, which saves costs; at the same time, the horizontal well is located in the rock formation, which avoids the well collapse and blockage accidents that occur when drilling in the coal seam.

Description

A coalbed methane extraction method for complex old goaf areas formed by lower caving mining

technical field

The invention relates to a method for extracting coalbed methane in a composite old goaf formed by lower caving mining, and belongs to the technical field of extracting coalbed methane.

Background technique

Due to long-term industrialized mining, there are countless old empty areas with huge areas in our country. Taking Shanxi Province as an example, by the end of 2013, there were more than 4,700 abandoned mines in Shanxi Province, and the area of old empty areas had reached 5,000 square kilometers. Most of these old empty areas were excavated by old-style blasting with low recovery rate. Coal mining technology, the coal recovery rate is generally 50%~60%, or even lower, so the above-mentioned old empty areas have considerable coalbed methane resources and gas reserves. Relevant data show that only Shanxi Province is an example of old empty areas Coalbed methane resources are about 3 billion cubic meters. Gas is a kind of clean energy, and the energy utilization of residual coalbed methane in the old empty area can effectively alleviate the shortage of natural gas supply in my country; at the same time, as a harmful gas, the greenhouse effect produced by the emission of gas into the atmosphere is 21 times that of carbon dioxide. times, so the extraction and utilization of this part of the gas has good economic and environmental benefits.

At present, the gas drainage of the old goaf is mainly aimed at the drainage of the old goaf on a single working face. The method is to drill the ground in the upper fracture zone of the old goaf to extract the gas from the old goaf. During the drilling construction process, the construction is difficult, the accident rate is high, and the porosity rate is low. Moreover, one ground wellbore can only be used for drainage of an old empty area, and the output of the extracted coalbed methane is low and the cost is high. Chinese patent CN105114038A discloses a method of relying on supercritical CO ₂ jet fracturing coal pillars in adjacent old void areas to extract gas from two old void areas at the same level; A method for mining residual coalbed methane in multi-layered old goaf areas by coal pillar drainage.

All the above methods have made important explorations for the vertical shaft drainage of gas in many old empty areas. However, the above-mentioned patents have problems such as a small contact surface between the vertical drilling on the ground and the coalbed methane reservoir, limited range of extraction, and poor extraction effect.

In fact, coal seams in coalfields are often stored in the form of multiple layers of coal at a certain distance apart. After the mining of the upper and lower layers of coal is completed, a composite old empty area will be formed. Due to historical and limited mining conditions, the coal resource recovery rate of the existing composite old goaf is limited (mostly less than 60%), which contains a considerable amount of coalbed methane resources. Collaborative extraction is still in a relatively blank stage.

Contents of the invention

In view of the above-mentioned problems, the present invention proposes a compound old empty area formed by mining the upper part by the knife column method and the lower part by the caving method, and the upper and lower parts are formed by the caving method from the perspective of maximizing the exploitation of coalbed methane resources while considering the economic cost. Combined with the method of simultaneous extraction of coalbed methane in old empty areas, it solves the phenomenon of a large amount of resource waste caused by the abandonment of existing coalbed methane resources.

The present invention provides a method for extracting coalbed methane from composite old goaf areas formed by lower caving mining, comprising the following steps:

(1) According to the geological mining data of the mine, comprehensively use physical exploration means to determine the parameters of the old goaf that has been excavated in the upper and lower coal seams (the excavation range of the old goaf, the distribution of cavities, and coal pillars), the old goaf in the lower part and the upper part The distance parameter between old voids;

(2) Construct a horizontal well from the corresponding ground position above the coal pillar at the boundary of the old goaf to 1 to 5 meters above the fissure zone of the old goaf below;

The horizontal well extends from the downhole to the ground and can be divided into the horizontal section of the horizontal well, the deflection section, the vertical section of the horizontal well, and the surface end of the horizontal well. The flow pipe, in which the branch on one side of the extraction pipe is connected with valve I, and the branch on one side of the injection pipe is connected with valve II, is sealed near the surface of the horizontal well, and there is a sealing device on the surface;

(3) Open the valve Ⅰ on the ground, conduct coalbed methane extraction through the extraction pipe, and record the amount Q of coalbed methane extraction per unit time at this time;

(4) When the coalbed methane extraction volume per unit time drops to 10% to 20% of Q, divide the horizontal section of the horizontal well into several fracturing sections at intervals of 10 to 30 meters, and each fracturing section There is a fracturing interval in between, and the fracturing interval is 3-10 meters long. The tee is disassembled and lowered from the wellhead. The staged fracturing equipment uses the horizontal well staged fracturing technology to divide the staged fracturing stage up to the upper old empty area. Fracturing of rock formations between floor plates;

(5) Reinstall the tee, seal the wellhead, open the valve I on the extraction pipe, and conduct coalbed methane extraction through the extraction pipe again;

(6) When the extraction volume of coalbed methane per unit time drops to 10%~20% of Q again, close valve I, open valve II, and press into the old empty area from the side of the injection pipe at a temperature of 32~40 ℃, supercritical CO ₂ at a pressure of 8~12MPa for 12~36 hours, and wait for 24~36 hours;

(7) Open valve I again, close valve II, and conduct coalbed methane extraction through the extraction pipe again;

(8) When the coalbed methane extraction volume per unit time drops below 10% of Q, close valve I and stop pumping for 8 to 24 hours, then open valve I and reduce the extraction pressure to continue coalbed methane extraction; when the unit When the coalbed methane extraction volume drops below 10% of Q again within the specified time, close valve I again and stop pumping for 8 to 24 hours, then open valve I again to lower the extraction pressure for coalbed methane extraction; cycle the above pumping stop- The process of decompression extraction until the extraction pressure is reduced to 80~100kpa lower than the atmospheric pressure;

(9) Stop coalbed methane extraction when the unit time coalbed methane extraction volume drops to 6m ³ /min.

In the above scheme, the vertical section of the horizontal well passes through the boundary coal pillar of the old empty area, and the horizontal distance from the end of the boundary coal pillar is 10 to 60 meters, and the vertical depth of the horizontal section of the horizontal well is formed by the excavation of the lower coal seam The development height of the fracture zone above the old goaf in the lower part is determined, and the kickoff point selection of the kickoff section of the horizontal well is determined by the determined layers of the horizontal section of the horizontal well, the vertical section of the horizontal well, and the drilling technology on site.

In the above solution, the staged fracturing technology is one of: casing flow-limited fracturing, multi-stage packer staged fracturing, and hydraulic jet fracturing.

In the above scheme, the old empty space is an upper knife column type and a lower caving type composite old empty area or an upper and lower caving type composite old empty area.

From the perspective of coordinated extraction of coalbed methane resources, the present invention takes into account a large amount of residual coalbed methane resources in the upper and lower old empty areas at the same time, and proposes an innovative method for coordinated extraction of coalbed methane. This method effectively solves the problem that the effective contact area between the drainage drilling and the old goaf reservoir is small and the extraction range is limited when the old goaf is only extracted by ground vertical drilling; At the same time, the coalbed methane resources adjacent to the upper old empty area are extracted together, so that one well can be used for multiple purposes, which greatly saves costs; at the same time, the horizontal well is located in the interlayer rock between the upper and lower old empty areas, avoiding drilling directly When the coal seam is hit, the well collapse accident and the well blockage accident occur because the coal seam is too loose.

Description of drawings

Fig. 1 is a schematic diagram of extracting coalbed methane in Embodiment 1 of the present invention.

Fig. 2 is a schematic diagram of extracting coalbed methane in Embodiment 2 of the present invention.

In the figure, 1. Drainage pipe, 2. Valve I, 3. Valve II, 4. Injection pipe, 5. Vertical section of horizontal well, 6. Boundary coal pillar, 7. Build-up section, 8. Lower old empty area , 9. Fracture zone in the lower old goat area, 10. Segmented fracturing section, 11. Fracturing interval section, 12. Horizontal well horizontal section, 13. Upper old goat area, 14. Horizontal well, 15. Sealing section; 16 1. Sealing device; 17. Tee, 18 Fracture cracks in stages.

Detailed ways

The present invention is further illustrated by the following examples, but not limited to the following examples.

Example 1: The method of extracting the coalbed methane in the composite old goaf formed by the caving method of the upper part of the cutter column and the lower part

This embodiment takes a working face of Yuecheng Mine of Shanxi Coal Group as an example, as shown in Figure 1, to illustrate the extraction method of the invention. Yuecheng Mine is located in Qinshui Coalfield, which is one of the important coalfields rich in coalbed methane resources in my country. The recoverable coal seams in the coalfield are No. 3 coal seam of Shanxi Formation and No. 9 and No. 15 coal seams of Taiyuan Formation. Due to history and outdated mining methods, the recovery rate of No. 3 coal in the main coal seam in the coalfield is low, a large amount of coal is left underground, and the old goaf area is quite rich in coalbed methane resources. The No. 9 coal in the thin coal seam with an average distance of 47.16 meters from the floor of Coal No. 3 has an average coal thickness of 1 meter. When the upper and lower layers and two layers of coal are excavated, the old void area formed is the upper knife column type and the lower part caving type composite old void area. In order to solve the problem of coordinated exploitation of coalbed methane resources, the specific method provided by the invention is:

1) According to the existing geological mining data such as mine mining conditions, coal seam histograms, well-upper and lower comparison maps, and comprehensively use physical exploration methods to determine the parameters of the old goaf that has been excavated in the upper and lower coal seams (mainly including the excavation of the old gob range, cavity, coal pillar distribution, etc.), the distance between the lower old empty area and the upper old empty area, etc.;

2) Construct a horizontal well (14) from the ground position above the coal pillar (6) at the boundary of the old goaf to 2 meters above the fissure zone (9) in the lower old goaf,

The horizontal well (14) can be divided into the horizontal section (12) of the horizontal well (12), the deflection section (7), the vertical section of the horizontal well (5) and the ground end of the horizontal well in sequence from the downhole to the ground, wherein the ground end of the horizontal well consists of three The pipeline (17) is divided into two branches. The side branch of the extraction pipe (1) is connected with the valve I (2), and the side branch of the injection pipe (4) is connected with the valve II (3). The ground end is sealed into a sealing section (15), and the ground has a sealing device (16); the sealing is sealed with cement and mortar.

3) Open the valve I (2) on the ground, and extract the coalbed methane from the extraction pipe (1), and record the extraction volume Q of the coalbed methane per unit time at this time;

4) When the coalbed methane extraction volume per unit time drops to 20% of Q, divide the horizontal section (12) of the horizontal well into several fracturing sections (10) every 20 meters, and each fracturing section There is a fracturing interval (11) in between, the fracturing interval (11) is 5 meters long, the tee (17) is disassembled and the staged fracturing equipment is lowered from the wellhead, and the staged fracturing is performed using the horizontal well staged fracturing technology. Fracturing of the strata above the split section (10) to the bottom plate of the upper old goaf (13), resulting in horizontal and vertical cracks between the rock layers of this layer, connecting the upper old goat (13) and the horizontal well (14);

5) Re-install the tee (17), seal the wellhead, open the valve I (2), and conduct coalbed methane extraction through the extraction pipe (1) again;

6) When the coalbed methane extraction volume per unit time drops to 20% of Q again, close valve I (2), open valve II (3), and press the injection pipe (4) into the old empty space with a temperature of Supercritical CO ₂ at 32°C and a pressure of 9MPa for 36 hours, then wait for 24 hours;

7) Open the valve I (2) again and close the valve II (3), and conduct coalbed methane extraction through the extraction pipe (1) again;

8) When the coalbed methane extraction volume per unit time drops below 10% of Q, close the valve I (2), stop pumping for 8 hours, then open the valve I (2) and reduce the extraction pressure to continue the coalbed methane extraction ; When the coalbed methane extraction volume per unit time drops below 10% of Q again, close the valve I (2) again, stop the pumping for 8 hours, then open the valve I (2) again, and reduce the extraction pressure again for the coalbed methane Drainage; cycle the above-mentioned stop pumping-depressurization extraction process until the extraction pressure is reduced to 80kpa lower than the atmospheric pressure;

9) Stop coalbed methane extraction when the unit time coalbed methane extraction volume drops to 6m ³ /min.

The vertical section (5) of the above-mentioned horizontal well passes through the boundary coal pillar (6) of the old empty area, and the horizontal distance from the end of the boundary coal pillar is 40 meters. The vertical depth of the horizontal section (12) of the horizontal well is excavated from the lower coal seam The height of the fracture zone (9) above the formed lower old goaf (8) is determined by the development height of the old goaf fracture zone (9), and the kickoff point selection of the horizontal well kickoff section (7) is determined by the determined horizontal well horizontal section (12), The horizon of the vertical section (5) of the horizontal well is determined by the on-site drilling technology.

The staged fracturing equipment installed in the above-mentioned horizontal well directional staged fracturing needs to be determined according to which staged fracturing technology is used. The specific staged fracturing technology can be casing flow-limited fracturing, multi-stage fracturing Any one of packer staged fracturing and hydraulic jet fracturing technology needs to be determined in combination with field conditions and well completion methods in specific implementation.

Example 2: The method of extracting coalbed methane in the composite old goaf formed by caving mining in both the upper part and the lower part

Taking a certain working face of Jinsheng Coal Mine of Shanxi Coal Group as an example below, the inventive method is illustrated. Jinsheng Coal Mine is located in Qinshui Coalfield, which is one of the important coalfields rich in coalbed methane resources in my country. The mineable coal seams within the scope of the coalfield are the No. 3 coal seam of the Shanxi Formation and the No. 9 and No. 15 coal seams of the Taiyuan Formation. Due to history and outdated mining methods, the recovery rate of No. 3 coal in the main coal seam in the coalfield is low, a large amount of coal is left underground, and the old goaf area is quite rich in coalbed methane resources. The No. 9 coal in the thin coal seam with an average distance of 53.20 meters from the floor of Coal No. 3 has an average coal thickness of 0.81 meters. The specific method provided by this invention for the coordinated exploitation of coalbed methane resources in compound old empty areas is:

1) According to the existing geological mining data such as mine mining conditions, coal seam histograms, well-upper and lower comparison maps, and comprehensively use physical exploration methods to determine the parameters of the old goaf that has been excavated in the upper and lower coal seams (mainly including the excavation of the old gob range, cavity, coal pillar distribution, etc.), the distance between the lower old empty area and the upper old empty area, etc.;

2) Construct a horizontal well (14) from the ground position above the coal pillar (6) at the boundary of the old goaf to the place 1.6 meters above the fissure zone (9) in the lower old goaf,

The horizontal well can be divided into the horizontal section (12), the deflection section (7), the vertical section (5) of the horizontal well and the surface end of the horizontal well in sequence from the downhole to the ground. ) is divided into two branches, the side branch of the extraction pipe (1) is connected with the valve I (2), and the side branch of the injection pipe (4) is connected with the valve II (3). It is sealed into a sealing section (15), and a sealing device (16) is provided on the ground; the sealing is sealed by cement and mortar.

3) Open the valve I (2) on the ground, and extract the coalbed methane from the extraction pipe (1), and record the extraction volume Q of the coalbed methane per unit time at this time;

4) When the coalbed methane extraction volume per unit time drops to 20% of Q, divide the horizontal section (12) of the horizontal well into several fracturing sections (10) every 18 meters, and each fracturing section Between them is the fracturing interval (11). The fracturing interval (11) is 6 meters long. The tee (17) is disassembled and the staged fracturing equipment is lowered from the wellhead. Fracturing of the strata above the split section (10) to the bottom plate of the upper old goaf (13), resulting in horizontal and vertical cracks between the rock layers of this layer, connecting the upper old goat (13) and the horizontal well (14);

5) Re-install the tee (17), seal the wellhead, open the valve I (2), and conduct coalbed methane extraction through the extraction pipe (1) again;

6) When the coalbed methane extraction volume per unit time drops to 20% of Q again, close valve I (2), open valve II (3), and press the injection pipe (4) into the old empty space with a temperature of Supercritical CO ₂ at 36°C and pressure of 10MPa for 26 hours, wait for 30 hours;

7) Open the valve I (2) again and close the valve II (3), and conduct coalbed methane extraction through the extraction pipe (1) again;

8) When the coalbed methane extraction volume per unit time drops below 10% of Q, close the valve I (2), stop the pumping for 14 hours, then open the valve I (2) and reduce the extraction pressure to continue the coalbed methane extraction ; When the coalbed methane extraction volume per unit time drops below 10% of Q again, close the valve I (2) again, stop the pumping for 14 hours, then open the valve I (2) again, and reduce the extraction pressure again for the coalbed methane Drainage; cycle the above-mentioned stop pumping-depressurization extraction process until the extraction pressure is reduced to 88kpa lower than the atmospheric pressure;

9) Stop coalbed methane extraction when the unit time coalbed methane extraction volume drops to 6m ³ /min.

The vertical section (5) of the above-mentioned horizontal well passes through the boundary coal pillar (6) of the old empty area, and the horizontal distance from the end of the boundary coal pillar is 30 meters. The vertical depth of the horizontal section (12) of the horizontal well is excavated from the lower coal seam The height of the fracture zone (9) above the formed lower old goaf (8) is determined by the development height of the old goaf fracture zone (9), and the kickoff point selection of the horizontal well kickoff section (7) is determined by the determined horizontal well horizontal section (12), The horizon of the vertical section (5) of the horizontal well is determined by the on-site drilling technology.

The staged fracturing equipment installed in the above-mentioned horizontal well directional staged fracturing needs to be determined according to which staged fracturing technology is used. The specific staged fracturing technology can be casing flow-limited fracturing, multi-stage fracturing Any one of packer staged fracturing and hydraulic jet fracturing technology needs to be determined in combination with field conditions and well completion methods in specific implementation.

Claims (5)

1. The extraction method of the composite old goaf coalbed methane that a kind of bottom caving method mining forms, it is characterized in that: comprise the following steps: (1) According to the geological mining data of the mine, comprehensively use physical exploration methods to determine the parameters of the old goaf that has been excavated in the upper and lower coal seams, and the distance parameters between the lower old goaf and the upper old goaf; the parameters of the old goaf include the old goaf Excavation scope, cavities and coal pillar distribution in the goaf; (2) Construct a horizontal well from the upper ground position corresponding to the coal pillar at the boundary of the old goaf to the place 1 to 5 meters above the fissure zone of the lower old goaf; The horizontal well extends from the downhole to the ground and can be divided into the horizontal section of the horizontal well, the deflection section, the vertical section of the horizontal well, and the surface end of the horizontal well. The flow pipe, in which the branch on one side of the extraction pipe is connected with valve I, and the branch on one side of the injection pipe is connected with valve II, is sealed near the surface of the horizontal well, and there is a sealing device on the surface; (3) Open the valve Ⅰ on the ground, conduct coalbed methane extraction through the extraction pipe, and record the amount Q of coalbed methane extraction per unit time at this time; (4) When the coalbed methane extraction volume per unit time drops to 10% to 20% of Q, divide the horizontal section of the horizontal well into several fracturing sections at intervals of 10 to 30 meters, and each fracturing section There is a fracturing interval in between, and the fracturing interval is 3-10 meters long. The tee is disassembled and lowered from the wellhead. The staged fracturing equipment uses the horizontal well staged fracturing technology to divide the staged fracturing stage up to the upper old empty area. Fracturing of rock formations between floor plates; (5) Reinstall the tee, seal the wellhead, open the valve I on the extraction pipe, and conduct coalbed methane extraction through the extraction pipe again; (6) When the coalbed methane extraction rate per unit time drops to 10-20% of Q again, close valve I, open valve II, and press the injection pipe into the old empty area. The injection temperature is 32-40℃, Supercritical CO ₂ with a pressure of 8~12MPa for 12~36 hours, wait for 24~36 hours; (7) Open valve I again, close valve II, and conduct coalbed methane extraction through the extraction pipe again; (8) When the coalbed methane extraction volume per unit time drops below 10% of Q, close valve I and stop pumping for 8 to 24 hours, then open valve I and reduce the extraction pressure to continue coalbed methane extraction; when the unit When the coalbed methane extraction volume drops below 10% of Q again within the specified time, close valve I again and stop pumping for 8 to 24 hours, then open valve I again to lower the extraction pressure for coalbed methane extraction; cycle the above pumping stop- The process of decompression extraction until the extraction pressure is reduced to 80~100kpa lower than the atmospheric pressure; (9) Stop coalbed methane extraction when the unit time coalbed methane extraction volume drops to 6m ³ /min. 2. the extraction method of the composite old goaf coalbed methane formed by the lower caving method mining according to claim 1, characterized in that: the vertical section of the horizontal well passes through the old goaf boundary coal pillar, and The horizontal distance at the end of the coal pillar is 10-60 meters. The vertical depth of the horizontal section of the horizontal well is determined by the development height of the fracture zone above the old goaf area formed by the excavation of the lower coal seam. The kickoff point of the horizontal well is selected It is determined by the determined layers of the horizontal section of the horizontal well, the vertical section of the horizontal well, and the on-site drilling technology. 3. The extraction method of the composite old goaf coalbed methane formed by the mining of the lower caving method according to claim 1, characterized in that: the staged fracturing technology of the horizontal well is: casing flow-limiting fracturing, multi-stage sealing It is one of the staged fracturing and hydraulic jet fracturing technologies. 4. The method for extracting coalbed methane from the composite old goaf formed by the lower caving method according to claim 1, characterized in that: the old goaf is an upper knife column type and a lower caving composite old goaf. 5. The method for extracting coalbed methane from the composite old goaf formed by lower caving mining according to claim 1, characterized in that: the old goaf is a composite old goaf of upper and lower caving.