Disclosed are a hole protection system and a method for coal seam slotting and fracturing combined drainage. The system includes a hydraulic slotting subsystem, a hydraulic fracturing subsystem and a flexible hole protection system. The hydraulic slotting subsystem includes an ultra-high pressure water jet generating module, a drill pipe drilling tool module, an orifice sealer, a gas slag separator and a drilling rig. The hydraulic fracturing system includes an emulsion pump station, a water tank, a hole sealing device, a fracturing string and a casing. The flexible hole protection system includes a front end fixing device, a water injection support pipe, a first flexible support and a water injection connecting section.

Disclosed are a hole protection system and a method for coal seam slotting and fracturing combined drainage. The system includes a hydraulic slotting subsystem, a hydraulic fracturing subsystem and a flexible hole protection system. The hydraulic slotting subsystem includes an ultra-high pressure water jet generating module, a drill pipe drilling tool module, an orifice sealer, a gas slag separator and a drilling rig. The hydraulic fracturing system includes an emulsion pump station, a water tank, a hole sealing device, a fracturing string and a casing. The flexible hole protection system includes a front end fixing device, a water injection support pipe, a first flexible support and a water injection connecting section.

A full-length screen pipe hole protection device and method with pressurized hole packing in a soft coal seam relates to the field of gas drainage technologies. The device includes a grouting system, a drainage system and a hole fixing system. The grouting system injects a pressurized sealing material into a borehole through a pressure pump to increase a sealing effect of the borehole. The drainage system drains gas in the middle of air holes on metal baffle plates and hole fixing screen pipes through a drainage pipe to increase flowability of gas. The hole fixing system is inside the borehole and fixed with the metal baffle plates, and the hole fixing screen pipes are fixedly connected with each other through fitting mouths and fitting buckles. The device is fixedly mounted in the gas drainage borehole. After hole packing, the drainage pipe is connected with a drainage pump to drain gas.

A full-length screen pipe hole protection device and method with pressurized hole packing in a soft coal seam relates to the field of gas drainage technologies. The device includes a grouting system, a drainage system and a hole fixing system. The grouting system injects a pressurized sealing material into a borehole through a pressure pump to increase a sealing effect of the borehole. The drainage system drains gas in the middle of air holes on metal baffle plates and hole fixing screen pipes through a drainage pipe to increase flowability of gas. The hole fixing system is inside the borehole and fixed with the metal baffle plates, and the hole fixing screen pipes are fixedly connected with each other through fitting mouths and fitting buckles. The device is fixedly mounted in the gas drainage borehole. After hole packing, the drainage pipe is connected with a drainage pump to drain gas.

A multi-level cross-district surface well pattern deployment method is provided. Firstly, a first horizontal well is drilled from a location on a land surface corresponding to a junction H.sub.1 of a district rise coal pillar of the first district C.sub.1 in a first level and an upper mine field boundary coal pillar. A multilateral well is drilled from a location on the land surface corresponding to a junction H.sub.3 of a level coal pillar between the first and second levels, and the district rise coal pillar of the first district C.sub.1 in the first level. Liquid nitrogen is injected for permeability improvement after a gas drainage quantity decreases to 20% of an initial quantity. Gas drainage is repeated multiple times until the drainage quantity of coal bed methane through a gas drainage pipe of the horizontal pipe is reached 3 m.sup.3/min.

A multi-level cross-district surface well pattern deployment method is provided. Firstly, a first horizontal well is drilled from a location on a land surface corresponding to a junction H.sub.1 of a district rise coal pillar of the first district C.sub.1 in a first level and an upper mine field boundary coal pillar. A multilateral well is drilled from a location on the land surface corresponding to a junction H.sub.3 of a level coal pillar between the first and second levels, and the district rise coal pillar of the first district C.sub.1 in the first level. Liquid nitrogen is injected for permeability improvement after a gas drainage quantity decreases to 20% of an initial quantity. Gas drainage is repeated multiple times until the drainage quantity of coal bed methane through a gas drainage pipe of the horizontal pipe is reached 3 m.sup.3/min.

The present invention provides an inversion calculation method of coal-bed gas parameters of fast test while-drilling. The technical solution is that an inversion calculation method of coal-bed gas parameters of fast test while-drilling includes: during drilling in a coal bed, testing a gas flow and a gas concentration of an orifice in real time while-drilling, calculating drilling gas discharge amounts of the orifice, inversely calculating a coal-bed gas pressure at a drill bit based on borehole and coal-bed permeability parameters, and calculating a coal-bed gas content according to a gas content and gas pressure relational expression. The present invention has the beneficial effects that the present invention does not occupy the drilling and drill rod replacement time, is accurate, convenient, real-time and fast, and can test and calculate the coal-bed gas parameters of each section along the whole borehole length.

A simulation test method for gas extraction from a tectonically-deformed coal seam in-situ by depressurizing a horizontal well cavity. A coal series stratum structure reconstruction and similar material simulation subsystem simulates a tectonically-deformed coal reservoir. A horizontal well drilling and reaming simulation subsystem constructs a U-shaped well in which a horizontal well adjoins a vertical well, and performs a reaming process on a horizontal section thereof. A horizontal well hole-collapse cavity-construction depressurization excitation simulation subsystem performs pressure-pulse excitation and stress release on the horizontal well, and hydraulically displaces a coal-liquid-gas mixture such that the mixture is conveyed towards a vertical well section. A product lifting simulation subsystem further pulverizes the coal and lifts the mixture. A gas-liquid-solid separation simulation subsystem separates the coal, liquid and gas. A monitoring and control subsystem detects and controls the operation and the execution processes of equipment in real time.

A method for precisely extracting coal-mine gas is suitable for improving the accuracy of design and construction of coal-mine gas extraction and ensuring the efficiency of borehole extraction. In the method, a gyroscope and an endoscopic camera are first used to investigate coal-seam strike trend, coal-seam dip trend, and coal-seam thickness data of a to-be-extracted area. According to gas extraction standard requirements of a to-be-extracted area, boreholes are then designed and constructed, and trajectories of boreholes are tracked to obtain a correspondence relationship between designed borehole parameters and actual borehole trajectory parameters. Next, drilling parameters are adjusted according to the correspondence relationship between the designed borehole parameters and the actual borehole parameters to construct boreholes at predetermined borehole locations. Subsequently, the boreholes are connected to an extraction pipeline, and gas extraction flow rates and gas extraction amounts per meter of the boreholes are observed. Eventually, other boreholes are designed and constructed according to the adjusted borehole construction parameters and extraction data. After being constructed, the boreholes are connected to perform gas extraction.

A system for extracting gas from a tectonically-deformed coal seam in-situ by depressurizing a horizontal well cavity is provided. A horizontal well is constructed by a horizontal well drilling and reaming subsystem and adjoins a vertical well to form a U-shaped well, and a horizontal section of the horizontal well is reamed to enlarge hole diameter. A horizontal well hole-collapse cavity-construction depressurization excitation subsystem performs pressure-pulse excitation and stress release on the horizontal well of tectonically-deformed coal bed methane, and hydraulically displaces a coal-liquid-gas mixture such that the mixture is conveyed towards a vertical well section along a depressurizing space. A product lifting subsystem further pulverizes the coal and lifts the mixture towards a wellhead of a vertical well. A gas-liquid-solid separation subsystem separates the coal, liquid and gas. A monitoring and control subsystem detects and controls the operation conditions and the execution processes of technical equipment in real time.