Method of extracting gas from tectonically-deformed coal seam in-situ by depressurizing horizontal well cavity

Abstract

A method of extracting gas from a tectonically-deformed coal seam in-situ by depressurizing a horizontal well cavity is provided. A horizontal well drilling and reaming subsystem constructs a U-shaped well in which a horizontal well adjoins a vertical well, and performs a reaming process on a horizontal section of the horizontal well to enlarge a 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 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.

Description

BACKGROUND OF THE INVENTIONField of the Invention[0001]The present invention relates to the field of coal bed methane extraction, and relates to a method for coal bed methane extraction, and in particular, to a method of extracting gas from a tectonically-deformed coal seam in-situ by depressurizing a horizontal well cavity.Description of Related Art[0002]Tectonically-deformed coal refers to coal whose coal seam is subject to tectonic stress and whose primary structure and construction are significantly destroyed due to cracking, resulting in fractures, wrinkles, polished surfaces, and other structural changes. The extensive development of tectonically-deformed coal and the richness of tectonically-deformed coal bed methane (referred to as CBM) resources are distinguishing features of coal and coal bed methane resources in China. Tectonically-deformed coal resources account for a very high proportion of coal resources that have been discovered in China, and a proportion of a quantit...

AI Technical Summary

Benefits of technology

The present invention provides a method for extracting gas from a tectonically-deformed coal seam in-situ by depressurizing a horizontal well cavity. This allows for the construction of a large-diameter horizontal well in a loose tectonically-deformed coal reservoir, effective lifting of mixed fluids, and efficient separation of produced mixtures. The invention also includes a drilling tool designed into a three-stage drilling and reaming tool, which increases the diameter of the horizontal section and avoids wellbore collapse. The use of high-pressure and high-speed fluids for pressure-pulse excitation and stress release on the horizontal well is ensured through real-time detection and control of the operation conditions and the execution processes of the technical equipment. The invention achieves efficient and continuous in-situ extraction of tectonically-deformed coal bed methane.

Problems solved by technology

Tectonically-deformed coal refers to coal whose coal seam is subject to tectonic stress and whose primary structure and construction are significantly destroyed due to cracking, resulting in fractures, wrinkles, polished surfaces, and other structural changes.

Due to its hazards and difficulty in extraction and utilization, the tectonically-deformed coal is mostly discharged into the atmosphere in coal production.

Due to the extremely low permeability of tectonically-deformed coal reservoirs and the poor effect of a reconstruction method such as hydraulic fracturing, the theory of hydrophobic depressurization, desorption, and gas recovery is not suitable for tectonically-deformed coal reservoirs.

The results of exploration and development practice also show that all coal bed methane exploration and development technologies based on the theory of hydrophobic depressurization, desorption, and gas recovery, including SVR technologies (vertical well fracturing, U-shaped well fracturing, multi-branched horizontal well fracturing, horizontal well fracturing, and the like), ECBM technologies (CO2-ECBM, N2-ECBM, and the like) and their combined technologies, fail to achieve efficient development of tectonically-deformed coal bed methane.

Therefore, efficient exploration and development technologies and equipment for tectonically-deformed coal bed methane have become one of important technical bottlenecks restricting the rapid and scale development of the China's coal bed methane industry.

However, in actual extraction application, due to the characteristics of tectonically-deformed coal, there are problems such as wellbore fractures caused by overburden deformation and difficulty in connecting coal to coal bed methane production.

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