Horizontal Well Cavity Depressurization for Coal Seam Gas Extraction
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Solution Overview
Problem
Current methods for extracting coal bed methane from tectonically-deformed coal seams, characterized by low permeability and structural deformation, are inefficient due to wellbore fractures and difficulty in connecting with production, limiting the development of this significant energy resource in China.
Innovation Solution
A system for extracting gas from tectonically-deformed coal seams in-situ by depressurizing a horizontal well cavity, comprising a horizontal well drilling and reaming subsystem, a depressurization excitation subsystem, a product lifting subsystem, a gas-liquid-solid separation subsystem, and a monitoring and control subsystem, which includes a three-stage drilling tool with expandable blades and a hydraulic jet pump for efficient separation and continuous extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional vertical well or horizontal well fracturing methods are used in tectonically-deformed coal seams, then gas extraction is attempted, but wellbore fractures occur and permeability remains extremely low due to tectonic deformation
Solution Approach 1:
The wellbore is divided into multiple segments with different diameter expansions at different locations. The three-stage reaming tool creates sequential cavity expansions (first-stage, second-stage, third-stage cavities) along the horizontal well, allowing each segment to be optimized for specific functions such as stress release, gas desorption, and fluid flow.
Solution Approach 2:
Different regions of the coal seam are treated with different cavity diameters and expansion rates according to local tectonic deformation characteristics. The reaming tool adjusts blade expansion angles and cavity volumes based on specific geological conditions at each well location, creating locally-optimized extraction zones.
2Productivity
If the coal seam is tectonically-deformed with low permeability, then gas remains trapped, but conventional fracturing methods fail to improve permeability effectively
Solution Approach 1:
The system performs preliminary cavity expansion and stress release before attempting gas extraction. The multi-stage reaming process pre-creates enlarged cavities and fracture networks in advance, preparing the coal seam structure to accommodate subsequent gas desorption and flow without requiring intensive fracturing during production.
Solution Approach 2:
The invention transitions from traditional single-diameter wellbores to multi-dimensional cavity systems with varying radii. The third-stage reaming creates the largest cavities with maximum radius expansion, creating a hierarchical cavity structure that enhances permeability through multiple spatial dimensions rather than uniform radial expansion.
3Productivity
If large-diameter horizontal wells are completed to extract gas, then extraction efficiency improves, but wellbore collapse risk increases due to overburden deformation
Solution Approach 1:
The system performs preliminary cavity stabilization through controlled multi-stage expansion. Each reaming stage progressively enlarges the cavity while maintaining structural control, preventing sudden wellbore collapse that would occur with single-stage large-diameter expansion in tectonically-stressed coal seams.
Solution Approach 2:
The multi-stage reaming process creates intermediate cavity structures that act as cushioning zones between the original wellbore and the final large extraction cavity. These intermediate stages distribute stress and prevent catastrophic wellbore failure by gradually accommodating overburden deformation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This system enables large-diameter horizontal well completion, stress release, and efficient separation of mixed fluids, ensuring continuous and efficient in-situ extraction of coal bed methane, overcoming the limitations of existing technologies by preventing wellbore collapse and enhancing extraction efficiency.
Implementation Method 1
a product lifting subsystem, a gas-liquid-solid separation subsystem
Implementation Method 2
hydraulic jet pump for efficient separation and continuous extraction
Implementation Method 3
System for extracting gas from a tectonically-deformed coal seam in-situ by depressurizing a horizontal well cavity
Implementation Method 4
A method based on the theory of hydrophobic depressurization, desorption, and gas recovery
Implementation Method 5
a gas-liquid-solid separation subsystem, efficient separation of produced mixtures
Implementation Method 6
hydraulic jet pump for efficient separation and continuous extraction
Data Source
AI summary
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.