Horizontal Well Cavity Construction for Tectonically-Deformed Coal Gas Extraction
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Solution Overview
Problem
Current methods for extracting gas from tectonically-deformed coal seams, such as hydrophobic depressurization and gas recovery, are inefficient due to low permeability and structural challenges, leading to difficulties in wellbore fractures and gas production in China's coal seam gas industry.
Innovation Solution
A simulation test method for gas extraction from tectonically-deformed coal seams involves constructing a large-diameter horizontal well, performing stress release and hydraulic displacement of coal-liquid-gas mixtures, and efficient separation of products using a subsystems approach that includes coal series stratum reconstruction, horizontal well drilling, and real-time monitoring and control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If hydrophobic depressurization and gas recovery methods are used for tectonically-deformed coal seams, then gas extraction is attempted, but extraction efficiency is poor due to extremely low permeability
Solution Approach 1:
The patent applies preliminary action by performing hydraulic fracturing and cavity construction before gas extraction. The horizontal well cavity is constructed and stress release is performed in advance to create permeability channels, which then enable effective gas desorption and extraction. This preliminary preparation of the reservoir structure resolves the contradiction by establishing conductive pathways before the actual gas recovery process begins.
Solution Approach 2:
The patent changes physical parameters of the coal seam by applying hydraulic pressure to create fractures and cavities. The stress release process alters the mechanical state of the tectonically-deformed coal, transforming it from a low-permeability state to a high-permeability state suitable for gas extraction. This parameter change enables the gas recovery process to be effective in previously unsuitable reservoirs.
2Productivity
If conventional well fracturing methods are applied to tectonically-deformed coal, then gas production is attempted, but wellbore fractures occur due to overburden deformation
Solution Approach 1:
The patent applies local quality by creating a specifically designed horizontal well cavity with particular geometric characteristics suited for tectonically-deformed coal. Instead of using conventional vertical wells or standard horizontal wells, the cavity is constructed with specific orientation, diameter, and stress release characteristics that accommodate the local geological conditions. This localized adaptation prevents wellbore fractures while enabling gas production.
Solution Approach 2:
The patent performs stress release and cavity construction as preliminary actions before gas production. By pre-establishing the horizontal well cavity and releasing stresses in advance, the system prevents subsequent wellbore fractures that would occur during normal production operations. This preliminary structuring protects wellbore integrity while maintaining productivity.
3Productivity
If large-diameter horizontal well cavity is constructed for stress release, then gas extraction efficiency improves, but device complexity increases
Solution Approach 1:
The patent uses hydraulic methods to construct the large-diameter horizontal well cavity and perform stress release. By utilizing fluid pressure and flow, the complex task of creating a large cavity is simplified into a controllable hydraulic process. The hydraulic system enables precise control of cavity formation and stress release, managing the complexity through fluid-based mechanisms rather than mechanical excavation.
Solution Approach 2:
The patent changes the physical and chemical parameters of the coal seam through hydraulic fracturing and stress release processes. By controlling pressure, temperature, and fluid composition parameters, the system transforms the coal structure to enable efficient gas extraction. The large-diameter cavity is achieved through controlled parameter changes rather than mechanical construction, managing complexity through parameter control.
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 method enables continuous and efficient in-situ extraction of tectonically-deformed coal seam gas by simulating the extraction process, guiding the development of surface wells and overcoming the challenges of low permeability and structural changes in tectonically-deformed coal.
Implementation Method 1
horizontal well cavity-construction stress release
Implementation Method 2
depressurizing horizontal well cavity
Implementation Method 3
hydraulic displacement of coal-liquid-gas mixtures
Implementation Method 4
efficient separation of produced mixtures
Data Source
AI summary
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.