Resistive Heating Coal Bed Methane Recovery
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Solution Overview
Problem
Current methods for recovering coal bed methane are inefficient due to limited permeability and slow desorption in coal cleat systems, resulting in trapped methane and suboptimal recovery levels, even with enhanced techniques.
Innovation Solution
Applying electric current through water in a coal formation to achieve resistive heating, which preheats the coal below pyrolysis temperatures, facilitating methane desorption and recovery, while concurrent dewatering increases permeability and enhances gas release.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If water is removed from open fractures to enable methane desorption, then methane can be recovered, but limited permeability of the cleat system results in trapped methane and incomplete desorption
Solution Approach 1:
The patent applies electrical heating to change the temperature parameter of the coal bed, which accelerates methane desorption kinetics and improves gas mobility in the cleat system. This thermal energy input overcomes the permeability limitations by enhancing the driving force for methane migration to production wells.
Solution Approach 2:
The patent performs preliminary dewatering operations before or during methane production to remove water from the cleat system. This preliminary action clears the flow pathways, reducing permeability barriers and enabling more complete methane desorption and recovery throughout the coal bed.
2Productivity
If electric current is applied to heat water for methane desorption, then desorption is enhanced, but excessive heating may cause pyrolysis of the coal
Solution Approach 1:
The patent carefully controls the temperature parameter through regulated electrical heating, maintaining it within a range that accelerates methane desorption (typically 50-150°C) while staying below the pyrolysis threshold (approximately 200-300°C). This selective parameter control enables enhanced recovery without coal decomposition.
Solution Approach 2:
The patent implements temperature monitoring and control systems that provide feedback on the thermal state of the coal bed. This feedback mechanism allows real-time adjustment of heating parameters to maintain optimal desorption conditions and prevent excessive heating that would lead to pyrolysis.
3Quantity of substance
If conventional dewatering methods are used, then water is removed from the formation, but slow desorption and limited permeability result in suboptimal recovery levels
Solution Approach 1:
The patent applies thermal energy through electrical heating to change the temperature parameter of the coal matrix and cleat system. This temperature increase enhances methane desorption kinetics, improves gas phase mobility, and accelerates mass transfer rates, thereby significantly improving recovery efficiency beyond what conventional isothermal dewatering can achieve.
Solution Approach 2:
The patent creates a composite thermal-electrical system where electrical current heats the formation fluids and coal matrix, combining thermal and mechanical (pressure reduction) effects. This composite approach synergistically enhances both dewatering and methane desorption, overcoming the limitations of either method alone.
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 increases methane recovery by improving desorption and diffusion, allowing for more efficient gas extraction without the need for excessive heating, maintaining the electrical conduit and optimizing coal bed permeability.
Implementation Method 1
passing electric current through water from a first well to a second well by applying a voltage across the first and second wells. The current results in resistive heating of the water within a formation containing coal
Implementation Method 2
production of the methane utilizing wells drilled into the coal beds relies on desorption of the methane from surfaces of solid coal forming a matrix system of the coal bed
Data Source
AI summary
In-situ heating of coal facilitates desorption and diffusion of the methane for production of the methane through a wellbore. Water within fractures of the coal forms an electrical conduit through which current is passed. The heating relies at least in part on resistivity of the water, which thereby preheats the coal for the recovering of the methane.