Concentric Casing ECD Drilling for Coal Seam Methane Recovery
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Solution Overview
Problem
Drilling in over-pressured coal seams often damages coal permeability due to the use of chemicals in weighted drilling fluids, which reduces methane recovery and causes wellbore instability.
Innovation Solution
A continuous circulating concentric casing system that uses annular friction control and surface choking to maintain hydrostatic pressure without chemicals, creating an Equivalent Circulating Density (ECD) equivalent to heavier fluids, thereby preventing formation damage and stabilizing the wellbore.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If weighted drilling fluids containing chemicals are used to increase hydrostatic pressure, then wellbore stability is improved, but coal seam permeability is damaged
Solution Approach 1:
The patent removes harmful weighting agents and chemicals from the drilling fluid system entirely. Instead of using chemically-laden weighted fluids, the invention employs a continuous circulation system with clean water or near-clean drilling fluid that achieves wellbore stability through mechanical means (friction and choking) rather than chemical composition modification.
Solution Approach 2:
The patent introduces an intermediary circulation system consisting of continuous fluid circulation through the wellbore and friction/choke mechanisms. This intermediary system mediates between the need for hydrostatic pressure (wellbore stability) and the need to avoid formation damage, allowing pressure control without direct contact of harmful chemicals with the coal seam.
2Strength
If heavier drilling fluids are used to counteract over-pressure in coal seams, then wellbore collapse is prevented, but formation damage increases
Solution Approach 1:
The patent changes the parameter of fluid density from static (heavier drilling fluid composition) to dynamic (continuous circulation with friction and choking). Instead of altering the chemical composition to increase density, the system maintains lighter fluid composition but achieves equivalent hydrostatic pressure through continuous circulation and mechanical restriction points.
Solution Approach 2:
The patent replaces the chemical-mechanical system of weighted drilling fluids with a purely mechanical circulation and restriction system. Friction along the annulus and choke mechanisms provide the mechanical means to generate back pressure, substituting for the chemical composition-based pressure generation of traditional weighted fluids.
3Object-affected harmful factors
If continuous circulation with friction control is used to create ECD pressure, then formation damage is eliminated, but system complexity increases
Solution Approach 1:
The patent employs self-service mechanisms where the continuous circulation system utilizes the wellbore geometry and fluid flow itself to generate the necessary friction and back pressure. The system serves its own pressure control needs through inherent fluid dynamics and geometric constraints rather than requiring external complex control mechanisms.
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 allows for non-invasive and stable drilling and completion of coal bed methane reservoirs, preventing wellbore collapse and maximizing methane recovery by maintaining equilibrium hydrostatic pressure without using harmful chemicals.
Implementation Method 1
applying friction or choke manifold to the water circulating down the well bores so that the water creates an Equivalent Circulating Density (ECD) pressure within the well bore sufficient to maintain an equilibrium with the hydrostatic pressure in the coal bed formation
Implementation Method 2
the water creates an Equivalent Circulating Density (ECD) pressure within the well bore sufficient to maintain an equilibrium with the hydrostatic pressure in the coal bed formation
Data Source
AI summary
A method of drilling multiple boreholes within a single caisson, for recovery of methane gas from a coal bed, including the steps of drilling first and second vertical boreholes from a single location within a single caisson; drilling at least one or more horizontal wells from the several vertical bore hole, the horizontal wells drilled substantially parallel to a face cleat in the coal bed; drilling at least one or more lateral wells from the one or more horizontal wells, the lateral wells drilled substantially perpendicular to one or more face cleats in the coal bed; continuously circulating water through the drilled vertical, horizontal and lateral wells to recover the water and entrained methane gas from the coal bed; applying friction or choke manifold to the water circulating down the well bores so that the water appears to have a hydrostatic pressure within the well sufficient to maintain an equilibrium with the hydrostatic pressure in the coal bed formation; and drilling at least a third vertical borehole within the single caisson, with one or more horizontal boreholes and one or more lateral boreholes for returning water obtained from the lateral wells into a water zone beneath the surface.