E - Fixed Constructions – 21 – B
Patent
E - Fixed Constructions
21
B
E21B 10/32 (2006.01)
Patent
CA 2306322
A novel apparatus for an underreamer for reducing damage to coal seams is disclosed. Natural fracture systems form the main permeable pathways for gas migration in coal and are a major control on coal's ability to produce methane or adsorb injected gases, as is desirable for sequestration of carbon dioxide or other green house gases. Maintenance of these fractures in an open state is critical for the transfer of gas between the coal seam and a bore hole. These natural fractures exist as orthogonal sets, with vertical or substantially vertical fractures cut by horizontal or substantially horizontal fractures such that the entire fracture system resembles as assemblage of tightly packed cubes. Research has shown that these natural fracture systems are easily damaged by particulate plugging of clays liberated from surrounding strata during drilling or prior art underreaming operations. This particulate plugging and subsequent damage can severely hamper the ability of the coal to produce methane or accept injected gases. Underreaming of coal seams is desirable to remove coal adjacent to the borehole that was damaged during drilling operations in order to maximize gas flow between the borehole and the natural fracture system. The disclosed invention can confine underreaming to desirable coal seams while leaving potentially damaging clays in the surrounding strata untouched, minimizing the likelihood of newly liberated clays plugging the fractures during underreaming operations, thus maximizing potential methane recovery or gas injection volumes.
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