Method for enhancing methane production from coal seams

Abstract

Discloses a three step process to stimulate well production of methane from coal seams, wherein step one provides for injection of a treating gas into a well bore intersecting a coal seam, step two includes a shut-in period and step three comprises the placement of a propped fracture treatment. In step one, the injection of the treating gas physically opens pre-existing paths of weakness in the coal. As the treating gas travels along these planes of weakness, it preferentially adsorbs onto the coal and displaces the methane. This displacement process induces shrinkage of the coal matrix, which further increases the size of the intervening existing fractures. The second step, or shut-in period, allows time for this gas exchange process to substantially complete, thereby maximizing the effect of matrix shrinkage and enhancement of the intervening fractures. The third step provides for placement of a propped fracture treatment into this enhanced fracture system. Propping of the enhanced fractures ensures that they remain open, even as removal of water and methane work to close the fractures by increasing effective stress within the coals. The result is a stimulated coal seam that maintains enhanced permeability during production operations.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation-in-part of application Ser. No. 10 / 668,019 filed Sep. 23, 2003, now abandoned.FIELD OF THE INVENTION [0002] This invention relates to the stimulation of coal seams for methane recovery and more particularly provides for stimulation of methane recovery from coal seams by inducing coal matrix shrinkage and placement of a propped fracture treatment. BACKGROUND OF THE INVENTION [0003] Coal seam gas production is primarily dependent on the permeability of the coal seam. Coal seam reservoirs are fractured reservoirs wherein the fractures intervene between essentially impermeable blocks of coal matrix. As the fractures are the only effective pathways for movement of methane through a reservoir to a well-bore for recovery, the size, intensity and connectedness of the fractures determine the permeability and, hence, producibility of the reservoir. No known method exists for artificially creating fracturing with...

AI Technical Summary

Benefits of technology

[0014] In one of its aspects, the present invention provides a process to stimulate well bore production of coalbed methane gases. The invention improves on the previously disclosed techniques as it uses the reaction of a predetermined gas with the coal to induce shrinkage within the coal matrix, thus reducing effective stress and enhancing the fracture void volume. This increased fracture void volume increases coal bed permeability and resultant increase in methane gas flows. It also allows placement of proppant within the coals to maintain open fractures in the regions surrounding the propped fracture, thus allowing the enhanced fracture system to communicate more effectively with both the natural fracture system and the wellbore and aiding methane recovery.

Problems solved by technology

This increased fracture void volume increases coal bed permeability and resultant increase in methane gas flows.