1. Field of the Invention
The present invention pertains to a method of generating a cavity in a subterranean mineral seam, such as coal, and producing gas from a degasification well using rapid hydraulic pressurization of the coal seam in the vicinity of the wellbore.
2. Background
Certain subterranean mineral seams, such as coal, produce relatively large volumes of hydrocarbon gases through wells which have been drilled into the seam. Various techniques have been used to stimulate the production of gases, primarily methane, from underground coal seams. U.S. Pat. No. 4,995,463, issued Feb. 26, 1991 to Kramm, et al, and assigned to the assignee of the present invention, describes a fracturing technique wherein the coal seam is hydraulically fractured using a water-based fracturing fluid with a wetting agent for converting the coal fines which are formed during the fracturing of the coal to a hydrophilic state and dispersing the fines throughout the fracturing fluid volume. U.S. Pat. No. 5,147,111, issued Sep. 15, 1992 to Carl T. Montgomery, and assigned to the assignee of the present invention, describes a method of improving methane production from a well drilled into a coal seam wherein liquid carbon dioxide is pumped into the well and the pressure generated in the well is quickly released to cause the coal in the vicinity of the wellbore to fragment and generate a cavity in the coal seam. Still further, U.S. Pat. No. 5,199,766, issued Apr. 6, 1993 to Carl T. Montgomery, and also assigned to the assignee of the present invention describes a cavity induced stimulation of coal degasification wells using certain solvents which are forced into the coal seam in the vicinity of the wellbore for a sufficient period of time to weaken the coal structure wherein high pressure gas is then injected into the seam and the pressure is suddenly released to effect disintegration of the coal around the wellbore.
However, in a continuing effort to improve the effectiveness of coal degasification wells while pursuing relatively uncomplicated methods to increase gas production from these wells, another method has been developed which has certain advantages in producing a larger volume of fragmented coal and releasing greater volumes of adsorbed gas. It is to this end that the present invention has been developed with a view to providing a unique, uncomplicated method for stimulating the production of gas from coal degasification wells and the like.