Decrease of Desorption Intensity of Coalbed Methane due to Hydraulic Fracturing

Abstract

During the prospecting extraction of methane from coal seams in Ostrava district by the method of hydraulic fracturing in many cases it has been observed that the gas releasing does not follow the assumed pattern of continuous flow with gradually decreasing intensity as it is known from the degassing of drilling cores by canister test. On the contrary, after a short initial outburst, the gas stream quickly decreases to a minimum. Due to the fact that in the pumped water a high sludge content was present, it was assumed that the sludge formed during the disintegration of the coal seam by the shock wave of pressurized water may restrict the gas release owing to clogging of transport pores by very fine particles. The overpressure of water towards gas present in coal introduces these particles into the orifices of transport pores, blocking them partially and thus reducing the gas escape.