Vast reserves of gas-bearing coal deposits are located in Queensland. Owing to the extremely low permeability and porosity of the coal, very low gas flow rates are normally encountered. In an effort to enhance the gas production to economic quantities and to degasify the coal to provide a safer mining environment, four experimental wells were drilled into coal seams near Blackwater, Queensland.Based on extensive laboratory testing of coal samples, computerised fracture design calculations were performed to determine a suitable stimulation programme. The wells were hydraulically fractured with up to 15 000 US gal of foamed stimulation fluid containing 75 per cent nitrogen. To prop open the induced fracture system, 15 000 lb of sand was pumped with the foam. The maximum concentration was eight pounds of 20-40 mesh sand per gallon of fluid. Gas production from the unstimulated wells was too low to measure. Early production data soon after the fracturing suggested a gas flow rate of approximately 50 Mcf/D.
Geochemical conditions of hydrocarbon accumulation in low-permeability shale sequences