Pre-feasibility Study for Yanjing Coal Mine, Chongqing Municipality

With funding from USEPA, under the auspices of the Global Methane Initiative (GMI), Raven Ridge Resources, Incorporated performed a prefeasibility study at the Yanjing #1 Mine, located in southwest China within the Chongqing Municipality, to determine the potential for employing directionally-drilled boreholes from the surface into the mineable coal seams to capture gas prior to mining. The study proposes implementing a seven well pilot gas drainage program in which the coal seams are hydraulically fractured to stimulate gas production and lessen the potential for coal and gas outbursts.  Located on the edge of the Sichuan Basin and the Eastern Sichuan Fold and Thrust Belt, the geologic strata containing 61.5 million tons of coal reserves at the Yanjing Mine have undergone complex geological deformation.   Seven Permian coal seams are being mined using continuous miners to develop longwall faces positioned along the highly fractured and steeply dipping southeast limb of the Libixia anticline. Mine managers plan to extract coal from two underground levels, at -150 m and -350m.  Emissions of methane gas into the mine’s workings presents a safety risk to the mine. These emissions are a result of the high gas content of the coal seams, ranging between 5.61 cm³/g to 22.95 cm³/g, exacerbated by migration of gas updip through the highly fractured coal and surrounding strata from which the coals are being mined.

The proposed drilling scheme was developed considering the complex geology and mining conditions. Reservoir simulation was performed to develop a typical production profile forecasting production rate and cumulative production over a 10 year period.  Using the proposed drainage system would allow for increased coal production and safety by decreasing methane concentration of ventilation air. Drained and recovered methane could be sold into the local quickly expanding gas market.  Chongqing has one of the oldest and best-developed natural gas distribution infrastructures in China, and supply has been the most important constraint to more rapid growth in consumption.  Using the forecast methane production profiles, the Raven Ridge team estimates that the proposed pilot project could supply 433.3 million cubic meters of methane to the local gas market.  The capital costs are estimated to be $11.45 million USD and carbon emissions would be reduced by 883,895 tons CO₂e over the project’s ten year life.