Abstract:

Favorable coalbed methane (CBM) development area is characterized by high CBM content, high coal reservoir permeability and high gas productivity. Finding out the primary geological parameter representative of the three high properties is a key to comprehensively evaluate CBM-bearing reservoirs. In this paper, a quantitative method was proposed to target favorable CBM area for a CBM development block. Coalbed gas content, reservoir pressure, critical desorption pressure and coal permeability obtained by injection/falloff well test were selected to be as primary geological parameters used for comprehensively evaluating favorable CBM area. Their weight coefficients and evaluation value functions were obtained by analyzing correlation degree of the geological parameters with the mean gas production rate at stable production period. Based on the soft of MapInfo professional, comprehensive evaluation values for the arbitrary locations of the study area were calculated, and then were calibrated by the mean gas production rate so as to divide different CBM development areas. This method was successfully applied to Zhengzhuang block in southern Qinshui Basin, and favorable CBM areas with the gas-production value larger than 2,000 m³/d were predicated; the result is significant to guide the CBM well drilling in the next stage.

Key words: favorable coalbed methane area, primary geological parameter, grey correlation degree, Zhengzhuang block, Qinshui Basin