Enhanced Coalbed Methane Recovery through CO_2Sequestration: A Laboratory and Simulation Investigation in Southern Part of Raniganj Coalfield, West Bengal

摘要

Coal core samples, collected from different coal seams encountered in boreholes drilled inSouthern part of Raniganj coalfield, have been investigated. The coal seams are evaluatedon the basis of in-situ gas content, gas composition, methane sorption isotherms as wellas porosity and permeability. In-situ gas content determined by Direct method, gascomposition evaluated by chromatography, methane sorption isotherm actuallyconstructed and carbon dioxide and nitrogen adsorption capacity within coal is estimatedwith the help of relationships for simulation of desorption characteristics. It is assumed thatcoal adsorbs almost three times as much carbon dioxide as methane. Permeability andporosity of the coal core samples are determined using whole core permeameter undervarying confining and inlet pressure. Numerical simulations have been conducted for performance of the ECBM recoveryperspective through carbon dioxide sequestration in a coalbed methane reservoirconsidering the quadrant of 320 acre well pattern with 20 ft pay zone in the study area. It isassumed that CBM reservoir is isotopic and homogeneous. Initially reservoir is assumedas 100% water saturated in cleats and a methane mole fraction of 1.0 in the matrix. Thepore volume compressibility and the exponent for permeability reduction are assumed aszero. The sorption time for methane and nitrogen is taken as 5 and 7 days respectively,The PVT properties for methane and nitrogen are internally calculated using the simulatorand a gas water relative permeability table is assigned for entire reservoir. The adsorption-desorption isotherms and permeability are characterized as the most sensitive simulationinput. in this simulation a CBM producing well is placed in one corner of the grid and CO2injecting well in the opposite corner. It is assumed that both the wells are stimulated with aninfinite conductivity fracture with half fracture length of 100 ft.