Sensitivity analysis of reservoir conditions and gas production mechanism in deep coal seams in Buchanan County, Virginia

The potential of commercial deployment of CO2 sequestration in unmineable coal seams, as a measure to mitigate the greenhouse gas effect, has been tested through a series of small- to medium-scale CO2 injection projects in the Appalachian Basin, USA. Essential tools for these projects are reservoir simulations in which the involved processes, prior to injection field tests are modeled to enhance understanding and to be used as a decision tool. Due to the large number of modeling input parameters and the high uncertainty in determining their values, an initial model sensitivity analysis of the key input parameters is required for the development of representative models. In this paper, preliminary single-well reservoir parametric simulations were conducted to identify how the variation of selected reservoir parameters and properties affect model results. More specifically, this sensitivity analysis focused on three areas: a) the effect of selected initial conditions (adsorption isotherm, fracture and matrix porosity, reservoir pressure, desorption time, water saturation and permeability), b) the influence of the production mechanism (permeability, face to butt cleat ratio, relative permeability, Langmuir volume, matrix and fracture porosities, desorption time, water saturation, initial reservoir pressure, and pressure gradient), and c) the contribution of the well characteristics (skin factor, explicitly defined hydraulic fractures and high permeability zones). This modeling work forms the basis for calibrating reservoir models used in simulations of CO2 injection.