An Analysis of Field Development Strategies for Methane Production From Coal Seams

Abstract

ABSTRACT Natural gas production from conventional gas reservoirs and methane production from coal seams are different not only because of the different physical characteristics of the producing horizons but also because of the existence of different gas storage mechanisms. In the design of an optimum development plan for a coal seam degasification process, as it is the case in conventional reservoirs, it will be necessary to have a good knowledge of the field parameters such as total reserves, well productivity and formation characteristics. One of the more significant planning concerns in the development of a coal seam is the determination of the most efficient geometric arrangement of drainage wells for the purpose of establishing a uniform pressure decline throughout the coal seam. Since most of the methane gas in the coal seams is in the adsorbed stage, achievement of a uniform pressure distribution will assure the continuity of the free gas phase in the system. Existence of a pronounced permeability contrast in two principal directions coupled with the sorption characteristics necessitates the identification of certain criteria that will infer the optimum pattern configuration for coal seams. In this paper we present the results of a series of numerical exercises targeted for a better understanding of the effectiveness of several drainage patterns. Along these lines, the effects of coal seam properties such as porosity, permeability, and permeability contrast have been isolated to understand the role of each individual parameter in the selection of optimum vertical and horizontal drainage well configurations. In the case of sparsely drilled well configurations, several infill drilling scenarios have been considered in an effort to maximize the ultimate recovery.