COAL SEAM RESERVOIR SIMULATION

Abstract

Numerical reservoir simulation in coal seams is different from conventional reservoir simulation because of the capacity for coal to adsorb large amounts of gas, including methane, carbon dioxide and nitrogen, and the need to model coal as a dual porosity system. These factors require specialised numerical simulators written to address these particular issues. This paper describes the development and applications of a reservoir simulator, SIMED II, to a number of applications in the coalbed methane context. SIMED II is an implicit finite-difference code developed to describe simultaneous gas and water flow in coal when there is more than one gas component present. Applications presented in this paper include (1) history matching and forecasting in vertical wells, (2) evaluation of dewatering during the cavity completion method of stimulating coal seams, (3) economic evaluation of nitrogen injection for enhanced coalbed methane recovery, and (4) application to the design and development of gassy coal mines involving gas drainage from horizontal wells. These applications have been directed at locations in the Sydney and Bowen basins in Australia, and the San Juan basin in the USA.