ABSTRACT
Insights have been gained into natural gas production from low permeability sandstone reservoirs in the western United States as a result of the U.S. Department of Energy's Multiwell Experiment (MWX). Three wells, between 110 and 215ft (34–66m) apart at depth, have been drilled at a site southwest of Rifle, Colorado, in the Piceance Basin, where the Cretaceous-age Mesaverde lies at a depth of 4,000 to 8,250ft (1220-2520m). Activities have been conducted in the lowermost Corcoran-Cozzette marine sandstones and in the overlying paludal, coastal, and fluvial nonmarine intervals. Insights include: (1) the depositional environment controls reservoir morphology, size, internal structure, and natural fracturing; thus, it must be discerned in order to optimize completions and interpret reservoir performance; (2) natural fractures, even if small and mineralized, are the dominant production mechanism in these, and probably most other, very tight reservoirs; (3) breakdowns and extended cleanup and test times are required for accurate reservoir assessment; (4) effectiveness of hydraulic fracturing appears limited by an anisotropic natural fracture system, high fracturing pressures, accelerated leakoff, and damage to the natural fracture system; and (5) in situ stress behavior varies with depth and lithology, is complex, and significantly affects stimulation and gas production.
