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Abstract: Log analysis of Mesaverde Sandstone Gas Reservoirs, Piceance Basin, Colorado


Fluvial sandstones in the Mesaverde Group produce gas in a broad east-west trend in the southern Piceance basin. Although known to contain substantial amounts of gas for many decades, significant development of this tight gas resource has occurred only in the last 15 years. Despite the best efforts of many organizations and individuals, including the development of log analysis models specific to tight gas sandstones, most of us agree that it is not: possible to predict long term well performance from open hole log; data alone. Attempts to merge detailed petrophysical analyses with basic completion and stimulation data have consistently failed to, yield predictive equations that will allow reservoir engineers to predict ultimate recoveries with any meaningful accuracy.

Using several wells with abundant core information, including the MWX-1, we can demonstrate that even simple, straightforward shaly sandstone log analysis techniques can yield accurate measures of pore volume and water saturation which are confirmed by special core analyses. Reasonable matrix permeability estimates can also be estimated. Statements to the effect that "logs don't work" or that there are fundamental shortcomings with current log analysis models are not supportable. The problem with log analysis in these rocks is that logs are unable to quantify, or in many cases see, several of the key variables that determine the ultimate recovery of a well. These variables include quantitative measures of natural fractures, reservoir compartment sizes, effectiveness of induced fractures, lateral extent of induced fractures, connectivity to nearby compartments not contacted by the well bore, drilling and completion fluid damage, and relative permeability.

AAPG Search and Discovery Article #90946©1997 AAPG Rocky Mountain Section Meeting, Denver, Colorado