A New Look at the Williams Fork Formation: Tight-Gas Sands in the American Rocky Mountains

Abstract

The Williams Fork Formation in western Colorado is a significant tight-gas producer, containing up to 423 Tcf of original-gas-in-place (Law, 2002). Production comes from isolated-to-amalgamated fluvial sandstones encased in floodplain muds and sourced by laterally- and vertically-adjacent coals. This interval, known as the Mesaverde Group, records the eastward progradation of siliciclastic material from the Sevier Orogeny into the Western Interior Seaway during the latest Cretaceous. The Mesaverde Group, and the Piceance Basin in general, has been the subject of tight-gas sand research for decades through collaboration between industry, government, and academia, reaching its peak in the 1980s and 1990s. Past field research has focused primarily on the western basin margin where outcrop is well-exposed at near-horizontal dips as opposed to the eastern margin where vertical-to-overturned strata and weathering have limited research to a handful of studies in recent years. Regional unconformities make matters worse by juxtaposing unique fluvial deposits (i.e., three separate formations) that span the rise of the American Rocky Mountains. Increased drilling and downspacing occurred during the natural gas boom of the early 2000s; however, the subsequent crash in natural gas prices has left little interest in this region, except for current operators and academics. This has left a surplus of new data in the public realm with little attention, including production volumes, completion reports, and subsurface well logs. Heightened well control now aids detailed subsurface correlation, allowing a real comparison to outcrop studies and their applicability for field development and future exploration. This study aims to integrate recent outcrop work along the eastern margin of the basin with current subsurface well control, production characteristics, and past research for a coherent understanding of stratigraphic variability and how it relates to basin productivity and the petroleum system. In addition, an attempt to clarify and constrain the nature and extent of regional unconformities is made to resolve the disconnect commonly seen between geologists working in outcrop versus operators working in the subsurface. Simple reservoir engineering techniques are also proposed as a novel method to help characterize effective formation permeability during late-time boundary-dominated flow.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015