MULLARKEY, JAMES C.
Westport Oil and Gas Company, Inc., Denver, CO

Abstract: Low Contrast, Low Resistivity, Upper Cretaceous Hydrocarbon Reservoirs in the Greater Green River Basin, Wyoming, USA

Well logs from five wells illustrate hydrocarbon production potential of low contrast, low resistivity sandstone reservoirs in the Upper Cretaceous of the Greater Green River Basin (GGRB), southwestern Wyoming. The example reservoir is the Frontier Formation two wells in the Lincoln Road and Mesa fields, at the northern end of the Moxa Arch in the western GGRB. In the eastern portion of the GGRB, examples will be shown from the Blair and Almond formations in Table Rock field and from the Almond Formation in Dripping Rock field. Cumulative production from the five examples totals over 16 BCFG and 85 MBO, all from zones that could have been bypassed due to the low, deep resistivity readings in the reservoir intervals.

The use of data collected by a wellsite geologist and mud logging equipment is extremely important in the integrated process of making a completion decision. Use of all available data, gathered by multiple disciplines, allows intervals that look non-productive on well logs to be perforated and completed profitably. The main cause of the low resistivity response, in the examples shown, is significant electrical conductivity by the immobile formation water. This water is bound mainly by anionic charges in clay minerals common in these upper Cretaceous reservoirs.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas