Abstract: Assessment of Oil and Gas Resources in Idaho-Wyoming Thrust Belt

Richard B. Powers

New oil and gas discoveries in the southern greater Cordilleran overthrust belt at Pineview field, Utah, and at Ryckman Creek and Yellow Creek fields, Wyoming, in the past two years indicate that the province has significant oil and gas resource potential. The province contains widespread source beds and reservoirs, particularly in Cretaceous, Jurassic, Triassic, and Permian rocks. On the basis of recent discoveries, the Nugget Sandstone reservoir of probably Triassic-Jurassic age and the overlying Jurassic Twin Creek Limestone constitute the main exploration targets.

Promising structural traps are indicated in overthrust and subthrust blocks. However, lateral facies foreshortening, trap distortion by thrusting, and lack of subsurface control make pinpointing these structural targets uncertain. Detailed interpretation of seismic data, geologic estimation of preexisting sedimentary-basin outlines, and knowledge of the regional structural evolution of the province are the primary approaches to solving these problems.

Hydrocarbon reserves in currently producing fields are estimated. Estimates of undiscovered recoverable resources are made by using volumetric-yield analytical procedures. Appraisals of undiscovered resources, based on geologic evaluations, are made by use of subjective probability techniques.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC