Abstract

The events and geologic concepts that led up to the discovery of Grieve Field on August 30, 1954 by Forest Oil Corporation are described. Grieve Field is by far the largest of several Muddy Sandstone oil fields discovered in the southeastern portion of the Wind River Basin, having produced 29,883,245 barrels of oil and 102.6 BCF of gas. In 1953 Forest opened an office in Casper and shortly thereafter took a 25,000 acre lease prospect submitted by Raymond Chorney, a local lease broker. Lack of oil saturated sandstones and faulting southwest and up dip of the prospect acreage prompted Forest to acquire a seismic survey to identify favorable structures. The seismic mapping identified six possible northwest trending faults with structural closure on the down dip side. Uncertainty surrounded the fault interpretations even to the extent of whether or not the faults were real. After careful examination of the interpreted faults it was concluded that Fault No.5 had the most favorable attributes. A 9,500 foot Tensleep test was approved by management and the well spud on May 21, 1954. An oil saturated sandstone was encountered at 6,714 feet. This sandstone proved to be the lower Muddy. Drilling was halted in the lower Sundance at a depth of 7,288 feet after no further shows were encountered. The well was completed flowing 1,220 bbls of 36.3 degree API gravity oil. Further drilling revealed this discovery was a stratigraphic trap and no evidence of faulting has ever been discerned on electric logs