Abstract

Flat Rock Field lies on the southeastern flank of the Uinta Basin. Shallow Wasatch oil production was discovered in the area in 1962 and natural gas production from the Cretaceous Dakota and Cedar Mountain formations began in 1999. In 2002, the first successful Jurassic Entrada tests were drilled and high volume gas production was established. The Entrada reservoir lies at a depth of approximately 11,500 ft and exhibits porosities over 20%. Flat Rock gas quality is high at 1030 Btu with a low content of inert gases (<3%). Pressure transient analysis indicates a high permeability system with individual Entrada wells testing at rates of up to 18 MMCFGPD.

Jurassic Entrada reservoirs at Flat Rock Field are interpreted to be part of a Jurassic erg or “eolian sand sea.” Outcrop studies document the presence of these ergs in Utah. In particular, these studies show that erg sequences are long, linear trends that contain eolian sandstone bodies with high quality reservoirs. Outcrop studies on the northern flank of the Uinta Basin and in central Utah identify the position of the Entrada erg, but extrapolation across the basin has been difficult due to a lack of deep well control. New deep drilling in the Flat Rock area allows a partial extrapolation of the erg system through this deep, mostly unexplored area. 3-D seismic has been used to identify drilling targets and intra-erg stratigraphic relationships. Recent development wells based on these interpretations confirm the enormous potential of an Entrada intra-erg stratigraphic and/or combination trap at Flat Rock Field.