I. Steinhoff, D. M. Stone, R. M. Harper, and D. S. Muller

BP America, Inc., Houston, Texas

ABSTRACT: Significant Gas Accumulations in Submarine fan Deposits of the Lewis Shale in the Greater Green River Basin of Southwestern Wyoming: A Success Story

Major fields have been producing hydrocarbons from the tight gas reservoir of the Maastrichtian Lewis Shale in the Red Desert Basin, Greater Green River Basin (GGRB), SW-Wyoming, with a total recoverable reserves of ~240 BCF, ~110 of which have been produced today (1976- recent). Lewis production averages ~4-5 BCF/640 acres in these areas. More, virtually untapped reservoirs in the Lewis Shale exist in the GGRB.

In the Wamsutter Development Area numerous turbidite reservoirs are encased in deeper marine shales which serve as efficient seals. This facies relationship forms stratigraphic traps with associated hydrocarbon accumulations in structural up-dip pinch out zones of individual sand lobes forming productive gas compartments.

A depositional model and a sequence stratigraphic framework were developed from regional facies associations and stacking patterns to break out chronostratigraphic (flow-) units, map associated net sandstone reservoir compartments, and understand the complex compartmentalization of these reservoirs. More than 20 parasequences are recognized in the prograding Lewis Shale/Fox Hills depositional system including an estimated 50 to 60 individual sand lobe complexes and channels. Shows a north south regional cross section through 19 wells penetrating the Lewis Shale section across about 50 miles of the basin. Colors indicate stratigraphic sequences within the Lewis.

Formation and production tests further help delineate the spatial arrangement of productive zones.

Well 9 is an example of the log signature and performance variation in the Lewis sands. Interval “sand 2” is a 180 foot sedimentary package in the upper part of the Lewis Shale including high porosity water bearing sands, Interval “sand 3” is a 25 foot thick high-porosity gas-bearing sand, Interval “sand 4” is a 210 foot package with tight non-productive sands in the lower part of the Lewis Shale. Distinguishing productive from non-productive sands is a continuing challenge.

The hydrocarbon potential of the Lewis Shale will be part of future development of the area and will also define additional step out opportunities. Further, targeting by-passed pay behind pipe and respective recompletion programs in existing wells producing from the deeper Mesaverde Group will unlock significant additional hydrocarbon reserves in the GGRB. Lewis Shale plays represent a highly profitable hunting ground for hydrocarbons in today’s high price environment.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado