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BP Amoco, Denver, Colorado, USA

Abstract: Prospecting for Stratigraphic Traps with 3-D Seismic and Well Information: Examples from the Lewis Formation, Red Desert Basin, Wyoming

The Cretaceous Lewis Formation of the Red Desert Basin is a known gas producing formation with productive fields including Hay Reservoir (240 BCF) and Wamsutter (50 BCF). Thin submarine fan deposits which pinch out against structural dip are the most productive. Many of these units are below seismic resolution but within the limit of seismic detection. Carefully integrating seismic and geological data is key to identifying the subtle image of these stratigraphic features on 3-D seismic.

Time stratigraphic and lithostratigraphic markers within the Lewis Formation were identified on logs and tied to seismic for each well in the Red Desert Basin study area. These markers were extended regionally throughout the 3-D survey and used to create isochron maps. For units above the limit of seismic resolution the areal extent of sandstones were mapped as a direct measurement of top and base of a unit. For units below resolution the areal extent of sandstones were indirectly mapped: using seismic character changes between top and base of a parasequence.

Lewis reservoir units in this area have a distinct water saturation profile with water saturation decreasing updip. More productive Lewis wells are often found where sands pinch out against structural dip. Porosity stays fairly constant across structural elevation within a given field.

Integrating 3-D seismic with the geological interpretation and petrophysical information was key to determining optimal drilling locations within the Lewis Formation. Successful application of this methodology resulted in drilling fourteen straight successful Lewis exploitation wells.

AAPG Search and Discovery Article #90919©1999 AAPG Rocky Mountain Section Meeting, Bozeman, Montana