Reservoir quality and stratigraphy of the Mowry and Muddy interval of the Powder River Basin, Wyoming, USA

Abstract

Interest in the Powder River Basin (PRB) of Wyoming, Northwest USA, has been increasing in recent years, as it is a mature basin with a number of prolific stacked plays, coupled with the promise and opportunity of a few key emerging plays. The Mowry Shale is one of the emerging unconventional plays and has historically been characterized as a key source rock for the underlying Muddy Sandstone and other shallower reservoirs. Both the Mowry Shale and the Muddy Sandstone are considered underex¬plored and to have potentially significant potential. Looking at these two plays in concert, the contrasts between the conventional and unconventional opportunities are clear. Despite its name suggesting otherwise, in its truest form, the Muddy Member is a fluvial estuarine sandstone and, when found, is most often clean and well sorted. The Mowry, on the other hand, is a shallow marine shale, ubiqui¬tous however quite heterogeneous in the basis. Drilling activ¬ity suggests that the industry is struggling to understand the stratigraphic and spatial controls on exploiting the Mowry as an unconventional target. In discussing prospectivity in the Mowry and Muddy interval, a common theme is: ‘We know where the Mowry is but we don’t know where it’s good; we know the Muddy is good but we don’t know where it is.’