Carrier-bed plays in the Denver and Powder River Basins

Abstract

Carrier-bed plays are a new type of unconventional oil play that are currently being developed in North America. The reservoirs are generally low quality because of any of the following: thin beds (heterolithic strata), diagenesis, or burrowing (heterogeneous, mixing of sandstones or carbonates and mudstones). The carrier beds are pervasively hydrocarbon saturated and can occur over an areally extensive (greater than than 50 square miles, greater than 129 square kilometers) area. These low-quality reservoirs generally do not meet traditional petrophysical cutoffs and because of the clay content can create low resistivity, low contrast pays. The reservoirs may be composed of clastics or carbonates or a mixture of both. A sub-category of a carrier-bed play is a halo play. Halo plays are the low permeability flanking edges of a conventional oil accumulation (i.e., waste zone or the fringe). The low reservoir quality is generally stratigraphic in origin (facies change from high quality to low quality reservoirs). Carrier-bed and halo plays are being developed with horizontal drilling and multistage hydraulic fracturing. Traditional vertical drilling yields marginal to uneconomic wells but are a clue to the existence of a carrier-bed play. This paper reviews Upper Cretaceous carrier bed plays in the Denver (Codell SandstoneMember of the Carlile Shale) and Powder River (Turner Sandy Member of the Carlile Shale) basins.