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 (>50 mi2 [>129 km2]) area. These low-quality reservoirs generally do not meet traditional petrophysical cutoffs, and because of the clay content, they can create low-resistivity, low-contrast pays. The reservoirs may be composed of clastics or carbonates or a mixture of both.
A subcategory 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 provide a clue to the existence of a carrier-bed play.
This paper reviews Upper Cretaceous carrier-bed plays in the Denver (Codell Sandstone Member of the Carlile Shale) and Powder River (Turner Sandy Member of the Carlile Shale) Basins.