Carrier Beds as Unconventional Reservoirs

Abstract

Carrier beds provide pathways for hydrocarbons to migrate from source rocks to reservoirs. Carrier beds may—but often don’t—have the same reservoir properties as the conventional reservoirs supplied by them. Indeed, the boundaries of many conventional fields are defined by changes in porosity, and, more often, permeability, associated with a change in facies between the carrier beds and the reservoir. The low permeability of some carrier beds does not preclude them from supplying conventional reservoirs, because generation rather than migration is the rate-limiting process at geological time scales. If sufficient porosity exists for economic volumes of hydrocarbons to be present, the low permeabilities that previously marked the economic limits of some fields need no longer preclude extension of the field downdip into surrounding strata. Horizontal drilling and multistage completions may allow low permeability carrier beds to become reservoirs. The offshore Mancos Shale play associated with Bisti field in the San Juan basin produces from the muddy, bioturbated offshore facies that served as carrier beds for the conventional reservoir. The term halo play has been used for certain unconventional light oil plays surrounding Pembina field in Alberta, Canada. Excluding bypassed pay, these plays are in fact producing from muddier, bioturbated offshore facies that served as carrier beds for the conventional reservoirs updip. Plays similar to the offshore Mancos Shale play and the halo plays surrounding Pembina field may be associated with isolated linear sandstones in the Cretaceous up and down the Western Interior Seaway— and elsewhere. Calling attention to this similarity by identifying carrier beds as a separate play type will focus attention on such plays and perhaps lead to future discoveries.

AAPG Datapages/Search and Discovery Article #90343 ©2019 AAPG Southwest Section Annual Convention, Dallas, Texas, April 6-9, 2019