Abstract: Reservoir-Quality Aspects of Eolian Deposits

R. Lupe, T. S. Ahlbrandt

The upper Paleozoic to Mesozoic eolian sandstones of the Colorado Plateau and the Rocky Mountains of Colorado and southern Wyoming represent an interaction of three closely related depositional environments: dune, interdune, and extradune. They carry the misnomer "blanket sandstones" but actually are texturally complex. They comprise porous and permeable dune sandstones enveloped by less porous and permeable extradune/interdune sedimentary rocks. Extradune sediments include all deposits marginal to a dune field which are related to dune sediments in time and space by having a similar source and by being elements of the same depositional system. They are mainly aqueous deposits but may include some eolian sands (e.g., serir sands). Interdune sediments here are restricted to those nondune sediments deposited in relatively flat areas between dunes. Extradune/interdune deposits can be differentiated from dune sandstones by their textures and structures which are reflected in characteristic well-log patterns.

The model of "blanket" sandstone inhomogeneity was applied to the Weber Sandstone, Brady field, Wyoming. Data supplied to the model were obtained both from the outcrop and from the subsurface, including the recognition of sedimentary environments from electric logs. As predicted, the texture of dune deposits in this model contrasted markedly with that of extradune/interdune material in the Brady field. Furthermore, the less porous and less permeable extradune/interdune sedimentary rocks surrounded dune sandstone, which is the primary reservoir rock. This potentially detrimental effect on fluid migration in the reservoir could influence significantly the efficient recovery of hydrocarbons.

AAPG Search and Discovery Article #90979©1975 AAPG – SEPM Rocky Mountain Sections Annual Meeting, Albuquerque, New Mexico