Sequence Stratigraphic Control on Reservoir Quality in Morrow Sandstone Reservoirs, Northwestern Shelf, Anadarko Basin

J. Puckette, Z. Al-Shaieb, A. Close, K. Rechlin, and M. McPhail
Oklahoma State University, Stillwater, OK

Upper Morrowan valley-fill sandstones are major oil and gas reservoir on the northwestern shelf of the Anadarko basin. Three major lithofacies assemblages were recognized in cores and extrapolated from wireline log responses: Marine, fluvial and estuarine. The primary marine lithofacies are dark fossiliferous shale and bioclastic sandstone. Fluvial facies are characteristic of a braided stream channel complex. The complex is further characterized by trough cross bedding containing stacked fining upward sequences, low-angle cross beds and fine- to coarse-grained sandstones and interbedded/ laminated with silty, shaly and coal intervals. Estuarine facies are characterized by interbedded fine- to medium-grained sandstones and shales, with abundant trace fossils or burrows.

Incised valley developed in response to major drops in relative sea level. Lowstand system tract (LST) deposits were not commonly preserved and are limited to a few thin clay-clast conglomerates. Subsequent sea-level rises resulted in valley filling with fluvial and estuarine facies of the transgressive systems tract (TST). As sea level continued to rise, sediment deposition shifted landward. Therefore, deposition of marine silt and mud represents the high stand systems tract (HST) sediment assemblage.

Reservoir quality is controlled by sequence stratigraphic framework coupled with compositional and textural parameters. Braided stream channel complex (F2, F3) deposited during the TST are the best reservoirs observed. The average porosity and permeability is 13.35% and 50.6 md respectively. On the other hand, marine sandstones (M1) contain abundant skeletal grains and carbonate cementoccluded porosity. Fine-grained estuarine sandstones are typically poor-quality reservoirs due to high detrital clay content and the affects of biogenic modification that destroyed primary porosity.

AAPG Search and Discovery Article #90903©2001 AAPG Mid-Continent Meeting, Amarillo, Texas