Abstract

Sequence stratigraphic interpretation of Middle Ordovician Simpson Group of the southern Mid-Continent indicates significant, untapped reservoir potential remains. This reservoir potential exists within stratigraphic traps that lie off-structure, or may be too thin to be seismically resolved. Stratigraphic traps can be predicted and exploited through application of fundamental sequence model principles. Historically, exploration for Simpson sandstone reservoirs in Oklahoma has been structurally driven. As a consequence, there has been little exploratory drilling for stratigraphic traps that may exist in sparsely drilled areas off-structure. A sequence stratigraphic interpretation has led to development of a revised depositional model for strata of the Oil Creek through Bromide formations of the Simpson Group, in the southern Mid-Continent. Through this revised depositional model, widely recognized but poorly understood stratal geometries and discontinuities of the Simpson Group strata are clarified and placed within a basinwide stratigraphic framework. Within this sequence framework, each of the Oil Creek, McLish, and Bromide formations is interpreted as a third-order stratigraphic sequence. Each of the lowermost sandstones of the Oil Creek, McLish, and Bromide formations is interpreted as an areally restricted, basal lowstand to widespread early transgressive unit of a third-order stratigraphic sequence. The overlying interbedded marine shale, shallow marine carbonates, and minor sandstone are interpreted as late transgressive to highstand deposition within each sequence. Sequence boundaries may be conformable in the southern Oklahoma region, but in more updip regions, sequence boundaries are demonstrably erosional.

Stratigraphic trap prediction by the described sequence model runs counter to widely held dogma that Simpson sandstones produce only from closed structural highs. This sequence interpretation facilitates prediction of stratal discontinuities in stratigraphic trap geometry, and recognition of internal reservoir heterogeneity which can lead to discovery of significant new field reserves and recovery of additional reserves from bypassed pay in existing fields.