Stratigraphy and Depositional Setting of the Lower Missourian (Pennsylvanian) Bethany Falls and Mound Valley Limestones, Analogues for Age-equivalent Ooid-grainstone Reservoirs

Abstract

Significant quantities of mobile oil remain in Pennsylvanian reservoirs in the midcontinent region of the United States. To recover this oil efficiently, we must understand the factors that control heterogeneity in these complex reservoirs. One way to accomplish this is to evaluate reservoir-quality carbonate units that occur in both the outcrop and the shallow subsurface as analogues to equivalent producing zones. In southeastern Kansas the lower Missourian Bethany Falls and Mound Valley limestones contain oolitic grainstones similar to coeval productive lithofacies that occur in the deeper subsurface to the west. Depositional sequence analysis of these grainstonebearing units suggests that (1) at least two cycles of relative sea-level change led to the deposition of discrete oolitic grainstones that are separated by subaerial exposure surfaces, with these surfaces strongly influencing the vertical distribution of porosity, and (2) the character and distribution of reservoir-scale grainstone buildups were strongly controlled by preexisting depositional topography.