Abstract: Walker Creek Field: Smackover Diagenetic Trap

Jack W. Becher, Clyde H. Moore

The Walker Creek field is the largest so-called stratigraphic trap yet discovered in the Smackover state-line trend. The porosity at Walker Creek is developed in an upper Smackover oolite sequence thought to represent a regressive, high-energy shoreline deposit modified by contemporaneous structural movements associated with salt diapirism. The southern Persian Gulf shelf is its Holocene analogue. The upper Smackover oolite reservoir is a continuous sequence of very well-sorted lime grainstones containing no interstitial, low energy lime muds. Porosity occlusion and ultimate trap formation are the result of early cementation associated with meteoric water-table conditions developed during periodic exposure of the Smackover during its depositional history. The porosity-occ uding, early carbonate cements formed in the meteoric phreatic zone directly beneath the water table, while primary porosity was being preserved in the overlying meteoric vadose zones. This primary porosity has been preserved preferentially over the active diapiric structures because vadose conditions persisted across the topographic highs for longer periods of time. Thus, porosity distribution within the Smackover at Walker Creek is not controlled by original depositional processes--such as the pinchout of a porous sand into a lagoonal clay--but is the direct result of the early cementation history of a carbonate-sand sequence that exhibited little variation in original porosity.

The demonstration that Walker Creek is a "diagenetic trap" rather than a true stratigraphic trap gives the explorationist and production engineer in the Arkansas-Louisiana Smackover trend a valid alternative model for potential reservoir characteristics.

AAPG Search and Discovery Article #90975©1976 GCAGS- GC Section SEPM Annual Meeting Shreveport, Louisiana