ABSTRACT

The unexpanded Lower Tuscaloosa Formation is a major oil producer in southwest Mississippi. Exploration of the Lower Tuscaloosa Trend began in the mid-forties with major fields being found on large uplifts and low-relief structural noses. Today the Trend is considered mature; however, the discoveries of several significant stratigraphically controlled fields since 1980, such as Liberty, Millbrook, Olive and Newtonia, have renewed exploratory interest. Seismic stratigraphy is critical in exploration for stratigraphic reservoirs of this type. Sands can be predicted chiefly because of the low velocity of the reservoir sands relative to the enclosing higher velocity shales. The environment of deposition of the Lower Tuscaloosa reservoir sands may be fluvial, transitional marine, or transgressive marine. The geologic arguments for the various environments of deposition become moot as the erratic geometry of sand distribution is common to all these environments. The projection of sand distributiuon away from well control without modern seismic data is very risky at best. Standard geologic exploration techniques such as sand isopachs and paleostructure maps are of limited value when looking for new fields in areas where well control is sparse or absent. A structure map on the top of the Lower Tuscaloosa and a petrophysical (sonic log) understanding of the objective section (Top Lower Tuscaloosa marker to Top Lower Cretaceous unconformity) can lead to the discovery of additional small to medium-sized stratigraphically trapped oil fields (1-7 million barrels of oil EEB's).