Exploration Methods--Lower Tuscaloosa Trend, Southwest Mississippi

James B. Hersch

The unexpanded lower Tuscaloosa Formation is a major oil producer in southwest Mississippi. Exploration of the trend began in the mid-1940s with major fields being found on large uplifts and low-relief structural noses. Today the trend is considered mature; however, the discoveries since 1980 of several significant stratigraphically controlled fields, 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 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 m rine. The geologic arguments for the various environments of deposition become moot, for the erratic geometry of sand distribution is common to all these environments. Without modern seismic data, the projection of sand distribution away from well control is very risky. Standard geologic exploration techniques, such as sand isopachs and paleostructure maps, are of limited value in exploring for new fields in areas where well control is sparse or absent. A structure map of the top of the lower Tuscaloosa and a petrophysical (sonic log) understanding of the objective section (top of lower Tuscaloosa marker to top of Lower Cretaceous unconformity) may lead to the discovery of additional small to medium-sized stratigraphically trapped oil fields (1-7 million bbl of oil equivalent).

AAPG Search and Discovery Article #91042©1987 GCAGS and GC-SEPM Section Meeting, San Antonio, Texas, October 28-31, 1987.