ABSTRACT

Mapping significant facies on a "time"-slice basis permits the interpretation of synchronous depositional environments in the transgressive-regressive Smackover Formation. These environments were influenced by relict Norphlet sandstone relief and by Louann Salt mobility in the "Jay trend" area. Pre-salt faulting influenced Louann deposition and may explain the salt mobility as well as stratigraphic differences between Big Escambia Creek field and the Jay-Blackjack Creek fields.

The "Jay trend" area, during Oxfordian time, was located within a deeply embayed shoreline that restricted marine circulation which, in turn, permitted deposition of relatively low-energy sediments. The transgressive carbonates of the lower Smackover are characterized by intertidal laminites, subtidal micritic-oncoidal limestones, and marine micritic-skeletal limestones. The micritic-oncoidal limestones aggraded and prograded in the progressively deepening transgressive sea. Later, these algal-flat, oncoidal limestones provided the positive stable areas upon which pelletal sediments accumulated during the early phase of regression. In the final phase of regression the fecal pellet sediment accumulated, and may have been generated, in nearly closed embayments and abandoned tidal channels. As the sea regressed from the area, a sabkha-brine pan complex prograded over the pelletal grainstones depositing evaporitic silici-clastic sediments which eventually sealed the reservoir.

Porosity is highly facies-selective in most of the trend area and closely follows the distribution of hardened fecal pellet dolomites. During the close of Smackover deposition, the arid climate of the area caused the formation of a deep vadose zone which retarded the normal process of intergranular cementation. Early dolomitization stabilized primary porosity. In early Kimmeridgian time, leaching in the deep vadose zone preferentially attacked the internal pores of the partially dolomitized favreinid pellets and enhanced porosity in the pelletal dolomite reservoir. Limited porosity was also produced by sporadic leaching of oncoidal grains and micrite matrix.