Depositional and Diagenetic Facies, Smackover Formation, Chunchula Field, Alabama: ABSTRACT

Abstract

The Chunchula field lies on the northeastern edge of the South Mississippi platform and produces from dolomitic carbonates of the Smackover Formation. The Smackover section overlies the subaerial to marine Norphlet Sandstone and itself represents a general transgressive-regressive sequence of shallow-marine to supratidal facies similar to those found on the Great Bahama Bank today. The Chunchula carbonate section is composed of at least three major units. The basal interval is the lowermost Smackover section and is composed of medium to coarsely crystalline dolomite and its upper boundary seems to be marked by a significant disconformity. The second unit is interpreted as upper Smackover and is composed of medium to coarse-grained dolomite in the central and western parts of the field, but becomes predominantly limestone along the northern and eastern edges of the field. The uppermost part of the carbonate section is a finely crystalline dolomite that represents part of a sabkha sequence and probably belongs to the overlying Buckner evaporite section. Porosity development is restricted to the dolomitic units and seems to be preferentially associated with paleotopographic highs. The best reservoir intervals are composed of intercrystalline dolomite and pelmoldic porosity and have their maximum development in the southeastern part of the field. Carbon and oxygen isotopes and strontium ion concentration data suggest that fresh or brackish fluids have played some role in the development of porosity in the Smackover carbonates. End_of_Article - Last_Page 607------------