Dolomitization and reservoir development of the Upper Jurassic Smackover Formation, Womack Hill Field, eastern Gulf Coastal Plain

An understanding of depositional and diagenetic processes that have affected sediment from deposition through burial is critical for efficient, cost-effective reservoir management. Carbonate sediments in the Upper Jurassic Smackover Formation of the Eastern Gulf Coastal Plain have a complex diagenetic history driven by sea-level change and burial. Differing tectonic and paleotopogaphic influences on sedimentation and diagenesis have led to a diagenetic history different from other major Gulf Coast Jurassic depocenters.; Upper Smackover deposition in the Eastern Gulf Coastal Plain occurred as a series of three shoaling-upward parasequences. Each parasequence has a basal peloid mudstone or wackestone grading upward into ooid-peloid packstone and capped by ooid grainstone. Depositional facies present resemble modern Bahamian ooid shoals.; Diagenesis of these sediments began with micritization and seafloor cementation. Exposure of the ooid shoal led to development of a paleosol surface in the uppermost Smackover. During this exposure, vadose and meteoric diagenetic processes altered the metastable carbonate sediments. Meniscus cementation was the primary vadose process. Meteoric processes include leaching and neomorphism of unstable carbonate sediments. Meteoric cements include isopachous calcite spar, blocky calcspar, and epitaxial overgrowths.; Three phases of dolomitization altered the sediment during early diagenesis. Fabric-selective, mimetic dolomitization occurred early after deposition and exposure of the sediment through a mixing of near-surface meteoric water and seawater. A mixed meteoric-seawater zone developed at the base of the meteoric lens during exposure. This mixing zone dolomite is characterized by relatively inclusion-free, euhedral rhombs having depleted δ18O values suggestive of a meteoric water influence during dolomitization. Following termination of Smackover deposition the Buckner Anhydrite was deposited through evaporative lagoonal and sabkha processes. During Buckner deposition, evaporitically-enhance normal seawater downward refluxed through the upper Smackover dolomitizing the uppermost sediment. This dolomite is characterized by inclusion-rich, subhedral crystals having slightly enriched δ18O values. Minor cation concentrations in the upper dolomite can be used to trace updip to downdip fluid migration during the reflux event. Updip sediments have enriched iron and manganese concentrations and are more stoichiometric than downdip dolomite. With increasing burial physical and chemical compaction dominated alteration of the sediment.