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Diagenesis
in the
Appleton Oilfield, Escambia County, Alabama
HAYWICK, DOUGLAS W., MARY B. HALL-BROWN, and LEIGH PFEIFFER , Department of Geology, Geography and Meteorology, University of South Alabama, Mobile, AL 36688
Diagenesis is an important control of reservoir quality within
carbonate rocks. In many cases, perhaps the majority of them, diagenesis is as significant
as primary depositional fabric in regulating porosity and permeability in limestone and
dolostone.
The Smackover Formation is an important producer of hydrocarbons along much of the Gulf
of Mexico and in southwestern Alabama, several small production areas have been developed.
The Smackover Formation is pervasively dolomitized throughout this area of Alabama
including the Appleton Oilfield in Escambia County. Here, four textural varieties of
dolomite were recognized in eight cores examined as part of a carbonate diagenesis
study.
They were distinguished on the basis of petrographic character (crystal size, shape and
turbidity), fabric preservation, localization and luminescence properties. All but the
last phase (Type 4) were formed during relatively early diagenetic events. The first phase
(Type 1), may be partially synsedimentary.
Cathodoluminescence suggests that the first three varieties of dolomite were derived from the same fluids and that they were possible hypersaline in character. Contrasts in petrographic character are due to differences in nucleation rate, growth rate, and intensity of concurrent limestone dissolution. Type 4 dolomite is "hydrothermal" in origin (c. <250 degrees C) and was associated with late-stage burial processes. It occurred simultaneously with fracturing and pressure solution and was postdated by a final phase of fracture-filling, luminescent calcite spar.
AAPG Search and Discovery Article #90908©2000 GCAGS, Houston, Texas