ABSTRACT

The Appleton Field was discovered in Escambia County, Alabama in 1983. The original oil in place is estimated to be 3.8 million stock tank barrels. Production from the field has been 2.6 million stock tank barrels of oil. The excellent primary recovery in the field is due to a combination of a strong water drive and the high connectivity of upper Jurassic Smackover porous and permeable reef rocks above and below the oil-water contact. The oil produced is sweet and light with an API gravity of 51.7 degrees. These unique geologic and engineering characteristics have made this field highly economical.

The trapping mechanism in the field is a combination of structure and stratigraphy. The structural component is an anticline associated with a basement ridge. Structural growth was most prominent during the late Jurassic but continued into the late Cretaceous. The stratigraphic component involves favorable reef and carbonate shoal facies. Upper Jurassic Buckner anhydrites are an effective seal rock. The principal reservoir lithologies are dolomitized limestones and dolostones. Porosity types include interparticulate, shelter, intercrystalline, and moldic. Diagenesis is a major factor in the evolution of porosity. Oil is produced from two distinct pay zones. The lower zone (reef facies), with porosities of 9.5 to 25.3 per cent, is productive throughout the field. The upper zone (shoal facies), with porosities of 7.2 to 21.5 per cent, is productive in the northwestern and southeastern parts of the field. The source of the oil is Smackover carbonates which contain ample amounts of algal and amorphous kerogen. The kerogen has undergone favorable burial and thermal conditions. Hydrocarbon migration and entrapment occurred during the late Jurassic into the late Cretaceous.