ABSTRACT

Exploration for Upper Jurassic and Lower Cretaceous reservoirs associated with updip basement structures is currently the most active exploratory oil play in Alabama. Excellent production rates, on the order of hundreds of barrels of oil per day, are commonly encountered at depths between 2,510 and 4,719 meters (8,235 and 15,478 feet). Over 26.9 million barrels of oil and 33.7 billion cubic feet of gas have been produced from fifty-five fields established in the Hosston, Haynesville, Smackover, and Norphlet Formations. The majority of this production has been from Smackover and Haynesville reservoirs. Production from Smackover carbonates began at Toxey field in 1967 and from Haynesville sandstones at Frisco City field in 1986. During December 1994, Smackover wells averaged 99 barrels of oil per day and Haynesville wells averaged 275 barrels of oil per day. The Norphlet at North Excel field and the Hosston at Pleasant Home field have also produced oil. In 1995, two new Haynesville fields, North and Southwest Excel, were established based on discoveries in the Frisco City sand. Fields in the updip basement structure play cluster in three distinct areas; (1) a western area on the Choctaw Ridge complex, (2) a central area on the Conecuh Ridge complex, and (3) an eastern area in the Conecuh Embayment. Reservoir lithologies include Smackover limestones and dolostones and Hosston, Haynesville, Smackover, and Norphlet sandstones. Hydrocarbon traps are structural, anticlines or faulted anticlines, and combination traps where reservoirs occur on the flanks or partially over the crests of basement paleohighs. An understanding of both the trap and reservoir properties is critical to ensure the successful discovery and development of Upper Jurassic and Lower Cretaceous oil reservoirs associated with the updip basement structure play of southwest Alabama.