ABSTRACT

Fourmile Creek and Splunge Fields contain dry gas reserves of about 17 billion cubic feet and 35 billion cubic feet, respectively, in Mississippian Chester Sands at depths above 1800 feet. Both are combination structural-stratigraphic traps. The trap at Fourmile Creek is formed by simple drape of an isolated sand body on a structural nose. Splunge is more complex, having at least four separate sand bodies, two faults and two hundred feet of vertical closure.

The fields lie in the north part of the Black Warrior Basin in an area of gentle south-southwest dip broken by a few, major, regional, down-to-the-basin normal faults. No evidence of Mississippian growth is found on these faults, and production is not related to them. Smaller, more local faults which are downthrown in the opposite direction do help form traps.

The producing sands appear to be marine and possibly fluvial, high energy deposits occuring in a southwestward-thickening wedge of sediments between the Millerella and Bangor limestones.

Discoveries at Splunge and Fourmile Creek Fields resulted from exploratory efforts based on very sketchy subsurface data. The primary target of the play was thick, Devonian, tripolitic chert porosity in a large, combination fault and pinchout trap. No hydrocarbons were found in the Devonian, probably because of late fault movement. Serendipity can not take full credit for the discoveries because the wells were drilled on prospective structural anomalies and the potential of the Mississippian sands was recognized prior to discovery.