ABSTRACT

Thirty Miocene natural gas fields have been established in Alabama since the discovery of Miocene gas in this area in 1979. These fields have produced over 16 billion cubic feet of natural gas from the middle Miocene Amos sand (24 fields) and upper Miocene Luce (3 fields), Escambia (1 field), and Meyer (3 fields) sands. Production from the Amos transgressive sands represents over 92 percent of the cumulative Miocene natural gas produced in Alabama. In addition, 16 offshore Miocene natural gas fields have been established in the Mobile, Viosca Knoll (north), and Chandeleur areas. Over 127 billion cubic feet of natural gas has been produced from upper Miocene sands in the Chandeleur Area.

The majority of the productive Miocene section in onshore and offshore Alabama is interpreted to represent transgressive marine shelf and regressive shoreface sands. Reservoir porosity is primary intergranular and ranges from 21 to 35 percent with permeabilities that may exceed 2,000 md. Petroleum traps are principally sandstone porosity pinchouts against regional dip. Subtle closure and anticlinal nosing are a secondary factor in many of the traps.

The middle Miocene Amos sand bars are the most productive reservoirs of natural gas in Alabama principally due to the porous and permeable nature of these transgressive sands and their stratigraphic relationship to the underlying basinal clays in this area. However, these middle Miocene sands thin and grade basinward into finer grained lithofacies farther offshore. In offshore Alabama, the upper Miocene sands become thicker and are generally more porous and permeable than their onshore equivalents.