JOHN, CHACKO J., D. E. POPE, B. L. JONES, M. E. SILVA, and R. P. McCULLOH, Louisiana Geological Survey, Baton Rouge, LA; and D. G. BEBOUT, Bureau of Economic Geology, Austin, TX

Major Gas Reservoir Production from South Louisiana Onshore Post-Eocene Plays

The South Louisiana Cenozoic is mostly dominated by siliciclastic sediments deposited by the Mississippi River, its antecedents and several lesser streams to the west. Cross sections of the Louisiana Gulf Coast demonstrate a general pattern of shallow to deeper water time transgressive facies in successively older and deeper strata. From north (landward) to south (basinward) those are (1) massive sandstones separated by thin shales, (2) alternating sandstones and shales in approximately equal amounts, and (3) thick shales containing thin sandstones. These three facies are interpreted as proximal-deltaic, distal-deltaic, and slope depositional systems, respectively. In this study, in which production (1965-1990) by major gas reservoirs (>10 Bcf) has been compiled for the first time, biostratigraphic markers have been used to divide the post-Eocene section into nine plays. The Plio-Pleistocene is considered a single unit. The Miocene is subdivided into upper, upper middle, lower middle, and lower units. The Anahuac is considered as a single unit. The Frio is subdivided into upper, middle, and lower units. Further division of plays into subplays was made based on lithology, log pattern, and depositional environment.

The Plio-Pleistocene play (onshore) has a cumulative production of 504 Bcf from 29 reservoirs in 13 fields. In the upper Miocene play, the cumulative production from 152 major gas reservoirs contained in 36 fields is 4.6 Tcf. The upper middle Miocene play has produced 7.6 Tcf from 237 reservoirs in 62 fields. The lower middle Miocene play has 56 fields containing 182 reservoirs with a total cumulative production of 4.9 Tcf. The lower Miocene play includes 59 fields containing 158 reservoirs with a total cumulative production of 6.0 Tcf.

Cumulative production from the Anahuac play totals 1.9 Tcf from 73 major gas reservoirs in 43 fields. The upper Frio play has 55 major reservoirs in 29 fields which together have a cumulative production of 2.8 Tcf. The middle Frio play has 35 fields containing 49 reservoirs with a total cumulative production of 1.3 Tcf. Finally, the lower Frio sandstone play has 12 fields containing 34 reservoirs that together have produced 1.1 Tcf. Although Louisiana production peaked in the early 1970's and has been declining since 1986, it is still substantial making Louisiana the second leading gas producer of the United States.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.