ABSTRACT: Stratigraphic Zone-Depth Predictions for Louisiana's Probable Hydrocarbon Exploration Floor

ZIMMERMAN, RONALD K. , Louisiana State University, Basin Research Institute, Baton Rouge, LA

Question: To what maximum drilling depth might one reasonably, expect to have some chance of finding gas in commercial quantities anywhere in Louisiana? In the final analysis, economic factors define the ultimate depth to which exploration for hydrocarbons can be conducted in any given area. However, the determination of one physical condition--the depth at which natural in situ hydrocarbon destruction would commence--is paramount when evaluating the practicality of even attempting to explore for gas reservoirs in the deeper parts of sedimentary basins.

In basins such as those present in Louisiana, with their thick sedimentary sections and presently active hydrocarbon generation windows, even gas-bearing reservoir host strata would loose commercial viability because of the onset of hydrocarbon destruction and overwhelming reservoir porosity-permeability degradation brought on by hostile burial conditions. Exploration drilling has not reached the base of the present hydrocarbon generation window in many parts of Louisiana. Therefore, a statewide basin analysis was conducted in order to predict the stratigraphic zone and depth at which hydrocarbon destruction begins. The predictions from this analysis are facilitated by palinspastic reconstructions based on projected subsurface data. A subsurface network of sea-level referenced geologic time-depth profiles provides the basic stratigraphic framework from which such predictions are possible.

The maximum depths at which presently active, terminally destructive conditions of hydrocarbons are predicted varies between less than 15,000 ft (4572 m) in the pre-Louann Salt section (pre-Jurassic) of northwest and central north Louisiana to at least 31,400 ft (9571 m) in the Lower Miocene of the extreme southern part of the state in Terrebonne, Lafourche, Jefferson, and Plaquemines parishes. A gradual south-north progression between these two stratigraphic zone-depth endpoints defines the probable hydrocarbon exploration floor across Louisiana.

AAPG Search and Discovery Article #90908©2000 GCAGS, Houston, Texas