Abstract: Chronology of Oil Generation in Louisiana's Fractured Austin Chalk Deep Horizontal Drilling Trend

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

Chronologically, the thermal maturation of potential hydrocarbon source rocks beneath basal Austin and pre-Austin strata across central and southeastern Louisiana has yielded a continuum of oil expulsion from upper Jurassic and younger source beds since the early Cretaceous. Estimation of volume contributions by these maturing strata below the main fractured chalk drilling trend are made by applying regional modeling and numerical simulation analysis.

Horizontal drilling targets are situated in a depth band between 12,500 and 17,500 ft (3,800 and 5,300 m) that has a width and length of approximately 20 X 236 mi (32 X 380 km). In-trend structural and stratigraphic drilling targets are found in areas of enhanced porosity and permeability which have resulted from fracture development caused by basin evolutionary processes. The primary processes of sedimentary loading, down-warping, and basin-ward gravity sliding over subjacent lower Cretaceous barrier reef trends have combined with divergent wrench faulting, and hydrocarbon generation/expulsion from underlying source beds to provide the most important zones of fracturing.

Although oil generation began in the area before the Eocene, it was not until after development of upper Cretaceous and Paleocene seal rocks and post-Paleocene fracturing of the chalk that oil began to fill the present reservoirs. Peak generation of oil occurred from lower Cretaceous source rocks during Paleocene-Eocene time. Another lesser pulse of generation from upper Cretaceous (mostly Tuscaloosa) source rocks occurred during early and middle Miocene. Hydrocarbon generation from upper Cretaceous strata continues to the present time.

AAPG Search and Discovery Article #90932©1998 GCAGS/GCS-SEPM Meeting, Corpus Christi, Texas