ABSTRACT: Origin of the Tertiary Reservoired Hydrocarbons along the Central Texas and Louisiana Gulf Coast Rim

Gary A. Cole, E. W. Chinn, N. Piggott, M. J. Gibbons, R. Sassen

Tertiary reservoired hydrocarbons along the central Texas and Louisiana Gulf Coast rim were most likely derived from Paleocene/Eocene Wilcox Group and Sparta Formation marine shales. Sixteen total soluble extracts and >200 oil samples were analyzed using carbon isotopic techniques (^dgr¹³C) and gas chromatography-mass dpectometry (GC-MS). Results demonstrated that interpretations must use all types of data because Cretaceous derived and Tertiary derived oils overlap in southern Louisiana. When isotopic, sterane, hopane, and light hydrocarbon data are combined, separation of classes become possible. Cretaceous oils and extracts have a full range of extended hopanes, a characteristic peak eluting immediately after C₃₀ hopane and no oleanane. Paleoge e oils and extracts have oleanane and a restricted range of extended hopanes. Regional trends indicate that eastern Louisiana oils were derived from the Sparta or a Sparta/Wilcox mix, the Mississippi delta oils from a Cretaceous clastic source, and western Louisiana and Texas oils from the Wilcox source. Regional variations in GOR/CGR are a function of timing and mechanism of migration.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990