ABSTRACT: Biomarker Geochemistry of Lacustrine-sourced Crude Oils: A Worldwide Survey

Zumberge, John E.¹, Harold Illich¹, Stephen Brown¹, and Nick Cameron²
(1) GeoMark Research, Inc, Houston, TX 
(2) GeoInsight, Chesham, Bucks, United Kingdom

Crude oils generated from lacustrine source rocks of various ages, deposited in different techtonostratigraphic regimes, show remarkably consistent key terpane/sterane biomarker parameters. The ratio of C26 to C25 tricyclic terpanes is usually >1.3 while the abundance of C31R homohopane to C30 hopane is often <0.25 in lacustrine oils. These key ratios are different than those found in oils sourced from marine shales and carbonates. Other biomarker parameters characteristic of lacustrine oils include relatively high C21/C23 tricyclic terpane values and low total sterane to terpane ratios. The latter relationship suggests a greater contribution of bacteria relative to algae in lacustrine versus marine environments. The waxy nature of many lacustrine oils is well known with n-paraffin C27/C17 ratios averaging 0.70 compared to deepwater marine shales that average only 0.26 in a large oil database. Lacustrine oils included in this study are from West African salt basins; Reconcavo and Campos basins of Brazil; Beibu and Pearl River basins of China; Natuna, Sunda, Penyu, and Mekong basins from the Far East; Inner Moray Firth of Scotland; Cuyo and San Jorge basins from Argentina; and the Unita Basin in Utah.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia