Maowen Li¹, Jianping Bao², Renzi Lin³, Levern Stasiuk¹, Mingsheng Yuan⁴

(1) Geological Survey of Canada, Calgary, AB
(2) Jianghan Petroleum University, Hubei, Hubei, China
(3) Petroleum University (Beijing), Beijing, China
(4) PetroChina Tu-ha Oilfield Company, China

ABSTRACT: Alternative Lacustrine / Marine Source Rocks for the "Coal-derived Oils"

The L-M. Jurassic coals have been considered to be the major source rocks for most oils discovered in the Turpan-Hami Basin, NW China. This study provides evidence for additional, significant contributions from the Carboniferous-Permian lacustrine/marine source rocks. One of the evidences for the predominance of vertical over lateral hydrocarbon migration in this basin is that all of the major petroleum accumulations discovered appear related to fault systems. Molecular and petrographic data indicate that most Jurassic strata are currently immature or marginally matur, with only a small portion of the coal-bearing strata near major depocenters having reached the conventional oil window. Hydrocarbons derived from the Upper Permian lacustrine and Carboniferous-Lower Permian marine/transitional sources are widespread in fractured Jurassic strata, with mixed biomarker signatures being detected in many of the produced oils. Maturity comparison between the produced oils and potential source rocks indicates that most of the oils must have migrated significant vertical distances. The occurrence and geochemistry indicate that most of the discovered hydrocarbon gases were thermogenic in origin, most likely from type II sources not low rank coals. Quantitative biomarker studies reveal that the contribution from Jurassic coals may be significantly exaggerated when adhering strictly to a conventional approach of biomarker interpretation. The dominance of liquid over gaseous hydrocarbon resources in this basin suggests that most oils in the Jurassic reservoirs of the basin are not strictly "coal-derived oils". We propose here an alternative model to explain the known hydrocarbon occurrence and to predict future exploration directions in this basin.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado