A quantitative study of aromatic hydrocarbons in a natural maturity shale sequence - the 3-methylphenanthrene/retene ratio, a pragmatic maturity parameter

The aim of this study is to illustrate the use of multivariate statistical methods in identifying potential maturity parameters. A study of the quanti tative aromatic hydrocarbon results from a natural maturity sequence throug h a thick (> 3000 m) organic lean shale followed by multivariate statistica l treatment of the data was performed. The study series consists of low TOC (ca. 0.5 wt.%) and Rock-Eval S-2 (generally below 1 mg HC/g rock) shales s howing a continuous maturity increase from T-max values of 410 degrees C to ca. 490 degrees C. This trend is mirrored by a concomitant decrease in the hydrogen index from values of around 150 mg HC/g TOC to ca. 40 mg HC/g TOC . Based on the production indices and GC-MS analysis of the saturated hydro carbon biomarkers no indications of migrated hydrocarbons or major facies v ariations were found in the studied samples. In essence this shale sequence represents a near perfect natural maturity series. The 3-methylphenanthren e/retene ratio shows an exponential increase with maturity and is proposed as a very sensitive maturity indicator extending into the late oil window. This maturity ratio has since been successfully applied to both source rock extract (kerogen type III, II/III and II) and oil studies. (C) 1998 Elsevi er Science Ltd. All rights reserved.