Last modified: 2011-08-16
Abstract
Palynological and organic geochemical analyses have been carried out on 37 ditch cutting and 12 core samples taken from the SAB-1 well, Central Yemen, to evaluate the hydrocarbon potential of the SAB-1 formations. The late Jurassic (late Oxfordian-early Tithonian) clastics of the Madbi Formation show higher total organic carbon content (TOC) than the overlying Sabatayn and Nafya formations. Therefore, the Madbi Formation has been given much attention, and also because it is regarded as a principal source rock in some basins in Central Yemen.
Organic carbon richness in terms of TOC of the analysed Madbi Formation samples ranges between 1.2 and 7 wt% and with an average value of 4 wt%, indicating a very good potential source rock and with estimated good petroleum potential (PP) of 6-12 mg HC/g dry rock. The Rock–Eval pyrolysis and palynofacies analysis on the investigated samples shows the presence of kerogen type II (oil-prone) of hydrogen index (HI) values ranges between 300 and 410 mg HC/g TOC. The maturity of the Madbi Formation source rock is early mature-oil window, as indicated by the Tmax values, which range from 430 to 440 °C. This maturity level has been also indicated by the visual colour alteration of Classopollis pollen grains with depth.
The present study reveals that the calcareous shale of the lower member of the Madbi Formation, the Meem Member (Oxfordian-Kimmeridgian) is more enriched in thermally mature, oil-prone organic matter than the overlying Lam Member (Kimmeridgian-early Tithonian). Accordingly, the Meem Member is considered as a potential active source for the oil accumulations in the overlying sandstone reservoir of the Sabatayn Formation in the SAB-1 well.