Palynofacies and Source Rock Potential of the ST-7H Well, Offshore Tano Basin, Western Region, Ghana

Abstract

Samples from ST-7H well offshore Tano basin in western region of Ghana have been subjected to palynofacies, palynological and geochemical analysis. Five palynofacies associations (I – V) have been identified based on the percentage relative abundances of the sedimentary organic matter (SOM). Palynofacies type I and type IV reflects deposition in a distal dysoxic-anoxic shelf (nearshore) environment, palynofacies type II suggest distal dysoxic to anoxic shelf to deep basin environment with abundant AOM, palynofacies type III is indicative of distal dysoxic to oxic shelf (fluvio-deltaic) environment of deposition and palynofacies type V, a mud –dominated oxic distal shelf (open marine) environment. Based on marker palynomorphs, an Aptian to Maastrichtian age, have been assigned to the sediments in the ST 7H well, with an unconformity between the Cenomanian and Campanian sediments. Geochemical data indicate that the samples from ST 7H well have fair to very good petroleum potential. Most of the samples, however, fall out of the hydrocarbon generating zone because of the low (< 0.10) Production Index (PI). Kerogen types show type II, II/III and III which are oil prone, oil-gas prone and gas prone respectively. Thermal maturity from within the well indicates immature to early mature hydrocarbons.