Geochemical characteristics of the Silurian-Devonian Kroh black shales, Peninsular Malaysia: An implication for hydrocarbon exploration

Abstract

In this study, the hydrocarbon potential of the Silurian-Devonian Kroh black shales in Peninsular Malaysia was investigated. To this aim, seventy-five samples from the Kroh black shales were analyzed to identify their geochemical and mineralogical composition using X-ray diffraction (XRD) and X-ray fluorescence (XRF), respectively. XRD results showed that the samples consist of two main components: kaolinite and quartz. From the XRF analysis, the most dominant oxides in the Kroh black shale samples were SiO2 (75.1 wt%) and Al2O3 (13.5 wt%). The ratio of Al2O3/TiO2 suggests that the black shales are originated from an intermediate to felsic igneous rock. The ratio of V/(V + Ni) varies from 0.8 to 1, and V/Ni ranges from 4.3 to 7.1. These values suggest suboxic to relatively anoxic depositional conditions and purely marine sources of organic matter (OM). However, a cross-plot of Ni vs. V indicated that depositional conditions of the Kroh black shales are terrestrial oxic to marine-terrestrial oxic-dysoxic. Also, Rock-Eval 6 pyrolysis was applied to assess the hydrocarbon potential of the Kroh black shales and acquire more information on the thermal maturity of organic matter (OM). Data from the Rock-Eval pyrolysis revealed that the total organic carbon (TOC) content of the seventy-five black shale samples from seven outcrops (i.e., KR-1 to KR-7) varies from 0.33 wt% to 8.56 wt%. The TOC values indicate that the Kroh black shale samples have preserved a fair to a good quantity of the OM richness. Moreover, Rock-Eval analysis affirmed that the samples predominantly fall within a weak version of Type III kerogen, as gas-prone window, and Type IV kerogen, as inert solid bitumen. Furthermore, the relationship between hydrogen index (HI) and production index (PI) with vitrinite reflectance (Ro) confirms an immature to overmature of the OM in the Kroh black shales. Those findings bring to light the Kroh black shale samples are at a minimal level of HC generation; hence, commercial considerations for the Kroh Formation might not be worthwhile. It also adds new insight into the peninsular depositional conditions, contributing to the region's paleogeography understanding.