Organofacies Characteristics of the Albian to Turonian Lower Post-Rift Sediments in the Orange Basin, South Africa: Insights into Type III Source Rock

Abstract

The present study describes the quantity, type, maturity, and petroleum generative potentials of potential source rock horizons using Rock-Eval pyrolysis for twenty-four (24) rock samples from the Orange Basin 4-K wells. The results showed an overall abundance of gas-prone organic matter. Since the HI value is generally less than 200mgHCgTOC in all the analyzed samples, it suggests type-III kerogen. Very low S₁ and S₂ yields indicate a low source rock generating potential in the lower post-rift deposits, which are probably more gas prone. Thermal maturity of the organic matter was predicted based on geochemical maturity indicators like Tmax (°C) and Production Index (PI). Tmax values vary from 425 to 476°C, signifying the presence of immature to early mature to late mature and post-mature source rocks. Meanwhile, the PI as a maturity indicator is between 0.10 and 0.27, containing early mature to peak mature source rocks. KH-1 well have PI values ranging from 0.18 to 0.24, with most of the samples at the peak of the oil window. This indicates that the KH-1 well organofacies are more likely to have good generative potential to produce oil.