Integrated geochemical and statistical evaluation of the source rock potential in the deep-water, Western Basin of Ghana

Abstract

Ghana is recognised as one of the recent oil and gas producing countries in the Gulf of Guinea, West Africa. However, despite the significant hydrocarbon accumulation in the Western Basin of Ghana, not much is known about the current potential of source rocks in this Basin. To broaden the scope of current knowledge on the Western Basin of Ghana, this paper identifies the current formation potential, organic matter origin, thermal maturity, and possible ages within the Cretaceous Period for hydrocarbon generation in the basin, using geochemical techniques and statistical analyses of 1530 cuttings and core samples. The geochemical parameters include pyrolysis data such as free hydrocarbon (S₁), hydrocarbon generated (S₂), carbon dioxide released (S₃), hydrogen index (HI), production index (PI), maximum temperature (T_max), oxygen index (OI) and total organic carbon (TOC). The formations encountered in the Western Basin, which have various ages within the Cretaceous Period , show a good to very good possibility of producing hydrocarbon with mainly kerogen type II/III and some amount of type I in certain formations. The majority of the Cretaceous ages fall in the early mature to peak maturity zone, with Campanian and Santonian considered as additional hydrocarbon sources to the Albian, Cenomanian, and Turonian. Pearson coefficient showed that TOC has a strong positive correlation with S₂, positive correlation with S₁ and HI, and negative correlation with T_max. Two-Step and K-means clustering on the studied samples show that TOC, S₂, and S₃ are the major parameters for source rock potential prediction. Factor analysis gave three factors affecting source rock evaluation. Factor 1 highlights TOC, S_1, and S₂ as the parameters for identifying the quantity and quality of organic matter. This is confirmed by factor 2, which identifies HI and OI as the determining variables. Factor 3 identifies PI and T_max as indicators of the thermal maturity of the source rock.