Geochemical fingerprints and hydrocarbon potential of Paleocene mudrocks in the Tano Basin, Ghana: insights from biomarkers and stable carbon isotopes

Abstract

The Paleocene mudrocks in Ghana’s Tano Basin have received limited attention despite ongoing efforts to explore hydrocarbon resources. A thorough geochemical analysis is imperative to assess these mudrocks’ petroleum generation potential and formulate effective exploration strategies. In this study, a comprehensive geochemical analysis was carried out on ten Paleocene rock cuttings extracted from TP-1, a discovery well within the Tano Basin. Various analytical techniques, including total organic carbon (TOC) analysis, Rock–Eval pyrolysis, gas chromatography-mass spectrometry, and isotope ratio-mass spectrometry, were employed to elucidate their hydrocarbon potential and organic facies. The findings in this study were subsequently compared to existing geochemical data on Paleocene source rocks in the South Atlantic marginal basins. The results indicated that the Paleocene samples have TOC content ranging from 0.68 to 2.93 wt%. The prevalent kerogen types identified in these samples were Type II and Type III. Molecular and isotope data suggest that the organic matter found in the Paleocene mudrocks can be traced back to land plants and lower aquatic organisms. These mudrocks were deposited in a transitional environment with fluctuating water salinity, characterized by sub-oxic redox conditions. Maturity indices, both bulk and molecular, indicated a spectrum of maturity levels within the Paleocene mudrocks, spanning from immature to marginally mature, with increasing maturity observed with greater depth. In comparison, the organic composition and depositional environments of Paleocene source rocks in the Tano Basin closely resemble those found in the Niger Delta Basin, Douala, and Kribi-Campo Basins, the Kwanza Formation in Angola, and certain Brazilian marginal basins. However, it is worth noting that Paleocene source rocks in some of the basins, such as the Niger Delta and Brazilian marginal basins, exhibit relatively higher thermal maturity levels compared to those observed in the current Paleocene samples from the Tano Basin. In conclusion, the comprehensive geochemical analysis of Paleocene mudrocks within Ghana’s Tano Basin has unveiled their marginal hydrocarbon generation potential. The shared geochemical characteristics between the Paleocene mudrocks in the Tano Basin and those in the nearby South Atlantic marginal basins offer valuable insights into source rock quality, which is crucial for shaping future strategies in petroleum exploration in this region.