Nature and hydrocarbon potential of organic matter in offshore Mahanadi Basin, east coast of India

Abstract

Evaluating the hydrocarbon-generating potential of buried organic matter in marine sediments is critical in offshore oil/gas exploration. Organic matter sources, total organic matter content (TOC), and maturity state play key roles in hydrocarbon generation when subjected to suitable temperature–pressure conditions. In the present study, we have characterized organic matter source and maturity to evaluate the hydrocarbon-generating potential of organic matter in the offshore Mahanadi Basin along the east coast of India. Although onshore hydrocarbon reservoirs, including coal, coalbed methane (CBM) and shale gas, are extensively explored in the Mahanadi Basin, a systematic characterization of the offshore buried organic matter is lacking. Towards this endeavour, we have adopted an integrated approach using TOC, (TOC/TN)m, Rock-Eval pyrolysis, and bulk carbon isotopic analyses. Organic geochemical screening (Rock-Eval pyrolysis) reveals predominance of type III and IV kerogen, with TOC content ranging from 0.61 to 1.71 wt.%. The hydrogen index (HI) values (37–156 mg HC/gTOC) infer that the organic matter is prone to generate gaseous hydrocarbons (dry to wet gases). Bi-modal distribution pattern of the S2 peak observed in six samples suggests the presence of both labile and refractory organic matter. The (TOC/TN)m ratios and δ13CTOC values indicate that the organic matter is derived from both terrestrial and marine sources