Petroleum system elements analysis of sediment outcrops in the edda area of the Afikpo sub-basin

Abstract

This study analyzed the petroleum system elements of sediment outcrops deposited within the Edda area in the Afikpo Sub-basin. The area comprises the Nkporo Group and the Coal measures Group (Mamu, Ajali, and Nsukka Formations) in the Southern Nigeria sedimentary basin. The deposits are characterized by a range of lithological units, including shales, sandstones, siltstones, heterolithic units, and coal seams. This work aims to integrate lithostratigraphic, structural, and sedimentological parameters to understand the petroleum prospectivity and unlocks hydrocarbon opportunities within the Afikpo Sub-basin. The methods used in this study includes detailed field/outcrop descriptions, sedimentological and structural analyses. Over ten outcrops were studied and sampled for this study.  The field investigations identified thick, organic-rich strata belonging to the Nkporo and coal measure Groups as potential source rocks. The medium- to coarse-grained, well-sorted Afikpo, Owutu and Ajali sandstones, with high porosity and bioturbation, are viable reservoir rocks. At the same time, the interbeds shales and indurated/iron rich siltstones were identified aseffective seals. Hydrocarbon traps identified in the area include: fault, anticlinal folds, and ferruginized indurated siltstones interbedded within the larger sandstone deposits. The depositional environment ranges from deltaic/tidal to shallow marine. The sedimentary sequences present in the study indicate suitable conditions for hydrocarbon generation, migration, and preservation. The vertical stacking of lithostratigraphic units observed in the study area indicates favourable conditions for efficient hydrocarbon production planning and development.