Subsurface Lithologies and Rock Eval Pyrolysis Analyses of Amansiodo-I and Akukwa-1 Well Sections, Nkporo Formation, Southeastern Part of the Anambra Basin, Nigeria: Implication for Petroleum Source Rock Potentials

Abstract

Azuka Ocheli*, Godwin Okumagbe Aigbado, Nkonyeasua Abanjo

Subsurface lithologies and rock eval pyrolysis analyses were conducted on Amansiodo-I and Akukwa-1 well sections that penetrated the Nkporo Formation,  located in the southeastern part of the Anambra Basin, Nigeria. A set of eleven ditch cuttings from the lithologies retrieved from depths 11500-2150 m were evaluated for their source rock viability, stage of hydrocarbon generation, and thermal maturity of the drilled well section. The lithofacies delineated in the Amansiodo-I well section were: greyish shale (low depositional process), compacted fissile shale and sandy (lower-medium depositional processes), and greyish shale, sandy, silty heterolithics (lower-medium depositional processes). The lithofacies delineated in the Akukwa-1 well section were sandstone and siltstone facies (medium energy of deposition) and shale lithofacies (lower energy depositional process). The environment of deposition in the studied wells is inferred to be a shallow marine environment with brackish-water incursions. Based on the  total organic carbon, oxygen index, hydrogen index, genetic potential, kerogen types, and the various bivariate plots, the shale lithologies in the studied well sections are good sources with the potential  for the production of oil and gas. However, some of the lithologic units were designated missing units because of the non-availability of their ditch cuttings.