Petroleum of the Deep: Palynological proxies for palaeoenvironment of deep offshore upper Miocene-Pliocene sediments from Niger Delta, Nigeria
Date
2016-03
Authors
Olayiwola, Moshood A.
Bamford, Marion K.
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Abstract
Better understanding of the palaeoenvironments under which the lithologies of the deepwater
petroleum systems were deposited is necessary to unravel the problem surrounding the deep
offshore petroleum exploration and production. Therefore, the integration of palynological,
lithological and gamma ray log data of ditch-cutting samples from wells A and B from the Niger
Delta region are utilized to delineate the upper Miocene-Pliocene depositional environments.
The detailed palynological analysis revealed diverse and abundant palynomorph assemblages, which consisted of angiosperm pollen 85.7 %, monolete spores 5 %, fungal elements 4 %, trilete fern spores 4 %, freshwater algae 1 % and marine elements 0.3 %. Eight informal palynological assemblage zones (PAZ I-PAZ VIII) with corresponding eustatic sea level changes are delineated in Wells A and B. Four lithofacies, namely sandstones, siltstones, claystones and mudstones, are recognized in association with three depositional environments in the studied wells. Distributary channels are characterized by the erosive base and filled with moderate to fine, uniform and blocky sand-grain size sediments that are of good reservoir quality. Mud-rich sediments, which are of excellent sealing rock potential, capped this sand formation. Moreover, tidal channels are typified by the erosive base and filled with fining-upwards sand sequences with tops covered by muddy sediments. Finally, the regressive barrier sands are filled by coarsening-upwards sediments with basal organic-rich deposits that are likely to be good quality source rock. The oil potential of these sites is of interest to the oil company and the reconstructed palaeoenvironments will be useful for deepwater exploration and exploitation, and probably remove or minimize the risks that are commonly involved in this task.
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Keywords
palynological proxies, palaeoenvironments, lithofacies, deep offshort, ditch-cuttings