Depositional Environment Reconstruction of OM-4 and OM-A Wells, Niger Delta, Nigeria, Using Palynomorphs and Wireline Logs

Abstract

Microfacies analysis combined with palynological studies were carried out on two wells (OM-4 and OM-A wells) in the Niger Delta to reconstruct the depositional environment of the penetrated wells from 8200 – 11350 ft each in both wells. The succession studied yielded rich terrestrial components of the palynomorph assemblage, which gave zero to low PMI values in both wells, suggesting a paralic (freshwater to marginal marine) environment. Also, the abundance of mangrove swamp species such as, Zonocostites ramonae, Acrostichum aureum, Botryococcus braunii and Psilatricolporites crassus in both wells (which are brackish water indicators) denotes an environment of deposition with higher terrestrial influences and pockets of marine intrusions, confirming a paralic environment of deposition. The facies established from the wireline log signatures gave an alternating cylindrical to funnel shaped log motif with few units of bell shapes. This was interpreted as continental to marginal marine environment. The results of the facies analyses were correlated with the PMI values of the wells and generally cylindrical to funnel shaped facies were established with corresponding nil to low PMI values, confirming a paralic environment of deposition in both wells.