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

Taiwo O M,Okosun E A,Goro A I,Alkali Y B

doi:10.13189/ujg.2019.070103

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.

Highlights

Palynological information from present day studies of modern organisms can be used to infer environmental conditions in the past and predict future environmental conditions, since the distribution of organisms generally, are controlled by a combination of physical conditions of the surrounding area including terrain, vegetation structure, The study area is located in the Western part of the NigerDelta which is situated in the gulf of Guinea on the WestCoast of Central Africa
The facies established from the wireline log signatures gave an alternating cylindrical to funnel shaped log motif with few units of bell shapes
The results of the facies analyses were correlated with the palynomorphs marine index (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

Summary

Introduction

Palynological information from present day studies of modern organisms can be used to infer environmental conditions in the past and predict future environmental conditions, since the distribution of organisms generally, are controlled by a combination of physical conditions of the surrounding area including terrain, vegetation structure, The study area is located in the Western part of the Niger. The. Depositional Environment Reconstruction of OM-4 and OM-A Wells, Niger Delta, Nigeria, Using Palynomorphs and Wireline Logs. Niger Delta basin is bounded in the West by the Benin flank, in the East by Calabar flank in the south most part of Nigeria. The Akata Formation, which is composed of prodeltatic sediments, which are dominantly made up of under compacted marine shales and may contain patches of high pressured siltstone or fine grained sandstones. Overlying the Akata formation is the Agbada Formation is composed of alternations of sand and shale sequences of delta-front, distributary channel and deltaic plain origin. The topmost Benin Formation consists mainly of sandstones which are massive, highly porous and freshwater–bearing with thin shale interbeds distributed locally and are considered to be of braided-stream origin [2]. The age of the formation varies from Oligocene (or earlier) to Recent

Materials and Methods

Result and Discussion

Marker Species and Dominant Species Groups for Paleoenvironmental Studies

Findings

Wireline Log Interpretation

Conclusions