Pore Pressure Prediction of an Oil-Field in Part of the Niger Delta Basin, Nigeria

F.I Chiazor,F.T Beka

doi:10.4314/jasem.v23i12.28

Abstract

In this study, overpressure prediction was carried out for ten oil wells in a selected oil-field in part of the Niger Delta basin, Nigeria. The age of key stratigraphic surfaces (9.5Ma-65Ma), depth, thickness and sedimentationrates from well logs and biostratigraphic data was used to build pressure models. The generated pressure model was calibrated using key petrophysical, geochemical and pressure data until a match was achieved. The model predicts occurrence of localized under-compaction driven overpressure at about 11.5Ma. From the results, the onset of overpressure is likely at depths beyond 14,760ft which corresponds to the 11.5Ma marker shales, while fluid pressures ranging from 0.53-0.7psi/ft are estimated at 15,744ft and hard overpressures ranging from 0.7-0.9psi/ft are likely at depths beyond 19,680ft which corresponds to the 12.8Ma marker shales. This study provides good prediction on the occurrence of pressure in the deeper prospect.Keywords: overpressures, under-compaction, sedimentation rate, marker shales, deeper prospect

Highlights

Predicting pore pressure is critical especially for deeper prospects of some economic fields in the Niger Delta Basin (Figure 1) A good understanding of overpressure distribution and formation strength in an area is very important for the safe and cost effective drilling in an over pressured environment
Overpressure prediction was based on empirical data analysis from well logs and seismic data (Eaton 1972; Bower 2002)
From the 1D Pore pressure model for well 005 the deepest well, the pressure model showed a deviation from the hydrostatic at about 14760ftss (4500M) and a marked high sedimentation rate at the same depth in the stratigraphic column that corresponds to the 11.5Ma marker shale

Summary

Introduction

Predicting pore pressure is critical especially for deeper prospects of some economic fields in the Niger Delta Basin (Figure 1) A good understanding of overpressure distribution and formation strength in an area is very important for the safe and cost effective drilling in an over pressured environment. Overpressure prediction was based on empirical data analysis from well logs and seismic data (Eaton 1972; Bower 2002). Adeoye (2001) used existing well pressure data and empirical method similar to that of Krusi (1990) to generate various regional overpressure distribution maps of the Niger Delta. Such approach has limitations in constrained data setting and static nature. The objective of this paper is to estimate and model the overpressure developments across ten oil wells in a selected field in the Niger Delta basin, Nigeria using the basin modeling approach

Objectives

Methods

Results