Predicting and Characterizing Pore Pressure of a Selected Field in the Niger Delta Basin, Nigeria

Abstract

Predicting pore pressure is critical in every exploration venture because it prompts safe drilling, fluid design, casing emplacements, improved wellbore dependability, and water driven cracking enhancement. Hence, the objective of this paper was to predict and evaluate the pore pressure characteristics of a selected field in the Niger Delta Basin of Nigeria using appropriate standard methods. The results of the 1D pore pressure model from the Eaton and Bower’s sonic techniques revealed that the deviation from Normal Compaction Trend started at about 8350 ft as a result of overpressure. The determined break angle from the Fracture gradient formular, utilizing the Effective Stress Ratio (ESR), Overburden Pressure (OVP) and the anticipated Pore Pressure (PP) was estimated to be between 0.65 psi/ft and 0.725 psi/ft. Due to the use of overbalanced drilling in the Niger-Delta, wellbore pressure should be higher than the Hydrostatic pressure, but not as high as the fracture pressure. Therefore, the safe drilling window should likely be from 0.613 psi/ft to 0.645 psi/ft for the study area.

Keywords

• Pore pressure; cross plots; shale zones and fracture gradient