Overpressure Prediction In The North-West Niger Delta, Using Porosity Data

Abstract

Overpressure prediction in the North West of Niger Delta, using porosity data was carried out to safeguard hazards associated with drilling accident due to blowout. In the absence of seismic data to predict overpressure, porosity-dependent parameters and acoustic impedance could be used to predict the tops of overpressured zones in the area of study in the Niger Delta. Overpressure prediction is vital for safe and economic drilling. Composite logs were used to obtain the required data by digitizing the logs and deduction using the appropriate relationships. The findings from the study show that porosity decreases with depth, with overpressure zone detected at about 3500m depth due to porosity deviation from normal trend. Pressure gradient in the upper normal pressure of the field is determined to be 0.989 psi/ft, this implies that within the established normal pressure gradient of 0.71 - 1.1 psi/ft in the Niger Delta. Formation overpressure gradient is determined to be 1.40 psi/ft. The overpressure zone coincides within the high shale-to-sand ratio of Agbada under compacted Formation. The identification of the tops of overpressure zones in any formation penetrated by a borehole enhances the use of normal drilling techniques of the borehole. This also reduces the cost of drilling the entire well as the special drilling technique will be applied only in the overpressure zones. This finding can aid in the prevention of drilling accident and resource wastage in exploration activities.