Pore pressure prediction in a carbonate reservoir: a case study from Potwar Plateau, Pakistan

Abstract

Deep sedimentary successions, which are usually over-pressured, require accurate prediction of abnormal pressures to avoid catastrophic incidents, e.g., well blowouts; thus, pore pressure prediction (PPP) makes an important step for efficient reservoir modeling, cost-optimization and safe well-planning procedures in the hydrocarbon exploration. The objective of this study focuses on the estimation of formation pore pressure (PP) within the Eocene Chorgali Formation, using well logs data (from MYL-X1 and MYL-X2 wells) of Meyal Oil Field, Potwar Plateau, Pakistan, and its integration with outcrop, microscopic and seismic data. The formation PP is estimated from geophysical well logs (gamma-ray and sonic logs), by applying the widely used Eaton’s method. The pore pressure gradient (PPG) indicates the presence of pressured zone(s) in the Chorgali Formation in both wells. In MYL-X1, Chorgali Formation PPG and PP ranged from 9 to 13 lbs/gal and 5800 to 8400 psi, respectively, at about depth of 3760–3800 m. The reservoir Chorgali Formation in MYL-X2 wells also displayed pressure zone at about depth interval of 3820–3890 m with PPG and PP values of 8.9–11.6 lbs/gal and 5700–7500 psi, respectively; however, it indicated less pressure than MYL-X1. The synthesis of outcrop, microscopic, well logs and seismic data sets illustrates variations in pore pressure within the Eocene Chorgali Formation that is influenced and controlled by depositional, diagenetic and tectonic fabric among other factors. The variations in PP are necessary to determine to avoid any geologic disaster. Such incidents may cause potential loss during drilling operations in the geologically complicated settings of the Himalayan Fold-and-Thrust belt.