The present study is focused on formation evaluation of the Lockhart Limestone in two wells (Meyal-05P and Meyal-10P) located in Northern Deformed Potwar Zone of the Potwar sub-basin, Pakistan. The geological formations ranging from Triassic to Pliocene have been drilled in these wells. The formation evaluation of the Lockhart Limestone mainly involves reservoir potential evaluation, interpretation of depositional environment and transgressive–regressive sequences using petrophysical logs. In either wells, the reservoir characterization is steered by various petrophysical parameters including calculation of volume of shale, porosity, permeability and hydrocarbon saturation. The thickness of the Lockhart Limestone is 50 m and 77 m in the Meyal-05P and Meyal-10P wells, respectively. In Meyal-05P and Meyal-10P wells, the average petrophysical parameters values and ranges are given as follows: volume of shale 48% and 20%; density porosity 1–5.6% and 1–31.7%; neutron porosity 1–23% and 1–42.9%; sonic porosity 1–29% and 1–39%; effective porosity < 1–> 5% and 1–21%; and hydrocarbon saturation 92.21–99.8% and 97–99.6%. The petrophysical parameters indicate that the Lockhart Limestone of Meyal-10P well is quantitatively better reservoir than that of the Meyal-05P. In Lockhart Limestone of either wells, the permeability is < 0.1 mD. The bulk volume water deciphered the presence of vuggy and intercrystalline porosity in the Lockhart Limestone. Similarly, the lithological interpretation using logs shows mainly limestone with minor shales. Different electrofacies are interpreted from the log trends of gamma ray log such as aggrading, prograding and retrograding depositional sequences deposited in tidal channel fill, shallow water, shore line and offshore buildup and regressive-to-transgressive shore face depositional setting.

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.