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.

This study investigates the hydrocarbon generation potential of the Eocene (Ypresian) Nammal Formation throughout the Potwar Basin, Pakistan. Lithostratigraphic, organic geochemical and palynofacies analyses, along with isochore and isopach mapping of five wells (Dakhni-11, Toot-20, Garhi-X1, Fimkasar-04 and Rajian-08) and one outcrop section, were used in the current study. The Nammal Formation comprises shallow-marine to lagoonal shales interbedded with limestone and occasional marls. It is distributed throughout the Potwar Basin, showing a variable thickness that ranges from 3 m in the eastern Rajian-08 well to 66 m in the western Dakhni-11 well. The depth isochore map for the Garhi-X1 well shows that the formation is present at a depth of 4886 m, compared to southern parts where it is exposed at the surface along the Salt Range Thrust. Organic geochemical and palynofacies analyses indicate that the formation is dominated by Type II kerogen with minor Type III kerogen. Data show that the formation gets more mature towards the northwestern part of the Potwar Basin, demonstrating fair total organic content (TOC) values (>1%) that suggest it is a potential source rock. Palynofacies assemblages are consistent with the organic geochemical analysis, which suggest suboxic to anoxic conditions during deposition of the Nammal Formation. The thermal alteration index and T _max values show that the formation is more mature towards the north.