Assessing thermal maturation and source rock potential of the Eocene (Ypresian) Nammal Formation, Potwar Basin, Pakistan

This study investigates the Eocene (Ypresian) Nammal Formation for hydrocarbon generation potential throughout the Potwar Basin, Pakistan. Lithostratigraphic, organic geochemical, and palynofacies analyses 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 of shallow marine to lagoonal shales interbedded with limestone and occasional marls. It is distributed throughout the basin showing a variable thickness from 3 meters in eastern Rajian-08 well to 66 meters in western Dakhni-11 well. The depth isochore map of the Garhi-X1 well shows that the formation is present at 4886m depth, compared 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 with minor Type III kerogen. Data shows that the formation gets more mature towards the north-western part of the Potwar Basin, with promising fair TOC values (>1%) reflecting it as a potential source rock. Palynofacies assemblages are consistent with organic geochemical analysis suggesting suboxic to anoxic conditions during deposition of the Nammal Formation. The thermal alteration index and Tmax show that the formation is more mature towards the north.