An Application of Integrated Geophysical Studies in Pakistan Offshore

Zia Ul Hasan Shah, Ahmed Naveed, and Mubarik Ali

Integrated geophysical studies facilitate to delineate the deep crustal structure of the earth worldwide. In the present study, gravity, magnetic, bathymetry and deep seismic reflection data was used to obtain a geologically plausible model from the deep crustal structure and also for the hydrocarbon prospects in Indus Offshore basin of Pakistan beneath the seismic line PC/9074-86. Steep positive gravity gradient towards southwest of the area, above thick sedimentary strata (greater than 10 Km) in the offshore depression area, is attributed to a prominent rise in the mantle. Intuitively, extending the depth model beyond the present day shelf break and computing its gravity indicates that the overall gravity effect is one of the typical shelf edge (“Edge Effect”) anomalies. The crustal thickness which is approximately 24.5 Km thick towards northeast is reduced to 6.5 Km on the mantle rise and it may be the area of transitional crust. Presence of thick sedimentary rocks of varying lithologies which commonly form source-reservoir-seal trilogies, optimum geothermal gradients, analogies with other basins, oil/gas shows in and around the offshore area, number of structural traps including reefs and bright spots in sediments ranging in age from Cretaceous to Early Miocene shows positive evidence to the presence of hydrocarbons. Furthermore, it is speculated that the younger sediments in the offshore area may have attained maturity, due to thinning of the crust as a consequence of mantle rise in the outermost shelf regions, and may produce hydrocarbons.