Study of Tectonic Evolution of Structures and Their Hydrocarbon Potential Using Seismic Data, Southern Sindh Monocline, Pakistan

Abstract

Structural styles evolved in various tectonic settings are extremely important and most prolific for the accumulation of hydrocarbons. Variety of structures, structural styles and hydrocarbon structural traps are broadly associated with the unified mechanism of their formation in different plate tectonic settings. World’s major hydrocarbon fields and major portion of hydrocarbon potential is located in extensional basins. The area selected for the study is also characterized by extensional structures and because of that many hydrocarbon fields have already been discovered from Southern Sindh Monocline. As Sindh Monocline is producing 30% of country’s oil and 12% of country’s gas production is from Sindh Monocline. There are number of structures and structural styles found in extensional basins of the world but Some structures hold better prospects than others and the identification of these structures using seismic data is a big challenge as well. On the basis of overall results the conclusions of the study can be made as: Study area is largely characterized by normal faults. Basic structures of study area has been classified into nine types as Large normal faults Small normal faults, Spoon shape normal faults, Master normal faults, Rider normal faults, Folding, Flexure, Vertical faults and Listric shovel. Structural styles have been classified into six types as Horst and grabens, Dominos, Crotch, Synthetic and antithetic faults, Negative and Flashlight structural styles. New type of structural style i.e. “Flashlight structural style”, is reported first time from extensional basin during current study. The structures with in the study area revealed evidence for three major structural episodes first one associated with the rifting during Late Jurassic to Early Cretaceous, modification and reactivation of earlier structures during the Middle Cretaceous and inversion and reactivation during Early Eocene. Present day trap was also formed in third episode. Large normal faults have more chance of success as compared with other structural styles. The migration of hydrocarbons from source rock (Sembar Fm) to reservoir rock (Lower Goru Sands) probably have been greatly facilitated by faults and juxtaposed lithology.