--> Hydrocarbon Exploration Challenges in Fold and Thrust Belts—Bhittani Range, Trans Indus Range, Pakistan

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Hydrocarbon Exploration Challenges in Fold and Thrust Belts—Bhittani Range, Trans Indus Range, Pakistan

Abstract

The Bhittani Range is located in western part of Trans Indus ranges and separates Bannu Basin in the north from Tank depression in the south. It represents the leading deformational front of the Kohat fold and thrust belt believed to be the most recent thrusting phase. Pezu is northwest-southeast oriented asymmetric, faulted surface anticline, forming the main topographic expression of Bhittani range; it is a structural high interpreted as a complex pop-up bounded on each side by steeply dipping reverse faults. A gas seep is present in Bhittani Range which confirms maturity of source rocks and subsequent migration of hydrocarbons. Analyses of gas seep shows that it is mainly methane derived from a deep thermogenic source. An exploration well was drilled in 1968 near gas seepage on a surface anticline down to 2,222m in Datta sandstone of Jurassic age which was plugged & abandoned since well flowed water with combustible gas. Drilling results confirmed presence of good quality reservoir seal pairs in clastics of Cretaceous and Jurassic formations which could be charged from adjacent basin. Post drill seismic acquisition reveals steeply dipping reverse faults that pop-up central part. The most likely traps of supra-thrust and sub-thrust structural geometry may be much complex as strike-slip fault mapped on surface is not properly imaged by seismic. It is interpreted that crestal geometries of supra and sub-thrust structures is uncertain due to meager quality of seismic data. Available seismic is unable to compute throw of bounding faults, therefore fault seal and juxtaposed lithologies across faults is questionable, especially for sub-thrust play. Based on active petroleum system and multiple target reservoirs at drillable depth including Tertiary, Mesozoic and Paleozoic rocks; this area merit detailed G&G studies with new seismic to mature supra-thrust and sub-thrust play which will lead to firm up a drillable prospect.