Oil and Gas Exploration and Production
The first oil well drilled in present-day Pakistan was at Kundal on the Potwar Plateau in 1866. The first commercial oil discovery was made in the Greater Indus Basin in 1914 when the Attock Oil Company completed a 214 ft well on a thrust-faulted anticline near Khaur on the Potwar Plateau (Khan and others, 1986). Early success in the Kohat-Potwar geologic province served to focus much of the early exploration activity in that area. The Sui field in the Sulaiman-Kirthar Foreland geologic province was the first discovery outside of the Kohat-Potwar geologic province and is the largest gas discovery in Pakistan, with more than 5 trillion cubic feet (TCF) of gas reserves. Discovered in 1952, the Sui field is a dome-shaped reef structure with an anticlinal surface expression. The largest reserves were found in the 625 m thick Eocene Sui Formation Sui Main Limestone Member. The Sui Upper Limestone Member and upper Eocene Habib Rahi Limestone were also productive. In 1999, Upper Cretaceous Pab Sandstone Formation gas production began at Sui field. Although exploratory wells had been previously drilled in the Middle and Lower Indus Basins, the discovery of the Sui field accelerated exploration efforts in the 1950's. More discoveries followed in that area with the Zin gas field in 1954, the Uch gas field in 1955, and the Mari gas field in 1957. Exploration activity increased again in the 1980's, when identification of a tilted fault block in the Lower Indus Basin led to the discovery of a series of oil fields. Although there have been significant oil discoveries in the Lower Indus Basin, it remains a gas-prone province. Gas discoveries that are attributed to the Sembar-Goru/Ghazij TPS have been made in Eocene, Paleocene, and Lower Cretaceous rocks on the Mari-Kandhot High in the Rajasthan Province of India. The Cambrian oil discoveries in Rajasthan, however, are beyond the extent of Sembar deposition and are either sourced by updip hydrocarbon migration from the Sembar or more likely by proximal older Mesozoic and early Paleozoic rocks. Sembar-Goru/Ghazij Composite Total Petroleum System
The Sembar-Goru/Ghazij Composite Total Petroleum System (TPS) as defined for this assessment, is a north-south elongated area extending from the Potwar-Kohat geologic province in the north to the 2,000 m bathymetric contour in the Arabian Sea . The west boundary coincides with the axial belt and western edge of the Indian plate and the eastern boundary extends into India on the Indian Shield . Geochemical analyses of potential source rocks and produced oil and gas have demonstrated that the Lower Cretaceous Sembar Formation is the most likely source of oil and gas for most of the producing fields in the Indus Basin. Source Rocks
While the Sembar has been identified as the primary source rock for much of the Greater Indus Basin, there are other known and potential source rocks. Rock units containing known or potential source rocks include the Salt Range Formation "Eocambrian" shales, Permian Dandot and Tredian Formations, Triassic Wulgai Formation, Jurassic Datta Formation, Paleocene Patala Formation, Eocene Ghazij Formation, and lower Miocene shales. Of all the possible source rocks in the Indus Basin, however, the Sembar is the most likely source for the largest portion of the produced oil and gas in the Indus foreland. In the Kohat-Potwar geologic province the Paleocene Patala Shale is the primary source rock for most, if not all of the province. In the offshore areas of the Indus geologic province, Miocene rocks are postulated to be good hydrocarbon sources, with the Sembar contributing in the shelf area. The Lower Cretaceous Sembar Formation consists mainly of shale with subordinate amounts of siltstone and sandstone. The Sembar was deposited over most of the Greater Indus Basin in marine environments and ranges in thickness from 0 to more than 260 m (Iqbal and Shah, 1980)....
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