proven sandstone reservoir in all basins of pakistan and in which field???????/ sir please reply as soon as possible..
Thanks for your question.
Most part of answer to your question has already given by Mr. Tariq Has any an expert (allexpert) in this field. (You can refer to answers given by him on this subject)
Some more details that i could provide you with the help of Google search are given below.
The long-tested reservoirs have been Paleocene-Eocene limestones and Jurassic Datta sandstones. They were joined during the last decade or so by the oldest reservoirs, Cambrian-Permian in the Upper Indus and Upper Cretaceous Lower Goru in the Lower Indus.
As a result of recent discoveries in the last two years, new petroleum systems have been added:
Middle Jurassic Chiltan limestone at Zarghum, Upper Cretaceous Parh limestone and Mughalkot at Jandran, Upper Cretaceous Pab sandstone at Mari Deep, Sui Deep, Bhit, and Zamzama, Mughalkot at Bhadra, Paleocene Ranikot at Savi Ragha, and Base Ghazij sands at Sara.Cambrian Khewra sandstone is comprised of red-colored, well-bedded sandstone, poorly bedded sandstone, and laminated, rippled sandstone. It is considered to have been deposited as high-energy, braided stream deposits, as unconfined braided stream deposits, or sheet flows accumulated in a distal alluvial fan/sand flat environment. In general, the ice-rafted laminate facies of Permian Tobra represent glacial outwash sediments deposited into a marine base, with the exception of a few fining-upward units deposited within a shallow marine environment from turbidite flows. Well-bedded sandstone facies at the top of the Khewra formation have the best reservoir quality. Both are reservoirs at Adhi, Missa Keswal, Rajian, and Kal fields in the Upper Indus (Potwar) basin.
Lower Jurassic Datta sandstone is the main reservoir at Toot and subsidiary reservoir at Meyal and Dhulian oil fields. Net pay porosity averages up to 15-18%. Deposition is deltaic, and sands have the appearance of stream-mouth point bars, prograding westward and downward to proximal distributary mouth bars. Most sands grade coarser upward in a cylic manner with a well-developed shale as base. These are cycles of progadation sequence in which a delta is moving outward from the east into a standing body of water to the west.
The Middle Jurassic Chiltan formation was drilled in wells including Nabisar, Digh, Patar, Talhar, Bhadmi, and a gas reservoir in Zarghum. Formation thickness, 420 m in the Nabisar well comprised shelf limestone with pisolitic to oolitic character, increased to more than 983 m in the Digh well . The Jurassic depocenter axis reflects thick shelf-edge deposition and burial. Chiltan has negligible intergranular porosity but may have secondary porosity due to fractures and vugs.
Deposition of the middle and basal sands of Lower Cretaceous Lower Goru occurred in a shoreline setting with actual environments ranging from marine shelf to fluvial channels. Late Cretaceous-Early Tertiary trapping of hydrocarbons could have resulted in local preservation of reservoir quality. These reservoirs contain well-preserved sequence boundaries that have clear potential to be picked up on seismic sections and mapped, assisting in delineation of stratigraphic traps.The upper sands' depositional environment has been largely controlled by interaction of major inter-regional eustatic trangressive-regressive cycles with structural evolution of the Indus basin.
The Upper Cretaceous Pab sandstone is a gas and condensate reservoir in Dhodak, Rodho, Loti, and Pirkoh fields in Cental Indus formed in low energy marine environment. Recently it has been found gas bearing in Sui deep and Mari deep and the Zamzama and Bhit wells in Lower Indus. In the latter two wells it represents a product of a tide modified, braid delta system with moderate to very good porosities. It can be divided into nine reservoir units based on recognition of surfaces believed to be of sequence stratigraphic significance.7
Paleocene is the most prolific reservoir after Low- er Cretaceous/Lower Goru and is productive at Dakhni, Chak Naurang, Dhulian, and Meyal (Upper Indus), Dhodak, Loti, and Pirkoh (Central Indus), and Hundi and Sari (Lower Indus). Eocene carbonates are commercially the most significant in Pakistan and comprised of widespread carbonate platforms and shale basins. A study of the geological history of the distribution of Laki sediments suggests that Laki was deposited in relative shallow areas where conditions could have favored organic growth. Lack of horizontal layering at some places in the seismic picture is anomalous.
In the Lower Indus/Kirthar basin all the proven reservoirs have fair to good producibility (5-10 MMcfd for Upper and Lower Ranikot; more than 20 MMcfd for Pab at Bhit and Zamzama). Porosity of Upper Ranikot limestone is 8-15%. Migration of gas into structures has been from Lower Cretaceous shales via extensional faults and more recent thrust faulting. The TCF reported for the Bhit and Zamzama wells shows that adequacy of source rock is not a problem even for relatively young structures in the fold belt.