By the USGS Lower Indus Basin Assessment Team: Christopher J. Schenk, Marilyn E. Tennyson, Timothy R. Klett, Thomas M. Finn, Tracey J. Mercier, Stephanie B. Gaswirth, Kristen R. Marra, Phuong A. Le, Sarah J. Hawkins and Heidi M. Leathers-Miller
The U.S. Geological Survey assessed the undiscovered, technically recoverable oil and gas of the Lower Indus Basin in Pakistan — both conventional fields and continuous resources in shale.
The Lower Indus Basin and its six assessment units (AUs). USGS.
How the basin formed
- Permian to Middle Jurassic: as part of Gondwana, the Indian-Pakistan plate was stretched in several phases, ending with its separation from Somalia in the Late Jurassic to Early Cretaceous (Robison and others, 1999; Zaigham and Mallick, 2000; Ahmad and others, 2012a).
- Early Cretaceous to Eocene: its western edge was a passive margin. Along it, the source rocks of the Lower Goru and Sembar Formations were laid down.
- Late Cretaceous to Paleogene: Madagascar and the Seychelles broke away, stretching the crust further and forming the structural traps that exploration has focused on (Naeem and others, 2016).
- From the Eocene: the plate collided with Eurasia, raising the Kirthar fold belt and the foreland basin beside it. The collision also caused inversion, uplift and erosion across the Indus Basin, but most of the deformation was in the fold belt.
A west–east cross section of the southern Lower Indus Basin, modified from Robison and others (1999). USGS.
What was assessed
The USGS defined two total petroleum systems with six AUs.
Lower Cretaceous Composite system — source rock in shales of the Lower Goru and Sembar Formations (Quadri and Shuaib, 1986; Ahmad and others, 2012b; Siddiqui and others, 2014; Qayyum and others, 2016): up to 300 meters thick and 9.5 weight percent organic carbon, with Type II/III organic matter, both marine and terrestrial.
| AU | Type | Basis |
|---|---|---|
| Kirthar Fold Belt Conventional Gas | conventional | tectonic setting; structural and stratigraphic traps, which may hold low-permeability reservoirs (Nizamuddin and others, 2010; Majeed and Mahessar, 2016) |
| Kirthar Foredeep Conventional Oil and Gas | conventional | same |
| Jacobabad-Mari Conventional Gas | conventional | same |
| Lower Goru-Sembar Shale Oil | continuous | some oil and gas stayed in the shales through migration, inversion and uplift after the Eocene collision |
| Lower Goru-Sembar Shale Gas | continuous | same |
Jurassic system — one AU, Jurassic Shale Gas: organic-rich marine shales (Type II, up to 2.8 weight percent organic carbon, up to 50 meters thick) buried deep enough to generate dry gas, some of it retained in the shale (Robison and others, 1999).
The basin's stratigraphic column, modified from Mahmoud (2015). USGS.
For the continuous units, well drainage areas, estimated ultimate recoveries and success ratios come from U.S. shale-oil and shale-gas analogs.
The estimates
Mean estimates of undiscovered, technically recoverable resources, with F95–F5 ranges (F95: a 95-percent chance of at least that much; F5: a 5-percent chance):
| Oil (million barrels) | Gas (billion cubic feet) | Gas liquids (million barrels) | |
|---|---|---|---|
| Conventional | 12 (5–21) | 7,139 (2,838–13,414) | 139 (52–276) |
| Continuous (shale) | 152 (0–415) | 17,486 (3,195–43,841) | 462 (66–1,206) |
| Total | 164 (5–436) | 24,625 (6,033–57,255) — about 24.6 trillion cubic feet | 601 (118–1,482) |
By assessment unit (means):
| AU | Oil (million barrels) | Gas (billion cubic feet) | Gas liquids (million barrels) |
|---|---|---|---|
| Lower Goru-Sembar Shale Gas | — | 14,455 (3,195–32,068) | 438 |
| Kirthar Fold Belt Conventional Gas | — | 4,005 (1,520–7,662) | 79 |
| Jurassic Shale Gas | — | 2,641 (0–10,665) | 14 |
| Jacobabad-Mari Conventional Gas | — | 1,790 (727–3,327) | 8 |
| Kirthar Foredeep Conventional Oil and Gas | 12 (5–21) | 32 with the oil (13–60); 1,312 on its own (578–2,365) | 1; 51 |
| Lower Goru-Sembar Shale Oil | 152 (0–415) | 390 with the oil (0–1,108) | 10 |
An F95 of zero reflects the chance that a continuous resource is absent: its AU probability was judged less than one.
More: USGS Energy Resources Program.
Sources
Based on Assessment of Undiscovered Oil and Gas Resources in the Lower Indus Basin, Pakistan, 2017, by the Lower Indus Basin Assessment Team, USGS Fact Sheet 2017–3034, U.S. Geological Survey; a work of the United States government in the public domain. The map, cross section and stratigraphic column are taken from the fact sheet's PDF, which the import had left out.
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