By the USGS Khorat Plateau Province Assessment Team: Christopher J. Schenk, Timothy R. Klett, Tracey J. Mercier, Thomas M. Finn, Marilyn E. Tennyson, Stephanie B. Gaswirth, Kristen R. Marra, Phuong A. Le and Ronald M. Drake II
Using a geology-based method, the U.S. Geological Survey estimated undiscovered, technically recoverable shale gas and tight gas in the Khorat Plateau Province of northeast Thailand and western Laos: a mean of 2.3 trillion cubic feet.
The Khorat Plateau Province and its seven assessment units (AUs). USGS.
A complicated past
The province is part of Sundaland, a patchwork of terranes that broke from the northern edge of Gondwana and joined Eurasia from the late Paleozoic through the Mesozoic (Barber and others, 2011; Metcalfe, 2011; Morley, 2012; Hall, 2013; Morley and others, 2013). The collisions left a mosaic of terranes, suture zones, accretionary wedges and arc rocks — a history that may have hurt the formation and survival of petroleum systems.
- Source rocks: laid down in rift basins of the late Carboniferous–late Permian — marine and carbonaceous shales and coals — and the Late Triassic — deep lake shales (Booth and Sattayarak, 2011; Racey, 2011).
- Gas generation: burial by more than 5 kilometers of Khorat Group rocks in the Late Jurassic–Early Cretaceous pushed them into the window for dry gas.
- The risk: several rounds of deformation, uplift and erosion since then may have let the gas escape from tight sandstones, siltstones and shales.
- Evidence so far: gas shows from tight rock in wells (Booth, 1998; Malila, 2011; Racey, 2011), but no reports of recoverable gas from shale (Chumkratoke and Dunn-Norman, 2015).
Stratigraphy of the Khorat Plateau, modified from Koysamran and Comrie-Smith (2011). USGS.
What was assessed
| Petroleum system | Gas in | AUs |
|---|---|---|
| Triassic Kuchinarai | organic-rich lake shales of the Triassic Kuchinarai Group, formed during rifting | Khorat, Sakon Nakhon, Phu Phan and Savannakhét Kuchinarai Shale Gas |
| Upper Carboniferous–Triassic Composite | tight clastic reservoirs of the Upper Triassic, Jurassic and Cretaceous | Khorat, Sakon Nakhon and Savannakhét Basin Tight Gas |
The units follow published maps of Permian and Triassic basin centers (Booth and Sattayarak, 2011). The province saw three episodes of basin formation, but the units are named for today's landforms. Well drainage areas, recoveries and success ratios come from U.S. shale-gas and tight-gas analogs.
The estimates
For all seven units, the mean estimates are:
- Gas: 2,301 billion cubic feet — about 2.3 trillion cubic feet (F95–F5 range 0 to 9,268): 586 in shale, 1,715 in tight reservoirs.
- Natural gas liquids: 17 million barrels (0 to 67).
F95 means a 95-percent chance of at least that much; F5, a 5-percent chance. The wide ranges — and the zeros at F95 — reflect real doubt that gas survived the region's tectonic history: each unit's chance of holding gas was judged less than one.
| AU | AU probability | Gas, mean (billion cubic feet) |
|---|---|---|
| Khorat Basin Tight Gas | 0.5 | 1,389 |
| Khorat Kuchinarai Shale Gas | 0.6 | 312 |
| Sakon Nakhon Basin Tight Gas | 0.5 | 250 |
| Phu Phan Kuchinarai Shale Gas | 0.6 | 162 |
| Savannakhét Basin Tight Gas | 0.5 | 76 |
| Sakon Nakhon Kuchinarai Shale Gas | 0.6 | 62 |
| Savannakhét Kuchinarai Shale Gas | 0.5 | 50 |
More: USGS Energy Resources Program.
Sources
Based on Assessment of Continuous Gas Resources in the Khorat Plateau Province, Thailand and Laos, 2016, by the Khorat Plateau Province Assessment Team, USGS Fact Sheet 2017–3023, U.S. Geological Survey; a work of the United States government in the public domain. The map, the stratigraphic column and the results by assessment unit are taken from the fact sheet's PDF, which the import had left out.
Licence: CC0 1.0 (public domain) · Adapted from pubs.usgs.gov
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