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U.S. Geological Survey Fact Sheet 2018–3019, U.S. Gulf Coast Petroleum Systems Project. By the Downdip Paleogene Formations Assessment Team.
Using its geology-based method, the USGS estimates mean undiscovered, technically recoverable conventional resources of 100 million barrels of oil and 16.5 trillion cubic feet of gas in the downdip Paleogene formations of the U.S. Gulf Coast — onshore and in state waters.
What was assessed
The study covers conventional sandstone reservoirs in Paleogene formations laid down in an arc from south Texas through Louisiana, part of the Upper Jurassic–Cretaceous–Tertiary Composite Total Petroleum System. Updating earlier assessments, the USGS defined 11 assessment units (AUs): eight conventional units were assessed, and three continuous (unconventional) units were not.
The eight conventional assessment units along the Gulf Coast; offshore boundaries are drawn side by side for clarity. Base map from the National Park Service. USGS.
The geology
- Reservoirs may lie as deep as 30,000 feet: sandstones deposited on the ancient continental slope — channel fills cut into it, slope-fan channels, and turbidites ponded in small basins on the slope. The model draws on geophysical data, fossil markers and detrital zircon studies of where the sand came from.
- Seals are fine-grained slope deposits, seen as condensed sections on well logs and seismic lines.
- Traps are both stratigraphic (channel sands pinching out under mudstones) and structural (growth faults).
- Source rocks grade from land-derived in Texas to marine in Louisiana, so several Mesozoic–Paleogene sources are possible; maturity is in the oil window or higher.
- Challenges: poor porosity and permeability, and high temperatures and pressures, may deter exploration.
The eight conventional units
The units are mostly stacked one above another, and nearly all run east from the Mexican border and north from about the state–federal waters line.
| Assessment unit | Reservoirs |
|---|---|
| Hackberry Slope Sandstones | upper Oligocene sandstones of the Frio Hackberry trend, eastern Texas and southwestern Louisiana, in slide blocks, fault basins, canyons and fans; bounded by the limit of historical Hackberry production |
| Anahuac Formation Slope Sandstones | sparse channel, fan and sheet sands of the upper Oligocene Anahuac, possibly with carbonate turbidites in eastern Louisiana |
| Frio Formation Slope Sandstones | Oligocene Frio slope sands, including aprons fed by the Norma and Norias deltas in south Texas |
| Vicksburg Group Slope Sandstones | lower Oligocene delta-fed aprons in Texas and scattered turbidites (hence a lower probability) |
| Jackson Group Slope Sandstones | upper Eocene–lower Oligocene Moodys Branch and Yazoo equivalents, centred below the Rio Grande embayment and ending near the Texas–Louisiana line |
| Upper Claiborne Group Slope Sandstones | middle Eocene Cockfield, Cook Mountain, Yegua and Sparta sands |
| Lower Claiborne Group Slope Sandstones | middle Eocene Queen City Sand, carried from the south Texas Rio Grande embayment, not past the Texas–Louisiana line |
| Wilcox Group Slope Sandstones | Paleocene–Eocene Wilcox delta- and shelf-fed aprons, onshore Texas and Louisiana |
The three continuous units — Lower Claiborne, Wilcox and Midway — mark where organic-rich marine mudstones might hold shale oil or gas. With no known development and little known about their source potential, they were not assessed.
Results
Totals (mean, with the F95–F5 range):
| Resource | Mean | Range |
|---|---|---|
| Oil | 100 million barrels | 13 to 310 million |
| Gas | 16,500 billion cubic feet (16.5 trillion) | 4,033 to 38,851 billion |
| Natural gas liquids | 409 million barrels | 91 to 1,001 million |
F95 is a 95 percent chance of at least the amount shown; F5 a 5 percent chance.
Mean gas in gas accumulations, by unit (billion cubic feet): Hackberry 164; Anahuac 759; Frio 1,780; Vicksburg 1,833; Jackson 866; Upper Claiborne 2,517; Lower Claiborne 1,521; Wilcox 6,841. Every unit had an assessment probability of 1.0 except the Jackson (0.9).
Sources
- Buursink, M.L., and others, 2018, Assessment of undiscovered conventional oil and gas resources in the downdip Paleogene formations, U.S. Gulf Coast, 2017: U.S. Geological Survey Fact Sheet 2018–3019. https://doi.org/10.3133/fs20183019 · https://pubs.usgs.gov/publication/fs20183019
- The map, the results by unit and the assessment team come from the fact sheet's PDF.
- Rewritten in hubnx's own words.
Licens: CC0 1.0 (allmän egendom) · Bearbetat efter pubs.usgs.gov
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