The U.S. Geological Survey assessed how much undiscovered, technically recoverable oil and gas — both conventional and unconventional (continuous) — may remain in the Los Angeles Basin Province of California.
The four assessment units (AUs) in the Los Angeles Basin Province. USGS.
The bottom line
| Resource | Mean estimate | Range (F95–F5) |
|---|---|---|
| Oil | 61 million barrels | 10–201 million barrels |
| Gas | 240 billion cubic feet | 33–741 billion cubic feet |
| Natural gas liquids | 5 million barrels | 1–20 million barrels |
About 80 percent of the undiscovered oil and gas is estimated to lie in the conventional reservoirs unit. (F95 means a 95-percent chance of at least that amount; F5, a 5-percent chance.)
How the basin formed
The basin's history is complex, tied to the change along southern California's continental margin from subduction to right-lateral transform (side-slipping) motion.
- Two phases of extension, in the Miocene and Pliocene, opened room for up to 9 kilometers of sediment — including world-class petroleum source and reservoir rocks.
- Compression followed in the late Pliocene to Pleistocene, reshaping many of the basin's structures.
- That deformation may have fractured reservoirs and let oil and gas escape, as the basin's many seeps show.
Where the oil and gas come from
The USGS defined the Monterey Total Petroleum System: oil and gas generated from the organic-rich Miocene Monterey Formation, and possibly from the Miocene Puente and Modelo Formations.
The Monterey Formation has:
- Type II and Type IIS kerogen — more sulfur-rich (IIS) on the basin's western side;
- total organic carbon up to 18 weight percent, and hydrogen index values up to 600 mg of hydrocarbon per gram of organic carbon;
- a thickness of up to 300 meters;
- high silica content that fractures easily.
Oil generation is modeled to have begun in the late Pliocene.
The four assessment units
Three continuous (shale) units estimate oil and gas still held in the shales themselves:
| Unit | Where generation begins (approximate, uncertain) |
|---|---|
| Central and Eastern LA Basin Monterey Shale Oil | Oil window near the −12,000-foot structure contour, near the base of the Monterey |
| Central and Eastern LA Basin Monterey Shale Gas | Gas window near the −21,000-foot contour, from one-dimensional modeling |
| Western Shelf LA Basin Monterey Shale Oil | Oil from shales below about 9,000 feet — shallower because the sulfur-rich Type IIS kerogen generates oil earlier than the Type II matter to the east |
The geologic model for these units is that oil and gas were partly retained in the shales after forming. But the siliceous Monterey shales are commonly fractured, so much may have migrated out along fractures into conventional reservoirs, or escaped to the surface.
One conventional unit — the Los Angeles Basin Conventional Reservoirs AU — covers most of the province: oil and gas that migrated from the Monterey and related rocks into sandstone reservoirs in structural and stratigraphic traps. The reservoirs include deltaic and shallow-marine sandstones, slope-channel and basin-floor sandstones, and possibly sand injectites like those described in similar deepwater systems.
Key assumptions
| Input | Shale oil (central/eastern) | Shale gas (central/eastern) | Shale oil (western shelf) |
|---|---|---|---|
| Potential production area, acres (min / mode / max) | 1,000 / 90,000 / 180,000 | 1,000 / 15,000 / 30,000 | 20,000 / 55,000 / 127,000 |
| Success ratio, % (min / mode / max) | 5 / 10 / 40 | 10 / 30 / 50 | 5 / 10 / 50 |
| Average recovery per well (mean) | 0.006 million barrels | 0.146 billion cubic feet | 0.006 million barrels |
| Untested area | 100% | 100% | 100% |
For the conventional unit, the assessment assumed a median of 12 undiscovered oil fields (range 1–30) and 3 gas fields (range 1–15), with a median oil-field size of 0.7 million barrels (up to 500) and gas-field size of 18 billion cubic feet (up to 1,000).
Results by unit (means)
| Assessment unit | Oil (million barrels) | Gas (billion cubic feet) | NGL (million barrels) |
|---|---|---|---|
| Central and Eastern Monterey Shale Oil | 6 | 9 | 0 |
| Central and Eastern Monterey Shale Gas | — | 25 | 0 |
| Western Shelf Monterey Shale Oil | 5 | 7 | 0 |
| All continuous units | 11 | 41 | 0 |
| Conventional Reservoirs (oil fields) | 50 | 65 | 3 |
| Conventional Reservoirs (gas fields) | — | 134 | 2 |
| All conventional | 50 | 199 | 5 |
| Total | 61 | 240 | 5 |
The shale-gas unit was assigned a probability of 0.9; the other three, 1.0. All results are fully risked.
Sources
Based on U.S. Geological Survey Fact Sheet 2024–3051, "Assessment of undiscovered oil and gas resources of the Los Angeles Basin Province, 2023," by the Los Angeles Basin Province Assessment Team (Christopher J. Schenk and others); a work of the United States government in the public domain.
ライセンス： CC0 1.0（パブリックドメイン） · 出典 pubs.usgs.gov
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