Undiscovered Gas in California's Sacramento Basin: 2019 USGS Assessment

The U.S. Geological Survey assessed undiscovered, technically recoverable gas in the Upper Jurassic–Neogene Total Petroleum System of California's Sacramento Basin Province.

The zeros at F95 reflect geologic risk: some elements of the petroleum system may not work.

The two assessment units of the Sacramento Basin Province. Base map from the National Park Service. USGS.

The basin

• Setting: the Sacramento and San Joaquin basins fill California's Great Valley, a remnant forearc basin between the Sierran–Klamath volcanic arc and the Franciscan accretionary complex, divided by the Stockton Arch.
• Discoveries: more than 120 gas fields in Upper Cretaceous to Tertiary sandstones — from deltaic sands to deep-water channel and basin-floor sands. Exploration in the Dobbins Shale and younger units is extremely mature.
• History: oil seeps along the basin's western edge drew exploration as early as the late 1800s; gas discoveries in the 1930s shifted attention to the shallower rocks.

The new idea

This assessment asks whether gas remains in older, deeper rocks — Upper Jurassic and Cretaceous reservoirs below the Dobbins Shale in the western basin, where few wells have been tested. (Whether Upper Jurassic rocks exist there at all is uncertain.)

• Sources: marine shales in the Stony Creek, Lodoga, Boxer, Venado, Yolo, Sites, Funks and Guinda formations may have generated oil and gas.
• Cracking: oil formed would mostly have cracked to gas during deepest burial in the Cretaceous.
• Traps: gas might remain in sandstones in deep structural traps or in low-permeability sandstones; some may have migrated up and mixed with gases from other sources.
• Heat: the basin has always had a low thermal gradient, so the oil window today begins at about 10,000 feet.
• Pressure: overpressure is widespread; it's often blamed on hydrocarbon generation, but may be tectonic here.

Generalized cross section: Jurassic and Lower Cretaceous rocks and the younger rocks above them. Modified from Dickinson and Seely (1979). USGS.

Assessment units

Input data

Drainage areas and success ratios draw partly on U.S. shale-gas analogs; EUR is estimated ultimate recovery.

Results (gas in BCFG; natural gas liquids in million barrels)

Stratigraphic column of the Sacramento Basin. Modified from Moore and Nilsen (1990), Nilsen (1990), Ghosh and Lowe (1993) and Williams and Graham (2013). USGS.

Sources

Based on Assessment of Undiscovered Gas Resources of the Sacramento Basin Province in California, 2019, U.S. Geological Survey Fact Sheet 2020–3036 (publication page), by the Sacramento Basin Province Assessment Team (Christopher J. Schenk, Tracey J. Mercier, Marilyn E. Tennyson, Cheryl A. Woodall, Kristen R. Marra, Heidi M. Leathers-Miller and Phuong A. Le). Both tables and three figures are restored from the fact sheet's PDF. A work of the United States government in the public domain.