The Bureau of Economic Geology The University of Texas at Austin Jackson School of Geosciences

 

Repetto Formation, Los Angeles Basin

General Setting

The Los Angeles Basin is a structurally complex, polyphase Neogene basin in a tectonically active margin along the North American and Pacific plates in Southern California. The early basin development was in the mid-Miocene during an extensional phase associated with strike slip and rotation of the Transverse Ranges (Biddle, 1991). Extension continued throughout the late Miocene and early Pliocene, followed by folding and thrusting from the early Pliocene to recent times.

A substantial fraction of the oil and gas production from the Los Angeles Basin is derived from multiple fields in the Pliocene Repetto Formation. The Repetto Formation is interpreted to have been deposited in a submarine-fan setting (Conrey, 1967; Redin, 1991). Lithofacies of the Repetto Formation consist of conglomeratic and sandy submarine channel-fill facies, flanked by sandy and silty levee and lobe facies. Reservoir heterogeneity is extreme, with abrupt lateral sandstone and conglomerate pinch-outs into silty mudstones. Vertical seal of reservoir facies is provided by abyssal mudstone drapes.

There is an abundance of basic lithologic and fluid data from this stratigraphic unit as a potential target for CO2 injection. The trapping mechanism for Repetto fields is dominantly structural, with many fields occurring on anticlines and in overturned strata along fault zones (Yeats and Beall, 1991). Secondary hydrocarbon accumulations occur in stratigraphic traps where deep-sea fan deposits pinch out in mudstones (Redin, 1991).

Information Search and Selection

Subsurface data from the Repetto Formation are well documented. Primary sources of formation structure, depth, thickness, and lithology data are derived from Conrey (1967), Henry (1987), Redin (1991), and Wright (1991). Permeability, porosity, pressure, temperature, and water-chemistry data are provided chiefly by the California Department of Conservation (1991). The principal parameters for the Repetto Formation are briefly described below.

Comments on Geologic Parameters

References

Biddle, K. T., 1991, The Los Angeles Basin: an overview, in Biddle, K. T., ed., Active margin basins: American Association of Petroleum Geologists Memoir 52, p. 5–24.

California Department of Conservation (Division of Oil and Gas), 1991, California oil and gas fields, v. 2: Southern, central coastal, and offshore California, 689 p.

Conrey, B. L., 1967, Early Pliocene sedimentary history of the Los Angeles Basin, California: California Division of Mines and Geology Special Report 93, 63 p.

Henry, M. J., 1987, Los Angeles Basin—an overview, in Clarke, D., and Henderson, C., eds., Oil-producing areas in Long Beach: American Association of Petroleum Geologists Field Trip Guidebook, Pacific Section, p. 1–29.

Redin, T., 1991, Oil and gas production from submarine fans of the Los Angeles Basin, in Biddle, K. T., ed., Active margin basins: American Association of Petroleum Geologists Memoir 52, p. 239–260.

U.S. Geological Survey, 1996, Ground water atlas of the United States: segment 1: California.

Wright, T. L., 1991, Structural geology and tectonic evolution of the Los Angeles Basin, in Biddle, K. T., ed., Active margin basins: American Association of Petroleum Geologists Memoir 52, p. 35–134.

Yeats, R. S., and Beall, J. M., 1991, Stratigraphic controls of oil fields in the Los Angeles Basin, in Biddle, K. T., ed., Active margin basins: American Association of Petroleum Geologists Memoir 52, p. 221–238.

Prepared by William Ambrose.

 
 
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