Abstract: The Role Oil and Gas Seeps Played in Petroleum Exploration in California
MAGOON, LESLIE, U.S. Geological Survey, Menlo Park, CA; SUSAN HODGSON, California Division of Oil, Gas, and Geothermal Resources, Sacramento, CA
Fifty (16%) of the 315 oil fields and two (1%) of the 176 gas fields in California have been discovered because of nearby seeps. However, there are almost twice as many oil fields as gas fields in the state. Comparing these numbers with 482 oil and 97 gas seeps reported in California, we see that there are five times more oil than gas seeps; and clearly, because oil seeps are easier to find than gas seeps, they are a more useful tool for petroleum exploration. The Wheeler, Trask and Coleman Tunnel dug near seeps in 1861 resulted in the first California oil discovery---Santa Paula field in Ventura County. The most recent field discovered near seeps is Livermore field, discovered in 1967 by McCulloch Oil near the town of Livermore in Alameda County. Only two gas fields, La Goleta (1932) and Sutter Buttes (1933) were found because of nearby gas seeps.
The difficulty of attributing a single geologic parameter, such as petroleum seeps, to the discovery of a field is an over-simplification considering that most explorationists employ more than one line of evidence before drilling a wildcat well. For example, surface geology in California frequently reveals anticlinal features or topography indicating four-way closure at depth. However, whenever oil and gas seeps are present in the area of interest, tangible evidence exists that petroleum has been generated in sufficient quantity to migrate to the surface. Also, for small companies or individuals closely watching exploration expenditures, the presence of seeps is tangible evidence to investors that oil is nearby, thereby facilitating funding. Several exploration case histories will be examined where seeps played a dominant role in field discoveries.
AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California