Structure and oil and gas perspectives of the Californian borderland

Abstract

The Californian borderland is the largest oil and gas region of the Pacific coast of the United States. Here, a series of large and minor sedimentary basins with established or inferred oil and gas bearing properties are recognized. The Californian borderland is located on a Nevadan-type active continental margin. The bodies of such margins are composed of giant accretion formations and occupy not only their underwater parts but also vast land areas. The accretion formations are dominated by rocks of a deep-water origin. The Californian borderland represents a system of basins and ranges that compose the underwater margin and the Coastal Ranges of California and the basement within the Great Valley. In the depressions of the accretion orogen, which are small in size but feature high subsidence rates, significant thicknesses of deposits are accumulated (up to 6−8 km). In the depressions of the Californian borderland, they are represented by young Neogene (rarer Eocene-Oligocene) formations of mainly terrigenous or siliceous-terrigenous compositions. The active tectonic regime resulted in a sharp reduction of the age range of the oil and gas bearing deposits, which are represented only by Late Cretaceous and Cenozoic rocks. Full-scale oil and gas production here is performed in the Santa Barbara-Ventura and Santa Maria basins. The principal oil and gas bearing unit is the Monterrey Formation of the Middle Miocene. By January 2006, the production on the Californian borderland comprised about 17.8 million tons of oil and over 1 billion m3 of gas. Up to 1.4 billion tons of oil and 200 billion m3 of gas reserves are regarded to be not recovered on the Pacific coast of the United States in the region of the Californian borderland.