oil sand - Edna Member of the Mio-pliocene Pismo Formation impregnated with oil - hand/display specimen

Oil sand - Edna Member of the Pismo Formation - late Miocene to early Pliocene

This oil sand forms a seal at the surface of the Arroyo Grande Oilfield in Price Canyon, east of Pismo Beach in San Luis Obispo County, California. It unconformably overlies the diatom-rich Monterey Formation.

Numerous surface seeps of oil are located in the Arroyo Grande oilfield and have been for centuries. Possibly the first written account of the surface seeps comes from the Spanish explorer, Gaspar de Portola. In a journal entry from 1770, he describes the many outcrops of tar.

The Arroyo Grande Oilfield is unusual, since the trap containing the hydrocarbons is a syncline with a tar sand seal and high angle reverse faults controlling hydrocarbon distribution in one limb of the syncline.

Fluid production from a typical Arroyo Grande oil well is a mixture of oil and water that has to be separated. Standard oilfield equipment is used to separate the oil from the water. The water is then filtered and split into two streams. One stream is softened for use in the Enhanced Oil Recovery process called Steam Flooding. The remaining water is sent thru a Water Reclamation Facility using a high tech filtration system followed by reverse osmosis filters. Three quarters of the water sent through the facility is purified and released into Pismo Creek.

Field photo shows control of oil distribution by faulting along Price Canyon Road.

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