Abstract

The Santa Ynez Unit of Offshore California consists of three main structures known to contain hydrocarbons; Pescado, Hondo, and Sacate Fields. Hondo Field is currently being produced from two platforms, Harmony and Hondo. The Pescado Field is being developed from the Heritage Platform. These fields are east-west trending anticlines related to extensional and compressional events dating back to the Oligocene.

The productive stratigraphic section includes clastic rocks from the Eocene to the Miocene. The sandstone reservoirs account for only a small percentage of the hydrocarbon reserves in the Santa Ynez Unit. These clastic rocks are overlain by deep-water, fine-grained rocks of the Rincon, Tranquillon, and Monterey Formation. The Monterey Formation is the major reservoir unit. These pelagic and hemipelagic rocks contain a high proportion of silica, and are extensively fractured. The fractures are the critical element to production from the Monterey. The fractures provide not only the necessary permeability for fluid flow in the subsurface, but also a significant amount of hydrocarbon storage capacity.

Geochemical analysis has revealed that two different hydrocarbon systems exist in the unit. The Monterey Formation contains oil generated from within the Monterey Formation. This oil is generally high in sulfur, with API gravity ranging from less than 10 to 24 degrees. The sandstone reservoirs below the Monterey Formation contain hydrocarbons derived from a more “standard” clastic-rich source rock and are characterized by API gravity of 30 degrees and greater.