Monterey fractured reservoir, Santa Barbara Channel, California

The South Elwood field in the Santa Barbara Channel is a faulted anticline with cumulative production of 14.5 million bbl from the Monterey Formation as of September 1, 1982. The distributions of pressure, flow rates, and oil-water contacts and the low average matrix permeability of 0.2 md require a fractured reservoir. Core and outcrop studies show a dominant fracture set characterized by vertical, lithologically controlled fractures oriented across strike, and breccias controlled by lithology and structure. Generally, the fracture intensity is unaffected by structural position or bed curvature but is controlled by lithology and bed thickness. Other varieties of fracturing in the Monterey are related to a protracted history of diagenesis, deformation, and fluid injection. Three types of tar-bearing breccias occur in the Monterey Formation: stratigraphic breccia, coalescent-fracture breccia, and fault-related breccia. Formation of breccias probably involves high pore pressures. Because of their polygenetic origin, breccia masses have diverse orientations paralleling bedding or fracture/fault systems. In conclusions, fracturing and brecciation of the Monterey Formation reflect the interplay between processes of diagenesis, deformation, and fluid dynamics. The most important features of the reservoir in the area of the present study are: (1) vertical fractures oriented normal to the structural trends andmore » inferred to be favorably oriented (to remain open) with respect to the regional minimum horizontal stress; and (2) breccias that are both stratigraphically and structurally controlled and inferred to be related to the interaction of rock stress and fluid dynamics.« less