Miocene and Oligocene Petroleum Reservoirs of the Santa Maria and Santa Barbara-Ventura Basins, California

This volume presents papers that have been assembled for a Core Workshop on Miocene and Oligocene Petroleum Reservoirs of the Santa Maria and Santa Barbara - Ventura Basins, California. The main emphasis of the workshop in the Miocene Monterey Formation, the most important petroleum reservoir in both the Sana Maria Basins and a very important reservoir in the Santa Barbara - Ventura Basin, particularly in the offshore. In addition to the Monterey Formation, core studies are also presented on the post-Monterey Sisquoc Formation and on pre-Monterey reservoirs including the Sespe, Alegria, and Vaqueros Formations.
Sedimentological and Reservoir Characteristics of the Upper Sespe Formation at Sockeye Field, Offshore California Available to Purchase
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Published:January 01, 1990
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CiteCitation
Phil J. Rarey, 1990. "Sedimentological and Reservoir Characteristics of the Upper Sespe Formation at Sockeye Field, Offshore California", Miocene and Oligocene Petroleum Reservoirs of the Santa Maria and Santa Barbara-Ventura Basins, California, Margaret A. Keller, Mary K. McGowen
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Abstract
Three hundred feet of continuous upper Sespe Formation core were cut in E-1, the first development well drilled from Platform Gail. The cored interval includes the "A zone" and the upper part of the underlying "B zone". The "A zone" consists of alternating sandstones, siltstones, and mudstones. Sandstones are light grey, quartzofeldspathic, very fine- to medium-grained, friable, and typically moderately sorted. They were probably deposited in a fluvial environment as channel bars and as overbank crevasse-splays. Levee siltstones and floodplain mudstones are light grey to reddish brown, bioturbated, calcareous, contain rootlets, and exhibit various stages of pedogenesis. The "A zone" was probably deposited by moderate sinuosity, mixed-load rivers resulting in a complex distribution of channel sandstones, crevasse-splays, and floodplain deposits. The underlying "B zone" consists primarily of light grey, medium- to coarse-grained, horizontally laminated sandstone which was most likely deposited in a distal braidplain environment.
SEM and petrographic data show that most upper Sespe Formation sandstones have 20% to 33% primary porosity and contain only minor clay matrix and clay cement. Calcite cement is generally minor but is pervasive in isolated thin intervals. Sandstone permeabilities are generally very high (200 md. to 2 darcies) . The light color and presence of minor pyrite in sandstones may indicate that hematite was originally present and later reduced to pyrite by hydrocarbon solutions.
The upper Sespe Formation at Sockeye Field consists of many individual reservoirs because of discontinuous sandstones and efficient mudstone seals. The E-1 core reveals an alternating sequence of gas and oil bearing sandstones. The core data have been tied into wireline data so that hydrocarbon type and reservoir parameters in thin sandstones can be better evaluated where core data are not available.
Paleosol maturity has been used to estimate lateral continuity of seals and to determine the best datum for stratigraphic modeling. Stratigraphic modeling suggests a general east-west orientation of meanderbelt complexes. This is consistent with regional facies and paleocurrent data.