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Organic geochemistry and comparative diagenesis: Miocene Monterey Formation, Lost Hills oil field and vicinity, West San Joaquin Basin, California

Thesis/Dissertation ·
OSTI ID:7013615
Because of the geologic structure, the Monterey in the subsurface near Lost Hills in the San Joaquin Basin forms a natural laboratory for the study of the diagenetic responses of biogenic sediment. Rocks of similar age and lithology are buried to depths ranging between 500 and 3500 m, and are thus exposed to a temperature range of 45-130/sup 0/C. Silica phases exhibit a clear diagenetic progression with depth from the opal-A of the diatom frustules to opal-CT and ultimately to microquartz. Biomarker geochemistry provides effective alternative maturity indicators. Of particular interest are the stereochemical variations observed in the assemblages of steranes and triterpanes extracted from oil well core samples. Samples from petroleum production zones are distinguished by anomalously mature biomarker assemblages considering their depth of burial. It appears that any immature indigenous bitumen in production zone samples is overwhelmed by a mature component, which presumably migrated updip from deeper, warmer strata. While both source and reservoir rock are lithologically similar and lie within the same formation, biomarker geochemistry indicates that substantial generation occurs only in deeply buried Monterey shales.
Research Organization:
California Univ., Berkeley (USA)
OSTI ID:
7013615
Country of Publication:
United States
Language:
English