--> Abstract: Geochemical Data Provide Insights into Oil Migration History of Elk Hills Field, California; #90063 (2007)

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Geochemical Data Provide Insights into Oil Migration History of Elk Hills Field, California

 

Countryman, Robert L.1, Judy Russell2, Stephen A. Reid3, John Zumberge4 (1) Occidental Oil and Gas, Tupman, CA (2) Occidental Oil and Gas, Houston, TX (3) Occidental Oil and Gas, Muscat, Oman (4) GeoMark Research, Houston, TX

 

Geochemical analysis of oils from a mature field when combined with regional and reservoir geology may provide insights into oil migration routes, relationships between reservoirs, and seal quality of traps. At the Elk Hills field in the San Joaquin basin, stable carbon isotopes and biomarkers of oils from Upper Miocene reservoirs define four families. Most Miocene reservoirs at Elk Hills lack low maturity oil characteristic of the Monterey Formation, which implies that traps or migration routes formed after the early pulse of migration. Family A1 oils are present only in deep-water channel reservoirs and are derived from a source rock of a consistent composition that became increasingly mature. Oil migrated from the generative area to the reservoirs updip along the channel system. Family A2 oils, present in deep-water fan lobe reservoirs, are derived from a source rock of consistent maturity. The consistent maturity indicates the possibility of rapid filling of the reservoirs along a newly established migration routes from generative areas. Oil from porcelanite reservoirs represents another family (SH), and migration must have occurred following an enhancement of permeability during diagenesis. The presence of low maturity oil (Family C) in one reservoir presents a paradox: the oil may represent a remnant of the initial pulse of Monterey oil, or may be the last oil generated from a location immediately adjacent to Elk Hills.

 

In general, a strong stratigraphic relationship exists between oil migration routes and reservoir intervals. Within the field, mixing of oil between stratigraphic intervals occurs but is rare. The distribution of oil families also confirms that some adjacent reservoirs have excellent lateral stratigraphic seals.

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California