Changes

==Example: near-surface loss==

==Example: near-surface loss==

Kern River field (San Joaquin basin, California) is an [[accumulation]] of 4 billion bbl of original oil in place of 13°API, biodegraded, water washed, and devolatized oil at a subsurface depth of tens to hundreds of feet. The trap is a combination hydrodynamic/structural trap on the south and west sides<ref name=ch11r19>Kodl, E., J., Eacmen, J., C., Coburn, M., G., 1990, A geologic update of the emplacement mechanism within the Kern River Formation at the Kern River field, in Kuespert, J., Reid, S., eds., Structure, Stratigraphy, and Hydrocarbon Occurrences of the San Joaquin Basin California: Pacific Section SEPM Guidebook 64, p. 59–71.</ref> with stratigraphic trapping due to tarsealing and sand pinch-outs on the homoclinally dipping east side of the field.<ref name=ch11r27>Nicholson, G., 1980, Geology of the Kern River field, in Kern River Oilfield Field Trip: AAPG Pacific Section Guidebook, p. 7–17.</ref> Oil source is the same for undegraded, 34° oils farther downdip on the Bakersfield nose.

Kern River field (San Joaquin basin, California) is an [[accumulation]] of 4 billion bbl of original oil in place of 13°API, biodegraded, water washed, and devolatized oil at a subsurface depth of tens to hundreds of feet. The trap is a combination hydrodynamic/structural trap on the south and west sides<ref name=ch11r19>Kodl, E. J., J. C. Eacmen, and M. G. Coburn, 1990, A geologic update of the emplacement mechanism within the Kern River Formation at the Kern River field, in J. Kuespert, and S. Reid, eds., Structure, Stratigraphy, and Hydrocarbon Occurrences of the San Joaquin Basin California: Pacific Section SEPM Guidebook 64, p. 59–71.</ref> with stratigraphic trapping due to tarsealing and sand pinch-outs on the homoclinally dipping east side of the field.<ref name=ch11r27>Nicholson, G., 1980, Geology of the Kern River field, in Kern River Oilfield Field Trip: AAPG Pacific Section Guidebook, p. 7–17.</ref> Oil source is the same for undegraded, 34° oils farther downdip on the Bakersfield nose.

By assuming that asphaltene and resin volumes were just concentrated and not altered by near-surface processes, the amount of oil components lost in the near-surface environment can be calculated. An estimated 77% of the oil reaching the Kern River field was lost by near-surface processes, 92% of the saturates were lost, and 60% of the aromatics were lost. This means approximately 16 billion bbl of oil reached the vicinity of Kern River field, of which about 12 billion bbl were lost by near-surface processes as the field was charged.

By assuming that asphaltene and resin volumes were just concentrated and not altered by near-surface processes, the amount of oil components lost in the near-surface environment can be calculated. An estimated 77% of the oil reaching the Kern River field was lost by near-surface processes, 92% of the saturates were lost, and 60% of the aromatics were lost. This means approximately 16 billion bbl of oil reached the vicinity of Kern River field, of which about 12 billion bbl were lost by near-surface processes as the field was charged.