DETRITAL ZIRCON ANALYSIS OF THE LATE MIOCENE KERN RIVER FORMATION, KERN RIVER OILFIELD, SOUTHERN SAN JOAQUIN BASIN, CALIFORNIA

The Kern River oilfield is a giant field in the southeastern San Joaquin Basin (SE SJB) California. It has produced over one billion barrels of heavy oil from shallow (100 – 500 m) reservoirs in the late Miocene Kern River Formation. Detrital zircon (dz) ages from two outcrops and 22 core samples of Kern River Formation sandstones are compared to a large zircon age database of southern Sierra Nevada batholithic (SNB) rocks and modern stream sediments from a variety of local drainages. The data were used to better resolve sediment provenance and dispersal patterns during late Miocene-early Pliocene time as well as the incision history of the modern lower Kern River gorge near Bakersfield, California. All but three of the 24 samples contain a distinct plutonoclastic lithosome that, based on dz data, was derived from the extreme SE Sierra Nevada—not from the modern Kern River drainage basin. Several of the samples contain Neogene zircons (ca. 21 Ma) derived from the Cache Peak volcanic center in the Tehachapi Mountains. This volcanic area lies outside and southeast of the modern day Kern River drainage basin. This lithosome was delivered to the SE SJB through a major river that flowed westward into the SJB near the current location of Caliente Creek--~ 10 miles south of the modern day Kern River gorge. This suggests that development of the modern Kern River drainage did not occur until after late Miocene time.

This also has important implications for the overall trend of reservoir sandstones as well as the net-to-gross sand characteristics in the Kern River field. Two dimensional resistivity-amplitude maps show channel orientations trending north-northwest with a minor west-southwest component. The sands occur as thick sequences of overlapping channel deposits that appear to represent a braidplain, however individual channel deposits often show meandering characteristics in the resistivity amplitude maps as well as in outcrops near the field. The net sand map shows that net-sand thickness decreases to the north, reinforcing the evidence for a southerly source for the sands. Areas with higher net reservoir lithology (ie. sand) are preferable when steam flooding a heavy oil reservoir because less heat is required to warm non-reservoir lithologies (ie. clays).