Effects of Steam-Induced Diagenesis on Heavy-Oil Production in Miocene-Pleistocene Sands at Kern River Oil Field, California
R. A. Horton, Jr.1, L. Knauer2, D. A. Pennell3, and K. Coodey1
1California State University, Bakersfield, CA, [email protected], [email protected]
2Chevron U.S.A. Inc., Bakersfield, CA, [email protected]
3Aera Energy LLC, Bakersfield, CA, [email protected]
The Kern River oil field reservoir consists of braided alluvial sands and gravels of the Kern River Formation (Miocene-Pleistocene). Heavy oil (12°-13° API) is produced using steam injection. This typically results in good production from well sorted medium to very coarse sands, but poor production from less well sorted sands and gravels. These areas are commonly bypassed and remain unproduced, with residual oil saturations 10-30 saturation units higher than the adjacent rock despite heating to temperatures of 220° F and greater. This study examined mineralogy and pore geometry in sands that had not been heated, sands that had been heated but were not drained, and sands that had been swept of hydrocarbons by steam. Kern River Formation sands are predominantly quartz, K-feldspars (orthoclase and microcline), plagioclase (andesine-oligoclase), granitic microphanerites, and minor biotite reflecting their Sierra Nevadan source. Clays typically make up 5-13% of the rocks. Clays are dominated by mixed illite/smectite (80-90% smectite layers) with minor kaolinite. Samples that have been heated but not drained of oil are generally similar to unheated samples. Introduction of steam into the rocks as the sands were drained of oil resulted in the breaking apart of microphanerites, dissolution of feldspars, a slight increase in the amount of clays, but no significant change in total porosity. However, there are significant differences in the distribution of clays and the geometry of the pore networks between unheated sands and those swept of hydrocarbons by steam. Disintegration of microphanerites and subsequent rotation of the grain fragments has changed the sorting and reduced pore-throat diameters. Recrystallization and precipitation of mixed illite/smectite resulted in an increase in the amount of pore-filling clay cements, including bridges across pore throats, which may have restricted fluid flow. The extent to which this may have affected subsequent production is under investigation.
AAPG Search and Discovery Article #90088©2009 Pacific Section Meeting, Ventura, California, May 3-5, 2009