Study of Kern River Formation Channel Sands with Residual-Oil Saturation and Gradually-Decreasing Resistivity, Kern River Oil Field

Abstract:
Kern River oil field contains lithologic intervals with high oil saturations but that show no signs of drainage despite high reservoir temperatures caused by steam injection. Many of these intervals exhibit gradual decreases in resistivity with increasing depth; this study examines these intervals in an attempt to determine why oil is not draining.

Resistivity and oil-saturation contour maps were created to look for trends. Petrographic, SEM-EDS, XRD, specific-permeability, viscosity, laser particle-size, and capillary-pressure analyses, were performed using whole-core samples to investigate lithologic variability.
The results from this research indicate changes in mineralogy across the intervals. Whole-core analyses, petrographic analyses, and laser particle-size analyses show variations in clay percentages across the intervals. Petrographic analyses show positive correlations between percentage of rock fragments, amount of steam-induced grain dissolution, and percentage of clays. Plagioclase grains show the largest amount of dissolution; K-feldspars and quartz grains are also affected, though no significant change in total porosity was noted. XRD analyses indicate random-ordered mixed-layer illite/smecite with 80-90% smectite layers as the main clay mineral. Capillary-pressure tests show that the pore structures become tighter toward the bottoms of the intervals. Hydrocarbon viscosities within these intervals increase with increased depth.
Authigenic clays are present as grain coatings, pore bridges, and pore-filling cements. These increase in abundance with increasing depth and are a possible explanation for the increase in pore-structure tightness. The positive correlation between percentage of clays and amount of grain dissolution suggests that the authigenic clays formed through steam-induced diagenesis. A combination of clays, varying grain sizes, and varying viscosities explain the lack of oil production within these zones.

About the speaker:

Kay Coodey is a Geoscience Specialist for Vintage Production's Ventura Inland East fields in the Ventura Basin. Kay started her geoscience career in 2002 as a Geology Intern for the Kern County Water Agency. In 2006 she began working as an Earth Science intern for Chevron's San Joaquin Valley Business Unit working both the Kern Rivr and Midway Sunset oilfields. She graduated in 2004 with a B.S. in Geology from California State University, Bakersfield where she is currently pursuing her M.S. in Petroleum Geology. Kay is a member of the AAPG, PSAAPG, AWG (Association for Women Geoscientists), AWMA (Air Waste Managmeent Association) and SJGS.

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