Study of Kern River Formation Channel Sands with Gradually Decreasing Resistivity, Kern River Oil Field, Kern County, California

Kay Coodey¹, Robert A. Horton,Jr.¹, and Larry C. Knauer^2
1California State University Bakersfield, 9001 Stockdale Hwy, Bakersfield, CA 93311
²1546 China Grade Loop Chevron, 1546 China Grade Loop, Bakersfield, CA 93308

Kern River oil field (Kern County, California) 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, laser particle-size, and capillary-pressure analyses were performed using whole-core samples to investigate lithologic variability. Viscosity tests were performed to evaluate the impact of this property on the movement of oil through the pore spaces. 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. XRD analyses indicate random-ordered mixed-layer illite/smectite 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.

AAPG Search and Discovery Article #90076©2008 AAPG Pacific Section, Bakersfield, California