Interpretation of Total Wave Field Data Over Lost Hills Field, Kern County, California
Stewart G. Squires, Daniel Y. Kim
During May 1987, approximately 5 mi of total wave field data were acquired over the southeastern edge of Lost Hills Field, Kern County, California. Data were acquired to assess the capabilities of multicomponent data to provide information about lithologic variation and fracturing within the Miocene Monterey Formation. Quality of the shear-wave sections was extraordinarily good, better than any P-wave sections reviewed from the area. The addition of a multicomponent VSP provided crucial tie information between P- and S-wave data. VP/VS ratios were computed that ranged from 2.79 to 1.63, with low VP/VS ratios in the interval (lower Reef Ridge Shale to McDonald Shale) corresponding to production.
Evidence for azimuthal anisotropy was found, so the SV and SH data sets were rotated into principal component axes. The fast shear wave (S1) and slow shear wave (S2) have orientations of N45°E and N45°W, respectively. After rotation, these data show clear evidence of shear-wave splitting. Delay ratios, used as a measure of fracture intensity, range from a maximum of 7.31% to a minimum of 0.09% across the structure. Delay ratios in the zone of interest are anomalously high (2.83-7.31%) in the vicinity of production. Additionally, a comparison of slope vs. percent of interval delay indicates a larger degree of fracturing on the flanks as opposed to the crest of the structure.
Use of a total wave field data set and associated analyses have provided significant structural and stratigraphic information on the Miocene Monterey Formation over the Lost Hills field, highlighting the productive interval.
AAPG Search and Discovery Article #91035©1988 AAPG-SEPM-SEG Pacific Sections and SPWLA Annual Convention, Santa Barbara, California, 17-19 April 1988.