1Core Laboratories Inc., Bakersfield, CA
2Chevron USA Production Co., Bakersfield, CA.
Determination of a reservoir's in-situ maximum horizontal stress azimuth provides essential information to geologists and engineers for tectonic history interpretation as well as data used for hydraulic fracture design and optimal well placement.
As part of a jointly funded Chevron / US DOE Class III reservoir study, shear wave velocity measurements were made using Core Laboratories' Porosity Sonic Profile (PSP) device on conventional core samples from the 653Z-26B well in the Buena Vista Hills Field, California. These measurements represent the first time this technology has been applied in siliceous shale reservoirs.
Acoustic anisotropy theory is based on the tendency of conventional core samples to “relax” when removed from their down hole in-situ stress state. This relaxation results in the formation of a micro fracture system oriented perpendicular to the maximum horizontal stress component. Measurements were made on five oriented core samples taken from the interval 4031 to 4566 feet representing both the Brown and Antelope Shale members of the Monterey Formation. PSP shear wave velocity measurements were made in 30 degree azimuth increments around the circumference of the core in order to determine the direction of maximum velocity.
The measurements indicate that the maximum horizontal stress azimuth rotates counter clockwise with increasing depth in the well bore from an azimuth of 25 degrees at 4031 feet to 330 degrees at 4566 feet. This information will have a significant impact on the design of future Buena Vista Hills Field enhanced recovery programs.
AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas