Application of
Shear Wave Anisotropy for Natural Fracture Detection in a Cased Well
Grayson, S. T.1, Adam Donald2,
Tom Bratton2, Romain Prioul3,
Monica Carlsen4, Lee Swager5 (1) Schlumberger, Ventura,
CA (2) Schlumberger, Greenwood Village, CO (3) Schlumberger-Doll Research,
Ridgefield, CT (4) Venoco Inc, Carpinteria,
CA (5) Schlumberger, Bakersfield, CA
Fracture detection in an open borehole
has become a routine process through the use of resistivity
imaging. However, once the well has been cased, this technique is no longer
viable and fracture detection becomes difficult. Certain acoustic measurements
can still be utilized, even with the presence of cement and casing. Shear waves
transmission is known to become anisotropic when fractures alter the intrinsic
nature of the rock, affecting the amplitude and velocity of the waves that
cross them. In addition, dispersion analysis, comparing shear slowness to
frequency response, shows a unique signature when this intrinsic anisotropy
exists. New acquisition hardware, software, and interpretation techniques have
been developed to observe this occurrence in cased wells. On a recent cased
well, in which openhole data were limited, these
techniques were used to identify fractured zones. Waveform, dispersion, and spatial
analysis were performed on the oriented shear sonic data and then combined with
knowledge of the geologic model to select perforation intervals to maximize
production from the fractured zones.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California