Evaluating VTI Anisotropy
in Shale Using New Borehole
Sonic Measurements for Improving Seismic Ties
Pluemer, Brian1, Adam Donald2, Tom Bratton2 (1) Schlumberger, Denver, CO (2) Schlumberger, Greenwood Village, CO
Anisotropy
describes an attribute as a function of the
direction of measurement. Quantifying and identifying 3-dimensional
anisotropy
is critical for surface, borehole and micro-seismic calibration. Shale
formations are of importance for conventional and unconventional hydrocarbon
recovery. Shale is also anisotropic due to its layering microstructure. It has
been well documented that elastic wave propagation through shale is affected by
this
anisotropy
, which can lead to improper correlation between borehole
measurements and surface seismic surveys.
The latest sonic technology combined with a 3D anisotropic
algorithm transforms the compressional, shear (fast and slow) and Stoneley
slownesses to anisotropic elastic moduli. These moduli are then used to classify
the formation as to its type and amount of anisotropy
. Shear and compressional
velocities within shale are often faster in the horizontal plane than the
vertical plane due to layering. This formation characteristic can be described
as transversely isotropic with a vertical axis of symmetry (VTI). Quantifying
the VTI
anisotropy
parameters in shale is required for AVO analysis, VSP
analysis in deviated wellbores and micro-seismic calibration.
A case study will be presented from an unconventional shale-gas play in Arkansas where the formation VTI parameters were computed and analyzed for seismic and micro-seismic calibration.
AAPG Search and Discovery Article #90055©2006 AAPG Rocky Mountain Section Meeting, Billings, Montana