Ultrasonic P and S – Wave Velocity Anisotropy Measurements of Barnett Shale.

Nikolay I. Dyaur¹, Victor Pena¹, Mike Ammerman², and Evgeni Chesnokov^1
1Institute For Theoretical Geophysics, College of Earth and Energy University of Oklahoma;
²Devon Energy Inc., Oklahoma City, Oklahoma

Results of longitudinal (Vp) and shear (Vs) wave velocity measurements of core of Barnett shale are presented. The oriented core of shale from various depths was used to investigate the azimuthal distributions of velocities. The ultrasonic pulse techniques were used. Frequency of both P- and S-wave transducers were 1 MHz. Core samples (10.1cm diameter) of Barnett shale were studied Bedding of shale was approximately normal to axis of core. There were a few samples with calcite filled fractures oriented in subvertical direction. P and S-wave velocity anisotropy were measured along and perpendicular to bedding. The measurements along the bedding were carried out in each 22.5 degree. The obtained results shown: 1. absence of P-wave velocity anisotropy (Ap) along the bedding. Small value of Ap (0.5%-3.5%) can be explained by a coarse influence of a sub vertical fracture orientation or an angle of a bedding of the shales; 2. maximum shear wave anisotropy As (shear wave spitting : SWS) along the bedding and an absence of SWS perpendicular to bedding. Changing angle of propagation of elastic waves to bedding from parallel to normal we found the decreasing of P-wave velocity from 4.25 km/s to 1.93 or 2,2 km/s. So, the studied shales can be characterized by transversally isotropic type of symmetry.

AAPG Search and Discover Article #90065©2007 AAPG Southwest Section Meeting, Wichita Falls, Texas