Ultrasonic anisotropic P-wave attenuation of shales under elevated pressures

Ou, Liwei (Colorado School of Mines) | Prasad, Manika (Colorado School of Mines)


The mechanisms of ultrasonic attenuation in reservoir rock are known to be sensitive to multiple rock physical properties; this study focuses on ultrasonic experiments that measure the anisotropic attenuation in shales as function of hydrostatic confining pressure; four Eagleford and Bakken samples were measured using new experimental setup that allows measuring anisotropic acoustic properties of sample simultaneously with only one core plug. Our tests show that P-wave attenuation is sensitive to confining pressure, and attenuation anisotropy is stronger than velocity anisotropy, especially for more isotropic samples; the highly active change of attenuation with pressure supports the opinion that attenuation is a highly sensitive parameter to rock intrinsic properties. Moreover, attenuation as a function of pressure clearly suggests a two-phase attenuation mechanism exists in shale: high aspect ratio pores/microcracks closure and the related scattering attenuation on crack surfaces dominate attenuation behavior under low pressure, while at high pressure the main mechanism shifts to intrinsic attenuation caused by grain/crack friction and anelasiticity. The measured anisotropy data could be used for understanding the loss mechanisms responsible for seismic attenuation, and would benefit the development of theoretical attenuation rock physics models, as well as the interpretation of well logging and seismic surveys in shale reservoirs.

Presentation Date: Wednesday, October 19, 2016

Start Time: 10:20:00 AM

Location: 167

Presentation Type: ORAL