SPE Reservoir Evaluation & Engineering
Volume 13, Number 2, April 2010, pp. 265-274

SPE-116129-PA

Pore-Pressure-Coefficient Anisotropy Measurements for Intrinsic and Induced Anisotropy in Sandstone

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DOI  More information 10.2118/116129-PA http://dx.doi.org/10.2118/116129-PA

Citation

  • Al-Tahini, A. and Abousleiman, Y. 2010. Pore-Pressure-Coefficient Anisotropy Measurements for Intrinsic and Induced Anisotropy in Sandstone. SPE Res Eval & Eng  13 (2): 265-274. SPE-116129-PA. doi: 10.2118/116129-PA.

Discipline Categories

  • 6.6.2 Core Analysis
  • 6.8 Fundamental Research in Reservoir Description and Dynamics

Keywords

  • anisotropy, Biot's coefficient, stress, static, dynamic

Summary

In this study, we determine experimentally the effect of inherent and stress-induced anisotropy on stiffness components, elastic moduli, and Biot's pore-pressure coefficients (PPCs) for Lyons outcrop Colorado sandstone, which exhibits a clear transverse isotropic rock structure. Both dynamic and quasistatic methods were used under a nonhydrostatic state of stress to perform the measurements on dry core samples. Our assumption of apparent transverse anisotropy was confirmed initially with acoustic velocity measurements and at a later stage in the loading with experimental transverse anisotropic failure analysis. The objective of this study is to identify and isolate the effect of stress-induced anisotropy from the inherent transverse anisotropy on the measured stiffness components, elastic moduli, and Biot's PPCs. The effect of stress-induced anisotropy appears to have significant control on measured stiffness components, elastic moduli, and Biot's PPCs in comparison to the inherent-transverse-anisotropy effect. Our work shows that the stiffness components, Mij, and thus the computed elastic moduli, are highly influenced by the stress-induced anisotropy, especially the off-diagonal stiffness components, M12 and M13, where the increase in their magnitudes from the dynamic measurements before failure is determined to be 100 and 81%, respectively. The difference in the magnitude between the axial and lateral Biot's PPCs in line with bedding planes and perpendicular to them is measured to be 24 and 16% from the quasistatic and dynamic methods, respectively; whereas, the effect of stress-induced anisotropy reduced the dynamic average magnitude of the Biot's PPCs along the bedding planes and transverse to these planes by 63% across a stress range of 145 MPa.

© 2010. Society of Petroleum Engineers

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History

  • Original manuscript received: 6 July 2008
  • Meeting paper published: 21 September 2008
  • Revised manuscript received: 3 March 2009
  • Manuscript approved: 30 March 2009
  • Published online: 14 January 2010
  • Version of record: 20 April 2010