Previous Talks

 

Wednesday April 14th, 2010

Determination of in-situ stress and rock strength using borehole acoustic data

Colin M. Sayers, Schlumberger

Abstract

In-situ stress, pore pressure, and rock strength are required for the analysis and prediction of geomechanical problems encountered in the petroleum industry. In this presentation, the use of sonic data to determine horizontal stress and rock strength is discussed.

In the first part of the talk, the use of sonic data to determine maximum horizontal stress and rock strength in poorly consolidated sandstones is described for two case studies. The maximum horizontal stress is determined from estimates of the three far-field shear moduli, corresponding to the principal stress planes. These are estimated from the dipole flexural waves and Stoneley wave. The rock strength is determined by analyzing the variation in the velocity of polarized shear waves as functions of azimuth and distance from the borehole.

In the second part of the talk, the use of sonic data to characterize the anisotropy of shales is described, and implications for the determination of minimum horizontal stress in gas shales are discussed. Estimates of the horizontal stress in shales may be significantly in error if the anisotropy of the shale is neglected. Isotropic stress models applied to anisotropic shales lead to an incorrect prediction of the contrast in horizontal stress between layers, and therefore fail to describe the containment of hydraulic fractures correctly.

Speaker Biography

Colin Sayers is a Scientific Advisor in the Schlumberger Data & Consulting Services Geomechanics Group in Houston, USA, providing consultancy in drilling and reservoir geomechanics, rock physics, geophysics, and the characterization of fractured reservoirs. He entered the oil industry to join Shell's Exploration and Production Laboratory in Rijswijk, The Netherlands in 1986, and moved to Schlumberger in 1991.

His technical interests include drilling and reservoir geomechanics, pore pressure prediction, wellbore stability analysis, analysis of production-induced reservoir stress changes, subsidence, fault reactivation, 3D mechanical earth modeling, sanding, rock physics, geophysics, fractured reservoir evaluation, borehole/seismic integration, stress-dependent acoustics, advanced sonic logging, AVAZ, and fluid flow in fractured reservoirs.

He is a member of the AGU, EAGE, SEG, and SPE, a member of the Research Committee of the SEG, and a member of the editorial board of The Leading Edge and the International Journal of Rock Mechanics and Mining Science. He has a B.A. in Physics from the University of Lancaster, U. K., a D.I.C. in Mathematical Physics and a Ph.D. in Physics from Imperial College, London, U. K. In 2010 he is presenting the SEG/EAGE Distinguished Instructor Short Course "Geophysics under stress: Geomechanical applications of seismic and borehole acoustic waves".

References

The following references cover much of the material presented in the talk, and may be useful for those wanting to start reading about the use of elastic waves to determine in-situ stress and rock strength:

Sensitivity of elastic-wave velocities to stress changes in sandstones by Sayers (2005) The Leading Edge, 24 , no. 12, 1262-1266.

Determination of Rock Strength Using Advanced Sonic Log Interpretation Techniques, SPE 124161 by Sayers et al. presented at the SPE Annual Technical Conference and Exhibition, 4-7 October 2009, New Orleans, Louisiana.

Determination of Rock Strength Using Advanced Sonic Log Interpretation Techniques by Sayers et al. (2009) SEG, Expanded Abstracts, 28 , no. 1, 3505-3509.

Seismic anisotropy of shales by Sayers (2005), Geophysical Prospecting, 53 , no. 5, 667-676.

Anisotropic Stress Models Improve Completion Design in the Baxter Shale, SPE 115736 by Higgins et al., presented at the SPE Annual Technical Conference and Exhibition, 21-24 September 2008, Denver, Colorado, USA.