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The elastic properties of shale gas reservoirs are significantly different from those of conventional clastic reservoirs. Specifically, shale reservoirs are highly anisotropic, usually with the axis of symmetry vertical or near vertical (VTI anisotropy). The anisotropy characterized by shale elastic properties comes from a number of sources, among them the deposition history and environment, the total organic content, the maturity of the hydrocarbon, and the aligned cracks and grains. The VTI anisotropy detected in gas shales may be quite large, and significantly affects seismic imaging as well as the estimation of geomechanical properties for hydraulic fracture design. There is not a single borehole measurement that can easily measure all the necessary parameters to fully characterize the VTI elastic anisotropy in gas shales. However, by a combination of measurements, we can do so. We can use the Stoneley wave and the Flexural (dipole) mode in acoustic logs to estimate the shear wave anisotropy, and we can use walkaway VSPs to measure the P wave anisotropy. The other type of anisotropy common in gas shale reservoirs is azimuthal anisotropy (HTI anisotropy), caused mainly by vertically aligned fractures or cracks. Again, it is not straight forward to measure the anisotropy using a single borehole measurement. We can use shear wave splitting from cross-dipole acoustic logs to estimate the shear wave anisotropy, and azimuthal/walkaround VSPs to estimate the P wave anisotropy. In this presentation, I will present methods and examples for each case, and discuss the sensitivity of these methods to various borehole and acquisition parameters.

Figure.Laboratory measured P and S wave velocity anisotropy in a number of different shales. The data illustrates that there is significant velocity anisotropy in shales. Beware that the normal assumption of weak anisotropy does not apply to most shales. The data also shows that in general P and S wave anisotropy are similar, and wet or liquid-saturated shales show a bit more S wave anisotropy than P wave anisotropy, while dry or gas-saturated shales show more P wave anisotropy than S wave anisotropy.

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Event Contact	Event Coordinator
Fred Hilterman	Fred Hilterman

Technical Luncheon (Pelazzio)

Tuesday 21-Feb-2012 11:00 AM to 1:30 PM CST

Speaker Arthur Cheng

Company: Halliburton, Houston

Biography

Arthur C.H. Cheng is the Senior Manager for Acoustics and Borehole Seismics at Halliburton. He received a B.Sc. with Distinction in Engineering Physics from Cornell University in 1973, and a Sc.D. in Geophysics from MIT in 1978. He was one of the co-founders of the Earth Resources Laboratory at MIT in 1982, and was Project Leader of the MIT Borehole Acoustics and Logging Consortium until 1996, when he joined Western Atlas. He has also worked for Baker Hughes Inteq, OHM Rock Solid Images, as well as consulting for various companies.

Arthur has served on a number of academic and industry positions through the years; he is currently an Associate Editor for Geophysics in Borehole Geophysics and Rock Properties, and a member of the SEG Foundation Board of Directors (2012-4). Previously he was the Vice President of the SEG Executive Committee, (2009-2010), Chair of the SEAM Board of Directors (2008-9); Chair of the SEG Research Committee (2005-6), and a member of the Visiting Committee for the Department of Earth, Atmospheric, and Planetary Sciences at MIT.

Technical Luncheon (Pelazzio)

Tuesday 21-Feb-2012 11:00 AM to 1:30 PM CST

Pelazzio/The new Omni Palace

12121 Westheimer Rd
Houston TX 77077
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Technical Luncheon (Pelazzio)

Tuesday 21-Feb-2012 11:00 AM to 1:30 PM CST

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