1887
Volume 40 Number 8
  • E-ISSN: 1365-2478

Abstract

A

The accuracy of estimating crack‐strike from the algebraic equivalent of a popular technique, the dual source cumulative technique (DCT), for analysing shear‐wave splitting in seismic experiments is evaluated for earth models permeated by different alignments of micro‐cracks. A complementary analysis is performed using another analysis procedure, the dual‐independent source‐geophone technique (DIT), to investigate any benefits of the alternative formulation. The investigation considers synthetic vertical seismic profile (VSP) and reflection data for an earth model with two layers over a half‐space, and three different classes of crack‐strike variation with depth: uniform crack‐strike, an abrupt change of crack‐strike between the upper and lower layer, and a continuous increase over both layers. The synthetic data for zero‐offset and near‐offset VSPs and a reflection profile are computed using a full‐wave modelling package in which equivalent anisotropic media simulate distributions of aligned vertical, parallel, water‐filled microcracks. Estimates from the two techniques agree for the constant crack‐strike model, but differ for the VSP data with crack‐strike changes. The asymptotic behaviour of the two angular parameters θ and θ from DIT suggest that it may be used to determine crack‐strike under appropriate circumstances in these VSPs, when the time‐delay between the split shear‐waves for the layer of interest exceeds the peak period of the wavelet. In this limit, θ tends to follow the crack‐strike change with θ tending to a constant value, whereas DCT will give a misleading value between the upper and lower crack‐strike. Although the behaviour of DIT is not understood in all cases, θ and θ values from the VSP data always appear to diverge near the point where an abrupt crack‐strike change takes place. This could be used as a qualitative indicator for layer stripping. Both techniques agree for the reflection data as the recorded data matrix is necessarily symmetric, but still give misleading results for deeper layers in the presence of crack‐strike changes. This study suggests that more care should be taken when designing and analysing experimental configurations for detecting crack properties in reservoir rocks, to consider the response and resolution limits of the analysis techniques. A note of caution is offered to those who directly interpret polarization estimates as crack‐strike.

Loading

Article metrics loading...

/content/journals/10.1111/j.1365-2478.1992.tb00556.x
2006-04-27
2020-04-05
Loading full text...

Full text loading...

References

  1. Alford, R.M.1986. Shear data in the presence of azimuthal anisotropy: Dilley, Texas. 56th SEG meeting, Houston, Expanded Abstracts, 476–479.
  2. Crampin, S.1984. Effective elastic constants for wave propagation through cracked solids. Geophysical Journal of the Royal Astronomical Society76, 135–145.
    [Google Scholar]
  3. Crampin, S.1990. Alignment of near‐surface inclusions and appropriate crack geometries for geothermal hot‐dry‐rock experiments. Geophysical Prospecting38, 621–631.
    [Google Scholar]
  4. Crampin, S.1991. Effect of point singularities on shear‐wave propagation in sedimentary basins. Geophysical Journal International107, 531–544.
    [Google Scholar]
  5. Crampin, S., Lynn, H.B. and Booth, D.C.1989. Shear‐wave VSPs: a powerful new tool for fracture and reservoir description. Journal of Petroleum Technology5, 283–288.
    [Google Scholar]
  6. Hudson, J.A.1981. Wavespeeds and attenuation of elastic waves in material containing cracks. Geophysical Journal of the Royal Astronomical Society64, 133–150.
    [Google Scholar]
  7. Hudson, J.A.1980. Overall properties of a cracked solid. Mathematical Proceedings of the Cambridge Philosophical Society88, 371–384.
    [Google Scholar]
  8. Igel, H. and Crampin, S.1990. Extracting shear‐wave polarizations from different source orientations: synthetic modelling. Journal of Geophysical Research95, 11283–11292.
    [Google Scholar]
  9. Kennett, B.L.N.1983. Seismic Wave Propagation in Stratified Media. Cambridge University Press.
    [Google Scholar]
  10. Lawson, CL. and Hanson, R.J.1974. Solving Least Squares Problems. Prentice‐Hall, Inc.
    [Google Scholar]
  11. Lefeuvre, F., Cliet, C. and Nicoletis, L.1989. Shear‐wave birefringence measurement and detection in the Paris Basin. 59th SEG meeting, Dallas, Expanded Abstracts, 786–790.
  12. Lefeuvre, F. and Mandal, B.1991. Fracture evaluation using a 3‐D propagator matrix method. 61st SEG meeting, Houston, Expanded Abstracts, 1628–1632.
  13. Lefeuvre, F., Winterstein, D., Meadows, M. and Nicoletis, L.1991. Propagator matrix and layer stripping methods: a comparison of shear‐wave birefringence detection on two data sets from Railroad Gap and Lost Hills fields. 61st SEG meeting, Houston, Expanded Abstracts, 55–60.
  14. Liu, E., Crampin, S. and Yardley, G.1990. Polarizations of reflected shear‐waves. Geophysical Research Letters17, 1137–1140.
    [Google Scholar]
  15. MacBeth, C. and Crampin, S.1989. Automatic processing of VSP data to extract details of upper‐crustal anisotropy. SEG summer research workshop on Recording and Processing Vector Wavefield Data, Snowbird, Utah, Expanded Abstracts, 115.
  16. MacBeth, C. and Crampin, S.1991. Automatic processing of seismic data in the presence of anisotropy. Geophysics56, 1320–1330.
    [Google Scholar]
  17. Martin, M.A. and Davis, T.L.1987. Shear‐wave birefringence: a new tool for evaluating fractured reservoirs. The Leading Edge6, 22–25.
    [Google Scholar]
  18. Nicoletis, L., Cliet, C. and Lefeuvre, F.1988. Shear‐wave splitting measurements from multishot VSP data. 58th SEG meeting, New Orleans, Expanded Abstracts, 527–530.
  19. Queen, J.H. and Rizer, W.D.1990. An integrated study of seismic anisotropy and the natural fracture system at the Conoco borehole test facility, Kay County, Oklahoma. Journal of Geophysical Research95, 11255–11274.
    [Google Scholar]
  20. Slack, R.D., Ebrom, D.A., McDonald, J.A. and Tatham, R.H.1991. Thin layers and shear wave splitting. 61st SEG meeting, Houston, Expanded Abstracts, 1549–1552.
  21. Squires, S.G., Kim, C.D. and Kim, D.Y.1989. Interpretation of total wavefield over Lost Hills fields, Kern County, California. Geophysics54, 1420–1429.
    [Google Scholar]
  22. Tatham, R.H. and McCormack, M.D.1991. Multicomponent seismology in petroleum exploration. Investigations in Geophysics, No. 6, Society of Exploration Geophysicists. E. B.Nieitzel and D. F.Winterstein (eds).
    [Google Scholar]
  23. Taylor, D.B.1987. Double contour integration for transmission from point sources through anisotropic layers as used in ROCPAC software. Geophysical Journal of the Royal Astronomical Society91, 373–381.
    [Google Scholar]
  24. Taylor, D.B.1991. ANISEIS II Manual. Available to licensees of ANISEIS from Applied Geophysical Software Inc., Houston .
    [Google Scholar]
  25. Thomsen, L.1988. Reflection seismology over azimuthally anisotropic media. Geophysics53, 304–313.
    [Google Scholar]
  26. Warpinski, N.R. and Teufel, L.W.1991. In situ stress measurements of Rainier Mesa, Nevada Test Site – influence of topography and lithology on the stress state in Tuff. International Journal of Rock Mechanics, Mining Science and Geomechanical Abstracts28, 143–161.
    [Google Scholar]
  27. Winterstein, D.F. and Meadows, M.A.1991a. Shear‐wave polarizations and subsurface stress directions at Lost Hills field. Geophysics56, 1331–1348.
    [Google Scholar]
  28. Winterstein, D.F. and Meadows, M.A.1991b. Changes in shear‐wave polarization azimuth with depth in Cymric and Railroad Gap oil fields. Geophysics56, 1349–1364.
    [Google Scholar]
  29. Yardley, G.S. and Crampin, S.1991. Extensive‐dilatancy anisotropy: relative information in VSPs and reflection surveys. Geophysical Prospecting39, 337–355.
    [Google Scholar]
  30. Yardley, G.S., Graham, G. and Crampin, S.1991. Viability of shear‐wave amplitude versus offset studies in anisotropic media. Geophysical Journal International107, 493–504.
    [Google Scholar]
http://instance.metastore.ingenta.com/content/journals/10.1111/j.1365-2478.1992.tb00556.x
Loading
  • Article Type: Research Article
This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error