1887

Abstract

Summary

Time-lapse studies not only allow to monitor the reservoir but are also useful to access risk in the overburden. They usually assume that the velocity change during reservoir depletion is isotropic, but, from a geomechanical perspective, velocity changes have no reason to be isotropic. Numerous authors observe that the velocity changes in the overburden suggest rock damage such as crack opening which implies anisotropic elastic property changes. Rock damage depends on several geomechanical parameters such as the initial rock elastic properties, the in situ stress, the stress state change, the crack shapes and their orientations, etc.

We show that retrieving an anisotropic time-lapse velocity change is possible using a pre-stack seismic tomographic approach. The anisotropic time-lapse velocity change is decomposed into a functions basis which respects the travel-time perturbation symmetries. The anisotropic time-lapse velocity change predicted by the rock physics models can be expressed in this general basis with some algebra.

We apply the proposed tomographic inversion on a cross-section of a real reservoir and we relate the anisotropic time-lapse velocity change to horizontal crack distribution in the overburden. Results show a good qualitative consistency between the prediction of the rock physics model and the tomography results.

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/content/papers/10.3997/2214-4609.201900820
2019-06-03
2019-12-14
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References

  1. Backus, G.
    [1970] A geometrical picture of anisotropic elastic tensors. Reviews of geophysics, 8(3), 633–671.
    [Google Scholar]
  2. Červený, V.
    [2001] Seismic Ray Theory. Cambridge University Press.
    [Google Scholar]
  3. Chapman, C.t. and Pratt, R.
    [1992] Traveltime tomography in anisotropic media—I. Theory. Geophysical Journal International, 109(1), 1–19.
    [Google Scholar]
  4. De Gennaro, S., Onaisi, A., Grandi, A., Ben-Brahim, L. and Neillo, V.
    [2008] 4D reservoir geomechanics: a case study from the HP/HT reservoirs of the Elgin and Franklin fields. first break, 26(12), 53–59.
    [Google Scholar]
  5. Edgar, J. and Mastio, N.
    [2017] Time-lapse velocity change tomography. In: 79th EAGE Conference and Exhibition.
    [Google Scholar]
  6. Felício Fuck, R. and Tsvankin, I.
    [2009] Analysis of the symmetry of a stressed medium using nonlinear elasticity. Geophysics, 74(5), WB79–WB87.
    [Google Scholar]
  7. Guilbot, J. and Smith, B.
    [2002] 4-D constrained depth conversion for reservoir compaction estimation: Application to Ekofisk Field. The Leading Edge, 21(3), 302–308.
    [Google Scholar]
  8. Hatchell, P. and Bourne, S.
    [2005] Rocks under strain: Strain-induced time-lapse time shifts are observed for depleting reservoirs. The Leading Edge, 24(12), 1222–1225.
    [Google Scholar]
  9. Herwanger, J. and Horne, S.
    [2005] Predicting time-lapse stress effects in seismic data. The Leading Edge, 24(12), 1234–1242.
    [Google Scholar]
  10. Kudarova, A., Hatchell, P., Brain, J. and Macbeth, C.
    [2016] Offset-dependence of production-related 4D time shifts: Real data examples and modeling. In: SEG Technical Program Expanded Abstracts 2016, Society of Exploration Geophysicists, 5395–5399.
    [Google Scholar]
  11. MacBeth, C., Kudarova, A. and Hatchell, P.
    [2018] A semi-empirical model of strain sensitivity for 4D seismic interpretation. Geophysical Prospecting, 66(7), 1327–1348.
    [Google Scholar]
  12. Rickett, J., Duranti, L., Hudson, T., Regel, B. and Hodgson, N.
    [2007] 4D time strain and the seismic signature of geomechanical compaction at Genesis. The Leading Edge, 26(5), 644–647.
    [Google Scholar]
  13. Røste, T., Dybvik, O.P. and Søreide, O.K.
    [2015] Overburden 4D time shifts induced by reservoir compaction at Snorre field. The Leading Edge, 34(11), 1366–1374.
    [Google Scholar]
  14. Røste, T., Stovas, A. and Landrø, M.
    [2006] Estimation of layer thickness and velocity changes using 4D prestack seismic data. Geophysics, 71(6), S219–S234.
    [Google Scholar]
  15. Staples, R., Ita, J., Burrell, R. and Nash, R.
    [2007] Monitoring pressure depletion and improving geome-chanical models of the Shearwater field using 4D seismic. The Leading Edge, 26(5), 636–642.
    [Google Scholar]
  16. Williamson, P., Cherrett, A. and Sexton, P.
    [2007] A new approach to warping for quantitative time–lapse characterisation. In: 69th EAGE Conference and Exhibition incorporating SPE EUROPEC 2007.
    [Google Scholar]
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