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7th Middle East Geosciences Conference and Exhibition
Manama, Bahrain
March 27-29, 2006
Geophysical Technology, Saudi Aramco, C/OSaudi Aramco, P.O. box 1372, Dhahran 31311 Saudi
Arabia, phone: 966 3 873 2020, [email protected]
Inversion of post-stack surface seismic amplitudes for estimation of acoustic impedance is routine in the industry, today. Not
yet routine is the assessment of uncertainty in the impedance estimate. This missing step could be critical in the Middle
East, where land seismic data quality issues dominate. For example, in Saudi Arabia, impedance volumes are often used
for development well location in stratigraphically controlled clastics reservoirs. The mathematical techniques for uncertainty
analysis have been available for many years, but, historically, little use has been made of them in exploration geophysics.
However, this is beginning to change as interest in the problem
grows. Saudi Aramco is currently pursuing an internal
project to assess this
problem
, and this presentation will review some of the progress that has been made. Some of the
issues addressed are: (1) can the uncertainty analysis proceed post-inversion, or must it be included as part of the inversion
process? (2) Making a clear distinction between error propagation and the estimation of errors (to be propagated). (3) Error
propagation techniques – including method of moments and Bayesian methods (the latter offers the opportunity for
improved impedance estimates, as well). (4) Solution methods for the Bayesian
problem
(5) Assumptions in the
mathematical model for computational tractability, (6) Estimation of seismic noise covariance matrices (7) Wavelet
covariance and start model/low frequency trend uncertainty. Both synthetic and real data examples will be shown and
outstanding problems discussed. Finally, applications of inversion uncertainty analysis to porosity uncertainty estimates for
reservoir model building, automatic history matching, and reserves analysis will be discussed.