• journal_title：Geophysics
• Contributor：Nikita Chugunov ; Yusuf Bilgin Altundas ; T. S. Ramakrishnan ; Ozgur Senel
• Publisher：Society of Exploration Geophysicists
• Date：2013-05-01
• Format：text/html
• Language：en
• Identifier：10.1190/geo2012-0359.1
• journal_abbrev：Geophysics
• issn：0016-8033
• volume：78
• issue：3
• firstpage：WB77
• section：Assessing Uncertainty

Quantification of reservoir uncertainty is an essential part of a monitoring design. A systematic approach that quantitatively links predicted uncertainties in a monitoring program to the underlying reservoir variability is, however, needed. We developed a methodology for quantifying uncertainty in crosswell seismic monitoring combined with neutron-capture logging and applied global sensitivity analysis (GSA) to compute and rank contributions of uncertain reservoir parameters to the predicted uncertainty of the measurements. The workflow is illustrated by a numerical study using a simplified model of a x mml-math">x-code"><mml:math display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>CO</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>x-text">CO2 storage site where crosswell measurements have not actually been taken. Synthetic seismic responses are computed through the integration of multiphase flow, a new thermodynamically consistent fluid substitution model, and a fast marching eikonal solver. We quantified uncertainty in first-arrival times to illustrate the potential utility of crosswell seismic surveys and their limitation. Consistent with these calculations, uncertainties in neutron capture cross-section logs are also computed and related to predicted x mml-math">x-code"><mml:math display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>CO</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>x-text">CO2 migration. The predicted uncertainty range for neutron-capture measurements indicated significant sensitivity to the uncertainty of the reservoir properties (standard deviations [STDs] of up to 6 c.u. in the injector and up to 3.5 c.u. in the monitoring well). However, the STD of predicted time-lapse crosswell seismic responses for two different source locations did not exceed 0.75 ms during the life of the project, suggesting limited value of first-arrival measurements for reservoir-parameter inversion in this case. With the time-dependent uncertainty of the predicted measurements, calculated GSA indices provided a quantitative basis for the monitoring program design. Practical implications of GSA results for model reduction and subsequent inversion were also evaluated.