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Stanford Center for Reservoir Forecasting
Direct updating of geostatistical reservoir models using iterative resampling with DISPAT Xiaojin Tan & Jef Caers SCRF 2012 SCRF 2012
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Motivation Question addressed: How to update a single legacy reservoir model with new production data? Example Single legacy model matches history but there is No geostat input (variograms, TI) No parameterization No software for model updating
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Basic idea Use the current existing reservoir model as a training image in a non-stationary geostatistical algorithm termed dispat. Using iterative spatial resampling (ISR) to update the current legacy model with the additional production data
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DisPat Why Dispat? Every single real legacy model has non-stationary elements Conditioned to wells Conditioned to seismic Imposed layering and trends (vertical/horizontal) CPU-efficient for large models
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Mariethoz et al., 2010 m1 m2 m3 Sampling Sampling r1 r2
1.only one parameter required 2.keep the same spatial continuity Mariethoz et al., 2010
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Metropolis Sampling Current model mi proposal model m*
Perturb using ISR proposal model current model flow simulation flow simulation Water Rate Water Rate target Accept with p=L(m*)/ L(mi) target days days
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Updating with Dispat and ISR Summary
Current reservoir = TI, Current reservoir = mi Start Sampler ISR proposes m* Run the flow simulator to obtain L(m*). Accept/rejection according to the Metropolis criterion The training image remains the same
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Results Study properties of resampling with dispat
apply ISR to realizations generated by dispat Updating with regions freeze a part of domain Flow modeling the influence of the amount of perturbation on a flow response
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Properties of resampling with dispat
Training image Single realization Data extracted dispat The only input required with dispat a base case to create perturbation with different amount of data extracted regular grids coarse grid locations avoid discontinuity near data locations
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Conditioning with resampled points
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Effect on ensemble average
# resampled points =121 # resampled points =361 more perturbation blurry less perturbation crispy
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Updating with regions # resampled points =18 # resampled points =128
fix the bottom part and perturb the top part
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Updating with regions # resampled points =18 # resampled points =128
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Effect on Ensemble Average
# resampled points =18 # resampled points =128 no discontinuity at the region boundary more perturbation less perturbation
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Flow modeling Investigate the influence of the amount of perturbation on a flow response Water Rate Water rate Time, days Producer well Injector well
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Flow modeling Investigate the influence of the amount of perturbation on a flow response Large perturbation (small # resampled points) Large perturbation (small # resampled points) Large perturbation (small # resampled points) Water Rate Water Rate Water Rate Water Rate Black = base case Black = base case Black = base case Black = base case Small perturbation (large # resampled points) days
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Reservoir updating: proof of concept
A simple illustrative example: Legacy model new data Water rate Forecast with current model History data Producer well days Injector well
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Reservoir updating proof of concept
Updated with Metropolis a single legacy reservoir model updated model Water Rate target data days
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Conclusions What is the appeal of the idea ? Practical No model parameterization No need for ensemble construction Applications envisioned Mature fields 4D seismic
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