Robust ensemble-based multi-objective optimization
conference paper
We consider robust ensemble-based multi-objective optimization using a hierarchical switching algorithm
for combined long-term and short term water flooding optimization. We apply a modified formulation of
the ensemble gradient which results in improved performance compared to earlier formulations. We also
apply multi-dimensional scaling to visualize projections of the high-dimensional search space, to aid in
understanding the complex nature of the objective function surface and the performance of the
optimization algorithm. This provides insights into the quality of the gradient, and confirms the presence
of ridges in the objective function surface which can be exploited for multi-objective optimization. We
used a 18553-gridblock reservoir model of a channelized reservoir with 4 producers and 8 injectors. The
controls were the flow rates in the injectors, and the long-term and short-term objective functions were
undiscounted net present value (NPV) and highly discounted (25%) NPV respectively. We achieved an
increase of 15.2% in the secondary objective for a decrease of 0.5% in the primary objective, averaged
over 100 geological realizations. The total number of reservoir simulations was around 20000, which
indicates the potential to use the ensemble optimization method for robust multi-objective optimization of
medium-sized reservoir models
for combined long-term and short term water flooding optimization. We apply a modified formulation of
the ensemble gradient which results in improved performance compared to earlier formulations. We also
apply multi-dimensional scaling to visualize projections of the high-dimensional search space, to aid in
understanding the complex nature of the objective function surface and the performance of the
optimization algorithm. This provides insights into the quality of the gradient, and confirms the presence
of ridges in the objective function surface which can be exploited for multi-objective optimization. We
used a 18553-gridblock reservoir model of a channelized reservoir with 4 producers and 8 injectors. The
controls were the flow rates in the injectors, and the long-term and short-term objective functions were
undiscounted net present value (NPV) and highly discounted (25%) NPV respectively. We achieved an
increase of 15.2% in the secondary objective for a decrease of 0.5% in the primary objective, averaged
over 100 geological realizations. The total number of reservoir simulations was around 20000, which
indicates the potential to use the ensemble optimization method for robust multi-objective optimization of
medium-sized reservoir models
TNO Identifier
514666
Source title
ECMOR XIV - 14th European Conference on the Mathematics of Oil Recovery, Catania, Sicily, 8-11 September 2014
Pages
1-14
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