Summary
Although typically large uncertainties are associated with reservoir
structure, the reservoir geometry is usually fixed to a single interpretation
in history-matching workflows, and focus is on the estimation of geological
properties such as facies location, porosity, and permeability fields.
Structural uncertainties can have significant effects on the bulk reservoir
volume, well planning, and predictions of future production.
In this paper, we consider an integrated reservoir-characterization workflow
for structural-uncertainty assessment and continuous updating of the structural
reservoir model by assimilation of production data. We address some of the
challenges linked to structural-surface updating with the ensemble Kalman
filter (EnKF).
An ensemble of reservoir models, expressing explicitly the uncertainty
resulting from seismic interpretation and time-to-depth conversion, is created.
The top and bottom reservoir-horizon uncertainties are considered as a
parameter for assisted history matching and are updated by sequential
assimilation of production data using the EnKF. To avoid modifications in the
grid architecture and thus to ensure a fixed dimension of the state vector, an
elastic-grid approach is proposed. The geometry of a base-case simulation grid
is deformed to match the realizations of the top and bottom reservoir
horizons.
The method is applied to a synthetic example, and promising results are
obtained. The result is an ensemble of history-matched structural models with
reduced and quantified uncertainty. The updated ensemble of structures provides
a more reliable characterization of the reservoir architecture and a better
estimate of the field oil in place.
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
8 September 2009
- Meeting paper published:
20 October 2009
- Revised manuscript received:
19 December 2009
- Manuscript approved:
19 March 2010
- Published online:
5 August 2010
- Version of record:
2 December 2010
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