Time-dependent Inversion of Surface Subsidence due to Dynamic Reservoir Compaction |
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| Authors: | A G Muntendam-Bos I C Kroon P A Fokker |
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| Institution: | (1) TNO Built Environment and Geosciences, Princetonlaan 6, P.O. Box 80015, Utrecht, 3508 TA, The Netherlands |
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| Abstract: | We introduce a novel, time-dependent inversion scheme for resolving temporal reservoir pressure drop from surface subsidence
observations (from leveling or GPS data, InSAR, tiltmeter monitoring) in a single procedure. The theory is able to accommodate
both the absence of surface subsidence estimates at sites at one or more epochs as well as the introduction of new sites at
any arbitrary epoch. Thus, all observation sites with measurements from at least two epochs are utilized. The method uses
both the prior model covariance matrix and the data covariance matrix, which incorporates the spatial and temporal correlations
between model parameters and data, respectively. The incorporation of the model covariance implicitly guarantees smoothness
of the model estimate, while maintaining specific geological features like sharp boundaries. Taking these relations into account
through the model covariance matrix enhances the influence of the data on the inverted model estimate. This leads to a better
defined and interpretable model estimate. The time-dependent aspect of the method yields a better constrained model estimate
and makes it possible to identify non-linear acceleration or delay in reservoir compaction.
The method is validated by a synthetic case study based on an existing gas reservoir with a highly variable transmissibility
at the free water level. The prior model covariance matrix is based on a Monte Carlo simulation of the geological uncertainty
in the transmissibility. |
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| Keywords: | Subsidence Compaction History matching Covariance Inversion |
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