A hybrid stochastic-deterministic model calibration method with application to subsurface CO2 storage in geological formations

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Engineers increasingly attract notice to the natural subsurface for very different and possibly competing kinds of applications. On the one hand, the subsurface contains natural resources. On the other hand, it is used for temporary or permanent storage of waste and gas. For all of these competing use types, it is indispensable for our society to assess their performance, limitations, risks and mutual restrictions. The quality of model predictions depends strongly on the quality of the model parameters. Within this proposal, we have a major focus on gas storage in the subsurface, and in particular we focus on CO2 storage in deep saline formations since we have a strong background and experience in this field. However, we emphasize that the methods applied and developed for this field of engineering application can be transferred to other related fields in a straightforward way. From previous studies it is known that the main prediction errors and uncertainties in simulating processes in the subsurface associated with gas storage, or more general with injection of a fluid, arises from uncertainties in the subsurface structure and material parameters. A most recent example is the modelling and simulation for the Ketzin pilot storage site in the state of Brandenburg/Germany. A comprehensive exploration and monitoring program has been conducted in order to provide best possible data according to the state of the art. Most important in the context of this proposal is the history matching of the observation data, i.e.(,) mainly observed time series of pressure and the arrival time of injected CO2 in two observation wells. Models are required to have predictive power for the future behavior of the reservoirs with increased confidence so that they can be used to provide robust decision support for managing the injection and storage. This proposal aims to develop computationally efficient and reliable method for history matching with application to subsurface CO2 storage. The methods of quantifying uncertainties and parameter sensitivities in history matching can be divided into two classes: (1) statistics/stochastic-based approaches (e.g., in which multiple samples are drawn from conditional distributions) and (2) deterministic optimization-based approaches (e.g., in which a single optimal model is calibrated and some estimates of post-calibration covariance are provided). The current project will discuss both the approaches. The goal of this project is a comparison and hybridization of stochastic and optimization-based methods for uncertainty quantification in model calibration and history matching, thus combining the best aspects of both worlds.