Statoil has injected CO2 into a saline aquifer for disposal. Monitoring the behaviour of the CO2 in the sand formation and the sealing capacity of the overlying shale cap rock are key elements in understanding the dynamics of the injection process. A repeated 3D seismic dataset was therefore acquired in 1999, after injection of about 2 million metric tons of CO2. The time-lapse data show a large increase in reflectivity and a large push-down of reflections caused by the injected CO2. Gas at different levels within the sand are probably trapped by thin shale layers. Only a small part has reached the top of Utsira Fm., and no signs of CO2 are observed above the top seal.
A generic method for performing history matching of reservoir flow models using 4D seismic data is described. Several key technology components are used in the procedure, including seismic attribute analysis and classification, reservoir simulator technologies, domain transformation algorithms, as well as the optimization algorithms that guide the history-matching process. The novel 4D history-matching procedure was applied to the Tordis Field in the North Sea. As a result the transmissibilities of the fault network in the reservoir model were modified. In addition a production well was successfully side-tracked using results of the analysis from the time-lapse data.
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