Residual Trapping in Geological Storage of CO2 : Determination from Field Experiments and Data Analysis Using Numerical Modeling

Abstract: Geological storage of CO2 in deep saline aquifers is one of the methods to mitigate the release of this greenhouse gas into the atmosphere. The efficiency of this solution can be improved by better understanding of the relevant trapping processes, as well as by improving available injection techniques and developing tools for more accurate site characterization.  This Thesis has implemented numerical simulations to investigate the processes that affect the capillary trapping of the injected CO2 in a saline aquifer with the focus on two field experiments carried out in Heletz, Israel. The two experiments, applying different test sequences and characterization techniques, were carried out with the focus on determining the parameter of the maximum residual gas saturation. The collected data and a detailed description of the injection site and operational procedures are presented in Paper I. In Paper II, numerical modeling is used to interpret the pressure and temperature data recorded during the first residual trapping experiment (RTE I). The second residual trapping experiment (RTE II) and the corresponding numerical modelling for interpretation of hydraulic and partitioning tracer tests is presented in Paper III. Overall, the data analysis and the results from numerical simulations for both experiments were in agreement and suggested that push-pull hydraulic test is a robust technique that can provide useful information to estimate the parameter of residual gas saturation in situ with reasonable costs. Both thermal and tracer tests can provide valuable data to further characterize the formation however the operational difficulties can be limiting factors.   In Paper IV, the effect of different parameters to increase the efficiency of the Water alternating Gas (WAG) technique are investigated. For this study numerical simulation was used to model a heterogeneous formation based on parameters obtained from the Heletz site. For the formation used in this study, it was shown that higher water injection rate has a stronger effect on dissolution trapping than CO2 injection rate. The most important design parameter was, however, the WAG ratio. It was also concluded that the design parameters of WAG technique are site-specific and application of this method requires extensive site characterization.