Simulation of Near-Well Pressure Build-up in Models of CO2 Injection

Reservoir simulation plays an important role in predicting the outcome of a CO2 storage project, although it is challenging to simulate all the processes that arise. In particular, we need to predict the build-up of pressure in the near well region to be able to estimate the optimum injection rate whilst ensuring that the formation and overlying caprock are not fractured. In this work, we compare simulations of horizontal homogeneous models, with both 1D radial and 2D Cartesian grids, with analytical calculations of pressure build-up. Our results show that several inaccuracies arise when using too coarse a grid, due to the inability to resolve the shock fronts adequately. In a coarse cell, the amount of dissolution is over-estimated and the gas saturation builds up slowly. The presence of a large cell with intermediate gas saturation gives rise to a peak in the pressure build-up curve (due to low mobility). The pressure eventually reduces to the “correct” value when the dry-out region forms. However, if injection ceases before this time, the final pressure will be over-estimated. As the grid size is reduced, these effects become less severe.