2D modeling of salt precipitation during the injection of dry CO2 in a depleted gas reservoir

Abstract

The precipitation of halite around a CO 2 injection well has been studied to investigate the possible effects on well injectivity for a pilot test of CO 2 injection in a depleted gas reservoir. The numerical simulations performed with the TMGAS simulator, using both 1D and 2D radial grids, show that the injection of dry supercritical CO 2 vaporizes the formation brine promoting NaCl concentration and the precipitation of halite. Different behaviors are observed depending on the initial liquid saturation: when the brine has a low mobility, the evaporation front advances with limited halite precipitation and only minor effects on well injectivity. On the other hand, when the brine has sufficient mobility, the precipitation front is recharged by the brine flowing towards the wellbore, due to the capillary pressure gradient driven by the evaporation. In this case the concentrated precipitation can strongly reduce the formation permeability. These effects depend on formation properties and on the porosity–permeability relationship which describes the effects of halite precipitation on permeability reduction. In the attempt to improve the prediction of halite precipitation effects, an extension of the so-called tube-in-series model of Verma and Pruess was developed, with pore-size distribution evaluated from the measured grain-size distribution of the sandy formation considered for the execution of the pilot CO 2 sequestration test.