Analytical expression for the skin factor of the salt deposition zone around a CO[formula omitted] injection well: Extension to the case of ternary miscible displacement

Abstract

Anthropogenic CO2 disposal in saline aquifers is broadly acknowledged a feasible technique to mitigate climate changes. Scale deposition in the near-wellbore region can however reduce the performance of the CO2 injection wells utilized in the subsurface storage. In this study, we aim at evaluating the rate of salt precipitation and deposition and associated permeability reduction near a CO2 injection well completed in a saline aquifer. We employ a mathematical model of the CO2–H2O–NaCl fluid flow in a porous medium and take into account all relevant phase transitions. Then using a rather simple graphical construction with the fractional flow curve, we present a new analytical solution describing a radial flow of CO2 from the well. We demonstrate under certain assumptions that the solution contains two shocks traveling with a characteristic velocity and a rarefaction between them. The leading shock is the familiar Buckley–Leverett displacement front, whereas the trailing shock bounds the region of halite deposition in the near-wellbore region. We consider this region a skin zone and using the analytical solution, eventually derive a new simple relationship for the skin factor. We show that the skin factor caused by the halite deposition is most sensitive to the brine salinity and the relative permeability of the liquid phase. For particular reservoirs, a rather high value of the skin factor can be reached after injecting just several thousand tons of CO2. We show that the injection into reservoirs characterized by a high brine salinity and a large critical water saturation can cause the skin factor to be as high as four at an early stage of injection and as high as seven at a later stage. The proposed relationship can be useful for an instantaneous quantification of the skin and in reservoir simulations of the CO2 storage.