Effects of Cyclic Salt Precipitation on CO2 Injectivity: From Pore-Scale to Near-Wellbore

Abstract

Abstract The rate and severity of potential loss of CO2 injectivity in saline aquifers due to brine dry-out and salt accumulation near-wellbore is one of the main uncertainties in CCS project planning. Default parameters implemented in commercial reservoir simulators overestimate the degree of salt precipitation and resulting permeability impairment. The current study used lab and digital core analyses of Berea sandstone to estimate the petrophysical and dynamic properties for adjustment of predicted precipitation and flow reduction in reservoir simulation models of intermittent CO2 injection with aquifer drive. A set of 23 core plugs were subjected to repeated brine infiltration and drying for varying cycles and drying methods, and characterized by dried-state measurements of helium porosity, Klinkenberg permeability and mercury intrusion capillary pressure, plus non-destructive 3D X-ray imaging. In early cycles, permeability showed a gradual linear decrease with porosity loss, followed by a much steeper decline over later cycles, due to preferential accumulation of salt near the end faces. The plug-scale 3D porosity map was used to history match the flow experiments, to remove these end-effects from the salt-blocking porosity-permeability trend and generalized Kozeny-Carman exponent. High-resolution 3D imaging of a Berea subsample through an analogous sequence of small-scale brine infiltration-drying experiments was used to visualize the precipitated salt in pores, for pore-scale simulation of the porosity-permeability trend in the absence of larger-scale heterogeneities in salt distribution. Further, the co-flow of brine and CO2 during drainage and imbibition was also simulated in this salt-blocked image sequence, to generate curves of relative permeability and capillary pressure versus saturation of brine and dried salt. The resulting flow properties at pore- to plug-scale were integrated into a conceptual reservoir model to evaluate injectivity impairment caused by salt clogging.