Fines Migration Associated with Rock Dry-Out During CO2 Injection

Abstract

One of the key risks for a Carbon Capture Storage (CCS) project is injectivity decline. Evaporation of the connate brine in near-wellbore region during Carbon dioxide (CO2) injection may result in migration of clay particles leading to decline rock permeability and consequent loss of well injectivity. This paper presents results of three coreflooding experiments aiming investigation of the effect of rock dry-out during CO2 injection. Three sandstone core plugs with various permeabilities have been used. Pressure drops across the cores, brine saturation and produced clay fines concentration versus Pore Volume Injected (PVI) have been measured. The results show that higher core permeability is associated with a shorter core drying process. Core drying time has a magnitude of 105 PVI. A fast detachment of clay particles has been observed during brine displacement by gaseous CO2 which is explained by dominant detaching capillary force. Further brine evaporation yields additional particle detachment due to disappearance of brine pendular rings holding clay particles on the rock surface. A 1.6 to 4.75-fold of gas permeability reduction has been observed during evaporation of connate brine. Damaged permeability for gas can be explained by both salt precipitation and clay fines migration, while damaged permeability for brine is due to clay fines migration and consequent pore blockage.