  One of the key risks for a Carbon Capture Storage (CCS) is injectivity
decline. Evaporation of the connate brine in near-wellbore region during CO2
injection may result in drying-up the rock yielding the mobilisation and
migration of clay particles leading to decline rock permeability and consequent
loss of well injectivity. Influx of the reservoir brine into the dried-up zone
yields accumulation of precipitated salt and injectivity decline. This paper
presents the results of eight coreflooding experiments aiming investigation of
the effect of rock dry-out, fines migration, and salt precipitation during CO2
injection. Pressure drops across the cores, brine saturation and produced clay
fines concentration versus Pore Volume Injected (PVI) have been measured. All
lab tests exhibit the following features: intensive fines production at the
very beginning of gas-water production period following reduced-rate fines
production during overall evaporation period and continuous fines disappearance
at the late stage; abrupt increase in gas permeability in the middle of
evaporation, and non-monotonic evaporation rate and pressure drop. To explain
these phenomena, we distinguished three sequential regimes of fines detachment
during two-phase displacement: (i) moving gas-water menisci; (ii) pendular
rings of residual water; (iii) dry flux, and found that for the conditions of
our corefloods, detachment is possible in regime (i) only. Fines production
during overall evaporation period is explained by simultaneous occurrence of
three regimes during unstable displacement of water by gas in
micro-heterogeneous rock.
