Experimental validation of self-sealing in wellbore cement fractures exposed to high-pressure, CO2-saturated solutions

Abstract

We present constant-flow experiments of high-pressure CO2-saturated fluid through fracture channels in Portland cement with three different fracture geometries and with three different flow rates. The experiments were conducted in etched cement wafers within a microfluidics device. The evolution of pH was observed optically using phenolphthalein dye and changes in channel volume due to dissolution and/or precipitation were characterized with profilometry and scanning electron microscopy. Abundant precipitation for all three geometries was observed in the low flow-rate experiments, while only dissolution was observed in the high-flow rate experiments. The results bracket self-sealing versus self-opening behavior. The observed functional relationship among flow rate, fracture geometry and aperture in relation to self-sealing is consistent with a diverse set of experiments in the literature conducted under widely varying conditions and with behavior predicted in recent numerical models (Brunet et al., 2016; Cao et al., 2015; Guthrie et al., 2018; Iyer et al., 2017). The results confirm that self-sealing is a quantifiable behavior in ordinary Portland cement systems that is favored at low flow rates and in small-aperture or small hydraulic diameter fracture systems with clear limits imposed by dissolution-dominated conditions of high flow rates.