A review of experimental investigations on salt precipitation during CO2 geological storage

Abstract

Salt precipitation due to formation drying is a critical secondary alteration process that significantly impairs reservoir injectivity in the context of CO₂ geological storage. In this work, salt precipitation during CO₂ injection is reviewed primarily through various experimental studies. First, the experimental systems for salt precipitation studies, namely core-flooding, microfluidic-chip, static batch, and surface drying experimental systems, have been described to present their respective experimental procedures and merits, as well as corresponding applications. Subsequently, following the general description of the formation mechanisms of salt precipitation, the macro and micro salt distribution patterns at the reservoir and pore scales have been summarized. Finally, and most importantly, this study provides a comprehensive analysis of the controlling factors for salt precipitation, categorized into four different groups, according to the brine, rock, gas, and injection scenario aspects. Among all these factors, brine salinity, CO₂ injection rate and initial reservoir properties are considered the most critical in determining the amount and distribution of precipitated salts and the degree of injectivity impairment. The effects of multi-scale reservoir heterogeneity and rock wettability on salt precipitation are attracting growing consideration, while the brine and gas composition studies are receiving less attention due to their relatively minor influences on reservoir alteration. Due to the limited specimen sizes, the ex-situ brine replenishment may be underestimated in core-flooding and microfluidic-chip experiments. This may result in a potentially significant underestimation of the volume of local salts and the potentially inaccurate prediction of the drying process during CO₂ injection in many such experiments.