Analysis of shale property changes after geochemical interaction under CO2 sequestration conditions

Abstract

Abstract This study implements a supercritical CO2 (scCO2) sequestration environment in a laboratory and investigates the geochemical effects of scCO2 on the properties of rock specimens. Shale specimens constituting caprock were kept in a laboratory reactor chamber with scCO2 for 63 days. Chemical interaction between rock surface and the scCO2 was then induced, and the changes in the properties were inspected before and after the reaction through various tests. The non-destructive tests comprised measurement of elastic wave velocity, shore hardness followed by investigation using the inductively coupled plasma mass spectrometer, and scanning probe microscope. The destructive tests include uniaxial compressive strength, Brazilian tensile strength, and X-ray fluorescence tests. Results show that mechanical properties are significantly weakened when shale specimens are exposed to both scCO2 and brine. The specimens reacting with only scCO2 induced a self-healing effect by precipitation of secondary sediments, becoming a more intact rock with increased strength and elastic modulus. The results denote that the geochemical alteration of shale occurs in a short time and are highly dependent on the reaction conditions. These results provide fundamental information for the stability of CO2 storage sites regarding the physical and chemical reactions between rocks under geological sequestration conditions.