Interactions between hydrocarbon-bearing fluids and calcite in fused silica capillary capsules and geological implications for deeply-buried hydrocarbon reservoirs

During the burial processes of deep/ultra-deep hydrocarbon reservoirs, the interactions between hydrocarbon-bearing fluids and reservoirs significantly affect the quality evolution of hydrocarbons and reservoirs; thus, this topic requires further investigation. In this study, the continuous evolution and the coupling mechanisms in various anhydrous and hydrous n C 16 H 34 -(water)-(calcite) systems in fused silica capillary capsules (FSCCs) were investigated using laser Raman spectroscopy, fluorescence color analysis, and fluorescence spectroscopy, and the mineral alterations were analyzed using scanning electron microscopy (SEM). The experimental results show that extensive organic-inorganic interactions occur in the systems if water is present, and different inorganic components have different effects on hydrocarbon degradation. Distilled water promotes free-radical thermal cracking and steps oxidation, forming more low-molecular-weight hydrocarbons, CO 2 , and organic acids (e.g., acetic acids) but suppresses the free-radical cross-linking, generating less high-molecular-weight hydrocarbons. However, in the presence of CaCl 2 water, the yields of hydrocarbon gases are lower than in the distilled water system because high concentrations of Ca ions inhibit the generation of free radicals. Calcites, which exhibit different surface reactivities in different fluid conditions, affect hydrocarbon degradation in different ways. In the anhydrous n C 16 H 34 -calcite system, calcites promote the generation of both hydrocarbon gases and high-molecular-weight hydrocarbons. In contrast, in the hydrous n C 16 H 34 -distilled (CaCl 2 ) water-calcite system, calcites promote the generation of hydrocarbon gases and suppress the generation of high-molecular-weight hydrocarbons. Calcite also reacts with organic acids via surface reactions to form secondary pores. Therefore, except for the formation temperature and pressure, organic-inorganic interactions are controlled by multiple factors, such as the water saturation, water type, water salinity, and the mineral content, resulting in different evolutions of the hydrocarbon degradation and reservoir properties.