Evolution of nC16H34-water-mineral systems in thermal capsules and geological implications for deeply-buried hydrocarbon reservoirs

Organic-inorganic interactions between hydrocarbons and most minerals in deeply buried reservoirs remain unclear. In this study, gold capsules and fused silica capillary capsules (FSCCs) with different combinations of nC(16)H(34), water (distilled water, CaCl2 water) and minerals (quartz, feldspar, calcite, kaolinite, smectite, and illite) were heated at 340 degrees C for 3-10 d, to investigate the evolution and reaction pathways of the organic-inorganic interactions in different hot systems. After heating, minerals exhibited little alteration in the anhydrous systems. Mineral alterations, however, occurred obviously in the hydrous systems. Different inorganic components affected nC(16)H(34) degradation differently. Overall, water promoted the free-radical thermal-cracking reaction and step oxidation reaction but suppressed the free-radical cross-linking reaction. The impact of CaCl2 water on the nC(16)H(34) degradation was weaker than the distilled water as high Ca2+ concentration suppressed the formation of free radicals. The presence of different waters also affects the impact of different minerals on nC(16)H(34) degradation, via its impact on mineral alterations. In the anhydrous nC(16)H(34)-mineral systems, calcite and clays catalyzed generation of low-molecular-weight (LMW) alkanes, particularly the clays. Quartz, feldspar, and calcite catalyzed generation of high-molecular-weight (HMW) alkanes and PAHs, whereas clays catalyzed the generation of LMW alkanes and mono-bicyclic aromatic hydrocarbons (M-BAHs). In the hydrous nC(16)H(34)-distilled water-mineral systems, all minerals but quartz promoted nC(16)H(34) degradation to generate more LMW alkanes, less HMW alkanes and PAHs. In the nC(16)H(34)-CaCl2 water-mineral systems, the promotion impact of minerals was weaker than that in the systems with distilled water. This study demonstrated the generation of different hydrocarbons with different fluorescence colors in the different nC(16)H(34)-water-mineral systems after heating for the same time, implying that fluorescence colors need to be interpreted carefully in investigation of hydrocarbon charging histories and oil origins in deeply buried reservoirs. Besides, the organic-inorganic interactions in different nC(16)H(34)-watermineral systems proceeded in different pathways at different rates, which likely led to preservation of liquid hydrocarbons at different depth (temperature). Thus, quantitative investigations of the reaction kinetics in different hydrocarbon-water-rock systems are required to improve the prediction of hydrocarbon evolution in deeply buried hydrocarbon reservoirs. (C) 2021 China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V.

Automated summary

This study investigates the evolution and reaction pathways of organic-inorganic interactions in different hot systems. The results show that water and different minerals have different effects on the degradation of hydrocarbons, and the presence of different waters also affects the impact of minerals on hydrocarbon degradation. The pathways and rates of hydrocarbon evolution in different hot systems are crucial for the study and prediction of deeply buried hydrocarbon reservoirs.