Abstract

In-situ combustion (ISC), being one of the most successful thermal enhanced oil recovery methods, is highly sensitive to reservoir heterogeneities. In the present study, we investigate the impact of perpendicular (E1) and lateral (E2) fractures to the air injection direction in ISC performance through one dimensional combustion tube experiments on a Canadian bitumen (8.6 °API, 53,000 cP), which possesses good burning characteristics. Two ISC experiments are conducted at identical initial (42% oil and 34% water saturations) and experimental (3.4L/min air rate, 100psig back pressure) conditions. The fracture formation is visualized with an X-ray computed tomography. During the experiments, temperature profiles, gas compositions, and oil and water production data are recorded continuously. The in-situ oil upgrading is investigated through viscosity measurements and weight percent of Saturates, Aromatics, Resins, and Asphaltenes (SARA) fractions. Fourier Transform Infrared Spectroscopy (FTIR) is used to characterize the SARA fractions. The metal content of produced water samples is determined with Inductive Coupled Plasma Mass Spectroscopy (ICP-MS). Both fracture types interrupt stable propagation of the combustion front; however, vertical fractures to air injection direction (E1) less likely affect the fate of ISC. The oxygen utilization rate is detected lower for the experiment with fractures parallel to the air injection direction (E2). Thus, E2 demonstrates poorer ISC performance by resulting in lower front velocity and oil production rate than E1. Moreover, the lower oxygen utilization rate increases the interaction between displaced oil and oxygen at lower temperature regions. This interaction results in Low Temperature Oxidation reactions (LTO) and increases the amount of aromatic fractions of the produced oil. This phenomena lowers the produced oil viscosity (83 cP) by increasing the solvent power of aromatic fractions. The produced oil density is found higher for E2 than E1. This difference is attributed to the structural differences in resins and asphaltenes molecules that are determined through FTIR analysis. Moreover, it has been observed that the oil-water interaction in terms of metal content of produced water is found insignificant in both experiments since in both experiments high temperature oxidation (HTO) reactions are observed.

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