The Effect of Fractures' Geometrical Properties on the Recovery Mechanism of the Top-down In Situ Combustion Process

Abstract

The top-down in situ combustion (ISC) involves the stable propagation of the combustion front from the top vertical injector to the bottom horizontal producer. Apart from laboratory studies in conventional sandstones, no application of the process in fractured carbonates has been addressed yet. The authors modified a successful combustion tube history matched model of an Iranian low-permeable heavy oil reservoir called Kuh-E-Mond to investigate the feasibility of ISC in fractured carbonate reservoirs mimicking block-scale combustion cells. Effects of fractured geometrical properties such as orientation, location, extension, density, spacing, and dispersion were considered. Results confirmed a higher outcome in the case of optimum vertical or horizontal fracture density and spacing. Vertical fractures located at the lateral sides of the cell enhanced the process in terms of ultimate oil recovery and oxygen sweep efficiency. The longer vertical fractures and higher dispersion through the reservoir improved the recoveries compared with the lower efficiency in the case of extended horizontal fractures and raised their dispersion through the reservoir. Simulation analysis confirmed that top-down ISC has higher feasibility in the case of highly networked fractures through reservoirs such as those in the Persian Gulf coast.