Abstract
The top down In-Situ Combustion (ISC), involves the stable propagation of combustion front from top vertical injector to the bottom horizontal producer. Besides laboratory studies in conventional sandstones, no application of the process in fractured carbonates has been addressed yet. In this paper a successful combustion tube experiment and history match of Iranian low permeable fractured heavy oil reservoir called Kuh-E-Mond, is presented and accompanied with details of experimental and simulation model. Validated model has been modified further to investigate the feasibility of Top-down ISC in fractured reservoirs mimicking block scale combustion cells. Effects of fractures geometrical properties such as orientation, location, extension, density, spacing, disconnection and dispersion have been considered. Investigation of aforementioned geometrical properties performed for the case of presence of networked fractures (presence of both vertical and horizontal fractures). Results confirmed higher outcome in the case of optimum vertical or horizontal fractures density and spacing. Laterally located vertical fractures enhanced the process in terms of ultimate oil recovery and sweep efficiency. Longer vertical fractures and higher degree of fractures dispersion through the reservoir improved the recoveries compared to the case of extended horizontal fractures and higher degree of horizontal fractures dispersion through reservoir. Depending on the reservoir parameters (such as fracture and matrix permeability) there is an optimum length of vertical fracture in which it enhances the recovery. This means very long extension of vertical fractures could cause early oxygen breakthrough and as a result lower sweep efficiency and oil recoveries. Simulation analysis revealed that Top-down In-Situ Combustion has higher feasibility for the reservoirs with highly networked fractures such as those occurring in the Persian Gulf coast.
