The Operational and Reservoir Parameters Influencing the Performance of Top-Down In Situ Combustion in Fractured Reservoirs: 2D Block-Scale Simulation of Networked Fractures

Abstract

Top-down in situ combustion (ISC) involves the stable propagation of a combustion front from the top vertical injector to the bottom horizontal producer. With the exception of laboratory studies of conventional sandstones, no application of the process in fractured carbonates has been addressed. The aim of the present work is to study ISC in the presence of a system of networked fractures using a thermal reservoir simulator from the Computer Modeling Group (CMG; Calgary, AB, Canada). The performance of ISC is compared with nonfractured system under similar conditions. To obtain more realistic results, a history-matched and validated combustion model of an Iranian naturally fractured low-permeability carbonate heavy oil reservoir, Kuh-E Mond, was used, and the performance of ISC in a fractured porous medium model was compared with a conventional (nonfractured) reservoir. Operational and reservoir parameters that may influence the performance of the process in the case of a fractured reservoir, such as air injection rate, initial oil saturation, initial water saturation, reservoir pressure, matrix permeability, vertical and horizontal fracture density, and the effect of water–oil capillary forces on the recovery of the process have been investigated. Simulation results showed that in the presence of fractures the recovery rate was slower compared to conventional model. Air breakthrough occurred at almost the same time in both models but the amount of oxygen in the exhaust gas for the fractured model was quite high compared to the conventional model, which was near zero. The presence of fractures resulted in lower API gravity of the recovered oil; that is, upgrading of crude oil during the ISC process was lower for the fractured system.