A New Understanding of an Old EOR Concept for In Situ Combustion Processes

Abstract

Abstract The practice of in situ combustion has traditionally been based on the concept that extinction of the process occurs when the air flux falls below the level where bond scission reactions can no longer sustain the advance of the combustion front at the temperatures required for effective mobilization of the oil. Very important economic parameters such as sweep efficiency and design parameters such as air injection rate and spacing between the injection and the production wells are directly dependent on the level of the air flux at exhaustion. The most common method for estimating the minimum air flux is based on the work of Nelson and McNeil who proposed that for a radial burn the minimum combustion front velocity is 0.038 m per day (0.125 feet per day). Based on this minimum velocity and assuming air requirements falling in the 100 to 350 sm3/m3 range, the minimum air flux would be expected to fall in the range from 0.1 to 0.6 sm3/m2·h. This range of minimum air flux has a significant level of uncertainty in terms of both combustion front velocity and air requirement parameter. In an attempt to address this uncertainty, a conical combustion cell was constructed with the goal of directly determining the minimum flux for specific oils under conditions which are representative of a field scale operation. To date, tests involving core from a typical Athabasca Oil Sands reservoir have operated at air fluxes (based on the air injection rate and area at the downstream front location) of under 1 sm3/m2·h. This paper describes the nature of the combustion zone under this low air flux condition and it provides important information on the nature of reactions and the physics of the process which must be considered when attempting to predict combustion front exhaustion using a numerical simulator.