A Theoretical Analysis of Heat Flow in Reverse Combustion

Abstract

Published in Petroleum Transactions, AIME, Vol. 219, 1960, pages 124–131. Paper presented at Joint AIChE-SPE Symposium, Dec. 7–8, 1959 in San Francisco. Abstract Reverse combustion is one thermal method of recovering hydrocarbons from porous underground formations containing oil or tar. In applying this method, air is introduced via an injection well and the mixture of air and hydrocarbons is ignited in the production well. A combustion zone then recedes toward the injection well, counter-current to the air flow. If the combustion-zone temperature is sufficiently high, the oil or tar in place is distilled and cracked. The hydrocarbon flows as a vapor to the production well and subsequently is condensed at the surface. Maximum temperature and velocity of movement are the two dependent variables defining the progress of the combustion zone. A theoretical analysis has been made of heat flow in the reverse-combustion process assuming linear flow in a homogeneous system. The differential equations, which include the oxygen-hydrocarbon reaction rate, have been solved numerically. Results indicate that the maximum temperature reached and the combustion-zone velocity both increase with an increase in air-injection rate. Heat loss to surroundings has little effect on the maximum combustion-zone temperature achieved, but it is reflected in a reduced combustion-zone velocity. It is also predicted that an increase in the oxygen-hydrocarbon reaction rate results in a reduction in the maximum temperature reached. The calculated results are in agreement with results from reverse-combustion experiments using samples of a tar sand. Introduction Reverse combustion is one thermal method of recovering hydrocarbons from porous underground formations containing oil or tar. In applying this method, air is introduced into the underground formation via an injection well. In one or more adjacent production wells. the mixture of air and hydrocarbons is ignited at the sand face. The combustion zone thus formed recedes toward the injection well, counter-current to the air flow (Fig. 1).