In situ combustion, and its modified forms, continue to be important oil recovery processes. The applicability of in situ combustion to a wide range of reservoirs, and the recent advances, show that this process has unique advantages (and disadvantages).

Laboratory studies of in situ combustion are hampered by the lack of suitable scaling criteria for the design of experiments. Apart from that, the experiments are usually labour-intensive and costly This paper provides useful guidelines for the design of such experiments, and also discusses the laboratory methods currently used.

The general problem of in situ combustion in a three-dimensional system is formulated, with attention to reaction kinetics and non-equilibriwn phenomena. Appropriate boundary conditions, both for field and laboratory, are stated. Next, the partial differential equations are used to derive a set of scaling criteria. A number of alternative schemes are considered in this regard. Suggestions are offered concerning the use of the various options available for experimental design.

The scaling criteria derived are. used to examine the validity of results derived from "fire tube tests, which are widely used to obtain basic information on the combustion bevaviour of crude oils. It is shown that among the parameters measured in such experiments, only a few, such as fuel content, have validity. Results of laboratory fire tube tests of wet combustion can be misleading.


The in situ combustion process has been a source of interest, effort, and, at times, frustration for at least 30 years. The concept of burning heavy fractions of the reservoir oil in order to generate heat in situ is attractive and consequently has led to over 100 field tests of such processes [40 listed in Chu and Crawford1]. However, due to very unusual complications only a few of these have reached commercial status. Even though operational problems have been pointed out as the major cause of such economic failures, a more subtle reason is the selection of reservoirs for in situ combustion applications. Selection criteria used in the past appear to be inadequate in the face of growing recognition of the complexity of the mechanisms involved. Although there has been extensive laboratory study of most aspects of in situ combustion, there remain several areas which are poorly understood. The objective of this paper is to elucidate the mechanisms involved in in situ combustion processes and to present various scaling options in order to model such a process.

Mechanisms of In Situ Combustion

Recently Islam, Chakma and Farouq Ali 2 revealed the mechanisms involved in in situ combustion and proposed a new mathematical model in order to model some extraordinary features which have been largely ignored by previous researchers.

In situ combustion is based on burning the coke deposit laid down by the crude oil. The mechanism of in situ combustion varies depending on whether forward or reverse combustion is taking place. In all cases, however, oxygen containing gas (most commonly air) is injected into the reservoir to achieve combustion.

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