A Canadian Perspective On In Situ Combustion

Abstract

Abstract Field in situ combustion projects are traditionally designed using air and fuel requirements as determined from a laboratory combustion tube test. While these parameters are important, of greater significance in predicting field performance is the observed stability of the combustion process in laboratory tests which are conducted at the operating pressures of the field project. This paper provides a review of the laboratory combustion performance of different reservoirs as a background for interpreting the field performance of some of the approximately 30 in situ combustion projects which had been or were still in operation in Canada as of 1993. Canadian field tests have been performed in reservoirs having oil gravities varying between 8 and 28 ° API; five of these projects involved the injection of pure oxygen. Although some of the information contained in this paper as of the current publication is now out of date, due to companies changing hands and projects closing, the paper still provides a valuable review of the history of combustion in Canada up to and including the year 1993. Introduction Many of the operating problems which have contributed to the lack of success of in situ combustion as an enhanced recovery technique in Canadian field projects can be attributed to a poor understanding of the kinetics of the process. Laboratory combustion tube tests, which have been used for many years as a means for evaluating the air and fuel requirement parameters necessary for the design of field projects, tend to operate in the high temperature combustion mode. This has led to the classical definition of combustion, that being "the propagation of a high temperature front for which the fuel is a coke-like substance laid down by thermal cracking reactions." Although the high temperature combustion mode represents the desired state for dry or normal-wet combustion, it may be very difficult to achieve this condition under the air fluxes and operating pressures of many field projects. On this basis, deviations between field and laboratory measured combustion parameters such as the air/fuel ratio or the fraction of oxygen converted to carbon oxides (which are dependent on the carbon oxides content of the produced gas) should not be assumed to indicate that the combustion tube test is faulty. Rather, the differences should be interpreted as indicating that the field project is not operating in the same combustion mode as the laboratory test. Once this is understood, it is possible to make educated guesses as to the actual state of the oxidation reactions as they are operating in a field project. This paper will describe some of the abnormal, in the sense that it deviates from classical concepts of combustion, behaviour observed during the 20 years of laboratory experiments carried out by the In Situ Combustion Research Group at the University of Calgary. The group has performed 267 combustion tube tests on over 30 different reservoirs worldwide as of 1993; these tests have involved oils having gravities between 6 ° and 40 ° API at pressures up to 20 MPa. Approximately 65 of these tests have involved 95% oxygen enriched air.