J.D.M. Belgrave

In situ combustion in Canadian heavy oil reservoirs

This paper reviews the laboratory combustion performance of different heavy oil and oil sand reservoir samples, and discusses the field performance of some of the in situ combustion projects which have been or continue to be operated in Canada. Abnormal behaviour (deviation from classical concepts of combustion) encountered in the field and in the laboratory are interpreted in the light of the combustion kinetics developed by the In Situ Combustion Research Group at the University of Calgary. The results are used to suggest design considerations for successful field projects.

A model for improved analysis of in-situ combustion tube tests

Abstract Laboratory combustion tubes have been extensively used to study in-situ combustion mechanisms. Many of these studies have recognized that radial heat transfers, induced by equipment operation, can significantly distort temperature levels recorded inside the sand pack. The fact that the design and operation of combustion tubes have not been standardized, indicates the difficulty of physically eliminating this heat transfer problem. If thermal reservoir simulators are to be reliably calibrated using data from such experiments, these heat transfers must be understood and accounted for in the history matching. A general-purpose numerical model for simulating laboratory combustion experiments is presented that rigorously accounts for the on-off operation of the adiabatic heaters as well as external thermal-energy storage and convective circulations—a deconvolution of the laboratory phenomena. Included in the paper are applications of the model which show that combustion tubes of different diameters, being subjected to the same operating conditions (air injection flux, heater operating strategy, saturations, etc.) can produce significantly different results. Smaller tubes will tend to produce lower combustion front velocities and peak temperatures, and higher fuel loads. These results demonstrate why caution is required when translating laboratory data to field project design. This paper offers considerable insights into the role of heat losses in the combustion process. It rationalizes the significant differences in experimental data derived from different equipment configurations, but for similar oils. It also shows the direction of change to be expected in the experimental results when different size tubes are used.

New Insights Into Enriched-Air In-Situ Combustion

This paper presents the results of 10 enriched-air in-situ combustion-tube tests performed on core from the Athabasca oil sands deposit. The tests show that at high pressures, the use of oxygen-enriched air results in increased low-temperature reactions between the oxygen and the oil, resulting in an increased fuel load and decreased burn stability. Although water injection may enhance the performance of oxygen combustion, it may also lead to increased oxygen storage in the swept zone.

The thermal behavior of vertically-operated near-adiabatic in-situ combustion tubes

Abstract A commonly used approach for studying in-situ combustion processes has employed vertically-operated adiabatic combustion tubes. The data obtained from such apparatus are sometimes subject to interpretation problems because of convective circulations in the annulus, which are induced by the operation of the guard heaters. The main objective of this study was to systematically investigate the operational domain and impact of these convective heat transfers, and, in general, to provide a comprehensive framework for interpreting such experimental data. A microcomputer-based system was developed to automate the operation of the guard heaters and to provide a record of the power outputs of each heater with time. The automated system was used to gather data from five combustion experiments in which operating pressure, injected oxygen concentrations, water/oxygen ratio, and the type of gas in the annulus were varied. The experimental results showed that thermal energy from the heaters, as they responded to the combustion front, was transported upward by convection in the annulus. This energy elevated temperatures in the core behind the front. The tendency for annular convection to occur was found to increase with operating pressure, the on-time of the heaters, and with the Rayleigh number of the gas used in the annulus. Also, as the severity of convection increased there was (a) a reduction in the thermal efficiency of the heaters, and (b) an overall increase in heat loss from the combustion zone which required higher oxygen fluxes in order to avoid declining peak temperatures and to improve oxygen utilization. An analysis of the thermophysical properties of the annulus gases used explained these experimental observations, and demonstrated that gases of lower thermal conductivity may not necessarily reduce heat loss from the combustion tube.