Abstract

In-situ combustion is a highly complex process and there is a continuing effort to understand the relationships among its characteristic physical and chemical reaction mechanisms. The analysis of combustion tube data produced from experiments performed under realistic reservoir conditions is currently the most valid method of investigating this process.

In this study, the optimization of water-air ratio for B. Kozluca heavy crude oil, and the comparison of the performance of dry and wet forward combustion processes were studied. An analytical model was used to extend the laboratory results so that the oil production and steam zone volume can be estimated under field conditions. A total of nine combustion tube experiments were carried out under adiabatic conditions in the laboratoryusing stell tube which has 10 cm diameter and 90 cm length. Temperature distribution, air and water injection pressures and rates, produced gas analysis and rate, oil and water production rates were recorded to analyse and calculate the combustion parameters.

Instead of solving complex multiphase fluid flow and energy equations, an analytical model is developed based on energy balance using measured data from combustion tube experiments and basic reservoir and fluid properties. The analytical model can be used to determine the oil production from burned zone and steam zone. Calculated oil production values were successfully matched with the experimental values.

Finally, the field performance was investigated by using a computer program based on the estimation of volume-burned. The program was run by changing areal sweep efficiency, pattern size and air injection rate to achieve the optimum conditions. It has been shown that the oil recovery can be increased from 1.4 % to 33.4 % of OOIP through this optimization.

Introduction

In-situ combustion is a commercial process for recovering heavy oils. In this process, air or more generally an oxygen containing gas is injected into a formation containing viscous oil. A burning front supported by air injection is created and subsequently propagated through a reservoir. The burning front travels in the same direction as the injected air (forward combustion) or counter to the direction of air (reverse combustion). The high cost of air compression for dry forward combustion is one of the major factors that influences the economics. Therefore, oil industry introduced a new concept that is water injection with air into the reservoir. Because water carries much more heat from the behind of the combustion front rather than air and air requirement is low in this process. Another important advantage of the wet combustion is the less fuel consumption with respect to the dry type combustion.

Laboratory combustion tube tests should be used to obtain useful information about in-situ combustion. We can observe the change in oil recovery, fuel consumption rate, produced gas composition, air requirement, rate of burning front advance under different water-air injected ratios. This is important to find the optimum water-air ratio for field applications. Experimental results are also important to predict the production history of a field.

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