Evaluation of the applicability of in-situ combustion in a heavy oil carbonate field with high initial oil saturation

Abstract

The present work describes a set of four in-situ combustion (ISC) tests for assessing the applicability of the technology for the heavy oil (19° API) carbonate field and determining the optimal initial oil saturation. The potential candidate for the ISC is a carbonate reservoir with a depth ranging from 1133 m to 1196 m, a porosity of 9–13%, and an average permeability of 280 mD. The performed screening study examined the quality and the quantity of available fuel, air requirements, and the ability of the combustion front to propagate through the porous media. Based on screening results, the ISC technology was chosen for a detailed laboratory study. A high-pressure ramped temperature oxidation (HPRTO) test and three medium-pressure combustion tube (MPCT) tests were performed to estimate the effect of initial oil saturation and to assess the suitability of the target field for the ISC method. This study was conducted at reservoir conditions to take into account the phase behavior at elevated pressures and temperatures. The effect of different oil saturation on combustion performance was investigated. Combustion parameters such as fuel and air requirements, recovery efficiency, front velocity, and composition of produced gases were obtained and analyzed. Based on the experimental results, it was proposed to reduce the oil saturation with hot water treatment and further switch to ISC. The study determined the initial oil saturation level of 0.38–0.70 within which the ISC can be implemented on target heavy-oil carbonate field. This research demonstrated potential technology application problems and defined a set of favorable conditions for ISC applicability. Additional features (such as oil plugging and calcite decomposition), which may occur in the process of on-field implementation, were observed at applied reservoir conditions. The equipment operation parameters for the target field were calculated and specified based on the obtained ISC parameters.