Experimental Evaluation Of In Situ Combustion In Naturally Consolidated Cores

Abstract

Abstract To evaluate the field of application of in situ combustion in consolidated reservoirs, a new experimental set-up has been designed for analyzing the specific features of in situ combustion in core materials. In order to perform experiments under realistic reservoir conditions, new technologies were applied on the building of this physical model and contributed largely to demonstrate the feasibility of the combustion process in core materials. In particular, different solutions were tested to prevent fluids from by-passing the porous medium during combustion tests. It was found that cores covered with thin multi-layer coatings were able to support large temperature gradients and high differential pressures between the inlet and the outlet of the core. A new special setting was designed to seal the pressurized annular space between the coated core and the external enclosure. The core is equipped with narrow heating collars and the set-up is combined with a transverse heat losses control system as well as with computerized data acquisition and processing of the experimental results. The tests were performed with sandstone cores having different permeabilities. The effects of pressure and airflow rates were studied with heavy-oil-saturated cores. Successful results obtained with a 850 mD permeability sandstone show that the fuel availability and the air requirement are affected very slightly by these parameters. Later combustion tests performed with initial gas and/or water saturations and cores having larger permeabilities show, under certain conditions, steadily moving, self-sustaining combustion processes. A discussion concerning the relative effects of porosity and packing properties (specific surface area sand grain distribution, cementation) on the fuel laydown is presented. These results will contribute largely to evaluating the process under actual field conditions. Introduction Several papers have been published, in the last 20 years on in situ combustion tube experiments to evaluate the field of application of this complex process. These lab works concern generally the study of in situ combustion in unconsolidated matrix. Recently, Sibbald et al. presented a paper(3) describing combustion experiments performed in a system using both unconsolidated and consolidated core materials. The aim of this paper is to describe the lab work done at the Institut Francais du petrole (I.F.P.) to study the specific features of in situ combustion in core materials under realistic conditions. For this purpose, new equipment was designed at I.F.P. for this research. New technologies were applied in the building of this physical model, which largely helped demonstrate the feasibility and the reproducibility of the combustion process in core materials. This paper describes the main features of the equipment and the results obtained by a significant number of air combustion tests with four different cores and one oil having a sufficiently high specific gravity (0.96). The effects of pressure, air flow rates, water and gas saturations are also shown. Equipment-Main Features Core Coverings To prevent fluids from by-passing the core during the experiments and to take into account the heat transfer problems generated by the exothermic reactions, several technological solutions were tested.