Reservoir Engineering Aspects of Oil Recovery from Low Permeability Reservoirs by Air Injection

Abstract

Abstract This paper addresses the reservoir engineering aspects of air injection as an Enhanced Oil Recovery (EOR) technique for low permeability light oil reservoirs. In its most successful form, the process is currently known as High Pressure Air Injection (HPAI), and has been applied in deep, carbonate reservoirs. The development of this process in conjunction with an application of the in-situ combustion (ISC) process to light oil reservoirs, as well as the main mechanisms pertaining to ISC and to gas miscible flooding, are analyzed. It is seen that various air injection processes can be classified, depending on their spontaneous ignition potential and gas miscibility at reservoir conditions, into four different processes. Based on an in-depth literature review, the best reservoir conditions for application of each of these four processes are derived. The main differences in operational aspects (pollution, corrosion, safety) for these processes are also discussed. Air injection can be applied either as a horizontal flood or as a vertical flood. For reef reservoirs, only a vertical mode of displacement is contemplated, while for non-reef reservoirs both these forms may be feasible. The application of air injection to fractured carbonate reservoirs is evaluated, although so far, the reported successful projects have been only in non-fractured carbonate reservoirs. A preliminary analysis shows that for fractured reservoir applications, only the vertical flooding mode is feasible. Design considerations for pilot testing of the technique are discussed, and the differences in piloting for a horizontal flood are pointed out. The crucial point is the location of the pilot on the structure, which is a key element in a proper evaluation of the pilot, and its subsequent development to a commercial size operation. Finally, specific recommendations on laboratory work in support of design and evaluation of a field pilot are presented.