Proposed Air Injection Recovery of Cold-Produced Heavy Oil Reservoirs

Abstract

Abstract This concept paper explores the potential applications of air injection (in situ combustion) as a follow-up to cold production of heavy oils. Cold-produced fields are ideal potential candidates for air injection due to the significant resource that remains at the economic limit of cold production, and because wormhole- type channels are present in the depleted reservoir. The authors propose steaming the depleted reservoir for a short period of time to collapse the wormholes, thus creating high permeability heated channels. Reservoir ignition and air injection would follow, with the heated channels providing a flow path for the mobilized oil to reach the production wells. The steam/combustion combination would be highly effective in thin reservoirs, where extended steam injection is uneconomic. Additionally, this process addresses the three technical causes for failure in heavy combustion projects: ineffective ignition, inadequate air injection rates, and temporary plugging of the formation due to blockages caused by high liquid saturations. An overview of cold heavy oil production and heavy oil by in situ combustion is provided, as well as a detailed discussion of the proposed process. Introduction Cold Production in Western Canadian Heavy Oil Regional Sands Western Canada contains extensive heavy oil and bitumen deposits, as is shown in Figure 1. Early primary production of this resource using reciprocating pumps in vertical, directional, or slant wells was only economic in the Lloydminster Block; thus, most of the existing geologic studies are for this area(1–3). Following the development of progressing cavity (PC) pumping technology in the 1980s, cold production from these wells (vertical, directional or slant) was expanded rapidly to several additional areas, including Frog Lake, Elk Point, Lindbergh, and portions of Cold Lake and the Primrose Block. This exploitation methodology provides a large percentage of the produced oil volume for most Western Canadian heavy oil producers; in fact, some producers use only this method. Most cold production of heavy oil has been conducted in regional sands from the Lower Cretaceous Mannville Group (see Figure 2). Stratigraphic nomenclature varies locally, but, in general, most Lloydminster area regional sand cold production is from the Sparky and Waseca sands, while most of the Frog Lake, Elk Point, and Lindbergh cold production is from the Cummings.Regardless of the nomenclature, from a reservoir engineering perspective, these sands are characterized as being relatively thin, clean, with high porosity and permeability, and containing high saturations of heavy oil(4). Figure 3 is a plot of the estimated distribution of oil in place vs. sand thickness for the Lloydminster area, and Table 1 describes regional sand properties. Bottom water and edge water are common features, and a significant fraction of the wells in this region become uneconomic due to rapid water influx. Despite continued efforts to improve PC pump-based cold production technology, current methods generally leave 80 to 95% of the OOIP behind at the economic limit. This is a large oil-in-place target for follow up EOR processes; however, the cold production process appears to have strongly altered reservoir conditions from their original state.