Role of Injection-production Strategy In the Solvent-steamflooding of the Athabasca Oil Sands

Abstract

A comprehensive study was carried out of the in-situ recovery of bitumen from a three-dimensional model, packed with Athabasca Oil Sand, with injection in the centre, near the base and production from the our corner wells, over the entire interval. Five injection-production schemes were tested in a recovery process involving the use of a solvent (Suncor's synthetic crude) with steam. Solvent slug sizes varied from 5to 30% pore volume, with varying amounts of steam injected. Recoveries varied from 5 to 50% of the bitumen in place depending on the slug size, rate of solvent injection and steam volume. It was found that both large and small solvent slugs are less effective than an "optimal" slug size. Of the injection strategies tested, solvent injection into the production wells was found to be most effective, with steam injection into the injection well. Splitting of the solvent slug among the injection and production wells was the next best choice. Base runs involving steam injection alone facilitated interpretation of results, and showed that on the whole solvent-steam injection is a far more promising technique. Among the variables studied rate of solvent injection appears to be a significant factor in determining bitumen recovery. Implications of the results obtained are considered from the standpoint of field application. Introduction In-situ recovery from the Athabasca Oil Sands poses special problems, in view of the virtually immobile nature of the inplace bitumen. Implementation of a suitable recovery method, usually thermal, requires creation of flow paths for the initial injection of a hot fluid. The present research on the subject, now in its tenth year, proposes the use of a solvent for this purpose which is followed by steam injection. Among other non-thermal schemes for creating initial communication between wells, the most notable are those proposed by Redford(l) and formation fracturing using emulsions or air, as employed by Shell Canada (1961) and Amoco Canada, respectively, in the Athabasca Oil Sands region. Thermal methods include cyclic steam stimulation with air or gas, electrical heating of the formation and combustion under fracture pressures. This paper outlines the principal results of the experimental research conducted during the last four years on the use of solvents and steam for in-situ recovery from the Athabasca Oil Sands, encompassing three separate studies (2,3,4) by the co-authors. The data reported here should be of value in judging the applicability of the processes considered, even though the largely unscaled experiments would preclude direct application of the data to field situations. For complete details of individual experiments, the aforementioned works may be referred to. Background and Objectives Previous work on the use of solvents and steam has been reviewed in Reference (5). It led us to believe that Suncor's synthetic crude holds considerable potential for the Athabasca Oil Sands, as an additive to steam injection, in a carefully planned operating strategy. Apart from the desirable properties of this "solvent" vis-a-vis the Athabasca bitumen, it is readily available and cheaper than any other solvent or comparable refinery stream.