Bitumen Recovery From Oil Sands, Using Solvents In Conjunction With Steam

Abstract

Abstract Results of an experimental investigation of bitumen recovery from Athabasca oil sand, using solvents in conjunction with steam, are discussed. Most of the runs were carried out in a vertical tar sand pack, with restricted fluid entry near the bottom of the pack, simulating conduction- convection heating with gravity flow. A few runs were conducted in a large three-dimensional model of a five-spot configuration. The synthetic crude manufactured by Great Canadian Oil Sands Ltd. was the principal solvent used. A few runs employed naphtha and the "Mobil Solvent". Actual Athabasca oil sand was used to pack the models, which did not permit scaling. It was found that bitumen recovery is determined by thetype of the solvent, the volume used and the solvent placement. For example, when the solvent was injected into the producing well, followed by steam injection into the injection well, the recovery was much higher than when both solvent and steam were injected into the same well. The water-bitumen ratio was higher in this latter case than the previous injection scheme. The bitumen recovery tended to be higher when using naphtha, however breakthrough occurred rapidly in this case. Also, naphtha caused asphaltene precipitation in several instances. The GCOS synthetic crude did not have these problems, and yielded higher bitumen-solvent ratios. The Mobil solvent matched the perfomance of the other two solvents, different respects. Temperatures were measured at many points in both models, at various times. In many cases, cores were extracted and analyzed at the end of a run. These data permitted plotting of the temperature and bitumen saturation contours, which provide valuable insight into the prevalent recovery mechanisms. Introduction Several in-situ methods have been successfully field tested for the recovery of bitumen or very viscous oil from oil sands, These include cyclic steam injection in the Cold Lake region, reverse and forwardcombustion in the Athabasca region, and conductive heating combined with steamflooding in the Peace River region. Many more in-situ recovery methods have been proposed, including those which rely on solvents to varying degrees. This paper describes the results of such an investigation, being the fourth in a series of experimental studies devoted to the recovery of bitumen from tar sands by the use of a combination of solvents and steam. Background, General Considerations and Objectives Solvents and light ends of crudes are frequently used in heavy oil recovery as diluents to facilitate pumping and pipeline transportation. For example, much of the current production of 80,000 BID from the Orinoco oil sands, Venezuela, is through downhole dilution with a light crude. The use of solvents has been proposed in combination with steam(1, 2), explosives(4), etc. Any in-situ recovery process involving solvents is likely to be expensive, and it is therefore necessary to use the smallest possible volume of the cheapest and most readily available solvent. Earlier work by the authors in this direction involved the application of pure compounds, later substituted by an aromatic naphtha.