The Use of Solvents And Gases With Steam In Tbe Recovery of Bitumen From Oil Sands

Abstract

Abstract The use of the CO2, ethane and/or naphtha together with steam was investigated as a means of improving recovery and other operating parameters in the interwell vertical steamstimulation process for recovery of bitumen from oil sands. A total of sixty-three experiments were conducted using a two-well, 45-cm-diameter, three-dimensional elemental physical simulator operating at an overburden pressure of 3.5 MPa. The results of twenty of these experiments are presented. By examining the results, the major mechanisms by which recovery occurs were determined and the impact that these mechanisms would have on field operations are discussed. Introduction The Athabasca deposit of the Alberta Oil Sands is one of the major petroleum deposits of the world. Its high viscosity (5,000,000 cps at reservoir conditions) and high bitumen saturation and hence low injectivity, however, provide some unique recovery problems. Because of its high viscosity, the bitumen has no mobility and cannot be moved forward by an advancing fronts because of its high bitumen saturation, there is limited access to the deposit to enable the entry of agents such as heat, solvents, gases, surfactants and bacteria which could alter the viscosity of the bitumen. The Alberta Research Council has developed a process whereby access to the deposit is initially achieved by using hydraulic fracturing or horizontal boreholes near the base of the deposit. These initial communications are then expanded to provide a hot communications path between injectors and producers. A cyclic process is then initiated involving pressure build-up and depletion cycles, whereby the heated front is forced to progressively move up the formation thereby achieving bitumen recovery. The process has been termed interwell vertical steam stimulation. In earlier work reported by Redford and McKay(1), it was shown that the process, when operating at 2.1 MPa, was substantially improved by the addition of hydrocarbons to the steam. This work has now been extended to the study of CO2 and ethane, the combination of CO2 and hydrocarbons, and a study of the recovery mechanisms taking place. Experimental Equipment The experiments were conducted in a three-dimensional elemental model referred to as the 45-cm simulator which has been briefly described elsewhere(2,3). The term "elemental model"(4) indicates that the experimental approach is to take an element of the formation and to conduct experiments on that element at conditions comparable to field operating conditions. This type of model is useful for screening a wide variety of recovery processes, but accurate scaling of the experimental results to predictions of field performance requires a complicated mathematical manipulation of the data. (By contrast, the results from a scaled model may be more easily transferred to field performance predictions, but the problem is to design the model in the first place.) The simulator (Fig. I) is a cylinder, 45 cm in internal diameter and 40 cm in height, capped at each end with blind flanges. The vessel is equipped at the top with a piston which is used to apply an overburden pressure of up to 7 MPa on the oil-sands pack.