There are extensive deposits of heavy oil in Saskatchewan and Alberta which can only be recovered with low efficiency by conventional methods. Primary recovery in the best of these heavy oil reservoirs can yield about 6 percent of the OOIP. Waterflooding can improve the recovery, but only to an extent of f-2 percent because of the adverse mobility ratio. Thermal recovery processes using steam can be effective, but these are uneconomic in many Lloydminster type reservoirs because the deposits are relatively thin and heat losses to the overburden and underburden are excessive.
One potential means for overcoming the problem of heat loss is to make use of vapourized hydrocarbon solvents at their dew point. This paper discusses the results of experiments with Tangleflags heavy oil and propane carried out in a large, scaled, physical model. It focuses on the area of potential problems encountered with the use of saturated hydrocarbon vapours as a solvent. In particular, it addresses the issue of precipitation of asphaltenes which may lead to reduced permeability and lower production rates. Rates, recoveries, gas to oil ratios and other important parameters will be presented and field performance of the process will be predicted from the data obtained in the scaled laboratory model.
Production of heavy oils and bitumens from the extensive deposits in Alberta and Saskatchewan is hampered by the high viscosity of these materials caused by the high content of asphaltenes. After these heavy crudes have been produced, often by thermal methods, dilution with light hydrocarbons is required to facilitate transport through pipelines to upgrading plants and refineries. The cost of steam injection to mobilize the heavy crude is large, mostly because there are inherent heat losses associated with heating surrounding rock formations that do not bear oil. This situation is further exacerbated in thinner reservoirs.
A new idea is to recover heavy oils using saturated hydrocarbon vapours under carefully controlled conditions which lead to separation of asphaltenes from the heavy crude. The asphaltenes are thus left behind deposited on the reservoir matrix while the much lighter oil is recovered. The handling, processing and transport of such in situ upgraded oil is easier and more economical.
In our previous paper[l] we described a new process for recovering heavy oil with the aid of a saturated hydrocarbon vapour. In this paper we present further experimental data to support the feasibility of the process and explore the benefits of in situ upgrading by asphaltene removal and deposition on the rock matrix.
