Bitumen Upgrading- Its Importance to the In-Situ Producer

Abstract

Abstract This paper explores the substantial effect on the producing operation of the selection and design of upgrading and utilities plant8 in an in-situ oil sands scheme. Oil sands bitumen contains large amounts of impurities which have to be removed in converting (upgrading) to synthetic crude. This upgrading increases the hydrogen-carbon ratio and removes the Sulphur and nitrogen present in the crude bitumen. There are a number of processes which are suitable for bitumen upgrading. Two of the most promising processes are described, including schematic process flow diagrams and yield slates. The energy requirements of such an i1lrtegrated producing-upgrading-utility complex are immense, but can be significantly reduced by complete process integration of the facilities. Among the major energy consumers in the upgrading-utility complex are the hydrogen plant and electric power generating equipment. The nonlinear relationship of synthetic crude price to conversion (upgrading bitumen feed to synthetic crude) to overall (produced bitumen to synthetic crude) recovery is demonstrated. Economic factors are examined qualitatively in the last part of the paper. Introduction IN-SITU RECOVERY of bitumen from the oil sands is a highly energy- intensive process, both- for in-situ steam stimulation or flooding and for in-situ combustion. The bitumen to synthetic crude upgrading processes produce a variety of by-products which can serve as fuel. These heavier or residual fractions, such as coke or pitch, serve to reduce the fuel deficiencywhich is expected to be common to in-situ recovery operations. This gives rise to a fundamental economic optimization problem. The higher the upgrading product yield, the less residual material there is available for internal fuel needs. This deficiency in fuel must be made up either from an outside source or by producing additional bitumen. In other words, the selection land design of an upgrading process, and the associated utilities, has a direct bearing on the size of the producing operation. It is therefore essential that the recovery efficiency of the upgrading process be selected to provide maximum economic synthetic crude per barrel of bitumen produced. Bitumen recovered from the oil sands is a viscous material with substantial amounts of impurities which make it an undesirable feedstock for conventional oil refineries. Table 1 shows a set of properties of Athabasca bitumen'. The salient properties are the high Viscosity, high impurities content (sulphur, nitrogen, oxygen), high metals content and small fraction of the bitumen vaporized in the operating temperature range of commercial distillation towers. The Conradson carbon number (CCR), which is an indication of the coking tendency of the oil, is quite high. Bitumen cannot be economically upgraded in present-day commercially available catalytic reactors due to high concentration of metals and high CCR. The usual approach is therefore to thermally convert the residual fractions of the bitumeninto lower-boiling hydrocarbons which are low in CCR and metals content (primary upgrading). This conversion produces saleable liquids, which are further processed (secondary upgrading) to 'final synthetic crude and byproducts (gas, coke, pitch) which can serve as fuel.