Unique qualities of Canadian bitumen and synthetic crudes
As production of Canadian bitumen and synthetic crude oil expands, North American refinery feed slates enter new territory in terms of crude oil quality
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The incentives for processing Canadian bitumen and synthetic crudes are clear in terms of a more secure supply and a significant price discount compared to conventional crude oils of similar API gravity and sulphur content. On the other hand, the challenges of moving to an increasing percentage of Canadian crude oil differ from those the refiner would face with most conventional crude oils. Much of the new production consists
of heavy bitumen diluted with synthetic diluent, heavy bitumen diluted with condensate, or heavy bitumen upgraded to synthetic crude. The unique characteristics of these blends usually mean that conventional refineries can only process them as blends with other conventional crude oils, making it harder to evaluate their effect on refinery operations.
This article highlights some of the challenges involved in evaluating Canadian grades of crude. Optimal crude selection and processing decisions require the refiner to understand the varying qualities of Canadian blends. The use of accurate data and models of the qualities of the various synthetic crudes, together with blending models, enables refiners to better understand and exploit the impact these crudes have on refinery operations.
Classes of Canadian crude oil
A myriad of Canadian crude oil grades exist in the Western Canadian Sedimentary Basin (WCSB) and some are quite different from typical conventional crude oils. Some of the commonly accepted classes of crudes produced in the WCSB are:
• Synthetic crude
• Light sweet crude
• Light sour crude
• Medium sweet crude
• Medium sour crude
• Heavy sour crude.
In most cases, the class name is self-explanatory and indicative of the quality of crude.
The primary focus here is on synthetic crude and heavy sour crude. The crudes in these two classes are produced by blending non-conventional materials and tend to be the most challenging to evaluate.
Synthetic crude is produced as a blended stream within a bitumen upgrader plant. There are currently five major bitumen upgrader plants in northwest Canada, each with a unique configuration of upgrading technology and blending capabilities (see Table 1). Others, such as MEG Energy’s site, are currently in the planning and construction phase, although the recent downturn in oil prices may delay the construction of additional facilities.
Heavy sour crude
Crudes that are typically classified as heavy sour crudes are volume-trically the largest classification of crudes produced in the WCSB. Since these crudes are produced primarily from bitumen, most of them are blended to some extent. The heavy sour crude class may be subdivided further into three categories:
• Conventional heavy sour crudes produced in the WCSB include the Lloydminster crudes: LLK, LLB and Bow River, among others. These tend to behave similarly to conven-tional heavy sour crudes produced in other regions of the world
• DilBits are blends of heavy bitumen with a lighter diluent. Typically, the common Canadian condensate, CRW, is used to dilute the bitumen in order to reduce sufficiently the viscosity of the material so it can be transported throughout the pipeline system. Examples of DilBits include Cold Lake, Wabasca Heavy and Peace Heavy
• SynBits are also blends of heavy bitumen with a diluent. However, in this case, the diluent is a synthetic crude produced at a bitumen upgrading facility. The SynBit category includes blends such as Christina Lake, Mackay River Heavy and Surmont Heavy Blend. Western Canadian Select may also fall into this category, using both condensate and synthetic crude oil as a diluent.
Challenges in processing Canadian crudes
The nature of production of these classes of crudes presents the refiner with significant challenges when evaluating them for processing. Some of the properties of the synthetic or blended streams are very atypical when compared to a conventional crude oil, with a similar density and sulphur level.
Both synthetic crudes and some of the heavy sour crudes exhibit unusual yield profiles compared to conventional crudes (see Table 2). The blends constituting these crudes vary over time, further complicating evaluation.
The heavy sour streams are diluted primarily for the purpose of reducing viscosity sufficiently to transport it through common carrier pipeline systems. In cold weather, the blend requires more diluent than in warm weather. There are some very apparent seasonal variations in other properties because of the different quantities of diluents used to produce the stream. The seasonal variation in the API gravity of Cold Lake crude oil is illustrated in Figure 1.
Crude oil properties
Blended WCSB heavy sour crudes and synthetic crudes exhibit property profiles that are sometimes quite different from conventional crude oils. The challenges of processing these crudes relate to both product specification and processing issues.
The qualities of synthetic crude streams also vary over time. These streams are made up of refined products that are back blended to meet a target density and sulphur content. There are sometimes variations in the way the blended products are combined to produce the final material. The ability to predict accurately the final blend properties based on some key bulk property measurements gives the refiner an advantage in under-standing the quality of synthetic crude streams.
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