Mar-2011

Unconventional crude oil selection and compatibility

Crude selection and compatibility considerations are a critical part of a successful refinery operation. Constantly changing quality conventional and unconventional crudes, as well as mixtures of these crudes, provides an opportunity for refiners to increase profitability.

Scott Sayles and D Mark Routt, KBC Advanced Technologies

Article Summary

But that profitability comes with a risk of equipment fouling or the failure to achieve desired objectives. Use of crude compatibility prediction processes and tools can effectively predict the performance of unconventional crudes and crude mixtures in a specific refinery before they are processed.

Introduction
Crude oil production has changed from 20 years ago to now include unconventional feedstock produced from upgraders, diluted bitumen, fire flood, steam and gravity-assisted drainage (SAGD) or other partially treated material. Changing crude quality has dramatically changed the landscape for evaluating, buying and processing crudes. Crude selection now requires closer and ongoing qualification of quality and a refinery’s ability to process the contemplated mix. Today, potential crudes need to be screened for incompatibility with other crudes, as some mixes can endanger the refinery or badly foul equipment.

This paper discusses different unconventional crudes, and the impact of crude blending on refinery energy consumption and equipment fouling. Case studies will be provided to demonstrate the methodology to determine crude compatibility and operability.

Unconventional crude sources
The two most globally significant regions of unconventional crudes are Canada’s Alberta Province and Venezuela’s Orinoco Belt. Significant quantities of unconventional crudes are produced in each region through upgrading, blending, and modifying heavy crude-like feedstocks with bitumen and cutter stock. In other countries, conventionally produced crudes are now also consistently being modified with production chemicals and flow modifiers that affect how they behave during processing in the refinery.

Upgrader definition
A crude upgrader is the term used to describe a processing plant designed to produce crude for feed to a traditional transport fuel refinery. Upgraders belong to the Exploration & Production (E&P) or upstream sector, while the traditional fuel refinery is in the downstream sector. However, like their downstream cousins, upstream crude upgraders share many of the same technical and design concepts.

Raw, unconventional crude, produced from oil sands upgraders, is highly viscous and typically requires significant dilution with naphtha or condensate to allow pipeline transport. A number of reasons may make the processing of large volumes of unconventional crude unsuitable in conventional downstream refineries. Some of these reasons are:
• higher sulphur levels than can be processed
• Little or no residual product, making vacuum tower operation difficult
• High residual yields exceeding bottoms handling capabilities
• High vacuum gasoil yields that do not match cracking capacity.

On the other hand, some unconventional crudes are highly desirable and closely match the capabilities of conventional refineries. To approach changing feedstock trends, some conventional refineries have been modified over time to allow more unconventional processing. Modifications might include increased use of higher metallurgical grades within the crude unit, increased hydroprocessing capability and increased sulphur handling. The trend, within capital constraints, is to selectively convert refineries and increase crude processing flexibility for an ever-changing market.

Canadian unconventional crude
With over 170 billion barrels of crude in place, Canadian oil sands reserves are only second to Saudi Arabia and represent one of the most important growth areas for non-OPEC energy supply in the near future. Most feedstock for unconventional crude production either comes from surface mining or in-situ production. Roughly 20% of production comes from mining operations, while the bulk of the remainder comes from SAGD. The locations of the primary Canadian oil sands deposits are shown in Figure 1.

Current production of roughly 2.7 MMBPD is forecast by KBC, to rise to a projected level of 4.5 MMBPD level by 2020. The forecast includes planned increases in both conventional crude production and unconventional feedstock. As seen in Figure 2, the forecast for conventional crude production declines while unconventional output rises.

Canadian quality
Not all upgraded, unconventional crude is the same. Different upgraders use unique processing technology, and upgraded crude is often blended with varying amounts of cutters or diluents.

Once extracted from the ground, bitumen can be upgraded into synthetic crude oil (SCO) or diluted with 25–30% condensate to produce diluted bitumen (DilBit). Both of these unconventional crude types can now flow through pipelines and be transported for feed to conventional fuel refineries.

A summary of key qualities for some of the unconventional Canadian crude production methods is shown in Table 1. The following definitions are used:
• Bitumen: Athabasca tar sands oil
• Synthetic crude oil (or SCO): a low-sulphur zerobottoms product
• DilBit: Bitumen diluted with approximately 25-30% condensate
• Synthetic bitumen (SyntheticBit): Typically 50% synthetic crude used as the bitumen diluent
• Coker bitumen (CokerBit): Coker distillates as the bitumen diluent.

Venezuelan unconventional crude
Venezuela is located at the northern coast of South America and is a little more than twice the size of California. It is bordered on the west by Colombia, Guyana to the east, and Brazil to the south. The capital, Caracas, is located on the northern coast.