Challenges of heavy crude processing
A review of upgrading options and refinery configurations to process heavy crudes profitably. Refiners have long faced a major dilemma when designing refineries to produce high-quality products.
KBC Advanced Technologies
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Lower investment refinery configurations that require expensive, high-quality crudes can be chosen, or higher investment configurations can be chosen that are capable of upgrading less expensive, low-quality crudes. This choice derives from the relative costs and availability of low- versus high-â€¨quality feedstock, and from the current and anticipated future market demands for products.
As unconventional oil recovery rises, companies turn their attention towards processing heavy crude oils. However, due to their properties, the unconventional oils are an interesting challenge for recovery, transportation and refinery processing.
This article reviews very heavy crude oil supplies, upgrading options and the key role of some refinery units in upgrading the heavy oil.
Heavy crude oil: sources and recovery
A basic fact: unconventional oil production is much more expensive than conventional oil production. After extraction, the next challenge that the unconventional crude oils present is transportation to refineries. Raw bitumen must either be diluted or upgraded next to the production site in order to make it possible to transport it to locations where it can be further processed.
Canadian and Venezuelan oil fields are two of the world’s most significant sources of unconventional crudes. Canadian crude production overall has been â€¨growing. Figure 1 shows that the forecast for Canadian conventional crude production is declining, while unconventional synthetic crude and raw bitumen continue to grow. The figure shows non-upgraded bitumen production to grow dramatically, assuming that there is sufficient diluent available. Total crude production forecast is rising to 4.5 million b/d by 2020.
The first Canadian producers of heavy bitumen known as Athabasca oil sands used surface mining with massive equipment to mine the oils sands, separate the bitumen from the sand and return the sand to the excavation site. More recent bitumen production uses the steam assisted gravity drainage (SAGD) method developed by the Alberta Oils Sands Technology and Research Authority in the 1980s. SAGD uses steam to heat the bitumen, allowing it to flow by gravity to a reservoir where is recovered.
There are several other methods of recovering bitumen from oil sands:
• Cyclic steam stimulation (CSS) uses cycles of steam injection, soak and recovery
• Vapour extraction process (VAPEX) is like SAGD but uses solvents instead of steam
• Toe to heel air injection (THAI)
• Combustion overhead gravity drainage (COGD) processes combust a portion of the bitumen to generate the heat needed to recover the bitumen.
Orinoco tar sand is the most common unconventional crude oil produced in Venezuela. Typical qualities for Venezuelan unconventional crude oils are 5°-15° API gravity, 4-6 wt% sulphur and 1-2 wt% nitrogen. There are also conventionally produced heavy crude oils (for instance, Ku-Maloob-Zap) that are very similar in quality to unconventional heavy crudes.
Options for producing and distributing these heavy crude oils vary, including:
• Selling directly to refineries that can handle less than 10° API crude oils
• Blending with a lighter crude or upgrading to create a crude with 20°-25° API, “Maya Crude Equivalent” to be processed at existing high-conversion refineries
• Blending with a lighter crude or upgrading to create a higher-â€¨quality, sweet 30°-40°+ API crude oil that many refineries can â€¨handle
• Produce high-quality finished products in the same crude upgrading facility.
There is a wide range of crude oil upgrading options that can allow a large selection of upgraded crude oil qualities. They range from the simple process of diluting with light sweet crude oil (naphtha or natural gas condensates) to produce Maya Crude Equivalent to complex flow schemes that include delayed coking and residue hydrocracking, as well as other various high-pressure hydrocracking technologies.
The market for selling heavy crude oil directly is extremely limited because few existing refineries are capable of receiving and/or processing such low-quality crude oils. It is likely that, at most, 50 000 b/d can be sold to these refineries at distressed prices for short periods.
Producing Maya Crude Equivalent is currently an attractive level of upgrading. Specifications for producing this type of crude include a gravity target range of around 20°-25° API and a target sulphur content of around 3-4 wt%. There is currently high demand for this quality crude oil because the production of Maya and other similar heavy crude oils has been declining in recent years. Exports of Maya crude oil have decreased by about 1 million b/d over the last seven years. Heavy oil processing capacity has increased significantly over the same period (notably at Reliance, Jamnagar, India; Motiva, Port Arthur, USA; and Marathon Garyville, USA).
Creating a higher-quality, sweet synthetic crude oil with an API gravity between 30° and 40° API opens up the potential market for upgraded crude oil by an order of magnitude, because most refineries are capable of processing crude oils within this gravity range. It may be difficult for the producer to justify the cost of the additional upgrading required. However, this level of upgrading could be phased in, if necessary, to accommodate potential market changes in the future.
Creating high-quality finished products directly from unconventional crude oils is possible, but unlikely to be economically viable unless the refinery’s location is near a large, high-value market for finished products, has economic logistical options available for product movement, or has a unique specification it can meet. For example, ultra-low pour point diesel is a high-value product in Western Canada, near the upgrader site, because of the cold winter season at that location.
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