The answer comes to me in an excellent Chemical Engineering Progress (CEP) article, Working with Tight Oil, by Emerson’s Tim Olsen. The article looks at the impact of tight oil, also known as light tight oil, from shale on refineries.
These refineries have been updated and modernized over the years to process heavier, more sour grades of crude oil. Tim notes that refineries are:
…designed to process crude oil of a particular composition and produce products with specified properties, with some flexibility based on the capabilities of equipment such as pumps, heat exchangers, and the particular catalysts within the reactors.
Crude oil blending of two or more sources is performed:
…if a single crude oil with the required composition is not available or economical.
The classification of sweet or sour crude oil is determined by its sulfur content with sweet crudes containing less than 0.5% sulfur and sour containing greater than 0.5%. The classification of light or heavy crude is measured by its specific gravity:
…expressed in degrees (°API), and is an inverse measure of the relative density of a petroleum product and the density of water. Light crude oil has an API gravity higher than 31°API, medium crude between 22°API and 31°API, and heavy crude an API gravity below 22°API.
Tim explains that tight oil is typically light and sweet and the refineries along the U.S. Gulf Coast are configured to refine sour, heavy crude oils from Venezuela and Canada. This mismatch explains the paradox opening this post.
While light and sweet sounds like it would be less of a challenge, it in fact is not. Tim lists several challenges including lack of pipeline infrastructure from shale producing regions to the refineries, entrainment of hydrogen sulfide gas, include paraffin wax and other large filterable solids and may be incompatible to blend with heavier, more sour crudes.
From a processing standpoint, the poisonous and flammable hydrogen sulfide gas must treated with amine-based H2S scavengers to reduce safety hazards during transport and processing. The paraffin wax coats rail cars, tank walls, piping and can foul the preheat sections of crude heat exchangers. Also:
Paraffin waxes that stick to piping and vessel walls can trap amines against the walls, which can create localized corrosion.
To address some of these challenges Tim recommends that [hyperlink added]:
…each heat exchange bundle upstream of the crude desalter should be equipped with online temperature monitoring at the inlet and outlet of both the tubeside and shellside to detect any changes in the rate of heat transfer as they occur.
Fouling from filterable solids should be addressed at the filters at the entrance of the refinery equipped with automated monitoring to provide early warning. Wetting agents are also added at the desalter to help prevent solids from going further downstream.
Crude oil blend must be done carefully and at the proper ratios to avoid asphaltene precipitation which can foul the heat exchanger train downstream. Automatic monitoring of the heat exchangers can help identify these incompatibilities to avoid future problems.
You’ll want to read the article for more on addressing energy imbalances, catalyst problems, export regulations, and the impact of changing crude oil prices on refiners.
Tim concludes with the challenges posed by tight oil:
Refiners must learn to process this challenging crude supply and make the required modifications to their processing configuration to best utilize the lighter crude oil.
You can connect and interact with Tim and other refining experts in the Refining group in the Emerson Exchange 365 community.