crude oil assay – the oil drum

Posted: May 30th, 2008 by: h-2

A very informative piece in the oil drum about how crude oil is refined, in terms of light sweet versus heavy crude, how much of each product (gas, gasoline, diesel, bunker fuel, etc) they get from each type, using different refining technologies.

This should help you understand a bit better how refineries are limited in the ratios of say gasoline and diesel / heating oil (‘distillates’ below) from every barrel. Keep in mind also, there is an energy cost to converting the heavier crudes which this article didn’t get into much, but the article’s comments did mention that question. Interesting stuff, well written, and informative, helps clarify the processes involved in creating our various fuels.

When a refinery purchases crude oil, the key piece of information they need to know about that crude, besides price, is what the crude oil assay looks like. There has been a lot of discussion here at various times about “light sweet”, or “heavy sour”, and how these qualifiers affect the ability of a refiner to turn these crudes into products. So, I thought it would be good to devote an essay to this subject, and discuss how different types of crude can affect a refiner’s bottom line.

Let’s compare light sweet oil to heavy sour oil by looking at a pair of assays:

Liquid Volume % Generic Light Sweet Generic Heavy Sour
Gas (Boiling Point to 99°F) 4.40 3.40
Straight Run (99 to 210°F) 6.50 4.10
Naphtha (210 to 380°F) 18.60 9.10
Kerosene (380 to 510°F) 13.80 9.20
Distillate (510 to 725°F) 32.40 19.30
Gas Oil (725 to 1050°F) 19.60 26.50
1050+ Residuals 4.70 28.40
Sulfur % 0.30 4.90
API 34.80 22.00

Table 1. Comparison Between Assays of Light and Heavy Crudes

Refining 201: The Assay Essay

I say, if we’re going to be addicted to, then run out of, this petroleum stuff, then let’s at least understand what the stuff is, and what it’s used for, and how it’s processed into all those fun compounds we’ve grown so overly fond of….

Another nice recent oildrum article, though ultimately unfullfilling, was Richard Heinberg’s Coal in the United States, an overview of US coal reserves. And, no matter what the long term survival of most species on this planet would prefer, we are going to end up using up as much coal as we can, no matter how badly it destroys our ecosystem. Why? Because we refuse to drop growth based economic systems feeding absurd desires and unrealistic expectations.

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