Letters

Sept. 27, 2004
In your Aug. 9, 2004, issue on this subject (HUBBERT REVISITED-5: Is oil shale America's answer to peak-oil challenge?" p. 16), the authors mentioned that the Unocal retort design was a failure.

Is oil shale the answer?

In your Aug. 9, 2004, issue on this subject (HUBBERT REVISITED-5: Is oil shale America's answer to peak-oil challenge?" p. 16), the authors mentioned that the Unocal retort design was a failure. As the retort process foreman during the last 3 years of that project, I would like to correct this impression.

During those 3 years, we produced 2 million bbl of syncrude. While that is not a significant amount in the current supply picture, it is certainly not a trivial amount either.

Unocal shut down the project in 1991 saying that "U they had learned all they had to learn U" A political statement if there ever was one, made most likely for the benefit of the stockholders.

From my standpoint in the front line, day-to-day operations, I felt that our learning curve was still nearly vertical. We were continuously making operating improvements until the day we shut down, and we were able to operate for several months at a time in the black (albeit with the government guarantees).

Essentially, there were five things that were eating our lunch: three at the retort and two at the upgrade facility, none of which was insurmountable.

I will only review the three difficulties we were dealing with at the retort. The first was the size of the retort feed. The retort was designed for 2-in. oil shale. We soon discovered that rock of that size would not fully retort through to its center. The retorting process became much more efficient with a consist of 0.50 to 0.75 in. This increased the wear on the crushers in the mine to the point that they needed frequent repairs. A tertiary crusher would have eliminated this problem.

The second problem was the mine itself. Perhaps we were victims of our own success. The mining horizons got to be so far from the crushers and crushed oil shale gallery that haul times became excessive. On many occasions during the last 6 months of the operations, I had to slow the retort down to allow the mine to catch up.

As you might expect when retorting oil shale, the mineral matrix of the shale breaks down when the kerogen is removed from it, leaving a fine grit in the shale oil. The higher the grade of oil shale, the greater the tendency for it to decrepitate. We had two deashers on the retort bench for removing the grit. They operated just like desalters. However, the deashing operation tended to form a very tight emulsion or rag layer that was lost to the deasher brine.

We had two small tanks on the bench for breaking this emulsion, and for recovering additional oil. However, they weren't always big enough to allow sufficient time for the emulsion to break. You can only squeeze so much onto a five acre bench.

The use of a naphtha recycle stream acted to lower the viscosity of the kerogen. That allowed us to lower the delta P across the deasher mixing valve, which reduced the size of the rag layer. While this proved very beneficial, we could not take it to optimum because of fractionator limitations.

None of these were deal breakers that prevented the retort from operating. They were all financial problems. Perhaps Unocal would have been more inclined to overcome them had the investment climate and the price of crude oil been more supportive. And therein lies the problem. Unocal committed to its Parachute Shale Oil Project when the price of crude oil was $34/bbl, and tried to sustain its operation when crude oil was just $18/bbl.

Had Unocal stayed with it, the Parachute Shale Oil Project would be a financial success at today's crude oil prices. But will current crude oil prices remain at present levels long enough to make a retort designed and built in today's financial environment viable at future crude oil prices? Only someone with thick skin and the deep resolve necessary to stick it out until second and third-generation ex situ retorts are designed and built will find out.

Sunoco had a few rough years after it started its tar sands operation in 1967, but they stuck it out long enough to realize those improvements.
James D. Weith
Practical Enginuity
Mission Viejo, Calif.