Friday, June 29, 2007

Alaskan Heavy Oil may be Tapped?

BP and ConocoPhillips are trying to solve one of the most technologically difficult problems they have so far encountered, namely how to recover the heavy oil from the Ugnu formation. The Ugnu is a huge deposit of low-grade oil trapped in sandstone rocks that overlay the conventional oil-producing fields of the Alaskan North Slope. An incentive for their efforts is provided by estimates that there are billions of barrels worth of oil held within the Ugnu. The companies have already decided on a strategy for recovering the somewhat higher grade oil from the West Sak and Schrader Bluff deposits, which lie below the Ugnu, and themselves contain several billion barrels of heavy oil.

Only a fraction of the amount of oil can be economically extracted, but it is thought that if even some hundreds of millions of barrels can be pumped-out it still represents a good business venture. BP and ConocoPhillips are banking on viscous and heavy oil to come on-stream in order to help offset the anticipated fall in production from the large conventional oil-fields. Economics are central to the whole enterprise, and the extraction of these heavy oils depends to some extent on the production taxes levied by the State of Alaska.

The Ugnu oil is in relatively shallow deposits and fairly cold, meaning that it flows less easily than is the case from deeper deposits of North Slope conventional oil. West Sak is rather more deeply seated than Ugnu and hence warmer, but extracting its oil has nonetheless already proved very difficult. The latter oil is said to have a consistency that ranges between that of maple syrup and honey, while Ugnu oil is like peanut butter! In practical terms, West Sak oil does at least flow, but Ungu oil does not. "We burned out a big pump trying to get it to flow," said Blaine Campbell, who is ConocoPhillips' supervisor for heavy oil development.

It seems likely that the technique of "steam assisted gravity drainage" will be employed to try and get the Ugnu oil out. This involves drilling two wells, one to inject steam and the second to recover the oil from. The injector well is drilled into the reservoir above the producing well, and the steam warms the reservoir rock, thus loosening-up the thick oil to make it flow more easily. Then the force of gravity causes the oil to slip in the direction of the producing well, beneath the area that has been warmed. A variation of this is the intriguingly named "cyclic steam stimulation" method, in which steam is injected into the bottom of the well to soak and warm locally the reservoir, and to then recover the oil from the same well as it floats-up. One of the biggest challenges for these techniques at Ugnu is the necessity to inject steam down through permafrost to the oil-containing formation, since this can melt the permafrost and cause problems of subsidence near the injection wells. Heat will also be transferred from the steam en route - cooling it - thus rendering it less effective for loosening the oil when it gets there.

A more indirect approach might be to form the steam underground, hence obviating these troubles incurred in pumping it through the permafrost. Possibly, water in the underground reservoir itself might be exploited, since a layer of water has been found to lie underneath the oil and gas in many of the North Slope fields. The energy needed to convert liquid water into steam may also prove an issue and tip the economic balance of the process, if its requirements are substantial.

My feeling is that, beyond than the desire to get hold of whatever oil may be recoverable from Ugnu, once perfected some of the technologies that finally prove themselves effective there, may be employed across the world to extract heavy oil from its many declining wells, and to exploit deposits in polar regions. We will inexorably depend on heavy oil as the light crude oil becomes exhausted. Indeed world light crude production peaked in 2005, and its supply will decline accordingly. A corollary to this is that an increasing number of vehicles will run on diesel engines which can use heavier fuel-oil, and more efficiently too, than the spark-ignition engines that rely on petrol (gasoline).

Related Reading.
"Producers roll up sleeves to tackle heavy oil," by Tim Bradner. From The Alaska Journal of Commerce Online.

No comments: