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Friday, December 16, 2005

Canadian production model - Weyburn

Take a look at the following chart of production from the Weyburn oil field in Canada (from TOD):

The classic shape of the green region reminded me a lot of the original micro version of the oil shock model. Notice the asymmetric profile reminiscent of a gamma curve.

The Weyburn field makes news today as an experiment in CO2 injection and sequestration (which gives the secondary peak in Purple). I went to the original paper, and transcribed the data to see how well I could understand the shape in terms of the generic model which works so well for depletion profiles in the context of a much larger macro-depletion scope. I concentrated on the initial depletion behavior first.
Discovery delta51 million m3 (320 million barrels) backdated to 1954
Fallow phase1.25 years
Build phase2.5 years
Maturation phase2.5 years
Depletion rate7% of remaining total per year

The article (which shows the original curve in m3 of crude) states that Weyburn has 1.4 billion barrels of original oil in place with about 34% of that available under water flood. That comes out to 476 million barrels available. The difference between the estimate and the model (320 million barrels) comes out to 154 million barrels extra from additional infill drilling.
An estimated 34% of the oil in place will be recoverable under waterflood. In excess of 80% of this oil has already been produced according to government statistics. Incremental production with injection of CO2 is estimated to be in the order of 15% of initial oil in place, in the area of the field to be flooded. This will produce an additional 130 million barrels (21 million m3) of oil over the anticipated 25 year life of the tertiary recovery project.
If I put in the difference from the recent infill drilling, treating it as essentially a new discovery circa 1986, the new model looks like the following:

Interesting how well this model, which uses the same depletion rate as the USA lower-48 oil shock model, qualitatively fits the data from a much smaller exploration region. Even though the Weyburn field pales in comparison to the size of all the USA's (or the world's) fields combined, the essentially scalability of the oil shock model provides more evidence of its general applicability.

As for the remaining 15%, how much the substantial CO2 injection will cost us in dollars and sweat remains a big question.


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