Calculating crude oil reserves
I have been mystified by Shell's problem about reserves.
In this day and age of secondary recovery, it must be very difficult to come up with good reserves figures. A great case in point must lie with the vast Kern River oil field just north of Bakersfield, Calif.
Going back to the 1890s it was decided that this field of 13° API crude oil had some 4.5 billion bbl stock tank oil in place.
Due to the viscous nature of the crude, it was decreed that the ultimate recovery with 21/2-acre spacing might be in the range of 5%. This would mean the recovery of only 225,000 bbl.
Shell pioneered the use of what was called "huff and puff," where steam was injected into the wells to heat the surrounding areas. This had followed the use of bottom hole heaters (steam coils) which had raised the ultimate recovery by some amount. Then came the steam sweep where steam injection wells drove the oil into the producing wells.
The latest figures regarding ultimate recovery are now past 50%. Getty worked over one area and got 85%.
Not all oil fields are like the Kern River one. But using modern technology, it is certain that the ultimate recovery in "conventional" fields will far surpass the usual figure of 35%.
So how does on calculate reserves when facing unknown future ultimate recovery methods?
James McDonald
James McDonald Associates
San Marino, Calif.