Comparing the source rock plays

Assuming that the actual amount of shale oil producible on the North Slope lies somewhere around the average of the range of uncertainty in the North Slope shale oil assessment that the U.S. Geological Survey has just published, the scale of the potential total North Slope shale oil resource would seem to compare favorably with shale oil plays in the Lower 48, coming in a little larger than the Eagle Ford oil play in Texas although substantially smaller than the Bakken oil play in North Dakota.

But, when making comparisons of this type, it is helpful to compare individual assessment units or plays, rather than the entire North Slope, USGS geologist Dave Houseknecht told Petroleum News Feb. 27. It is particularly important to consider the geographic area of a play, as well as the volume of oil that the play might produce, Houseknecht said. The larger the area of a play for a given volume of oil, the less likely it becomes that a well will encounter a viable oil resource. And the ease with which wells encounter viable oil will ultimately be critical in determining shale oil development success.

The USGS North Slope assessment has identified three assessment units for shale oil resources: the Shublik, the Kingak and the Brookian, with the Shublik having the highest potential.

The Bakken is thought to hold 3.6 billion barrels of oil, a much larger volume than likely to be in the Shublik assessment unit on the North Slope. But the Bakken encompasses an area of 12.6 million acres, a significantly larger area than the Shublik assessment unit’s 7.3 million acres. And the sweet spot areas likely to actually be developed in the Shublik represent a still smaller area when compared with the Bakken or with the Eagle Ford, Houseknecht said.

—Alan Bailey