OBSERVATION 4: Random Observations Regarding the USGS 2013 Assessment of the Bakken: The Pronghorn Member

From the report:

The Pronghorn Member of the Bakken Formation, although geologically and stratigraphically defined as part of the Bakken Formation (LeFever and others, 2011), is assessed with the Three Forks Formation.

Where present, the Pronghorn Member is in fluid communication with the underlying Three Forks reservoirs.

Two comments:

• this is an administration decision, to include the Pronghorn Member with the underlying Three Forks reservoirs (note the plurality of reservoirs when discussing the Three Forks Formation)
• noting that the Pronghorn Member is geologically and stratigraphically defined as part of the Bakken Formation (and has been so defined at least since 2011) provides scientific basis for the NDIC's decision to redefine stratigraphic limits as requested by the oil industry

And that's it. Nothing controversial. Simply an observation and a couple of comments.

But, I cannot resist: It would be interesting to read the 2011 Julie LeFever paper that explains why the Pronghorn Member, lying below a tight shale formation, and communicating with the Three Forks Formation, is geologically and stratigraphically defined as part of the Bakken Formation; and, then, of course, why oil from the Pronghorn Member will be considered Three Forks oil.

I assume the answer to the second part of that question/statement is based on precedence and commingling. It makes sense to assess Pronghorn Member oil with the Three Forks Formation oil,  going back to hydrocarbon "fingerprints."

But the 2011 Julie LeFever paper should make interesting reading:

LeFever, J.A., LeFever, R.D., and Nordeng, S.H., 2011, Revised nomenclature for the Bakken Formation (Mississippian-Devonian), North Dakota, in Robinson, J.W., LeFever, J.A., and Gaswirth, S. B., eds., The Bakken-Three Forks Petroleum System in the Williston Basin: Denver, Colo., Rocky Mountain Association of Geologists, p. 11 - 26.

The North Dakota Geological Survey, Geologic Investigation No. 165 (GI-165) provides a very nice graphic of the three members of the Bakken, as well as five (5) members of the Three Forks. This is a must-read document: it points out that "current industry terminology refers to the member 5, 4, 2, and 1 as benches (i.e., member 5 is referred to as the "First Bench").

.... It is interesting to compare the oil saturations against the water saturations. Oil saturations are consistent through the Bakken, but tend to taper off below member 5 ("First Bench"). Correlations become especially important in the Continental Resources, Inc. -- #1-3H Debrecen well where the highest oil saturations are in the Pronghorn Member of the upper Three Forks. In contrast to the cross-sections wells, the EOG Resources, Inc. -- #2-11H Liberty has oil saturations throughout the Three Forks section.

... An abundance of fractures appear to coincide with higher water saturations in the Three Forks. The opposite is reflected by fractures in the Bakken. ... The absence of significant amounts of clay suggests that the marker bed that denotes the top of member 4 ("Second Bench") may not confine a fracture stimulation treatment as previously thought. ... A preliminary examination of the Three Forks  Formation raises some interesting questions as to how extensive is the resources, what are the controlling factors, and what constitutes the reservoir. Additional examination of new cores may answer some of the questions.