Communication Between Formations?

Continental Resources (CLR) has opined that the Bakken formation is a separate formation from the Three Forks Sanish which sits directly below the Bakken.


To test this theory, CLR drilled two wells offset at the surface by 316 feet, the Mathistad 1-35H and the Mathistad 2-35H in 2009 in coordination (and authorized) by the NDIC.

Mathistad #1 targeted the Three Fork Sanish and its permit is #16983.

Mathistad #2 targeted the Middle Bakken and its permit is #18013.

In fact, there was communication between the two fracks (between the two formations), but CLR says the communication can be eliminated by separating the wells a nominal distance. Click here for the report.  There was one abbreviation (acronym) that was not explained in the report: BHP stands for bottom hole pressure, which is a data point to determine flow rate.


These were the results: "The results showed that the #2 fraced into the #1 wellbore in all frac stages but, even with the well-to-well communication, the #2 is estimated to recover an additional 400 [thousand barrels of oil] over the base case of only drilling and producing the #1. Pressures measured in the #1 showed communication from at least 13 of the 14 stages and fluid tracers recovered in the #1 production showed the frac fluid from all 14 of the #2 stages."

However, within the body of the report: "Optimum spacing was evaluated by using the model....[T]he model shows recovery is maximized and still economic by drilling wells 1320 feet apart in the zone and 660 feet apart in different zones. This would allow drilling 7 wells per 1280-acre spacing unit if 660-foot setbacks from the lease line are used. Unusually large hydraulic fractures or natural fractures could cause some localized pressure depletion in new infill wells."


The final paragraph: "Initial pressure....data...shows different ranges of communication. One well showed no communication between zones with an initial reservoir pressure of 7250 psi (pounds per square inch). Another showed the Bakken had been communicating to the TFS but only along a portion of the lateral. In this case the second well showed pressure increasing even while the first well was still producing. This pressure behavior indicates areas of higher pressure were crossflowing along the lateral repressuring the portion of the lateral in the Middle Bakken that had been partially depleted."


Comment: it was my impression that the public release suggested this test confirmed these two formations were separate. It appears there is more to the story, based on this report. 

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For The Archives

PDF press release from CLR, August 6, 2009.