In the process of looking up something else, I came across this nice graphic showing where the Pronghorn formation is, sitting between the Lower Bakken and the Three Forks.
See comments below. One of the comments:
Some operators (Continental comes to mind) appear to be calling the Sanish/ Pronghorn 'TF1'. If one compares the TVD/ target depth of their TF1 wells to offsetting well logs they are often targeting within 30' of the basal Lower Bakken Shale- which would be in the Pronghorn. The September Investor Presentation illustrates this on page 14.From an OXY USA report in the Manning oil field, general area of Whiting's Pronghorn prospect:
I haven't compared the geologic presence of the Pronghorn to the number of Three Forks target intervals in Continental's experimental high-density areas, but perhaps they are drilling fewer wells per pad where this formation is absent.
**************************************
Bakken Geology
This might be a good time to review the geology of the Bakken (for newbies).
The following is taken from the geologist's report for #27139:
Tyler formation: 7,736 feet TVD; shale inter-bedded with limestone in the upper half of the formaiton; shale inter-bedded with limestone in the lower half; the shale is red to orange in the uper formaiton; dark gray to black in the bottom half of the formation.
Mission Canyon formation (Madison Group): 9,190 feet TVD; primarily limestone interbedded with dolomitic limestone; gray to brown limestone.
Lodgepole formation (Madison Group): 9,824 feet TVD; gray to light gray-grown, mudstone
False Bakken: 10,730 feet TVD; dark brown earthy shale; multiple fracture gas shows reaching upwards of 2,000 units
Upper Bakken Shale member, the top of the Bakken formation: 10,672 feet TVD; shale; 1,655 unit gas show was recorded.
Middle Bakken member: 10,689 feet TVD; a sequence of siltstone, limestone, and silty sandstone;
End of this report; the target was the middle Bakken.
************************************
Tyler: shale, soft to very soft
False Bakken (Mississippian Lodgepole): earthy texture, slightly calcareous
Bakken formation: two black shales with a silty, calcite and dolomite-cemented sandstone middle member; the middle Bakken is a clean limestone that is harder than the rest of the formation; usually ranges from 4 - 12 feet thick with hardest formation being near the base close to the sandstones; the Sandstones units of the middle Bakken formation was 9 - 10 feet thick
Pronghorn / Three Forks formation: the dolomite within the Pronghorn formation was 31 feet thick; medium gray dolomite;
Carbon shows: the highest gas recorded in this well in the middle Bakken porosity was 5,000 units.
Target zone was 13 feet to 23 feet below the lowest Bakken shale, about 10 feet thick.
