Saturday, October 4, 2014

Random Graphic Of Stratigraphic View Of The "Pronghorn"

[See comments: a reader has simplified this, and has also provided a link to a pdf.  It's really quite a great link: 173 pages with great graphics, and very, very recent (2013); Colorado School of Mines.]

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.

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.
From an OXY USA report in the Manning oil field, general area of Whiting's Pronghorn prospect:
**************************************
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.

************************************

The following is taken from the geologist's report for #24694:
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.

6 comments:

  1. Someone wrote a whole masters thesis on it. I get lost with some of the geology-speak, but I got these impressions:

    1. Varies if present at all.
    2. more of a sandstone, more of a reservoir (like the middle bakken). Doesn't make its own oil, but a sponge for what comes from the lower bakken shale.
    3. "sanish sand" is a subset of the pronghorn member
    4. 4 different types of pronghorn (little differences of the rock, how deposited).

    ReplyDelete
    Replies
    1. Yes, I would agree completely.

      "Sanish sand" is up near Watford City area, and "pronghorn" is more to the south. And they are practically the same, I imagine -- two different names for almost the same thing; just located in different geographical areas.

      Thank you for taking time to write; much appreciated.

      Delete
  2. Meant to link the MS thesis:

    http://digitool.library.colostate.edu///exlibris/dtl/d3_1/apache_media/L2V4bGlicmlzL2R0bC9kM18xL2FwYWNoZV9tZWRpYS8yMDczMzE=.pdf

    You can just skim it and get a sense for things without understanding all the minutia.

    ReplyDelete
    Replies
    1. Got it, thank you. I appreciate that. It's amazing how many folks actually end up at the site (through googling, surfing) to find some very useful information -- and it all comes from readers Much appreciated.

      It's an incredible resource: 173 pages long - with graphics. It will give me something to read tonight.

      Delete
  3. 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.

    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.

    ReplyDelete
    Replies
    1. Great note, thank you. I will move this to the post for easier access. Thank you.

      Delete