Strong Horizontal Activity in Williston’s Middle Bakken

Operators working the Williston Basin know it well—the middle Bakken dolomite is hot. Those of us not focused there may not know just how hot. In Richland County, Montana alone there were about 160 horizontals at year-end 2004 and another 70+ have been drilled by mid-year. Activity in North Dakota continues to grow, evidenced by recent discoveries by Jordan Oil and Gas (Burke County) and Headington Oil (Williams County).

Production reflects this activity. In Richland County, production in 2000, before the Middle Bakken horizontal play took off, was 2.6 million barrels with Bakken production representing less than 1% of this total. In 2004 production had risen to 10.2 million barrels with 73% coming from the Bakken. The success rate for middle Bakken horizontals has been phenomenal with only a handful of dry holes in Montana to date.

Early Bakken horizontals in the 1980s to mid-1990s targeted the upper shale interval. The middle Bakken, the target of current activity, is a silty dolomite sandwiched between upper and lower black organic shales. It has been termed a "resource play," being widespread, continuous and repeatable with a tremendous resource in place.

The pay zone or interval within the middle Bakken averages 8 to 12 feet in thickness, but wells have been successfully drilled in thinner zones. Directional control is critical with geosteering data based on sample shows and MWD with gamma ray, with a gyro used for directional orientation. The interval is very tight, having permeabilities much less than a mD. Massive hydraulic fracturing treatments on the order of 1 million pounds of proppant and 500,000 gallons of gelled water are required.

Wells are typically long-reach dual laterals with the second lateral doubling reservoir exposure for about half the cost of the first lateral. Underbalanced drilling is common. True vertical depths are 10,000-14,000 feet and lateral displacements extend 4,000 ft or much more in zones as thin as three feet. Operators selectively isolate and frac each lateral, something modern completion packers and sleeves make possible. Some operators frac initially, others let production drop down to a certain level before stimulating. Optimizing the completion/ stimulation process is a current focus area, one example being work reported in SPE Paper No. 90697 (see excerpt in www.pttc.org/news/4qtr2004/v10n4p4.htm#2).

Along with the Montana Geological Society, PTTC's Rocky Mountain Region co-sponsored a recent short course at AAPG's Rocky Mountain Section meeting on "Bakken Play Essentials." Six speakers, five from industry, shared insights on exploration and completion issues. Contact PTTC's Rockies Director Sandra Mark (smark.95@alum.mines.edu) for more technical information.

Content excerpted with permission from three articles appearing in The American Oil & Gas Reporter (July and August 2005 editions).