|New Proppant Choices |
Improve Bakken Shale Production
The Bakken Formation is one of the largest continuous deposits of oil and natural gas in the United States. Although this
area was initially discovered in the 1950’s, it was considered uneconomic until recently due to the formationís low
permeability. Recent advancements in drilling and completion technologies along with increases in oil prices have made this
play a viable resource. These developments include horizontal drilling and improved hydraulic fracturing methods, making
proppant selection essential to maximizing well production.
This formation consists of black shale, sandstone, and siltstone located beneath northwestern North Dakota,
northeastern Montana, southern Saskatchewan and southeastern Manitoba.
Although the productive zones are at varied depths throughout the Bakken, the average targeted depth is shallowest at the north
end and gets progressively deeper toward the southern play border. The average depths of the wells drilled in Canada range from 3,600
to 7,200 ft (1,097 – 2,194 m) with average closure stresses between 2,000 and 6,000 psi (14 – 41 MPa). Both vertical and
horizontal wells are still drilled in this area; however, horizontal wells with laterals between 3,000 and 5,000 ft (914 – 1,524 m)
are quickly becoming the norm. The majority of the wells drilled in the United States Bakken are horizontal 8,500 to 10,000 ft
(2,590 – 3,048 m) laterals at vertical depths up to 10,000 ft (3,048 m). Closure stresses generally vary between 5,500 to
9,500 psi (38 – 66 MPa) depending on depth and location. The small number of vertical wells are generally not used for production
purposes, but to determine the best location for drilling horizontal laterals.
As this is an emerging play, operators are continually testing different proppants while looking for an effective, economical
completion strategy. In the United States Bakken, the most common mesh sizes include 20/40, 30/50, 40/70, and 100 mesh; whereas north
of the border, larger mesh sizes such as 12/20 and 16/30 are also quite popular. Although a variety of proppant types have been used,
uncoated frac sand has been most common recently due to low commodity prices. The deep Bakken wells in North Dakota and Montana have
been fractured with uncoated ceramics; however they have not proven to be as cost-effective as their resin coated counterparts.
Bakken operators are now turning to resin coated curable sand. It performs more effectively than uncoated frac sand and more
costly ceramic proppants which donít exhibit the expected performance under downhole conditions.
Horizontal Well Proppant Technology
The horizontal wells drilled in the Bakken pose a unique challenge for operators. At Hexion, we recognize these factors and have
developed XRT Gold H™, which is specially formulated for use on horizontal wells such as those in North Dakota and Montana. These
curable resin coated proppants consolidate with closure stress in the fracture, not in the wellbore, creating a consolidated pack
that retains over 90% of its original bond strength after prolonged slurry times at elevated temperatures. This bonded proppant pack
also greatly reduces fracture embedment and fines generation, which both lead to decreased conductivity. XRT Gold H’s unique resin
system also encapsulates fines, so most fines that do occur are held within the coating. Testing was done on several different proppants
at 8,000 psi (55 MPa) closure stress using the Wet, Hot Crush Test. Lightweight ceramics generated 6.9% fines, while uncoated frac sand generated 30.4%. By comparison XRT Gold H generated only 3.4% fines. (as shown in the chart).
This excellent fines control explains why XRT
Gold H has higher effective conductivity than an uncoated lightweight ceramic. Many proppant suppliers report lab-based baseline conductivity
figures which do not make adjustments for issues such as fines migration. Effective conductivity takes these factors into account, providing more accurate downhole conductivity figures.
XRT Gold H works exceptionally well for horizontals, however the shallower, low temperature nature of the Canadian Bakken is well suited for SiberProp™ which
prevents fines migration and proppant flowback. This product, available in either 20/40, 12/20, or
16/30 mesh sizes, is specially formulated with a low-temperature cure resin system designed to bond without the use of external chemical activators.
For those operators who prefer waterfracs in the Bakken, Prime Plus™ would be an excellent proppant choice. Prime Plus is the only curable, 40/70 mesh resin coated proppant offered in North America. Since its introduction in late 2006, Prime Plus has been utilized in
thousands of wells in every major waterfrac basin in the United States and Canada. It is recommended for applications with closure stress
ranging from 6,000 to 10,000 psi (41 – 69 MPa). It has demonstrated its ability to provide improved fracturing treatment results
over both uncoated frac sand and ceramics.
Hexion has recently opened a new transload facility in Fairview, ND which is located right in the heart of the Bakken play. With
the three manufacturing facilities located in the US, coupled with the increased capacity of the nearby plant in Sturgeon County, Alberta, Canada, we offer Bakken operators
more economical options for proppant selection.
Although overall drilling rates may be down in North America, horizontal wells requiring large proppant volumes are still being drilled in
the Bakken. We are going forward with infrastructure expansion plans to ensure that we are able to support operators working in the Bakken
and other challenging unconventional plays.