Chemical Process for Improved Oil Recovery From Bakken Shale

Abstract There is a new chemical improved oil recovery (IOR) process for Bakken reservoirs. In this concept a custom surfactant agent may be incorporated into standard hydraulic fracturing treatments for the Bakken to increase oil recovery. These are reservoirs from the Late Devonian to Early Mississippian age occupying about 200,000 square miles (520,000 km2) of the subsurface of the Williston Basin, covering parts of Montana, North Dakota, and Saskatchewan. The rock formation consists of three members: Lower shale, Middle dolostone/siltstone, and Upper shale. The shales were deposited in relatively deep marine conditions, and the dolostone/siltstone was deposited as a coastal carbonate during a time of shallower water. The Middle member is the principal oil reservoir, roughly two miles (3.2 km) below the surface. Both the Lower and Upper members are organic-rich marine shales. The oil in place in the Bakken shale play is very large, with an April 2008 USGS report estimating the amount of technically recoverable oil in the Bakken Formation at 3.0 to 4.3 billion barrels. Production from the Bakken has been limited in the past, but now has become a very active area of development with the widespread advent of drilling horizontal wells and large-volume hydraulic fracturing treatments. One key to the economic production rates of oil from these formations is to create an extensive well-connected fracture system. Laboratory experiments demonstrate that specialized surfactant formulations will interact with this mixed- to oil-wet low permeability Middle member to produce more oil. Specifically, including such a surfactant chemical formulation in an aqueous phase (e.g. hydraulic fracturing fluids) will promote the spontaneous imbibition of this fluid into the tight matrix and microfractures containing high oil saturation. This promotes expulsion of oil otherwise trapped to migrate into the fracture system and then be produced into the wellbore. Thus including an appropriate surfactant in frac fluids or in other aqueous-based treatment fluids can produce additional oil.