Abstract
The Bakken reservoirs represent a large untapped resource of oil. One of the challenges is extracting the crude oils from their low-permeability formations at economic rates. These reservoirs contain multiple pay zones, including some with carbonate (dolomite) lithology. Recent common practice is to drill horizontal wells and perform a series of large, multi-stage hydraulic fracture treatments. The fractures penetrate deeply into the reservoir and promote more efficient drainage of the oil. This situation suggests that a surfactant technology designed to enhance oil recovery from fractured carbonate formations is a fit for these typical Bakken cases with Middle Layer complex fractured lithology. The concept of this technology is to incorporate appropriate surfactant formulations at a low dosage in the well stimulation fluids. If properly designed, such additives in the fracture fluids will penetrate into the highly oil-saturated matrix or natural fracture region and accelerate the extraction of the oil in place by rapid imbibition. This extracted oil can readily move from the matrix into the propped fracture system to be produced. Another benefit of the additive is its engineered property to leave the matrix or natural fracture face water-wet to facilitate oil movement during production.
This paper presents a study of a series of such stimulation fluid additives developed for enhanced oil recovery. Over 10 special customized product blends were evaluated in the laboratory for effectiveness in increasing recovery of Bakken crude oil samples. Tests included compatibility with formation brine, emulsion tendency, recovery factors from spontaneous imbibition with crude oil and formation brine, and compatibility with proposed fracturing fluids. These results show that more than one of these products improve recovery of Bakken crude oil by spontaneous imbibition from both outcrop limestone cores and from Bakken core material. The best of these products is recommended for field application.
