Surfactant preflood to improve waterflooding performance in shale formations

The lower primary oil recovery from shale formations accelerated the application of waterflooding technology as a secondary recovery mechanism at earlier time compared with conventional reservoirs. This situation suggests the EOR surfactant technology designed to promote additional oil recovery from fractured carbonate formations is a fit for these shale formations that are characterized by complex fractured lithology. The presented study investigates the idea to incorporate appropriate surfactant formulations at a low dosage as a preflood to waterflooding in shale formations. If properly designed, such surfactant in the preflood fluid will penetrate into the high oil saturation 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, and then is produced. Another benefit of the preflood surfactant is engineered in such that it leaves the matrix or natural fracture face water wet to facilitate oil movement during production. This paper presents a study of a series of surfactant additives developed for extracting additional oil. Over 10 of special customized product blends were evaluated in laboratory for their effectiveness in increasing oil recovery of Bakken formation. Only one surfactant (Stim aid A) that was compatible with Bakken formation brine and crude oil, so it was the only one used for spontaneous imbibition experiments. The average porosity of the used Bakken reservoir samples was 5.8% with an average bulk density of 2.75 g/cc. The Bakken rock samples were pre-treated with different surfactant solutions and then used for water spontaneous imbibition experiments. During the spontaneous imbibition, the maximum oil recovery was from the samples that were pre-treated with 2 wt% of (Stim aid A) surfactant. The measured contact angles on Bakken samples showed an alteration in rock wettability that interpreted the improvement of Bakken higher recovery factors from spontaneous imbibition in surfactant solutions compared with brine solutions only.