Water- and Surfactant-Based Huff-n-Puff Injection into Unconventional Liquid Hydrocarbon Reservoirs: Experimental and Modeling Study

The combination of horizontal well drilling and multistage hydraulic fracturing is currently the leading method for developing shale reservoirs. However, oil recovery from these techniques does not exceed 10%, and supporting technologies are being sought. The injection of water or surfactant solutions in huff-n-puff mode is often considered an enhanced oil recovery option for shales, which can be used alone or in combination with other technologies, such as CO₂ injection. This study presents experimental and numerical investigations into the huff-n-puff treatment of low-permeability shale cores using water-based compositions. Additionally, an attempt was made to displace oil by applying a nanofluid booster. Computational tomography was used as one of the methods to determine the oil recovery factor. Two core flooding tests with different designs and injection fluids were conducted. The first experiment involved brine filtration in one direction, followed by nanofluid injection. Second core flooding/huff-n-puff test implied injection of a 0.5 wt % surfactant solution. The results showed that the oil recovery factor achieved using brine was approximately 50% and decreased after nanofluid injection until 31%. Besides that, there was no significant effect from the use of the surfactant. At the same time, critical issues were observed regarding a decrease in core permeability. A numerical simulation of the second experiment was performed to restore the relative phase permeability (RPP) in the surfactant-oil system and to study the dependency of the capillary number logarithm on the miscibility coefficient. The simulation showed a good convergence in terms of the recovery factor values, with an error of ∼1.5%.