Experimental Investigation of Surfactant Flooding in Shale Oil Reservoirs: Dynamic Interfacial Tension, Adsorption, and Wettability

The recovery factor of waterflood operations is constrained by formation geology and pore trapping mechanisms. This is particularly important for unconventional reservoirs such as shale oil with ultra-low permeability and porosity. Surfactant flooding can be used in these reservoirs to reduce oil trapping and increase sweep efficiency due to a reduction in interfacial tension and wettability alteration. On the other hand, a major concern with surfactant flooding is the adsorption of surface-active agents on the reservoir rock leading to loss of chemicals. In this study, the behavior of a non-ionic surfactant was investigated in order to enhance oil recovery from a producing shale oil reservoir using reservoir crude oil and rock samples. In the preliminary experiments, phase behavior tests were performed in the presence of reservoir shale rock to monitor micro-emulsion stability. The critical micelle concentration (CMC) of this surfactant was determined by both surface tension measurements and spectroscopy. Dynamic interfacial tensions (IFT) and contact angles (CA) of the non-ionic surfactant in brine/oil/shale systems were then measured by the rising/captive bubble technique using a state-of-the-art IFT/CA apparatus at reservoir conditions (6840 psi and 116?) for different surfactant concentrations (0.005 to 0.5 wt%). The amount of surfactant adsorption from surfactant-brine solutions onto crushed shale rocks were measured using UV-Vis spectroscopy at different surfactant concentrations. The data could be fit to a Langmuir type adsorption isotherm. The adsorption parameters were determined and results were compared and discussed. This work shows that the non-ionic surfactant is able to reduce the reservoir oil-brine IFT from its original value (27 mN/m) down to 15 mN/m while exhibiting minimal adsorption on the shale surface.