Uncertainty quantification of shale capillary desaturation curves for surfactant EOR in shale through fracturing fluids using predictive modeling

Surfactant is often added into hydraulic fracturing fluids for shale reservoirs because it can minimize formation damage. The surfactant is also known for its EOR potential for sandstone/ carbonate reservoirs. Given both benefits, some previous papers studied the feasibility of surfactant EOR for shale reservoirs. Evaluation of surfactant EOR potentials requires accurate capillary desaturation curves (CDCs) of the shale rocks because CDCs determine how easily the surfactant will recover the residual oil saturation and improve the relative permeabilities. However, there is currently no experimental CDC data of shale rocks because of the difficulty in the experiment. This study builds a validated predictive model to quantify the effect of the CDC uncertainty on EOR. The objective is to numerically assess how the CDCs uncertainty affects the feasibility of surfactant EOR in shale reservoirs using Monte Carlo simulation of 100,000 possible CDCs. This paper also performs sensitivity analysis on the surfactant's wettability alteration direction and its alteration extent and target interfacial tension value. Our model reveals that surfactants can offer optimum EOR potentials in shale reservoirs if they strongly alter the shale's wettability to water-wet while maintaining a high interfacial tension. However, even when using such optimum surfactants, there are still some possibilities of decreasing the ultimate oil recovery because of the CDC uncertainty. Lastly, this study quantitatively presents the degree of the risks.