Understanding the Effect of Nanopores on Flow Behavior and Production Performance of Liquid-Rich Shale Reservoirs

This study evaluates the effect of nanopores on the production performance of liquid-rich shale reservoirs, which have become one of the most significant energy sources globally. Liquid-rich shale reservoirs are characterized by complex heterogeneous fracture networks and numerous nanopores. Traditional fluid flow models do not entirely capture the fluid flow behavior in porous media when a substantial hydrocarbon volume is stored in the nanopores. The flow mechanism in nanopores is different from the flow in large pores present in conventional reservoirs. This deviation in flow behavior is caused by the significant interactions between the hydrocarbon molecules and the pore walls. The hydrocarbon-wall interaction should not be ignored and must be accounted for in numerical simulators. In this study, we use a compositional reservoir simulator to model the reservoirs with different fluid properties and the distribution of nanopores. We integrate the deviated phase behavior into the reservoir model by shifting the critical properties based on extensive simulated results for simple and long-chain alkanes from a prior study. We compare the estimated ultimate recovery (EUR) of reservoirs at the end of two years for reservoirs with different degrees of pore confinement effect. The gas-oil ratio (GOR) for the reservoirs is also presented to describe the impact of the nanopores. The producing GOR for reservoirs with nanopores showed a significant deviation from the standard behavior expected for a conventional reservoir. Sensitivity analysis showed that the presence of nanopores in an unconventional reservoir could have a substantial impact on (EUR). The combined effect of initial fluid composition and nanopores on EUR is also evaluated and presented. The procedure presented in this study provides an effective method to incorporate the nanopores for better production performance evaluation and reserves estimation. The results show that the modified phase behaviors caused by the nanopores significantly affect the EUR from liquid-rich shale reservoirs.