An Analytical Model for Fluid Imbibition in Organic Nanopores

Estimating the fluid imbibition flow in natural system composed of nanopores is challenging due to the strong fluid/rock molecular scale interaction and the invalidation of the macroscopic thermodynamics treatment. We develop an analytical model for Lennard-Jones fluid imbibition into an organic nanopore considering the phase transition and fluid/rock intermolecular interactions. In addition, we apply the proposed model on octane molecules imbibition into 1–10 nm slit-shape graphite nanopores under the standard and shale reservoir condition. Predicted velocity and density profiles of 2 nm model at the standard condition show that octane molecules first imbibe as vapor phase at around 200–300 m/s and form adsorbed layers near the pore wall. Velocity and density profiles are compared with the molecular dynamic simulation results. Calculated mean velocities of the analytical model and simulation are around 10 3 –10 4 of those predicted by classical models, which are similar with previous experimental results. Reservoir condition results show octane can fast flow only when the driving pressure is greater than 0.12 MPa when the initial reservoir pressure is 5.72 MPa. Particularly, the impact of the fluid phase transition on the imbibition rate is significant in organic nanopores.