Molecular insight into the oil charging mechanism in tight reservoirs

Tight oil reservoirs are dominated by nano-pore throats that significantly impede the migration of crude oil. Understanding the oil charging behavior in these nanoscale channels is critical to assess the oil accumulation. In this work, molecular dynamics (MD) simulations were adopted to uncover molecular insights into the oil charging and migration through differently-sized hydrophilic nano-pore throats. On the one hand, the dynamic pathway and the energetic driving force of the oil charging process were clarified. On the other hand, with analyzing the force that the oil undergoes when going across nano-pore throats, the capillary pressure for different throat sizes was calculated; based on which, we propose an MD simulation method to assess the oil accumulation threshold of tight reservoirs. Taken together, this work expends our knowledge of the fluid migration through nano-pores, and it could facilitate future studies on the evaluation of tight oil reservoirs.