Molecular Dynamics Simulation of Nanoconfined Methane Flow Through Realistic Organic Shale Matrix

Academic investigations digging into the methane flow mechanisms at the nanoscale have been of high interests in the past decade. On one hand, the prosperity of shale gas/oil industry is supposed to take the responsibility at a certain degree. On the other hand, the complex essence and broad theoretical as well as application value possess great attraction. In this research work, utilizing the molecular dynamics methods nested in LAMMPS softwares, a fundamental framework is established to mimic the nanoconfined fluid flow through realistic organic shale matrix, i.e., composed of specific number of kerogen molecules. Back to the previous literatures related to the technical aspect in this paper, some adopted the graphit material to characterize the organic matter of shale matrix, rather than realistic kerogen molecules. Recently, promotion efforts have been implemented in the academic community with the use of kerogen molecules, the gas flow simulations are still lacking and also the pore shape in current papers is always hypothesized as slit pores. The assumption is regarded as the serious conflicts with the general observation phenomenon according to the advanced laboratory experiments, such as SEM image, AFM technology, and so on, that the organic pores in shale matrix tend to have circular pore geometry. In order to make things right and fill up the knowledge gap between simulation results against realistic cases, the circular nanopore with desirable pore size is constructed with surrounding kerogen molecules, expecting to be more physically and theoretically similar to the realistic organic 2 matter of shale matrix. Then, methane flow simulation is performed by utilization of non-equibrium molecular dynamics (NEMD), the density and velocity distribution under different pressure differences are presented. Furthermore, detailed discussion with respect to the simulation results is given. It suggests that pressure difference acts as a dominant role affecting methane flow velocity, while fails to influence the density distribution, which is considered to be mainly controlled by the strong molecular-wall interactions. In light of the fact that the simulation work is the first attempt for methane flow through circular nanopores inside realistic shale organic matrix, which can provide more accurate evaluation report with regard to the flow behavior and capacity of methane than that of existed documents.