WETTABILITY ANALYSIS IN SHALE ORGANIC PORES AT THE NANOSCALE

In view of the problems that wettability is difficult to distinguish in shale nanoscale organic matter pores and the organic matter model cannot truly characterize the pore properties of reservoirs, molecular dynamics research on wettability in shale gas nanoscale pores based on real kerogen organic matter model is proposed. The simulation of smooth and rough graphene ideal models as well as the actual organic matter model of kerogen are built, and wetting behavior characteristics in kerogen pores are analyzed by using the model visualization, the distribution of the density of space, and the analysis of potential energy. There is also an investigation of the effects of temperature, the size of the pores, and the size of the liquid bridge on the wetting condition. Since the traditional organic matter model is based on ideal assumptions, it is difficult to accurately describe the wetting behavior of water in graphene models. As a result of the complex molecular structure and various element types, the kerogen model is more realistic in characterization of wettability of water phase in the organic pore. The water phase in the organic nanopores presents two types of regions: high density region and low density region. Water molecules in the low density region concentrates on the gas-liquid phase interface, where the hydrogen bond interaction is weaker compared with that in the water bulk phase, indicating that this part of molecules are able to diffuse into the gas phase. In addition, the diffused water molecules can also be easily trapped by the kerogen matrix due to its strong attractive interaction. Afterwards, the water molecules will adsorb on the kerogen matrix, presenting a fake wetting condition from the visualization. However, the water phase in the high density region shows the presence of non-wetting condition, which is more realistic for water in the organic pores.