Methane-Water Interfacial Tension in Nanopores: A Dissipative Particle Dynamics Study.

ABSTRACT

Imbibition of fracturing fluid in deep shale nanopores has a significant effect on shale gas production. One of the key parameters affecting imbibition is the interfacial tension of the methane-water system. However, studies on the methane-water interfacial tension in nanopores are very limited, and obtaining the accurate value of the methane-water interfacial tension at the nanoscale is difficult and time-consuming. In this work, a dissipative particle dynamics simulation model was built to study the methane-water interfacial tension in nanopores. This model provides reliable access to methane-water interfacial tension for deep shales under high-temperature, high-pressure conditions at low computation cost. It can be easily used to compute the methane-water interfacial tension in nanopores or the confined space in wide application scenarios. A sensitivity study of methane-water interfacial tension on a variety of factors was conducted. Results demonstrate that under high-pressure conditions, the increase in pressure leads to the rise of interfacial tension. When pressure increases from 20 to 120 MPa, interfacial tension rises from 0.0275 to 0.12 N/m, which contributes to the severe imbibition of fracturing fluid in deep shales. The confinement effect was observed by investigating the influence of pore size. Interfacial tension almost remains unchanged in pores smaller than 7 nm because most of the confined space is occupied by interface layer molecules in these pores. When pore size increases from 7 to 15 nm, the confinement effect is reduced. The interfacial tension experiences a growth from 0.1155 to 0.27 mN/m. Compared with pressure and pore size, the effect of temperature on interfacial tension can be neglected during deep shale gas production.