考虑孔喉与流体分子相互作用及毛管力的相平衡计算

在致密气藏或者页岩气藏中,纳米级孔喉与流体的相互作用会影响到气相的凝析与蒸发,从而影响流体露点压力和泡点压力的计算。考虑到纳米孔喉与流体分子的相互作用,建立了考虑孔喉与流体分子相互作用的状态方程以及相关逸度方程。基于该状态方程和逸度方程,建立了考虑孔喉与流体分子相互作用和毛管力影响的相平衡计算方法。通过对甲烷、丁烷和辛烷混合物的相平衡计算发现,当孔喉直径小于10 nm时,孔喉与流体分子的相互作用对状态方程的影响显著,孔喉与流体分子的相互作用使得相包络线缩小,露点压力降低,泡点压力增大。毛管力作用使得露点压力降低,且孔喉越小,露点压力下降越显著。通过该研究更深入地认识到纳米孔喉对流体相态的影响。

Phase equilibrium calculation considering the interaction between pore and molecules and the capillary pressure effect

In the tight gas reservoirs or shale gas reservoirs, the interaction between nano-scale pore throat and fluid will influence the condensation and evaporation of gas phase, so as to impact the calculations of fluid dew point and bubble point. In consideration of the interaction between nano-scale pore throat and fluid molecules, the related state equation and fugacity equation were established. On this basis, the phase equilibrium calculation method was created in consideration of the interaction between nano-scale pore throat and fluid molecules as well as capillary force. Through the phase equilibrium calculation of methane-butane-octane mixture, it is found that when the diameter of pore throat is less than 10 nm, the interaction between pore throat and fluid molecules has significant influences on state equation, leading to the shrinking of phase envelope, the reduction of dew point pressure and the increase of bubble point pressure. The capillary force is able to reduce the dew point pressure. The smaller the pore throat was, the more significant the reduction of dew point pressure will be. The influences of nano-scale pore throat on fluid phase state are further realized through research.