Mechanistic Study On The Effect Of Petrophysical Properties On Microscale Imbibition In Low Permeability Reservoirs

Low permeability reservoir is an important part of reservoir in our country domenstrating great development potential and economic value.Spontaneous imbibition in porous media is helpful in displacing and expelling the oil phase.In order to improve oil recovery efficiency with the aid of spontaneous imbibition,investigation on the mechanism of spontaneous imbibition in porous media is essential.The petrophysical properties are closely related to imbibition.In order to explore the relationship between them,microfluidic technology was applied to study the quantitative relationship between imbibition and petrophysical properties by fabricating microfluidic chips with accurate pore throat structure.Static imbibition experiments were carried out using artificial core samples with different permeabilities to study the imbibition pattern and compare with the microscale imbibition experiments.The impact of rock petrophysical properties on the imbibition phenomenon was proposed.The experimental results showed that the relative imbibition rate is negatively correlated with the pore throat ratio,coordination number and tortuosity.Namely,the relative imbibition rate decreases with the increase of the pore throat ratio,coordination number and tortuosity.Pore-throat ratio is considered as the main factor affecting gas-liquid two-phase imbibition.Through the analysis of wetting phase saturation in single pore structure with different pore-throat ratio,it is considered that pore-throat ratio 17to 18 are the optimal pore-throat ratio for imbibition displacement.In oil-water two-phase imbibition,the relative imbibition rate is negatively correlated with the pore-throat ratio,coordination number and tortuosity.Coordination number is the main factor affecting oil-water two-phase imbibition.Through the analysis of wetting phase saturation in single pore structure with different pore throat ratio,it is considered that pore throat ratio 20 to 25 are the optimal pore throat ratio for imbibition displacement.For the core imbibition experiments,when the rock permeability is low,the core imbibition displacement efficiency increases with the increase of permeability,showing a positive correlation.Imbibition efficiency is negatively correlated with lithologic coefficient F and structural coefficientφ_p.The relationship between rock petrophysical properties and imbibition behaviors observed in microscale is consistent with the macroscopic experiment results.By modifying the classical L-W equation and introducing the imbibition parameterΩ,an imbibition model which can simultaneously describe the parameters of pore-throat ratio,coordination number and tortuosity was obtained.The model has certain reliability for predicting the pore-throat ratio and tortuosity.