致密油藏孔喉分布特征对渗吸驱油规律的影响

自发渗吸是致密油藏中一种重要开发机理,构建准确的渗吸驱油数学模型对明确致密油藏渗吸驱油规律具有重要意义。基于毛管束模型,考虑束缚水和残余油饱和度,利用二维高斯分布函数拟合从高压压汞测量得到的致密砂岩孔喉分布,构建岩心尺度致密砂岩基质渗吸驱油数学模型,并通过致密砂岩渗吸实验对数学模型进行验证,开展渗吸规律影响因素分析,明确孔喉分布、润湿角、界面张力等因素对渗吸驱油速率的影响。结果表明,致密砂岩微纳米孔喉分布在半对数图中呈二维高斯分布特征;在自发渗吸初期,渗吸驱油速率主要取决于大孔分布特征,岩心渗透率越高,渗吸驱油速率越大;在自发渗吸中后期,渗吸驱油速率主要受纳米孔喉分布影响;渗吸驱油速率随润湿角降低、油水界面张力增大、原油黏度降低而增大。明确致密储层孔喉分布特征能够准确预测致密油藏渗吸驱油速率,对致密油藏开采制度的确定具有一定的指导作用。

Influence of pore throat size distribution on oil displacement by spontaneous imbibition in tight oil reservoirs

Spontaneous imbibition is an important development mechanism for tight oil reservoirs.It is of great significance to develop a correct mathematical model of spontaneous imbibition to clarify the law of oil production with spontaneous imbibition.Based on the capillary model,considering the distribution of irreducible water and residual oil saturation,using the two-dimensional Gaussian distribution function to fit the pore throat size distribution of tight sandstone obtained from high-pressure mercury intrusion,a core-scale mathematical model for oil displacement with spontaneous imbibition in a tight sandstone matrix was constructed,and verified with imbibition experiment.The influencing factors of imbibition law were analyzed to clarify the effects of pore throat distribution,wetting angle and interfacial tension on the oil production rate by spontaneous imbibition.The results show that the distribution of micro and nano pore throats in tight sandstone has the characteristics of two-dimensional Gaussian distribution in the semi-log plot.In the early stage of spontaneous imbibition,the imbibition rate mainly depends on the distribution of large pores,and the larger the core permeability is,the greater the imbibition and displacement rate is.In the middle and later stage of spontaneous imbibition,the imbibition rate is mainly affected by nanopores.The imbibition rate increases with the decrease of wetting angle,the increase of interfacial tension between oil and water and the decrease of oil viscosity.It can accurately predict the imbibition rate of tight reservoir by defining the pore throat distribution characteristics,which has a certain guiding role in determining the production system of tight reservoirs.