低孔渗储层井周油藏侵入模拟及阵列感应电阻率校正方法

泥浆滤液侵入渗透性地层会改变井周地层流体的原始分布状态,使井周地层电阻率发生变化、储集层电测井响应失真。本文基于油水两相渗流理论和水对流扩散理论,应用数值模拟方法构建地层模型,研究低渗储层泥浆侵入过程中井周地层矿化度、含水饱和度、电阻率变化特征及井周油藏分布特征。对不同渗透率地层泥浆侵入的数值模拟结果表明:在低渗透储层,相同侵入时间内,随着地层渗透率的增加,泥浆侵入深度增加,且同一侵入深度的含油饱和度减小;随着侵入时间的增加,井周地层水矿化度、含水饱和度和地层电阻率的侵入剖面前缘均发生明显的变化。结合3口井的泥浆侵入数值模拟分析,发现阵列感应测井响应特征及其电阻率的幅度差异受泥浆侵入时间和侵入深度影响。不同流体性质层段的井周油藏动态演化规律模拟结果表明,井周油藏的变化情况与储层流体性质有明显关系。利用实例井侵入模拟结果与阵列感应测井响应的相关性,构建了侵入深度的计算公式;根据侵入阶跃剖面,利用几何因子理论构建了原始地层电阻率计算公式,用以辅助储层电阻率校正。正确认识井周地层泥浆侵入特征及井周油藏的分布情况有助于提高阵列感应测井评价储层的准确性。

Numerical Simulation of Mud Invasion Around the Borehole in Low Permeability Reservoir and a Method for Array Induction Log Resistivity Correction

The original distribution state of formation fluid and the formation resistivity around the borehole will be changed while mud filtrate invades the permeable formations.Based on both of the water-oil phase flow theory and convective diffusion theory,numerical simulation method is applied to build the formation model for the study of the mud invasion characteristics in low permeable reservoir,for studying the distribution characteristics of salinity,water saturation,resistivity and oil/gas reservoir around the borehole during mud invasion.The numerical simulation results of mud invasion in different permeable formation show that mud invasion depth increases as permeability increases in the same invasion time in low permeable reservoir,and the invasion profile of salinity,water saturation,resistivity and remaining oil change obviously as invasion time increases.The numerical simulation analysis of three practical boreholes shows that the array induction logging response characteristics and their resistivity amplitude difference are influenced by mud invasion depth and invasion time.According to the dynamic.evolution simulation of different reservoir fluid types around borehole,the distribution of reservoir has obvious relationship with fluid type.The invasion depth calculation formula is obtained based on the results of the case study borehole and the array induction log response,and also the original formation resistivity calculation formula is constructed based on geometrical factor theory according to the invasive step profile for assistant reservoir resistivity correction.Correct understanding the characteristics of mud invasion and the distribution of reservoir around the borehole can improve the accuracy in array induction logging reservoir evaluation.