北部湾盆地砂砾岩低阻油层成因及饱和度计算方法

Genetic Mechanism and Saturation Calculation Method of Low Resistivity Sandy Conglomerate Oil Layers in Beibu Gulf Basin

乌石M油田流沙港组砂砾岩油层由于受特殊沉积和成岩作用影响,电阻率呈现低阻特征,为测井流体识别及含水饱和度定量评价带来了较大困难。基于岩心化验分析资料对低阻油层微观岩石物理特征开展了研究,认为该区复杂孔隙结构引起的高束缚水饱和度是低阻油层的主要成因。在此基础上,提出了更加符合该区地质特征的等效岩石组分(EREM)模型,通过数值模拟及岩电实验资料确定了模型参数变化规律,形成了一套适用于复杂孔隙结构砂砾岩储层的含水饱和度计算方法。对比分析结果表明,新模型计算的含水饱和度与岩心分析含水饱和度的相对误差为4.1%,低于阿尔奇(Archie)模型计算的含水饱和度误差12.8%,从而提高了复杂孔隙结构砂砾岩低阻油层的饱和度计算精度。

Due to the influence of special sedimentation and diagenesis, the low resistivity of the sandy conglomerate oil layers of Liushagang Formation in Wushi M Oilfield makes it difficult to identify fluid type and quantify water saturation.This paper studies the micro-lithophysical characteristics of low resistivity oil layers based on the core analysis data.The study shows that the high irreducible water saturation caused by the complex pore structure in this area is the main reason for the formation of low resistivity oil layers. On this basis, the equivalent rock element model (EREM) is proposed,which is more in line with the geological characteristics of the study area. According to the numerical simulation and the variation law of model parameters determined by rock electrical experiment data, the water saturation calculation method suitable for complex porous sandy conglomerate reservoirs is formed.The result shows that the relative calculation error between the EREM and core analysis is 4.1%, which is significantly lower than 12.8% calculated by the Archie model, thus improving the calculation accuracy of low resistivity sandy conglomerate oil layers in Wushi M Oilfield.