非均质砂岩储层压汞分形特征与储层评价

Mercury injection fractal characteristics and reservoir evaluation of heterogeneous sandstone reservoirs

利用分形几何方法处理压汞曲线,求取相应的分形维数值能够作为定量指标评价储层物性。相关的前期研究中,分形模型常进行分段计算,但相应的地质含义表达不明,无法整体表达岩石的孔渗特征,综合分形维数求取过程中加权值缺乏理论依据。对综合评价分形模型进行改进,利用新模型处理了珠江口盆地白云凹陷15组样品的压汞数据,并与孔隙度、渗透率等物性参数相结合,分析分形维数的地质含义及影响因素。研究表明:双对数坐标系中进汞饱和度与毛细管压力拟合相关系数一般大于0.85,曲线具备分形特征;分形维数D_(1)代表较大孔隙的均一程度,与储层物性无直接联系,分形维数D_(2)主要受拐点压力影响;综合分形维数D_(p)求取时,利用D_(1)表征孔隙的均一程度,D_(1)的权值受控于排驱压力,两者共同表征较大孔隙对储层物性的贡献度,D_(2)及其权值表征中小孔隙对物性的贡献,D_(P)与物性参数存在良好的相关性。

By processing the mercury injection curve,the fractal geometry method and corresponding fractal dimension value can be used as a quantitative parameter to evaluate the physical properties of the reservoir.In previous studies,the fractal model was often calculated in two sections,but the corresponding geological meaning was unclear.In addition,the pore and permeability characteristics of rocks could not be expressed as a whole.In some studies,the concept of comprehensive fractal dimension has been applied,but the calculating weighted value lacks their theoretical support.An improved comprehensive fractal model is proposed.The new model was applied to process the mercury injection data of group 15 samples in Baiyun Sag of the Pearl River Mouth Basin.Combined with physical parameters such as porosity and permeability,the geological implications and influences of fractal dimension were analyzed.The results show that:the goodness of fit between mercury saturation and capillary pressure is generally greater than 0.85 in the logarithmic coordinate system,and the curve has fractal characteristics.The fractal dimension D_(1) represents the degree of homogeneity of large pores,which is not directly related to reservoir physical properties.The fractal dimension D_(2) is mainly affected by the pressure of inflection point.When calculating the comprehensive fractal dimension D_(p),D_(1) is used to represent the degree of homogeneity of pores.The weight of D_(1) is controlled by the displacement pressure.Both D_(1) and D_(2) represent the contribution of large pores to the physical property of reservoirs.D_(2) and its weight represent the contribution of small and medium-sized pores to physical properties,and D_(p) has a good correlation with physical properties parameters.