致密砂岩储层孔隙结构分形研究与渗透率计算——以川西坳陷蓬莱镇组、沙溪庙组储层为例

为厘清分形维数对储层物性特征的影响，并提高渗透率计算精度，通过对川西坳陷蓬莱镇组、沙溪庙组致密砂岩气藏12块岩心进行高压压汞实验；利用毛管束分形模型对进汞曲线进行分形处理，并结合物性资料，对分形维数与孔隙结构参数的关系进行研究；通过理论分析与多次试算，最终选取加权平均分形维数（D_ave）、分界压力（p_f）、中值半径（R₅₀）等对渗透率进行多元非线性回归计算。结果显示：研究区储层可划分Ⅰ类、Ⅱ类、Ⅲ类、Ⅳ类共4种孔隙结构类型；大、小孔孔隙结构相对独立，分形维数与孔隙结构参数关系复杂；多元回归计算的渗透率与实测渗透率相关系数平方达0.9。多元非线性回归计算模型对于渗透率的计算具有更高的精度，为致密砂岩储层渗透率的计算提供了新思路。

Fractal characteristics of pore structure and permeability calculation for tight sandstone reservoirs: a case of Penglaizhen Formation and Shaximiao Formation in Western Sichuan Depression

In order to clarify the influence of fractal dimension on macroscopic reservoir physical properties and improve permeability calculation accuracy, high pressure mercury injection experiments were carried out on 12 cores of tight sandstone gas reservoirs in Penglaizhen and Shaximiao Formation in Western Sichuan Depression. All the curves of mercury intrusion were processed by fractal model based on capillary tubes. Combined with poro-sity and permeability, the correlation between fractal dimension and pore structure parameters was analyzed. Through theoretical analysis and many times of trial, D_ave, P_f and R₅₀ were finally selected to calculate permeabi-lity by multiple nonlinear regression. The results show that the pore structure in tight sandstone could be divided into four types. The pore structures of big and small pores are relatively independent, and the relationships between fractal dimensions and pore structure parameters are complex. The calculated permeability by multiple nonlinear regression shows strong correlation with measured permeability, whose correlation coefficient squared is more than 0.9. The established model by multiple nonlinear regression shows more accurate in permeability calculation and it provides another thought for permeability calculation.