低渗储层孔隙结构分形特征及对水驱油效率的影响

FRACTAL FEATURE OF PORE STRUCTURE AND ITS EFFECT ON EFFICIENCY OF DISPLACEMENT OF OIL BY WATER IN LOW PERMEABILITY RESERVOIRS

低渗储层岩石的孔隙结构是影响储层岩石物性及水驱油效率的重要闳素之一，但一直以来难以确定一个有效的参数或方法定量的反映储层岩石孔隙结构的非均质性。通过使用分形几何方法及对6个地区的低渗储层岩石的毛管压力曲线进行分形特征分析及分形维数计算，分析研究了低渗储层岩石孔隙结构的非均质性。研究表明：低渗储层岩石孔喉的分形特征存在整体分形和分段分形两种特点，且各段分形特征具有明显的不同；分形维数与储层岩石的微观非均质性具有明显的关系，分形维数越大，储层岩石的微观非均质性越强；存在微裂缝的储层岩石，大孔隙与小孔隙的分形维数存在一个突变，而且裂缝的密度越大，突变越明显；分形维数越小，水驱油效率越高；运用孔隙结构的分形特征及分彤维数是研究低渗储层岩石微观非均质性的一个有效方法。同时，还提供了运用加权方法求取分段分形储层岩石分形维数的方法。

The pore structure of low permeability reservoir rocks is one of the significant factors that affect reservoir petrophysics and water displacement efficiency; however, until now, it is difficult to determine an efficient parameter or a method to quantitatively reflect the heterogeneity of pore structure of reservoir rocks. Appling fractal geometry method, based on the fractal dimension computation and fractal feature analysis of capillary pressure curve of low permeability reservoir rocks in four areas, this paper analyzes and studies the heterogeneity of pore structure of low permeability reservoir rocks. Results show： The fractal features of pore-throats in low permeability reservoir rocks include integral fractal and sectional fractal features, with all fractal characteristics being obviously different; Fractal dimension is obviously related to the microcosmic heterogeneity of reservoir rocks, the bigger the fractal dimension, the severer the microcosmic heterogeneity of reservoir rocks; In reservoir rocks with micro-fractures, the fractal dimension of big and small pores has an abrupt change, and the larger the fracture density, the more obvious the abrupt change; The smaller the fractal dimension, the higher the water displacement efficiency; Application of fractal characteristics and dimension of pore structure is an efficient method to research the microcosmic heterogeneity of reservoir rocks. Meanwhile, a method to obtain sectional fractal dimension of reservoir rocks by weighting is provided.