基于分形理论的页岩储层微观孔隙结构评价

Micro-structure Evaluation of Shale Gas Reservoir Based on Fractal Theory

页岩储层微观孔隙结构评价对页岩气勘探开发具有重要的意义,为了更有效地研究页岩储层微观孔隙结构特征,利用高压压汞实验结合分形理论对孔隙结构进行分析。高压压汞结果显示岩样孔径主要分布在3~18nm范围内,岩样孔隙以微孔和过渡孔为主,微孔和过渡孔提供了大部分孔体积。岩样比表面积主要由微孔贡献,微孔和过渡孔提供了页岩气主要的吸附空间。分形维数分析结果表明：页岩岩样的分形分布可明显的分为2段,过渡孔、中孔和大孔的分形维数接近3,说明该部分孔隙非均质性强,体现出较强的分形特征;微孔的分形维数小于1,分析原因可能是压汞实验仅可以描述微孔的一部分,对孔径〈3nm的微孔描述不到,因此对微孔的孔隙结构评价不够全面,使分形维数的计算结果超出理论范围。

Micro-structure evaluation of shale gas reservoir is the basis of shale gas exploration and development. High-pressure mercury injection and the calculation principle of fractal dimension of porous structure are employed to study the pore structure of shale and the pore structure parameters can also be obtained. The results of high pressure mercury injection show that the core diameter is mainly in the range of 3- 18nm,and the micropores and transitional pores are the main pore in shales. Micropore is the primary con- tributor to specific surface area and functions as the main adsorption space. The fractal dimension analysis results show that the fractal distribution of shales can be obviously divided into two sections： the fractal dimension of transitional pores,mesopores and macropores is close to 3, which indicate that this part of the pore is strongly heterogeneous and the distribution of pore structure is uneven. The fractal dimension of micropores is less than 1. The result is mercury injection experiment cannot describe the pores with a diameter less than 3nm,and the pore structure evaluation of micropores is not comprehensive enough, so that the fractal dimension is beyond the scope of theory.