致密砂岩储层孔隙结构分形特征表征方法研究

Fractal Characterization of Pore Structure in Tight Sandstone Reservoirs

分形理论为定量表征储层孔隙结构提供了有效手段,但致密砂岩储层孔隙结构复杂,常规孔隙结构分形特征表征方法是否适用需要进一步研究。系统梳理了孔隙结构分形特征表征方法,然后基于致密砂岩压汞曲线对各方法适用性进行了评价,并对致密砂岩储层的分形特征进行了研究。结果表明,分形定义法能够有效表征致密砂岩孔隙结构分形特征,贺成祖法适用于渗透率大于0.1×10^(-3)μm^2的致密砂岩储层,Li Kewen法适用于渗透率小于0.1×10^(-3)μm^2的致密储层,而Brooks-Corey上具有分形特征,不存在分段分形特征。分形维数是储层评价的重要参数,分形维数越大,储层物性越差,平均孔隙半径越小,排驱压力越大,束缚水饱和度越大。

Fractal theory provides an effective means for quantitative characterization of reservoir pore structure, while the pore structure of the tight sandstone reservoir is complicated. It needs further study that whether the conventional characterization of the fractal features of pore structure is applicable to tight sandstone reservoir or not. In this paper, present fractal characterization methods of pore structure are systematically sorted out, the applicability of each method is evaluated based on mercury injection curves of 5 tight sandstone samples, and the fractal characteristics of tight sandstone reservoir are studied. The results show that the fractal definition method can effectively characterize the fractal features of pore structure of tight sandstone, while the He Chengzu method is only applicable to tight reservoirs with permeability higher than 0.1×10^-3 μm^2 and the Li Kewen method is only applicable to tight reservoirs with permeability lower than 0.1×10^-3 μm^2, and the Brooks-Corey method are completely not applicable to tight sandstone reservoirs. Tight sandstone reservoir has fractal characteristics in the whole pore radius region, and no fractal features exist. Fractal dimension is an important parameter in reservoir evaluation. And the higher the fractal dimension, the worse the physical properties of reservoir, the smaller the average pore radius, the higher the displacement pressure and the higher the bound water saturation.