不同成熟度页岩孔隙及其分形特征

Pore and fractal characteristics of shale in different maturity

为探究页岩孔隙随成熟度的变化特征,文中研究选取了华北地区12个不同成熟度（镜质体反射率Ro介于1.10%-2.83%）的页岩样品。通过低温液氮实验对样品进行孔隙表征,并依据FHH分形模型,计算了不同成熟度页岩孔隙分形特征。结果表明：随着成熟度的增大,页岩孔容呈现＂减小—增大—减小＂的趋势,分界点在Ro=1.50%和Ro=2.50%左右,而孔隙分形维数D与孔容变化趋势相反,呈现＂增大—减小—增大＂的趋势,这与压实减孔作用和有机质生烃过程中的增孔作用关系密切;不同成熟度页岩储层中,孔隙总比表面积与分形维数呈现正相关关系,而平均孔径与分形维数呈现出明显的负相关关系,这反映出储层孔隙分形维数越大,比表面粗糙性越强,可提供更多的吸附位置,更有利于页岩吸附气的存储。

12 shale samples of different maturity（Ro=1.10%-2.83%） from North China were selected to explore variation features of pore structure with the change of maturity. By low-temperature liquid nitrogen experiment and the FHH fractal model, the pore characteristics and the fractal features of the samples are analyzed respectively. The results show that with the increasing of maturity, the shale pore volume shows a decreasing-increasing-decreasing tendency, the demarcation points at Ro=1.50% and Ro=2.50% respectively; on the contrary, the dimensions of pore fractal（D） show an increasing-decreasing-increasing tendency. It is closely related to the compaction decreasing pore and the generation process of the organic hydrocarbon increasing pore. In shale reservoirs of different maturity, the total pore specific surface area is positively correlated with fractal dimension, and the average pore size is negatively correlated with fractal dimension. This reflects that as the pore fractal dimension of reservoir is greater, the specific surface roughness becomes stronger, which can provide more adsorption sites, and is conducive to the storage of adsorbed shale gas.