高煤阶煤岩孔隙结构分形特征研究

The Fractal Feature of the Pore Structure for High Coal Rank Coal Porous Media

分形理论为定量描述储层非均质性提供了重要的手段,而煤层具有独特的孔隙-裂隙双重孔隙,其是否具有分形特征以及如何表征其分形特征亟待进行深入的研究。通过借鉴砂岩分形特征研究和分形维数计算的方法,对沁水盆地南部5块煤样压汞曲线进行了研究。结果表明,所研究煤样孔隙结构具有分段分形特征,具有孔隙半径r<0.1μm,0.1μm<r<10μm和r>10μm三个分形区间。据此,可将研究区块煤岩孔隙按大小分为三类:小孔和微孔(r<0.1μm)、中孔和大孔(0.1μm<r<10μm)和割理(r>10μm)。从整体趋势上看,对于不同煤样,分形维数越大,其孔隙度、渗透率越小,孔隙分选性越差,非均质性越强;对于同一煤样在不同分形区间中的分形维数越大,其孔隙半径在该区间内的分选性越差,即非均质性越强。

An effective way to describe the heterogeneity of pore structure quantitatively is provided by fractal theory,and the special pore-cleat dual-pore structure of coal rock makes iturgent to research further whether coal rock bears fractal feature and how to describe it. Using the present fractal feature research way and the fraetal dimensions calculation way of sandstone as reference, mereury injection curvesof five pieces of coal porous media are carefully studied. The results show that the coal porous media bears fraetal features in three separate zones, r〈0.1 μm,0.1μ m〈r〈（10μm and r〉10μm. And for each zone, these pores are micro pores and small pores, middle pores and big pores and cleat （r 〈 10 μm）correspondingly. In general trend, the greater the fraetal dimension is, the smaller the values of porosity and permeability and the worse the sorting and heterogeneity features of pores are. For different radius zones of a certain sample, the greater the fractal dimension is, the greater the heterogeneity of its pore radiusis.