鄂尔多斯盆地紫金山地区煤孔隙分形规律及其主控地质因素分析

The Fractal Regularity of Coal Porosity and Its Controlling Geological Factors in Zijinshan Area

通过对鄂尔多斯盆地东北缘紫金山地区气-肥煤样的孔隙结构测试,在重点阐述主煤层孔隙发育特征及分形规律的基础上,分析其主控地质因素,并挖掘了分维特征所暗示的煤层气可采潜力信息。结果表明:紫金山地区煤孔隙率整体偏低,孔隙结构以微孔为主,过渡孔与大孔次之,中孔最少,其中微孔孔容及孔比表面积贡献率最大,反映主煤层有利于煤层气的储集。基于压汞曲线将本区煤孔隙划分三种类型,结合压汞参数分析,指出8+9~#煤开放孔较多、孔喉分布比较集中且相对较大,比4+5~#煤更有利于煤层气渗流。基于压汞数据分形分析,将研究区煤样吸附孔与渗流孔界限确定为100 nm。孔隙分形特征受变质程度影响较大,4+5~#煤以深成变质作用为主,8+9~#煤则受到相对较强的区域岩浆热变质作用。其中深成变质作用有利于煤吸附能力的增加,而区域岩浆变质作用能够有效的改善煤孔隙结构,增强孔隙连通性,提高煤层的解吸、扩散、渗流能力。此外,分形特征还受灰分产率与煤岩组分的影响。结合含气性等参数分析,在资源量相近时,8+9~#煤具有较高的可采性。

Through the pore structure test of gas-fat coal from Zijinshan area in Eastern Ordos Basin, the main geological factors are analyzed and coalbed methane potential information implied by fractal dimension is suggested on the basis of describing the development characteristics and fractal law of the main coal seam. The results show that the porosity of coal is low in Zijinshan area The pore structure is mainly composed of micropores, macropores and transition pores take the second places, and mesopores are the least. Microporous had the most contribution rate to pore volume and specific surface area, reflecting that the main coal seam is beneficial to adsorbent CBM. There are three types of coal pores in the study area based on the analysis of mercury injection curve, combined with mercury injection parameters analyzing. No. 8 ＋9# has more open holes, and its pore throat distribution is relatively concentrated and relatively large, and hence it is more conducive to coalbed methane seepage than No. 4 ＋5#. The boundary of coal sample adsorption pore and seepage pore is determined as 100 nm in the study area based on the fractal analysis of mercury injection data. The fractal dimension of pore is greatly influenced by the degree of metamorphism, No. 4 ＋5# is mainly formed by deep metamorphism, No. 8 ＋ 9# is subjected to relatively strong regional magmatic thermal metamorphism. Deep metamorphism is beneficial to the increase of coal adsorption capacity. The regional magmatic metamorphism can effectively improve the structure of coal, enhance the connectivity of the pores and improve the desorption, diffusion and seepage capacity of coal seam. In addition, the fractal dimension is also influenced by the ash yield and coal macerals. Combined with the analysis of gas-bearing parameters, No. 8 ＋ 9# has a higher degree of recovery than No. 4 ＋5# coal when resources are similar.