华北石炭—二叠系煤的孔渗特征及主控因素

Characteristics of Porosity and Permeability and Their Geological Control of Permo-Carboniferous Coals in North China

煤的低孔、低渗问题已经成为制约我国煤层气勘探和开发的关键问题之一。选取华北河东、渭北、阳泉、晋城、大同和两淮等6个煤田,通过煤岩学特征测试、微裂隙分析和低温氮孔隙结构分析,对该区煤的孔渗发育特征及其控制机理进行了系统研究。华北地区煤的孔隙度在2%～10%之间,孔隙度的大小主要受3次煤化作用跃变所控制,在Ro,r约为1.2%附近达到最小值。矿物充填作用在一定程度上降低了煤的孔隙度。华北地区煤的渗透率一般都在5×10-3μm2以下,渗透率与孔隙度呈显著的幂指数关系。无烟煤以微孔为主,孔隙度都在6%以下,渗透率的大小主要取决于裂隙的发育程度;而中低煤级煤的渗透率不仅受裂隙影响,也受煤中各级孔隙发育的影响较大。

The low porosity and low permeability of coal reservoirs have brought about a big problem for the exploration and exploitation of coalbed methane in China.Based on the coal proximate,coal maceral composition and low-temperature N2 adsorption analyses,microfracture analysis by fluorescence microscope,helium porosity and air permeability analyses,this study investigated the geological control of porosity and permeability of coals in Hedong,Weibei,Yangquan,Jincheng,Datong and Huainan-Huaibei coalfields.The results showed that coal porosity ranged from 2% to 10%,and strongly related to the coalification degree.The porosity reached a minimum value when Ro,r was about 1.2%.The filling and mineralization of pores by minerals were proven to decrease the coal porosity.Coal permeability is commonly less than 5×10-3μm2,and shows an exponential increment relationship with porosity.The anthracite porosity is commonly less than 6%,which dominated by the micro-and meso-pores porosity.The anthracite permeability mainly related to the development of micro-and macro-fractures,while the permeability of bituminous and sub-bituminous coals related not only to the fractures but also to the pores.