煤层气的封存与富集条件

在水文地质条件简单的地区,煤层气的封存主要取决于煤层气富集区的构造及盖层岩性。通常情况下,压性断层可使煤层甲烷增多,张性断层使其降低。但在远离张性断层面的两侧,一般形成两个对称的平行条带状构造应力高压区,使得煤层甲烷含量相对升高,成为阻止煤层甲烷进一步向断层运移的天然屏障。背斜构造的中和面以上及向斜构造的中和面以下常会出现煤层甲烷的富集。依据煤层气盖层的排驱压力、渗透率等值,盖层可分为屏蔽层、半屏蔽层和透气层,它们在不同的构造发育区,其封盖性能不同,由此可划分出9类不同的构造封盖层岩性组合类型。平顶山矿区的实例分析表明:Ⅰ类组合煤层气含气性最好,其次为Ⅱ类、Ⅳ类、Ⅴ类,其它类型含气性最差。

CONDITIONS OF SEALING AND ACCUMULATION IN COAL BED GAS

In places with simple hydrogeological conditions,the sealing of coal bed gas is mainly determined by geological structures and cap rock lithologic propertices.In general,compressional fault could increase the content of coal-bed methane while tensional fault would decrease the content of coal bed methane.Symmetric high stress zones in parallel stripped shape would usually form in two sides far off the fault,thus causing the increase of coal bed methane content,and forming a natural curtain to block methane migration to the fault.Coal bed methane accumulation would occure above the balancing surface of anticlines and below the balancing surface of syncline.According to their expulsive pressure and permeability,the cap rocks of coal-bed methane could be divided into shielding bed,semi-shielding bed and permeable bed,which in turn could be subdivided into 9 types of lithologic assemblages.Examples of Pingdingshan coal dristrict show that,tpye-Ⅰ assemblage is more favourable for coal-bed gas;type-Ⅱ,type-Ⅳ and tpye-Ⅴ assemblages are secondany;the rest are poor.