青海聚乎更矿区煤层气富集条件

CBM Enrichment Conditions in Juhugeng Mine Area,Qinghai

青海聚乎更矿区是世界上首次在中低纬度冻土区发现天然气水合物的地区,并且天然气水合物的气源是该矿区的煤层气。矿区主要含煤地层为中侏罗统的木里组,煤层厚度大、变质程度一般在气煤~焦煤,镜质组质量分数普遍较高（60%~80%）,煤层结构简单-较复杂,煤储层微观结构以小孔和微孔为主,割理裂隙发育。等温吸附实验结果表明,该区兰氏体积偏低,而压力偏高,储层吸附特性为中-好级别,顶底板封闭性好,地下水活动弱,有利于煤层气的形成与赋存。区内煤层下1煤含气量在0.05~5.52m3/t,下2煤在0.05~11.14m3/t,含气量普遍偏低可能与后期构造使得煤层埋深变浅导致储层压力降低、煤层甲烷大量解吸有关,此外,向斜两翼地层倾角大,也是造成矿区煤层气逸散的主要因素之一,但是在向斜转折部位及矿区深部,煤层气相对富集,是今后勘探开发重点研究区域。

The Juhugeng mine area in Qinghai is the area the natural gas hydrate has been found in medium to low altitude permafrost area firstly in the world, while the hydrate origin is the CBM in the mine area. Main coal-bearing strata in mine area belong to Middle Jurassic Series Muri Formation. Coal seams are thick, coal rank is generally from gas coal to coking coal, vitrinite mass fraction is generally higher （60%~80%）, coal seam texture simple to rather complex, microstructure of coal reservoir is mainly tiny pores and micropores, with developed cleats. Isothermal adsorption tests have demonstrated that coal in the area has Langmuir volume on the low side, while pressure on high side, reservoir adsorptive property is medium to good, good roof closure, weak groundwater activity, thus in favor of CBM formation and preservation. Gas content of L1 coal seam is 0.05-5.52m3/t, L2 coal seam 0.05-11.14m3/t, thus on the low side at large, succeeding structures may cause coal buried depth shallower and make reservoir pressure lowering down and large amount coal bed methane desorbed. Besides, large strata dip angle of two limbs of syncline is also one of major factors caused mine area CBM dissipation; but in syncline hinge region and mine area deep part, CBM is relatively enriched, thus the primary study areas in further exploration and exploitation.