鄂尔多斯盆地东缘含煤地层水动力条件及其控气作用

      鄂尔多斯盆地东缘南北跨度大，含煤地层水动力区域分布规律不明。基于含煤地层含水层分布及孔渗条件、煤层气
井产水量、产出水化学及同位素特征、煤层甲烷浓度等的分析，探讨了区内煤层气生成和富集的水动力条件控制作用。结
果显示，砂岩含水层北部较南部发育，北部孔渗条件好于南部；太原组灰岩含水层在三交-吉县地区最为发育，导致山西
组煤层含气量高于太原组；煤层气井产水量及产出水钙、镁离子含量北部高于南部，煤层含气量与矿化度呈正相关关系。
分析认为，该区含煤地层水动力条件在北部较南部活跃，北部地区的山西组水动力强于太原组，三交-吉县地区太原组水
动力强于山西组 ；在保德以南的中- 高煤阶区，地下水弱径流－滞留带有利于煤层气富集 ；在保德及其以北的中－低煤阶区，
较活跃的水动力条件和良好的封盖条件为次生生物气的生成和富集提供了关键条件。

Hydrodynamic Conditions and Their Controls of Gas in Coal-bearing Strata in Eastern Edge of the Ordos Basin

The Eastern edge of the Ordos basin has a wide north-south span where the regional hydrodynamic conditions are still
unclear. Based on the data of the porosity, permeability, drilling water production, hydro-chemical and isotope composition and
coalbed methane (CBM) concentration, the control of the hydrodynamic condition to the CBM generation and accumulation in the
area was discussed. It was shown that the sandstone aquifers and their pores and permeability develop much well in north part of
the basin than in its south. Limestone aquifers in the Taiyuan Formation are most developed in the Sanjiao-Jixian area, resulting
in the higher CBM content of the Shanxi Formation than that of the Taiyuan Formation. Drilling water production and the calcium
and magnesium ion concentrations are higher in the north than in the south, and the water mineralization is positively correlated
to CBM content. It was indicated that the groundwater in the area is more active in the north than in the south. Hydrodynamic
condition in the north is stronger in the Shanxi Formation than in the Taiyuan Foramtion but it is opposite in the Sanjiao-Jixian
orea of the south. Weak run-off to stagnant groundwater in the middle and high coal-rank area located in the south of the Bode orea
is in favor of the CBM accumulation. Active groundwater and good cap-rocks in the low and middle coal-rank area in the north of
the Baode provide a key for the generation and accumulation of the secondary bio-gas.