宁武盆地南部煤层气富集的主控因素

Major controlling factors of coalbed methane enrichment in the southern Ningwu Basin

宁武盆地是我国典型的中煤阶构造残余盆地,勘探证实其南部具有很好的煤层气勘探潜力,但煤层气富集的主控因素尚不清楚。为此,分析了盆地南部主要含煤地层的沉积环境、煤质特征、热演化程度与煤阶分布、煤储层物性等地质特征,通过构造特征、地应力分布特征、封盖条件分析,结合前期勘探成果,综合研究后认为:宁武盆地南部煤层气的富集受构造部位、应力场以及煤层顶底板封闭条件控制,构造上斜坡带煤层气富集高产,构造应力场低值区煤层渗透性好,封闭条件好的地区煤层气保存条件好。进而预测出W02井以东、W04井以南地区具有获得高产煤层气井的有利条件,是有利的煤层气富集区。

The Ningwu Basin is a typical relic structural basin containing coals with moderate coal rank.Although exploration has proved the coalbed methane (CBM) potential in its southern part,the major controlling factors of CBM enrichment are still unclear.For this reason,we analyzed various geologic features of coal-bearing strata in the southern part of this basin,such as sedimentary environment,coal quality,thermal maturity,coal-rank distribution and physical properties of coal reservoirs.Based on analysis of the structural features,earth stress distribution features and sealing conditions and in combination with previous exploration results,the following conclusions are obtained.The enrichment of CBM in the southern Ningwu Basin is controlled by structural location,stress field and sealing conditions of the top and bottom coal-seam.The upside structural slope is prolific.Coal layer permeability is relatively high in low-value area of the tectonic stress field.Coal layers in the area with good sealing conditions are favorable for the preservation of CBM.It is predicted that a CBM play exists in the area to the east of the well WO2 and to the south of the well WO4,where conditions are favorable for CBM enrichment.