鄂尔多斯盆地南部侏罗系煤层气成因探究

摘要

Exploration activities have proved that Jurassic Formation of South Ordos Basin has great potential of CBM (coalbed methane) ,to clarify the genetic type of the CBM can effectively guide the further exploration ,for this purpose ,the geologic characters of the formation ,the gas samples and stable isotope of the CBM were analyzed ,and the results show that theδ13CCH4 value of the shallow layers of Bin County ,Jiao-ping and Huangling area range between -81‰ ~ -57‰ ,the dry factors are mainly above 100 ,δDCH4 mostly distribute between-236‰ ~ -234‰ ,all the features above proved that the CBM is biogenesis gas ,and the reservoir of these area is characterized by low water salinity and relatively good penetration condition ,which is favorable for biogenesis gas’s generation .While for the deeper zone of He Shui-Ning County area ,theδ13 CCH4 value ranged from - 49‰ ~ - 35‰ ,the CBM dry factors are less than 100 ,which is typically thermogenic gas ,and also ,its formation water is not conducive to the generation of biogenic gas because of the high salinity and acidic property .%鄂尔多斯盆地南部侏罗系具有较好的煤层气勘探潜力，但煤层气成因有待深入研究，弄清楚其成因类型能够有效指导该区下一步勘探开发方向。基于区域地质条件、煤层气样品组分、稳定同位素等分析，对其成因进行了探讨。结果表明，研究区浅部的彬县、焦坪、黄陵地区煤层气δ13 CCH4一般介于－81‰～－57‰，煤层气干燥系数一般大于100，δDCH4一般介于－236‰～－234‰，煤层气为晚期生物成因，同时，地层水矿化度低，煤岩孔隙度较高，渗透性较好，具备生物气生成的地质条件；深部合水-宁县地区煤层气δ13 CCH4一般介于－49‰～－35‰，煤层气干燥系数一般小于100，是典型的热成因气，地层水矿化度高，呈酸性，不利于生物气的生成。