陕西镇坪县钟宝断裂周缘下寒武统牛蹄塘组页岩气成藏条件浅析

Analysis of the shale gas formation conditions in the Lower Cambrian Niushutang Formation at the periphery of the Zhongbao Fracture in Zhenping County,Shaanxi,China.

陕南地区下古生界富有机质页岩层系较多,是页岩气勘查的有利地区。镇坪县钟宝断裂周缘下寒武统牛蹄塘组黑色页岩厚度大,分布稳定,以Ⅰ型干酪根为主,有机碳(TOC)分布在1.27%-11.72%,平均3.42%,有机质丰度高;镜质体反射率(Ro) 2.48-3.48%,平均3.18%,处于过成熟阶段,生烃潜力好;其页岩储集空间丰富,脆性矿物含量高,利于压裂储层改造。ZBDR01井发现了良好的油气显示,排水测试点火成功,火焰高度2-3m,气体来源分析表明为海相油型裂解气,成熟度较高;综合地质研究初步判断为牛蹄塘组烃源岩。揭示陕西安康南部地区具有较好的页岩气成藏条件,结合二维地震资料解释成果,初步圈定下寒武统牛蹄塘组有利区面积约100平方公里。

The organic-rich shale layer system present in the Lower Paleozoic period was more prevalent in southern Shaanxi,which is a prime location for shale gas exploration.The black shale of the Lower Cambrian Niutitang Formation at the Zhongbao Fracture periphery in Zhenping County has a substantial thickness and even distribution,and is dominated by type I kerogen.The distribution of organic carbon ranged from 1.27% to 11.72%,with an average of 3.42%,indicating a high abundance of organic matter.The reflectance of vitrinite in the shale ranges from 2.48-3.48%,with an average of 3.18%,which is in the over-mature stage with good potential for hydrocarbon production.Shale reservoirs possess ample storage space and a high content of brittle minerals,which are favorable for fracturing and reservoir transformation.The ZBDR01 well showed good oil and gas display,successful drainage test ignition,and a flame height of 2-3 m.Gas source analysis indicates that it is a marine oil-type cracked gas with high maturity.Preliminary geological studies suggest that it is the hydrocarbon source rock of the Niutitang Formation,indicating that the Ankang area of Shaanxi has favorable shale gas formation conditions.The 2D seismic data interpretation results show that the preliminary area of the favorable zone in the Lower Cambrian Niutitang Formation was approximately 102 square kilometers.