下扬子地区宁国凹陷大隆组-孤峰组泥页岩储层特征

Characteristics of the Dalong and Gufeng Formation shale reservoirs in Ningguo depression, lower Yangtze Region, China

以皖宣页1井为对象,研究皖南宁国凹陷二叠系深水陆棚相黑色硅质页岩储层特征,探讨宁国凹陷二叠系页岩的成藏条件。对二叠系大隆组和孤峰组页岩开展有机地化特征、X射线衍射全岩矿物成分、含气性以及储层的测井响应特征等研究,结果表明:大隆组和孤峰组有机碳含量高,大隆组有机碳质量分数为1.71%～9.28%,平均为4.13%(29个样品),孤峰组有机碳质量分数平均为8.02%;有机质类型为Ⅱ_2-Ⅲ型;R_o值为1.23%～3.03%(大隆组平均为1.35%,孤峰组平均为2.83%);泥页岩中普遍发育原生矿物晶间孔、有机质孔等次生孔隙,以及微裂缝,内部孔隙连通性好,有利于页岩气的赋存;页岩内石英和黏土矿物等含量高,大隆组脆性矿物指数为37%～51%,孤峰组脆性矿物指数为71.8%～85.8%。宁国凹陷大隆组和孤峰组具备页岩气富集的基本条件,是勘探的有利区域。孤峰组在生烃条件、脆性矿物指数、含气性等方面都优于大隆组,应该是宁国凹陷的主探层位。

The drilling well of WXY1 in Ningguo Sag of south Anhui Province is studied in order to understand the characteristics of the Permian deep-water shelf facies black siliceous shale reservoir and discuss the formation conditions of the Permian shale reservoir. The study of organic geochemical characteristics, X-ray diffraction mineral composition, gas-bearing property and logging response characteristics of the Permian Dalong and Gufeng Formations shale shows that the organic carbon content of the Dalong and Gufeng Formations is high. In fact, the mass fraction of organic carbon of the Dalong Formation is 1.71%~9.28%(average 4.13%, 29 samples) and the average mass fraction of organic carbon of the Gufeng Formation is 8.02%, characteristic of Type Ⅱ2-Ⅲ organics. The Ro value of shale is in the range of 1.23%~3.03%, and the average Ro value of the Dalong Formation is 1.35%, and Gufeng Formation is 2.83%. Primary mineral intergranular pore, organic pore and micro-crack are well developed in shale, and the connectivity of internal pore is good for the occurrence of shale gas. Quartz and clay mineral contents are high in shale, with the brittle mineral index of 37%~51% for Dalong Formation, and 71.8%~85.8% for Gufeng Formation. It reveals that the Dalong Formation and Gufeng Formation in Ningguo depression possess the basic conditions for shale gas enrichment and are favorable targets for shale gas exploration. Comparatively speaking, Gufeng Formation is superior to Dalong Formation in terms of hydrocarbon generation conditions, brittle mineral index and gas content, and should be the main exploration horizon in Ningguo depression.