苏北盆地古近系页岩油储层有效裂缝识别

Recognition of Effective Fractures Within the Oil Shale in the Fourth Member of Funing Formation in Northern Jiangsu Basin

为了查明苏北盆地古近系阜宁组四段(E_1f^4)裂缝型页岩油资源的富集规律,对钻孔岩芯所含裂缝进行了精细地观察与描述,对区内E_1f^4页岩基质和裂缝充填方解石进行了碳氧同位素测试、结合区域埋藏史、生烃史,总结了区内油页岩储层裂缝成因类型与特征,划分了裂缝形成期次并识别了有效裂缝。结果表明:研究区E_1f^4页岩裂缝可分为4种成因类型:平移式剪裂缝、正向剪切缝、逆向剪切缝和顺层缝;构造裂缝可分为5期次,其中,第Ⅰ期为平移式剪切缝,未见原油显示,形成于吴堡运动;第Ⅱ期为正向剪切缝,未见原油显示,形成于真武运动早期;第Ⅲ期为顺层缝,原油显示丰富,形成于三垛运动中期;第Ⅳ期为正向剪切缝,原油显示丰富,形成于三垛运动晚期;第Ⅴ期为逆向剪切缝,属压性缝,形成于三垛运动末期。第Ⅲ期和第Ⅳ期裂缝原油显示丰富,气测异常明显,为有效裂缝。

To investigate the distribution of shale oil in the fourth Member of Paleogene Funing Formation（F1f～4） in Northern Jiangsu Basin,the fractures contained in borehole cores were surveyed and describedin detail;the carbon and oxygen isotopes within shale matrix and filling calcite were determined,and with consideration of the burial history and hydrocarbon generation history,the genetic types of fractures and their features are summarized,the formation stages are divided and effective fractures are discerned.We conclude that the fractures in E1f～4 can be classified into four categories：strike-slip shear fracture,normal shear fracture,reverse shear fracture and bedding fracture;the development of fractures can be divided into five stages：on the first stage strike-slip shear fractures were formed in Wubao movement;on the second stage normal shear fractures were formed in early Zhenwu movement;on the third stage bedding fractures were formed in mid Sanduo movement;on the fourth stage normal shear fractures were formed in the late Sanduo movement and on the fifth stage reverse compressional shear fractures were formed in the end of Sanduo movement.Among these five stages,no oil occurs in the first,second and fifth stages of fractures while abundant oil appears in the third and fourth stages of fractures with obvious gas logging abnormality and therefore the third and fourth stages of fractures are effective ones for oil exploration.