陆相湖盆页岩层系基本地质特征与页岩油勘探突破——以渤海湾盆地沧东凹陷古近系孔店组二段一亚段为例

Geological characteristics of shale rock system and shale oil exploration in a lacustrine basin:A case study from the Paleogene 1st sub-member of Kong 2 Member in Cangdong sag,Bohai Bay Basin,China

基于2口井140 m连续岩心观察及上千余块次样品测试数据,应用非常规油气地质理论,对渤海湾盆地沧东凹陷古近系孔店组二段一亚段(Ek_2~1)细粒页岩层系基本石油地质特征进行系统分析。研究表明,页岩层系发育长英质页岩、灰云质页岩与碳酸盐岩3种岩类,组合形成互层状集合体;相对稳定的封闭环境下发育优质烃源岩,为页岩油富集奠定了物质基础;方沸石粒间孔、白云石晶间孔及层间微裂缝使致密碳酸盐岩、灰云质页岩、长英质页岩成为有效储集层,其中脆性矿物含量大于70%;Ek_2~1下部高丰度纹层状页岩层系为页岩油富集层段,累计厚度70 m,埋藏深度2 800~4 200 m,平均含油饱和度50%,甜点分布面积达260 km^2,预测资源量过5×10~8 t,是沧东凹陷孔店组石油勘探的重要接替领域。目前KN9页岩油直井改造后2 mm油嘴日产油29.6 t,水平井体积压裂正在实施,有望在中国东部实现陆相页岩油的勘探重大突破。

A deep understanding of the basic geologic characteristics of the fine-grained shale layers in the Paleogene 1 st sub-member of Kong 2 Member（Ek2^1） in Cangdong sag,Bohai Bay Basin,is achieved through observation of 140 m continuous cores and systematic analysis of over 1 000 core samples from two wells.Basic geological conditions for shale oil accumulation are proposed based on the unconventional geological theory of oil and gas.The shale rock system mainly developed interbedded formation of felsic shale,limy and dolomite shale and carbonates; high quality hydrocarbon source rock formed in the stable and closed environment is the material base for shale oil enrichment; intergranular pores in analcite,intercrystalline pores in dolomite and interlayer micro-fractures make tight carbonate,limy and dolomite shale and felsic shale effective reservoirs,with brittle mineral content of more than 70%; high abundance laminated shale rock in the lower section of Ek2^1 is rich in shale oil,with a total thickness of 70 m,burial depth between 2 800 to 4 200 m,an average oil saturation of 50%,a sweet spot area of 260 km^2 and predicted resources of over 5×10^8 t.Therefore,this area is a key replacement domain for oil exploration in the Kongdian Formation of the Cangdong sag.At present,the KN9 vertical well has a daily oil production of 29.6 t after fracturing with a 2 mm choke.A breakthrough of continental shale oil exploration in a lacustrine basin is expected to be achieved by volume fracturing in horizontal wells.