扬子克拉通西北缘震旦系油气成藏条件及勘探潜力

Sinian hydrocarbon accumulation conditions and exploration potential at the northwest margin of the Yangtze region,China

基于露头、钻井、测井和地震资料,对扬子克拉通西北缘超深层震旦系灯影组成藏条件、成藏模式与勘探潜力进行系统研究。结果表明:①扬子克拉通西北缘震旦纪—早寒武世早期为克拉通裂陷阶段,表现为同沉积断裂发育与裂陷快速沉降,沉积分异显著,裂陷两侧灯影组发育大型台缘带;②震旦系—寒武系发育陡山沱组与麦地坪组—筇竹寺组两套优质烃源岩,其中后者厚度为150~600 m,生烃强度为(100~200)×10^(8) m^(3)/km^(2);③震旦系灯影组断控台缘带丘滩体厚度大且成排成带分布,受同生期—准同生期和表生期岩溶作用叠加改造,形成厚度为200~400 m的孔洞型储集层;④两套烃源岩主生油期在二叠纪—早三叠世,石油近距离运移至灯影组丘滩体岩性圈闭中聚集形成规模巨大的古油藏群;晚三叠世—侏罗纪古油藏裂解成气,奠定现今天然气藏基础;⑤灯影组台缘带丘滩体与两套优质烃源岩形成多种有利源储配置关系,具备近源高效成藏的条件,可形成大型岩性气藏群。绵阳—剑阁地区是潜在的万亿立方米储量规模大气区,位于该区域的老关庙构造灯影组二段丘滩体面积约1300 km2,是近期超深层勘探值得探索的目标。

Based on outcrop,drilling,logging and seismic data,the reservoir forming conditions,reservoir forming model and exploration potential of the ultra-deep Sinian Dengying Formation at the northwest margin of Yangtze region were examined.(1)This area is in craton rifting stage from Sinian to Early Cambrian,characterized by syn-sedimentary faults and rapid subsidence,significant sedimentary differences,and development of Dengying Formation platform margins on both sides of the rift.(2)The Sinian–Cambrian in this area has two sets of high-quality source rocks,Doushantuo Formation and Maidiping-Qiongzhusi Formation;of which,the latter has a thickness of 150–600 m and hydrocarbon generation intensity of(100~200)×10^(8) m^(3)/km^(2).(3)The mounds and shoals in the platform margin of Sinian Dengying Formation controlled by faults are thick and distributed in rows and zones;they are reformed by contemporaneous–quasi-contemporaneous and supergene karstification jointly,they become pore-type reservoir with a thickness of 200-400 m.(4)The two sets of source rocks enter oil generation windows from Permian to Early Triassic,and the oil migrates a short distance to the lithologic traps of mounds and shoals to form a huge scale paleo-oil reservoir group;from Late Triassic to Jurassic,the oil in the paleo-oil reservoirs is cracked into gas,laying the foundation of present natural gas reservoirs.(5)The mound-shoal body at the platform margin of Dengying Formation and the two sets of high-quality source rocks combine into several types of favorable source-reservoir combinations,which,with the advantage of near source rock,can form large lithologic gas reservoirs.The Mianyang-Jiange area is a potential large gas field with trillion cubic meters of reserves.According to seismic prediction,the Laoguanmiao structure in this area has the Deng-2 Member mound-shoal reservoir of about 1300 km2,making it a ultra-deep target worthy of exploration in the near future.