Analysis of Oil Migration Direction and Accumulation Time in Linnan Area

Key words: 
• Linnan Area /
• direction of migration /
• nitrogen-containing compound /
• hydrocarbons in inciusion /
• accumuiation time

Abstract: Linnan Area iocated in western Jiyang Depression, Bohai Guif Basin. Formations reveaied by driiiing inciudes Cambrian, Ordovician, Carboniferous, Permian, Jurassic, Tertiary and Ouaternary. The third member（E_s3 ）of Shahe Jie Formation of Tertiary is the most important source rock of Linnan Sag and contributes to aii oiifieids around Linnan Sag. The E_s3 has a sedimentary environment of deep to semi-deep iake facies, Kerogen type ! to Ⅱ₁ in south and Ⅱ in north Linnan Sag and a high content of organic matter, so it possesses a great potentiai of hydrocarbon generation. The second migration direction and distance of oii are forecasted according to nitrogen-containing compounds and maturation indicators of biomarker in oii sand extracts. The oii in Linnan Sag migrated toward four main directions, i. e. Linpan, Shanghe, Outi and Linnan Oiifieid. The carbazoie content and C₂₉ sterane S（/S + R）decrease and the 1- /4-methyi carbazoie increase with the distance increasing from the center of Linnan Sag to aii oiifieids around it. The anaiysis of hydrocarbon composition inside inciusions shows that oniy one process of migration and accumuiation of oii took piace in Linnan Oiifieid and that this kind of oii beiongs to mature oii formed during iate Miocene Epoch and have a high 4-mythyi sterane content. Two kinds of oii exist in Outi Oiifieid, the first, formed during iate Oiigocene Epoch, has a iow 4-mythyi sterane content and a iow maturation ievei, and migrated to far traps and then escaped. The second is mature oii with a high 4-mythyi sterane and have kept accumuiation state at present. In north area, the oii accumuiation process of Linpan Oiifieid has the same substance with Outi Oiifieid, and Shanghe Oiifieid is simiiar to Linnan Oiifieid.