Oil Accumulation Mechanism Of Fuyang Oil Layer Inside And Outside Source Rocks Of Sanzhao Depression

This paper mainly discusses mechanism and process of oil migration, period and models of oil accumulation and main controlling factors of oil accumulation in Fuyang oil layer in and around Sanzhao Depression, Songliao Basin, and finally predicts the favorable regions for oil accumulation.Statistics of oil physical property, analysis of oil group composition and total hydrocarbon chromatogram, relationship between Pr/nC17 and depth, Ph/nC18 and depth, Pr/Ph and depth and relationship between Pr/nC17 and Ph/nC18 of Fuyang oil layer in Sanzhao Depression, Shangjia area, southern Songzhan and Changshi block show oil in these areas is from the same source-source rocks of Qingyi member in Sanzhao Depression. Development and distribution of source rocks and indexes of geochemistry indicate source rocks of Qingyi member in Sanzhao Depression can provide sufficient oil for Fuyang oil layer.Synthesizing studies of development features and activity period of faults and relationship between faults and source rocks of Qingyi member or reservoirs of Fuyang oil layer, we carry out source fault separation in Fuyang oil layer and draw that faults during depression period (â…¡type) and faults formed in downfaulted period and still active during depression period(â… toâ…¡type) are main source faults in Fuyang oil layer. We draw there exist two oil migration mechanisms of Fuyang oil layer, inside and outside source rocks, on the basis of researches on faults and types of sandbody migration pathway, of which are oil generated by source rocks of Qingyi member laterally migrated a short distance to form oil reservoirs after downward migrated to Fuyang oil layer, under the influence of paleo-hyperpressure; and oil yielded by source rocks of Qingyi member laterally moved to Fuyang oil layer under the action of buoyancy after source rocks of Qingyi member connected with Fuyang oil layer because source rocks were faulted by faults.Oil migration mechanism outside source rocks is oil generated by Qingyi member laterally migrated to high area of structures outside source rocks from Sanzhao Depression along sandbody-fault matching, as Fuyang oil layer in Shangjia and Songzhan region; or laterally migrated to high area of structures outside source rocks along fault-sandbody matching, as Changshi block, after oil down migrated or laterally migrated to Fuyang oil layer because of lateral connection of source rocks and Fuyang oil layer.Main controlling factors of oil accumulation of Fuyang oil layer inside and outside source rocks, based on migration mechanism of Fuyang oil layer inside and outside source rocks of Sanzhao Depression show oil accumulation inside source rocks is dominated by down-migration extension of oil of Qingyi member, fault concentrated zones and horst matched by faults and sandbody, while oil accumulation outside source rocks mainly commandeered by distance from source rocks, oil migration pathways and development of sandbody in traps.The two models of oil accumulation inside source rocks are as follows. First, on the condition that fault traps of Fuyang oil layer are directly under source rocks of Qingyi member and linked by T2 source faults, oil produced by Qingyi member directly down migrated to fault traps in Fuyang oil layer under the action of hyperpressure along T2 source faults, which can form reservoirs without long-distance migration along sandbody. Second, if there are lots of T2 faults between source rocks of Qingyi member and oil layer of Fuyang oil layer, the faults will stagger source rocks and link source rocks and oil layer, and then, oil will laterally migrate to and accumulate in Fuyang oil layer, laterally linked to source rocks of Qingyi member, by buoyancy. Oil accumulation model outside source rocks is oil generated by source rocks of Qingyi member laterally migrated to traps in high structure area outside source rocks to form reservoirs under the action of buoyancy along sandbody connected by faults or faults connected by sandbody after oil down migrated under the influence of paleo hyperpressure or laterally transported because of lateral connection to Fuyang oil layer. We predict favorable targets for oil accumulation of Fuyang oil layer in Sanzhao Depression, Shangjia region, songzhan area and Changshi block, on the basis of the above studies, and conclude 47 evaluation targets.Favorable exploring areas of Shangjia region are three ofâ… type and five ofâ…¡type, while which of Songzhan are four ofâ… type, six ofâ…¡type and three ofâ…¢type, that of Changshi block are totally eight.