Sandstone And Unconformity Transportation System And Its Influence On Petroleum Migration And Accumulation In Pengyang Area

The hydrocarbon supply center in Pengyang area is located beside the east of the study area.The petroleum derived from hydrocarbon kitchens moved vertically or laterally and accumulated in the entrapment of Yan'an Formation which is far from the hydrocarbon supply center,resulting in a consequence that the distribution pattern of the oil reservoirs is unclear.As transportation system is the channel that connects hydrocarbon kitchens and entrapments,research on the capacity of the transportation system is an accurate and intuitive method to know the distribution pattern of petroleum and predict the position and formation of petroleum.First and foremost,based on the burial history of the research area,the critical period of Yan'an Formation was determined by fluid inclusion microthermometry.As the critical period was determined,research on the capacity of sandbody and unconformity was carried out.Finally,after the dominant migration paths in critical period were determined by numerical simulation technology,the accuracy of the simulation results were verified in various methods.Study on sandstone transportation capacity,the distribution of sandstone transporting layer was clarified by the macro distribution features of sandbody.After that,on the basis of diagenesis,in combination with the characteristics of the today's porosity and permeability of the sandstone pathway system,the porosity and permeability in the critical period were reconstructed through seizing the main factors that changed the porosity and permeability.Meanwhile,model of sandstone fluid connectivity were built to evaluate the connectivity of sandstone transportation system.And then,the transportation capacity of sandstone transporting layer was evaluated by the physical characteristics and connectivity of sandstone.In the research on the capacity of unconformity,based on well logging data,the configurations between macro straigraphic contact relationships and micro lithologic combinations of the unconformity were adopted together with the permeability of unconformity transportation layers to evaluate the transportation capacity.With Petro Mod software,comprehensive numerical modeling of the paths that petroleum moved were realized.A 3D transportation framework model was established by the grid data obtained from quantitative evaluation after the top paleostructure of the transporting layer was recovered.Finally,the accuracy of the simulation results were verified by the variable features of petroleum physical characteristics,characteristics of carbazole compounds in crude oil,QGF/QGF-E and the production data.The study suggests that a large amount of oil was injected in the late Early Cretaceous.The connectivity study shows that sandstone transporting layers were connected in large area when the ratio of sand and formation is greater than 0.5.The diagenesis in the research area is strong enough to reach phase B of mesogenetic stage while the critical period physical characteristics are better than the current physical characteristics.The comprehensive transportation capability of the sandstone transporting layer indicates that Yan'an 8^th formation has the best transportation capability,followed by Yan'an 7^thfomation,Yan'an 9^th fomation,Yan'an 10^th fomation,while Yan'an 6^th fomation has the worst transportation capability.There are five vertical lithological associations and four vertical straigraphic contact relationships developed in the unconformity.The unconformity transporfting capacity in critical period shows that there are three preferential unconformity pathways from south to north.The comprehensive numerical simulation results of oil and gas indicate that petroleum from the hydrocarbon kitchens moved vertically or laterally via composite transporting layer,and accumulated at high tectonic positions.The validation results of migration paths show that with the increase of migration distance,the density and viscosity of oil increases while the gas oil ratio decreases in Z339-Z157,Z99-Y185 and Z533-M30 sections.Yan'an 8th formation of well Y116 and well Z188 was determined as an old oil layer or a petroleum migration pathway.Meanwhlie,the petroleum was determined to migrate from the source rock area which located beside the east of the study area along the Tianchi Yanwu direction through the non hydrocarbon compounds in the crude oil.Furthermore,Yan'an 7th formation of Z430reservoir was accurately predicted by simulation results while the matching degree between simulation results and production data is more than 80%in the study area.Therefore,based on the variable features of petroleum physical characteristics,organic geochemical tracers and production data,the simulation accuracy of the petroleum pathway was verified.Generally speaking,the location of oil accumulation was affected by the distribution of dominant transporting system.Meanwhile,the fomation of oil accumulation was affected by the developing degree and vertical configuration relationship of the transportation system.