Hydrocarbon-Source Correlation & Reservoir Formation And Evolution Of Marine Strata In Jianghan Plain Area

The marine strata were divided into five main hydrocarbon plays based on the analysis of hydrocarbon accumulation basic conditions.Through the characteristics of biological maker of organic material and bitumen in reseroivs,oil source could be identified.The thermal evolution history of the source rock of typical structures is recovered using the Easy % Ro(vitrinite reflectance) chemical kinetics model.Combined with the structural evolution history, the formation and evolution process of oil and gas accumulation of typical structures was analysed.Finally the thesis summarizes the key controlling factors of oil and gas accumulation,points out the favor accumulation areas.The main achievement of this thesis is as follows:(1)According to the characteristics of hydrocarbon source rocks,reservoirs and cap rocks from Sinian to Jurassic,five main hydrocarbon plays , named I,II,III,IV,V hydrocarbon play respectively which include Doushantuo Formation of Upper Sinian to Tianheban Formation of Lower Cambrian(Z2ds-∈1t),Shuijingtuo Formation of Lower Cambrian to Qinjiamiao Formation of Middle Cambrian(∈1t-∈2q), Qinjiamiao Formation of Middle Cambrian to Longmaxi Formation of Lower Silurian(∈2q–S1lO),Wufeng Formation of Upper Ordovician to Qixia Formation of Lower Permian(O2w–P1q),Qixia Formation of Lower Permian to Jurassic could be divided respectively.(2)Oil seepage or organic material in Permian or Triassic reservoirs came from Permian source rocks.Organic material in Carboniferous or Devonian came from Permian and Silurian source rocks.Bitumen in Silurian reservoirs came from Lower Cambrian and Silurian source rocks; Bitumen in Ordovician reservoirs came from Ordovician source rocks.Oil seepage in Jurassic gritrock reservoirs possibly came from the underlying Jurassic or the underlying others strara.It impossibly came from the Permian or its underlying strara(3) The formation and evolution process of oil and gas accumulation in Jianghan plain maily experienced some stages as follow:①The late Indosinian.Indosinian movement caused some small scale folds.Oil and gas accumulated in the palaeohigh area;②The Early Yanshanian.Burial depth of marine strata in folded doming-up areas became obviously shallow,or the marine strara exposed to the surface.The Lower Paleozoic exposed to the surface in varying degrees in some areas.The paleo-reserviors in marine strata has been a large degree of damage.However,the preservation conditions were still well of marine strata in the areas where the denudation thickness of Middle Triassic-Jurassic was small.③The late Yanshanian-The Early Himalayan.The faults unsealed in those areas where were affected by regional extensional stress.Oil and gas escaped along faults toward the earth surface substantially.The paleo-reserviors in marine strata were destroyed fatally;④The late Himalayan-Nowadays.No violent tectonic and breaking movements have occurred in this stage.The sealing property of all marine strara was relatively superior today.However, all source rocks had lost capacity of secondary hydrocarbon generation owing to the past of oil/gas generation fastigium.(4) Key controlling factors of oil and gas accumulation:①the effect of uplift and denudation,it mainly refers to the effect of violent fold, uplift, denudation in yanshanian.Burial depth of marine strata in folded doming-up region became obviously shallow and the marine strara exposed to the surface,even in some areas the lower Paleozoic was exposed to the surface in varying degrees;②The movement of fracture. The damaging effects on oil and gas reservoirs are relatively slight.The strara of some areas substantially breached the earth surface caused by faults in Yanshanian,and then they suffered intense denudation and leached by atmospheric water.Under the tectonic background of regional extension,faults remained opening in late Yansahnian-early Himalayan,and a large number of normal faults developed.The preservation conditions of marine strara where those faults well developed were destroied.③The space-time configuration of oil and gas accumulation did not match,mainly refers to the carboniferous-Lower Triassic petroleum system.The hydrocarbon source rocks in silurian and Permian is at the stage of hydrocarbon generation fastigium in late Yanshanian-early Himalayan.Under the tectonic background of regional extension,faults remained opening. Accordingly,oil and gas both in paleo-reservoir and generated by source rocks escaped along fault toward the earth surface substantially.Though the preservation conditions has been improved between late Himalayan to nowadays,all source rocks had lost capacity of secondary hydrocarbon generation owing to the past of oil/gas generation fastigium.(5) Yichuang inactive belt was a tectonic triangle belt,which was confined with Dahong mountain arc tectonic belt in the north,Bamian mountain-Damo mountain arc tectonic belt in the south,and Huangling lift in the west.Under the three directions confinements,the compression that was affected by the hedge to this area was weak. And in this area, the structure was stable,the fold was rolling and the fracture was not developed.Since Indosinian, the main structure in this area is overall elevating movement.So Yichuang inactive belt is the favor exploration area in Jianghan Plain.