| Taking the Wen'an slope zone of Ba County sag of Bohai bay basin as the target area,with the comprehensive utilization of sedimentology and high-resolution sequence stratigraphy and seismic lithologic prediction and numerical simulation technology,reservoir geology and other disciplines,the macro development characteristics of the sandstone conducting bed,sandbody hydraulic connectivity,micro development characteristics and the accommodation of conduit fault on lateral migration of oil and gas are studied in this paper on the basis of the determination of the type of oil and gas transportation systems and the division of sandstone conducting layer.Combined with the structure features,hydrocarbon source rock and caprock development characteristics,the fault sealing ability and other research achievements,this paper depicts the dominant migration pathways and studies hydrocarbon migration type of sandstone conduit layer controlling hydrocarbon accumulation with the method of comprehensive numerical simulation of oil and gas migration.At first,types of oil and gas transportation system is determined on the basis of hydrocarbon source comparision from the perspective of space match of trap and source rock in the formation reservoir period.It is indicated that there is mainly lateral migration in this area,which fault palyed the role of adjust in vertical and seal in lateral and the unconformity helps on short distance migration and sealing for accumulation.Therefore,the primary transportation system is sandstone.According to the definition of a conduction layer of sandstone by Xiaorong Luo,the middle layer of Es1 Formation(Hereinafter referred to as Es1 Formation conduit layer)and the Es2 Formation are main sandstone conduction layer in Palaeogene of this area by the study of caprock development characteristics and sedimentary origin and development characteristics of sandbody.Secondly,the sandbody development characteristics and its connection of two sandstone conduction layer are studied by field observations,the 3D seismic,well logging,mud logging,core,mercury injection,casting body slice,oil test and other oil field exploration data and lots of exploitation dynamic data.At macro level,these two conduit layers developed fan delta and river delta deposits.Sandstone thickness mainly is between 10 m and 50 m and sand-layer ratio is mainly between 0.2 and 0.8,which the closer to the provenance,there is more sandbody.At micro level,the property of Es2 Formation sandstone conduit layer is mainly medium porosity and low permeability accounts for much.The property of Es1 Formation sandstone conduit layer is mainly medium porosity and medium permeability.It is showed by thesandbody connection that different area and layers are effected by various geological factors so that lower limit sand-layer ratio of hydraulic connectivity of sandbody is different.The lower limit sand-layer ratio of hydraulic connectivity(C0)and large area connectivity(C)of Es2 Formation sandstone conduit layer in Wen'an slope area are 0.23 and 0.25 and those of Es1 are 0.25 and 0.61.Es2 Formation sandstone conduit layer has a larger distribution range of connectivity sandbody.Besides,fault active stages,fault system division and oil and gas vertical adjustment area were studied on the basis of fault geometry characteristicresearch.According to the previous study on accumulation period of Wen'an slope area,it is indicated that middle strike-slip stretching-late extension torsional fault,early stretching-middle strike-slip stretching-late extension torsional fault,late extension torsional fault in the middle and out of the area are vertical migration faults in this area,which make oil and gas transport from lateral to vertical adjustment in sandstone conduit layer.At last,the model of structure,source rock and connected sandbody were built up with the addition of fault lateral sealing ability,cap rock evaluation result,HI,PWD and SWIT conditions.By the 3D comprehensive numerical simulation of oil and gas migration with suitable thermal history,hydrocarbon generation history,hydrocarbon expulsion history and secondary migration history simulation method,the dominant pathways were depicted of oil and gas lateral migration.On this basis above and according to different sandbody layers of hydrocarbon lateral migration,the lateral migration of oil and gas can be divided into fault aside sandbody type and path changing fault aside sandbody type.The control on hydrocarbon accumulation of sandstone conduction layer have three points:(1)The hydrocarbon reservoirs distribution in plane is controlled by the dominant transportation pathway of fault aside connecting sandstone conduction layer;(2)The layer of hydrocarbon reservoirs distribution is controlled by sandstone conduction layer;(3)The period of large amount of oil and gas is controlled by the time match of the sandstone conduit layer,fault activity period and expelling hydrocarbon period. |
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