Characteristics And Main Controlling Factors Of The Oil And Gas Accumulation Of The Wulanhua Sag In Erlian Basin

WuLanhua sag is the main exploration sag in eastern Inner Mongolia in recent years This sag has good oil-source condition,develops various reservoir types and has complex faults and structure.There is a big difference in accumulation condition and main reservoir forming factor between the different structural belts.Based on the reservoir,structure,and oil source information,this paper analyses the reservoir forming conditions about clastic reservoir,igneous rock reservoir and ganite reservoir and finally summarizes the main control factors of the reservoir formingThe whole WuLanhua sag is the graben structure,developing five structural units which are two troughs,two slope and one step.The troughs deposit steadily,the positive structure of the surrounding areas in the trough is the favorable direction of the oil-gas migration.In the plane of the reservoirs,the surrounding south troughs appear zonal distribution in positive structures(TuMuer,SaiWusu,Hongjing and HongErge structural belts).The south trough is the center in the vertical,which develops divergent,intersecting and overlying hydrocarbon distribution from deep to shallow formationAccording to the results of source rock study and the resource evaluation,we consider that the argillaceous dolomite in the bottom of Teng one formation and the dark mudstone in A'Ershan formation are the main source rock in the WuLanhua sag.These two sets of the source rock have the features of high organic abundance,good matrix type,high thermal evolution degree,good organic conversion,extensive distribution and good oil generation conditions.Based on the method of asphalt' A',the total amount of the resource is calculated more than 10×108t.The WuLanhua sag has high inherited feature,the provenance is from the short-axis latitudinal direction,the sedimentation type is various and main types are fan-delta,braided dalta and subsea and has several provenance entries.Expect for clastic reservoir,the area develops igneous reservoir and ganite reservoir.The igneous reservoir distributes mainly in the southern sag,the ganite reservoir distributes mainly in the mid-southern of sag.The key element of the storage ability is the development of the fractures.The reservoir mode is also various.There are three reservoir types which are clastic rock reservoir,igneous rock reservoir and ganite reservoir.The main formations of the clastic rock reservoir are A'Ershan and Teng one,which develop structural reservoir,lithologic reservoir and structural-lithologic reservoir.The clastic reservoir forming is influenced by the structure,sedimentary facies.The favorable facies belt and the match between the structures and the source rock faults are the main control factors of the clastic reservoir.The dominate kind of igneous reservoir is andesite reservoir.The forming is controlled by two-way factors which are oil source and facies.The ganite reservoir is the buried hill reservoir,and the reservoir zones clearly in vertical.The top of the reservoir develops fracture-pore and fracture reservoir.The hydrocarbon accumulates in the weathered crust,thus we construct the weathered crust-buried hill type of the accumulation model which supplies oil in multiway and migrates oil between faults and unconformity.The development of the fractures and the matches between the source rocks are the main control factors of the igneous and ganite reservoir formation.