Characteristics Of Favorable Reservoir Facies Belts And Fracture-hole Identification In Longwangmiao Formation Of Gaomo Block

Ever since the magical well GS-1 mistering prospected in 2001 of Longwangmiao formation in Moxi-Gaoshiti area in the Sichuan basin,this surprise gave a birth to one of the most giant marine carbonate gas reservoirs,never before in this area has the potential of this dramatic discovery been going a long way towards enormous natural gas productivity,as a result,it made this treasury popular with its natural resources among the world.But,the massive and stable output generated by this colossal reservoir was somehow limited by its negative surrounding in light of low permeable zone,imbalanced distribution of favorable reservoir facies and complexed fracture-cave system,as well as entailing technical difficulties and high costs.The comprehensive research of logging response,three D seismic resources combined with its sedimentary condition are required as a way of researching influences brought by varied features of fracture-cave system etc.as such,we could deepen our findings and further our goals.The main achievements are as follows:(1)Sequence framework and sedimentary microfacies features:Seawater has experienced two large cyclical lifting movement during this period.Longwangmiao Fm.can be divided into two sequences in Moxi-Gaoshiti area,central Sichuan.SQ1 was deposited on the upper hand with reverse cycle mainly,while SQ2 was under it closely.The all-round sendimentary shows rarely respectively reverse.In a single cycle,the depositional subfacies such as restricted lagoon and grain shoal,and the grain beach subfacies consist of the beach core microfacies(beach main body)and beach wing microfacies.In a single cycle,there is a feature that the water body becomes shallow upwards,and the rock particles gradually become coarser from the bottom to the top.Particulate rocks are mainly distributed in the middle and upper parts and are the main reservoir rocks.(2)Favorable reservoir facies belt distribution and characteristics:According to different types of sub-facies and micro-facies in the content of different grain rocks to establish the plane sedimentary subfacies and micro-facies partitioning mode:When the land ratio is greater than 0.6,the plane is characterized as a beach core micro facies;When the land ratio is 0.4 to 0.6,the plane is characterized as a beach wing microfacies;When the ratio of land to ground is 0.2<0.4,the plane is portrayed as a beach-to-tank sub-facies;When the land ratio is<0.2,the plane is characterized as a lagoon subfacies.The beach core microfacies(beach main body)depicted on the plane is the distribution range of favorable reservoir facies belts,mainly in the MX102-MX101-MX12-MX10 well line,the MX8-MX18 well line,and the MX205-MX11-MX16 well block.Longitudinally,it is mainly located in the upper middle of the upper circle.The favorable reservoir facies belt has high content of granulite,low shale content,good porosity and permeability,and a large vertical monomer reservoir thickness,corresponding to the type III seismic facies(double peak double trough)in the seismic facies plan view.(3)Traction hole features:The fracture types of the Longwangmiao Formation in the project area are mainly structural fractures and erosion cracks.Large structural fractures are mainly divided into two groups:cracks in the northwest and cracks in the northeast.Small and medium-sized structural fractures are distributed around large faults and intersect with large faults in a low-angle relationship.The main cause is the generation of shear stress during the formation of large faults,which results in the formation of small-and medium-sized structural fractures.The structural fractures are mainly high-angle fractures.The types of dissolving holes in the Longwangmiao Formation in the study area are mainly divided into four types:? The karst caves:the karst caves with a variegated structure;? the common karst caves:the karst caves are usually unevenly distributed or isolated;?The pinhole:A pinhole with a "pigmented"structure;? Ordinary pinholes:Pinholes are unevenly distributed or isolated.(4)The effect of fractures and fissures on reservoirs:Dissolved pores are important storage spaces in carbonate reservoirs.The more developed areas of dissolved pores,the more favorable the development of high-quality reservoirs.The influence of fracture distribution on reservoirs is complex.Large-scale faults generally play a damaging role in the reservoirs.Large-scale faults usually cause damage to the traps.On the one hand,gases escape,and on the other hand,groundwater invades traps.Small cracks generally play an active role in reforming the reservoir,increasing the reservoir's permeability and reservoir capacity.The large faults in the Longwangmiao Formation in the study area are mainly two groups in the northwest and northeast directions,which are mainly distributed in the north and south of the Moxi area.Small cracks are mostly distributed in the middle area of the reservoir's distribution direction(near east-west direction);The more developed areas of dissolution holes are mainly located in the main area of grain beach.These far-reaching findings on a basis of comprehensive geological background and analysis data of cores best illustrate the way of targeting the favorable reservoir facies belt;Alongside that,The combination of both with logging and 3D seismic response helps us paint the promising picture of where gas and oil are located;profound influences upon the root causes of huge resources could be specified by study of varied fracture-cave systems;To that end,the gist of this essay would contribute to a further precisely geological research on Longwangmiao formation in Moxi-Gaoshiti area for much more sufficient exploration.