Comprehensive Study On The Characteristics Of Sedimentary Reservoirs Of The Lianglitage Formation Of The Upper Ordovician In The Shunxi Area And Prediction Of Favorable Zones

The paper is guided by discipline theories such as carbonate sedimentology,reservoir geology,geochemistry,well logging geology,seism stratigraphy,and karstology,and integrates core,lamella,logging,geochemistry,and seismic data.The stratigraphic distribution,the types,distribution and evolution of sedimentary facies,the geological framework of the platform margin,the basic characteristics,main controlling factors and development models of the reservoirs are studied to evaluate and predict distribution of the favorable reservoir zones.The paper mainly achieved the following findings:The Lianglitage Formation in Shunxi area is divided into three lithologic sections,12 layers from the top downward.The thickness of the formation is gradually thinned from the platform margin to intra-platform.Shunxi area mainly develops two major facies:the platform margin and th open platform.The platform margin is relatively broad and gentle.The platform margin is characterized by extremely thick sparrygrainstones of grain banks mixing up with mud mounds,and it is locally developed relatively small scale reef knolls.The inner platform is dominated by the inter-bank seas,also a small amount of low-medium energy shoals,and mud mounds are dotted in localized high-landforms.The reef bank sedimentary range of the platform margin has reached the most extensive during the deposition stage of the grainstone section,and is significantly reduced till the deposition stage of the argillaceous strip limestone section.The migration of the reef-bank complexes is characterized by regression to the platform margin in early stage,progradation to the inner platform in the sedimentary period of the grainstone section,and regression to the platform margin in late stage.The reservoir rocks in study area are dominated by calcarenites,bioclasticlimestones,and oolitic limestones.The reservoirs are mainly medium-low porosity and low permeability reservoirs,and reserving space is dominated by pore and pore-fracture.The grainstone section and argillaceous limestone section have better porosity and permeability.The thickness of the reservoir is reduced from the inner belt of the platform margin to the inner platform,the reservoir performance is reduced.The reef-bank reservoirs in Shunxi area are controlled by favorable sedimentary facies,multi-stage karstification,and strike-slip fault zones.Affected by relatively low sedimentary landforms,at the end of sedimentation,the subaerial karstification in early diagenesis of the Upper Ordovician Lianglitage Formation was weaker,and the exposure range was relatively small and the time was relatively short.Acidic formation water or hydrothermal fluids extensively dissolve along with pre-existing fractures,stylolites,pores and cavities which is key factor to reform reservoirs.The reservoirs of the Lianglitage Formation in study area are apparently controlled by the reef-bank complexes and strike-slip faults.The most favorable reservoirs which are stripped are mainly distributed in the outer belt of platform margin in the northwest of the well Shun 2 and parallel to the No.1 fault.The most favorable reservoirs in inner platform are scattered along the strike-slip fault;the favorable and moderately favorable reservoir development zones are distributed in strips along the strike-slip fault and its western part in inner platform.