Reservoir Characteristics And Efficiency Evaluation Of The Low Permeability Reservoirs Of Sangonghe Formation Of Jurassic In The Block 1 Of The Central Part In Junggar Basin

The major part of Block 1 of central Junggar basin is located in western well pen-1 sag,Center of the Junggar basin,and the southern is located in the north slope of Changji sag,having a characteristic of southeast-inclined single-slope configuration.From north to south,there are Shawodi,Moxizhuang and Zhengshacun three blocks,with poor developed fracture system and positive tectonics.The research stratum,Jurassic Sangonghe formation,is characterized by a thick and stable distributed set of delta front sandbodies,which is the major oil and gas exploration target in Block 1 of central Junggar.The recent exploration results show a favorable oil and gas exploration potential,however,the reservoir characteristic is not clear,which lead to many drilled dry layers in the target stratum or the great change of oil-test producing fluid volume.Therefore,aiming at the low permeability reservoir,Sangonghe formation,systematically conducting research on reservoir characteristics,defining controlling factors and distribution characteristics of effective reservoir are of great significance for the oil and gas exploration in the study area.Thus,this paper systematically studies the petrologic characteristics,diagenetic characterisctics,petrophysical lower limit,controlling factors and the distribution characteristics of effctive reservoir by means of core data,well logging data,casting thin sections,SEM observation,physical property test,image analysis and other technical methods.The major resluts and acknowledgement are as follows :First,the rock properties of the low permeability reservoir,Sangonghe formation in Block 1,central junggar basin,are mainly composed of fine sandstone,medium sandstone and coarse sandstone,followed by siltstone,while the content of conglomerate and glutenite are limited.Rocks are mainly composed of feldspathic lithic sandstone.The degree of reservoir diagenesis and evolution is lower,and mainly have entered the middle diagenetic stage A1,having a medium-strong compaction.The cementation is various,among them,the widely developed kaolinite cementation has an important effect on the low permeability,and the dissolution is generally weak,resulted in weak compaction-weak dissolution-weak cementation diagenetic facies,medium compaction-weak dissolution-weak cementation diagenetic facies,medium compaction-weak dissolution-medium-strong kaolinite cementation diagenetic facies and other five major types of diagenetic facies.Reservoir also has low porosity and low permeability,and the reservoir space is given priority to primary pores.According to the Pd and Pc50 value,the pore throat structure is divided into three types and six subtypes.Because of the great difference in structural location and buried depth,the compaction degree,physical property and pore throat structure of Sangonghe formation in Shawodi,Moxizhaung and Zhengshacun three blocks are also obviously distinct.Secondly,Comprehensively utilizing the distribution function curve method,oil testing method,production test method and other technical methods,the permeability lower limit of effective reservoirs were defined.Also,we can take the pore throat structure as a constraint to calculate the physical property lower limit of different pore throat structures.The major pore throat structure of Sangonghe formation are type ? A and type ? B.Choose porosity difference and permeability difference as the primary parameters,and analyze the controlling factors of effective reservoir,we can draw the following conclusion that the main controlling factors are lithofacies and diagenetic facies,while the impacts of sedimentary facies and formation pressure turn out to be small.Thirdly,According to the obvious difference of lithofacies and diagenetic facies,the major controlling factors of effective reservoir,as well as the reservoir physical property and well testing data,the sandstone reservoirs of Sangonghe formation,Block 1 of central Junggar,were classified and evaluated,which can be divided into type??type?1?type ?2?type ? and type ?.Furthermore,on the basis of logging identification results of lithofacies-diagenetic facies,the distribution of all kinds of effective reservoirs can be predicted.The research suggests that: 1)The type ? is the major reservoir of 1-4 sand bodies in Shawodi and northern Moxizhuang area,followed by type ?2 in fifth sand bodies;2)Type ?1 is the major reservoir in of 1-4 sand bodies Moxizhuang area,followed by type ? in fifth sand bodies;3)Type ? reservoir mainly distributes in Moxizhuang area,while type ?1 develops around the major channel;4)The sixth sand bodies of the whole research area mainly developed the Type ? reservoirs.