| Pore structure,as an important factor affecting reservoir quality,is an indispensable aspect of reservoir research.Sedimentation controls the formation of the original pore structure of the reservoir,and also has some influence on diagenesis.Therefore,it is certainly inextricably linked with the pore structure.But the current research on this is poor.In this thesis,based on the core observation,combined with the logging data and the analysis and testing techniques such as rock cast thin section,scanning electron microscope,conventional physical properties,high pressure mercury piezoelectricity and nuclear magnetic resonance,the research on the lithological characteristics and petrogenesis of the reservoir,the physical characteristics and diagenesis of the reservoir,and the characteristics and development rules of the pore structure has been carried out in Member Chang-71 and Member Chang-72 of Longdong area,Ordos Basin.The main progresses and achievements are as follows.First,the lithological characteristics,diagenetic types and reservoir space characteristics of the sandstone reservoirs in the study area are clarified.Lithic feldspathic sandstone is mainly developed in Member Chang-7,and the interstitial material is composed mainly of Illite,the particle size is mainly silt grade,the grinding circle is mainly subangular,and the sorting is poor.Compaction,cementation and solifluction are the main diagenetic effects,and the reservoir space is characterized by the coexistence of intergranular pores and feldspathic pores,with the average porosity ranging from 7.71%to 8.08%and the average permeability ranging from 0.078m D to 0.110m D,which is a typical extra-low pore-ultra-low permeability reservoir.Secondly,the genesis of sandstone reservoirs and the difference of pore structure are confirmed.The sandstone reservoir in this area are mainly caused by flood-type gravity flow（heterogeneous heavy flow）genesis,which can be subdivided into six sedimentary microfacies:erosional channel,transitional channel,sedimentary channel,overflow bank deposition,plate body and channel body.The quality of sandstone reservoir in the target formation is poor,with extra-low porosity and ultra-low porosity.There are differences in the pore structure of different microphases.Sedimentary channel has the best pore throat size,and the sorting and connectivity of pore throat are also good;the pore throat sorting of plate body is the best,but the pore throat size and pore throat connectivity are poor.On the whole,the pore throat structure of sedimentary channel is the best,the transition channel and channel body are the second,and the plate body is the worst.Finally,the reservoir is comprehensively classified and evaluated based on sand thickness,porosity and permeability,area porosity and mercury-pressure parameters,and the reservoir is divided into three types.The quality of typeⅠreservoir is the best,dominated by sedimentary channel and transitional channel;typeⅡreservoir quality is followed,dominated by plate body and channel body;and typeⅢreservoir quality is poor,dominated by erosional channel and overflow bank deposition. |
