Reservoir Characteristics Of Yanchang Formation In Yanchang Area,Ordos Basin

The Ordos Basin is located in the central and western part of the Chinese mainland and it is a multi-cycle sedimentary basin that has undergone long-term structural evolution,in general,it is a rectangle with short things and long north and south.As an important petroleum energy source in the Ordos Basin,the Yanchang area has become the focus of attention.The Yanchang Formation is the main oil production layer of many energy companies.It has the characteristics of low porosity and low permeability and has received extensive attention from researchers.At present,the Yanchang Formation has broad prospects for exploration.Due to the fact that many problems in the study area are not fully understood,It is mainly reflected in the research on sedimentary environment,sedimentary facies,diagenesis,reservoir heterogeneity and reservoir characteristics.This paper is directed at the problems that restrict exploration and development,and is guided by theories of sedimentology,stratigraphy,petroleum geology,sedimentary basin analysis,and sedimentary basins of clastic rocks,etc.According to field outcrop observation,core description,sedimentary facies,and sand body shape analysis,based on the analysis of regional structural features and sedimentary environment,combined with logging data,rock thin sections,cast thin sections,scanning electron microscopy and other analytical methods,the petrological and sedimentary characteristics of the Yanchang Formation in the Yanchang area of the Ordos Basin were studied.A comprehensive study was conducted on the characteristics of physical properties,diagenesis and heterogeneity.Based on this,a comprehensive classification evaluation of the Yanchang Formation reservoirs was carried out and the following conclusions were drawn.?1?In the sedimentary evolution of the Late Triassic Yanchang formation in Ordos Basin,the delta front depositional system is the main sedimentary type in the study area,among which there are many sedimentary microfacies such as underwater distributary channel,distributary bay,estuary dam,mat sand,underwater natural dike and floodplain;?2?The Yanchang Formation of the Chang 6 sandstone group,it can be seen from a large number of lithological identification results that the sandstone composition is complex and diverse as a whole,there are great differences in the interior.The main components are mainly fine feldspathic sandstone,followed by a certain amount of lithic feldspar sandstone;chlorite,turbidite,and calcite are the main types of interstitials.The pore type is dominated by intergranular pores.The diagenesis undergoes a complex evolution process,with compaction,cementation,and dissolution as the main factors,among them,dissolution.The storage performance of the storage group is greatly improved,particle sorting is generally better,roundness is mostly sub-angular-sub-circular,with a low component maturity and high structure maturity;?3?In Yanchang area,the Yanchang Formation has a strong reservoir heterogeneity,there are differences between layers,layers,planes during sedimentary and diagenetic processes.The main reason for this difference is the heterogeneity of reservoir properties;?4?In the study of the sedimentary environment,logging analysis,characteristics of sedimentary facies,spatial distribution of sand bodies,type of pore size,diagenesis and physical properties of reservoirs in the reservoir sand bodies of the Yanchang Formation,through quantified reservoir evaluation indicators and actual production data of the oilfield,the types of reservoir sand bodies of the Chang 6reservoir in the Yanchang Formation of the study area are divided into three types:I,II,and III.The reservoirs of type I and II reservoirs are well-defined,and the porosity is above 9%,the permeability is greater than 0.5×10^-3?m².The sandstone is dense and has poor physical properties.From the plane distribution map,it can be concluded that the Yanchang Formation reservoirs are mostly II and III,and the I distribution range is small;?5?In each sedimentary microfacies,the reservoir properties of underwater distributary channel sand bodies with delta front are better,and the strip-shaped sand bodies are mutually superposed vertically.The sand body in the plane enlarges the river channel due to lateral accretion,the sand body is wrapped by mudstone and acts as a sealing cap.Therefore it is the main site for oil and gas accumulation.Through the systematic research on the distribution law of the reservoir sand body in the Yanchang Formation Chang 6,it is clear that the distributing of the reservoir type is the starting point and the foothold of the research area,which provides an important basis for the further exploration and deployment of oil in the group.