Reservoir Characteristic Study Of The Chang 4+5 Oil Group Of Yanchang Formation In Chenghua Area,Ordos Basin

In this paper,Chang 4+5 reservoir group in Chenghua area of Ordos Basin is taken as the research object,sedimentology and petroleum geology theory are taken as the guidance,core observation data,drilling data,Casting sheet,scanning electron microscope and other testing and analysis methods are used to conduct in-depth analysis of sedimentary facies and reservoir characteristics in this area and comprehensive evaluation of reservoirs is carried out.According to the research and analysis,the 4+5 sediment source in the study area comes from the ancient rivers in the northeast and southwest and the river delta is mainly developed in the northeast,the delta front sediment type is the main type.Generally,underwater distributary channel and estuary dam are considered as important favorable facies zones for the development of front sand body and facies zones control the thickness of sand body deposition to some extent.The underwater distributary channel sand bodies in the delta front are obviously superposed and are the main reservoir sand bodies in the study area.Research on reservoir characteristics shows that the reservoirs of 4+5 reservoir group in the study area are mainly cliff lithic arkose and feldspathic lithic sandstone.It has good Sorting while primary intergranular pores,feldspar dissolution pores and cliff debris dissolution pores are common in the reservoir of the study area.Porosity and permeability analysis shows that the reservoirs in the study area are basically low porosity and low permeability reservoirs.The sandstone of Chang 4+5 member has an average porosity of 10.42%,an average permeability of 0.43×10^-3?m²,and moderate pore connectivity.The study found that the diagenesis in the study area is dominated by long-term and stable compaction?pressure dissolution?and cementation,and local dissolution and metasomatism.Compaction and cementation of carbonate cliff reduce porosity in the process of pore evolution to reduce reservoir capacity.Although dissolution can increase sandstone porosity and improve sandstone porosity and permeability,it is difficult to enhance reservoir capacity due to low carbonate development.The division of diagenetic stages in the study area indicates that the whole area is in the middle diagenetic stage a-b.On the basis of the above research,comprehensive reservoir evaluation is carried out.Type I and II reservoirs are mainly developed in Chang 4+5₁ reservoir group and Type III reservoirs are mainly developed in Chang 4+5₂ reservoir group.It shows that the quality of Chang 4+5₁ reservoir is higher than Chang 4+5₂.It provides favorable targets for the next oil and gas exploration and development in this area.