Research On Densification Factors Of The 1st Member Of Xiashihe Formation Reservoir In Hangjinqi District,Ordos Basin

It is an important tight sandstone gas production layer for the 1st Member of Xiashihe Formation in Hangjinqi District,northern Ordos Basin.Many scholars have conducted a lot of research on reservoir characteristics,diagenesis characteristics,pore evolution,etc.,and have accumulated abundant basic data and research results.Combing the previous research results,taking the theoretical guidance of Sedimentology,Reservoir Geology,Petroleum Geology and the latest domestic and international relevant research,comprehensively using core data,ordinary thin section identification,cast thin section identification,scanning electron microscope analysis,CT scanning analysis,cathodoluminescence analysis,physical property analysis,high-pressure mercury intrusion analysis,X-ray diffraction and fluid inclusions to study the reservoir characteristics and main controlling factors of densification in the 1st Member of Xiashihe Formation.And establish diagenetic evolution and reservoir pore evolutionary mode to explore the factors of reservoir densification in a qualitative-quantitative way.The research results are mainly as follows:?1?Based on the existing research results,drilling core data,logging data,granularity analysis data,it is clear that the 1st Member of Xiashihe Formation of the study area is braided river sedimentary facies,and analysised of channel-lag deposit,channel bar and floodplain sedimentary microfacies feature.According to the planar distribution of sedimentary facies in,it showed that the braided channel deposits of the1st Member of Xiashihe Formation spread from north to south,and developed four main channels.?2?The sandstones of the He-1 member in the Hangjinqi area are mainly unequal-grained,medium-coarse-grained detrital quartz sandstone and detrital sandstone,with high component maturity and low structural maturity.The types of cementation mainly includes carbonate cementation,kaolinite cementation,siliceous cementation and chlorite cementation,and the matrix is mainly?iron?clay and tuff.The storage space types are mainly remaining primary intergranular pores,secondary intergranular pores,and intragranular dissolved pores.The average porosity of the reservoir is 9.41%,and the average permeability is 0.854×10^-3?m²,which belongs to the range of low porosity,ultra-low permeability and ultra-low porosity,and ultra-low permeability.?3?The tight sandstone of the He-1 member had experienced compaction,cementation,dissolution and metasomatism.During diagenesis,it developed two-stage quartz cementation and two-stage carbonate cementation.The two-stage siliceous cements are secondary quartz enlargement and self-generated quartz particle cementation.The first stage of carbonate cementation is calcite cement,and the second stage is mainly calcite and iron calcite.The diagenetic stage reached the A-B stage of mesodiagenesis.?4?Sedimentation and diagenesis are the main factors affecting reservoir densification.The strength of the hydrodynamic force during deposition determines the storage quality of the sandstone.The initial porosity of the sandstone is 38.71%,and compaction is the main factor for the deterioration of reservoir physical properties.The remaining porosity after compaction is 10.18%.The porosity reduced by cementation was 6.16%,and the remaining porosity after cementation was 4.02%.The effect of dissolution increases the porosity by 0.61%,and the porosity after dissolution increases is 4.63%,which is not much different from the current analysis of 5.33%.?5?The densification process of the He-1 member is divided into rapid pore reduction stage,densification stage and post-densification adjustment stage.Penecontemporaneous-early diagenesis A is subjected to strong mechanical compaction,which is a rapid pore reduction stage;early diagenesis B stage-medium diagenesis A stage,the precipitation of siliceous cement accused the sandstone dense and entered into the densification stage.After that,the source rock entered the maximum hydrocarbon generation threshold,accompanied by the dissolution of organic acids,and entered into the densification adjustment stage.