Reservoir Microscopic Characteristics And Quantitative Evaluation Of Shanxi Formation In Southeastern Ordos Basin

Ordos Basin is one of the most prospecting petroliferous basins for oil and gas exploration and development in China.The exploration and development for tight sandstone gas in South-Eastern Ordos Basin has become the research hotspot in current.Studying the reservoir provenance,sedimentary characteristics and diagenetic characteristics of Shanxi Formation will be propitious to finding the geological genesis of large scale gas accumulation in Southeast basin in Upper Paleozoic.Comprehensive quantitative evaluation of reservoirs is beneficial to finding high quality reservoirs in tight sandstones.Based on regional geological data and drilling,logging and core analysis,with the help of heavy mineral analysis,common thin sections,casting thin sections,scanning electron microscope,mercury intrusion analysis and other analysis methods,this paper systematically studied the reservoir provenance,sedimentary characteristics and diagenetic characteristics of Shanxi Formation in South-Eastern Ordos Basin.Finally,the comprehensive quantitative evaluation of Shanxi Formation has been carried out,and 5 main conclusions of this paper are shown as follows:1.Provenance redifination:through the analysis of different distribution of heavy mineral and characteristics of partition distribution of lithic fragment types,this paper concludes that the study area is influenced by three main parts of the provenance:respectively from North North East,North North West and South.The NNE provenance of 2^nd member of Shanxi Formation can influence Ganquan vicinity,whereas the influence scope of South provenance was limited.During the deposition process of 2^nd member to 1^st member of the Shanxi Formation,the NNW provenance advanced constantly toward east till to the west of Ansai,with the sustainable supply of South provenance advancing to north,its influence scope was gradually growing,and the provenance of North and South had the trend of becoming mixed.2.Sedimentary distribution:Through core observation and analysis of drilling,logging and trace element,we concluded that the Shanxi Formation is transitional facies—meander delta front deposition,subaqueous distributary channels,subaqueous interdistributary bay,subaqueous overbank sand are the main microfacies.Sedimentary distribution presents as a banding distribution,and it is controlled by three main prevenance.3.Reservoir characteristics:Through the microscopic analysis,we concluded that Shanxi Formation is mainly lithic quartz sandstone,lithic sandstone and quartz sandstone,well-sorted,mainly semiround and semi-edge-angle,concave convex contact,porous cement,developing dissolution pore.The physical properties in the whole area is poor,the physical properties of 2^nd member is slightly better than 1^st member of the Shanxi Formation,the porosity and permeability of northwest area is poorer than northeast area,the porosity and permeability of south area has serious heterogeneity.4.Diagenetic characteristics:The Shanxi Formation sandstone is at middle diagenetic stage B,it has experienced strong diagenetic processes.Compaction and cementation made the reservoir tighter,the reservoir physical properties were improved obviously by dissolution and the growth of microcrack at some extent.Secondary pore zone shaped at middle diagenetic stage A.5.Reservoir quantitative evaluation:We make comprehensive quantitative evaluation of Shanxi Formation tight reservoir by grey correlation theory and analytic hierarchy process,the Shanxi Formation reservoir is divided into four categories,this paper maps the planar distribution regularities of different types of reservoir,2^nd member of the Shanxi Formation is given priority to ? and ? type reservoir,1^st member of the Shanxi Formation is given priority to ? and ? type reservoir.