Microscopic Pore Throat Characterization And Oil Availability Of Chang7 Formation Tight Sandstone In The X Area Of Northern Shaanxi Province

The Chang 7 oil layer group formation in the Ordos Basin is a typical layer of tight oil distribution in China.The Chang 7 tight sandstone is densely lithologic and the pore throat structure is complex.It is difficult to effectively evaluate its pore structure using a single experiment,which restricts The fine characterization of the microscopic pore structure of tight sandstone reservoirs of Chang 7 in the Ordos Basin.Thus affects the exploration and development of oil and gas in such reservoirs.In this paper,integrated application of the casting thin sections,field emission scanning electron microscopy(FESEM),high-pressure mercury injection and nuclear magnetic resonance(NMR)technology,the research of Chang 7 dense sandstone reservoir characteristics was analyzed,and further the reservoir micro pore throat was fine multi-scale representation,then through the fluorescence analysis and nuclear magnetic resonance(NMR)technology,the oily characteristics of the microporous pores of the reservoir were analyzed.Finally,combining varieties of technical analysis,reveals the microscopic pore throat's influence on the oil in the reservoirs.The main achievements are as follows:The lithology of the tight sandstone reservoir in the study area is mainly feldspathic sandstone,followed by lithic feldspar sandstone or feldspar lithic sandstone,which has the characteristics of low component maturity and high structural maturity.The diagenesis of the layer is widely distributed.There are three main types of diagenesis: compaction and pressure dissolution,cementation and dissolution.The porosity of the Chang 7 tight sandstone reservoir ranges from 3.0% to 17.50%,with an average of 7.1%.It belongs to the category of ultra-low pore to ultra-low pore;the permeability distribution ranges from 0.012×10-3?m2to3.046×10-3?m2,and the average value is 0.19×10-3?m2,which belongs to the category of ultra-low permeability-densification.The main pore type of the tight sandstone reservoir in the study area is secondary dissolution pores,including intergranular dissolved pores and intragranular dissolved pores,followed by residual intergranular pores,intercrystalline pores of clay minerals and a few micro-cracks.The pore combination types are mainly intergranular pores-dissolved pores,dissolved pores-intergranular pores,intergranular pores and microporous types.The microscopic pore throat size of the tight sandstone reservoir in the study area can be divided into micron and nanometer scales.The micron pore throat size is mainly distributed in1~200?m,and the main body is distributed in 1~10?m.The nanometer pore throat size is mainly distributed at 0.0046~1?m,the main body range is between 0.005~0.1?m.From the analysis of fluorescence technology,the lower limit of oil-bearing pore throat of the tight sandstone reservoir in the study area is 0.0049?m.By comparing the fluorescence of the five samples,the larger the minimum throat radius,the better the oil-bearing property of the reservoir;The poorer the oiliness of the layer.It reflects the control effect of microscopic pore throat on reservoir oiliness.