Comprehensive Evaluation Of Chang-7 Source Rocks In Yanchang Oil Field,Ordos Basin

Ordos Basin is the area that has the most abundant dense oil in our country.For dense oil,it is an important characteristic of the source rocks and reservoir as a whole or adjacence,and the efficient development of dense oil can not be separated from the effective evaluation of source rock.The degree of exploration and development of oil in Yanchang oil field is poor,In order to realize the large-scale development of dense oil,it is necessary to carry out further study whether it is source rock or reservoir.In this paper,the source rocks of chang-7 in Yanchang oil field,Ordos basin are the main research objects,and the quality and hydrocarbon generation potential of source rocks are comprehensively evaluated through literature research,data collection,core observation,laboratory analysis and statistical analysis and other means.The thickness of source rocks is large and the distribution is continuous and wide of chang-7 in Yanchang oil field,lithology is dominated by oil shale and mudstone.The thickness of most oil shales is more than 15m,and the average thickness is 20m.There are three high-value regions,which are located in the northwest edge,the middle edge and the southwest edge of the study area,some regions's thickness are above 35m.As a whole,it is gradually thinned from west to east and southward.The thickness of the dark mudstone is between 15³5m,there are also three high-value areas,which are located in the northwest of Dingbian,the middle of the study area and the south of the study area such as Zhiluo and Zhangjiawan.It is gradually decreased from west to east.Compared with the adjacent horizons,it can be seen obviously that the organic matter abundances of chang-7 are higher which are mainly distributed in 2%¹4%,the area that the organic carbon content more than 6%is about 43%of the total area of the study area,organic type is good,with?type and?₁ type are given priority to,the degree of thermal evolution is moderate and the vitrinite reflectivitydistribution is 0.7%¹.15%.The oil shale of chang-7³ is the main contributor of the chang-7 source rock,and the dark mudstone is the secondary source rock.There are two different degrees of hydrocarbon expulsion process,the first is low-grade oil,with Shallow buried depth,second is the large-scale pyrolysis hydrocarbon,with deep buried depth.In the whole process of hydrocarbon generation and hydrocarbon exhaust,all kinds of organic matter have higher hydrocarbon expulsion efficiency,with the degree of the thermal evalution deeped,the hydrocarbon expulsion efficiency increase sharply,until the end of oil-generating window,the efficiency of hydrocarbon expulsion close to 90%.The hydrocarbon generation ability is strong,the hydrocarbon generation intensity is mainly in the range of?300⁷00?×10⁴t/km²,the western is largest,the south is the second and the east is the smallest.The hydrocarbon exhaust intensity is mainly in the range of?150⁴00?×10⁴t/km²,and the trend is similar to that of hydrocarbon generation intensity.Based on the hydrocarbon generation intensity,hydrocarbon expulsion intensity distribution characteristics and source rock distribution characteristics,the source rocks of the study area are divided into three zones,?,?and?.Which provide suggestions for the oil exploration and development in the future,?area has a relatively small contribution.The intensity of hydrocarbon generation and hydrocarbon exhaust of?area are higher than?area.?area is mainly distributed in the west border in the study area,this area can be used as the main exploration area of dense oil.