Study Of Upper Paleozoic Hydrocarbon Source Rocks In Western Ordos Basin

Several sets of hydrocarbon source rocks have been developed in the Upper Paleozoic Carboniferous-Permian in the western Ordos Basin,and some of the areas where the coal seams(0?2m)are too thin still find low-flow natural gas,suggesting that the source can come from other hydrocarbon sources besides coal.In this thesis,the spreading characteristics,lithological characteristics and hydrocarbon geochemical characteristics of the Upper Palaeozoic hydrocarbon source rocks in the western Ordos Basin are summarised and analysed by combining regional field geological,drilling and logging data with hydrocarbon geochemical testing and analysis,and the hydrocarbon generation intensity of coal and dark mudstone in this area is calculated by hydrocarbon generation simulation experiments.The hydrocarbon generation and discharge characteristics of the coal and dark mudstone in this area are further explored through hydrocarbon simulation experiments.The results of this paper will provide a scientific reference for the exploration and development of natural gas resources in the western part of the Ordos Basin and its prediction and evaluation.The coal rocks in the west of Ordos Basin are mainly enriched in the north,with the thickness up to 30m in the north,and the coal seams in the south are relatively thin,generally around 10m.Different from coal rocks,the thickness of mudstones from Etoke Banner to Etoke Front Banner in the northern side of the western Ordos Basin is much thinner than that in the southern Dingbian and Huachi area.The thickness of mudstone in the north is about 10?40m,while in the south it is generally about 60?100m.According to the experimental analysis,the average organic carbon content of dark mudstone and carbonaceous mudstone in the Upper Paleozoic source rocks in the western Ordos Basin is 1.58%and 21.25%respectively,showing good hydrocarbon generation ability.The average organic carbon content of coal rocks is between 40%and 77.2%,with an average value of 56.1%.The maximum methane production rate from coal rock is109.7mg/g.The hydrocarbon source rocks in the study area are mainly gas generating with limited oil generation capacity.The carbonaceous mudstone has the strongest gas generating capacity,followed by coal and dark mudstone.The Upper Paleozoic source rocks in the western Ordos Basin were in the period of hydrocarbon expulsion from the Middle to Late Jurassic to the end of Early Cretaceous,and the hydrocarbon generation and expulsion intensity of natural gas reached the peak.The cumulative hydrocarbon generation intensity of the present source rocks in the study area is(10-17)×10~8m~3/km~2,which is mainly concentrated in the vicinity of Tiekesumiao and Etoke Qi in the north,with the highest hydrocarbon generation intensity.In terms of hydrocarbon expulsion intensity,the hydrocarbon expulsion intensity of mudstone in the middle and lower part of the study area,that is,near Shijiawan,Qingshimao,is higher than 10×10~8m~3/km~2,with a maximum of 23.3×10~8m~3/km~2.The characteristics of organic carbon content in the study area have the same trend as the vitrinite reflectance,around the area to form the organic carbon content,vitrinite reflectance and hydrocarbon expulsion intensity of high value area,according to the analysis of experimental results,the area dark mudstone for hydrocarbon expulsion intensity is higher than that of coal and rock,the contribution of the hydrocarbon source rocks is very important.