Source Rock Evaluation Of Yanchang Formation In The Dadonggou Area Of Fuxian,Ordos Basin

The Dadonggou area is a new exploration area in the Fuxian Oilfield in recent years.Good oil and gas displays have been seen in multiple intervals of the Triassic Yanchang Formation,showing great exploration prospects.Existing exploration practices show that source rocks have a significant control effect on reservoir development,but the previous research work mainly focused on sedimentary facies,sand body distribution and reservoir characteristics.The research on the source rock in this area has not been carried out specially.Based on a large number of drilling,logging,oil testing data,core analysis and testing data in the Dadonggou area,this paper uses the theory and methods of petroleum geology and oil gas geochemistry in the Yanchang Formation to determine deeply the abundance,types and maturity of organic matter and analysis deeply geochemical characteristics of source rocks in this area.The ?lgR model is used to identify source rocks and calculate TOC values and study the distribution of source rocks.The geochemical parameters of source rocks were used for oil-source comparison.The main results are as follows:? The thickness of Chang 7 source rocks is more than 100 meters,and there are thick organic carbon rich source rocks in the middle of Chang 8 and at the top of Chang 9.The distribution characteristics of calculate TOC values in the study area are as follows:The TOC values of Chang 7 source rock is high in the middle of the study area and low in the east and west in the study area.The TOC values of source rocks in the middle of Chang 8 is more than 4 in the middle of the study area and less than 1 in the east of the study area.The TOC values of source rocks at the top of Chang 9 is more than 4 in the middle of study area and less than 1 in the east of the study area.?The average value of S1+S2 of Chang 4+5,Chang 6,Chang 7,Chang 8 and Chang 9 source rocks are 2.27mg/g,3.01mg/g,9.22mg/g,7.03mg/g and 9.89mg/g respectly.The organic matter type of Chang 4+5,Chang 6 source rocks are type III,that of Chang 7,Chang 8,Chang 9 source rocks are type?-?2.The organic matter of Chang 4+5,Chang 6 source rock are mostly in mature stage.The organic matter of Chang7,Chang8,Chang 9 source rock are in mature stage.?The source rock of Chang 6 is characterized by mixed-source facies mudstones.The source rock of Chang 4+5,Chang 7,Chang 8 and Chang 9 are characterized by fresh water semi-deep lake or deep lake facies.The parent materials of Chang 2,Chang 6 and Chang 8 crude oil are terrestrial source rocks of lower organisms.?According to the comparison between crude oil and source rocks in terms of family composition,saturated hydrocarbons,steranes,terpanes and other biomarkers,we know that Chang 2,Chang 6 and Chang 8 crude oils are mainly derived from Chang 7 source rocks.From the comprehensive abundance,type and maturity of organic matter in the source rocks,we know that the source rocks of Chang 4+5 and Chang 6 in the study area are evaluated as better source rocks,and the source rocks of Chang 7,Chang 8 and Chang 9 are evaluated as good sources rock.