Development And Distribution Characteristics Of Source Rocks And Contribution To Reservoir Formation In The Dalong Formation,Sichuan Basin

There are many large and medium-sized oil and gas fields in the Changxing-Feixianguan Formation in the Sichuan Basin.Previous studies suggested that these gas were mainly crude oil cracking gas,and mainly came from the Permian,especially the source rocks of the Wujiaming Formation.In recent years,the Dalong Formation（30m-70m in thickmess）have been repeatedly encountered in the northeast Sichuan Basin,but the contribution of the Dalong Formation source rocks to the accumulation of these large and medium-sized gas reservoirs has not been systematically studied.Based on outcrop,core observation,geochemical analysis and logging interpretation data,this thesis coducts research on the lithologic,geochemical,distribution characteristics,and the development model of the Dalong Formation the source rocks in the Sichuan Basin.The contribution of the Dalong Formation to the gas accumulation of the Changxing-Feixianguan Formation in the Puguang and Yuanba gas fields is further determined.The main understanding is as follows:（1）The source rocks of the Dalong Formation are mainly calcareous mudstone,siliceous mudstone,mixed mudstone,siliceous mudstone,marl,etc.,which mainly develope in the deepwater continental shelf and slope facies.The organic matter is mostly in the form of scattered massive,banded and interstitiform.（2）The total organic carbon average of the Dalong Formation source rock is 5.13%,which belongs to the excellent source rock.The organic matter types of the Dalong Formation are mainly TypeⅠandⅡ,the Puguang area is mainly typeⅠ,while the Yuanba area isⅡ₁.The average organic matter maturity Ro of this formation is 2.1%,and its thermal evolution degree is in the late to the mature stage.（3）The Dalong Formation source rocks has obvious regularity in the longitudinal direction.The bottom is mixed calcrete source rock segment,the middle is siliceous,and the upper is calcrete.The development model is upwelling of the shelf margin.（4）In plane,the thickness of source rocks is about 40m～60m in Puguang and 20m～40m in Yuanba,showing a trend of thinning from Puguang to Yuanba and Tongnanba area.The hydrocarbon-generation intensity of the Dalong Formation source rock is 0～62×10?m3/km2.The hydrocarbon generation center is near the Puguang gas field.（5）According to the comparison of natural gas ethane,solid asphalt,and kerogen carbon isotope,it is believed that the contribution ratio of the Dalong Formation source rocks to the Changxing Formation in Yuanba gas field is 73%,and that of the Changxing-Feixianguan Formation in Puguang gas field is 57%.Based on the method of ethane,solid asphalt and kerogen nitrogen isotope correlation for the first time,the contribution ratio of the Dalong source rocks to the Changxing Formation in Yuanba gas field is 60%,and that to the Changxing-Feixianguan Formation in Puguang gas field is 64%.