Source Rocks Evaluation Of The Upper Cretaceous Nenjiang And Qingshankou Formations In Southern Songliao Basin

The Nenjiang Formation and Qingshankou Formation are two important sets of source rocks in the Songliao Basin,these Formations provides abundant oil source from medium and shallow reservoirs.However,the development and distribution of source rocks and their quality largely control to the oil and gas（especially tight oil and gas）.Therefore,qualitative and quantitative evaluation of source rocks and organic heterogeneity characterization are carried out,it is the great significance to understand the distribution of oil and gas and conduct oil and gas exploration.In this study,the Nenjiang Formation and Qingshankou Formation in the southern Songliao Basin are studied,the qualitative evaluation of source rocks has been carried out,the abundance of organic matter,type and maturity in the source rocks of each member was determined,and based on the improved△log R model,the organic heterogeneity of 266 exploratory wells in the study area was completed.In addition,based on the results of thermal simulation experiment of hydrocarbon generation in the source rocks and the sedimentary burial history and thermal history of the study area,the chart of hydrocarbon generation conversion rate of source rock is established.On this basis of chemical kinetics method and material balance method are used to realize the quantitative evaluation of hydrocarbon generation and expulsion in the Qingshankou Formation Member 1.The results show that organic abundance of Nenjiang Formation Member 1,Member 2 and Qingshankou Formation Member 1 is generally higher,in which more than 70%rocks are of good source rock grade,however only about 40%of the source rocks in the 2^nd and 3^rd Member of Qingshankou Formation have reached good grade;the organic matter mainly belongs to the type I and type II₁,when the burial depth of the source rock exceeds to the 1100m,it entered to the mature stage,a large amount of hydrocarbon generation began.Because the source rocks are deposited at the shallow depth in the Nenjiang Formation,only in deep part of the depression,then the source rocks have entered into the mature stage,the Qingshankou Formation has basically reached the mature stage in the central depression.Therefore,the Qingshankou Formation should become the main source rock in the middle and shallow layers in this area.Further evaluation of organic heterogeneity vertically and horizontally,revealed that there is a strong heterogeneity in the organic matter abundance in source rocks of the Qingshankou Formation Member 1,overall there is a certain difference in the abundance of organic matter between the upper and lower source rocks of the Qingshankou Formation Member 1,the organic matter abundance of the lower source rocks in most areas is higher than the upper source rocks;by the horizontal heterogeneity it can be seen that the distribution of source rocks are widely and good proportion in the Qingshankou Formation Member 1,widely developed in the central depression,and the source rocks of the upper part of the Qingshankou Formation Member 1 are reached at good proportion which have been distributed in Fuxin Uplift Zone,wells of the Honggang Terrace Hong-69,Hai-2,Hai-4,Cha-24;wells of the Changling Sag Gan-178,Hei-82,and some areas of Huazijing Terrace.Quantitative evaluation of hydrocarbon generation and expulsion from source rocks show that when the burial depth of source rocks in the Qingshankou Formation Member 1 reached at 1700 m,the hydrocarbon generation increased rapidly and at this time a large amount of hydrocarbon expulsion was also started.Among them the cumulative hydrocarbon generation in the upper part of the Qingshankou Formation Member 1 has 56.2×10⁸t,and the hydrocarbon expulsion amount is 30.1×10⁸t.The cumulative hydrocarbon generation in the lower part of Qingshankou Formation Member 1 is high as 74.5×10⁸t,and the amount of hydrocarbon expulsion 41.7×10⁸t.Generally we can say that the source rocks have higher abundance,have a good organic matter types,and maturity in the Qingshankou Formation Member 1 of the southern Songliao Basin,it has a larger capacity of hydrocarbon generation and expulsion.It provides sufficient oil source for the middle and shallow layers in the region,especially for the Fuyu tight reservoir,which is close to the source rocks in the lower Qingshankou Formation Member 1.The development and distribution of high-quality source rocks strictly control the horizontal distribution of tight reservoirs.