Abstract:

Well SK1 is the first whole coring hole of the Cretaceous strata in China for scientific research. Different layers of shale in the Well SK1 (scientific well) in the Songliao Basin were systematically analyzed by geochemical technique to determine the profile of total organic carbon content (TOC), maturity and depositional environment. The results show that the most organicrich source rock is the Qingshankou 1st (K2qn1) formation with an average of TOC at 321％ while most greater than 2％. Qingshankou 2nd3rd (K2qn2+3) formations, Yaojia member (K2y) and Nenjiang 1st2nd (K2n1+2) formations have subordinate content of organic carbon. The vertical distribution of TOC shows nine HTB (high TOC at the base, decreasing upward) units, indicating the cyclicity of climate, biomass productivity and organic preservation. The shales of Qingshankou 1st formation mainly contain lacustrine typeI kerogen and have higher content of steranes, indicating algae as the main organic input. The higher amount of gammacerane, relatively low value of Pr/Ph (pristane vs. phytane) and presence of dinosterane all suggest that the lake during the period of Qingshankou 1st formation deposition was subjected to salinity stratification, strong reducing deposition environment, and the potential marine transgression. The shales of Qingshankou 2nd3rd formations mainly contain typeI and typeII kerogens. Multi indices such as gammacerane index and the value of Pr/Ph indicate that the fluctuating lake and the organic carbon contents must have been mixed with more terrestrial organic debris during the period of Qingshankou 2nd3rd formations deposition. The kerogen types of Yaojia member vary widely, from typeI to type III. It is a general truth that shale with higher organic carbon content will be more oilprone, and sections with organicrich shale in Yaojia member are believed to have promising oil potential. Multi geochemical indices indicate that the deposition environment varied quickly during the deposition of Yaojia member. The shales of Nenjiang 1st2nd (K2n1+2) formations are dominated by typeI and typeII kerogens and the amount of 4methysterane may be attributed to dinoflagellate. The relatively higher amount of gammacerane and low value of Pr/Ph indicate the salinity stratification of water column during the deposition of Nenjiang 1st2nd formations deposition. The source rock of Qingshankou 2nd3rd formations became mature in the middepth with peak oilgeneration at 1500 m.

Key words: Key words: Songliao Basin; Well SK1; organic geochemistry; deposition environment