Evaluation of Shahejie Source Rock and Oil Source Research in the Liaoxi Depression, Liaodong Bay, China

Key words: 
• source rock

Abstract: The main reason for bad potential evaluation of Liaoxi depression is that hydrocarbon generation of Es3 and Es4 cannot be recognized, which is the principal issue of hydrocarbon exploration in Liaoxi depression. Based on source control theory and sedimentary faces study, analyzed geochemistry characteristics, through basin modeling and oil source research, we evaluated Shahejie Fm. source rock comprehensively. Based on a great quantity of seismic and well material, we identified fan delta faces coastal shallowlake faces middledeep lake faces of Shahejie Fm.  in Liaoxi depression, especially middle deep lake face of Es4. Source supply is sufficient in lower segment of Es3 and the size of middledeep lake is very small, its area of southern sag is largest, smaller in middle sag and least in northern sag. Source supply becomes smaller in middle segment of Es3 and the size of middledeep lake is very big that mainly locates in middle sag. The area of southern sag is larger and smaller in northern sag. Mud. stone of middledeep lake face is the precondition of forming source rock. Through 33 oil samples and 48 rock samples analysis of Liaoxi depression, we concluded that content of sapropelic and exinite of organic material is commonly higher and rich of planktonic algae in Shahejie Fm. source rock. Its kerogen type is ⅠⅡ. Basin modeling concluded that hydrocarbon generating threshold is 2 500 m, Es3 source rock below this depth and Es1 source rock is upper this depth. After oilsource correlation research, we considered that oil geochemistry characteristics are similar with source rock geochemistry of Es3 and Es4 in Liaoxi depression. Hence, Es3 and Es4 source rock is the most important oil source in Liaoxi depression. With organic faces and sedimentary faces researching, organic material of Es source rock is entirely rich. But there are some differences of these sags in Liaoxi depression. Geochemical indexes of northern sag of Liaoxi depression are higher, subordinate of middle sag, lower of southern sag. From distributions of middledeep lake face, the author  identified small scale of middledeep lake face of Es3 is developed in northern sag of Liaoxi depression, large scale of middledeep lake face of Es3 and Es4 are developed in middle sag of Liaoxi depression, and large scale of middledeep lake face of Es3 is developed in southern sag of Liaoxi depression. Middle sag of Liaoxi depression has a large potentiality of hydrocarbon generation, smaller in southern sag and least in northern sag based on comprehensive analysis.