Recognition of sequence boundary and its characteristics study in Qingshankou Formation of front zone
Zhang Yongwang1 Zeng Jianhui1 Deng Hongwen2 Wang Hongliang2 Gao Xia3 Liu Jun4
(1.Basin &|Reservoir Research Center|Chinese University of Petroleum|Beijing |102249； |2.School of Energy Resources in China University of Geosciences|Beijing |100083； |3.School of Earth Exploration and Information in China University of Geosciences|Beijing |100083； |4.Exploration Institute of Jilin Oil Field|Songyuan|Jilin |131100)
Guided with the theory of high resolution sequence stratigraphy and based on previous research results，we constructed sequence stratigraphic scheme of Qingshankou Formation which was in front zone of the west slope in southern Songliao Basin，where six sequence boundary surfaces were identified and 5 mediumterm baselevel cycles(fourth order sequence)were divided. Core identification marks of the surfaces were established，that is，channel scouring surfaces，formation stacking transformation，changes of facies type，exposure erosion surface. The sequence boundary existed in which abrupt changes of amplitude happened or in conversion point of composite forms on logging curve，and the identification marks of seismic profile were not apparent in this area. According to the identification marks，the sequence boundary surfaces were divided into unconformity surface，depositional turnaround surface and toplap surface，and a detailed analysis was given to their characteristics. Flooding surfaces in Qingshankou Formation included fluvial deposits，delta and deep lake facies. Identification of the sequence boundaries and the flooding surfaces was very significant for building framework of the sequence stratigraphy and researching the distribution and prediction of reservoir.