Abstract:

Based on the theory of high resolution sequence stratigraphy, the short-term base level cycle of delta front of Chang 8 oil reservoir set in Jiyuan Oilfield was divided into two types, including non-symmetric short-time cycle and symmetric short-time cycle. The non-symmetric short-time cycle includes upward-deepening and upward-shallowing cycles, and the symmetric short-time cycle includes three kinds of cycle: the ascending half cycle thickness is greater than the descending half cycle thickness, the ascending half cycle thickness is less than the descending half cycle thickness, and the ascending half cycle thickness is approximately equal to the descending half cycle thickness. According to the forming reason, the reservoir sand bodies of Chang 8 oil reservoir set were divided into three categories and six types, and each kind of sand body is obviously controlled by relationship between the accommodate space（A） and sediment supply（S）. In the process of the base level rising, when the A/S<1, mainly formed cutting distributary channel sandbody, while when the A/S>1, mainly formed complete type channel sand body. In the process of base level falling, when the A/S<1, mainly formed isolated type mouth bar sand body, while when A/S>1, mainly formed superposition type mouth bar sand body and far bar sand body. In a complete base level cycle, if there not only kept rising short-term base level of deposition, but also retained the decline phase deposition, so the composite dam sand bodies formed. Chang 8 oil reservoir set in Jiyuan Oilfield belongs to lithologic reservoir. Therefore, further study on shortterm base level change rule and its control effect on sand bodies, forecasting and looking for underwater distributary channel, the superposition type sand dam and mouth bar sand bodies will be the main direction of next exploration.

Key words:  sequence models, sequence framework, controlling factor, Paleogene Dainan Formation, Gaoyou Sag, northern Jiangsu Basin