A Sduty On Microfacies Characteristics In Delta Front Of Yaojia Formation, Northern Daqing Placanticline

After exploration and development of50years, most of the reservoir exploitation in Daqing Oil Field have entered into the high water cut stage. The condition of underground sand body and water distribution has changed dramatically, and thin reservoir to become the main potential target of mining.In this thesis, the main object is Yaojia Formation of Daqing Placanticline, Songliao Basin northern. Based on drilling, well logging and seismic data, the characteristics of high resolution sequence and microfacies distribution in shallow water delta has been analyzed under the control of the dense well conditions.Through the identification of high-resolution sequence stratigraphy interface, the high-resolution sequence classification of the target layer has been carried out. Two long-term base-level cycles, and10medium-term base-level cycles, and33short-term base level cycles were identified in Yaojia Formation of the study area. Meanwhile, the cyclic sequence type, stacking patterns of shallow water delta of are summarized.The results showed that Milankovitch cycles was well preserved in the stratas of Yaojia formation, there are2.679-3.972m thick long period cycles caused by eccentricity and1.379～2.576m thick mid-period cycles caused by the obliquity cycle and0.601-0.901m thick short-period cycles caused by precession. There is good consistency between high-frequency sequences and Milankovitch cycles. The mid-cycle, short-cycle and ultra-short-term cycles of high-frequency sequence are corresponding respectively to the long-period eccentricity, short-period eccentricity and the precession cycle of Milankovitch cycles. Lake level changes caused by the changes of Earth’s orbit major controlling factors of the formation of high frequency sequences.Combined with previous studies, the core observation showed that shallow water delta depositional system developed in Yaojia Formation of study area. Three types of sub-phase canbe identified in Shallow water delta depositional system, which including11kinds of microfacies:distributary channel, crevasse splay and crevasse channel, overflowing sand, floodplains, natural levees, underwater distributary channel, interdistributary bay, underwater overflow sand sheet sand, underwater natural levee. The deposition of shallow water delta influenced significantly by the climatic conditions. It can be identified two types of base-level cycles in Shallow water delta deposits:type A and type C short-term base-level cycles.