Study on sequence stratigraphy and sedimentary facies for the second member of Shahejie Formation of Qikou 18-1 Oilfield,Bohai Bay Basin

Based on the classic theory of Sequence Stratigraphy,the paper studies the sequence stratigraphic framework of Qikou 18-1 Oilfield and predicts the distribution of favorable reservoir facies belts,which can provide a geological basis for oilfield development planning. Through recognition of unconformity surfaces,first flooding surfaces and maximum flooding surfaces,the paper divides the third-order sequence into three system tracts,that is,lowstand system tract,transgressive system tract and highstand system tract and hence establishes the sequence stratigraphic framework for the second member of Shahejie Formation of Qikou 18-1 Oilfield.Subsequently,facies differentiation and evolution within each system tract of the framework is studied so as to predict the spatial distribution of favorable facies belts and sand bodies. The second member of Shahejie Formation of Qikou 18-1 Oilfield was deposited in a fan delta-lacustrine sedimentary system,the distribution range of favorable facies belts of each system tract was mapped and the spatial distribution of high-quality sandstone bodies was predicted. The distributary channels of fan delta within lowstand and highstand system tract,whichoverlay in space and possess excellent physical properties,are advantageous facies of the second member of Shahejie Formation in Qikou 18-1 Oilfield and make it the most favorable development targets for the oilfield.