Sequence Stratigraphic Characteristics of Fluvial Facies in the Guantao Formation of South Gentle Slope Belt, Huanghekou Sag

Abstract Through the comprehensive analysis of the data related to cores, logging and seismic, the author holded that there were two kinds of sedimentary systems in the study area, which were braided river deposits and meandering river deposits. According to the sequence stratigraphy method of fluvial facies proposed by Catuneanu et al, we established sequence stratigraphic framework in the Guantao formation of south gentle slope belt, Huanghekou Sag. It was divided into 2 third-order sequences, named as SQGU and SQGL, each of the third-order sequences contains a high accommodation systems tract (HAST) and a low accommodation systems tract (LAST). On this basis, the author summarized the sedimentary sequence evolution characteristics in the Guantao formation of south gentle slope belt, Huanghekou Sag. In the period of LAST in the SQGL, there were mainly composed of braided river facies in the study area, main developed multistage compound sand body. In the period of HAST in the SQGL, there were mainly composed of meandering river facies in the study area, main developed isolated point bar sand body and a high proportion of flood plain mud. The evolution characteristic of the SQGU was similar to the SQGL. Because of the accommodation space of the SQGU was at a high level, the grain size of sandstone and the percentage of sandstone are smaller than SQGL. It is generally accepted that it was mainly composed of braided river facies in Guantao formation of Huanghekou Sag, difficult to form oil and gas reservoir due to lack of mudstone cap rock. The exploration of Guantao formation has not attracted enough attention. Through this analysis, the author thinked that two sets of meandering river deposition can provide partial sealing and created conditions for oil-gas accumulation in the Guantao formation of south gentle slope belt, Huanghekou Sag. Under the guidance of this research, we have obtaineda certain oil and gas discovery in the study area.