It is very important to find the subtle reservoir by using the fine division of the sequence and the analysis of the sedimentary microfacies in the late stages of oil and gas exploration，especially when the structural oil-gas reservoirs are unable to meet the production needs. Through the comprehensive analysis of 3D seismic，drilling core and well log data，etc.，the spatial distribution of sedimentary facies was determined by using 3D seismic data，layers of sandbodies were divided by drilling and log data，by which the sedimentary facies and the sequence of the Qigequan area were described finely. And then the connectivity and spatial distribution of sandbodies were studied based on the sedimentary facies and sequence framework. The results show that the retrogradation is dominant during SSC5-SSC3 sedimentary period in the study area.After one regressive process occurs rapidly during SSC2，the sedimentary base level continues to decline during SSC2- SSC1 sedimentary period，and the fan delta sedimentation is dominant at the later period. It is found there are fan delta sedimentary facies and braided river delta sedimentary facies in the research area of lower member of Xiaganchaigou Formation of Oligocene. The braided river delta includes microfacies of underwater distributary channel，underwater distributary interchannel，mouth bar and sheet sand. Sedimentary facies of fan delta is divided into two subfacies：fan delta plain and fan delta front. According to the distribution of sandbodies and the porosity and permeability analysis and on the basis of sedimentary facies and sequence stratigraphic analysis，it is concluded that the sandstone lens and up-dip sandstone pinchout in the slope break near Well Qi32 are the key targets of reservoir exploration.