Abstract:

Comprehensive study of core, logging and seismic data, and classification of stratigraphic sequence interfaces show that various types of sandbodies, including beach and bar sands, coastal subaqueous fan and gravitational flow channel sands in Shahejie Formation, are developed on the western slope of Qinan sag. Basal overlapping, top denudation, and facies variation between them are evident in Shahejie Formation, thus multiple layer systems and various types of non-structural traps can be formed.The western slope in Qikou depression,an inherent structural slope,is the main directional area of hydrocarbon migration in the depression, and has excellent hydrocarbon supplying conditions. The beach and bar sandbodies in the 3 member of Shahejie Formation are widely distributed, and have an average porosity of 24.8% and average permeability of 175.5×10^-3μm²,thus belong to high porosity and high permeability reservoirs.Moreover, these sandbodies have never been disrupted by large tectonic movement since their sedimentation, thus the area would have favorable hydrocarbon preservation conditions. Various types of reservoirs have been discovered during previous exploration, including unconformity reservoirs, upwarping pinch-out reservoirs, and structural-lithologic reservoirs represented by Qi674 well reservoir, Lianmeng reservoir and Qinan 9-1 well reservoir, respectively, indicating that the area possesses the condition of forming certain size subtle reservoirs. According to the study of core, log and seismic facies, it is predicted that the low stand subaqueous fan sandbodies in the 3^rd member of Shahejie Formation on the western slope of Qinan sag and the slope break zone of the slope in Qibei sag would be the favorable areas in the later exploration; among which, the lithologic traps to the south of Kou 50 well and Zhuang 43 well fault block would firstly be selected as the exploration targets.

Key words: subtle oil/gas reservoir, slope exploration, beach and bar, sequence stratigraphy, Qinan sag