Turbidity fans and hydrocarbon prospecting of lower 3rd Member of Shahejie Formation from well Che15, Jiyang depression

Abstract：Based on seismic, well-logging and core data, the authors recognized the deep-water turbidity fans and slide turbidity fans developed in the lower 3rd Member of Shahejie Formation from the well block Che 15 in Chezhen sag, Jiyang depression. Well Chegu 25 is characterized by the slide turbidity fans with supplied or rooted channels, where the inner fan and its channels are especially developed, and are composed of debris-flow and a few turbidity-flow boulder-, cobble- and pebble-conglomerates with thickness of 10 to 20 m and gravel sandstones bedded with thin-layer dark grey or grey mudstones; the conglomerates of falling-boulder 1.06m in size reflect steep slope topography. On the seismic profiles, the fans assume wedge form, where the inner-fan is weakly reflected, and the middle- and outer-fans are of divergently and subparallelly continuous seismic reflection configuration. Well Che 57 of fine-grained sediments is characterized by the deep-water turbidity fans with rooted channels and deep lacustrine facies, where the middle-fans are especially developed, and are composed of debris-flow pebbly-conglomerates with thickness of 5 to 11m and gravel sandstones interlayered with dark grey mudstones; the well-logging curve pattern of channel sediments is bell-shaped. it is concluded that the slide turbidity fans experienced progradation along the channels from north to south, and the deep-water turbidity fans occurred in the central lake; two types of fans were disposed in the pinch-and-swell form along the main tectonic orientation, and were wrapped in extensively-distributed deep lake facies, assuming the sedimentary framework of “fans packaged in deep-lake”. The recognition and confirmation of boundaries of the turbidity fans is of great significance for hydrocarbon prospecting of the subtle traps.