Geophysical identification of river-tide controlled deltaic sedimentation and its implication for petroleum geology: a case study of Pingbei area, Xihu Sag, East China Sea Shelf Basin

Abstract

Understanding of sedimentary environment is the basis of oil exploration and development. Previous research on the characteristics and distinguishing of single sedimentary system by using logging curves and seismic data was mostly carried out on the determined sedimentary system. However, for the river-tide controlled cases, when the main bodies of fluvial and tidal actions are unclear, sedimentary systems are rarely studied. Based on the difference of the oscillation frequency of tide and river water bodies, combined with the correlation between the logging curves of gamma ray and the mud content as well as the influence on seismic facies by hydrodynamic strength and the difference of the size and scale of river-tide controlled delta, a geophysical method on the basis of natural gamma log difference (ΔGR) and seismic facies wave length/height ratio is proposed to distinguish river-tide controlled delta sedimentary systems. A case study was carried out with the sedimentary system of the Pinghu Formation in Pingbei area of the Xihu Sag, East China Sea Shelf Basin, and it was concluded that this method can effectively distinguish river-tide controlled delta system. At the side edge of the underwater low uplift, Baoyunting low uplift, relevant parameters have been effectively picked up to distinguish the river-tide controlled delta system, and to identify the tidal channel development zone and potential targets for channel filling. It is clear that the identification of river-tide controlled system has an indicative significance for the prediction of lithologic traps and favorable reservoir units.

Keywords

• geophysical characterization
• natural gamma log difference
• wave length/height ratio
• river-tide controlled delta
• xihu sag
• east china sea shelf basin