Seismic sedimentology of conglomeratic sandbodies in lower third member of Shahejie Formation (Palaeogene) in Shengtuo area, East China

The sand-conglomerate fans are the major depositional systems in the lower third member of Shahejie Formation in Shengtuo area, which formed in the deep lacustrine environment characterized by steep slope gradient, near sources and intensive tectonic activity. This work was focused on the sedimentary feature of the glutenite segment to conduct the seismic sedimentology research. The near-shore subaqueous fans and its relative gravity channel and slump turbidite fan depositions were identified according to observation and description of cores combining with the numerous data of seismic and logging. Then, the depositional model was built depending on the analysis of palaeogeomorphology. The seismic attributes which are related to the hydrocarbon but relative independent were chosen to conduct the analysis, the reservoir area of the glutenite segment was found performing a distribution where the amplitude value is relatively higher, and finally the RMS amplitude attribute was chosen to conduct the attribute predicting. At the same time, the horizontal distribution of the sedimentary facies was analyzed qualitatively. At last, the sparse spike inversion method was used to conduct the acoustic impedance inversion, and the inversion result can distinguish glutenite reservoir which is greater than 5 m. This method quantitatively characterizes the distribution area of the favorable reservoir sand.

The deep-lake deposit in the Upper Triassic Yanchang Formation in Ordos Basin,China and its significance for oil-gas accumulation

The deep-lake facies of the Yanchang Formation represents a large outflowing lake basin in the Ordos area.Its deposition can be divided into four stages:lake genetic and expanding stage,peak stage,inversion stage and dying stage.All the stages are obviously consistent with the evolution of depositional environment and the paleoclimate in the region.The study indicates that the lake basin has evolution fluctuations from highstand to lowstand for four times in its evolution history,and the deposition center of the lake has not obviously moved,staying along the Huachi-Yijun belt.The deep lake sedimentary system mainly consists of deep water deltas and turbidite fans during the entire evolution course of the lake basin in the Late Triassic.The former mainly developed on the slope of steep shore of the delta in the early period of the deep-water expansion and gradually experienced a big shift from deep-water deltas to shallow-water platform delta.And the latter appeared almost in all the above stages and had two types of turbidite fans,slope-moving turbidite fans and slump turbidite fans.The slope-moving turbidite fans have relatively complete facies belts overlapping one another vertically and consist of the slope channel of inter fans,the turbidite channel,inter turbidite channel and turbidite channel front of middle fans and outer fans(or lakebottom plain).However,the slide-moving turbidity fans are formed in the deep lake with their microfacies difficult to be distinguished,and only the center microfacies and edge microfacies can be determined.The two types of the turbidity fans are similarly distributing in the near-root-slope and far-root-slope regions.The deep-lake deposition governs the distribution of the hydrocarbon and reservoir,while the slope-moving turbidite fans are excellent reservoirs for oil-gas exploration due to their great thickness,widespread distribution and accumulation properties.