Application of Seismic Sedimentology to Predication of Lacustrine Turbidite Sandbodies: An Example of Paleogene in Biyang Area, Nanxiang Basin, Eastern China

Turbidite reservoir as a complex lithologic reservoir has bright prospect for oil and gas exploration and development. Turbidite sandbodies have favorable source/reservoir/cap combination and become one of the most promising targets. Because of complex thin interbedded deposition of turbidite sandbodies and technical limitation, it is difficult to describe and predict turbidite sandbodies in the Biyang area. This study provides a reliable approach to prospecting lacustrine subtle turbidite reservoirs and serves as a reference for seismic sedimentology study in lacustrine basins, especially in areas where detailed seismic work has been done but few wildcat wells are drilled. This study is aimed at predicting the distribution of turbidite sandbodies in the Biyang area with seismic sedimentology. By making use of the 90° phase shift technique, frequency spectrum decomposition and stratal slicing, sliced cubes were processed to display the distribution of sedimentary microfacies and reflect the evolutionary history. With core analysis, well-logging and lithology data, the turbidite sandbodies of the typical slices were interpreted, and the distribution and evolution of turbidite microfacies were predicted. Integration of seismic and geologic interpretations and balanced use of seismic sedimentology, high resolution sequence stratigraphy and seismic stratigraphy were the focus of our study. A large number of turbidite sandbodies developed between braided river delta and nearshore subaqueous fan. These sands were mostly oval and the larger turbidite was located in central deep lake facies zone in the the study area (nearly 2km2), extending WN-SE. Total turbidites area in the south was larger, most of them more than 1km2. Turbidite sandbodies in the west were relatively small, mostly only 0.2 ~ 0.5 km2. The turbidite sandstone reservoirs in different sequences could be effectively predicted. Formation of these turbidites was controlled by source type, source supply, and hydrodynamic condition etc., Based on detailed analysis of sedimentary characteristics and seismic sedimentology, this study established two typical beach and bar sedimentary systems in the Biyang area: braided river delta front-turbidite and nearshore subaqueous fan front-turbidite.