Application of Seismic Sedimentology on the Predication of Beach and Bar Sandbodies in Lacustrine: a case study of the Cretaceous in Chepaizi area, Junggar Basin, NW China

Dongna Zhao; Xiaomin Zhu; Yanlei Dong

Seismic sedimentology is a newly emerged interdisciplinary subject, which uses seismic data to gain insights into the rocks and their forming processes. It is regarded as a very effective tool for mapping high-frequency sequence and depositional systems, and plays an important role in the exploration and production of thin sandstone reservoirs. This study is aimed at predicting the distribution of beach and bar sandstone reservoirs in Chepaizi area by seismic sedimentological studying.

In Cretaceous, Chepaizi area, located in the northwestern margin of Junggar Basin, Northwest China, mainly deposited shore-shallow lacustrine beach bar microfacies, which are characterized by thin single sand layer (usually2-5m), fast lateral pinchout and strong reservoir heterogeneity. These beach-bar sandbodies are NE-extended, usually 5~10km long and 2~3km wide. Most of them are oil-bearing, and vertical superimposed, constituting the main production reservoirs of Cretaceous. There is a great amount of high-quality 3D seismic data in Chepaizi area where faults are not developed. In this study, under the guidance of seismic sedimentary theory, and by making use of the 90° phase shift technique, frequency spectrum decomposition and stratal slicing, the sliced cubes were processed to display the distribution of sedimentary microfacies and reflect the evolutionary history. With the assistance of the comprehensive analysis of core, lithology and well-logging date, the beach-bar sandbodies of the typical slices was interpreted subtly, and the distribution and evolution of beach-bar microfacies were predicted. This study was approached by following procedures: well-to-seismic tie, wavelet-phase adjustment, picking of geologic-time parallel seismic events, seismic resolution analysis, petrophysical analysis, selection of seismic attributes, stratal slicing, seismic depositional facies analysis, and applications to exploration and development. The whole workflow emphasized the integration of seismic and geologic interpretations and balanced use of seismic sedimentology, sequence stratigraphy and seismic stratigraphy.

In light of this study, the beach bar sandstone reservoirs of different sequences were effectively predicted. It was found the formation of these beach and bars was primarily controlled by the integrated effects of many factors, such as source type, source supply, hydrodynamic condition and so on. Meanwhile, based on the detailed analysis of sedimentary characteristics and seismic sedimentary results, this study established two typical beach and bar sedimentary systems in Chepaizi area, normal bedrock-beach bar and fan delta-beach bar. Overall, this study provided a reliable approach in exploration of subtle reservoirs in lacustrine and also can serve as a reference for seismic sedimentology study in non-marine basins, especially in areas where detailed seismic work has been extensively done but few wells drilled.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013