Depositional model of the fan delta of thick glutenite: Example from the Linhe Depression, Hetao Basin, China.

Abstract

The thick glutenite formed in the Linhe Depression of the Hetao Basin during the Early Cretaceous offers notable exploration potential. However, the sediment comprises a rapidly stacked succession of glutenite featuring poor sortability, with the individual sedimentary layers reaching up to 120 m in thickness. However, the limited core variations coupled with the "dentate box" shape of the well logging curves pose challenges in identifying the sedimentary microfacies of the study area, thereby hindering its exploration and development. This study selected the Jihua-2 block in the Linhe Depression as the study area and attempted to identify the sedimentary microfacies in the thick glutenite formed in this region. Results indicate that under arid and shallow-water conditions, the Langshan Fault continued to move, and a set of thick-bedded glutenite masses was deposited in the downthrown block. Detailed core observations revealed seven lithofacies and five lithofacies combinations. The study area is mainly characterized by a fan-delta front, which is further subdivided into the main part of underwater distributary channels, lateral margins of underwater distributary channels, and interdistributary bays. By integrating probabilistic distribution statistics with single well analysis, a quantitative standard for identifying well logging facies based on cored wells was established. Kriging interpolation was performed to clarify the spatial distribution of the sedimentary microfacies across the study area, enabling the establishment of a depositional model of fan-delta facies for the study area. The influence of faults on sedimentary facies and the relation between depositional patterns and hydrocarbon distribution in the study area were also discussed. The findings of this study can contribute to the development of improved methods for identifying sedimentary microfacies in glutenite fan deltas, with implications for guiding exploration and development.