Characteristics of gravity flow sedimentation of Chang 63 in the Huaqing area, Ordos Basin

Abstract

Objective The gravity flow sedimentary sand body found in a lake basin is considered a promising target area for tight oil exploration. Methods In this study, we investigated the characteristics, main controlling factors, and sedimentary model of the Chang 63 sand group in the Huaqing area of the Ordos Basin, through core observation, analysis, and logging data. Results Our findings indicate that the sediments of the Chang 63 sand group in the Huaqing area have a fine grain size, with a probability of grain size distribution showing an upper convex two-stage type. The overall sedimentary structure is characterized by the development of jumping and suspension, typical of deep-water gravity flow deposits. We identified three types of gravity flow deposits in the Huaqing area: slump deposits, clastic flow deposits, and turbidity deposits. These deposits form three subfacies: channel, lobe, and lobe lateral. The development of deep-water gravity flow deposits in the Chang 63 area of the Huaqing area is primarily influenced by several factors. These include an abundant source supply in the Northeast, sufficient water depth in the lake basin, deep-water slope break topography in the lake basin, and volcanic and seismic sedimentary events of the Yanchang Formation. Notably, there are distinct differences in gravity flow deposition type, sand body thickness, and internal structure across different facies belts. In the vicinity of the delta source, the channel is mainly composed of slump deposits and some sandy debris flow deposits, with thin sand bodies and limited distribution. In the middle part of the sediment, the lobes consist mainly of sandy debris flow deposits, including some turbidity current deposits with vertically overlapping sedimentary sand bodies distributed as thick layers. In the deep lake area, the lateral margin of lobes is primarily composed of turbidity current deposits, with sand bodies distributed as thin interbeds. Conclusion This study not only enhances our understanding of gravity flow sedimentation in lake basins but also provides a crucial geological foundation for future exploration and development of oil and gas resources in gravity flow sand bodies.

Keywords

• huaqing area
• gravity flow
• sandy debris flow
• turbidity current
• chang 63 of yanchang formation