A New Understanding of Stratigraphic Development in Subsurface Arid Alluvial Fans: Implications From the Northwest Margin of the Junggar Basin, China

Abstract

ABSTRACT Alluvial fans are common sedimentary deposits on Earth and serve as crucial reservoirs for underground oil and gas. However, our understanding of the stratigraphic development and sedimentary evolution of different alluvial fan types remains limited. This study examines the alluvial fan deposits of the Baikouquan Formation in the Bai21 Block of the Baikouquan Oilfield, located on the northwestern margin of the Junggar Basin. Guided by sequence stratigraphy theory and utilising three‐dimensional seismic, logging and core data, it applies well‐seismic integration, cyclical correlation and dynamic verification to investigate the stratigraphic development and sedimentary evolution of arid alluvial fans. The stratigraphic development of arid alluvial fans is characterised by unevenly thick strata, providing a more detailed view of the traditional stratigraphic scheme of ‘marker bed constraints, isotropic distribution and cycle contrast’. This divergence offers new insights into the stratigraphic framework of arid alluvial fans. The foreset body of each fan is sequentially deposited from the source area towards the sedimentary centre, typically forming a three‐part subfacies assemblage comprising the fan root, fan middle and fan margin. The correlation of conglomerate bodies aligned with the source direction, their connectivity across subzones between individual wells and the internal relationships within the reservoir assemblage all display marked differences from previous models. This understanding more accurately reflects the sedimentary context of alluvial fans. The study holds significant value in clarifying the formation and evolutionary processes of similar systems. The proposed stratigraphic and sedimentary evolution models offer crucial guidance for evaluating the connectivity of conglomerate bodies within alluvial fan reservoirs and for optimising the placement of injection and production wells.