Abstract:

The Jurassic strata in the areas around the Yakela fault-bulge in the northern Tarim basin are critical targets for hydrocarbon exploration, where a near-source alluvial fan-fan delta system with the fault-bulge as a provenance is developed. This cannot explain the extensive development of the sandbodies in Jurassic in the southern Yakela fault-bulge. Based on the analysis of the tectonic evolution of the Yakela fault-bulge, together with the seismic and core data and the reservoir characteristics, a comprehensive analysis was conducted on the sedimentary facies to determine the spatial distribution patterns of the sedimentary facies in the Jurassic Yangxia formation around the Yakela fault-bulge. It is found that during the Jurassic deposition the Yakela fault-bulge as a whole was higher in the west than in the east, with erosion occurring in the west and a peneplain state in the east at the late stage of Yangxia formation deposition. The sedimentary system primarily comprises two parts: one sourced from the western Yakela fault-bulge, forming an apron-like distribution of the near-source fan delta deposits along the fault-bulge; the other sourced from the southern Tianshan Mountains, forming a braided river delta system extending from north to south in the eastern Yakela fault-bulge. From the perspective of reservoir characteristics, the fan delta system is characterized by coarse lithology, mainly including conglomerates and gravel-bearing medium-coarse sandstones, with low textural and compositional maturities and poor physical properties. In contrast, the braided river delta system predominantly consists of gravel-bearing medium-fine sandstones, and records a long transport distance, with high textural and compositional maturities and good physical properties. The Yangxia formation in the eastern Yangxia sag may be a potential favorable exploration target.

Key words: Tarim basin, Yakela fault-bulge, Jurassic, Yangxia formation, tectonic evolution, sedimentary system