Sedimentary characteristics of humid alluvial fan and its control on hydrocarbon accumulation: A case study on the northern margin of the Junggar Basin, west China

摘要

Alluvial fans in humid regions are different from arid alluvial fans for the special sedimentary characteristics and distribution pattern. In this paper, we systematically studied the sedimentary facies of Jurassic Badaowan Formation in the northern margin piedmont belt of Junggar Basin based on the comprehensive analysis of geological and geophysical data acquired. The results show that under the comprehensive influences of tectonic setting, paleo-provenance and paleo-climate, large-scaled humid alluvial fans are developed in the piedmont belt of Hala'alt mountain. The fluvial activity of alluvial fan is stronger and more stable in the humid type than that in the arid type. Three subfacies are identified in the humid alluvial fan, i.e. the upper fan, middle fan and lower fan. The middle fan can be further divided into braided river channel and the peat bog. Then we build the sedimentary facies model based on the microfacies types and distributions. This model is significantly different from arid alluvial fan in lithologic features, sedimentary sequences, distribution scales and microfacies match patterns. The reservoir distribution is mainly controlled by the favorable microfacies, lithofacies and depositional fabric. We suggest that the braided river channel glutenite lithofacies and grit lithofacies in the middle fan subfacies are the most favorable reservoir facies belt for hydrocarbon accumulation.