Abstract:

According to outcrop investigation and well-logging identification, the sedimentary characteristics and distribution law of the alluvial fan in Kuche Formation of Neogene in Kuqa Depression were systematically studied with seismic and 3D electric method data, and the sedimentary models of the alluvial fan were obtained. The alluvial fan is dominated by the yellow or yellow-red conglomerates and coarse-grained sandstones, and there exist flush-filling structures, cross beddings and parallel beddings in conglomerates. The well-logging curves of the alluvial fan are in the characteristics of low GR and high resistance, and manifest themselves as box-like, infundibuliform and campaniform shapes. The seismic facies are dominated by clutter and foreset facies. In the areas lacking wells, the data of 3D electric method were also used to improve the research precision. The results of comprehensive research reveal that the scales of alluvial fans in the western region nearby well Bz1 and well Db1 are larger than those in the eastern region, and the tectonic movement is the main controlling factor; it experienced strong tectonic movements during the depositional period of Kuqa Depression, and the uplift caused lakes to shrink quickly to the south，and mountain blocks rose and suffered from erosion, providing sediment sources for alluvial fans; the scale and distribution of alluvial fans in the area nearby well Bz1 were expanding continuously; due to tectonic uplift, the alluvial fan in the area nearby well Db1 has the feature of multiple provenances. It is considered that there are two models of alluvial fans in Kuqa Depression, i.e. a model of single provenance of conglomerate, which reveals a long-term, stable and successional depositional process, and a model of multiple provenances of conglomerate, which is controlled by local structures.

Key words: Kuqa Depression, Kuche Formation, alluvial fan, sedimentary characteristic, sedimentary model