Internal architecture characteristics of Triassic arid alluvial fan in northwestern margin of Junggar basin,China

Taking Yizhong area of Karamay Oilfield as an example, we perform fine reservoir architecture analysis using hierarchical analysis method based on comprehensive application of well logs, core data, outcrop and modern... [ view full abstract ]

Taking Yizhong area of Karamay Oilfield as an example, we perform fine reservoir architecture analysis using hierarchical analysis method based on comprehensive application of well logs, core data, outcrop and modern deposition data. Based on facies belt division, we constructed the grading system of seven to nine level reservoir architectural elements. Then we made clear the formation causes, scale and distribution patterns of reservoir architectural elements, and finally the reservoir architecture model was constructed. The results show five aspects of cognition. ①An alluvial fan can be divided into four facies belts, including trench flow belt, sheet flooding belt, braided stream channel belt and run-off belt. ②The main subject of trench flow belt was broadband-like trench flow sediment bodies which vertically compounded by several trench flow gravel bodies. In inter-flood period, small scale streams erode the upper part of each trench flow gravel body, and a gully network formed. ③The main subject of sheet flooding belt was fan-like gravel-sand bodies which were laterally or vertically composed by several sheet flooding lobes. Muddy inter-layers covered at the top of lobes can be regarded as stable seepage barrier. ④The main subject of braided stream channel belt was braided channel association which was composed by several individual channels laterally (include flooding channel and inter-flood period channel). Among these channels, flooding channels were easier to be flooded due to a larger scale, a higher degree of lateral complexity and better physical properties. On the contrary, inter-flood period channels have lower degree of lateral complexity and poor physical property. ⑤The main subject of run-off belt was overbank fine sediments. Run-off channels had small scale, poor physical properties and can pinch out easily at the head of distal fan.