Depositional regimes and reservoir architecture characterization of alluvial fans of Karamay oilfield in Junggar basin, Western China

Abstract

We analyzed the lithology and sedimentary structures of the lower Karamay formation alluvial fan of Karamay oilfield in Junggar basin and subdivided its lithofacies into six types. The depositional regimes of the lower Karamay formation regressive alluvial fans contain (1) cohesive debris flows, (2) sandy debris flows, (3) grain flows, (4) turbidity currents, and (5) traction currents in the light of sedimentary fabrics and lithofacies association. In terms of lithofacies association, depositional succession, boundary surface hierarchy and wireline logs, fourth-order reservoir architectures for this alluvial fan are composed of nine types: (1) trench channel conglomerates, (2) trench sandy conglomerates, (3) trench proximal sandbody, (4) trench sheetflood lithosome, (5) trench distal sandbody, (6) braided channel, (7) channel gravel bar, (8) overflow sandbody, and (9) runoff channel. On the basis of the reservoir architecture identification of all wells, we established a three-dimensional (3D) architectural element model of the lower Karamay formation with a method of sequential indicator simulation to reveal the reservoir architecture spatial distribution. Integrated three-dimensional reservoir architecture models with contemporary depositional characteristics of alluvial fans, we concluded the depositional patterns of reservoir architectures for different alluvial fan subfacies, which shows the geometric features and aspects of the reservoir architectures. This information provided a technical foundation for the remaining oil prediction, development strategy optimization, and oil recovery enhancement of the conglomeratic oil reservoirs at the high water-cut stage.