Control of Sedimentary Model on the Interlayers, the Fluids Movements and Distribution in the Reservoir：A Case Study on the Carboniferous Donghe Sandstone in Hudson Oilfield, Tarim Basin, China

The Donghe Sandstone in Hudson Oilfield, Tabei Uplift, Tarim Basin, China, has been proven to be a set of transgressive-regressive littoral sandstone which was developed on the sedimentary margin controlled by a third-order... [ view full abstract ]

The Donghe Sandstone in Hudson Oilfield, Tabei Uplift, Tarim Basin, China, has been proven to be a set of transgressive-regressive littoral sandstone which was developed on the sedimentary margin controlled by a third-order sequence in the Early Carboniferous. This set of sedimentary sandstone, which consists of two system tracts (TST & HST), has a small thickness (17.3m on average) in the reservoir development region. The TST has a relatively minor thickness and scale while the HST covers the entire region and constitutes the main body of the Donghe sandstone in this region. Due to the gentle slope, strong wave energy and stable source supply during the sedimentary stage, the HST mainly developed progradational shore sand-bars. It comprises two layered prograding-type parasequence sets that pinch out landward and thicken seaward. The interfaces among these parasequence sets are approximately parallel to each other. Along these interfaces, shale content was so high that argillaceous interlayers that have large thickness and steady distribution formed in the diagenesis stage. Calcite cementation could also be developed along this type of interfaces and calcareous-argillaceous interlayers or calcareous interlayers could form later. Interlayers developed on this order of interfaces strongly hinder the vertical movements of the fluids. However, inside a single parasequence set, in the section perpendicular to shoreline, a single parasequence manifests as 1~2 wedge-shaped sand-bars and the adjacent sand-bars prograded seaward successively, the latter overlapping the former. Parallel to the shoreline, however, a parasequence manifests as a series of irregular-shaped sand-bars distributed along the shoreline. With a scale of 2~8 km and a average thickness of 2~5 m，a single sand-bar has a vertically upward-coarsening sequence and a slightly eroded top. Perpendicular to the shoreline, the sediments of a single sand-bar generally coarsen landward and fine seaward. The interfaces between two adjacent sand-bars are seaward-inclined, along which argillaceous, calcareous-argillaceous and calcareous interlayers were developed during the diagenesis stage. Interlayers developed on this order of interfaces mainly hinder the lateral movements of the fluids on the condition that they have a steady distribution. The joint distribution of these two types of interlayers splits the whole Donghe sandstone into many compartments. Oil and gas unevenly accumulated in these compartments during the infilling periods, which divided the whole reservoir into minor reservoirs.