## An Application Example  
### Geologic Setting  
The above workflow is applied to an example to predict the sandstone proportion of the M gas field, which is 439 km southeast of Shanghai and located in the X Depression in the northeast of the East China Sea shelf basin, one of the largest offshore Meso-Cenozoic sedimentary basins in China. The X Depression is mainly composed of Cenozoic sediments,  
Figure 1: Flowchart of determining the values of the three levels based on the confidence interval theory.  
and the large braided river sedimentary system is developed in the central and northern part of the sag, which forms giant thick diara- and riverbed-superimposed sand bodies. The source rocks of the Eocene Pinghu Formation (E2p) and Oligocene Huagang Formation (E3h) are mainly developed, which are the main spaces for oil and gas accumulation, of which the main gas layer H3 sand formation has the best reservoir property. The M gas field is located in the central inversion zone of the X depression and belongs to a low-permeability reservoir (Figure 2). The reservoir was formed under the background of large-scale compressions and contractions during the Oligocene period and belongs to the reversed anticlinal structure. The M gas field as a whole has a large burial depth, and it develops successively from bottom to top in the Eocene Pinghu Formation (E2p), Oligocene Huagang Formation (E3h), Miocene Longjing Formation (N1l), Yuquan Formation (N1y), Liulang Formation (N1l), and Pliocene Sandan Formation (N2s). Among them, the Huagang Formation is the main effective reservoir with little change in thickness, which can be divided into the upper members of the Huagang Formation (H1-H5) and lower members of the Huagang Formation (H6-H7). The trap area of the target interval ranges from 31.75 to 49.83 km\({}^{2}\). The M gas field is located in the main channel of the braided-river-delta underwater distributary channel, showing the characteristics of large sand body thickness and multi-stage superposition of channel. The H3b sand formation is the main gas-producing sand formation, and the diara is the most favorable reservoir. The target interval of the study area comprises the H4 and H3 members of the Huagang Formation, and the research data are the lithologic proportion data of five wells and ten beds within the H4 and H3 members. The regional structural geological background of the study area is shown in Figure 2a. The overall regional structural background of this area is not complicated, but there are many structural zones, which lead to complex fault systems and diverse fault combination styles, resulting in an unstable reservoir and migration modes of oil and gas. The paleogeographic overview and sedimentary environment of the study area are shown in Figure 2b. The sedimentary materials are mainly controlled by the NE provenance, and the drilling wells are distributed at the front of the braided river delta. The lithology distribution of the five wells is shown in Figure 2c, which also includes the H4 and H3 intervals. The lithology is mainly medium-fine sandstone and siltstone.  
Pebbled coarse sandstone, coarse sandstone, medium sandstone, fine sandstone, siltstone, and argillaceous siltstone are split into sandstone facies, while silty mudstone and mudstone are divided into mudstone facies to make the facies proportion calculation easier. Here, the reservoir is primarily made of sandstone. In order to lay the foundation for the subsequent reservoir characterization, the sandstone facies are used as an example to compute the proportion range of the sandstone facies and to examine the uncertainty of the sandstone proportion.