## 6 Conclusions  
1. Unconformity has a three-layer structure, including a residual layer, a weathered clay layer, and a weathered leaching zone. According to the difference between multiple logging curves, the identification factor Q\({}_{\text{i}}\) of the unconformity structure is summarized. The Q\({}_{\text{i}}\) value of the upper layer of unconformity is 0.4-0.5, the middle layer is 0.5-0.6, and the lower layer is 0.6-0.7, so as to distinguish the three-layer structure vertically. According to whether the weathered clay layer is developed and based on different lithologic configurations, the internal unconformity structure of Mahu Sag is divided into five types: sandstone-clay-sandstone, sandstone-clay-mudstone, sandstone-sandstone-mudstone, and sandstone-volcanic rock. Most of the study area is characterized by a clay-bearing layer type, and a few areas lacking the weathered clay layer types are concentrated in the south of the Mahu Sag.
2. The weathered clay layer is the key to the formation of unconformity oil and gas reservoirs. The physical simulation experiment is used to select the fracture pressure gradient and thickness as the most critical factors affecting its sealing. Taking the Ma 131 well area as an example, the fracture pressure coefficient of the roof and floor is distributed in a range of 2.0-2.3, and the fracture pressure coefficient of the reservoir is distributed in a range of 1.8-2.0. The logging curves are obviously different, and the average thickness of the roof and floor is 21 m, providing a good sealing effect. Under the action of the upper transport of the P/T overlapping unconformity structure and  
Figure 13: Diagram of the unconformity oil and gas reservoir accumulation pattern.  
the joint sealing of the middle and lower layers and the upper mudstone, the oil and gas are completely preserved in the trap.
3. The control exerted by the unconformity on oil and gas accumulation is reflected in several aspects: the effect of glutenite on oil and gas migration and accumulation in the structure; the sealing ability of mudstone and volcanic rock with dense structures; and the control effect of the combination of fracture and unconformity on oil and gas in different tectonic environments. After the oil and gas are generated from the source rock in the Mahu Sag, they migrate upward along the fault. The rocks above the unconformity and the tight sandstone developed under the sedimentary environment jointly serve as oil and gas transportation channels. The weathered clay layer under the unconformity surface has a stable structure and an excellent sealing effect, providing roof, floor, and lateral sealing conditions for oil and gas reservoirs.  
Conceptualization, Z.W., M.Z. and X.W.; methodology, Z.W., M.Z., X.W. and Q.X.; software, Z.W.; validation, Z.W., Y.B. and Y.C.; formal analysis, Z.W.; investigation, Z.W. and Y.C.; resources, M.Z., X.W., Z.A. and Q.X.; data curation, M.Z. and Z.A.; writing--original draft preparation, Z.W.; writing--review and editing, Z.W.; visualization, M.Z.; supervision, M.Z.; project administration, M.Z. and Z.A.; funding acquisition, M.Z., X.W. and Z.W. All authors have read and agreed to the published version of the manuscript.  
This research was funded by THE China National Petroleum Company Limited Forward-Looking Basic Research Major Project, grant number \"2021 DJ0405\", and the National Natural Science Foundation (41702135).  
Not applicable.  
All data and materials are available on request from the corresponding author. The data are not publicly available due to ongoing researches using a part of the data.  
[PERSON] and [PERSON] were employed by the PetroChina Xinjiang Oilfield Branch, Kelamayi 834000, China. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.