## 4 Result  
### Sedimentary Characteristics of Drilling  
Based on nine wells drilled in the basin, the sedimentary characteristics of carbonate rocks in each time slice of Wan'an Basin were analyzed in detail through parallel well comparison, and the lithologic assemblage characteristics in different regions in combination with logging information were identified. The findings show that during the Early Miocene, the western part of the Wan'an Basin was dominated by delta deposits in in Figures 4 and 5, with interbedded sand-shale deposits in lithology. In the middle and east of the basin, it was the sand and mudstone deposits in the shore-shallow sea. Well Mia-1 in the north of the basin reveals that carbonate deposits existed in this period but on a small scale and scattered on the periphery of the delta.  
Three of the four wells drilled through the Lizhun Formation in the north encountered carbonate rocks indicate that the Middle Miocene was also a main period of carbonate deposition in the Lizhun Formation, as shown in Figures 4 and 5. The 12B-1, DUA-1 and AM-1 wells in the south have encountered carbonate rocks. However, there are some differences in the three wells. There are only two thin layers of carbonate deposits in well 12B-1, interspersed like lenses with sand and mudstone. In well DUA-1, the carbonate and mudstones are interbedded with mudstones, and the thickness of each layer of carbonate is about 100 m. In addition, a large set of carbonate rocks was deposited in Well AM-1. During this period, the content of carbonate rocks in the Wan'an Basin gradually increased from west to east, while the GR values of the carbonate formations in wells DH-1, 4A-1 and DUA-1 were generally low. Moreover, the zigzag change in the logging curve indicates that the lithology of the carbonate rocks in the western part of the basin is impure, which may be caused by the input of some terrigenous clasti  
Figure 4: The associated stratigraphic columns of five wells in north of Wan’an Basin. Well location is shown in Figure 2.  
The GR value of well AM-1 in the eastern part of the basin during the same period is also relatively low, but the curve is box-shaped, reflecting that the carbonate rocks were relatively pure in lithology and had low impurity content. Moreover, the difference in the acoustic curve between the east and the west of the basin reflects that the layer velocity of the eastern carbonate rock is stable compared with that of the western carbonate rock. This velocity difference may have been caused by lithology difference, which is consistent with the GR curve. During the Late Miocene, a small amount of thin reef deposits existed in the northern part of the basin with the form of interlayers in the sand and mudstone, while in the south part, only a nearly 100 m thick reef was identified in well 12B-1; the other three wells revealed that much sand and mudstone had occured in the shallow sea environment. Specifically, the lithology is relatively single and dominated by mudstone, and the corresponding GR is relatively stable, which is very different from the GR curves of wells DH-1 and DH-2, which show zigzagged fluctuation in the Early Miocene. The lithology is relatively simple, mainly mudstone, and GR is relatively stable, which is quite different from the Early Miocene DH-1 and DH-2 GR curves with zigzag fluctuations. On the whole, the reefs were the main form of carbonate deposition in the Kunlun Formation, but the deposition thickness is thin and scattered. From the Pliocene to the Quaternary, the sedimentary environment was stable shallow sea shelf slope deposition, and the content of lithologic sandstone gradually increased from bottom to top, which may have been caused by the increasing input of terrigenous detritus that gradually pushed the shelf eastward.