## 4 Results
### Unconformity Sealing Evaluation  
#### 4.2.1 Unconformity Closure Evaluation Parameters  
According to the results of the unconformity identification, the weathered clay core of key wells in the Ma 131 well area was selected. Two of the samples were selected as examples: sample a is from the 4272.45 m depth mudstone of the Baikouquan Formation of Well Mahu 17 (Figure 7a), and sample b is from the 4666.53 m depth mudstone of the Baikouquan Formation of Well Mahu 18 (Figure 7b). The stress-strain curve was recorded by the above experiment. From the stress-strain curve, it is evident that, due to the re-compaction of the rock's micropores, the rock fractures initially undergo a closure and compaction stage. During this phase, the stress-strain curve exhibits a \"concave\" shape, after which it transitions into the elastic deformation phase, following [PERSON]'s law. In this phase, the slope of the stress-strain curve remains constant, without changing as the stress increases. Once the rock sample reaches its yield stress limit, it enters the plastic deformation stage. At this point, microcracks begin to develop within the rock, and the stress-strain curve deviates from linearity. The crack pressure differential reaches its maximum value during this phase. Figure 6: Five types of unconformity structure maps of the Mahu Sag: (**A**) sand-mud-sand type; (**B**) sand-mud-mud type; (**C**) sand - sand type; (**D**) sand-mud type; (**E**) sand-volcanic type. Figure 7: Core experimental results and stress–strain curve. ((**a**) Mahu17 Well sample; (**b**) Mahu 18 Well sample). As the rock sample fractures completely, the number of microcracks increases and intersects with the original pores, forming macroscopic fractures, which results in a rapid decline in the rock's load-bearing capacity. Despite the fractures, the rock retains some bearing capacity, and the final stress-strain curve stabilizes at a dynamic equilibrium \"platform value\" (Figure 7). The fracture pressure difference is the difference between the core pressure and the confining pressure (which simulates the pressure of underground fluid migration on the caprock). Based on the specific conditions of the rock samples in this experiment, the maximum fracture pressure difference for rock sample A is 5.55 MPa (Figure 7a), while for rock sample B, it is 8.96 MPa (Figure 7b). The cracks are cut longitudinally along the circular surface at one end of the columnar core, with relatively flat sections. The development of fracture height and fracture length in rock was simulated under varying fracture pressure differences of 1 MPa, 3 MPa, 6 MPa, and 10 MPa. The goal was to infer the extent of internal fracture development in underground rock strata with significant thickness. The results revealed that both fracture length and height increased with the rise in fracture pressure difference. When the bedding surface strength was 1 MPa or 3 MPa, the hydraulic fracture propagation morphology remained essentially the same. However, when the strength was adjusted to a medium level, hydraulic fracturing extended through the bedding plane and eventually propagated into the overlying strata. Based on the simulation curve, it was observed that with a bedding plane strength of 10 MPa, the fracture height eventually reached approximately 70 m (Figure 8a). If the thickness of the weathered clay layer is less than 70 m, the fracture will pass through the entire layer, allowing oil and gas to escape, which compromises the sealing effect. On the other hand, when the weathered clay layer exceeds 70 m in thickness, increasing the pressure further will not lead to additional height increase in the fracture, regardless of pressure conditions. Figure 8: The variation characteristics of (**a**) fracture height and (**b**) fracture length under different strengths are numerically simulated. Thus, the maximum fracture height development is influenced by the fracture pressure difference. The greater the thickness of the weathered clay layer, the more effectively it inhibits crack extension.