## 5 Conclusions  
This study categorized, statistically analyzed, and described the present casing damage scenario in the concentrated G155 block. A finite element numerical model was devised to examine stress levels in damaged well casings within this region. The ensuing conclusions are detailed below:  
1. Based on the calculation of typical single well fracturing data and the application of the in-situ stress inversion method, the structural stress coefficient of the study area is derived, and the maximum and minimum horizontal in-situ stress calculation formulas are obtained. Theoretical stress analysis is conducted on casing-damaged wells under uniform and non-uniform conditions.
2. According to the finite element analysis of the casing of X1 and X2 wells under non-uniform in-situ stress conditions at \(\sigma_{\text{h}}=30\) MPa and \(\sigma_{\text{H}}=20\)-40 MPa, it can be concluded that the reasons for casing damage in the study area are not only non-uniform in-situ stress but also some other creep additional loads.
3. Finite element analysis of casing subjected to mudstone creep revealed increased shearing and deformation post-water immersion, causing premature oil well failure over water wells. The equivalent force rose with higher injection production ratios. Ratios above 1.3 led to gradual compression and deformation, exceeding the yield limit, while ratios over 1.6 induced longitudinal stretching. At a ratio of 1.9, shear stress near water wells surpassed the casing's yield limit, resulting in deformation.  
Figure 15: Von Mises stress curve of J55 casing at different injection production ratios: (**a**) 1.0; (**b**) 1.3; (**c**) 1.6; (**d**) 1.9.  
The final Von Mises stress in the G155 block is influenced not only by the injection production ratio but also by pore pressure, permeability, and water injection pressure. Key mechanical factors contributing to casing damage are horizontal in-situ stress and mudstone creep.  
Conceptualization, T.W. and J.S.; methodology, M.L., N.L. and T.Z.; formal analysis, T.W.; investigation, T.W., N.L. and J.S.; resources, T.Z.; data curation, M.L. and N.L.; writing--original draft preparation, T.W. and M.L.; writing--review and editing, T.Z. and J.S.; supervision, J.S.; funding acquisition, T.W. and J.S. All authors have read and agreed to the published version of the manuscript.  
This work is supported by the National Natural Science Foundation of China (No. 42141011) and the National Science and Technology Major Project during the 13 th Five Year Plan (No. 2017 ZX05013-005).  
Not applicable.  
The data that support the findings of this study are available from the corresponding author upon reasonable request.  
We would like to sincerely acknowledge the National Engineering Laboratory for Exploration and Development of the Low Permeability Oil and Gas Field for providing experimental conditions and instruments.  
Authors [PERSON], [PERSON], [PERSON] and [PERSON] were employed by the company China National Petroleum Corporation. The remaining author 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.