## 5 Conclusions  
In this study, a comprehensive model for the stability analysis of horizontal wells in hydrate reservoirs was established, the coupling of multi-physical fields in the drilling process of hydrate reservoirs was realized, the stability of horizontal wells drilled in hydrate reservoirs was examined, and relevant sensitivity analyses were carried out. The conclusions are as follows:  
1. The intrusion of drilling fluid into the hydrate reservoir under differential pressures is the main factor leading to the decrease in the mechanical strength of the formation. Gases and liquids generated by hydrate decomposition in the formation increase the pore pressure in the formation, thereby reducing the effective stress in the formation.  
Figure 21: Variations of wellbore yield area at different permeabilities.  
Figure 20: The distributions of hydrate saturation and effective plastic strain. (**a**) Distributions of hydrate saturation around the wellbore, (**b**) Distributions of effective plastic strain around wellbore.  
The combination of the two causes the risk of wellbore destabilization to rise sharply in weakly cemented, poorly diagenetic hydrate reservoirs.
2. Since the stress distribution around horizontal wells is different from that around vertical wells, the plastic yield zone of horizontal wells is no longer in the shape of a regular fan ring but is unevenly distributed. The closer the formation is to the wellbore, the more complete the decomposition of hydrates in the formation is, and the greater the effective plastic strain is.
3. All other conditions being held constant, increases in drilling fluid intrusion pressure, temperature, and reservoir permeability will lead to an expansion of the range of decline in formation mechanical strength around the wellbore and the wellbore yield area. The wellbore production area will decrease with increasing reservoir porosity, which is beneficial for wellbore stability during drilling, but the risk of wellbore destabilization may increase dramatically once prolonged production occurs and the hydrates around the wellbore are fully decomposed. Due to limited time and energy, further in-depth research should be conducted in the following areas in the future: 1. Considering computational efficiency and accuracy, this article only established a two-dimensional numerical simulation model. In subsequent research, a three-dimensional physical model can be established to obtain more accurate research rules.
2. This article simplifies the influence of formation heat transfer, and in the future, research on the effects of formation heat transfer on rock skeleton and formation fluid properties can be considered.  
Conceptualization, Z.S. and Z.L.; Methodology, Z.S., Z.G. and N.M.; Software, Z.S., X.W. and Z.G.; Validation, X.W. and Z.L.; Formal analysis, Z.L., N.M. and J.Z.; Resources, Z.G.; Data curation, J.Z.; Writing--original draft, Z.L. and N.M.; Writing--review & editing, Z.W.; Visualization, J.Z.; Supervision, Z.W. and B.S.; Project administration, Z.W. and B.S.; Funding acquisition, Z.W. and B.S. All authors have read and agreed to the published version of the manuscript.  
This research was funded by [The Scientific and Technological Innovation Projects in Shandong Province] grant number [2022 CXGC020407], [the National Natural Science Foundation of China] grant numbers [52288101, 52434002, 52304016], and [the Fundamental Research Funds for the Central Universities] grant number [24 CX10004A].  
Not applicable.  
Data Availability Statement: Data is contained within the article.  
Conflicts of Interest: Authors [PERSON] and [PERSON] were employed by the company CNPC Offshore Engineering Co., Ltd. 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.