Wellhead stability during drilling in weakly consolidated marine hydrate-bearing sediments

Natural gas hydrates are undoubtedly an important clean energy source in the future. However, its temperature sensitivity poses a significant challenge to the stability of the wellhead and wellbore during the drilling process of hydrate-bearing sediments. In this study, the evolution characteristics of key parameters, including hydrate dissociation, bearing capacity and wellhead displacement, were analyzed using a thermo-hydro-mechanical-chemical coupled model. The results show that hydrate dissociation leads to a ∼40% reduction in bearing capacity, resulting in a final wellhead displacement of 4.1 cm under the base case. Meanwhile, the effects of factors such as hydrate saturation and drilling fluid temperature on wellhead stability were then analyzed. It was found that higher hydrate saturation in sediment and lower drilling fluid temperature significantly enhances wellhead stability. Specifically, increasing hydrate saturation from 20% to 60% reduces the final wellhead displacement from 5.4 cm to 1.7 cm, while raising drilling fluid temperature from 15 °C to 30 °C increases displacement from <0.2 cm to 7.5 cm. Furthermore, the effectiveness of vacuum insulation casing in maintaining wellbore stability was numerically evaluated through numerical simulation. The simulation results indicate that, hydrate dissociation is almost completely suppressed, bearing capacity remains stable, and wellhead displacement is nearly 0 cm when vacuum insulation casing is employed. This study provides valuable guidance for ensuring the safe and efficient drilling operation in hydrate-bearing sediment.