Dynamics of Horizontal Well Drilling in Deepwater Shallow Gas Hydrate Reservoirs: A Mass and Heat Transfer Study

Summary Natural gas hydrates represent a promising and environmentally friendly alternative energy source, with horizontal wells being an effective method for efficient extraction. However, the drilling process of horizontal wells presents challenges due to the prolonged contact between the drilling fluid and the hydrates. This interaction leads to a significant influx of drilling fluid, triggering hydrate phase transition and causing instability within the wellbore. To address these technical issues, this study focused on decomposition-induced wellbore instability and reservoir structure damage during deep-sea natural gas hydrate drilling. Specifically, we investigated the stability of the gas hydrate phase during drilling shallow, deep-sea horizontal wells. To accomplish this, we established a 2D mathematical model that describes the nonsteady-state mass and heat transfer process between the wellbore and hydrate reservoir. In addition, we explored the mass and heat transfer mechanisms between the drilling fluid and hydrates, obtaining a 2D distribution of temperature and pressure fields within the wellbore and hydrate reservoir. The findings of this research contribute to the theoretical and technical development of safe and efficient drilling fluids for hydrate reservoirs.