Research on Key Parameters of Horizontal Well Drilling in Marine Hydrate Reservoirs

While horizontal wells for gas hydrate exploitation allow for a larger effective contact area between the horizontal well and the reservoir, they also face severe wellbore stability problems. Two key issues are the dynamic drilling fluid safety density window and the limiting extension length of the horizontal section. This study established a horizontal well drilling model for hydrate reservoirs and a model for analyzing key parameters of the horizontal section based on the basic data of hydrate reservoirs at station SH2 in the South China Sea. The factors influencing the variation of the dynamic drilling fluid safety density window and the ultimate extension length of a horizontally drilled well section were analyzed using this model. The results showed that: The stress distribution in the surrounding rock of the well wall in the hydrate formation is dynamically changing due to changes in formation mechanical parameters resulting from hydrate decomposition after drilling fluid intrusion into the reservoir. This ultimately results in the safety density window for drilling fluids in horizontal wells drilled in marine hydrate reservoirs, which also changes dynamically over time. Drilling fluid physical properties play a vital role in limiting borehole extension length. As the drilling fluid injection temperature, rate and density increase, the ultimate extension length of the horizontal section decreases. Therefore, reducing the drilling fluid injection temperature, rate and density is an effective means to extend the borehole extension length and avoid wall stability problems. This study can provide theoretical and technical support for the safe and efficient drilling and extraction of natural gas hydrate in the future sea area.