Abstract: During the drilling of marine gas hydrate reservoirs, the drilling fluid easily invades the gas hydrate wellbore, causing the collapse and instability of the wellbore. The coupling effect of the collapse pressure of the gas hydrate formation and the hydrate phase equilibrium pressure at low temperature is an important influencing factor. Therefore, it is of great significance for the smooth exploitation of marine gas hydrate to carry out the evaluation experiment of the wellbore stability of hydrate reservoir under the action of low temperature drilling fluid system, and to study the mechanism of gas hydrate wellbore instability caused by drilling fluid invasion. The hydrate cores are prepared by simulating the temperature and pressure at the depth of the ocean, and by injecting drilling fluids of different systems, the temperature, pressure, mechanical characteristic parameters and hydrate mass abundance changes in the gas hydrate cores are monitored, and different conditions are studied. Wellbore stability under influence. The research shows that as the drilling fluid temperature increase, the peak strength near the wellbore after the invasion decrease. Large hydrate mass abundance also causes the fluctuation of hydrate core parameters. Compared with the uninvaded core, the stress peak point of the core decrease by 13.95% on average after 5 min of intrusion.

Key words: muddy silt hydrate, wellbore stabilization, physical parameters, mechanical properties, drilling fluid invasion