Research on the Mechanism and Suppression Method of Gas Migration Velocity Under Gas Invasion Conditions in Ultra‐Deep Well Drilling

ABSTRACT During ultra‐deep well drilling, the narrow safety density window of the drilling fluid makes it prone to complex conditions such as gas invasion. The high‐temperature and high‐pressure environment causes changes in the properties of the drilling fluid, making the gas invasion process highly covert and increasing the difficulty of well control. To address the challenge of accurately predicting gas migration velocity under gas invasion conditions in ultra‐deep wells, this study considers the impact of temperature and pressure on the properties of the drilling fluid. A fluid state equation for ultra‐deep wells was established. Based on the coupling effects of various parameters, a gas migration velocity model applicable to multi‐well types and multi‐factor coupling influences was developed. This model can calculate conditions for high‐viscosity drilling fluids and analyze the impact of different parameters on gas migration velocity in vertical and horizontal wells. Additionally, suppression methods for gas migration velocity in ultra‐deep wells were proposed. The study shows that an increase in drilling fluid viscosity, drilling fluid density, annular backpressure, and gas‐liquid density ratio reduces the gas content in the wellbore and suppresses the increase in gas migration velocity. An increase in formation permeability results in a higher gas content in the wellbore, promoting an increase in gas migration velocity. The impact of drilling fluid displacement on wellbore gas content is complex. To reduce gas migration velocity, high‐density and high‐viscosity drilling fluids can be used, along with appropriate increases in wellhead backpressure and drilling fluid flow rate, to prevent gas invasion. This study helps to better understand the multiphase flow characteristics in the wellbore under gas invasion conditions in ultra‐deep wells, ensuring the smooth operation of ultra‐deep well drilling.