Abstract: To elucidate the mechanism by which gas dissolution influences the concealment of gas kick in ultra-deep wells and to improve the capability for early gas kick detection and well control safety, a coupled wellbore multiphase flow model incorporating gas dissolution and exsolution effects was developed for operations under the extreme high-temperature and high-pressure conditions. The model was numerically solved using a fully implicit first-order upwind differencing scheme coupled with an adaptive mesh algorithm, enabling high-fidelity simulation of the transient gas kick process. The accuracy of the model was validated against experimental data. Based on this model, a systematic sensitivity analysis was conducted to investigate the effects of key engineering parameters on gas kick evolution, with particular emphasis on the comparison of bottomhole pressure, gas kick rate, pit gain, and gas distribution characteristics with and without considering gas dissolution. The results indicate that gas dissolution significantly delays the decline in wellbore pressure and the emergence of surface response signals, making it a key physical mechanism underlying the concealment of gas kicks in ultra-deep wells. High-density, high-flow-rate, and high-viscosity drilling fluids effectively suppress the total gas influx by increasing bottomhole pressure or annular pressure loss, thereby extending the distance over which gas migrates in the dissolved state and delaying subsequent gas exsolution and expansion, which further enhances the concealment of gas kicks. These findings provide a theoretical basis and quantitative support for the early warning of gas kicks and precise pressure control in ultra-deep well drilling.

Key words: ultra-deep well, gas kick, multiphase flow, gas dissolution, sensitivity analysis, well control safety

摘要： 为了揭示超深井气侵过程中气体溶解对气侵隐蔽性的影响机理，提高气侵早期识别能力与井控安全水平，针对超深井高温高压极端环境，建立了考虑气体溶解与析出效应的井筒多相流耦合模型。模型采用全隐式一阶迎风差分格式与自适应网格算法进行数值求解，有效实现了气侵瞬态过程的高精度模拟，并通过实验数据验证了模型的准确性。基于该模型，系统开展了关键工程参数对气侵演化规律的敏感性分析，重点对比了考虑与不考虑溶解效应条件下井底压力、气侵速率、泥浆池增量及气体分布特征的差异。研究结果表明：气体溶解效应显著延缓了井筒压力衰减与地面响应信号的显现，是超深井气侵隐蔽性的核心物理机制；高密度、大排量、高黏度钻井液通过提高井底压力或环空压耗，有效抑制气体侵入总量，延长气体在溶解态下的运移井段，从而推迟气相析出与膨胀过程，进一步增强气侵隐蔽性。研究成果可为超深井气侵早期预警与精细压力控制提供理论依据与量化支撑。

关键词: 超深井, 气侵, 多相流, 气体溶解, 敏感性分析, 井控安全