The prevailing research analyzing the transient pressure in the blowout preventer shut-off process using water hammer theory is not in accordance with the real-world situation due to the long blowout preventer shut-off periods. In this paper, to solve the well-control problem in the case of gas invasion, using downhole telemetry information, we propose a new mathematical model for analyzing the generating mechanism of transient pressure in the blowout preventer shut-off process and its effect on wellbore pressure. The mathematical model of transient pressure generated in the blowout preventer shut-off process is established using a fluid inertial pressure analysis of unsteady flow. The model clearly shows the influence of ram moving velocity, fluid velocity, fluid density, and blowout preventer structural parameters on the transient pressure. The propagation characteristics of the transient pressure along the wellbore are analyzed using Lamb’s law. The results show that the transient pressure amplitude generated in the blowout preventer shut-off process is small and rapidly decays when it propagates along the wellbore, so its influence on the wellbore pressure is negligible. The wellhead backpressure plays a major role in affecting the wellbore pressure. This study theoretically solves the dispute between choosing “hard shut-in” or “soft shut-in” of the blowout preventer, thus providing an alternative to relying on engineering experience, offering guidances for the accurate analysis of the influence of the blowout preventer shut-off process on wellbore pressure, and giving new operation advice for blowout preventer operation when gas invasion occurs.

由于防喷器关闭周期较长，目前采用水锤理论分析防喷器关闭过程中瞬态压力的研究并不符合实际情况。本文针对气体侵入情况下的井控问题，利用井下遥测信息，提出了一种新的数学模型来分析防喷器关闭过程中瞬态压力的产生机理及其对井筒的影响。压力。利用非定常流动的流体惯性压力分析，建立了防喷器关闭过程中产生的瞬态压力数学模型。该模型清楚地显示了闸板移动速度、流体速度、流体密度和防喷器结构参数对瞬态压力的影响。利用兰姆定律分析了瞬态压力沿井筒的传播特性。结果表明，防喷器关闭过程中产生的瞬态压力幅值较小，沿井筒传播时衰减较快，对井筒压力的影响可忽略不计。井口背压对井筒压力的影响起主要作用。本研究从理论上解决了防喷器选择“硬关井”还是“软关井”的争议，为依靠工程经验提供了替代方案，为准确分析防喷器关井的影响提供了指导。 - 井筒压力的关闭过程，并为发生瓦斯入侵时的防喷器操作提供新的操作建议。