深层气井油管柱特殊螺纹泄漏诱导环空带压机理与规律研究

Mechanism and Characteristics of Sustained Casing Pressure Induced by Premium Connection Leakage in Tubing Strings of Deep Gas Wells

摘要: 针对深层气井油管特殊螺纹微观泄漏导致油套环空持续带压问题，基于金属密封面微观接触泄漏理论、气泡受力分析和真实气体状态方程，建立特殊螺纹泄漏–气泡运移–井口气体聚集耦合计算模型。模型以螺纹泄漏速率为气泡源项，按时间步追踪气泡速度、位移和半径，并根据气泡到达井口后的气体累积量递推环空压力。在明确低含气率、离散球形小气泡及忽略聚并、破碎与溶解等假设的基础上，以某深层气井为例分析泄漏点井深、油管内压、密封面粗糙度和密封面平均直径的影响，并构建参数耦合的定性敏感性矩阵。结果表明：气泡在初始短时内快速加速，随后趋于稳定滑脱速度；随着上升过程中外部压力降低，气泡持续膨胀并在接近液面时加快；环空带压随气体聚集逐渐升高，同时泄漏速率受环空反压作用持续降低。油管内压与泄漏点井深、密封面粗糙度与密封长度之间存在明显的耦合制约关系。

Abstract: Sustained casing pressure (SCP) in the tubing-casing annulus induced by microscopic leakage from premium tubing connections in deep gas wells is investigated. A coupled computational model integrating metal-to-metal sealing microcontact leakage theory, bubble force balance, and a real-gas equation of state is developed to describe premium-connection leakage, bubble migration, and wellhead gas accumulation. The connection leakage rate is used as the bubble source term. Bubble velocity, displacement, and radius are tracked at each time step, and annular pressure is updated from the gas accumulated at the wellhead. The applicability of the model is defined by the assumptions of low gas holdup, discrete spherical small bubbles, and negligible coalescence, breakup, and dissolution. A deep gas well is analyzed to investigate the effects of leakage depth, tubing pressure, sealing-surface roughness, and mean sealing diameter, and a qualitative sensitivity matrix is established for parameter coupling. The results show that bubbles rapidly accelerate over a short initial period and then approach a stable slip velocity. Bubble expansion accelerates near the liquid level as the ambient pressure decreases. SCP increases with gas accumulation, whereas the leakage rate continuously decreases because of annular backpressure. Tubing pressure and leakage depth, as well as sealing-surface roughness and sealing length, exhibit clear coupled constraints on the leakage and pressure-buildup processes.