井喷关井水击分析及水击波速计算

Analysis of blowout shut in caused water hammer and calculationof water hammer wave velocity

摘要:

油气井发生溢流或井喷后，立即关闭防喷器，关井期间防喷器需经受关井产生的水击压力作用。本文在对井喷关井水击的传播物理特征分析的基础上，推导直接关井水击压力计算公式，综合考虑井筒流体含气率、气液两相流型、固相类型等对水击波速的影响，推导水击波在气、液、固三相混合流体中传播速度计算公式，并通过算例对水击波速影响因素进行分析。计算表明水击波速对含气率变化非常敏感，钻井液含气率在0～0.001的时候，水击波速几乎是发生了突变，水击波速在含气率为0.001时仅为385 m/s，相比纯钻井液情况下降了67%，而钻井液固相含量、套管的内径和壁厚对水击波传播速度影响较小。

Abstract:

The blowout preventer is closed immediately once the oil or gas well overflows or blows out. During the well shut in period, the blowout preventer will withstand the water hammer pressure generated by shut in. Based on the analysis of the physical characteristics of water hammer propagation in shut in wells, this paper derives the formula for calculating the direct shut in pressure from water hammer. With comprehensive consideration of the factors affecting the water hammer velocity such as gas content in the wellbore fluid, gas liquid two phase flow pattern, solid phase type, the calculation formula of the propagation velocity of the water hammer wave in the three phase mixed fluid of gas, liquid and solid is deduced with the influencing factors of the water hammer wave velocity analyzed through an example. Calculations show that the water hammer wave velocity is very sensitive to changes in the gas content: when the gas content in the drilling fluid is 0～0.001, the water hammer wave velocity changes abruptly. The water hammer wave velocity is only 385m/s when the gas content is 0.001, indicating a decrease by 67% compared with that in the pure drilling fluid; while the solid phase content in the drilling fluid, the inner diameter and the wall thickness of the casing have less influence on the propagation velocity of the water hammer wave.