摘要：
钻井环空多相流流型判定目前主要依靠经验公式,存在着一定的误差.为此,考虑钻井液相湍动、脉动速度、虚拟质量力、斯托克斯力、相界面动量传递等因素,在双流体模型的基础上,建立了密度波特征波速判定环空多相流流型转变的模型,并利用小扰动线性法,通过编程计算求解.研究结果表明:①由所建模型计算的数据与前人密度波不稳定判断流型结果一致;②虚拟质量力对密度波特征波速判断流型的影响较大,随虚拟质量力系数增大,泡状流向弹状流转变的空隙率增大;③随井深增加,分散气相密度增大、气相与钻井液相相对密度增大、界面膜稳定性增强,分散气相液滴不易发生聚集,泡状流向弹状流转变空隙率增大;④密度波一次不稳定性导致分散气相从泡状流聚合为弹状流,密度波二次不稳定现象导致气相继续聚合,逐渐形成连续的气体环状,从而发生弹状流向环状流转变,密度波的二次不稳定现象多发生在井口环空段.结论认为,利用密度波特征波速来判定井筒流型转变是可行的.%At present,the multiphase flow pattern in the annulus during well drilling is mainly discriminated on the basis of empirical formula,which has some errors.In this paper,a model for discriminating the multiphase flow pattern transition based on the characteristic wave velocity of density wave was established on the basis of two-fluid model.In this model,drilling mud phase turbulence,pulsation velocity,virtual mass force,Stokes force,and momentum transfer between phase interfaces are taken into consideration.Then,it was solved through programming calculation by the small disturbance linear method.The following results were achieved.First,the calculation results of this newly built model are consistent with the previous flow pattern discrimination results based on density wave oscillation.Second,the flow pattern discrimination results based on the characteristic wave velocity of density wave are more affected by the virtual mass force.With the increase of the virtual mass force coefficient,the void fraction for the transition from bubble flow to slug flow increases.Third,as the well depth increases,the density of dispersed gas phase and the relative density of gas phase to drilling fluid increase,the stability of interfacial film is enhanced,droplets of dispersed gas phase cannot aggregate easily,and the void fraction for the transition from bubble flow to slug flow increases.Fourth,the primary oscillation of density wave leads to the aggregation of dispersed gas phase from bubble flow to slug flow.The secondary oscillation results in the further aggregation of gas phase,and consequently continuous gas ring is formed gradually,and the slug flow is transited into the annular flow.The secondary oscillation of density wave mostly occurs at the wellhead annulus section.To sum up,it is feasible to discriminate the flow pattern transition using the characteristic wave velocity of density wave.
