欠平衡钻井地层出气量对环空压力影响分析

The Analysis of Effect of Gas Volume on Annulus Pressure in UBD

采用欠平衡钻井技术钻遇裂缝、溶洞或高气油比油气藏时,地层气体会在重力置换作用和压差作用下进入井筒,对环空压力剖面产生影响。出气量不同对环空压力的影响不同。建立了环空气液两相流动模型并采用Mathcad编制程序求解模型、实例分析了出气量对流型、环空含气率、密度及环空压力的影响。分析结果表明:环空不同井段流态不同,随着出气量的增加,环空依次会出现搅动流和环雾流,对携岩不利;随着出气量的增大,环空含气率增大,密度减小,且出气量对含气率和密度的影响程度井口比井底大得多;井底压力随出气量基本呈线性规律变化。

When drilling fracture-cave or high GOR reservoir by UBD,reservoir gas will enter into wellbore under the action of gravity displacement and drawdown,and this process will exert impact on annulus pressure profile.Different gas volume has different effect on annulus pressure.Gas-liquid two-phase flow model is built and programs are made to solve this model by using Mathcad.The effect of gas volume on flow pattern,annulus gas holdup,density and pressure is analyzed by example.Analysis results show that churn flow and ring-mist flow emerge as gas volume increases,this will have adverse effects on cutting carrying.As gas volume increases,gas holdup increase and mixture density decrease,the effect of gas volume on gas holdup and density in wellhead is much severe than it in bottom hole.Bottom hole pressure changes linearly with gas volume.