Characteristics of Wellbore Transient Flow during Sour Gas Influx
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摘要: 酸性气藏一般位于海相沉积,钻井液安全密度窗口极窄,钻井过程中酸性气体易侵入井筒,发生气侵后井筒流动变得十分复杂,易造成井涌、井喷等井下故障。为实现气侵时井筒流动的准确预测与控制,将井筒流动与地层非达西渗流耦合,井筒流动、传热和流体物性耦合,建立了酸性气体侵入井筒瞬态多相流动模型,并引入酸性气体溶解度公式,给出了模型的求解方法。利用某井的基本数据,模拟了酸性气体气侵时的环空气液两相瞬态流动参数的变化特征,并对酸性气体气侵时的瞬态流动影响因素进行了敏感性分析。结果表明:酸性气体溶解度大,侵入后更加隐蔽,不易被检测到,但靠近井口处酸性气体溶解度降低,酸性气体大量析出,体积迅速膨胀,井筒压力降低迅速,井控更加危险。研究结果可为酸性气藏钻井井控参数设计提供指导。Abstract: Sour gas reservoirs are generally marine sediments and usually have narrow safety mud density window.The sour gas influx occurs frequently in drilling process which lead to a complex wellbore multiphase flow,and even the overflow and blowout.In order to achieve the accurate prediction and control of wellbore flow during sour gas invasion,a numerical model was formulated in this paper to study the wellbore transient multiple-phase flow during sour gas invasion,adopting the sour gas solubility equations.In this model,the wellbore flow was coupled with the non-Darcy seepage through formation media,and the fluid properties were also coupled with the temperature and pressure fields in the wellbore.Based on field data,the characteristics of gas-liquid two-phase transient flow in the annulus were investigated.What’s more,the sensitivity analysis was performed to evaluate the key parameters effect on the wellbore transient flow during sour gas invasion.The sour gas has large solubility in downhole conditions and it’s difficult to detect the sour gas influx in the initial invasion stage.However its solubility reduces as mixed fluid flows to the wellhead and lots of gas releases which results in wellbore pressure decreasing sharply.As a result,the wellbore pressure is hard to predict and control during sour gas invasion.This study could provide guidance for the well control parameters design for sour gas reservoirs drilling.
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Keywords:
- sour gas /
- gas influx /
- overflow /
- transient flow /
- mathematical model
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