凝析气藏生产过程中气油比异常原因分析

An analysis of reasons for unusual GOR behaviors in the production of gas condensate reservoirs

在凝析气藏的衰竭式开发过程中,当井底压力高于露点压力时,生产气油比应恒定不变,当井底压力降低至露点压力后,地层中流体发生反凝析现象,生产气油比会增大。但是,在日本的Yufutsu凝析油气田、中国的雅克拉和大涝坝凝析气藏的开发中,当井底压力下降至露点压力以下时,部分气井的生产气油比并没有增大,反而出现了大幅度下降的现象。针对这一异常现象,分析了可能造成此异常现象的因素(水侵、组分梯度、组分异常、储层物性、毛细管数效应以及界面张力),通过数值模拟,对凝析气藏的气油比进行了预测。认为在凝析气藏的开发中,气油比的下降只是暂时的,随着压力的继续降低,地层中反凝析污染加重,凝析气井的生产气油比会迅速增大。

During the development of gas condensate reservoirs under depletion,when the bottomhole pressure is above the dew point pressure,the gas-oil ratio(GOR) is kept stable;when below the dew point pressure,retrograde condensation occurs in the formation fluids resulting in an increase of GOR.However,during the development of condensate gas fields in Yufutsu(Japan) and Yakela & Dalaoba(China),when the bottomhole pressure decreased below the dew point pressure,the GOR of some gas wells was reduced significantly instead of being increased.In view of this abnormal phenomenon,many possible factors are analyzed including water invasion,gradient of components,abnormal component,petrophysical properties of formation,capillary number effect,and interfacial tension.Numerical simulation was adopted to predict the GOR of gas condensate reservoirs.It is concluded that,in the development of gas condensate reservoirs,the decrease of the GOR is transient but along with the ongoing decline of formation pressure,the retrograde condensation damage is becoming severe and the GOR of gas condensate wells is rapidly increasing.