CO_2气井井筒流动综合模型

AN INTEGRATED MODEL OF WELLBORE FLOW IN CO_2 GAS WELLS

气井井筒的压力分布计算对于气井设计及其动态分析具有重要意义。CO2气体由于相态变化非常复杂,在高压下具有液体的密度,压力、温度稍微改变,密度与偏差系数等参数可能发生巨大的变化,常规计算气体井筒压力的方法不再适用。为此,优选了能准确描述CO2气体相态行为的状态方程以及井筒流动方程,并进行了相应改进,以联立状态方程和改进的井筒压力流动方程共同建立了CO2气井井筒流动综合模型,并把模型计算结果与测试数据进行了对比分析。研究结果表明,计算结果与测试结果吻合较好,表明本模型可以应用于CO2气井井筒流动压力分布预测,从而大大减少井下测试压力昂贵的作业费用和CO2强腐蚀的风险。

The calculation of wellbore pressure distribution in gas wells makes great sense for gas well design and performance analysis. Due to complex phase behaviors of CO2, great changes of such parameters as density and Z-factor may be resulted from slight changes of fluid density, pressure and temperature under high-pressure situations, which make conventional methods unfit for calculating the wellbore pressures. Therefore, this study set up an integrated model of wellbore flow in CO2 wells after selecting and modifying the state equations and wellbore flow equations accurately representing CO2 phase behaviors. Comparing between model results and test results, the study showed both of the results matched each other very well. In conclusion, this paper recommends that if this model is applied to the prediction of wellbore pressure distribution in CO2 gas wells, the previous issues like high operation fee and high risk in serious CO2 corrosion will surely be resolved to some extent.