地下储气库注采井温度压力耦合分析

地下储气库进行循环注气、采气作业,引起注采井筒温度、压力分布的交替变化,准确预测井筒温度、压力分布是优化设计管柱的基础。基于气体质量、动量、能量平衡方程和地层-流体径向非稳态传热模型,考虑气体的焦耳-汤姆逊效应,得到了井筒气体温度、压力、密度和流速的耦合微分方程组,采用四阶龙格-库塔方法数值求解。通过实例分析了注采工况下井筒的温度、压力分布特征及影响因素,并与Well Cat软件计算结果相比较,结果表明注气井口温度、注气压力、注采流量和作业时间影响井筒的温度压力分布。注气中,注入压力对井底压力的影响最大,对井底温度的影响很小;采气中,井口温度随流量的增加而增大,井口压力随流量的增大而减小;作业早期温度、压力随时间变化较大。

Coupling Analysis of Temperature and Pressure Distribution of Underground Gas Storage Injection-Production Wellbore

The temperature and pressure distribution along underground gas storage (UGS) injection-production wellbore vary alternately due to cyclic gas injection and production. Accurate prediction of wellbore temperature and pressure provides basic parameters for tubular failure analysis and UGS operation optimization. In view of Joule-Thomson effect, coupling differential equations on temperature, pressure, velocity and density along UGS wellbore under working conditions of injection and production are obtained based on gas mass, momentum and energy conservation equations and radial non-steady heat transfer between the surrounding rocks and internal flowing gas. The equations can be solved by the fourth-order Range-Kutta method numerically. An application example is used to analyze the temperature and pressure distribution under actual working conditions and related affecting factors such as inlet temperature and pressure during gas injection, gas injection and production rate and operation duration time. The calculated temperature and pressure are compared with the results of WellCat software to verify the model. As a result, during the operation of gas injection, the injection pressure at wellhead has the largest impact on the bottom-hole pressure but has little effect on the bottom-hole temperature. The temperature and pressure at bottom-hole decrease with the increase of gas injection rate. During gas production, the temperature at wellhead increases and the pressure at wellhead declines as gas production rate increases. The temperature and pressure vary greatly over time in the early period of injection and production.