地下储气库注采循环过程中储层干化问题研究

Drying Process in Underground Gas Storage Reservoir

地下储气库在注采循环过程中,井周围区域会发生储层干化,这会对储气库的正常运行产生影响。为此,在分析储层干化机理的基础上,基于大张坨储气库储层参数及地下温度压力条件,建立了单井控制区域的组分模型并模拟储气库周期性注采气过程。模拟结果表明:井周围储层干化的区域会逐年扩大,半径甚至超过百米;储层干化主要发生在注气周期,回采周期对储层的干化作用轻微;储层干化的速率及波及区域的大小取决于注采井的年循环气量及注入和采出天然气中水蒸气含量的差异;不同回采周期采出的天然气中水蒸气的含量呈现规律性变化,从开始接近干气逐渐升高到地下温度压力条件下饱和水蒸气含量,且该过程逐年后延。该研究结果为深入研究储层干化现象对储气库正常运营的影响奠定了基础。

During the injection/production cycling in underground gas storage,reservoir rock in area around the wellbore will be dried,which might affect its normal operation.Therefor after analyzing the drying mechanism,a two phase two component model for a single well controlled area was established for simulating the gas cycling process with parameters（reservoir properties and underground temperature and pressure）referenced from Dazhangtuo Gas Storage Reservoir.Simulation results show that the drying area around the wellbore would be enlarged year by year,the radius of the dried area may even exceed 100 meters;water evaporation that leads to reservoir rock drying mainly occurs in the period of dry gas injection,the drying effect during the production time could be negligible;the rate of reservoir drying and the size of affected area depends on the annual cycling gas volume for the injection-production well,as well as the water vapor content difference between the injected gas and the produced gas.The water vapor content in the produced gas during various withdrawn periods changes regularly.At the initial stage,it is near to value of the injected dry gas;then it gradually increases to the saturated water vapor content under the downhole temperature and pressure conditions;and this process tends to be postponed year by year.The research result would provide a foundation for studying the effects of reservoir drying on the normal operation of gas storage.