关井阶段CO2作储气库垫层气的动态影响规律

Dynamic influence law of CO2 used as cushion gas in gas storage during shut-in period

关键词:  地下储气库  CO₂  关井阶段  注气压力  注气速率  垫层气比例  混气带占比 

Key words:  underground gas storage  CO₂  shut-in period  gas injection pressure  gas injection rate  cushion gas ratio  proportion of gas mixing zone

摘要:

目的为应对地下储气库中的垫层气损失,采用经济气体CO₂作为垫层气,目前,CO₂作垫层气在实际应用中存在各种条件限制,且对其在关井阶段的应用研究较少,有必要对在关井阶段CO₂作垫层气对天然气储气库的运行影响因素进行研究。 方法利用有限元模拟CO₂作储气库垫层气时,研究关井阶段储气库动态参数(注气压力、注气速率和CO₂垫层气比例)对混气带的影响规律。 结果注气压力对混气带的影响不大,将其控制在12 MPa左右最为合理,此时混气带占储气面积的比例为23.731 5%；混气带面积占比随注气速率的增大而减小,但是在注气口附近会出现混合区域,导致回采天然气时出现大量的混合气体,所以注气速率控制在0.7×10⁸ m³/d时最为合理,这时混气带面积占比为18.324 6%；CO₂作垫层气的比例对天然气-CO₂之间的混合影响明显,当CO₂垫层气比例为20%时,混气带面积占比为7.236 5%。 结论根据实验结果设计针对混气带的控制措施,当注气压力控制为12 MPa时,注气速率为0.7×10⁸ m³/d,当CO₂垫层气比例为20%时,能让储气库的运作更为经济,实验结果可为实际储气库的建设提供参考。 

Abstract:

ObjectiveIn order to deal with the loss of cushion gas in underground gas storage, CO₂, an economical gas, is used as cushion gas. There are various restrictions in applying CO₂ as cushion gas, and few studies on its application have been conducted during the shut-in period. Therefore, it is necessary to study the influencing factors of CO₂ as cushion gas during the shut-in period in the operation of natural gas storage. Methods The influence of dynamic parameters of the gas reservoir (gas injection pressure, gas injection rate and CO₂ cushion gas ratio) on the gas mixing zone is studied when CO₂ is used as cushion gas by finite element simulation. ResultsThe results show that the injection pressure has little effect on the mixing zone during the shut-in period. The injection pressure is controlled at about 12 MPa, which is the most reasonable , and the proportion of gas mixing zone in the gas storage area is 23.731 5%. The proportion of the mixing zone decreases with the increase in gas injection rate, but the mixing zone near the gas injection port leads to a large amount of mixed gas when recovering natural gas. Therefore, it is reasonable to control the gas injection rate at 70×10⁶ m³/d, and the proportion of mixing zone is 18.324 6%. CO₂ cushion gas ratio has an obvious effect on the mixing between natural gas and CO₂. When the CO₂ cushion gas ratio is 20%, the proportion of the gas mixing zone is 7.236 5%. ConclusionsAccording to the experimental results, the control measures for the gas mixing zone are designed. When the injection pressure is controlled to 12 MPa, the gas injection rate is 70×10⁶ m³/d, and the CO₂ cushion gas ratio is 20%, the operation of the gas storage can be more efficient, and the reference can be provided for the actual construction of the gas storage.