新疆油田超临界二氧化碳管道投产置换过程温压及相变特性

Temperature,Pressure and Phase Transition Characteristics of Supercritical CO_(2) Pipeline During Commissioning Replacement Process in Xinjiang Oilfield

鉴于CO_(2)的相特性,超临界CO_(2)管道投产置换过程与原油、天然气管道存在显著差异。采用OLGA软件对新疆油田某超临界CO_(2)管道示范工程的投产置换过程进行了模拟,得到投产过程中压力、温度、密度、相态转变等参数变化规律。研究了初始背压大小、首站充注各相态CO_(2)质量流量、环境温度的变化对置换投产过程中置换时间、温度、压力、相态转化过程、CO_(2)用量的影响。研究结果表明,在液相CO_(2)充注阶段,气相CO_(2)不断被顶挤,在憋压作用下气相CO_(2)分子热运动加剧,导致在压力升高的同时温度也升高,后段管段流体由气相直接转变为超临界相;增加各相态CO_(2)充注质量流量可缩短置换时间,为控制管道最高温度不超过50℃,液相CO_(2)的充注流速不能超过0.5 m/s;环境温度的升高会极大提高液化压力,同时大部分管段流体较容易从气相直接转变为超临界相,不利于相态控制,不推荐在夏季进行投产。为方便投产方案评价,提出了安全指标(管道温度)、效率指标(投产用时)、经济指标(CO_(2)用量)三大指标,其中安全指标需优先满足。研究成果可为超临界CO_(2)输送管道投产方案的制定提供参考。

Due to the phase characteristics of CO_(2),the commissioning and replacement process of supercritical CO_(2) pipelines is signifi-cantly different from that of crude oil and natural gas pipelines.In this paper,OLGA software was used to simulate the commissioning and replacement process of the supercritical CO_(2) pipeline demonstration project in Xinjiang Oilfield,and the dynamics of pressure,temperature,density,phase transition and other parameters were captured.The effects of the initial back pressure,CO_(2) injection massive flow of various phases in first station filling and ambient temperature on the replacement time,temperature,pressure,phase transition process and CO_(2) consumption were investigated.Findings indicate that in the liquid CO_(2) injection stage,gaseous CO_(2) is constantly squeezed,and the thermal movement of gaseous CO_(2) molecules is intensified due to pressurization,leading to concurrent increases in pressure and temperature.Conse-quently,the fluids at the pipeline's end transitions directly from the gaseous to the supercritical phase.Enhancing the mass flow rate of CO_(2) injec-tion in each phase can expedite the replacement process.To ensure the pipeline's maximum temperature keeping below 50℃,the injection flow rate of CO_(2) in the liquid phase should be capped at 0.5 m/s.The increase in ambient temperature significantly elevates the liquefaction pressure,prompting the fluids in most pipe sections to transition directly from the gaseous to supercritical phase,which is unfavorable for phase control.Therefore,commissioning during summer is not advisable.To facilitate the assessment of the production plan,three key indexes were proposed:safety index(pipeline temperature),efficiency index(time consumption of commissioning)and economic index(CO_(2) consumption),with the safety index taking precedence.The research results offer valuable insights for the development of production plans for supercritical CO_(2) pipelines.