天然气相包线计算及其在烃露点控制领域的应用

天然气的相态特性参数是凝析气田开发、长输管网运营尤为关注的基础数据。基于立方形状态方程,建立了天然气临界参数、临界凝析压力、临界凝析温度,以及相包络曲线的计算方法。与天然气烃露点测试值的对比结果,验证了天然气相包络曲线计算方法的准确性。基于建立的计算方法,预测了满足不同烃露点指标要求的外输天然气相包络曲线,结果表明,在国内现行标准规定的烃露点指标下,天然气在长输管道上游交接点满足要求,不能规避其在中下游析出液烃的风险,不利于天然气输配系统的平稳高效运行;最后,建议以临界凝析温度为重要参考,明确量化天然气的烃露点指标要求。

Calculation of natural gas phase envelope curve and its application in hydrocarbon dew points control

Phase characteristic parameters of natural gas are of particular concern for condensate gas reservoir development and long distance pipeline transmission. Based on cubic equation of state, the calculation method for natural gas critical parameters, such as cricondenbar point, cricondentherm point and phase envelope curve is established. The comparison results between natural gas hydrocarbon dew point measurement values and prediction values has verified that the calculation method is quite accurate. The established calculation method is employed to predict the phase envelope curves of different natural gas compositions meeting different hydrocarbon dew point requirements. The result shows that the formation of hydrocarbon liquids cannot be avoided in the midstream or downstream of pipeline during natural gas transmission in the case of hydrocarbon dew point index meeting the requirement of the current national standards at upstream connection station, which is harmful to smooth and efficient operation of natural gas distribution system. Finally, the present article suggests that the cricondentherm temperature should be taken as an important reference to quantify the natural gas hydrocarbon dew point index.