多孔介质中凝析气液相变实验新方法研究

A novel experiment method on phase change of gas condensate in porous media

现有多孔介质相变实验方法的实验压力、实验温度偏低,不能反映油藏条件下凝析气的相变特点。根据凝析气组分随压力变化的原理,设计出研究油藏条件下凝析气相变的高温高压实验流程:采用气相色谱分析仪分析凝析气在岩心中发生反凝析相变后的流体组成,同时与该凝析气在PVT筒的相态特征进行对比,认识多孔介质对凝析气相变的影响。用该实验流程研究的结果表明:随着压力的降低,岩心中的烃类气体作等温衰竭,当压力降至上露点时,开始有凝析液析出,凝析油气体系进入两相区;反凝析过程中随着压力降低,液相中重烃组分含量增加、轻烃组分减少,气相中则是轻烃组分增加、重烃组分减少;当压力继续降低时,对应的衰竭压力低于多孔介质中凝析油气体系的露点,且已经进入油气两相区,流体组成发生明显变化,气相中轻烃组分增加,液相中重烃组分增加;但是在PVT筒中则还处于单相气区,采出气体的组成未发生变化。与现有相变实验方法相比,新方法具有可靠性高、精度高的特点。

The existing experiment method can't reveal the characteristics of phase change because of its lower pressure and temperature. Based on the theory of gas condensate composition change with pressure, a high temperature and pressure experiment course is designed for the research of condensate gas phase change under reservoir conditions. The fluid composition in core after the condensation of gas condensate is analyzed by chromatogram and compared with phase characteristics in PVT cell to study the influence of porous media on condensate gas phase change. The experiment results indicate that the composition of hydrocarbon in core changes with the fall of pressure under constant temperature, as the pressure reduce to upper dew point, the condensate liquid is released, and condensate liquid and gas enter two phase flow area; with the fall of pressure in the course of retrograde condensate, heavy hydrocarbon component increases and light hydrocarbon component decreases in liquid, but just the reverse in gas. As the pressure decreasing below the dew point and entering tow phase flow area, the composition of the gas-liquid system changes greatly, light hydrocarbon components increase in gas and heavy hydrocarbon components increase in liquid; but the gas composition does not change and remains in single phase at PVT cell. Comparing with current experiments, the new experiment results are more precise and credible.