挥发性油藏酸气回注的最小混相压力与组分优化

高含H_2S和CO_2酸性气体的低渗透挥发性油藏在开发过程中,H_2S和CO_2会以溶解气的形式被采出,并占有较高的摩尔分数。分离器条件下的气态轻烃通过回注地层,在油藏压力高于最小混相压力(MMP)时达到混相驱动,一方面可以显著提高驱油效率,另一方面可以起到减缓压力衰竭的目的。H_2S和CO_2作为污染气体,分离和回收成本较高;而与烃气一同回注地层势必会对MMP产生影响。因此,需要研究酸性气体对溶解气回注MMP的影响规律并且合理地优化回注气组分。在对目标区块原油组分拟合重组的基础上,通过混合单元格法预测MMP,研究了溶解气主要组分的混相能力以及H_2S和CO_2对烃气驱MMP的影响规律,通过正交试验方法优化了注入气比例。结果表明:作为酸性杂质气体H_2S和CO_2具有较强的混相能力,可以降低注气MMP;最优注气形式为溶解气直接回注地层。

The influence of sour gas on MMP and the component optimization for solution gas reinjection in volatile oil reservoir

Sour gas can be produced in solution gas with high percentage in the development of low permeable carbonate reservoir with rich H₂S and CO₂ dissolved in volatile oil. The hydrocarbon gas in separator condition injected into reservoir will become miscible with oil when formation pressure above MMP, which can greatly improve displacement efficiency and slow down the pressure depletion. On one hand, as pollution gases, H₂S and CO₂ separation and processing cost much; on the other hand, the reinjection with hydrocarbon gas will influence MMP. Therefore, the study of the influence of sour gas on MMP and the component optimization for reinjection are significant. We first studied the miscibility of main compositions in solution gas and the influence of H₂S and CO₂ on MMP using multiple mixing grid method on the basis of regress and recombination for compositions then optimized the components of injected gas through orthogonal design. The results indicate that H₂S and CO₂ as sour gases have strong miscibility which can help decrease MMP; reinjection with the entire solution gas is the optimal project.