富气驱混相判定方法

Judgment method of enriched gas miscible displacement

富气混相驱是目前进一步提高水驱采收率的主要方法之一。由于组成富气的液化石油气价格昂贵,若驱替过程中不是非混相驱或者发生气窜,注入的混合气在地层内没有与油藏剩余油发生混相作用即被采出,将造成巨大浪费;因此,实时监测油藏驱替动态,主动调整,保证驱替始终处于混相驱状态,就显得尤为重要。以北非某油田富气驱为例,研究了判断混相驱较为实用的方法——拟三元相图法、注入组成和油藏条件法、生产气油比和产出气组分法。结果表明:通过相平衡计算绘制的拟三元相图,不仅可清晰地表示驱替中多次接触混相的过程,还可确定最小混相组成和最小混相压力。为了实现富气混相驱替,首先要确保注入端的压力、温度和富气组成等达到混相要求;其次要监测采出端气油比和产出气中的C3,C4中间组分的变化,并以此作为是否混相的主要判断依据,而生产气油比受储集层物性影响,不确定性强,可作为次要判断依据;最后,根据判断结果,再对注入端参数实时加以调整。

Enriched gas miscible displacement is one of the main methods for further improving waterflooding recovery.Because of LPG consisted of enriched gas is expensive,if non-miscible displacement is not used or gas breakthrough are occurred during displacing,injected mixed gas will be produced without miscible effect on remaining oil and cause huge economic waste.Therefore,real-time monitoring displacement dynamic,initiative adjusting and guaranteeing the reservoir to always be a miscible displacement are particularly important.In this paper,taking the enriched gas miscible displacement in one oilfield of North Africa as an example,the practical methods of judging miscible displacement,including pseudo-ternary phase diagrams,injection composition,reservoir condition,produced GOR and produced gas component,are studied.The results show that pseudo-ternary phase diagrams drew based on phase equilibrium calculation can not only clearly show MCM process,but also can determine the MMC and MMP.In order to achieve enriched gas miscible displacement,we have to make sure that the injection pressure,temperature and enriched gas component can meet the miscible requirements or not,while monitoring produced GOR and C3,C4 intermediate component changing in produced gas,and taking this as the main basis for judgment.Produced GOR is strongly affected by reservoir physical property,therefore,it can be taken as a secondary basis for judgment.At last,the parameters at the injection end can be adjusted based on the judgment results.