考虑相态变化的凝析气藏压井液漏失机理与产能恢复

Killing fluid loss mechanism and productivity recovery in a gas condensate reservoir considering the phase behavior change

以某凝析气井为例,结合油气藏工程和油气相态理论,根据凝析气藏特征建立了单井数值模型,考虑了岩石的毛管压力及毛管滞后现象,研究不同正压差下压井液漏失机理及其对产能恢复的影响。研究结果表明:当近井地带压力增加到凝析油气的临界压力时,油、气、水三相流过渡为油、水两相流,气锁效应降低,水相相对渗透率增加,表现为压井液漏失速率大幅增加;压井液漏失量的增加会影响近井地带凝析油气的相态及储集空间流体分布,从而导致压井液恶性漏失。漏失量越大,再次开井生产时,压井液返排时间越长,返排率越低,凝析油、气恢复稳产所需时间越长。修井过程采取使用防漏型储集层保护液或降低液柱正压差(低密度压井液)的方法可有效避免恶性漏失,保障修井后的产能。

A single well numerical model considering rock capillary pressure and hysteresis was built to study killing fluid loss mechanism and its influence on productivity recovery under different positive pressure differentials based on the gas reservoir characteristics of the gas condensate well by combining the reservoir engineering and oil and gas phase behavior theory. The results show that when reservoir pressure of near wellbore zone increases to the critical pressure of condensate oil, the three-phase （oil, gas, water） flow will change to two-phase （oil, water） flow, the gas block effect will weaken, and water-phase relative permeability will increase, which can be manifested as sharp increase of killing fluid loss rate; and the rising fluid loss into the reservoir can affect the phase of condensate oil and gas and fluid distribution in the storage space near weUbore, and consequently lead to abnormal killing fluid loss. The larger the fluid loss volume, the longer the time is needed to flow back the killing fluid after going into operation again and the lower the fluid flow back efficiency, and the longer the time need to recover stable production of condensate oil and gas will be. Using fluid loss control solution or lowering liquid-column positive pressure differential （by using low-density killing fluid） can effectively avoid abnormal fluid loss during overbalanced well workover and guarantee productivity recovery after well workover.