加载方式对水泥石气密封性影响研究

摘要

Gas sealing performance of the cementsheath in natural gas wells is very important.Becaus-ethe cement sheath is subjected to complicated loads during natural gas well production,gas sealing is inevi-tably affected by such loads and furtherimpacts wellbore integrity.In order to investigate the sealing failure modeof cement sheath under different loading conditions and the influence law s of various factors,the gas sealing performance of set cement under different loading modes was studied on the basis of triaxial cyclic loading tests on set cement w hile monitoring its permeability and acoustic emission characteristics.Experi-mental results show that dilatancydamageoccurs,and the permeability of set stone increases rapidly with the appearance of dilatancy point during the loading process.When the peak load is higher than the stress on dilatancy point,the cyclic loading-unloadingprocess will seriously damage theset cement,the permeabili-ty rises rapidly,and the risk of gas sealing failure increases significantly.T he research demonstrates that the gas sealing performance of cement sheath can be improved by enhancing the set cement damage resist-ance capability.%页岩气井水泥环的气密封性能至关重要,而水泥环在页岩气井生产过程中所受的载荷复杂,其气密封性必然会受到影响,进而会影响整个井筒的完整性.因此,为了了解水泥环在不同载荷条件下的密封失效形式和各因素的影响规律,在对水泥石进行三轴循环加载试验的基础上,对其渗透率和声发射特性进行监测,研究了水泥石气密封性在不同加载方式下的变化.结果表明:水泥石在加载过程中,有扩容损伤的特性,且渗透率会随着扩容点的出现而迅速升高;循环加卸载峰值高于扩容点应力时,循环加卸载对水泥石的损伤严重,渗透率升高较快,气密封性失效风险明显增大.研究表明,添加增韧材料可以提高水泥石的抗损伤能力,从而提高水泥环的气密封性.