储层孔隙敏感性伤害的核磁共振实验研究

识别储层敏感性伤害机理对于避免油气井产能损失具有重大意义。为强化该领域室内研究,并克服目前有损测试方法的局限性,将核磁共振手段引入该领域。利用核磁共振T2谱测试,结合岩心流动实验,对我国KT油田两口生产井的盐敏和碱敏潜在伤害程度和伤害机理进行了研究。结果表明,KT油田储层的盐敏伤害程度可达39.5%,核磁T2谱显示伤害过程中存在明显的小孔隙增多、大孔隙减少的现象,据此推断盐敏伤害机理为黏土膨胀;KT油田储层碱敏伤害程度可高达77.8%,但T2谱并未显示伤害过程中存在孔隙类型及大小的变化;增大驱替倍数后出口端出现浑浊,且T2谱显示岩心中大小孔隙均增多,进而推断碱敏伤害机理为黏土分散运移。

Experimental Research on Sensitivity Damage in Reservoir Pores Using Nuclear Magnetic Resonance

Recognizing sensitivity damage mechanisms in reservoirs is of great significance for avoiding productivity loss of oil and gas wells. To strengthen laboratory study in this field and overcome shortcomings of the current destructive experimental methods, the nuclear magnetic resonance (NMR) is introduced in this paper. The potential damage degrees and damage mechanisms of salt sensitivity and alkali sensitivity in reservoirs of KT oilfield was investigated through NMR T2 spectrum test in conjunction with core flow experiment. Results show that, potential salt sensitivity damage degree of KT reservoir could reach 39.5%. T2 spectra tested in the process of damage showed an increase of small pores and decrease of big pores in the cores. Hence the salt sensitivity damage mechanism was directed to clay swelling. Potential alkali sensitivity damage degree of KT reservoir could reach up to 77.8%. However, changes of pore types and sizes were not observed in the tested T2 spectra. Then, the injection volume of lye was extended. As a result, effluent in the outlet became turbid and T2 spectrum tested at that time showed increases of both the small pores and big pores. According to phenomena above, the alkali sensitivity damage mechanism was attributed to clay dispersion and migration and the resultant blockage of pore throats.