Core wettability alteration is one of the key mechanisms for reducing drag using nanofluids,so it is very important to find a nondestructive and fast method to test the alteration of wettability.In this study,using a nuclear magnetic resonance(NMR)technique,a method for rapid wettability alteration testing of rock cores was proposed and investigated.The relation-ship between T2 cut-off value and wettability,and the influence of nanofluid HNF Ⅱ on wettability of cores were studied,and the effect and mechanism of resistance reduction were also examined.The results show that there is a linear relationship be-tween the T2 cut-off value and the core contact angle,in which both increase with the weakening of hydrophilicity.In the cores after nanofluid displacement,the water phase permeability increases by 33％to 72％,and the surface contact angles in-crease by 79％,103％,110％and 114％,with the corresponding T2 cut-off values increase by 17％,33％,54％and 116％,respectively.The T2 cut-off value of the core is consistent with the change trend of wettability and permeability,and the increase of contact angle is strongly correlated with the increase of T2 cut-off value(the correlation coefficient is 0.94).Nanofluid HNF Ⅱ can make the core conversion from hydrophilicity to hydrophobicity.It can increase the relaxation time,prolong the T2 cut-off value,weaken the gravity attraction of the pore wall to water,and thus decrease the water flow resist-ance.The T2 cut-off value is intrinsically consistent with wettability,providing a theoretical basis for the rapid testing method of core wettability alteration.
nanofluid HNF Ⅱdrag reductioncore wettabilityNMRT2 cut-off value
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