Diffusion of CO2 in n-hexadecane determined from NMR relaxometry measurements

•Computation of diffusion coefficient using the longitudinal relaxation time T1T1.•Correlating the relationship between T1T1 and CO2 concentration.•Computation of diffusion coefficient with the longitudinal relaxation time.

In this study, we discuss the feasibility in computation of diffusion coefficient (D  ) using the longitudinal relaxation time T1T1. CO2–n  -hexadecane in pure solutions and in a porous medium was tested separately by measuring the T1T1 of n-hexadecane at varying CO2 concentration (c  ). The relationship between T1T1 and c   was correlated. The results show that T1T1 exponentially rises with the increase of c. Thus, we proposed the method to estimate D of CO2 using T1T1 through the relationship above and Fick's law. We computed D   from T1T1 and compared this method with the traditional method. The two methods agree well with differences less than 10%. The new method is characterized by simpleness, convenience and flexibility, as it computes D   with the only requirement of monitoring T1T1. This new method will guide the use of nuclear magnetic resonance logging in in-field testing of CO2 diffusion and migration laws.