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.