Patent ID: 7839144

Claim:
A method for estimating a viscosity of a fluid in a rock formation, the method comprising: performing a first nuclear magnetic resonance (NMR) measurement with zero magnetic field gradient on at least a portion of a sample of the rock formation containing the fluid in order to obtain a first distribution of transverse relaxation time constants; estimating a first diffusive couple factor from the first distribution of transverse relaxation time constants, the first diffusive couple factor relating the first distribution of transverse time constants to the viscosity of the fluid and a saturation of the fluid; replacing the fluid on which the first NMR measurement was performed with a different fluid; performing a second NMR measurement with zero magnetic field gradient on the at least a portion of the sample containing the different fluid in order to obtain a second distribution of transverse relaxation time constants; estimating a second diffusive couple factor from the second distribution of transverse relaxation time constants, the second diffusive couple factor relating the second distribution to a viscosity of the different fluid and a saturation of the different fluid; and estimating the viscosity of the fluid in the rock formation by using the first diffusive couple factor and the second diffusive couple factor.