Patent ID: 7502692

Claim:
A method for estimating an internal gradient of an earth formation in response to a magnetic field, the method comprising: applying the magnetic field to the earth formation; directing pulsed RF energy for a first frequency to the earth formation and acquiring a first signal and directing pulsed RF energy to the earth formation for a second frequency and acquiring a second signal; determining a first signal decay corresponding to the first signal and a second signal decay corresponding to the second signal; and using the first signal decay and the second signal decay to estimate the internal gradient, wherein using the determinations comprises solving a relationship for the internal gradient, G int , the relationship comprising: E k , 1 E k , 2 = exp ( - D ⁡ ( γ · G int , 1 · TE 1 ) 2 ⁢ t k 12 ) / exp ( - D ⁡ ( γ · G int , 2 · TE 2 ) 2 ⁢ t k 12 ) ; where E k,1 represents the first signal decay; E k,2 represents the second signal decay; TE 1 represents a signal time for the first signal; TE 2 represents a signal time for the second signal; D represents a diffusion constant; γ represents a gyromagnetic ratio; t k represents time at a formation of a k th echo; G int,1 represents the internal gradient for the first frequency; and G int,2 represents the internal gradient for the second frequency.