| US 7,502,692 B2 | ||
| Method and computer program product for estimating true intrinsic relaxation time and internal gradient from multigradient NMR logging | ||
| Songhua Chen, Katy, Tex. (US) | ||
| Assigned to Baker Hughes Incorporated, Houston, Tex. (US) | ||
| Filed on Dec. 07, 2006, as Appl. No. 11/567,828. | ||
| Application 11/567828 is a continuation in part of application No. 11/403255, filed on Apr. 13, 2006, abandoned. | ||
| Prior Publication US 2007/0244648 A1, Oct. 18, 2007 | ||
| Int. Cl. G01V 3/18 (2006.01) | ||
| U.S. Cl. 702—8 | 23 Claims |
| 1. 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, Gint, the relationship comprising:
 Ek,1 represents the first signal decay;
Ek,2 represents the second signal decay;
TE1 represents a signal time for the first signal;
TE2 represents a signal time for the second signal;
D represents a diffusion constant;
γ represents a gyromagnetic ratio;
tk represents time at a formation of a kth echo;
Gint,1 represents the internal gradient for the first frequency; and
Gint,2 represents the internal gradient for the second frequency.
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