Patent Number: 6,166,543

Title: Method and apparatus for measuring nuclear magnetic resonance

Abstract: The present invention relates generally to an apparatus and method for measuring nuclear magnetic resonance properties of an earth formation traversed by a borehole by generating gradient-echoes. The measurement can be made while drilling or using a wireline tool. The apparatus applies a static magnetic field, B.sub.a, in a volume of the formation which polarizes the nuclei of hydrogenous connate fluids within the formation. The apparatus applies a second magnetic field, B.sub.b, in a volume of the formation. The magnetic fields B.sub.a and B.sub.b are substantially orthogonal in the volume of the formation. A change in the polarity of the magnetic field, B.sub.b, reverses the direction of precession of the nuclei thereby generating a train of gradient-echoes. Each gradient-echo signal is transformed into the frequency domain and the signal frequency is mapped to a radial position in the volume of the formation in order to generate an image of the formation. Various properties of the formation, such as the effective diffusion coefficient of the formation fluid, longitudinal relaxation time, spin--spin relaxation time, and porosity can be estimated from the train of gradient-echoes.

Inventors: Sezginer; Abdurrahman (Houston, TX), Sen; Pabitra N. (Ridgefield, CT), Taherian; Mohammad Reza (Stafford, TX), Sun; Boqin (Sugar Land, TX)

Assignee: Schlumberger Technology Corporation

International Classification: G01V 3/32 (20060101); G01R 33/44 (20060101); G01V 3/18 (20060101); G01U 003/00 ()

Expiration Date: 12/26/2017