Interferometric means and method for accurate determination of f

Communications – electrical: acoustic wave systems and devices – Seismic prospecting – Well logging

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356345, 356358, G01V 140, G01B 902

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active

048624241

ABSTRACT:
A method and means for determining the amount of stretch in a well logging cable is disclosed. An optical fiber is run into a well with a logging cable and looped back to the surface. A second optical fiber of nominal length is maintained on the surface. A source of monochromatic light is passed through both fibers and recombined. As the well logging tool is raised and lowered in the wellbore, the number of interference fringes passing a fixed point is determined. The change in length of the optical fiber and, therefore, the cable will be equal to 1/2 the number of interference fringes passing a fixed point times the wavelength of light used. A precise determination of vertical location can then be made when this information is combined with information from a surface mounted odometer or encoder. This information further allows a precise determination of interval bulk density or other formation parameters in which it is important to know the depth of a tool.

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