Apparatus and method for monitoring compaction
AssigneeShell Oil Company
InventorsFrederick Henry Kreisler Rambow, Dennis Edward Dria, David Ralph Stewart
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Abstract
An apparatus and method for continuous, passive detection and measurement of tensile and compressional strain in a structure utilizing a shielded optic fiber, the optic fiber having one or more Bragg gratings thereon, the gratings and shield being disposed in a curved path on the structure and a baseline response for the grating is made using an optical source and detector. Changes in tensile or compressional forces on the structure will result in changes in the curve of the grating, resulting in a frequency shift for the returned light.
Claims28
A transducer for passively monitoring displacement forces in a structure comprising:
- a) A source for providing a broadband or tunable narrow-band optical signal;
- b) An optical detection unit;
- and
- c) An optical fiber having one or more gratings thereon axially disposed to and in close proximity to a protective sheath of circular or noncircular cross section, said fiber grating and sheath characterized by one or more bends, causing a radial distortion in said grating, wherein said protective sheath is made of material sufficiently flexible to bend upon subjection to displacement forces, and wherein bending causes said grated fiber(s) to follow the shape of the protective sheath, the detection unit thereby measuring a change in frequency of a returned signal as a function of a change in radial distortion of the gratings.
A method for continuously, passively detecting and measuring displacement (compaction) of a structure which includes the following elements:
- a) Attaching to the structure to be monitored a protective sheath of circular or noncircular cross section and having axially disposed in close proximity thereto, and positioned to move therewith, an optical fiber(s) having one or more gratings thereon at selected points, said protective sheath and grating being characterized by one or more bends, said bend introducing radial distortion in said grating, wherein said protective sheath is made of material sufficiently flexible to displace upon subjection to displacement forces, and bending causes said grated fiber(s) to follow the shape of the protective sheath;
- and
- b) Coupling a light source and measuring wavelength response of the grating to said light source;
- c) Wherein subjecting the bent grated fibers to displacement forces causes a change in the radial distortion of said grating and the wavelength response is altered in a predictable way, and
- d) Comparing said wavelength response with a calibration curve and estimating the magnitude of displacement.
Dependencies are inferred from the claim text.