Halliburton Energy Services, Inc.

Yunmiao Wang

Mikko K Jaaskelainen

Seldon David Benjamin

A method is described for compensating measurement errors of fiber Bragg grating (FBG) sensors installed in fiber cables in down-hole oil and gas environments due to hydrogen darkening. The method involves loading a fiber of known length and multiple FBG sensors in a hydrogen chamber with control of temperature, hydrogen concentration, pressure, and time and adjusting each of the variables through a test matrix while continuously measuring and recording the fiber transmission loss and FBG spectrum changes, then creating a correlation map of fiber transmission loss vs. Bragg wavelength shift, and using that map for compensating the wavelength shift of downhole installed fiber cables as a function of their hydrogen induced transmission loss through time.

Method to compensate measurement error of fiber Bragg grating sensor caused by hydrogen darkening

Methods are proposed for compensation of distortion in fiber Fabry-Perot interferometric (FFPI) sensors induced by dynamic wavelength dependent attenuation in subsurface wells. The methods involve measurement techniques that correct the reflective spectrum from one or more FFPI sensors utilizing a background low frequency spectrum for normalization.

Methods to correct spectrum distortion of FFPI sensors induced by dynamic wavelength dependent attenuation

An optical sensor system may include an interrogation system coupled to one or more fiber-optic cables positioned in a wellbore. The interrogation system may interrogate a fiber Fabry-Perot interferometric sensor and one or more fiber Bragg sensors multiplexed in the fiber-optic cables. The optical sensor system may include a processing device to determine whether there is condition that may cause an error in the calculation of the cavity length of the fiber Fabry-Perot interferometric sensor in real-time based on a reference distance between peaks or valleys in the reflected light signal generated by the fiber Fabry-Perot interferometric sensor. The processing device may compare the reference distance to a distance between peaks or valleys detected in the spectrum to identify that an error condition exists and may correct the error prior to calculating the cavity length.

Active error correction in an optical sensor system

Various embodiments include apparatus and methods to measure pressure using an optical fiber. The optical fiber can be structured with fiber Bragg gratings arranged along the optical fiber. Optical signals can be transmitted through the optical fiber, where the optical signals have a wavelength of a slow-light peak of a respective one of the fiber Bragg gratings. Signals resulting from the optical signals transmitted through the optical fiber can be detected and a value of pressure from the detected signals can be determined.

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Houston, TX, United States of America

Yunmiao Wang