# US 10,309,830 B2 · Methods to correct spectrum distortion of FFPI sensors induced by dynamic wavelength dependent attenuation

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- Number: US 10,309,830 B2
- Document ID: US10309830B2
- Status: Granted
- Kind: B2
- Application number: 15/524,379
- Filed: 2014-12-23
- Published: 2018-10-04
- Granted: 2019-06-04
- Earliest claimed: 2014-12-23
- Assignees: Halliburton Energy Services, Inc.
- Applicants: Halliburton Energy Services, Inc
- Inventors: Mikko Jaaskelainen; Yunmiao Wang
- Web page: https://patentgrep.com/patent/US10309830B2

## CPC

- G01J 3/0218: {using optical fibers}
- G01D 5/35312: {using a Fabry Perot}
- G01J 3/26: using multiple reflection, e.g. Fabry-Perot interferometer, variable interference filters
- G01J 3/28: Investigating the spectrum (using colour filters G01J3/51)
- G01J 3/42: Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry (beam switching arrangements G01J3/08)
- G01K 11/32: using changes in transmittance, scattering or luminescence in optical fibres
- G01L 1/24: by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis {using infrared, visible light, ultraviolet}
- G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N)
- G01D: MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01K: MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR (radiation pyrometry G01J5/00)
- G01L: MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE (weighing G01G)

## Abstract

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.

## Claims

### Claim 1

A method for compensation of distortion in fiber Fabry-Perot interferometric (FFPI) sensors induced by dynamic wavelength dependent attenuation in subsurface wells, said method comprising:
a. installing one or more FFPI sensors into a region of interest in a subsurface well;
b. feeding a light source through a fiber optic cable into the one or more FFPI sensors;
c. returning an original reflective spectrum from the one or more FFPI sensors to a spectrometer for analysis;
d. filtering the original reflective spectrum from the one or more FFPI sensors through a low-pass filter to generate an original filtered reflective spectrum;
e. dividing the original filtered reflective spectrum by a filtered reflected spectrum obtained from the one or more FFPI sensors before installation into the region of interest in the subsurface well to obtain a normalized spectrum; and
f. using the normalized spectrum to calculate changes in cavity length.

### Claim 2 (depends on 1)

The method of claim 1, wherein the light source is a white light source.

### Claim 3 (depends on 1)

The method of claim 1, wherein the light source is a swept laser.

### Claim 4 (depends on 1)

The method of claim 1, further comprising comparing the filtered reflective spectrum acquired before and after installation of the one or more FFPI sensors to estimate a wavelength dependent loss of the fiber optic cable.

### Claim 5 (depends on 1)

The method of claim 1, further comprising performing a discrete Fourier-transformation on the original reflective spectrum acquired before installation of the one or more FFPI sensors to divide the signal into a low frequency region representing a background signal and a higher frequency region representing an amplitude modulated signal.

### Claim 6 (depends on 5)

The method of claim 5, wherein the low-pass filter is chosen to select the background signal.

### Claim 7 (depends on 1)

The method of claim 1, wherein the FFPI sensors are used to measure temperature changes.

### Claim 8 (depends on 1)

The method of claim 1, wherein the FFPI sensors are used to measure pressure changes.

### Claim 9 (depends on 1)

The method of claim 1, wherein the FFPI sensors are used to measure strain effects.