MEASURING DOWNHOLE TEMPERATURE BY COMBINING DAS/DTS DATA

• US 20170260846A1
• Filed: 03/08/2017
• Published: 09/14/2017
• Est. Priority Date: 03/09/2016
• Status: Active Grant

• Current Assignee: Conocophillips Company (ConocoPhillips)
• Original Assignee: Conocophillips Company (ConocoPhillips)
• Inventors: JIN, Ge, SWAN, Herbert W., ROY, Baishali, KRUEGER, Kyle R.
• Granted Patent: US 10,370,957 B2
• Time in Patent Office: Days
• CPC Class Codes: E21B 43/26 by forming crevices or fractures
• CPC Class Codes: E21B 47/0224 using seismic or acoustic means
• CPC Class Codes: E21B 47/0228 using electromagnetic energy or detectors therefor
• CPC Class Codes: E21B 47/07 Temperature
• CPC Class Codes: E21B 47/101 using acoustic energy
• CPC Class Codes: E21B 47/102 using electrical indications: using light radiations
• CPC Class Codes: E21B 47/107 using acoustic means
• CPC Class Codes: E21B 47/135 using light waves, e.g. infrared or ultraviolet waves
• CPC Class Codes: G01B 11/161 by interferometric means
• CPC Class Codes: G01H 9/004 using fibre optic sensors light guides per se G02B6/00, acousto-optical devices specially adapted for gating or modulating in optical wave guides G02F1/125
• CPC Class Codes: G01K 11/32 using changes in transmittance, scattering or luminescence in optical fibres
• CPC Class Codes: G01V 1/226 Optoseismic systems
• CPC Class Codes: G01V 1/40 specially adapted for well-logging

Abstract

This disclosure describes a method of combining DAS and DTS data to accurately estimate borehole temperature. The described method takes advantage of the thermal sensitivity of DAS signal in the low-frequency band, and combines with the absolute temperature measurement from DTS, to produce a distributed temperature estimation that is up to 10000 more accurate than the current commercial solution. The DAS and DTS data should be record simultaneously at the same well. The DAS data are first low-pass filtered and then converted into temperature variation measurement. Then an accurate temperature estimation is obtained by fitting both DTS and DAS data.

Claims

1. A method of measuring temperature variations along a wellbore, the method comprising:

a) providing one or more fiber optic cables along a length of a wellbore;

b) recording distributed acoustic sensing (DAS) signals along the wellbore well using at least one fiber optic cable;

c) simultaneously recording distributed temperature sensing (DTS) signals from the well using at least one fiber optic cable;

d) low-pass filter and down-sample the DAS signals to obtain low-frequency DAS data;

e) converting the low-frequency DAS data to temperature variation using the following equation (1);

wherein D(x,t) is the low-frequency DAS, μ

is the constant that converts optical phase rate to temperature variation, β

(t) is the drift noise existing in the DAS data;

f) estimating borehole temperature by minimizing the error function ε

using the following equation (2);

2. The method of claim 1, wherein said one or more fiber optic cables are embedded in a cement of the wellbore.

3. The method of claim 1, wherein said one or more fiber optic cables is included in a coiled tubing string, a wireline, or a carbon rod in the wellbore.

4. The method of claim 1, wherein DAS and DTS signals are obtained at 0-1 Hz.

5. The method of claim 1, wherein DAS and DTS signals are sampled at more than 1 kHz, preferably more than 5 kHz, more preferably more than 10 kHz to avoid aliasing from a high-frequency band.

6. The method of claim 1, wherein recorded DAS signals are low-pass filtered at 0.001-1 Hz and sub-sampled to a 1-second sample rate.

7. The method of claim 1, wherein DAS and DTS signals are obtained at 0-1 Hz and sampled at more than 1 kHz, preferably more than 5 kHz, more preferably more than 10 kHz to avoid aliasing from a high-frequency band.

8. The method of claim 1, wherein the wellbore is undergoing fracturing, shut-in, production, steam/water injection, or a combination thereof.

9. A system for measuring temperature in a wellbore, comprising:

g) a distributed acoustic sensing (DAS) monitoring device including an optical fiber that runs along a length of a wellbore, wherein the DAS optical fiber is coupled to an interrogating unit for emitting interrogating signals, the DAS monitoring device detects DAS signals when temperature variations cause deformation of said optical fiber;

h) a distributed temperature sensing (DTS) device, wherein said DTS device is coupled to said optic fiber or a second optic fiber, the DTS device having a DTS interrogating unit for emitting interrogating signals, and the DTS device having a DTS monitoring unit for detecting DTS signals;

i) a computer coupled to the DAS monitoring device for recording DAS signals detected by the DAS monitoring device, the computer also coupled to the DTS device for recording DTS signals detected by the DTS monitoring device;

wherein the computer performs the following steps to obtain temperature estimation along said wellbore from said recorded DAS and DTS data;

i) processing DAS data to obtain low-frequency DAS data;

ii) converting low-frequency DAS data to temperature variation using the following equation (1)

10. The system of claim 9, wherein said fiber optic cable is embedded in a cement of the wellbore.

11. The system of claim 9, wherein said fiber optic cable is included in a coiled tubing string, a wireline, or a carbon rod in the wellbore.

12. The system of claim 9, wherein the wellbore is undergoing fracturing, shut-in, production, steam injection, or a combination thereof.

13. The system of claim 9, wherein DAS and DTS signals are obtained at 0-1 Hz.

14. The system of claim 9, wherein DAS and DTS signals are sampled at >

1 kHz to avoid aliasing from the high-frequency band.

15. The system of claim 9, wherein recorded DAS signals are low-pass filtered at 0.001-1 Hz and sub-sampled to a 1-second sample rate.

16. The system of claim 9, wherein DAS and DTS signals are obtained at 0-1 Hz and sampled at more than 1 kHz, preferably more than 5 kHz, more preferably more than 10 kHz to avoid aliasing from a high-frequency band.