APPARATUS AND METHOD FOR DETECTING PRESSURE SIGNALS
An apparatus for detecting data in a fluid pressure signal in a conduit comprises an optical fiber loop comprises a measurement section and a delay section wherein the measurement section is disposed substantially circumferentially around at least a portion of the conduit, and wherein the measurement section changes length in response to the fluid pressure signal in the conduit. A light source injects a first optical signal in a first direction into the measurement section and a second optical signal in a second direction opposite the first direction into the delay section. An optical detector senses an interference phase shift between the first optical signal and the second optical signal and outputs a first signal related thereto.
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The present disclosure relates generally to the field of telemetry systems for transmitting information through a flowing fluid. More particularly, the disclosure relates to the field of signal detection in such a system.
Sensors may be positioned at the lower end of a well drilling string which, while drilling is in progress, continuously or intermittently monitor predetermined drilling parameters and formation data and transmit the information to a surface detector by some form of telemetry. Such techniques are termed “measurement while drilling” or MWD. MWD may result in a major savings in drilling time and improve the quality of the well compared, for example, to conventional logging techniques. The MWD system may employ a system of telemetry in which the data acquired by the sensors is transmitted to a receiver located on the surface. Fluid signal telemetry is one of the most widely used telemetry systems for MWD applications.
Fluid signal telemetry creates pressure signals in the drilling fluid that is circulated under pressure through the drill string during drilling operations. The information that is acquired by the downhole sensors is transmitted by suitably timing the formation of pressure signals in the fluid stream. The pressure signals are commonly detected by a pressure transducer tapped into a high pressure flow line at the surface. Access to, and penetration of, the high pressure flow line may be restricted due to operational and/or safety issues.
A better understanding of the present invention can be obtained when the following detailed description of example embodiments are considered in conjunction with the following drawings, in which:
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the scope of the present invention as defined by the appended claims.
DETAILED DESCRIPTIONReferring to
As shown in
MWD tool 30 may include sensors 39 and 41, which may be coupled to appropriate data encoding circuitry, such as an encoder 38, which sequentially produces encoded digital data electrical signals representative of the measurements obtained by sensors 39 and 41. While two sensors are shown, one skilled in the art will understand that a smaller or larger number of sensors may be used without departing from the principles of the present invention. The sensors 39 and 41 may be selected to measure downhole parameters including, but not limited to, environmental parameters, directional drilling parameters, and formation evaluation parameters. Such parameters may comprise downhole pressure, downhole temperature, the resistivity or conductivity of the drilling mud and earth formations, the density and porosity of the earth formations, as well as the orientation of the wellbore.
The MWD tool 30 may be located proximate to the bit 32. Data representing sensor measurements of the parameters discussed may be generated and stored in the MWD tool 30. Some or all of the data may be transmitted in the form of pressure signals by data signaling unit 35, through the drilling fluid in drill string 14. A pressure signal travelling in the column of drilling fluid may be detected at the surface by a signal detector unit 36 employing optical fiber loop 230. The detected signal may be decoded in controller 33. The pressure signals may be encoded binary representations of measurement data indicative of the downhole drilling parameters and formation characteristics measured by sensors 39 and 41. Controller 33 may be located proximate the rig floor. Alternatively, controller 33 may be located away from the rig floor. In one embodiment, controller 33 may be incorporated as part of a logging unit.
Loop 230 has a length, L, and comprises measurement section 220 and delay section 225. In one embodiment, measurement section 220 may be 2-10 meters in length. In this example, measurement section 220 is wrapped at least partially around conduit 211, which may be standpipe 11 of
Delay section 225 may be on the order of 500-3000 meters in length. The small diameter of optical fibers contemplated (on the order of 250 μm) allows such a length to be wound on a relatively small spool. As shown in
Counter-propagating beams 231, 232 traverse loop 230 and recombine through coupler/splitter 215, and detected by photo-detector 210. Under uniform (constant in time) conditions, beams 231, 232 will recombine in phase at the detector 210 because they have both traveled equal distances around loop 230. Consider counter-propagating beams 231, 232 and a time varying pressure P(t) in standpipe 11. Beams 231, 232 will be in phase after they have traveled the distance X in their two paths, and they will be in phase after they have continued through the distance L−X as well. Now, let the pressure within the pipe be changing at a rate of dP/dt during the time Δt while beams 231, 232 travel the distance L−X, then
Δt=(L−X)n/c,
where c is the speed of light, and n is the refractive index of the optical fiber. During this time interval, the pressure within the pipe changes by an amount ΔP, which acts to radially expand standpipe 11. This expansion results in a change ΔX in the length, X, of the measurement section 220 of optical fiber 230 wrapped around conduit 211. Although at the end of the interval Δt the two beams are in phase, they will go out of phase for the last portion of the circuit before they recombine, because the length of measurement section 220 has changed during the previous interval Δt. For the final leg of the trip around the loop, the counter-clockwise beam 232 will travel a distance that is different by an amount ΔX from the clockwise rotating beam 231. When the beams combine at detector 210, they will be out of phase by a phase difference, Δφ, where
Δφ=2π(ΔX)/nλ,
where λ is the wavelength of the light emitted by source 202. As beams 231, 232 are combined, it can be shown that a factor in the signal will be cos(Δφ/2). Thus, counter propagating beams 231, 232 will be out of phase when ΔX=λ.
The change of the pressure in the pipe during the interval Δt is given by
ΔP=(dP/dt)Δt=(dP/dt)(L−X)(n/c).
Let K be the sensitivity of the pipe to internal pressure; that is, the change in circumference of the pipe ΔC due to a change in pressure ΔP given by,
ΔC=K(ΔP)
K can be computed from dimensions and material properties of the pipe materials. For example, for a thin-walled pipe, where Dpipe>10*pipe thickness, t, it can be shown that
K=πDpipe2/2Et
where E is the modulus of elasticity of the pipe material.
For a thick walled pipe, where Dpipe≦10*pipe thickness, t, it can be shown that
K=2πDoDi2/E(Do2−Di2)
where Do and Di are the outer and inner pipe diameters, respectively.
If Ncoil is the number of turns of fiber around the pipe, then
ΔX=N(ΔC)=NcoilK(dP/dt)(L−X)(n/c).
Thus, the change in length indicated by the interferometer is a function of the time derivative of the pressure signal, the number of turns Ncoil of fiber on the pipe, and the length L of the delay portion of the fiber.
Numerous variations and modifications will become apparent to those skilled in the art. It is intended that the following claims be interpreted to embrace all such variations and modifications.
Claims
1. An apparatus for detecting data in a fluid pressure signal in a conduit comprising:
- an optical fiber loop comprising a measurement section and a delay section wherein the measurement section is disposed substantially circumferentially around at least a portion of the conduit and wherein the measurement section changes length in response to the fluid pressure signal in the conduit;
- a light source injecting a first optical signal in a first direction into the measurement section and a second optical signal in a second direction opposite the first direction into the delay section; and
- an optical detector to sense an interference phase shift between the first optical signal and the second optical signal and outputting a first signal related thereto.
2. The apparatus of claim 1 wherein the first signal is related to a time derivative of the fluid pressure signal in the conduit.
3. The apparatus of claim 1 wherein the measurement section and the delay section are sequentially disposed.
4. The apparatus of claim 1 further comprising a controller in data communication with the optical detector wherein the controller integrates the first signal with respect to time and generates an output signal substantially similar to the fluid pressure signal.
5. The apparatus of claim 4 wherein the controller decodes the output signal into the data transmitted in the fluid pressure signal.
6. The apparatus of claim 1 wherein the light source is chosen from the group consisting of a laser, a laser diode, and a light emitting diode.
7. The apparatus of claim 1 further comprising a pliant substrate having the optical fiber of the measurement section attached thereto.
8. The apparatus of claim 7 wherein the pliant substrate is attachable around at least a portion of the conduit.
9. The apparatus of claim 1 wherein the delay section is about 500 meters to about 3000 meters long.
10. The apparatus of claim 1 wherein the measurement section is about 2 meters to about 10 meters long.
11. A method for detecting data in a fluid pressure signal in a conduit comprising:
- providing an optical fiber loop comprising a measurement section and a delay section;
- disposing the measurement section substantially circumferentially around at least a portion of the conduit wherein the measurement section changes length responsive to the fluid pressure signal in the conduit;
- injecting a first optical signal in a first direction into the measurement section and a second optical signal in a second direction opposite the first direction into the delay section; and
- sensing an interference phase shift between the first optical signal and the second optical signal and outputting a first signal related thereto.
12. The method of claim 11 wherein the first signal is indicative of a time derivative of the fluid pressure signal in the conduit
13. The method of claim 12 further comprising integrating the first signal with respect to time and generating an output signal substantially similar to the fluid pressure signal in the conduit.
14. The method of claim 13 further comprising decoding the output signal into data transmitted in the fluid pressure signal.
15. The method of claim 11 further comprising attaching the measurement section optical fiber to a pliant substrate.
16. The method of claim 15 further comprising attaching the pliant substrate at least partially around the conduit.
17. An apparatus for detecting a fluid pressure pulse signal propagating in a conduit comprising:
- an optical fiber loop comprising a measurement section and a sequentially disposed optical delay section wherein the measurement section is disposed substantially circumferentially around at least a portion of the conduit and changes in length in response to the pressure pulse in the conduit;
- a light source injecting a first optical signal in a first direction into the measurement section and a second optical signal in a second direction opposite the first direction into the delay section;
- an optical detector to sense an interference phase shift between the first optical signal and the second optical signal to indicate a time derivative of the pressure pulse in the conduit and generating a first signal indicative thereof; and
- a controller in data communication with the optical detector, wherein the controller integrates the first signal with respect to time and generates an output signal substantially similar to the fluid pressure pulse signal.
18. The apparatus of claim 17 wherein the controller decodes the output signal into data transmitted in the fluid pressure pulse signal.
19. The apparatus of claim 17 wherein the optical fiber of the delay section is about 500 meters to about 3000 meters long.
20. The apparatus of claim 17 wherein the optical fiber of the measurement section is about 2 meters to about 10 meters long.
21. A fluid telemetry system comprising:
- a transmitter located at a downhole location transmitting data as an encoded pressure signal through a fluid flowing in a conduit;
- an optical sensing system detecting the encoded pressure signal proximate a surface location wherein the optical sensing system comprises: an optical fiber loop comprising a measurement section and a sequentially disposed optical delay section wherein the measurement section is disposed substantially circumferentially around at least a portion of the conduit and changes in length in response to the encoded pressure signal in the conduit; a light source injecting a first optical signal in a first direction into the measurement section and a second optical signal in a second direction opposite the first direction into the delay section; an optical detector sensing an interference phase shift between the first optical signal and the second optical signal indicative of a time derivative of the encoded pressure signal in the conduit and generating a first signal indicative thereof; and
- a controller in data communication with the optical detector wherein the controller integrates the first signal with respect to time and generates an output signal substantially similar to the encoded pressure signal.
22. The fluid telemetry system of claim 21 wherein the controller decodes the output signal into the data.
23. The fluid telemetry system of claim 21 further comprising a pliant substrate having the optical fiber of the measurement section attached thereto wherein the pliant substrate is attachable around at least a portion of the conduit.
24. The fluid telemetry system of claim 21 wherein the optical fiber of the delay section is about 500 meters to about 3000 meters long.
25. The fluid telemetry system of claim 21 wherein the optical fiber of the measurement section is about 2 meters to about 10 meters long.
Type: Application
Filed: Mar 18, 2008
Publication Date: May 19, 2011
Applicant: Halliburton Energy Services, Inc. (Houston, TX)
Inventors: Ronald L Spross (Humble, TX), Paul F. Rodney (Spring, TX), James H. Dudley (Spring, TX), John L. Maida (Houston, TX)
Application Number: 12/812,779
International Classification: G01B 9/02 (20060101);