Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
  • G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
  • G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
  • G01H9/006—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors the vibrations causing a variation in the relative position of the end of a fibre and another element
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S3/00—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received
  • G01S3/80—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received using ultrasonic, sonic or infrasonic waves
  • G01S3/801—Details
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
  • G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
  • G01V1/22—Transmitting seismic signals to recording or processing apparatus
  • G01V1/226—Optoseismic systems
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
  • G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
  • G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
  • G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
  • G01V1/40—Seismology; Seismic or acoustic prospecting or detecting specially adapted for well-logging

Definitions

• the invention relates to fiber optic devices and in particular to a fiber optical
• DAS Distributed Acoustic Sensing
• DAS distributed acoustic sensing
• DAS systems typically detect backscattering of short (1 - 10 meter) laser pulses from impurities or inhomogeneities in the optical fiber. If fiber is deformed by an incident seismic wave then 1) the distance between impurities changes and 2) the speed of the laser pulses changes. Both of these effects influence the backscattering process. By observing changes in the backscattered signal it is possible to reconstruct the seismic wave amplitude.
• the first of the above effects appears only if the fiber is stretched or compressed axially.
• the second effect is present in case of axial as well as radial fiber deformations.
• the second effect is, however, several times weaker than the first.
• radial deformations of the fiber are significantly damped by materials surrounding the fiber.
• a conventional DAS system with a straight fiber is mainly sensitive to seismic waves polarized along the cable axis, such as compression (P) waves propagating along the cable or shear (S) waves propagating
• the present invention provides an improved fiber optic cable system for distributed acoustic sensing that is more sensitive to signals travelling normal to its axis and is thus better able to distinguish radial strain from axial strain on the system. Acoustic signals travelling normal to the cable axis may sometimes be referred to as "broadside” signals and result in radial strain on the fiber.
• the present invention also provides three-component (3C) sensing, from which the direction of travel of the sensed signal can be determined.
• a distributed fiber optic acoustic sensing system comprises an elongated body having an outer surface, an optical fiber disposed on the outer surface at a first predetermined wrap angle, and light transmitting and receiving means optically connected to the fiber for, respectively, transmitting an optical signal into the fiber and receiving a backscattered component of the signal out of the fiber.
• the system may further include a second optical fiber disposed on the outer surface at a second predetermined wrap angle. The wrap angles may be measured with respect to a plane normal to the axis of the body and the first wrap angle may be 90° and the second wrap angle may be less than 45°.
• the system may further include a third fiber disposed on the outer surface at a wrap angle between 90° and 45°. At least one of the fibers may include Bragg gratings.
• the body may have a circular cross-section or an elliptical cross-section and may include a layer of swellable elastomer surrounding the body.
• a sensing rod may be disposed in the elongated body and may contain at least one additional fiber.
• the additional fiber(s) may be substantially straight, helical, or sinusoidal.
• the system may further include layer of swellable elastomer between the sensing rod and the elongate body. Additionally or alternatively, the system may include a first sheath layer on the outside of the body and covering the fiber.
• the first sheath layer may have an oval external cross- section.
• the elongate body may have a non-circular cross-section having a larger semi-axis and the first sheath layer may be configured so that its larger semi-axis is perpendicular to the larger semi-axis of the elongate body.
• the system may include a second optical fiber wrapped around the outside of the first sheath layer.
• the first fiber and the second fiber may define different wrap angles.
• the system may include a second sheath layer on the outside of the first sheath layer and covering the second fiber. At least one of the sheath layers preferably comprises a polyamide or material having a similar elastic impedance.
• a distributed fiber optic acoustic sensing system comprise an elongate body having an outer surface that includes at least one substantially flat face, a first optical fiber housed in the body, and light transmitting and receiving means optically connected to the fiber for transmitting an optical signal into the fiber and receiving a backscattered component of the signal out of the fiber.
• the body may have a polygonal or triangular cross-section.
• the first fiber may be sinusoidal and the system may include a second sinusoidal fiber defining a plane perpendicular to the plane of the first fiber.
• the system may include a third fiber, which may be substantially straight or helical, and may define a wrap angle with respect to a plane normal to the axis of the body. The wrap angle may be less than 45° or less than 30°.
• the substantially flat face may have a visual appearance that is different from the appearance of the rest of the outer surface.
• Still other embodiments of the invention include a distributed fiber optic acoustic sensing system comprising an inner tube, a layer of swellable elastomer surrounding the tube, a tube of swellable elastomer surrounding the elastomer layer and defining an annulus therewith, and at least one sensor pad or strip disposed in the elastomer tube, each sensor pad comprising a stiffener and at least one longitudinal fiber affixed thereto or embedded therein.
• the system may include at least four sensor pads are disposed in the elastomer tube. At least one optical fiber may be housed in the inner tube.
• the inner tube may comprise a steel tube and the elastomer layer and the elastomer tube may be configured such that when they swell the annulus disappears.
• the elastomer layer is further configured such that when it swells without being constrained, its diameter exceeds a predetermined value that is selected to correspond to the inner diameter of a hole in the earth.
• the elastomer tube may be further configured such that when it swells in a borehole, the sensor pad(s) is/are disposed at the outer surface of the elastomer tube.
• the longitudinal fiber in each sensor pad may be sinusoidal, and/or each sensor pad may include one sinusoidal longitudinal fiber and one straight longitudinal fiber. At least one of the optical fibers may contain Bragg gratings.
• the inner tube may also houses at least one electrical transmission line.
• the system may further including an anchor that is configured to overlie the body and includes at least one arm for anchoring the anchor and body to the surface.
• the arm may be straight or curved.
• Figure 1 is a schematic side view of a cable constructed in accordance with one embodiment of the invention.
• Figure 3 is a schematic transverse cross-section of a cable constructed in accordance with another embodiment of the invention.
• Figure 4 is a schematic axial cross-section of an optical sensing system in accordance with the invention in a borehole
• Figure 5 is another view of the system of Figure 3 after swelling of a swellable layer
• Figure 6 is another view of the system of Figure 4 showing placement of a sensing rod in the system
• Figure 7 is another view of the system of Figure 5 after swelling of a second swellable layer
• Figure 9 is a schematic illustration of an optical sensing system in accordance with another embodiment.
• Figure 10 is a schematic end view of the system of Figure 9;
• Figure 11 is an axial cross-section of an optical sensing system in accordance with another embodiment
• Figures 16 and 17 are alternative embodiments of a support device for use with the present invention.
• DAS cable with helically wrapped fibers for improved broadside sensitivity comprises a DAS fiber helically wrapped around a cable or mandrel for the purpose of providing improved broadside sensitivity.
• a helically wound fiber will always include portions of the fiber that form relatively small angles with the incident wave, independently of the angle of incidence. Assuming that the cable and fiber are perfectly coupled to the formation, one can determine the fiber angular sensitivity S by projecting the wave strain along the fiber axis. This gives:
• a is the wrapping angle, i.e. the angle between the fiber and a plane perpendicular to the cable or mandrel axis
• ⁇ is the angle of incidence with respect to the cable of mandrel axis
• the above sensitivity S refers to unit fiber length.
• the sensitivity of a helically wrapped fiber per unit cable length is thus (1/ sin a) times higher than the above value of S.
• the concepts described herein can be implemented using one, two, or three fibers with different wrapping angles.
• Preferred embodiments of the sensing system include at least one fiber with a wrap angle of 90°, i.e. parallel to the cable axis, and one fiber with a wrap angle less than 45°.
• Still more preferred embodiments include a third fiber with a wrap angle between 45° and 90°. Fibers with different wrapping angles have different directional sensitivity, and by comparing their responses one can determine the direction of wave propagation with respect to the fiber axis.
• multiple fibers can be wrapped inside a single cable at different radii.
• multiple cables each having a single helically wrapped fiber can be used.
• the fiber need not actually encircle the body but may instead change or reverse direction so as to define fiber segments having a predetermined wrap angle alternating with bends or reversing segments.
• a particular preferred embodiment comprises an inner liner 15, a first sheath layer 16, and a second sheath layer 17. Wrapped around liner 15 and covered by sheath layer 16 are a plurality (three, as illustrated) of optical fibers 18. Fibers 18 are preferably wrapped at a first wrap angle with respect to the plane normal to the cable axis.
• a plurality (three, again, as illustrated) of optical fibers 19 are preferably wrapped around liner 16 and covered by sheath layer 17.
• Fibers 19 are preferably wrapped at a second wrap angle that is different from the first wrap angle of fibers 18.
• one of fibers 18 or 19 is straight, i.e. with a wrap angle of 90° and the other is wrapped with a small wrap angle, i.e. a wrap angle less than 45° with respect to the plane normal to the cable axis.
• the use of different wrap angles provides different directional sensitivities from which, by comparing their responses, it is possible to determine the direction of wave propagation with respect to the fiber axis. It will be understood that additional fibers having additional wrap angles can also be included.
• an optical sensing system may include a first, straight fiber, a second fiber with a wrap angle of 30° with respect to the plane normal to the cable axis, and a third fiber with a wrap angle of between 30° and 90°.
• the fiber wrapped at 30° gives exactly 2 m of fiber per 1 m of axial length and the third fiber allows for verification of data from other two fibers.
• a fiber wrapped around a circular cylinder does not discriminate between waves propagating normally to the cable axis from different azimuthal directions.
• Azimuthal sensitivity can be added by using helixes of noncircular, e.g. elliptical,wrapping shapes, which allow detection of all three components of the incident waves.
• the cable could include a distributed strain sensing (DSS) fiber similar to the one used in real-time compaction monitoring (RTCM) systems.
• DSS distributed strain sensing
• RTCM real-time compaction monitoring
• FBGs fiber Bragg gratings
• the optical fiber(s) are integrated in the wall of the high pressure-hose or tubes used by the drilling system.
• the pressure-hose/tubes incorporating the sensing system are left behind in the hole.
• the data-hole may include a surface exit.
• the sensing system can be pulled into the hole via the surface exit when the drill-string is being retrieved from the hole.
• the annulus between the sensing tube and the formation may be filled with fluid, a gel or cement.
• Sensing rod 30 may contain a plurality of straight, sinusoidal, and/or wrapped fibers 32. If wrapped (not shown), fibers 32 preferably have a large pitch, i.e. a small wrap angle, e.g. less than 45° and more preferably less than 30°. If desired, rod 30 may be centralized and fixed inside the sensing tube by means of a layer of swellable rubber, fluid, gel, cement, etc., as shown at 34 in Figure 7.
• a straight cable Since a straight cable is sensitive only to one direction (along the cable), it allows a simple partitioning of the signal recorded on a wrapped fiber into along-the-cable and across-the- cable components, assuming that both fibers (wrapped and straight) are made of the same material and embedded in the same medium. If they are of different materials or in different parts of the cable (center vs. periphery), their overall sensitivities to external formation strain may be different - i.e., they may have different A and B coefficients in the equation above. In that case, a straight cable may still help calibrate or constrain the partitioning of the wrapped fiber signal but the calibration would not be through direct subtraction of the along-the-cable component.
• an alternative construction for an optical sensing system with 3 fibers comprises a cable 40 having a triangular cross-section and at least two orthogonal sinusoidal optical fibers 42, 44 and a straight fiber 41 therein.
• An advantage of the triangular cross-section is that the cable has a flat bottom surface 43, which can be fixedly oriented with respect to, e.g., the inner or outer wall of a tubular, which in turn facilitates azimuthal sensing. It will be understood that while cable 40 is shown with a triangular cross-section, any polygon would be suitable. Further, if a flat bottom surface is not desired, the cable cross-section may be round, elliptical, oval, or any other shape. In order to facilitate installation of the cable with a known orientation, bottom surface 43, or all or a portion of one of the other surfaces may be color-coded or otherwise visually marked. In the absence of such external indicator, the determination of the azimuthal orientation of the cable must be made through first-arrival analysis.
• fiber 42 will be sensitive to signals having components in the inline (x) and vertical (z) directions.
• fiber 44 will be sensitive in the inline (x) and cross— line (y) directions.
• Fiber 41 has sensitivity in the inline (x) direction.
• the three fibers are assumed to be identically coupled to the formation. Accordingly, a combination of the responses of fibers 41, 42 and 44 enables a decomposition of the signal into the x, y, and z directions.
• a sinusoidal fiber may be disposed along one, two, three, or more surfaces of a body having a polygonal cross-section.
• three sinusoidal fibers may be disposed, each against one side of a body having a triangular cross- section. Signals from those three fibers could also be decomposed to three orthogonal sets.
• Such cable may be easier to manufacture.
• the embodiment shown in Figures 9 and 10 comprises a cable 46 having a hemi-circular cross-section and a flat bottom surface 47.
• cable 46 one fiber 48 is helically wrapped with a small wrap angle and a second fiber 49 is sinusoidal. Fiber 48 will be sensitive in the inline (x), cross-line (y), and vertical (z) directions.
• additional straight fibers 41 can be included in the cable, as discussed above.
• Straight fiber 41 will be sensitive to the inline direction (x). By using a combination of horizontal, vertical, and straight fibers, preferably recording in the same conditions, it is possible to generate 3C data.
• a multi-component cable 50 in accordance with a preferred embodiment comprises an inner tube 51, an expandable layer 52 surrounding tube 51, and an expandable tube 60 surrounding layer 52.
• Inner tube 51 is preferably substantially rigid and may comprise steel, polyamide, or the like.
• Inner tube 51 may be filled with a gel such as is known in the art or may be made solid using polyamide or the like.
• Layer 52 is preferably made of water- or oil-swellable elastomers, such as are known in the art.
• Tube 60 is preferably constructed from a deformable material such as an elastomer.
• Elongate sensor pads or strips 62 preferably extend the entire length of the cable.
• the material of which tube 60 is made is preferable flexible and elastomeric so as to enable it to respond to the expansion of the underlying swellable layer 52.
• the pads are made of Nylon 11, which is preferably also used for encapsulating the fiber optic and hydraulic control lines. Nylon 11 has a crush resistance in excess of 100 tons per square inch and excellent abrasion resistance.
• sensor pads 62 define all or the majority of the outer surface of multi-component cable 50, so that tube 60 is not or not substantially exposed to the borehole wall. In these embodiments, multi-component cable 50 may have a more or less square cross- section. It will be understood that there are a variety of configurations in which sensor pads and/or additional protective layers might be applied to or near the outer surface of tube 60.
• the annulus between 52 and 60 is preferable empty and sealed, or filled with a fluid that will not activate the expandable components.
• Sinusoidal fibers 64 and optional straight fibers 57 may be embedded in sensor pads 62 in an extrusion process.
• Sensor pads 62 may comprise any suitable extrusion materials such as are known in the art, including polyamide polymers, metal, or ceramic.
• swellable material(s) of layer 52 can be caused to swell by pumping an appropriate fluid (e.g. water) through the annulus between layer 52 and tube 60.
• an appropriate fluid e.g. water
• layer 52 and tube 60 will occupy the entire space between inner tube 51 and the hole wall.
• Inner tube 51 will be substantially centered in the hole and sinusoidal fibers 64 will be placed in proximity to the hole wall.
• layer 52, tube 60 and sensor pads 62 are configured such that when swelling is complete, sensor pads 62 are pressed against the inside wall of the data-hole 72.
• Figures 13 and 14 describe multi-component cable 50 with respect to a data-hole, it will be understood that cable 50 is equally useful for surface applications.
• the embodiment shown in Figure 15 comprises an optical sensing system 80 configured for use on the earth's surface.
• optical sensing system 80 includes an inner tube 51 that houses one or more optical fibers 54.
• tube 51 may house one or more communication or power transmission lines 55.
• optical sensing system 80 includes at least one, and preferably a plurality, of sensor pads 62 that each include at least one sinusoidal fiber 64. Pads 62 are preferably arranged so that fibers 64 are sensitive to signals that are normal to the axis of the system 80. As in the embodiment illustrated in Figure 15, one pad is preferably placed adjacent to bottom surface 83. In other preferred embodiments, at least one pad is substantially vertical.
• Body 82 is preferably constructed from a material having a Young's modulus, similar to or higher than the Young's Modulus of the sensor pad 62 or materials similar to the encapsulation materials used for fiber optic and hydraulic downhole control lines, as are known in the art, so as to provide crush- and abrasion- resistance.

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• Physics & Mathematics (AREA)
• Remote Sensing (AREA)
• Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• General Physics & Mathematics (AREA)
• Acoustics & Sound (AREA)
• Geology (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Environmental & Geological Engineering (AREA)
• Geophysics (AREA)
• Radar, Positioning & Navigation (AREA)
• Geophysics And Detection Of Objects (AREA)
• Length Measuring Devices By Optical Means (AREA)
• Optical Transform (AREA)
• Measurement Of Mechanical Vibrations Or Ultrasonic Waves (AREA)
• Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)

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• 2012
  • 2012-12-13 AU AU2012352253A patent/AU2012352253C1/en active Active
  • 2012-12-13 GB GB1407676.4A patent/GB2510996B/en active Active
  • 2012-12-13 CA CA2858226A patent/CA2858226C/en active Active
  • 2012-12-13 BR BR112014014565-2A patent/BR112014014565B1/pt active IP Right Grant
  • 2012-12-13 US US14/365,231 patent/US9494461B2/en active Active
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• 2016
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• 2017
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