JP2011027533A - Optical fiber type acoustic-wave logging system and soil logging structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact acoustic-wave logging system using an optical fiber. <P>SOLUTION: The optical fiber type acoustic-wave logging system D which is applied when logging a geological layer as an object to be detected surrounding a boring hole H bored in an appraisal drilling of an oil field, includes: a WDM light source 10; a sonic module 20; a measuring device 30; a relay optical fiber 40 and a sound source device 50. The sonic module 20 contains a plurality of FOD sensor parts and is outward fit to a casing pipe to be inserted into the boring hole H. A gap between the boring hole H and the casing pipe is filled up with a cement, thereby fixing the sonic module 20 to the surrounding geological layer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical fiber acoustic wave logging system that identifies the material of the detection object based on the velocity of sound waves propagating through the detection object, and a soil logging structure to which the optical fiber acoustic wave logging system is applied.

  In the case of oil field exploration, it is required to log the formation around the excavation hole in order to confirm the existence of a commercially available oil reservoir. As such a well logging technique, there is a sound wave logging method as described in Non-Patent Document 1, for example. This method uses the fact that the propagation time of sound waves varies depending on the type of formation. FIG. 13 is a schematic diagram showing the measurement principle of sonic logging. A long columnar probe 90 having a sound wave transmitter 91 on one end side and first and second sound wave receivers 92 and 93 spaced from each other on the other end side is inserted into the excavation hole 9. The

  When a sound wave pulse is transmitted from the sound wave transmitter 91, it enters the peripheral wall of the excavation hole from the point A at a critical angle of sound wave propagation, and propagates along the peripheral wall and the surrounding formation. Thereafter, the sound wave pulse is incident on the first sound wave receiver 92 on the side closer to the point B and subsequently on the second sound wave receiver 93 on the side farther than the point C. After the transmission of the sound wave pulse, a time difference Δt between a time t1 until the sound wave pulse is detected by the first sound wave receiver 92 and a time t2 until the sound wave pulse is detected by the second sound wave receiver 93 is obtained. By determining, it is possible to estimate the formation in the vicinity of point C from point A.

  By the way, as a sensor element for detecting vibration such as a sound wave, for example, a FOD (Fiber Optic Doppler) sensor as shown in Non-Patent Document 2 is known. The FOD sensor is a sensor that utilizes the fact that the frequency of transmitted light is modulated by the Doppler effect as the path length of the optical fiber expands and contracts due to vibration applied to the optical fiber. Such FOD sensors are also being studied for application to the measurement of microfault sound of rock (see Non-Patent Document 3, for example).

“Oil and Natural Gas Glossary of Terms” / “Sonic Logging” issued by the Japan Natural Oil and Metals National Corporation “Doppler Effect in Flexible and Expandable Light Waveguide and Development of New Fiber-Optic Vibration / Acoustic Sensor”, Kazuro Kageyama et al, JOUNAL OF LIGHTWAVE TECHNOLOGY, VOL.24, NO.4, APRIL 2006 "High-sensitivity optical fiber vibration sensor and AE measurement when soft rock specimen is broken" Takao Mori et al., Proceedings of the 36th Symposium on Rock Mechanics 2007.1, pp. 239-244

  The sound wave transmitter and the sound wave receiver used in the conventional sound wave logging method are exclusively electrical devices. For this reason, wiring of electric wires becomes indispensable, and when many sound wave receivers are mounted in order to improve resolution, the wiring becomes complicated and an increase in the size of the probe is inevitable. Furthermore, it is difficult to permanently install these electrical devices in the drilled production well, and there is a problem that it is impossible to monitor changes in the surrounding formations of the production well where oil production continues.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a compact acoustic logging system using an optical fiber and a soil logging structure to which this is permanently applied.

  An optical fiber acoustic wave logging system according to one aspect of the present invention includes a WDM light source that generates a plurality of detection lights having different wavelengths, and a plurality of sound detection lights that are individually incident on the plurality of detection lights. A sonic module having a fiber sensor; a measuring means for detecting the plurality of detection lights passing through the optical fiber sensor; the plurality of detection lights; the WDM light source; the measurement means; and the optical fiber sensor. One of a plurality of detection lights transmitted through the repeater optical fiber is interposed between the repeater optical fiber transmitted between the repeater optical fiber and a connection part between the repeater optical fiber and the optical fiber sensor unit. Optical multiplexing / demultiplexing means for forming a transmission state assigned to each of the fiber sensor units, and fixing means for fixing the sonic module to a detection target capable of propagating sound waves. Characterized in that (claim 1).

  According to this configuration, since the sonic module is fixed to the detection target by the fixing means, the sound wave is propagated from the detection target to each optical fiber sensor unit. Also, detection light is transmitted to each optical fiber sensor unit. Since the characteristics of the detection light that has passed through the optical fiber sensor unit to which the sound wave has been applied change, it is possible to detect the arrival of the sound wave to the optical fiber sensor unit by measuring the detection light with a measuring means. it can. Here, the plurality of detection lights transmitted to the sonic module are collectively transmitted from the WDM light source through the relay optical fiber, and are allocated to the respective optical fiber sensor units by the optical multiplexing / demultiplexing means. It can be simplified. Furthermore, an optical communication path using an optical fiber can be secured along the detection target.

  In the above configuration, it is desirable to further include a sound source device that generates a sound wave that propagates the detection target. According to this configuration, the sound wave propagating through the detection target can be spontaneously generated, so that the efficiency of the sound wave logging work can be improved.

  Alternatively, the detection object is a formation, and a microearthquake may be used as a sound wave propagating through the formation (Claim 3). According to this configuration, since micro earthquakes that occur naturally at a high frequency are used, the incorporation of the sound source device into the system can be omitted.

  In the above configuration, the optical fiber sensor unit includes an optical fiber vibration sensor using a Doppler effect, and the relay optical fiber transmits the detection light from the WDM light source to the optical fiber sensor unit. A second relay optical fiber that transmits the detection light from the optical fiber sensor unit to the measurement unit, and the measurement unit detects frequency modulation of the detection light that has passed through the optical fiber vibration sensor. It can be set as a structure (Claim 4). According to this configuration, the arrival of a sound wave can be detected using a so-called FOD (Fiber Optic Doppler) sensor.

  Alternatively, the optical fiber sensor unit is configured by a fiber Bragg grating, and the relay optical fiber includes a third relay optical fiber that transmits the detection light from the WDM light source to the optical fiber sensor unit, and the measurement unit includes The Bragg wavelength shift of the reflected light of the detection light reflected by the fiber Bragg grating can be detected. According to this configuration, the arrival of a sound wave can be detected using a so-called FBG (Fiber Bragg Grating) sensor.

  In the above-described configuration, it is desirable that the sonic module includes a holding member that holds the plurality of optical fiber sensor portions in a state of being separated from each other. According to this configuration, it is possible to improve the handleability of the sonic module and facilitate the installation and fixing work to the detection target.

  In this case, it is desirable that the holding member is made of an elastic member having lower sound transmission than the detection target. According to this configuration, the sound transmission property of the holding member can be reduced, and sound waves can be attenuated between the optical fiber sensor portions.

  In the above configuration, it is one of preferred embodiments that the detection object is a formation and the fixing means is cement (Claim 8). According to this configuration, the adherence of the sonic module to the formation, that is, the sound transmission from the formation can be improved.

  A soil logging structure according to another aspect of the present invention includes a casing pipe inserted into a drilling hole excavated in the soil, and the above-described optical fiber type acoustic logging system for logging a surrounding formation of the drilling hole. The sonic module is attached to a predetermined position of the casing pipe (claim 9). According to this configuration, it is possible to provide a compact soil logging structure capable of detecting the features of the formation around the excavation hole when the oil field is tested.

  In this case, a gap exists between the peripheral wall of the excavation hole and the outer peripheral surface of the casing pipe, the sonic module is attached to the outer peripheral portion of the casing pipe, and the fixing means is cement that fills the gap. It is desirable to be present (claim 10). According to this structure, the sound transmission property from the formation to the sonic module can be improved.

  According to the present invention, it is possible to provide a compact acoustic logging system having a simple configuration and a soil logging structure to which the acoustic logging system is applied, using an acoustic detection technique using an optical fiber. Therefore, it can contribute to the efficiency improvement of the logging work performed at the time of oil field trial drilling or the like.

It is a figure showing a schematic structure of an optical fiber type sound wave logging system concerning an embodiment of the present invention. It is a figure which shows an example of a sonic module, (a) is a side view, (b) is a top view. It is a side view which shows the other example of a sonic module. (A)-(c) is typical sectional drawing which shows the excavation procedure of an oil well. It is a typical sectional side view which shows the structure of an oil well. It is a sectional side view which shows the installation aspect of a sonic module. It is a block diagram which shows the structure of an optical fiber type acoustic logging system. It is a block diagram for demonstrating the sound wave detection by a FOD sensor system. It is a block diagram which shows the other structure of an optical fiber type acoustic logging system. It is a side view which shows the example of the sonic module of a FBG sensor system. It is a block diagram for demonstrating the sound wave detection by a FBG sensor system. It is a schematic diagram for demonstrating the sound wave logging by a sonic module. It is a schematic diagram for demonstrating the conventional sonic logging.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of an optical fiber type acoustic logging system D (soil logging structure) according to an embodiment of the present invention. In the present embodiment, an optical fiber type acoustic logging system D applied when logging around a borehole H (excavation hole) drilled in an oil field trial drilling as a detection target is illustrated. The acoustic logging system D includes a WDM (Wavelength Division Multiplexing) light source 10, a sonic module 20, a measuring device 30 (measuring means), a relay optical fiber 40, and a sound source device 50. The WDM light source 10 and the measuring device 30 are unitized and assembled in one logging device 100. The logging device 100 is disposed on the ground.

  The WDM light source 10 is a light source that generates a plurality of detection lights having different wavelengths. The WDM light source 10 includes a multi-wavelength light source in which a plurality of laser diodes (LDs) having different emission wavelengths are mounted, and a light source in which a plurality of the same type of LDs are mounted. The element temperature, drive current, or filter condition of each LD is determined. By making them different, a light source having multiple wavelengths can be used. Alternatively, a super continuum (SC) light source, an ASE light source, or the like can also be used. When a single mode optical fiber is used as the relay optical fiber 40, it is desirable that the light source be capable of generating light of a plurality of wavelengths in the 1.3 μm band or 1.5 μm band that can suppress transmission loss.

  The sonic module 20 is a module for detecting acoustic information having a plurality of optical fiber sensor units for detecting sound waves (described later based on FIGS. 2 and 3). In the present embodiment, the sonic module 20 detects sound waves that propagate in the surrounding formation (detection target) of the borehole H. For this reason, the sonic module 20 is fixed to the peripheral wall so that sound transmission from the peripheral wall of the borehole H can be satisfactorily performed at the logging target portion of the borehole H. This fixing structure will be described later with reference to FIG.

  The measuring device 30 detects a plurality of detection lights that have passed (via) each optical fiber sensor unit of the sonic module 20, and measures whether or not each optical fiber sensor unit has detected a sound wave in association with time information. . In the present embodiment, an example in which an optical fiber vibration sensor (FOD sensor) using the Doppler effect is used as the optical fiber sensor unit will be described first. In this case, the measuring device 30 detects sound waves by detecting frequency modulation of the detection light that has passed through the FOD sensor (details will be described later with reference to FIGS. 7 and 8). In another embodiment in which a fiber Bragg grating sensor (FBG sensor) is used as the optical fiber sensor unit, a sound wave is detected by detecting a Bragg wavelength shift of the reflected light of the detection light reflected by the FBG sensor. (Details will be described later with reference to FIGS. 9 to 11).

  The relay optical fiber 40 is configured to detect a plurality of detection lights emitted from the WDM light source 10 between the WDM light source 10 and the measuring device 30 (arranged on the ground) and the optical fiber sensor unit (arranged in the borehole H) of the sonic module 20. Transmit between. In the present embodiment, the relay optical fiber 40 includes the first relay optical fiber 41 that transmits the detection light from the WDM light source 10 to the optical fiber sensor unit of the sonic module 20, and the detection light that has passed through the optical fiber sensor unit. , And a second relay optical fiber 42 that transmits to the measuring device 30.

  The sound source device 50 generates a sound wave to be propagated to the surrounding stratum around the borehole H. As the sound source device 50, an ultrasonic transmitter that electrically generates an ultrasonic pulse of about 20 kHz to 30 kHz can be used. Of course, the sound source device 50 that generates an audible sound may be used. The sound source device 50 can be arranged at an appropriate position of the boring hole H. For example, as shown in FIG. 1, the sound source device 50 is arranged at the hole bottom, attached to the peripheral wall of the boring hole H, or a boring hole H with a suspension member. It can be hung inside. For supplying electricity to the sound source device 50, it is possible to use a means for laying the electric wire in the boring hole H or incorporating a battery power source. Alternatively, a metal-coated optical fiber may be used as the relay optical fiber 40 and the metal layer may be used as a power supply path for the sound source device 50.

  2A and 2B are diagrams showing an example of a sonic module 20A (20) provided with an FOD sensor as an optical fiber sensor unit. FIG. 2A is a side view and FIG. 2B is a top view. The sonic module 20A includes a holding member 21, a first optical multiplexer / demultiplexer 22, a second optical multiplexer / demultiplexer 23 (optical multiplexing / demultiplexing means), and a plurality of FOD sensor units S1, S2, S3, S4,. Including.

  The holding member 21 is a member that holds a plurality of FOD sensor portions S1, S2, S3, S4,... Sn in a state of being separated from each other, and is a cylindrical member having a size that can be fitted onto a casing pipe described later. It is. Although various materials can be used as the constituent material of the holding member 21, it is preferable to use an elastic member that clearly has lower sound transmission than the surrounding formation of the borehole H. For example, a member formed into a cylindrical shape using carbon fiber is one of the preferable holding members. With such a holding member 21, the sound transmission property of the holding member 21 is lowered, and the propagation of sound waves between the FOD sensor units S1, S2, S3, S4,. it can.

  The first optical multiplexer / demultiplexer 22 and the second optical multiplexer / demultiplexer 23 are optical multiplexers / demultiplexers using, for example, an arrayed waveguide type diffraction grating (AWG) used for WDM communication. The first optical multiplexer / demultiplexer 22 is interposed in a connection portion between the first relay optical fiber 41 and the FOD sensor units S1, S2, S3, S4... Sn, and is transmitted through the first relay optical fiber 41. The detection light is demultiplexed so that one detection light is transmitted to each of the FOD sensor units S1, S2, S3, S4... Sn. Further, the second optical multiplexer / demultiplexer 23 is interposed in the connection portion between the FOD sensor units S1, S2, S3, S4,... Sn and the second relay optical fiber 42, and the FOD sensor units S1, S2, S3, S4. ... A plurality of detection lights that have passed through Sn are combined and transmitted to the second repeater optical fiber 42. The first optical multiplexer / demultiplexer 22 and the second optical multiplexer / demultiplexer 23 are fixed to pedestals 221 and 231 attached to the outer peripheral surface of the holding member 21, respectively.

  The FOD sensor portions S1, S2, S3, S4,... Sn are made of optical fibers 431, 432, 433, 434,... 43n wound around the outer peripheral surface of the holding member 21 by a predetermined number of turns. The optical fiber 431 constituting the FOD sensor unit S1 has one end connected to the first optical multiplexer / demultiplexer 22 and the other end connected to the second optical multiplexer / demultiplexer 23, and an intermediate portion wound around the outer peripheral surface of the holding member 21. It has been turned. Similarly, one end of the optical fiber 432 constituting the FOD sensor unit S2 is connected to the first optical multiplexer / demultiplexer 22 and the other end thereof is connected to the second optical multiplexer / demultiplexer 23, and an intermediate portion thereof is connected to the optical fiber 431. The holding member 21 is wound around the outer peripheral surface at a predetermined interval with respect to the winding position. The same applies to the other optical fibers 433, 434,.

The FOD sensor utilizes a phenomenon in which the wavelength of transmitted light expands and contracts as the optical fiber expands and contracts in accordance with the vibration of the detection target. That is, when the optical fiber expands and contracts and the path length changes in a state where the inspection light having the frequency f ₀ is transmitted, the wave number of the inspection light existing from one end to the other end of the optical fiber is constant. The wavelength of the inspection light expands and contracts. That is, the propagation speed of the inspection light because it is constant, so the frequency is changed by f _d (laser Doppler effect). This frequency modulation amount _fd is proportional to the displacement speed when the optical fiber is expanded and contracted.

  Therefore, if the optical fiber length of the FOD sensor portion is made as long as possible, the sensing sensitivity can be increased by increasing the expansion / contraction displacement speed of the optical fiber when a sound wave vibration is applied. For this reason, the optical fibers 431, 432, 433, 434... 43n increase the number of turns to the holding member 21 as much as possible, and increase the optical fiber length in each FOD sensor unit S1, S2, S3, S4. It is desirable to scale.

  In order to protect the optical fibers 431, 432, 433, 434... 43 n, around the holding member 21 around which the optical fiber is wound with a sheet or a heat-shrinkable tube that does not impair sound transmission from the formation. It may be covered. Alternatively, optical fibers 431, 432, 433, 434... 43 n may be embedded in the holding member 21.

  FIG. 3 is a diagram illustrating another embodiment of the sonic module 20B (20) including the FOD sensor. In the sonic module 20B, the holding member 21, the first optical multiplexer / demultiplexer 22, and the second optical multiplexer / demultiplexer 23 are the same as the sonic module 20A of FIG. The difference is the installation mode of the optical fibers 441, 442, 443... 44n in the plurality of FOD sensor units S11, S12, S13.

  The optical fiber 441 used in the FOD sensor unit S11 has one end connected to the first optical multiplexer / demultiplexer 22 and the other end connected to the second optical multiplexer / demultiplexer 23. A sensing part 441R wound in a loop on the surface is provided. Similarly, the optical fiber 442 used in the FOD sensor unit S12 has one end connected to the first optical multiplexer / demultiplexer 22 and the other end connected to the second optical multiplexer / demultiplexer 23, respectively. It has a loop-shaped sensing part 442R formed at a position spaced apart from the sensing part 441R. The other optical fibers 443,... 44 are the same, and each has a sensing part 443R,.

  In the sonic module 20 </ b> A of FIG. 2, since the optical fiber is turned around the entire circumference of the cylindrical holding member 21, the radial direction of the turn is a direction orthogonal to the extending direction of the boring hole H. Therefore, the FOD sensor portions S1, S2, S3, S4,... Sn of the sonic module 20A are highly sensitive to a transverse wave (shear wave) propagating in a direction horizontally across the borehole H. On the other hand, in the sonic module 20 </ b> B of FIG. 3, an optical fiber loop is formed on a part of the peripheral surface of the holding member 21, so the radial direction of the loop is a direction parallel to the extending direction of the boring hole H. . Therefore, the FOD sensor units S11, S12, S13,... S1n of the sonic module 20B are highly sensitive to longitudinal waves propagating in the extending direction of the boring hole H.

  A preferred embodiment of the sonic module 20 is to install such two sonic modules 20 </ b> A and 20 </ b> B on one holding member 21. For example, one loop type FOD sensor unit S11 is arranged in the vicinity of the arrangement position of the turn type FOD sensor unit S1, and one type of loop type FOD sensor unit S12 is arranged in the vicinity of the arrangement position of the turn type FOD sensor unit S2. At the sound detection point, both the turn type optical fiber of FIG. 2 and the loop type optical fiber of FIG. 3 are arranged. This means that at each sound detection point, a sensor unit having high sensitivity to the transverse wave and the longitudinal wave is provided, so that the detection sensitivity of the sound wave can be increased.

  Such a sonic module 20 is fixed to the peripheral wall surface of the borehole H so that the sound wave is propagated from the surrounding formation of the borehole H. In this embodiment, concrete Ce (see FIG. 6) is used for this fixation. Before explaining such a fixing structure, a general oil well structure will be explained. (A)-(c) of Drawing 4 is a typical sectional side view showing the excavation procedure of an oil well.

  First, as shown in FIG. 4 (a), the primary hole H1 (a part of the boring hole H) is excavated from the ground surface G into the ground by, for example, a rotary excavation method. The rotary excavation method is an excavation method in which a drill string having a bit attached to a rock at the tip is rotated around an axis, and excavation fluid is circulated to remove digging waste and dig into the formation. Once the primary hole H1 having a predetermined depth is excavated, the drill string is once pulled up.

  When the primary hole H1 having a predetermined depth is excavated, as shown in FIG. 4B, the first casing pipe Ca1 is inserted into the primary hole H1. The first casing pipe Ca1 is inserted to protect the excavated primary hole H1, and is composed of a seamless iron pipe or the like, and its outer diameter is slightly smaller than the diameter of the primary hole H1. Thereafter, the cement liquid is press-fitted into the gap between the first casing pipe Ca1 and the primary hole H1, and the first cement layer Ce1 is formed around the first casing pipe Ca1. By this cementing, the first casing pipe Ca1 is fixed.

  Subsequently, as shown in FIG. 4C, a deeper excavation hole is formed by the same method. That is, the drill string is lowered through the inside of the first casing pipe Ca1, the formation is further dug deeper from the bottom surface of the primary hole H1, and the secondary hole H2 is excavated. The secondary hole H2 is substantially the same as the inner diameter of the first casing pipe Ca1. The second casing pipe Ca2 is inserted into the secondary hole H2, and the cement liquid is press-fitted into the gap between the secondary hole H2 and the second casing pipe Ca2, thereby forming a second cement layer Ce2. The Thereafter, digging is carried out to a desired depth in the same procedure. In recent years, holes deeper than 5000 m have been excavated.

  FIG. 5 is a schematic side sectional view showing the structure of an oil well. It is assumed that there is an oil layer in the formation surrounding the n-th n-th hole Hn excavated n-th time. In this case, the n-th casing pipe Can inserted into the n-th hole Hn and a part of the surrounding n-th cement layer Cen are blasted to form a perforation part Ca-P. Crude oil impregnated in the oil layer enters the n-th hole Hn through the perforation part Ca-P.

  Thereafter, a tube Tu for pumping crude oil is inserted into the borehole H. The lower end of the tube Tu is disposed in the vicinity of the perforation part Ca-P. In addition, the packer P (lid) is disposed around the tube Tu at a position above the perforation portion Ca-P.

  The above is the general structure of an oil well, but a borehole is drilled by a similar method in order to detect the oil reservoir. That is, the trial drilling hole also has a casing pipe and a surrounding cement layer. The optical fiber type acoustic logging system D according to the embodiment is applied to such a test boring hole, and detects whether or not an oil layer exists around the hole based on the propagation speed of the sound wave.

  FIG. 6 is a side cross-sectional view illustrating a laying mode of the sonic module 20 with respect to the boring hole HA for trial digging. A casing pipe Ca is inserted into the boring hole HA. A sonic module 20 (here, the sonic module 20A illustrated in FIG. 2 is illustrated) is attached to the outer periphery of the casing pipe Ca. Specifically, the holding member 21 is fitted on the outer periphery of the casing pipe Ca, and the FOD sensor portions S1, S2, and S3 disposed on the outer periphery of the holding member 21 are opposed to the peripheral wall of the boring hole HA.

  In this state, the gap between the casing pipe Ca and the boring hole HA is filled with the cement layer Ce. As a result, there is substantially no air gap between the FOD sensor portions S1, S2, S3 and the peripheral wall surface of the boring hole HA, and both are grounded via the cement layer Ce. With this configuration, the adhesion of the sonic module 20 to the formation around the boring hole HA, that is, the sound transmission from the formation to the FOD sensor portions S1, S2, and S3 can be improved.

  When laying the sonic module 20, it is desirable that the sonic module 20 is fitted and fixed in advance at a predetermined position of the casing pipe Ca. Then, the normal method for forming the excavation hole in which the casing pipe Ca with the sonic module 20 is inserted into the boring hole HA and then the cement liquid is injected into the gap between the casing pipe Ca and the boring hole HA. Thus, the sonic module 20 can be laid.

  FIG. 7 is a block diagram showing the configuration of the optical fiber acoustic logging system D. As shown in FIG. The system D includes the first half mirror 11, in addition to the WDM light source 10, the sonic module 20, the measuring device 30, the repeater optical fiber 40, the first optical multiplexer / demultiplexer 22, and the second optical multiplexer / demultiplexer 23 described above. A second half mirror 12, a frequency modulator (AOM) 13, a third optical multiplexer / demultiplexer 24, and a fourth optical multiplexer / demultiplexer 25 are provided. These elements are assembled in the logging apparatus 100 except for the sonic module 20 and the relay optical fiber 40. The logging apparatus 100 further includes a CPU 101 and a controller 102 operated by the CPU 101. Here, an example in which the sonic module 20A shown in FIG. 2 is applied as the sonic module 20 and a measurement device 30A corresponding to the sonic module 20A is provided.

The first half mirror 11 includes detection light λ ₁ , λ ₂ , λ ₃ , λ ₄ ,... Λ of each channel generated by the WDM light source 10 between the WDM light source 10 and the third optical multiplexer / demultiplexer 24. _n is assembled into an output optical fiber 411 that transmits _n , and a part of each of the detection lights λ ₁ , λ ₂ , λ ₃ , λ ₄ ,... λ _n is branched from the output optical fiber 411. The branched light is led out by a branched optical fiber 413 for each channel.

The second half mirror 12 is arranged between the fourth optical multiplexer / demultiplexer 25 and the measuring device 30A so that the detected lights λ ₁ ′, λ ₂ ′, λ ₃ ′, λ ₄ ′,. The λ _n ′ is assembled to the input optical fiber 412 to be transmitted, and the branch optical fiber 413 of each channel is joined to the input optical fiber 412.

The AOM 13 includes a transmission circuit that generates reference light having a constant frequency (for example, 80 MHz), and is disposed in the middle of the branch optical fiber 413. The AOM 13 adds reference light to each of the detection lights λ ₁ , λ ₂ , λ ₃ , λ ₄ ,... Λ _n derived by the branch optical fiber 413, and detects each of the detection lights λ ₁ , λ ₂ , λ ₃ , λ _4, to modulate the frequency of ··· λ _n. Each detection light lambda ₁ after _{modulation, λ 2, λ 3, λ} 4, ··· λ n via the second half mirror 12, the detection light lambda ₁ for transmitting an input optical fiber 412 ', lambda ₂ ′, Λ ₃ ′, λ ₄ ′,... Λ _n ′. These configurations are configurations for detecting frequency modulation of detection light caused by the Doppler effect in an optical heterodyne method.

Similarly to the first and second optical multiplexer / demultiplexers 22, the third and fourth optical multiplexer / demultiplexers 24 and 25 are optical multiplexers / demultiplexers using AWG. The third optical multiplexer / demultiplexer 24 is interposed in the connection portion between the output optical fiber 411 and the first repeater optical fiber 41, and the detection light λ ₁ , λ ₂ , λ ₃ , λ _{4 of} each channel generated by the WDM light source 10. the · · · lambda _n multiplexes, is transmitted to the first relay optical fiber 41. The fourth optical multiplexer / demultiplexer 25 is interposed at the connection between the second repeater optical fiber 42 and the input optical fiber 412, and detects each of the detection lights λ ₁ ′, λ ₂ ′, λ ₃ transmitted through the second repeater optical fiber 42. ′, Λ ₄ ′,... Λ _n ′ are demultiplexed so as to be transmitted through the input optical fibers 412 of the respective channels.

  The measurement device 30 </ b> A includes a photoelectric conversion unit (O / E) 31, a frequency / voltage conversion unit (F / V) 32, and a display device 33. The O / E 31 includes a photodiode or the like, and converts detection light incident on the measurement device 30A via the input optical fiber 412 into an electrical signal. The output signal of the O / E 31 includes a Doppler signal having frequency modulation information. F / V 32 is an element that converts frequency modulation information into a voltage value and generates a demodulated signal. The display device 33 is a device that generates a sound wave detection signal based on the demodulated signal output from the F / V 32 and displays the image.

  The controller 102 controls the operation of various devices of the logging apparatus 100 in addition to the WDM light source 10 and the measurement apparatus 30A. The CPU 101 operates the controller 102 in a predetermined sequence according to a program stored in advance. When an operation signal is given from the user, the CPU 101 activates the controller 102, and the controller 102 operates the WDM light source 10, the measuring device 30A, and peripheral devices based on the sequence to execute the sound wave logging operation.

  Next, the operation of the optical fiber type acoustic logging system D will be described with reference to FIG. FIG. 8 is a block diagram for explaining sound wave detection by the FOD sensor method. Here, one channel of the FOD sensor unit S is extracted to schematically represent the system configuration, and the frequency modulation amount of the detected light accompanying the arrival of the sound wave at the FOD sensor unit S is detected by heterodyne interferometry. Indicates the system.

Laser light (detection light) having a frequency f ₀ emitted from the WDM light source 10 is transmitted by the first half mirror 11 to the FOD sensor unit S of the sonic module 20A through the first relay optical fiber 41 and to the AOM 13. And demultiplexed. Assuming that the path length of the optical fiber in the FOD sensor unit S is L, frequency modulation f _d proportional to the time change dL / dt of the path length L caused by the sound wave vibration is generated in the detection light passing through the FOD sensor unit S. Therefore, the frequency of the detection light transmitted through the second repeater optical fiber 42 through the FOD sensor unit S in a state in which sound wave vibration is applied is f ₀ −f _d .

On the other hand, the reference light (80 MHz) having the frequency f _M is superimposed on the detection light traveling toward the AOM 13 and modulated to f ₀ + f _M. The modulated light of f ₀ + f _{M and} the modulated light of f ₀ -f _d passing through the FOD sensor unit S are merged by the second half mirror 12 and f _M + f in which the frequency difference between the two is manifested. The modulated light _d is detected. The modulated light f _M + f _d is photoelectrically converted by the O / E 31 and converted into a Doppler signal. The Doppler signal is converted into a voltage signal (demodulated signal) corresponding to the frequency modulation amount by the F / V 32, and the waveform of the demodulated signal is displayed on the display device 33.

  Based on the principle as described above, the arrival of sound waves to each of the FOD sensor units S1, S2, S3, S4,... Sn of the sonic module 20A is detected. In the measuring device 30A, the arrival time of the sound wave to each FOD sensor unit S1, S2, S3, S4... Sn is specified. And the arrival time difference between FOD sensor part S1, S2, S3, S4 ... Sn is handled as the sound wave propagation time of the surrounding stratum between sensors, and the constituent material of the surrounding stratum is estimated based on the sound wave propagation time.

  Subsequently, as another embodiment, an optical fiber acoustic wave logging system D1 using the FBG method will be described. FIG. 9 is a block diagram showing the configuration of the optical fiber acoustic logging system S1. The system D1 includes the WDM light source 10 described above, the sonic module 20C including the FBG optical fiber sensor unit, the measuring device 30B, the third relay optical fiber 44, the fifth optical multiplexer / demultiplexer 26, and the sixth optical multiplexer / demultiplexer. 27, a seventh optical multiplexer / demultiplexer 28, a circulator 14 and a branch optical fiber 45.

  The sonic module 20C includes a plurality of FBG sensor units S21, S22, S23, S24,... S2n arranged in parallel as optical fiber sensor units. In the FBG sensor, a Bragg reflector (diffraction grating) whose refractive index is periodically changed is formed in the longitudinal direction of the optical fiber core, and reflects light having a wavelength (Bragg wavelength) corresponding to the pitch between the gratings. When an external force such as strain is applied to the formation part of the Bragg reflection part of the optical fiber, the wavelength of the reflected light reflected by the Bragg reflection part changes as the interstitial pitch changes. This wavelength change is called a Bragg wavelength shift, and the shift amount is proportional to the magnitude of the applied distortion.

Each of the FBG sensor units S21, S22, S23, S24,... S2n has one Bragg reflector, and the detection lights λ ₁₁ , λ ₁₂ , λ ₁₃ , λ _{14 ,.} . Each Bragg reflector has an interstitial pitch with the detection light of these wavelengths as the Bragg wavelength. Detection light λ ₁₁ , λ ₁₂ , λ ₁₃ , λ ₁₄ ,... Λ _1n is reflected by each Bragg reflector, and reflected light λ ₁₁ ′, λ ₁₂ ′, λ ₁₃ ′, λ ₁₄ ′,. • λ _1n ′ is generated. When distortion accompanying the arrival of sound waves is applied to the FBG sensor units S21, S22, S23, S24... S2n, the pitch between lattices changes according to the magnitude of the sound waves, and the reflected light λ ₁₁ ′, λ ₁₂ ′, The center wavelengths of λ ₁₃ ′, λ ₁₄ ′,... λ _1n ′ are shifted by the Bragg wavelength. On the other hand, when no distortion is given, the light with the initial Bragg wavelength becomes reflected light.

As a modified embodiment, each FBG sensor unit S21, S22, S23, S24... S2n may have two or more Bragg reflectors. For example FBG sensor section S21 is in the longitudinal direction of the sensor unit for optical fiber, at a predetermined interval, may be provided with a plurality of Bragg reflection portions corresponding to the detected light lambda _11.

  As shown in FIG. 10, the sonic module 20C includes a cylindrical holding member 21C similar to the one illustrated in FIG. Optical fibers 461, 462, 463, 464,... 46n each having FBG sensor portions S21, S22, S23, S24... S2n formed thereon are vertically attached to the outer peripheral surface of the holding member 21C. Each FBG sensor part S21, S22, S23, S24... S2n is arranged at a predetermined interval in the extending direction of the boring hole H. This holding member 21C is also fitted on the casing pipe Ca, and is fixed by the cement layer Ce as shown in FIG.

Similarly to the first optical multiplexer / demultiplexer 22, the fifth, sixth, and seventh optical multiplexer / demultiplexers 26, 27, and 28 are optical multiplexers / demultiplexers using AWG. The fifth optical multiplexer / demultiplexer 26 is interposed in a connection portion between the output optical fiber 414 connected to the output end of the WDM light source 10 and the third relay optical fiber 44, and detects light λ of each channel generated by the WDM light source 10. ₁₁ , λ ₁₂ , λ ₁₃ , λ ₁₄ ,... Λ _1n are combined and transmitted to the third repeater optical fiber 44. The sixth optical multiplexer / demultiplexer 27 is interposed in the connection between the third relay optical fiber 44 and the FBG sensor units S21, S22, S23, S24... S2n, and is transmitted through the third relay optical fiber 44. The detection light is demultiplexed so that one detection light is transmitted to each of the FBG sensor units S21, S22, S23, S24... S2n. The seventh optical multiplexer / demultiplexer 28 is interposed in the connection portion between the branch optical fiber 45 and the input optical fiber 415 connected to the input end of the measuring device 30B, and each reflected light λ ₁₁ ′ transmitted through the branch optical fiber 45. , Λ ₁₂ ′, λ ₁₃ ′, λ ₁₄ ′,... Λ _1n ′ are demultiplexed so as to be transmitted through the input optical fibers 415 of the respective channels.

  The circulator 14 is an irreversible optical component in which incident light and outgoing light have a cyclic relationship with their terminal numbers. That is, the light incident on the first terminal is emitted from the second terminal while not emitted from the third terminal, and the light incident on the second terminal is emitted from the third terminal while the first terminal. The light incident on the third terminal is not emitted from the first terminal, but is emitted from the first terminal, but not from the second terminal. A third relay optical fiber 44 extending from the fifth optical multiplexer / demultiplexer 26 is provided at the first terminal of the circulator 14, and a third relay optical fiber 44 extending toward the sixth optical multiplexer / demultiplexer 27 is provided at the second terminal. Branch optical fibers 45 are connected to the three terminals, respectively. Accordingly, the inspection light generated by the WDM light source 10 is directed to the sonic module 20B through the third relay optical fiber 44, and the reflected light is not directed to the WDM light source 10, but the seventh optical multiplexer / demultiplexer 28 (measurement device 30B). ).

  The measurement device 30B includes a photoelectric conversion unit (O / E) 34, a band pass filter (BPF) 35, and a display device 36. The O / E 34 includes a photodiode or the like, and converts the reflected light incident on the measuring device 30B via the input optical fiber 415 into an electrical signal. The BPF 35 is a filter circuit that extracts a signal around the Bragg wavelength. The display device 33 is a device that generates a graph indicating the wavelength-light intensity characteristics based on the electrical signal output from the BPF 35 and displays the graph.

  Next, the operation of the optical fiber acoustic wave logging system D1 will be described with reference to FIG. FIG. 11 is a block diagram for explaining sound wave detection by the FBG sensor method. Here, a system configuration is schematically shown by extracting one channel of the FBG sensor unit SB, and shows a system that detects a Bragg wavelength shift of reflected light accompanying a sound wave arriving at the FBG sensor unit SB.

Laser light (detection light) having a wavelength λ emitted from the WDM light source 10 passes through the circulator 14 to the FBG sensor unit SB of the sonic module 20C through the third relay optical fiber 44. The detection light is reflected by the FBG sensor unit SB, and reflected light having a Bragg wavelength λ _B is transmitted through the third relay optical fiber 44. The reflected light enters the branch optical fiber 45 through the circulator 14, is received by the O / E 34, and is photoelectrically converted. Thereafter, the waveform of the reflected light having the wavelength λ _B is displayed on the display device 36 through the BPF 35.

Here, when the distortion caused by the sound wave vibration is given to the FBG sensor unit SB, the center wavelength of the reflected light is shifted by the Bragg wavelength as described above. That is, the wavelength λ _{B of the} reflected light observed on the display device 36 is shifted by Δλ _{B and} the reflected light having the wavelength λ _B ′ is observed. Accordingly, it is possible to know the arrival of the sound wave vibration to the FBG sensor unit SB.

  Based on the principle as described above, the arrival of sound waves to each of the FBG sensor units S21, S22, S23, S24... S2n of the sonic module 20C is detected. In the measuring device 30B, the arrival time of the sound wave to each FBG sensor unit S21, S22, S23, S24... S2n is specified. And the arrival time difference between FBG sensor part S21, S22, S23, S24 ... S2n is handled as the sound wave propagation time of the surrounding stratum between sensors, and the constituent material of a surrounding stratum is estimated based on the said sound wave propagation time.

  FIG. 12 is a schematic diagram for explaining acoustic logging by the sonic modules 20A, 20B, or 20C. It is assumed that the sound source device 50 is disposed at the bottom of the boring hole H, and the optical fiber sensor portions S1 to S7 of the sonic module are disposed at an equal pitch along the extending direction of the boring hole H. When an ultrasonic pulse is emitted from the sound source device 50, the ultrasonic pulse is incident on the peripheral wall surface of the borehole H at a critical angle of propagation of the acoustic wave, and propagates along the surrounding stratum of the borehole H. And the vibration based on an ultrasonic pulse is sequentially detected over time in order of the sensor units S7, S6, S5.

  In general, the propagation speed of sound waves is high in solid rock formations, and the propagation speed of sound waves is slow in porous rock formations (layers with high porosity) that contain crude oil. For example, as shown in FIG. 12, it is assumed that an oil layer exists in the surrounding formation of the sensor unit S3 and the other formation is a formation with a low porosity. In this case, ultrasonic pulses propagate at a relatively high speed to the sensor units S7, S6, S5, and S4. However, between the sensor units S4 and S3 and between S3 and S2, the propagation speed of the ultrasonic pulse is reduced due to the presence of the oil layer, so that the arrival of the ultrasonic pulse at the sensor units S3 and S2 is delayed. On the other hand, since there is no oil layer between the sensor parts S2 and S1, ultrasonic pulses propagate at a relatively high speed.

  Since the ultrasonic pulse propagates through the formation around the borehole H with the behavior as described above, the existence of the oil layer can be found by analyzing the arrival time of the ultrasonic pulse to each sensor unit S7 to S1. it can. In addition, since the width in the depth direction of the oil layer is often about several meters to several tens of meters, the arrangement pitch of the optical fiber sensor parts S1 to S7 should be about several meters to several tens of meters according to this. desirable.

  Note that the use of the sound source device 50 may be omitted, and a microearthquake may be used as a sound wave propagating through the formation around the borehole H. A magnitude 2.0-2.9 class microearthquake occurs about 1.4 million times a year. In this way, logging can be performed using micro earthquakes that occur naturally at a high frequency. In this case, when the epicenter is deeper than the bottom of the borehole H, the propagation speed of the sonic vibration from the sensor unit S7 to the other sensor units S6 to S1 may be detected using the deepest sensor unit S7 as a reference sensor. According to this configuration, since the incorporation of the sound source device 40 into the system D can be omitted, the system D can be simplified.

  Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and for example, the following modified embodiments can be taken.

  (1) In the above embodiment, the mode in which the optical fiber constituting the optical fiber sensor unit is wound around the holding member 21 is illustrated. However, the use of the holding member 21 is omitted, and the optical fiber is wound directly on the casing pipe. You may make it attach. Further, although the cylindrical holding member 21 is illustrated, an arc-shaped or strip-shaped holding member 21 may be used.

  (2) In the above embodiment, an example in which the holding member 21 is disposed on the outer periphery of the casing pipe Ce has been described. Instead of this, the holding member 21 may be attached to the inner peripheral wall surface of the casing pipe Ce. Further, when the holding member 21 is formed of a member having high sound conductivity such as a steel material, a sound insulation portion such as a slit is provided between the optical fiber sensor portions to reduce the sound conductivity of the holding member 21 itself. It is desirable.

  (3) In the above embodiment, the sonic modules 20A and 20B using the FOD sensor and the sonic module 20C using the FBG sensor are exemplified. It is good also as a sonic module which used these FOD sensors and FBG sensors together. That is, an FOD sensor type optical fiber and an FBG sensor type optical fiber may be mounted on one holding member 21.

  (4) In the above embodiment, the example in which the optical fiber type acoustic logging systems D and D1 of the present invention are applied to the logging of the formation around the borehole H drilled for the oil well test drilling is shown. The object to be detected is not limited to this. Logging of the surrounding stratum of the borehole H drilled for purposes other than oil field development, logging of surface and deep sea surface layers, or nondestructive detection of structures other than the stratum The systems D and D1 of the present invention can also be applied to layers and the like.

  (5) In the said embodiment, the cement layer was illustrated as a fixing means to adhere a sonic module to a detection target. This is an example, and for example, a mode in which a sonic module is welded to a detection target with a molten resin, or a sonic module is pressed against the detection target by applying a mechanical pressing force may be used.

D, D1 Optical fiber type acoustic logging system (soil logging structure)
H Boring hole (drilling hole)
S1, S2, S3, S4 ... Sn, S11, S12, S13, S14 ... S1n FOD sensor unit (optical fiber sensor unit)
S21, S22, S23, S24 ... S2n FBG sensor part (optical fiber sensor part)
Ca casing pipe Ce cement layer (fixing means)
10 WDM light source 20, 20A, 20B, 20C Sonic module 22, 23 First optical multiplexer / demultiplexer and second optical multiplexer / demultiplexer (optical multiplexing / demultiplexing means)
30, 30A, 30B Measuring device (measuring means)
40 repeater optical fiber 41 first repeater optical fiber 42 second repeater optical fiber 50 sound source device

Claims (10)

A WDM light source that generates a plurality of detection lights having different wavelengths;
A sonic module having a plurality of optical fiber sensor parts for detecting sound waves, wherein the plurality of detection lights are individually incident;
Measuring means for detecting the plurality of detection lights via the optical fiber sensor unit;
A relay optical fiber that transmits the plurality of detection lights between the WDM light source and the measurement unit, and the optical fiber sensor unit;
One of a plurality of detection lights that are interposed in the connecting portion between the relay optical fiber and the optical fiber sensor unit and transmitted through the relay optical fiber form a transmission state assigned to each optical fiber sensor unit. Optical multiplexing / demultiplexing means to perform,
Fixing means for fixing the sonic module to a detection object capable of propagating sound waves;
An optical fiber acoustic wave logging system comprising:   The optical fiber acoustic logging system according to claim 1, further comprising a sound source device that generates a sound wave that propagates the detection target. The detection object is a formation,
2. The optical fiber acoustic wave logging system according to claim 1, wherein a microearthquake is utilized as a sound wave propagating through the formation. The optical fiber sensor unit is composed of an optical fiber vibration sensor using the Doppler effect,
The relay optical fiber includes a first relay optical fiber that transmits the detection light from the WDM light source to the optical fiber sensor unit, and a second relay optical fiber that transmits the detection light from the optical fiber sensor unit to the measurement unit. Including
The optical fiber acoustic wave logging system according to any one of claims 1 to 3, wherein the measuring means detects frequency modulation of the detection light that has passed through the optical fiber vibration sensor. The optical fiber sensor unit is composed of a fiber Bragg grating,
The relay optical fiber includes a third relay optical fiber that transmits the detection light from the WDM light source to the optical fiber sensor unit,
The optical fiber acoustic wave logging system according to any one of claims 1 to 3, wherein the measuring unit detects a Bragg wavelength shift of reflected light of the detection light reflected by the fiber Bragg grating.   The optical fiber type acoustic logging system according to claim 1, wherein the sonic module includes a holding member that holds the plurality of optical fiber sensor units in a state of being separated from each other.   The optical fiber acoustic wave logging system according to claim 6, wherein the holding member is made of an elastic member having a lower sound transmission property than the detection object.   The optical fiber acoustic logging system according to any one of claims 1 to 7, wherein the detection object is a formation, and the fixing means is cement. A casing pipe inserted into a drilling hole drilled into the soil;
The optical fiber type acoustic logging system according to any one of claims 1 to 7, which logs the formation around the excavation hole,
A soil logging structure characterized in that the sonic module is attached to a predetermined position of the casing pipe. There is a gap between the peripheral wall of the excavation hole and the outer peripheral surface of the casing pipe,
The sonic module is attached to the outer periphery of the casing pipe,
The soil logging structure according to claim 9, wherein the fixing means is cement filling the gap.

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