WO2013098321A2

WO2013098321A2 - Smart hydrocarbon fluid production method and system

Info

Publication number: WO2013098321A2
Application number: PCT/EP2012/076943
Authority: WO
Inventors: Johannis Josephus Den Boer; Andre Franzen; Lex A. GROEN; Daniel Joinson; Paul Gerard Edmond LUMENS
Original assignee: Shell Internationale Research Maatschappij B.V.; Shell Oil Company
Priority date: 2011-12-30
Filing date: 2012-12-27
Publication date: 2013-07-04
Also published as: GB2510775A; WO2013098321A3; AU2012360911A1; GB201409415D0

Abstract

A smart hydrocarbon fluid production method and system monitor seismic and other acoustic events using a bow spring assembly (40,41) that converts broadside acoustic waves (49) travelling in a non-axial direction relative to a longitudinal axis of an elongate fiber optical sensor (43) into substantially longitudinal vibrations (46A, 46B) and associated microstrain variations in the fiber optical sensor (43) which can be monitored more accurately than broadside vibrations by a Distributed Acoustic Sensing (DAS) interrogation assembly connected to the fiber optical sensor (43).

Description

SMART HYDROCARBON FLUID PRODUCTION METHOD AND SYSTEM

BACKGROUND OF THE INVENTION

The invention relates to a smart hydrocarbon fluid production method and system wherein seismic and/or production data from seismic and other acoustic events generated during exploration and/or production of hydrocarbons from underground hydrocarbon bearing formations are collected and interpreted.

US patent application US2004/237648, UK patent application GB 2459975, US patent 7134219, European patent EP 1816432, International patent application WO00/33046, US patent application US2002/154860, US patent 7,068,869, Japanese patent application

JP2005091151, US patent applications US 2002/196995 and 2005/050962 and International patent applications

WO2010/136723 and WO2010/136724 disclose known sensing methods using fiber optical sensors that are provided with bowspring signal conversion assemblies adjacent to Fiber Bragg Gratings (FBGs) and/or Fabry Perot

interferometers, which are point sensors and are not configured to measure physical effects along a

substantial part of the length of the fiber.

Fiber optical acoustic sensing assemblies that provide information about acoustic events along at least a substantial part of the length of an optical fiber based on the Rayleigh backscattering effect are known as Distributed Acoustic Sensing (DAS) assemblies.

The Rayleigh backscattering effect uses Rayleigh backscatter of optical light pulses to measure micro- strain variations along the length of the optical fiber caused by local acoustic and/or thermal noise.

None of the prior art references cited above discloses that broadside acoustic signals can be converted into longitudinal vibrations in a DAS assembly. The prior art references cited above therefore express a prejudice that bow spring signal converters can only be used in conjunction with point sensors provided by FBGs and Fabry Perot interferometers and not with DAS

assemblies that measure acoustic phenomena along at least a substantial part of the length of an elongate optical fiber .

Currently available fiber optical sensors are more sensitive to acoustic signals travelling in a

substantially longitudinal direction relative to a longitudinal axis of the fiber optical sensor than to acoustic signals travelling in a substantially

transversal, known as broadside, direction relative to said longitudinal axis.

International patent application WO2011076850 discloses a (possibly) looped DAS assembly used in a well to monitor acoustic events associated with seismic exploration activities and/or production of hydrocarbons from an underground formation.

US patent 5, 877, 426 discloses a Bourdon tube pressure sensor . The Bourdon tube is connected to at least one optical strain sensor mounted to be strained by movement of the Bourdon tube such that when the Bourdon tube is exposed to the pressure of the system, movement of the tube in response to system pressure causes a strain in the optical sensor .

US patent 6,549,488 discloses a fiber-optic

hydrophone having a compliant sensing mandrel around which an optical fiber is wound, so that the optical fiber is cyclically stretched if the sensing mandrel is deformed as a result of acoustic vibrations.

A disadvantage of the hydrophone known from US patent 6,549,488 is that the compliant sensing mandrel comprises a relatively large cylindrical elastomeric body which is difficult to install in a well.

There is a need to improve the transduction of transverse accelerations generated by acoustic waves and other signals travelling in a substantially transversal, broadside, direction into axial strains in fiber optical DAS and other sensing cables, which may be used for the measurement of acoustic and/or other signals in rock or seismic waves or other sources which would otherwise cause the energy to arrive at the optical fiber

travelling in a direction which could be characterised wholly, or predominantly, transverse to the longitudinal axis of the optical fiber or fiber assembly.

Furthermore there is a need for an improved smart hydrocarbon fluid production method and system wherein broadside acoustic signals are converted into

longitudinal vibrations in a fiber optical sensor that is interrogated by a Distributed Acoustic Sensing (DAS) interrogation assembly.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided a smart hydrocarbon fluid production method, wherein:

- seismic and/or production data from seismic and other acoustic events generated during exploration and/or production of hydrocarbons from underground hydrocarbon bearing formations are collected and enhanced using a bow spring signal conversion assembly for converting an broadside acoustic signal into a substantially

longitudinal vibration in a fiber optical sensor;

- the bowspring signal conversion assembly comprises at least one bowspring blade, which is configured to deform in response to the broadside signal and is connected to the fiber optical sensor such that the deformed bowspring blade deforms the fiber optical sensor in a substantially longitudinal direction relative to a longitudinal axis of the fiber optical sensor; and

- the fiber optical sensor does not comprise Fiber Bragg Gratings (FBGs) and/or a Fabry-Perot interferometer strain sensor in the vicinity of the bow spring signal

conversion assembly and is coupled to a DAS interrogator assembly that measures Rayleigh backscattering to monitor microstrain variations generated by vibrations in the fiber optical sensor.

The bowspring assembly may comprise a first and a second sleeve, which sleeves are interconnected by a plurality of curved bowspring blades which maintain the fiber optical sensor in a substantially co-axial position relative to a longitudinal axis of a tubular confinement. The first and second sleeves may be rigidly connected to the fiber optical sensor or alternatively the first sleeve may be rigidly secured to the fiber optical sensor while the second sleeve may be slideably secured to the fiber optical sensor.

The bowspring assembly may be connected to a mass formed by an elongate central member which is maintained substantially parallel to the fiber optical sensor within the tubular confinement by the bowspring assembly that allows the mass to vibrate within the tubular confinement in a substantially orthogonal direction relative to a longitudinal axis of the tubular confinement in response to the broadside acoustic signal travelling in a non- parallel direction relative to the longitudinal axes of the Sensor and the tubular confinement.

A pair of bowspring assemblies may be arranged at longitudinally spaced locations within the tubular confinement such that the bowspring assemblies have a pair of mutually nearby first sleeves and a pair of mutually remote second sleeves, wherein the first sleeves are rigidly secured to the mass and the second sleeves are slideably secured around the mass and rigidly secured to the fiber optical sensor.

In accordance with the invention there is further provided a smart hydrocarbon fluid production system, wherein :

- seismic and/or production data from seismic and other acoustic events generated during exploration and/or production of hydrocarbons from underground hydrocarbon bearing formations are collected and enhanced using a bow spring signal conversion assembly for converting an acoustic broadside signal into a substantially

longitudinal vibration in a fiber optical sensor;

The bowspring assembly may comprise a first and a second sleeve, which sleeves are interconnected by a plurality of curved bowspring blades which maintain the fiber optical sensor in a substantially co-axial position relative to a longitudinal axis of a tubular confinement within an underground wellbore. When used in this specification and accompanying claims the term "broadside acoustic signals" refers to acoustic signals, including pressure and shear waves, travelling at any angle different from zero relative to the longitudinal axis of a fiber optical sensor and result in radial strain on the fiber optical sensor.

When used in this specification and accompanying claims the term fiber optical sensor refers to an

elongate optical fiber and not to the arrangement of the optical fiber within and including a protective tubing and/or set of protective tubings, known as Fiber In Metal Tube (FIMT) .

These and other features, embodiments and

advantages of the method and/or system according to the invention are described in the accompanying claims, abstract and the following detailed description of non- limiting embodiments depicted in the accompanying

drawings, in which description reference numerals are used which refer to corresponding reference numerals that are depicted in the drawings.

Similar reference numerals in different figures denote the same or similar objects.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic diagram of an inertial acoustic sensor;

Figure 2 shows inertial acoustic sensor transfer

functions, for several values of a relative damping coefficient b as a function of normalized frequency ω/ω_η; Figure 3 shows a first embodiment of the bowspring assembly according to the invention;

Figure 4 shows how the bowspring assembly induces axial movement of one of the sliding sleeves shown in Figure 3; Figures 5A and 5B show a second embodiment of the

bowspring assembly according to the invention;

Figure 6 shows a third embodiment of the bowspring assembly according to the invention;

Figures 7A and B show a fourth embodiment of the

bowspring assembly according to the invention;

Figures 8A and B show a fifth embodiment of the bowspring assembly according to the invention;

Figures 9A and B show a sixth embodiment of the bowspring assembly according to the invention;

Figure 10 shows a seventh embodiment of the bowspring assembly according to the invention;

Figure 11 shows an eighth embodiment of the bowspring assembly according to the invention;

Figure 12 shows a ninth embodiment of the bowspring assembly according to the invention; and

Figure 13 shows a tenth embodiment of the bowspring assembly according to the invention. DETAILED DESCRIPTION OF THE DEPICTED EMBODIMENTS

Currently available seismic transducers operate on the principle of measuring the ground motion relative to that of an inertial mass.

A schematic realisation of such a design is

displayed in Figure 1. The mass m is suspended by a spring with spring constant k and a damper with damping coefficient c. In most acoustic sensors, the movement of the mass m is measured. Since this measurement is done in the sensor's frame of reference, the measured quantity relates to the displacement x(t) of the mass relative to the ground and case. The goal is to measure the ground displacement u (t) . The resultant configuration is a variation of the classical mass/spring/damper problem that will be described with reference to Figure 1. Figure 1 is a schematic diagram of an inertial sensor, showing the mass m free to move uni-directionally within the case under the influence of a spring and damper.

Applying Newton' s second law to the mass results in the following force balance: d²u d² dx

kx C "

\ dt^{2 +} dt² , dt

, which can be transformed into a frequency-dependent transfer function by applying the Laplace transform:

with x(s) and u(s) being the Laplace transform of x(t) and u (t) respectively, as a function of complex frequency variable s. Two characteristic parameters have been introduced here as well. Firstly, a natural frequency <¾:

which determines the resonance of the inertial system. Secondly, a relative damping factor b: c

The effect of damping can be observed in Figure 2, where normalized transfer functions for a range of values of b are plotted. Lightly damped sensors (b « 1) have a - possibly problematic - exaggerated response at <¾, whereas a values of b = 0.7 gives the flattest frequency

response .

For an accelerometer it is observed that when s « <¾, the relative motion of mass and case is very small and proportional to s². This represents a double

differentiation in the time domain, so the displacement of the mass relative to the case is proportional to ground acceleration. In physical terms, the motion of the mass and case are almost identical and the extension of the spring is a measure of the force necessary to

accelerate the mass. The accelerometer operates on this principle .

For a seismometer it is observed that when s » <¾, the transfer function is approximately -1, i.e. the mass does not move with respect to an inertial frame of reference and the relative motion of the case and the mass perfectly mirrors the ground motion. This is the classical seismometer mode of operation.

For a geophone it is observed that a geophone is a combination of a seismometer and a velocity transducer. The velocity transducer is typically realised by

attaching a coil to the moving mass, and applying a magnetic field at right angles to the coil motion. This induces a current in the coil, which is proportional to the velocity of the coil. Damping is determined by the electrical load resistance of the coil circuit.

Figure 2 shows inertial sensor transfer functions, for several values of the relative damping coefficient b as a function of normalized frequency ω/ω_η· The complex function is illustrated by separate graphs for amplitude (top) and phase (bottom) response. On the amplitude response graph, the upper curve shows the strong

amplification at ω/ω_η.

Current solutions are based on point sensors interconnected with wires. These designs can be

considered as digitised systems which do not provide a full image or measurement of the situation at hand.

Distributed sensors achieve array type performance in a continuous way and are therefore more like analogue systems which describe a measurement fully and

continuously. If designed correctly (and sometimes corrections are required to compensate for other effects) then a distributed measurement system is capable of fully describing the state of the measurand, or in other words, what is measured.

In order to make elongate fiber-optic sensors more sensitive to acoustic signals impinging perpendicular to the elongate sensor, one option is to design the sensor assembly such that an acceleration perpendicular to the elongate sensor is converted into longitudinal strain along the fiber. Current concepts exploiting inertial members to induce strain on a fiber, essentially deploy a fiber between the moving mass and the case.

Instead of using the fiber itself as a spring, bowsprings can be used to suspend a central member. Due to external movement or strain on the fiber, one or more bowsprings will see a broadside (transverse) strain, resulting in a change in the distance between the legs of the bowspring. A fiber coupled to two or more legs of bowsprings, will therefore be subjected to an axial strain .

Figure 3 depicts a symmetric bowspring sensor consisting of two sets of two bowspring assemblies 40 and 41. Each bowspring assembly comprises a pair of curved bowspring blades 40A,B and 41A,B that are at one end thereof connected to a first sleeve 40C,41C that is rigidly secured to an elongate central member 42 and at another end to a second sleeve 40D,41D that is slidingly secured around the elongate central member and is rigidly secured to a fiber optical Sensor 43 which is covered by a protective coating 44 that is bonded to the first and second sleeves 40D,41D.

Figure 4 shows that compression of either bowspring assembly 40, 41 due to broadside vibration 45 resulting from broadside acoustic waves 49 initiates vibration of the central member 42 relative to the tubular inner wall 48 of a surrounding enclosure leads to longitudinal vibration 46A, 46B of the sliding sleeves 40D and 41D, which induces axial strain 47 on the section of the fiber optical sensor 43 between the sliding sleeves 40D and 41D, since the sliding sleeves 40D and 41D are induced by the bowspring assemblies 40,41 to move in opposite longitudinal directions relative to each other in

response to broadside vibration of the central member 42 relative to the tubular inner wall 48 of the enclosure.

Figures 5A and 5B show a balanced bowspring

assembly with two pairs of bowspring blades 50A,B and 51A,B that are at a first end thereof fixedly secured to an elongate central member 52 and at a second end thereof fixedly secured to a sliding sleeve 53A,B which is slidingly arranged around the elongate central member 52. A fiber optical Sensor 54 is rigidly secured, for example by bonding or strapping, to the sliding sleeves, such that if the central member 52 vibrates laterally relative to a tubular inner wall of a surrounding enclosure 55, as illustrated by arrow 56, this lateral vibration of the central member 52 is converted in a longitudinal

vibration of the sleeves illustrated by arrows 58 and of the section 57 of the fiber optical Sensor between the sleeves 53A and 53B.

While the symmetric bowspring assembly shown in Figures 3 and 4 is sensitive to broadside strain or pressure, the balanced bowspring assembly shown in Figures 5A and 5B is only sensitive to broadside movement of the central member 52 relative to the tubular inner wall of the surrounding enclosure 55. Like in a geophone or

accelerometer, the central member 52 shown in Figures 5A and 5B will move out of phase with the tubular inner wall of the enclosure 55 in large parts of the frequency spectrum. This will cause the sliding sleeves 53A and 53B to move and vibrate in opposite longitudinal directions relative to each other as illustrated by arrow 58, inducing an axial strain on section 52 of the fiber optical Sensor 54 between the sliding sleeves 53A and 53B.

Figure 6 shows a unipolar bowspring assembly.

The unipolar bowspring assembly shown in Figure 6 is very similar to the balanced bowspring assembly shown in

Figures 5A and 5B, but here the bowspring blades 61 and 62 are each at one end 65, 66 thereof rigidly secured to the central member 63 and at another end thereof to separate sliding sleeves 67 and 68. Only one sleeve 67 is bonded to the fiber optical DAS fiber 69. In this way, only one sleeve 67 will create strain on the fiber 69, while the other sleeve 68 one only provides a reaction force to maintain an effective spring stiffness of the unipolar bowspring assembly. This unipolar design works for relative movement of the central member 63 with respect to a surrounding enclosure (not shown) , but also for compressional strain on the bowspring blades 61,62. The key advantage of this unipolar design is that only one half of the spring pair needs to be a bow spring i.e. the side 62 coupled to the fiber 69. The other side 61 can be coiled springs and can also include damping

(ideally with a factor of 0.707 to match standard

geophone response) . The unipolar bowspring assembly 61,62 shown in Figure 6 may be gravity confined (in a substantially horizontal direction) .

Where the unipolar bowspring assembly 61,62 is to be deployed horizontally at surface or downhole and where the orientation can be determined and controlled, only one spring train is required, with gravity holding the assembly down. Obviously other consideration (stability, balance) must be considered. For increased stability, two springs could be used to ensure the assembly remains standing in the correct orientation.

Figures 7A and 7B depict longitudinal and cross- sectional views of a unipolar bowspring assembly 70 provided with a pair of coil resistor springs 71 and 72. One side 73 of the unipolar bowspring assembly 70 is rigidly secured to a central rod 74 and another side is rigidly secured to a sliding sleeve, which is slidably arranged around the rod 74 and which is bonded to the fiber optical Sensor 76.

Where gravity is insufficient to maintain contact with the tubular inner wall of the surrounding enclosure 77 or the ground, then the bowspring blade assembly 77 could be bonded with glue 78 or other means to the enclosure 77. This may however reduce the linearity of the system and it may be beneficial to include additional springs 71,72 to ensure that the transducer spring 70 (the bow spring coupled to the fiber optical sensor 76) always remains in a state of pre-tension or compression and in a linear region of its mechanical response.

Multiple springs 71,72 could be used to ensure the stability of the system in this mode of operation.

To assure high signal quality, resonance systems are not preferred. Instead, flat response curves over larger bandwidths are required. Considering Figure 2, this can optimally be realised by a geophone/ seismometer

configuration: a low natural frequency in combination with an optimized damping coefficient. This would ideally lead to a flat frequency response of -1 at frequencies above the natural frequency. To achieve this, some way of damping has to be added to any realisation.

Damping can be achieved in several ways with differing levels of complexity and performance. A mechanical damping solution based on material properties over-molded on the springs or molded into the inside of the spring may offer a simple approach. More refinement may be achieved using dash-pot style dampers, although the thermal stability and performance of the damping fluid may be a constraint.

Figures 8A and 8B show that an alternative would be to use in addition to the spring 85 a moving magnet 80 with a coil 81 (much like the geophone described earlier) with the coil connected to a suitable load resistor 82. With the coil and magnet connected to the free mass provided by the central member 83 and the reference location provided by the tubular inner wall of the enclosure 84 respectively (i.e. one moving one not) then differential movement of the central member 83 relative to the

enclosure 84 will generate an Electro Magnetic Field (EMF) in the coil 81, the load resistor 82 allows a current to flow and electrical energy absorbed in the resistor 82 causes real damping of the movement of the free mass provided by the central member 83. This

arrangement would not require any external electrical connections or power and would work in a manner

indistinguishable from an ideal damper within certain frequency range limitations.

Apart from optimising the signal response, it is also important to consider manufacturability and robustness. Handling of fibers imposes limits on the manufacturing process. Robustness is essential for reliable use of fiber-optic cables down hole, for which the stress on the fiber due to temperature changes, bending and shock has to be minimized.

An advantage of the bowspring concept according to the invention is the possibility to tune spring stiffness and mass of the mechanical system separately. The

stiffness is a characteristic of the bowspring, while the mass is mainly determined by the central member.

In tested embodiments of the bowspring assembly according to the invention, the fiber is separated from the central member. In that way it can be used to measure

differential strain between two sets of bowsprings . This could lead to maximized strain readings, but also

requires a more homogeneous strain and pre-tension state between the two sets of bowsprings.

The fiber can also be integrated in the central member and in that way measure a strain induced directly on the central member. Since the central member is now both anchoring and sensing element of the assembly, it only can measure strain between the legs of one set of bowsprings rather than differential strain between two separated sets of bowsprings.

Advantages are the simplification in design due to a reduction in components, while the maximum achievable signal might be lower.

The bowspring acoustic signal conversion concept according to the invention can be realised on different length scales, from cable level to well completion level.

Figures 9A and B illustrates that on completion level, the central member could be a tubing string 90, the bowspring assemblies 91 realised by centralizer blades connected to the tubing string 90, and strained within the surrounding casing 92 which is secured within an underground wellbore 93 by cement 94. The fiber optical sensor 95 could be packaged in a standard

downhole cable assembly and strained between two

centralizer sleeves 96, 97, of which one sleeve 96 is rigidly secured to the tubing 90 and one sleeve 97 is slidingly secured around the tubing 90. The sleeves 96, 97 are interconnected by a number of bowspring blades 98 that centralize the tubing 90 within the casing 92.

Shaking or compressing of the casing 92 as illustrated by arrow 98 would then via compression of the bowspring centralizer blades 98s lead to an increase in axial strain on the fiber optical sensor 95.

On cable level, the bowspring acoustic signal conversion concept according to the invention can be miniaturized to fit within a standard downhole control line (often ¼"(~5 mm) tubular) .

Figure 10 illustrates a specific bow spring assembly realisations that could involve only minor adaptations to commercially available fiber optical sensor assembly 100, known as Fiber In Metal Tube (FIMT) by replacing the buffer between protective inner and outer metal tubes 101 and 102 with (periodic) bowspring assemblies 103. In that way, the bowspring assemblies 103 directly exert a strain on the inner tube 101 and on the fiber optical sensor assembly 100 that is sensitive to axial strain and that is secured within the inner

protective tube 101 by means of a gel.

For geophysical measurements, the ability to distinguish from which direction signals impede is of high importance.

Figures 11, 12 and 13 illustrate that this can be realised by spanning bowspring assemblies 110, 111, 120 and 130 only in one specific plane that intersects a longitudinal axis of the fiber optical Sensor 112,122.

In Figures 11 and 12 this specific plane is the plane of the drawing and in Figure 13 this specific plane is a horizontal plane that intersects with a horizontal mid section of the surrounding tubular 133. Measurements in multiple directions can be realized by packing sensors for perpendicular directions together, for example by combining multiple fiber optical sensors 112,122, 132 with differently aligned bowsprings (not shown) .

Essentially, bowspring assemblies may be considered as point signal converters, but periodic repetition along the well or fiber length converts the associated fiber acoustical sensors 112, 122, and 132 into distributed sensors. Measures have to be taken to prevent the induced strain to cancel out. If the optical fiber is perfectly straight and homogeneous, compression induced on the fiber by a bowspring assembly leads to equal amounts of elongation besides that bowspring assembly. This can be mitigated either by geometrical measures (for example creating overstuff in the fiber between bowspring

assemblies, which would lead to bending instead of axial straining) or changes in stiffness (for example a stiffer part between bowspring assemblies, such that the strain there is lower) .

Various options for connecting bowspring assemblies to fiber optical Sensors are summarized below:

- The simple linkages and springs can act as

transducers to convert transverse acceleration into axial strain in an optical fiber assembly in a DAS system where the fiber is sensitive only to axial strains (and pressure effects to a lesser extent) The arrangement may include a free mass, defined spring constants and optionally damping which can provide selectable frequency responses

The springs can be arranged as coupled pairs

(Symmetric Springs)

The springs can be arranged in oppositely acting pairs (Balanced Springs)

The springs can be arranged as independent springs (Unipolar springs)

When the assembly is intended for horizontal

deployment (surface or downhole) and where unipolar springs are used that the upper spring train can be omitted if sufficient mass is used to maintain contact with the ground

Springs which are not coupled to fiber assemblies can be replaced by other spring designs such as coil springs .

When the assembly is intended for horizontal

deployment and where there is insufficient mass in the system to maintain contact with the ground during signal reception (or generation - i.e. the ^xshots' ) , that springs can be employed to connect the moving mass to the reference mass to provide pre-stress in the transducer spring coupled to the fiber .

Only springs used as transverse to axial transducers need be of bow spring type, others can be of coil or other types, including elastic fluids/gels.

Rotation of the springs may affect the nature of the acceleration-strain transduction as observed by the fiber assembly - depending on the incoming signal arrays of opposed spring pairs may be preferable to springs arranged in the same sense. - Damping would enable the assembly to exhibit an optimised spectral response.

- Dampers could be mechanical, fluidic or

electromagnetically based, which dampers may comprise a moving magnet and/or a static coil with load resistor.

- By covering a symmetric spring assembly containing at least two radially arranged springs that a pressure/hydrophone response can be produced where surrounding iso-static pressure field can be transduced into an axial strain.

Experimental evaluations have already been successfully carried out in the laboratory and the field with various embodiments of the method and system according to the invention .

Claims

A smart hydrocarbon fluid production method, wherein:

- seismic and/or production data from seismic and other acoustic events generated during exploration and/or production of hydrocarbons from underground hydrocarbon bearing formations are collected and enhanced using a bow spring signal conversion assembly for converting a broadside acoustic signal into substantially

longitudinal microstrain variations in a fiber optical sensor;

- the fiber optical sensor does not comprise Fiber Bragg Gratings (FBGs) and/or a Fabry-Perot

interferometer strain sensor in the vicinity of the bow spring signal conversion assembly and is coupled to a DAS interrogator assembly that measures Rayleigh backscattering to monitor microstrain variations generated by vibrations in the fiber optical sensor.

The method of claim 1, wherein the bowspring assembly comprises a first and a second sleeve, which sleeves are interconnected by a plurality of curved bowspring blades which maintain the fiber optical sensor in a substantially co-axial position relative to a

longitudinal axis of a tubular confinement in an underground wellbore. The method of claim 2, wherein the first and second sleeves are rigidly connected to the fiber optical sensor .

The method of claim 2, wherein the first sleeve is rigidly secured to the fiber optical sensor and the second sleeve is slideably secured to the fiber optical sensor .

The method of claim 2, wherein the assembly furthermore comprises a mass formed by an elongate central member which is maintained substantially parallel to the fiber optical sensor within the tubular confinement by the bowspring assembly that allows the mass to vibrate within the tubular confinement in a substantially orthogonal direction relative to a longitudinal axis of the tubular confinement in response to the broadside acoustic signal travelling in a non-parallel direction relative to the longitudinal axes of the sensor and the tubular confinement.

The method of claim 5, wherein a pair of bowspring assemblies are arranged at longitudinally spaced locations within the tubular confinement such that the bowspring assemblies have a pair of mutually nearby first sleeves and a pair of mutually remote second sleeves, wherein the first sleeves are rigidly secured to the mass and the second sleeves are slideably secured around the mass and rigidly secured to the fiber optical sensor.

A smart hydrocarbon production system, wherein:

longitudinal vibration in a fiber optical sensor;

The system of claim 7, wherein the bowspring assembly comprises a first and a second sleeve, which sleeves are interconnected by a plurality of curved bowspring blades which maintain the fiber optical Sensor in a substantially co-axial position relative to a

longitudinal axis of a tubular confinement within an underground wellbore.

The system of claim 8, wherein the assembly furthermore comprises a mass formed by an elongate central member which is maintained substantially parallel to the fiber optical sensor within the tubular confinement by the bowspring assembly that allows the mass to vibrate within the tubular confinement in a substantially orthogonal direction relative to a longitudinal axis of the tubular confinement in response to the broadside acoustic signal travelling in a non-parallel direction relative to the longitudinal axes of the sensor and the tubular confinement.

10. The system of claim 9, wherein a pair of bowspring assemblies are arranged at longitudinally spaced locations within the tubular confinement such that the bowspring assemblies have a pair of mutually nearby first sleeves and a pair of mutually remote second sleeves, wherein the first sleeves are rigidly secured to the mass and the second sleeves are slideably secured around the mass and rigidly secured to the fiber optical sensor.

11. The system of claim 9, wherein a plurality of pairs of bowspring assemblies are arranged at longitudinally spaced locations within the tubular confinement such that the bowspring assemblies generate axial vibrations and associated microstrain variations in at least a substantial part of the length of the fiber optical sensor .

12. The system of claim 11, wherein the fiber optical sensor comprises an optical fiber arranged in a

protective metal tube, known as a Fiber In Metal

Tube (FIMT) .