Three-dimensional vibration optical fiber grating sensor for logging-while-drilling engineering parameter sub

Abstract

The present application relates to the technical field of optical fiber grating sensors, and provides a three-dimensional vibration optical fiber grating sensor for a logging-while-drilling engineering parameter sub. The sensor comprises a hollow housing provided with a fiber input port and a fiber output port; three support assemblies sequentially arranged in the hollow housing in the axial direction, normal directions of end faces of the three support assemblies in which embedding grooves are formed being different; and a bend-insensitive optical fiber sequentially passing through the embedding grooves, and provided with grating regions on corresponding optical fiber segments, each grating region and the corresponding support assembly constituting a sensing body for acquiring a multi-axial vibration signal.

Description

Three-dimensional vibration fiber optic grating sensor for logging-while-drilling engineering parameter subsections

[0001] This application claims priority to Chinese Patent Application No. 202510358348.6, filed with the State Intellectual Property Office of China on March 25, 2025, entitled "Three-dimensional Vibration Fiber Bragg Grating Sensor for Logging While Drilling Engineering Parameter Subsection", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of fiber optic grating sensor technology, and in particular to a three-dimensional vibration fiber optic grating sensor for logging-while-drilling engineering parameter subsections. Background Technology

[0003] Fiber-optic communication while drilling is an advanced communication technology used in the oil and gas industry. Based on fiber optic communication, this technology benefits from the high frequency of light waves, offering greater capacity and bandwidth than conventional cable communication, making it suitable for high-speed, broadband information transmission. The low loss of fiber optics significantly increases the transmission distance without repeaters. Fiber optic communication transmits optical signals with minimal outward radiation, providing superior security. It also avoids crosstalk between fibers within the same cable, is immune to electromagnetic interference, and eliminates the safety hazards of electrical sparks to oil wells, offering excellent explosion-proof performance. The raw material for manufacturing glass fiber is quartz, which is more abundant than copper and aluminum used in cable manufacturing. Furthermore, fiber optics are environmentally friendly and have a long service life.

[0004] In downhole measurement while drilling (MWD), accurate measurement of three-dimensional vibration parameters near the drill bit is crucial for safe and efficient drilling. However, existing MWD technologies primarily utilize electrical vibration sensors, which are costly to apply in the harsh downhole environment characterized by high temperatures, high pressures, and strong electromagnetic interference. Furthermore, applying downhole electrical sensors to MWD fiber optic measurement systems requires additional photoelectric conversion modules, increasing the risk to safe operation. Fiber Bragg grating (FBG) sensing technology, with its advantages of high temperature and high pressure resistance and electromagnetic interference immunity, has been widely used in petroleum engineering monitoring. FBG sensors can be directly connected to MWD fiber optic measurement systems, efficiently transmitting acquired physical quantity information via optical signals. However, significant basic optical transmission loss exists in downhole MWD fiber optic measurement systems, primarily due to two reasons. First, MWD fiber optic measurement systems require multiple fiber optic connectors to form a complete link, including downhole wet connectors, wellhead wet connectors, and photoelectric slip rings. The coordination of these connectors solves the problem of difficult fiber optic cable installation, simplifying the process and improving construction efficiency. However, the use of these connectors increases the basic optical transmission loss of the downhole fiber optic measurement system. Simultaneously, the harsh working environment of high temperature and pressure downhole accelerates the aging and deformation of the sealing rings, leading to the intrusion of moisture and contaminants, and creating a risk of further increasing the optical transmission loss of the downhole fiber optic communication system. Secondly, because fiber optic cables need to be continuously released during downhole fiber optic measurement, a certain length of cable needs to be stored in the main and relay cable compartments. The cable is spirally wound on the cable rod inside the compartment, and the macro-bending loss caused by this spiral winding method further increases the basic loss of the downhole fiber optic measurement system. On the other hand, to meet the requirements of high temperature and high pressure engineering operations, the design of the downhole drill pipe engineering parameter short section should ensure the strength of the short section as much as possible. Therefore, the sensor installation area designed in the engineering parameter short section is generally small and flat. In summary, designing a low-loss fiber optic grating three-dimensional vibration sensor in a confined space is a major challenge for its application in downhole fiber optic measurement.

[0005] Therefore, it is essential to provide a three-dimensional vibration fiber optic grating sensor for logging-while-drilling (LWD) engineering parameter subsections, which adopts a linear, separate arrangement, placing the three-dimensional sensing units on the same straight line and utilizing the vibration in three axial directions on a single-mode fiber to achieve LWD output with a compact structure. Summary of the Invention

[0006] In view of this, this application proposes a compact three-dimensional vibration fiber optic grating sensor for logging-while-drilling (LWD) engineering parameter subs, which can be used to measure three axial vibration accelerations separately and is suitable for LWD output in the application scenario of logging-while-drilling engineering parameter subs.

[0007] This application provides a three-dimensional vibration fiber Bragg grating sensor for logging-while-drilling engineering parameter subsections, comprising:

[0008] The hollow shell has fiber inlet and fiber outlet ports at both ends extending along a first preset direction, the first preset direction being the length extension direction of the shell, and the shell is fixedly connected to the engineering parameter section.

[0009] Three support components are arranged sequentially and at intervals in the housing along the first pre-examination direction. Each of the three support components has a through groove, and the normal directions of the end faces of the three support components with the grooves are different.

[0010] The bend-insensitive optical fiber is inserted into the housing and passes sequentially through the fiber inlet port, the slots on the three support components, and the fiber outlet port. The portion of the bend-insensitive optical fiber passing through the three support components is provided with a grid area.

[0011] The grid area and its supporting components together constitute the sensor, which is used to acquire vibration signals in different axes during logging while drilling.

[0012] In some embodiments, each of the three support components includes a fixed base, a cantilever beam, and a mass block. The fixed base is fixedly connected to the inner surface of the housing. The mass block is spaced apart from the fixed base, and a slot passes through the mass block and the fixed base of the same support component. The end faces of the mass block and the fixed base with slots are flush. The cantilever beam is disposed between the mass block and the fixed base and is fixedly connected to the adjacent end faces of the mass block and the fixed base, respectively. The bend-insensitive optical fiber is fixedly connected to the slots on the mass block and the fixed base, respectively. The grid region of the bend-insensitive optical fiber is tensioned and suspended between the mass block and the fixed base, and is spaced apart from the cantilever beam. The mass block and the cantilever beam are spaced apart from the inner surface of the housing.

[0013] In some embodiments, the thickness of the cantilever beam along the radial direction of the bend-insensitive fiber is less than the thickness of the fixture or the mass block along the radial direction of the bend-insensitive fiber, and the mass of the cantilever beam is less than the mass block.

[0014] In some embodiments, when the vibration signal from external drilling acts on the three sensors, under the action of inertia, the end of the cantilever beam away from the fixed seat and the mass block are axially offset, compressing or stretching the grid area on the three sensors, causing the center wavelength of the reflected light from the grid area to change. By demodulating the signal of the reflected light from the grid area, the vibration signal from external drilling is obtained. The axial offset of the mass block is a rotation relative to the end face of the fixed seat of the sensor in which the groove is opened.

[0015] In some embodiments, the surface of the bend-insensitive optical fiber is bonded to the inner surface of the groove, or a metal coating is provided on the bend-insensitive surface located at the sensor, and the metal coating is welded to the inner surface of the groove; the depth of the groove is greater than the diameter of the bend-insensitive optical fiber, and the width of the groove is equal to the diameter of the bend-insensitive optical fiber.

[0016] In some embodiments, let the length of the cantilever beam be L, the cross-sectional area of ​​the cantilever beam be A = wh, w be the current width of the cantilever beam, h be the current thickness of the cantilever beam, w0 be the initial width of the cantilever beam, h0 be the initial thickness of the cantilever beam, the distance between the center of the mass block and the end of the fixed seat near the cantilever beam be L2, the length of the mass block along the axial direction of the bend-insensitive fiber be d, the thickness of the mass block along the radial direction of the bend-insensitive fiber be e, the total mass of the mass block and the cantilever beam be M, and E be the elasticity of the cantilever beam. The elastic modulus is given by E(T, P) = E0(1+βΔT)(1+γP), where E0 is the initial value of the elastic modulus, β is the temperature coefficient of the elastic modulus, γ is the pressure coefficient of the elastic modulus, ΔT is the temperature change, and P is the current pressure. The corrected cantilever beam length is given by L(T, P) = L0(1+αTΔT)(1-δP), where L0 is the initial length of the cantilever beam, α... T δ is the coefficient of thermal expansion of the cantilever beam, and δ is the coefficient of compression of the cantilever beam; the distance between the center of the corrected mass block and the end of the fixed seat closest to the cantilever beam is L2(T,P)=L 20 (1+αTΔT)(1-δP), L 20 The initial length from the center of the mass block to the nearest end of the fixed seat; the corrected moment of inertia of the section is I(T, P) = I0(1 + αTΔT - δ). w P)(1+α T ΔT-δ h P) 3 δ w δ is the width compression factor. h The compression factor is [value missing]; the thickness of the corrected mass block along the radial direction of the bend-insensitive fiber is e(T, P) = e0(1+α). e ΔT)(1-δ e P), e0 is the initial height of the mass block, α e δ is the coefficient of thermal expansion of the mass block. e The compression factor of the mass block; the corrected grating reflection wavelength λ. B (T,P)=λ B0 [1-(α λ +ξΔT)+(1-P e )F P ], λ B0 α is the initial center wavelength of the grating region.λ ξ is the thermal expansion coefficient of the optical fiber, ξ is the thermo-optical coefficient of the optical fiber, and P is the thermal expansion coefficient of the optical fiber. e F is the elastic coefficient. P The axial strain of the optical fiber caused by pressure satisfies the following relationship: the first axial sensitivity is... The second axial sensitivity is The third axial sensitivity is Among them I x (T, P) = I x0 (1+α T ΔT-δ w P)(1+α T ΔT-δ h P) 3 , Let I be the first initial moment of inertia. y (T, P) = I y0 (1+α T ΔT-δ w P)(1+α T ΔT-δ h P) 3 , This is the second initial moment of inertia.

[0017] In some embodiments, the measurement wavelength ranges of different gate regions do not overlap.

[0018] In some embodiments, the device further includes a plurality of mounting blocks, wherein a plurality of placement grooves are provided on the inner surface of the housing, and the plurality of placement grooves are spaced apart along a first preset direction; one end of the mounting block is embedded in the placement groove, and the other end extends out of the placement groove and toward the interior of the housing; a fixing seat is provided at the end of the plurality of mounting blocks away from the inner surface of the housing and is fixedly connected to the mounting blocks.

[0019] In some embodiments, the spacing between different mounting bases is greater than the spacing between the corresponding mounting blocks.

[0020] In some embodiments, a cover plate is also included, wherein the housing has an opening and the cover plate covers the opening. Attached Figure Description

[0021] Figure 1 is a front view of a three-dimensional vibration fiber optic grating sensor for logging-while-drilling engineering parameters disclosed in this application after the cover plate is hidden.

[0022] Figure 2 is a three-dimensional view of a three-dimensional vibration fiber optic grating sensor for logging-while-drilling engineering parameter subsection disclosed in this application, after the cover plate is hidden and the bending insensitive fiber is bent.

[0023] Figure 3 is a three-dimensional view of the explosion state of a three-dimensional vibration fiber optic grating sensor for logging-while-drilling engineering parameter sub disclosed in this application after the hidden cover plate and the bending insensitive fiber are removed.

[0024] Figure 4 is a front view of the mounting block and the placement groove of the housing of a three-dimensional vibration fiber optic grating sensor for logging-while-drilling engineering parameter sub-section disclosed in this application.

[0025] Figure 5 is a front view of a three-dimensional vibration fiber optic grating sensor for logging-while-drilling engineering parameter sub disclosed in this application after the mounting block has been removed.

[0026] Figure 6 is a top view of the support assembly of a three-dimensional vibration fiber optic grating sensor for logging-while-drilling engineering parameter subsection disclosed in this application.

[0027] Figure 7 is a front view of the support assembly of a three-dimensional vibration fiber optic grating sensor for logging-while-drilling engineering parameter subsection disclosed in this application.

[0028] Figure 8 is a schematic diagram of the relative positions of the bending-insensitive optical fiber, the three support components, and the housing of a three-dimensional vibration fiber optic grating sensor for logging-while-drilling engineering parameter subsection disclosed in this application before assembly. Detailed Implementation

[0029] Designing a low-loss fiber Bragg grating three-dimensional vibration sensor for use in downhole logging-while-drilling fiber optic measurements is a major challenge. Conventional fiber winding methods and multi-fiber connector connections introduce macro-bending loss and transmission loss. Therefore, as shown in Figures 1, 2, and 3, this application provides a three-dimensional vibration fiber Bragg grating sensor for logging-while-drilling engineering parameter sections, comprising:

[0030] The hollow housing 1 has fiber inlet and fiber outlet ports 7 at its two ends extending along a first preset direction. The first preset direction is the length extension direction of the housing 1, i.e., the horizontal extension direction shown in Figure 1. The housing 1 is fixedly connected to the engineering parameter short section. The fiber inlet and fiber outlet ports 7 at both ends of the housing 1 are used for the fiber to pass through and prevent the inside of the housing 1 from being contaminated. Bolt holes can be provided inside the housing 1 for threaded connection with the engineering parameter short section.

[0031] In some embodiments, a cover plate is also provided on the housing 1, and an opening is provided on the end face of the housing 1 away from the engineering parameter section, with the cover plate covering the opening. The cover plate is not shown in the accompanying drawings.

[0032] Three support components are sequentially spaced within the housing 1 along the first pre-approval direction. Each of the three support components has a through slot 100, and the normal directions of the end faces of the slots 100 on the three support components are different. The slots 100 are used to place optical fibers. As shown in Figure 2 and Figure 8, the three support components are designated as first support component 2, second support component 4, and third support component 5 for differentiation. As shown in Figure 1, the end face of the first support component 2 with the slot 100 is horizontal, and the normal direction of the end face with the slot 100 is vertically upward, defined as the X-axis direction; the end face of the second support component 4 with the slot 100 is vertical, and the normal direction of the end face with the slot 100 is perpendicular to the plane and outward, defined as the Y-axis direction; the end face of the third support component 5 with the slot 100 is vertical, and the normal direction of the end face with the slot 100 is the opposite direction of the first pre-approval direction, defined as the Z-axis direction.

[0033] The bend-insensitive fiber 3 is inserted into the housing 1 and passes sequentially through the fiber inlet port, the slots 100 on the three support components, and the fiber outlet port 7. The portion of the bend-insensitive fiber 3 passing through the three support components is provided with a grating region 200. The fiber grating is sensitive to parameters such as stress or acceleration. When subjected to external force, the center wavelength of the reflected light in the grating region 200 will drift. By demodulating the wavelength drift of the reflected light signal, the magnitude of the physical quantity to be measured loaded in the grating region 200 can be calculated.

[0034] In this embodiment, the grid region 200 and its supporting components together constitute a sensor, which is used to acquire vibration signals along different axes during logging while drilling. By continuously arranging three supporting components in different orientations within the housing 1, the orientation of the sensor is defined, thereby reducing the overall length of the bend-insensitive optical fiber 3, which helps to reduce the bending loss of the optical fiber and improve the transmission quality of the optical signal detected by the sensor. In actual use, the housing 1 shown in Figure 1 needs to be rotated 90° clockwise and placed vertically, which is the working orientation. According to the right-hand coordinate system rule, the thumb, index finger, and middle finger point in different directions and are perpendicular to each other. Taking the surface where the thumb and index finger are located as the end face of the slot 100, the direction pointed by the middle finger is the normal direction of the end face of the slot 100 of each supporting component. Similarly, the sensors containing the three supporting components are named the first sensor, the second sensor, and the third sensor according to the first preset direction.

[0035] In some embodiments, the measurement wavelengths of the three grating regions 200 etched on the completely insensitive optical fiber are different. To avoid mutual interference between the reflected light signals of different grating regions 200, the measurement wavelength ranges of different grating regions 200 do not overlap. For example, the upper limit of the measurement wavelength range of the grating region 200 of the first sensor differs from the lower limit of the measurement wavelength range of the second sensor by at least 5 nm; the upper limit of the measurement wavelength range of the second sensor differs from the lower limit of the measurement wavelength range of the third sensor by at least 5 nm. This avoids wavelength overlap during operation due to excessively small wavelength spacing between the grating regions 200. The three grating regions 200 correspond to vibration sensing detection on the X-axis, Y-axis, and Z-axis, respectively. Vibration sensing measurement can be performed simply by detecting the center wavelength drift of the measurement wavelength range of the corresponding grating region 200.

[0036] This application involves placing individual bend-insensitive optical fibers within a compact housing, setting three gratings on the fibers, and combining them with three support components to form three different sensors. This allows for the measurement of vibration signals along three axes of an engineering parameter section, reducing sensor bending losses and improving the reliability and transmission quality of sensor measurement results.

[0037] As shown in Figures 6, 7, and 8, each of the three support components includes a fixed base 300, a cantilever beam 400, and a mass block 500. The fixed base 300 is fixedly connected to the inner surface of the housing 1. The mass block 500 is spaced apart from the fixed base 300, and the groove 100 passes through the mass block 500 and the fixed base 300 of the same support component. The end faces of the groove 100 on the mass block 500 and the fixed base 300 are flush. The cantilever beam 400 is disposed between the mass block 500 and the fixed base 300 and is fixedly connected to the adjacent end faces of the mass block 500 and the fixed base 300, respectively. The bend-insensitive optical fiber 3 is fixedly connected to the groove 100 on the mass block 500 and the fixed base 300, respectively. The grid region 200 of the bend-insensitive optical fiber 3 is tensioned and suspended between the mass block 500 and the fixed base 300 and is spaced apart from the cantilever beam 400. The mass block 500 and the cantilever beam 400 are spaced apart from the inner surface of the housing 1. The cantilever beam 400 does not contact the grating area 200. Under the action of axial vibration, the two ends of the grating area 200 on different sensors are subjected to axial tension or compression by the corresponding fixed seat 300 and mass block 500, respectively, causing the grating area 200 to drift with the initial center wavelength of the reflected light. By demodulating the drifted reflected light signal, the vibration can be sensitively measured.

[0038] In some embodiments, the thickness of the cantilever beam 400 along the radial direction of the bend-insensitive optical fiber 3 is less than the thickness of the fixing seat 300 or the mass block 500 along the radial direction of the bend-insensitive optical fiber 3, and the mass of the cantilever beam 400 is less than the mass of the mass block 500. If the mass of the cantilever beam 400 is much less than the mass of the mass block 500, the cantilever beam 400 and the mass block 500 can be regarded as a whole.

[0039] In other embodiments, the spacing between the different mounting brackets 300 is greater than the spacing between the corresponding mounting blocks. This arrangement is to reduce bending loss of the optical fiber due to excessive bending during installation, while also allowing sufficient installation slack.

[0040] As shown in Figure 1 and Figure 8, before installing the sensors inside the housing 1, the three support components need to be pre-fixed to the bend-insensitive optical fiber 3 in the indicated orientation. Changing the sensor arrangement direction effectively prevents the optical fiber from breaking due to torsional shear force during installation. This allows for the encapsulation of three sensors located on the same bend-insensitive optical fiber 3. It should be noted that when the second and third sensors in Figure 1 are installed on the housing 1, the radius of curvature formed by the installation must be greater than the minimum bending radius of the optical fiber. This is to reduce bending loss caused by excessive bending during installation and also to allow sufficient installation slack for the three sensors within the housing 1.

[0041] As shown in Figures 3, 4, and 5, to ensure that the sensors do not directly contact the inner surface of the housing 1, several mounting blocks 6 are also provided inside the housing 1. Several placement grooves are provided on the inner surface of the housing 1, and these grooves are spaced apart along a first preset direction. One end of each mounting block 6 is embedded in a placement groove, and the other end extends out of the groove and into the housing 1. A fixing seat 300 is located at the end of each mounting block 6 away from the inner surface of the housing 1 and is fixedly connected to the mounting blocks 6. The fixing seat 300 and the mounting blocks 6 can be fixed by threaded connection or welding. The mounting blocks 6 and the housing 1 can be fixedly connected by welding.

[0042] In some embodiments, when the vibration signal from external drilling acts on the three sensors, under the action of inertia, the end of the cantilever beam 400 away from the fixed base 300 and the mass block 500 are axially offset, compressing or stretching the grid area 200 on the three sensors, causing the center wavelength of the reflected light from the grid area 200 to change. By demodulating the signal of the reflected light from the grid area 200, the vibration signal from external drilling is obtained. The axial offset of the mass block 500 is a rotation relative to the end face of the fixed base 300 with the slot 100, that is, the mass block 500 rotates clockwise or counterclockwise by a certain angle relative to the end face of the fixed base 300 with the slot 100.

[0043] Let the length of cantilever beam 400 be L, the cross-sectional area of ​​cantilever beam 400 be A = wh, w be the current width of cantilever beam 400, h be the current thickness of cantilever beam 400, w0 be the initial width of cantilever beam 400, h0 be the initial thickness of cantilever beam 400, the distance between the center of mass block 500 and the end of fixed seat 300 near cantilever beam 400 be L2, the length of mass block 500 along the axial direction of bending-insensitive fiber 3 be d, the thickness of mass block 500 along the radial direction of bending-insensitive fiber 3 be e, the total mass of mass block 500 and cantilever beam 400 be M, E be the elastic modulus of cantilever beam 400, and I be the moment of inertia of cantilever beam 400. If subjected to an external acceleration a, according to the analysis of mechanics of materials, the rotation angle θ(L) of cantilever beam 400 at the end away from fixed seat 300 is... This formula is for angles under ideal conditions.

[0044] Further incorporating the effects of temperature T and pressure P on material parameters and geometry, the corrected elastic modulus is E(T, P) = E0(1+βΔT)(1+γP), where E0 is the initial value of the elastic modulus, β is the temperature coefficient of the elastic modulus, γ is the pressure coefficient of the elastic modulus, ΔT is the temperature change, and P is the current pressure; the corrected cantilever beam length L(T, p) for 400 mm is L0(1+αP). T ΔT)(1-δP), L0 is the initial length of the cantilever beam of 400, α T δ is the coefficient of thermal expansion of cantilever beam 400, and δ is the coefficient of compressibility of cantilever beam 400; the distance L2(T,P) between the center of the corrected mass block 500 and the end of the fixed seat 300 near the cantilever beam 400 is L2(T,P) = L 20 (1+α T ΔT)(1-δP), L 20 The initial length from the center of mass block 500 to the nearest end of fixed seat 300; the corrected moment of inertia of the section is I(T,P)=I0(1+α T ΔT-δ w P)(1+α T ΔT-δ h P) 3 δ w δ is the width compression factor. h The compression factor is [value missing]; the thickness of the corrected mass block 500 along the radial direction of the bend-insensitive fiber 3 is e(T,P)=e0(1+α). e ΔT)(1-δ e P), e0 is the initial height of mass block 500, α e The coefficient of thermal expansion of the mass block is 500, δ e The compression factor for mass block 500; the corrected grating reflection wavelength λ B (T, P) = λB0 [1+(α λ +ξΔT)+(1-P e )F P ], λ B0 α is the initial center wavelength of the 200 ohm gate region. λ ξ is the thermal expansion coefficient of the optical fiber, ξ is the thermo-optical coefficient of the optical fiber, and P is the thermal expansion coefficient of the optical fiber. e F is the elastic coefficient. P The axial strain of the optical fiber caused by pressure satisfies the following relationship: the first axial sensitivity is... The second axial sensitivity is The third axial sensitivity is Among them I x (T, P) = I x0 (1+α T ΔT-δ w P)(1+α T ΔT-δ h P) 3 , Let Iy be the first initial moment of inertia. ( T, P) = I y0 (1+α T ΔT-δ w P)(1+α T ΔT-δ h P) 3 , Let L be the second initial moment of inertia. Replace the parameters L and L2, E and I in the rotation angle formula with the corrected L(T, p), L2(T, P), E(T, P), and I(T, P), respectively. This will give the rotation angle θ(L, T, P) of the cantilever beam 400 at the end furthest from the fixed seat 300 after temperature and pressure corrections.

[0045] In this embodiment, the support components all include a fixed base 300 for fixing, a cantilevered mass block 500, and a cantilever beam 400 connecting the fixed base 300 and the mass block 500. Under the influence of axial acceleration, the mass block 500 will undergo a certain axial deformation relative to the fixed base 300, thereby compressing or stretching the grating region 200, causing the center wavelength of the emitted light from the grating region 200 to drift. By demodulating the optical signal, the change in center wavelength and the actual size of the current cantilever beam 400 can be obtained, and the rotation angle of the cantilever beam 400 can be calculated.

[0046] It is worth noting that the effects of temperature and pressure on the working environment of the engineering parameter short section were taken into account when calculating the axial sensitivity, thus making the sensitivity of each axis more accurate.

[0047] In some embodiments, the surface of the bend-insensitive optical fiber 3 and the groove 100 are fixed by bonding the surface of the bend-insensitive optical fiber 3 to the inner surface of the groove 100, or by providing a metal coating on the surface of the bend-insensitive optical fiber located at the sensor and welding the metal coating to the inner surface of the groove 100. The depth of the groove 100 is greater than the diameter of the bend-insensitive optical fiber 3, and the width of the groove 100 is equal to the diameter of the bend-insensitive optical fiber 3. This combination provides a larger contact area on the surface of the bend-insensitive optical fiber 3.

Claims

1. A three-dimensional vibration fiber Bragg grating sensor for logging-while-drilling engineering parameter subsections, comprising: The hollow shell has fiber inlet and fiber outlet ports at both ends extending along a first preset direction, the first preset direction being the length extension direction of the shell, and the shell is fixedly connected to the engineering parameter section. Three support components are arranged sequentially and at intervals in the housing along the first pre-examination direction. Each of the three support components has a through groove, and the normal directions of the end faces of the three support components with the grooves are different. The bend-insensitive optical fiber is inserted into the housing and passes sequentially through the fiber inlet port, the slots on the three support components, and the fiber outlet port. The portion of the bend-insensitive optical fiber passing through the three support components is provided with a grid area. The grid area and the supporting components together constitute the sensor, which is used to acquire vibration signals in different axes during logging while drilling. Each of the three support components includes a fixed base, a cantilever beam, and a mass block; Let the length of the cantilever beam be L, the cross-sectional area of the cantilever beam be A=wh, w be the current width of the cantilever beam, h be the current thickness of the cantilever beam, w0 be the initial width of the cantilever beam, h0 be the initial thickness of the cantilever beam, the distance between the center of the mass block and the end of the fixed base close to the cantilever beam be L2, the length of the mass block along the axial direction of the bend-insensitive optical fiber be d, the thickness of the mass block along the radial direction of the bend-insensitive optical fiber be e, the total mass of the mass block and the cantilever beam be M, E be the elastic modulus of the cantilever beam, I be the cross-sectional moment of inertia of the cantilever beam; the influence of temperature T and pressure P on the material parameters and geometric dimensions is introduced, the corrected elastic modulus be E(T, P)=E0(1+βΔT)(1+γP), wherein E0 be the initial value of the elastic modulus, β be the temperature coefficient of the elastic modulus, γ be the pressure coefficient of the elastic modulus, ΔT be the temperature change, P be the current pressure; the corrected length of the cantilever beam L(T, p)=L0(1+α T TΔT)(1-δP), L0 be the initial length of the cantilever beam, α T T be the thermal expansion coefficient of the cantilever beam, δ be the compression coefficient of the cantilever beam; the corrected distance between the center of the mass block and the end of the fixed base close to the cantilever beam L2(T, P)=L 20 (1+αTΔT)(1-δP), L 20 0 be the initial length of the mass block center to the nearest end of the fixed base; The corrected cross-sectional moment of inertia is I(T, P) = I0(1 + α T ΔT - δ w P)(1 + α T ΔT - δ h P) 3 , δ w is the width compression coefficient, δ h is the height compression coefficient; the corrected thickness of the mass along the radial direction of the bend-insensitive fiber is e(T, P) = e0(1 + α e ΔT)1-δ e P), e0is the initial height of the mass, α e is the thermal expansion coefficient of the mass, δ e is the compression coefficient of the mass; the corrected grating reflection wavelength is λ B (T, P) = λ B0 [1 + (α λ + ξΔT) + (1 - P e )F P ], λ B0 is the initial center wavelength of the grating region, α λ is the thermal expansion coefficient of the fiber, ξ is the thermal-optic coefficient of the fiber, P e is the elasto-optic coefficient, F P is the axial strain of the fiber caused by pressure; the following relationship is satisfied: the first axial sensitivity is The second axial sensitivity is The third axial sensitivity is where I x (T, P) = I x0 (1 + a T ΔT - δ w P)(1 + a T ΔT - δ h P) 3 , I1 is the first initial moment of inertia y (T, P) = I y0 (1 + a T ΔT - δ w P)(1 + a T ΔT - δ h P) 3 , This is the second initial moment of inertia.

2. The three-dimensional vibrating fiber grating sensor for logging engineering parameters while drilling according to claim 1, wherein, The mounting base is fixedly connected to the inner surface of the housing. The mass block is spaced apart from the mounting base, and the slot passes through the mass block and the mounting base of the same support component. The end faces of the mass block and the mounting base with the slots are flush. The cantilever beam is set between the mass block and the mounting base and is fixedly connected to the adjacent end faces of the mass block and the mounting base respectively. The bend-insensitive optical fiber is fixedly connected to the slots on the mass block and the mounting base respectively. The grid region of the bend-insensitive optical fiber is tensioned and suspended between the mass block and the mounting base and is spaced apart from the cantilever beam. The mass block and the cantilever beam are spaced apart from the inner surface of the housing.

3. The three-dimensional vibrating fiber grating sensor for a logging-while-drilling engineering parameter sub according to claim 2, wherein, The thickness of the cantilever beam along the radial direction of the bend-insensitive fiber is less than the thickness of the fixing seat or the mass block along the radial direction of the bend-insensitive fiber, and the mass of the cantilever beam is less than the mass block.

4. The three-dimensional vibrating fiber grating sensor for a logging-while-drilling engineering parameter sub according to claim 3, wherein, When the vibration signal from external drilling acts on the three sensors, under the action of inertia, the end of the cantilever beam away from the fixed seat and the mass block are axially offset, compressing or stretching the grid area on the three sensors, causing the center wavelength of the reflected light from the grid area to change. By demodulating the signal of the reflected light from the grid area, the vibration signal from external drilling is obtained. The axial offset of the mass block is a rotation relative to the end face of the fixed seat of the sensor in which it is located, which has a groove.

5. The three-dimensional vibrating fiber grating sensor for a logging-while-drilling engineering parameter sub according to claim 4, wherein, The surface of the bend-insensitive optical fiber is bonded to the inner surface of the groove, or a metal coating is applied to the surface of the bend-insensitive fiber located at the sensor, and the metal coating is welded to the inner surface of the groove for fixation; the depth of the groove is greater than the diameter of the bend-insensitive optical fiber, and the width of the groove is equal to the diameter of the bend-insensitive optical fiber.

6. The three-dimensional vibrational fiber grating sensor for a logging-while-drilling engineering parameter sub according to claim 4, wherein, The measurement wavelength ranges of different grating regions do not overlap.

7. The three-dimensional vibration fiber optic grating sensor for logging-while-drilling engineering parameter sub according to claim 2 further includes a plurality of mounting blocks, wherein a plurality of placement grooves are provided on the inner surface of the housing, and the plurality of placement grooves are spaced apart along a first preset direction; one end of the mounting block is embedded in the placement groove, and the other end extends out of the placement groove and toward the interior of the housing; a fixing seat is provided at the end of the plurality of mounting blocks away from the inner surface of the housing and is fixedly connected to the mounting blocks.

8. The three-dimensional vibrating fiber grating sensor for a logging-while-drilling engineering parameter sub according to claim 7, wherein, The spacing between different mounting brackets is greater than the spacing between the corresponding mounting blocks. 9.The three-dimensional vibration fiber grating sensor for the LWD engineering parameter sub of claim 1, further comprising a cover plate, and the housing is provided with an opening, and the cover plate is arranged at the opening.

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