Optical cable for sensing seismic waves

Abstract

The invention relates to an optical cable for sensing seismic waves. The optical cable includes: a reinforcement; the elastic sleeve is arranged on the outer side of the reinforcing piece in a sleeving manner; the optical fiber assembly is arranged on the outer side face of the elastic sleeve, the optical fiber assembly comprises a plurality of winding sections and a plurality of linear sections, the winding sections are wound on the outer side of the elastic sleeve, the linear sections are arranged in the extending direction of the reinforcing part, and the winding sections and the linear sections are alternately arranged in the extending direction of the reinforcing part; the protective layer is coated on the optical fiber assembly; and the counterweight piece is arranged on the protective layer. Compared with a common optical cable, the optical cable can effectively avoid the problem that seismic wave vibration sensing is not sensitive due to too many middle layers, can receive seismic wave vibration in different directions, and improves seismic wave sensing sensitivity. Compared with other spiral optical cables, the spiral optical cable can control the length of the optical fiber in the optical cable by adjusting the winding length and the winding interval of the winding section of the optical fiber assembly, and the problem that the collection task is increased due to the fact that the optical fiber in the optical cable is too long is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of fiber optic acoustic sensing, and particularly to an optical cable for sensing seismic waves. Background Art

[0002] Distributed fiber Acoustic Sensing (DAS) technology has been applied to oil exploration fields such as borehole VSP and dynamic monitoring in recent years. Compared with conventional surface geophones, DAS has the advantages of distributed dense sampling, low cost, and high efficiency. However, the quality of the collected data is severely affected by the optical cable. Currently, the optical cables used in engineering projects are ordinary optical cables and spiral optical cables. Most of the optical fibers inside the ordinary optical cable are straight or approximately straight optical fibers. At the same time, in order to make the optical cable work stably in the harsh downhole environment, the optical fibers in the optical cable are wrapped by a multi-layer structure to achieve the effects of tensile resistance, compressive resistance, and moisture resistance. This structure of straight or approximately straight optical fibers makes the optical cable easily sense seismic waves close to the axial direction parallel to it, but very insensitive to seismic waves close to the axial direction perpendicular to it. At the same time, the multi-layer structure of the optical cable also weakens the signal transmitted from external seismic wave vibrations to the optical fiber, reducing the sensitivity. In addition, the signal-to-noise ratio of the data collected by DAS is also affected by the laying method of the optical cable. Common optical cable coupling methods are mostly used for downhole operations. Affected by environmental factors such as ocean currents, these coupling methods are difficult to expand to be used in the ocean environment, restricting the seismic acquisition application of DAS in the ocean environment.

[0003] The spiral optical cable winds the entire optical fiber around the inside of the optical cable at a certain angle to form a spiral optical cable structure. Although this design solves the problem that the structure of straight or approximately straight optical fibers is difficult to sense seismic waves perpendicular to its axial direction, the length of the optical fiber inside the optical cable increases significantly, increasing the data acquisition volume. At the same time, in order to improve the sensitivity of seismic wave sensing, only one layer of acoustic transmission layer is designed on the outer layer of the optical fiber component. Compared with ordinary optical cables, its lateral pressure resistance ability is significantly reduced. At the same time, because ordinary spiral optical cables must rely on media (such as rock, steel and other media) and be closely attached to the media to effectively capture seismic waves, in the ocean environment, it is necessary to use an underwater excavator of an optical cable laying ship to dig a trench on the seabed, and then bury and couple all ordinary spiral optical cables on the seabed for use, which in turn causes the problems of large coupling difficulty and high cost of the optical cable.

[0004] In summary, the current optical cables for seismic wave detection have the following problems:

[0005] Ordinary straight optical cables are very insensitive to seismic waves approaching a direction perpendicular to their axial direction. The multi-layer structure is not conducive to the perception of seismic waves by the optical cable, and the coupling method is difficult to apply in the marine environment, lacking flexibility. Compared with ordinary straight optical cables, the fiber length of ordinary spiral optical cables is significantly increased, which in turn leads to an increase in the amount of collected data and a significant decrease in the lateral pressure resistance. Moreover, the laying and coupling of ordinary spiral optical cables in the marine environment are difficult and costly. Summary of the Invention

[0006] In view of this, the present invention provides an optical cable for sensing seismic waves. Through the alternating spiral structure setting and the cooperation with counterweights, the optical cable with counterweights can be well coupled to the seabed, without the need to fully couple the optical cable to the seabed, reducing the coupling difficulty and cost, improving the DAS data acquisition quality, and expanding the application scenarios of the optical cable.

[0007] Specifically, the present invention is implemented through the following technical solutions:

[0008] According to a first aspect of the present invention, there is provided an optical cable for sensing seismic waves, the optical cable comprising: a strengthening member; an elastic sleeve sleeved outside the strengthening member; an optical fiber assembly disposed on the outer side surface of the elastic sleeve, the optical fiber assembly including a plurality of winding segments and a plurality of straight segments, the winding segments being wound around the outside of the elastic sleeve, the straight segments being arranged along the extending direction of the strengthening member, and the winding segments and the straight segments being alternately arranged along the extending direction of the strengthening member; a protective layer covering the optical fiber assembly; and a counterweight disposed on the protective layer.

[0009] In some embodiments, the optical fiber assembly includes: an optical fiber and a compressive member, the optical fiber and the compressive member being arranged side by side on the outer side surface of the elastic sleeve.

[0010] In some embodiments, the cross-section perpendicular to the extending direction of the optical fiber on the optical fiber is a first cross-section, and the cross-section perpendicular to the extending direction of the compressive member on the compressive member is a second cross-section, and the area of the first cross-section is smaller than the area of the second cross-section.

[0011] In some embodiments, the material of the compressive member includes TPU material.

[0012] In some embodiments, the length of the optical fiber assembly of the winding segment is less than or equal to 50 m; and / or the length of the optical fiber assembly of the straight segment is less than or equal to 100 m; and / or the angle formed by the winding direction of the winding segment and the extending direction of the strengthening member is greater than or equal to 85° and less than or equal to 90°.

[0013] In some embodiments, the protective layer includes: a steel-plastic composite tape layer covering the outside of the optical fiber assembly; and an outer sheath sleeved on the steel-plastic composite tape layer.

[0014] In some embodiments, the material of the outer sheath includes polyethylene.

[0015] In some embodiments, the counterweight is clamped on the winding section or the straight section.

[0016] In some embodiments, the counterweight includes tungsten blocks, lead blocks, tungsten packages and lead packages. The tungsten package includes a nylon package and tungsten grains, and the maximum outer dimension of the tungsten grains is less than or equal to 2 cm; the lead package includes a nylon package and lead grains, and the maximum outer dimension of the lead grains is less than or equal to 2 cm.

[0017] In some embodiments, the reinforcing member includes steel wires.

[0018] In some embodiments, the elastic sleeve includes a thermoplastic polyurethane elastic sleeve.

[0019] In some embodiments, the winding diameter of the optical fiber assembly in the winding section is less than or equal to 15 mm.

[0020] In some embodiments, an anti-corrosion layer is provided on the outer surface of the counterweight.

[0021] In some embodiments, the winding pitch of the winding section wound around the outer side of the elastic sleeve is equal to the outer diameter of the optical fiber assembly.

[0022] The technical solution provided by the present invention at least brings the following beneficial effects: The optical cable for sensing seismic waves provided by the present invention includes a reinforcing member, an elastic sleeve, an optical fiber assembly, a protective layer and a counterweight. The reinforcing member can play a role in tensile resistance, and the protective layer can play a role in moisture resistance and resistance to external forces, so as to protect the optical fiber from being broken. By setting the counterweight, the coupling degree between the optical cable and the environment and the stability of the optical cable in the fluid are effectively enhanced, and at the same time, the flexibility of the optical cable is ensured. Therefore, the optical cable can be used in the marine environment, expanding the scenario of the optical cable sensing seismic wave vibrations. At the same time, since the optical fiber assembly in the present application is divided into winding sections and straight sections and arranged alternately on the outer surface of the elastic sleeve, compared with ordinary optical cables, the problem of insensitive seismic wave vibration sensing caused by too many intermediate layers can be effectively avoided, and seismic wave vibrations in different directions can be received at the same time, enhancing the seismic wave sensing sensitivity. Compared with other spiral optical cables, the spiral optical cable of the present application can control the length of the optical fiber inside the optical cable by adjusting the winding length and winding interval of the winding section of the optical fiber assembly, avoiding the problem of increased acquisition tasks caused by too long optical fiber inside the optical cable. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The drawings herein are incorporated into the specification and constitute a part of this specification, showing embodiments consistent with the present invention and, together with the specification, are used to explain the principles of the present invention.

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or related technologies. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0025] Figure 1 Schematic structural diagram of an optical cable for sensing seismic waves provided by an embodiment of the present invention;

[0026] Figure 2 One of the cross-sectional views of an optical cable for sensing seismic waves provided by an embodiment of the present invention;

[0027] Figure 3 Another cross-sectional view of an optical cable for sensing seismic waves provided by an embodiment of the present invention;

[0028] Figure 4 Schematic diagram of an optical cable for sensing seismic waves provided by an embodiment of the present invention being impacted by ocean currents;

[0029] Figure 5 Three-dimensional schematic diagram of optical fiber winding provided by an embodiment of the present invention.

[0030] Among them, Figures 1 to 4 The corresponding relationship between the reference numerals and component names in

[0031] 1 Reinforcing member, 2 Elastic sleeve, 3 Optical fiber assembly, 32 Winding section, 34 Straight section, 36 Optical fiber, 38 Compression-resistant member, 4 Protective layer, 42 Steel-plastic composite tape layer, 44 Outer sheath, 5 Counterweight member. Detailed implementation manners

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0033] See Figure 1 、 Figure 2 And Figure 3, an embodiment of the present invention provides an optical cable for sensing seismic waves. The optical cable includes a strengthening member 1, an elastic sleeve 2, an optical fiber assembly 3, a protective layer 4, and a counterweight member 5. The elastic sleeve 2 is sleeved outside the strengthening member 1. The optical fiber assembly 3 is disposed on the outer side surface of the elastic sleeve 2. The optical fiber assembly 3 includes a plurality of winding segments 32 and a plurality of straight segments 34. The winding segments 32 are wound outside the elastic sleeve 2, and the straight segments 34 are disposed along the extending direction of the strengthening member 1. The winding segments 32 and the straight segments 34 are alternately arranged along the extending direction of the strengthening member 1. The protective layer 4 covers the optical fiber assembly 3. The counterweight member 5 is disposed on the protective layer 4.

[0034] The optical cable for sensing seismic waves provided by an embodiment of the present application includes a strengthening member 1, an elastic sleeve 2, an optical fiber assembly 3, a protective layer 4, and a counterweight member 5. The strengthening member 1 can play a role in tensile resistance, and the protective layer 4 can play a role in moisture resistance and external force resistance, so as to protect the optical fiber 36 from being broken. By setting the counterweight member 5, the coupling degree between the optical cable and the environment and the stability of the optical cable in the fluid are effectively enhanced, and at the same time, the flexibility of the optical cable is ensured. Therefore, the optical cable can be used in the marine environment, expanding the scenario of the optical cable sensing seismic wave vibrations. At the same time, since the optical fiber assembly 3 in the present application is divided into winding segments 32 and straight segments 34 and alternately arranged on the outer surface of the elastic sleeve 2, compared with ordinary optical cables, the problem that the seismic wave vibration sensing is insensitive due to too many intermediate layers can be effectively avoided, and at the same time, seismic wave vibrations in different directions can be received, enhancing the seismic wave sensing sensitivity. Compared with other spiral optical cables, the spiral optical cable of the present application can control the length of the optical fiber 36 inside the optical cable by adjusting the winding length and winding interval of the winding segments 32 of the optical fiber assembly 3, avoiding the problem of increased acquisition tasks due to too long optical fiber 36 inside the optical cable.

[0035] In some embodiments, the optical fiber assembly 3 is closely wound on the outer side surface of the elastic sleeve 2.

[0036] In this embodiment, the optical fiber assembly 3 can be closely wound around the outer side surface of the elastic sleeve 2. Of course, it can also be non-closely wound, and the specific winding method can be set according to the actual situation.

[0037] In some embodiments, the optical fiber assembly 3 includes: an optical fiber 36 and a compressive member 38. The optical fiber 36 and the compressive member 38 are arranged side by side on the outer side surface of the elastic sleeve 2.

[0038] In this embodiment, the optical fiber assembly 3 includes an optical fiber 36 and a compressive member 38. The optical fiber 36 and the compressive member 38 are arranged side by side on the outer side surface of the elastic sleeve 2, so that the optical fiber 36 can be protected by the compressive member 38.

[0039] In some embodiments, a cross-section perpendicular to the extending direction of the optical fiber 36 on the optical fiber 36 is a first cross-section, and a cross-section perpendicular to the extending direction of the pressure-resistant member 38 on the pressure-resistant member 38 is a second cross-section, and the area of the first cross-section is smaller than the area of the second cross-section.

[0040] In this embodiment, a cross-section perpendicular to the extending direction of the optical fiber 36 on the optical fiber 36 is a first cross-section, and a cross-section perpendicular to the extending direction of the pressure-resistant member 38 on the pressure-resistant member 38 is a second cross-section, and the area of the first cross-section is smaller than the area of the second cross-section. It can be understood that the outer diameter of the pressure-resistant member 38 is larger than the outer diameter of the optical fiber 36. Therefore, the pressure invading the optical fiber assembly 3 will act on the pressure-resistant member 38 preferentially, thereby improving the lateral pressure resistance of the optical cable and overcoming the problem of weak lateral pressure resistance of other spiral optical cables. At the same time, the external seismic wave vibration can also be transmitted to the optical fiber 36 through the pressure-resistant member 38, enhancing the seismic wave sensing sensitivity of the optical cable.

[0041] In some embodiments, the material of the pressure-resistant member 38 includes TPU material.

[0042] In some embodiments, as Figure 3 shown, the length of the optical fiber assembly 3 on the winding section 32 is less than or equal to 50 m.

[0043] In this embodiment, when winding the optical fiber assembly 3 on the winding section 32, it can be wound according to the length of the optical fiber 36. For example, 50 m of the optical fiber 36 is wound on the winding section 32.

[0044] In some embodiments, the length of the optical fiber assembly 3 on the straight section 34 is less than or equal to 100 m.

[0045] In this embodiment, the length of the optical fiber assembly 3 on the straight section 34 is less than or equal to 100 m. Since the optical fiber arranged on the straight section 34 is approximately parallel to the straight section 34, therefore, the length of the optical fiber assembly 3 on the straight section 34 is approximately equal to the length of the straight section 34.

[0046] In some embodiments, the angle formed by the winding direction of the winding section 32 and the extending direction of the strengthening member 1 is greater than or equal to 85° and less than or equal to 90°.

[0047] In some embodiments, the length of the optical fiber assembly 3 on the winding section 32 is 5 m.

[0048] In some embodiments, the length of the optical fiber assembly 3 on the straight section 34 is 5 m.

[0049] Among them, the three-dimensional schematic diagram of the optical fiber winding is as Figure 5 shown, E is the seismic wave vector, D is the optical fiber winding direction vector, and α is the winding angle. The range limitation of α can be determined by the seismic wave perpendicular to the optical cable direction and the axial strain degree E of the optical fiber sThe relationship is determined as follows:

[0050] E s = E·D = |E|·|D|cos(90 - α); (1)

[0051] It can be seen from the formula (1) that when the fiber winding angle α approaches 90°, the sensing ability of the optical cable to seismic waves perpendicular to the direction of the optical cable reaches the best. Therefore, in this application, the fiber winding angle is limited to 85° - 90°.

[0052] In some embodiments, the lead of the winding section 32 is approximately equal to the sum of the outer diameter of the optical fiber 36 and the outer diameter of the compression member 38, that is, the circumferentially wound optical fibers 36 are closely adjacent. Among them, Figure 3 L1 represents the length of the straight section 34, that is, the close winding interval, L2 represents the lead of the winding section 32, and α represents the included angle formed by the winding direction of the winding section 32 and the extending direction of the strengthening member 1, that is, α is the winding angle of the optical fiber.

[0053] Among them, various values such as the winding length, the length of the straight section 34, the angle of the included angle, and the lead can be adjusted. For example, when the DAS spatial sampling rate is 5m, the length of the optical fiber of the straight section 34 is designed to be 5m, and the length of the wound optical fiber is also 5m, so that the data sampling points of the DAS system are all at the close winding positions, thereby while taking advantage of the spiral optical cable structure, avoiding the increase of the acquisition task due to the too long length of the internal optical fiber 36.

[0054] In some embodiments, the protective layer 4 includes: a steel-plastic composite tape layer 42, which is coated on the outside of the optical fiber assembly 3; an outer sheath 44, which is sleeved on the steel-plastic composite tape layer 42.

[0055] In this embodiment, the protective layer 4 includes a steel-plastic composite tape layer 42 and an outer sheath 44. The steel-plastic composite tape layer 42 is coated on the outside of the optical fiber assembly 3, and the outer sheath 44 is sleeved on the steel-plastic composite tape layer 42, thereby realizing the protection of the optical fiber assembly 3. It can be understood that since the outer diameter of the compression member 38 is larger than the outer diameter of the optical fiber 36, the steel-plastic composite tape layer 42 is coated on the compression member 38, so that the optical fiber 36 does not directly contact the steel-plastic composite tape layer 42, avoiding the abrasion of the optical fiber 36.

[0056] In some embodiments, the material of the outer sheath 44 includes polyethylene.

[0057] In some embodiments, the counterweight member 5 is clamped on the winding section 32 or the straight section 34.

[0058] In some embodiments, the counterweight 2 includes a high-density material piece. It can be understood that for counterweights of the same volume, the greater the density, the stronger the ability to resist ocean current impact. Therefore, the stability of the optical cable installation can be effectively ensured, and the coupling degree between the optical cable and the environment can be enhanced.

[0059] In some embodiments, the counterweight 5 includes tungsten blocks, lead blocks, tungsten packages, and lead packages. The tungsten package includes a nylon package and tungsten grains, and the maximum outer dimension of the tungsten grains is less than or equal to 2 cm; the lead package includes a nylon package and lead grains, and the maximum outer dimension of the lead grains is less than or equal to 2 cm.

[0060] In this embodiment, the counterweight 5 includes tungsten blocks, lead blocks, tungsten packages, and lead packages. The tungsten package is formed by filling tungsten grains with a maximum outer dimension of less than or equal to 2 cm into a nylon package. The lead package is formed by filling lead grains with a maximum outer dimension of less than or equal to 2 cm into a nylon package. The tungsten grains and lead grains have fluidity, and the nylon outer packaging has flexibility. Although their density is lower than that of tungsten blocks and lead blocks, the tungsten packages and lead packages ensure the flexibility of the optical cable.

[0061] In some embodiments, the particle size of the tungsten grains and lead grains is greater than or equal to 60 mm and less than or equal to 90 mm.

[0062] Optionally, the particle size of the tungsten grains is 75 mm.

[0063] It can be understood that the counterweight 5 needs to ensure the ability to resist ocean currents, enhance the coupling degree between the optical cable and the environment, and the stability of the optical cable in the fluid. Therefore, the maximum static friction force of the counterweight 5 is greater than the thrust force received. Among them, the thrust force received by the counterweight 5 can be calculated according to the flow velocity of the ocean current and the area of the counterweight 5. The maximum static friction force of the counterweight 5 can be obtained by calculating the mass of the counterweight 5 and the ocean bottom friction coefficient.

[0064] Specifically, the thrust force received by the counterweight is calculated using the following formula (2):

[0065]

[0066] Among them, F represents the impact force of the ocean current, with the unit kN; k represents the drag coefficient, which is taken as 0.7 when the width and length of the counterweight are approximately equal; γ w represents the unit weight of water, with the unit kN / m 3 ; S represents the force-bearing area of the counterweight, with the unit m 2 ; g represents the acceleration due to gravity, which is selected according to the actual situation. As Figure 4 shown, the arrow represents the direction of the water flow impact, β represents the angle between the water flow impact direction and the flow-blocking surface; v represents the average flow velocity of the water flow cross-section near the flow-blocking surface, with the unit m / s.

[0067] The maximum static friction force of the counterweight can be calculated using the following formula (3):

[0068] f = μ × g × V(ρ1 - ρ2); (3)

[0069] Where f represents the maximum static friction force, with the unit N; μ represents the friction coefficient; ρ1 and ρ2 respectively represent the densities of the counterweight and seawater, with the unit kg / m 3 ; g represents the acceleration due to gravity, with the unit N / kg; V is the volume of the counterweight, with the unit m 3 . The above formulas are all calculated under ideal conditions, and corresponding adjustments need to be made according to the actual situation in actual use.

[0070] When the maximum static friction force f is greater than the thrust F received by the counterweight, the anti-ocean current effect can be achieved. It can be seen from the above formula that the anti-ocean current effect depends on factors such as the force-bearing area and density of the counterweight. Therefore, when actually selecting a counterweight, a suitable counterweight can be selected according to the actual flow rate of the ocean current. For example, tungsten grains with a suitable density can be selected.

[0071] In some embodiments, the reinforcing member 1 includes steel wires; and / or the elastic sleeve 2 includes a thermoplastic polyurethane elastic sleeve 2.

[0072] In some embodiments, as Figure 3 shown, the winding diameter d of the optical fiber assembly 3 around the winding section 32 is less than or equal to 15 mm.

[0073] In this embodiment, a suitable winding diameter and winding angle can be selected according to the minimum bending radius of the optical fiber to prevent the optical fiber from being damaged during winding. For example, the winding diameter of the optical fiber assembly 3 around the winding section 32 is less than or equal to 15 mm.

[0074] In some embodiments, the outer surface of the counterweight 5 is provided with an anti-corrosion layer. By providing the anti-corrosion layer, the service life of the counterweight 5 can be effectively guaranteed, and the use scenario of the optical fiber can be expanded.

[0075] In some embodiments, the winding pitch of the winding section 32 around the outside of the elastic sleeve 2 is equal to the outer diameter of the optical fiber assembly 3. That is, the optical fiber assembly 3 is tightly wound around the outside of the elastic sleeve 2.

[0076] Optionally, the reinforcing member 1 is formed by stranding seven steel wires.

[0077] An embodiment of the present invention provides an optical cable for sensing seismic waves. The optical cable includes a central strengthening member (strengthening member 1), an elastomer (elastic sleeve 2), an optical fiber layer (optical fiber assembly 3), a steel-plastic composite tape, an outer sheath 44, and a counterweight. The central strengthening member is composed of high-strength load-bearing steel wires. The elastomer is wrapped around the outer layer of the central strengthening member. The optical fiber layer is composed of an optical fiber 36 and a compressive member (compressive member 38) with an outer diameter slightly larger than that of the optical fiber 36. The two are wound around the outer layer of the elastomer side by side in a circumferential direction. The steel-plastic composite tape is wrapped around the outer layer of the optical fiber layer. The outer sheath 44 is bonded to the outer layer of the steel-plastic composite tape, and the two form a comprehensive protective layer to play the role of moisture resistance and resistance to external forces. The counterweight is clamped on the outer layer of the outer sheath 44.

[0078] Optionally, the central strengthening member is formed by stranding seven steel wires.

[0079] Optionally, the elastomer is a TPU elastomer.

[0080] Optionally, the winding method of the optical fiber layer on the elastomer is as Figure 3 shown. The optical fiber 36 and the compressive member are closely arranged side by side, and at the same time, they are attached to the surface of the elastomer in an alternating manner of circumferential winding and straight optical fiber 36. The winding interval L1 is 0m - 100m, the winding angle α is 85° - 90°, the length of the optical fiber at the winding segment 32 is 0m - 50m, and the lead L2 is approximately equal to the sum of the outer diameters of the optical fiber 36 and the compressive member 38, that is, the circumferentially wound optical fiber 36 and the compressive member 38 are closely adjacent, and all the numerical values can be adjusted.

[0081] Optionally, the compressive member is made of TPU material and has an outer diameter slightly larger than that of the optical fiber 36. Therefore, the optical fiber 36 does not directly contact the steel-plastic composite tape, avoiding abrasion of the optical fiber 36. At the same time, external seismic wave vibrations can also be transmitted to the optical fiber 36 through the compressive member, enhancing the seismic wave sensing sensitivity of the optical cable. When lateral pressure invades the optical fiber layer, the compressive member will bear the pressure prior to the optical fiber 36, achieving the purpose of protecting the optical fiber 36 and improving the lateral pressure resistance of the optical cable.

[0082] Optionally, the outer sheath 44 is a polyethylene (PE) sheath.

[0083] Optionally, the counterweight is clamped at the position of the circumferential winding or winding interval of the optical fiber 36. The types of counterweights include tungsten blocks and tungsten packages. The tungsten package is formed by filling tungsten grains with an average particle size of about 75mm into a nylon (PA) rectangular bag. The tungsten grains have fluidity, and the nylon outer package has flexibility. Although its density is lower than that of the tungsten block, the tungsten package ensures the flexibility of the optical cable.

[0084] The beneficial effects of this application are:

[0085] 1. In this application, the optical fiber layer of the optical cable is intermittently wound around the outer layer of the elastomer in a circumferential direction. Compared with ordinary optical cables, it can effectively avoid the problem that the middle layer is too thick and insensitive to seismic waves, and at the same time can receive seismic wave signals from different directions, enhancing the seismic wave sensing sensitivity.

[0086] 2. Compared with other spiral optical cables, the spiral optical cable of this application can control the length of the optical fibers 36 inside the optical cable by adjusting the winding length and winding interval of the optical fiber layer, avoiding the problem of increased acquisition tasks caused by the excessive length of the optical fibers 36 inside the optical cable.

[0087] 3. This application adopts a scheme of clamping various types of weights outside the optical cable, effectively enhancing the coupling degree between the optical cable and the environment and the stability of the optical cable in the fluid. At the same time, the flexibility of the optical cable is also ensured (using tungsten-coated and lead-coated weights). Therefore, this optical cable can be used in marine environments, expanding the scenario of the optical cable sensing seismic wave vibrations.

[0088] 4. In addition to designing traditional tensile and lateral pressure resistance schemes such as a central strengthening member, a steel-plastic composite tape, and an outer sheath 44, the optical cable of this application also adds a pressure-resistant body with an outer diameter slightly larger than that of the optical fiber 36 to the optical fiber layer. Therefore, the pressure invading the optical fiber layer will act on the pressure-resistant body preferentially, thereby improving the lateral pressure resistance of the optical cable and overcoming the problem of weak lateral pressure resistance of other spiral optical cables.

[0089] Although this specification contains many specific implementation details, these should not be construed as limiting the scope of any invention or the scope of what is claimed, but are mainly used to describe the features of specific embodiments of a particular invention. Certain features described in multiple embodiments in this specification can also be combined and implemented in a single embodiment. On the other hand, various features described in a single embodiment can also be separately implemented in multiple embodiments or implemented in any suitable sub-combination. In addition, although features can function in certain combinations as described above and are even initially claimed as such, one or more features from the claimed combination can be removed from the combination in some cases, and the claimed combination can refer to a sub-combination or a variant of the sub-combination.

[0090] Thus, specific embodiments of the subject matter have been described. Other embodiments are within the scope of the appended claims. In some cases, the acts recited in the claims can be performed in a different order and still achieve the desired result. In addition, the processes depicted in the drawings are not necessarily in the particular order or sequential order shown to achieve the desired result. In some implementations, multitasking and parallel processing may be advantageous.

[0091] It should be noted that in this document, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements not only includes those elements but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising said element.

[0092] The above are only specific embodiments of the present invention, enabling those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. An optical fiber cable for sensing seismic waves, characterized in that, Comprising: Reinforcing member; Elastic sleeve, sleeved on the outer side of the reinforcing member; Optical fiber assembly, disposed on the outer side surface of the elastic sleeve, the optical fiber assembly includes a plurality of winding segments and a plurality of straight segments, the winding segments are wound around the outer side of the elastic sleeve, the straight segments are arranged along the extending direction of the reinforcing member, and the winding segments and the straight segments are alternately arranged along the extending direction of the reinforcing member; Protective layer, covering the optical fiber assembly; Counterweight member, disposed on the protective layer.

2. The optical fiber cable for sensing seismic waves according to claim 1, characterized in that, The optical fiber assembly includes: Optical fiber and compressive member, the optical fiber and the compressive member are arranged side by side on the outer side surface of the elastic sleeve.

3. The optical fiber cable for sensing seismic waves according to claim 2, characterized in that, The cross-section perpendicular to the extending direction of the optical fiber on the optical fiber is the first cross-section, and the cross-section perpendicular to the extending direction of the compressive member on the compressive member is the second cross-section, and the area of the first cross-section is smaller than the area of the second cross-section.

4. The optical cable for sensing seismic waves according to claim 2, characterized in that, The material of the compressive member includes TPU material.

5. The optical cable for sensing seismic waves according to claim 1, characterized in that, The length of the optical fiber assembly of the winding segment is less than or equal to 50 m; and / or The length of the optical fiber assembly of the straight segment is less than or equal to 100 m; and / or The angle formed by the winding direction of the winding segment of the optical fiber assembly and the extending direction of the reinforcing member is greater than or equal to 85° and less than or equal to 90°.

6. The optical cable for sensing seismic waves according to claim 1, characterized in that, The protective layer includes: Steel-plastic composite tape layer, covering the outer side of the optical fiber assembly; Outer sheath, sleeved on the steel-plastic composite tape layer.

7. The optical cable for sensing seismic waves according to claim 6, wherein, The material of the outer sheath includes polyethylene.

8. The optical cable for sensing seismic waves according to claim 1, characterized in that, The counterweight member is clamped on the winding segment or the straight segment.

9. The optical cable for sensing seismic waves according to claim 1, wherein, The counterweight member includes tungsten blocks, lead blocks, tungsten packages and lead packages, the tungsten package includes a nylon package and tungsten grains, and the maximum outer dimension of the tungsten grains is less than or equal to 2 cm; The lead package includes a nylon package and lead grains, and the maximum outer dimension of the lead grains is less than or equal to 2 cm.

10. The optical cable for sensing seismic waves according to any one of claims 1 to 9, characterized in that, The reinforcing member includes steel wire; and / or The elastic sleeve includes a thermoplastic polyurethane elastic sleeve; The winding diameter of the optical fiber assembly of the winding segment is less than or equal to 15 mm; The outer surface of the counterweight member is provided with an anti-corrosion layer; The winding pitch of the winding segment wound around the outer side of the elastic sleeve is equal to the outer diameter of the optical fiber assembly.

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