Optical fiber micro-logging device and method

Abstract

The present invention provides a fiber optic micro-logging method and device, which includes: an optical cable, a distributed optical fiber vibration demodulator, and a probe rod; the probe rod is cylindrical, and the optical cable is densely wound helically on the side of the probe rod; the head end of the optical cable is connected to the distributed optical fiber vibration demodulator, and the tail end of the optical cable is lowered into the well to be measured. The present invention solves the problem of inelastic deformation of shallow formations caused by high-energy excitation and the inability of seismic wave signals to be transmitted to the bottom of the well to be measured due to low-energy excitation; at the same time, it improves the spatial resolution of the distributed optical fiber vibration demodulator for the formation; the probe rod adopts a cylindrical shape, which better conforms to the actual shape of the well to be measured and is more convenient for actual well descent. The optical cable is helically embedded in the probe rod, so that the longer length of optical cable can pick up the sound wave signal acting on the probe rod, and better receive seismic signals.

Description

Technical Field

[0001] The present invention relates to the technical field of seismic exploration, and in particular to an optical fiber micro-logging device and method for seismic exploration. Background Art

[0002] In seismic exploration, efficient and accurate acquisition of earthquake-related information is crucial for earthquake analysis, monitoring, and early warning. Conventional wellbore seismic exploration involves collecting seismic wave information through surface excitation and in-well reception to determine near-surface geophysical parameters. Traditional well logging methods involve lowering a cable equipped with multiple piezoelectric geophones to the bottom of the well, with the geophones spaced 2 to 5 meters apart. Alternatively, a cable is attached to the end of the cable for testing, and the cable is lowered into the well until the weight reaches the bottom. The cable has a depth scale attached to the lead, and after firing one or several shots, the cable is raised to the next depth. To increase the resolution of the measured formation, the cable must be raised multiple times. Consequently, traditional well logging methods are cumbersome, have low spatial resolution, and are ineffective in acquiring seismic signals. Summary of the Invention

[0003] The present invention provides an optical fiber micro-logging method and device, which solves the problem that seismic wave energy cannot be collected efficiently and centrally in traditional seismic exploration.

[0004] An optical fiber micro-logging method comprises the following steps:

[0005] S1: Determine the type of probe rod, structure and length of optical cable according to the depth of the well to be measured. When the well is deep, a combination of probe rod and optical cable is used;

[0006] S2: Connect the head end of the optical cable to the distributed optical fiber vibration demodulator, and tightly wind the optical cable spirally around the detection unit on the detection rod, and fix the optical cable and the detection unit with adhesive;

[0007] S3: After installation, lower the optical cable and the probe rod into the casing, making the probe rod parallel to the well wall to be measured (shallow well micro-logging), and push the remaining optical cable against the inner wall of the casing (deep well seismic exploration);

[0008] S4: Turn on the distributed fiber optic sensor demodulator and use low-energy excitation (heavy hammer, etc.) to conduct micro-well logging production in the shallow layer to avoid inelastic deformation of the shallow surface. Use high-energy excitation (well gun, source vehicle, etc.) to conduct seismic exploration and production in the deep well section to avoid insufficient seismic wave energy to reach the bottom of the well to be measured;

[0009] Furthermore, in step S1, when the well depth is shallow, only the probing rod detection method is used;

[0010] Furthermore, if a probe rod is used for detection alone, the first section of the probe rod optical cable is connected to the distributed optical fiber vibration demodulator in steps S2 and S3, the probe rod is lowered to the inner wall of the casing, and the well to be tested is filled with sand to ensure good coupling between the probe rod and the formation;

[0011] Furthermore, in step S1, when the well is deep, an optical cable can be used for downhole detection;

[0012] Furthermore, if the optical cable detection method is used, the head end of the optical cable is connected to the distributed optical fiber vibration demodulator in steps S2 and S3, and the optical cable is lowered into the inner wall of the casing so that the optical cable is pushed against the casing wall.

[0013] The working principle of this solution is: by densely winding the optical cable spirally on the detection unit of the detection rod, when the seismic signal excited by the ground is transmitted to the detection rod, the detection rod will drive the optical cable to vibrate and receive the transmitted seismic signal; the combination of low-energy excitation (heavy hammer, etc.) for shallow micro-logging production and high-energy excitation (well gun, source car, etc.) for deep well section seismic exploration and production solves the problem of inelastic deformation of shallow formations caused by high-energy excitation and the inability of seismic wave signals to be transmitted to the bottom of the well to be measured due to low-energy excitation; at the same time, in this technical solution, the optical cable is spirally arranged in the detection unit, and since the optical cable is in the direction of the formation The optical fiber vibration demodulator has been compressed, and the spatial resolution of the distributed optical fiber vibration demodulator along the axis of the optical cable is constant, that is, the spatial resolution of the distributed optical fiber vibration demodulator for the formation is improved; since the detection rod has a certain weight, it is very convenient to put the optical cable into the well to be measured during seismic detection, and in the process of lowering the optical cable into the well and lifting the cable, it can prevent the optical cable from being broken or deformed due to excessive friction and tension; the detection rod adopts a cylindrical shape, which is more in line with the actual shape of the well to be measured and is more convenient for actual lowering into the well. The optical cable is spirally embedded in the detection rod, so that a longer length of optical cable can pick up the sound wave signal acting on the detection rod, and better receive seismic signals.

[0014] The present invention provides an optical fiber micro-logging device, comprising: a distributed optical fiber vibration demodulator, an optical cable and a detection rod; the detection rod is cylindrical; the head end of the optical cable is connected to the distributed optical fiber vibration demodulator, and the middle part of the optical cable is spirally and densely wound around the detection unit on the detection rod.

[0015] A further optimization solution is that there is no gap between the spirally densely wound optical cables and the cables are neatly wound;

[0016] A further optimization solution is that the detection rod is composed of several cylindrical detection units;

[0017] The cylindrical detection unit consists of a shell, a mass block and an elastomer. The mass block and the elastomer are cylindrical. The upper and lower bases of the mass block are each connected to an elastomer and then wrapped in the shell. The side of the elastomer is densely wound with a spiral optical cable.

[0018] The shell is provided with an optical cable entrance and exit. After the optical cable enters the shell, it is spirally and densely wound around the top elastic body. Then the optical cable follows the mass block to reach the elastic body at the bottom of the mass block. After the optical cable is wound around the elastic body, it enters the next detection unit from the exit on the shell.

[0019] A further optimized solution is that the elastomer is a thermoplastic elastomer and the mass block is made of metal.

[0020] The shell is made of thin metal, polymer material and nylon material; it can reduce the weight of the detection unit and at the same time play a supporting role for the mass block and the elastic body.

[0021] A further optimized solution is that the diameter of the mass block is smaller than the diameter of the elastic body.

[0022] The elastic body is arranged on both sides of the mass block, and the mass block and the elastic body are fixed with an adhesive. The elastic body is cylindrical and made of thermoplastic elastomer, polyurethane elastomer, styrene-butadiene rubber, silicone rubber, etc., in order to make the elastic body produce greater deformation for seismic waves of the same magnitude. The diameter of the mass block is smaller than that of the elastic body, which facilitates the connection of the optical cable to the next elastic body.

[0023] The mass block is cylindrical and made of lead, copper, iron or the like.

[0024] When seismic wave signals act on the detection unit, the mass block remains stationary due to inertia, forcing the elastic body on one side of the mass block to shorten and the elastic body on the other side to lengthen, which in turn causes the optical cable wrapped around the elastic body to change along its length, forming a push-pull structure. This converts the relative motion between the housing and the mass block into optical fiber tension, acting as a ring energy element. The detection rod acts as a transducer element, converting seismic waves along the formation direction into strain along the optical fiber axis, increasing the signal energy acting on the optical cable. At the same time, the combination of the detection rod and the vertically lowered optical cable can realize the combination of shallow well micro-logging and deep well seismic exploration, achieving low-energy excitation in shallow wells and high-energy excitation in deep wells in the same well, avoiding the problems of inelastic and nonlinear deformation of the optical cable in shallow well sections and insufficient excitation energy in deep well sections.

[0025] A further optimized solution is that the detection rod is composed of a single cylinder, and the side of the cylinder has two diameters alternately distributed, and the diameter difference is greater than or equal to twice the diameter of the optical cable;

[0026] The optical cable is spirally wound around a cylindrical structure with a smaller diameter. This allows for longer optical cables to be installed in specific areas, allowing the longer length of fiber to pick up the acoustic wave signals acting on the probe rod and better receive seismic signals. The lengths of the two cylindrical structures can be adjusted according to the well depth and stratum structure.

[0027] A further optimized solution is that the detection rod is made of polyamide or polyethylene.

[0028] The material of the detection rod is polyamide or polyethylene, which has a greater hardness and can support the optical cable; at the same time, the detection rod made of polyamide or polyethylene reduces the cost of use.

[0029] A further optimization solution is to use adhesive to fill the gap between the optical cable and the cylinder, so that the optical cable and the detection rod are coupled with each other; when the detection rod receives the seismic signal, it can effectively transmit the seismic signal to the optical cable.

[0030] A further optimization solution is that the optical cable uses a bare optical fiber or a bend-insensitive optical cable with a diameter of 0.9 mm to 2 mm.

[0031] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0032] 1. The combination of low-energy excitation (heavy hammer, etc.) for shallow micro-logging production and high-energy excitation (well gun, source vehicle, etc.) for deep well section seismic exploration and production solves the problems of high-energy excitation causing inelastic deformation of shallow formations and low-energy excitation causing the inability of seismic wave signals to be transmitted to the bottom of the well to be tested.

[0033] 2. The optical cable is spirally installed in the detection unit. Since the optical cable is compressed along the formation direction, and the spatial resolution of the distributed optical fiber vibration interrogator along the cable axis is constant, the spatial resolution of the distributed optical fiber vibration interrogator for the formation is improved.

[0034] 3. The optical cable wrapped around the probe structure improves the optical cable's ability to respond to dynamic signals of seismic waves along the formation direction;

[0035] 4. The optical cable is wound around the detection rod structure to solve the problem of the optical cable being broken or deformed due to excessive friction and tension during the process of lowering the optical cable into the well and lifting the cable. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention.

[0037] Figure 1 It is a structural schematic diagram of the downhole optical cable detection device of the present invention.

[0038] Figure 2 Schematic diagram of the structure of detection rod A.

[0039] Figure 3 Schematic diagram of the structure of detection rod B.

[0040] In the attached Figure 1 Middle: 1-optical cable, 2-distributed optical fiber vibration demodulator, 3-detection rod, 31-detection rod A, 32-detection rod B, 4-detection unit, 41-housing, 42-mass block, 43-elastic body, 5-helical dense winding part of optical cable, 6-well to be measured. DETAILED DESCRIPTION

[0041] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with examples and drawings. The exemplary embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0042] Example 1:

[0043] An optical fiber micro-logging method comprises the following steps:

[0044] S1: Determine the type of probe rod, structure and length of the optical cable according to the depth of the well to be measured. If high spatial resolution detection of shallow formations is required, a combination of probe rod and optical cable is used. If high spatial resolution of shallow formations is not required, only the optical cable is used in the vertical well.

[0045] S2: Connect the head end of the optical cable to the distributed optical fiber vibration demodulator, and tightly wind the optical cable spirally around the detection unit on the detection rod, and fix the optical cable and the detection unit with adhesive;

[0046] S3: After installation, lower the optical cable and the probe rod into the casing, making the probe rod parallel to the well wall to be measured (shallow well micro-logging), and push the remaining optical cable against the inner wall of the casing (deep well seismic exploration);

[0047] S4: Turn on the distributed fiber optic sensor demodulator and use low-energy excitation (heavy hammer, etc.) to conduct micro-well logging production in the shallow layer to avoid inelastic deformation of the shallow surface. Use high-energy excitation (well gun, source vehicle, etc.) to conduct seismic exploration and production in the deep well section to avoid insufficient seismic wave energy to reach the bottom of the well to be measured;

[0048] Furthermore, if there is no requirement for high spatial resolution of shallow strata, the head end of the optical cable is connected to the distributed optical fiber vibration demodulator in steps S2 and S3, and the optical cable is lowered into the inner wall of the casing so that the optical cable is pushed against the casing wall.

[0049] This embodiment combines low-energy excitation (heavy hammer, etc.) for shallow micro-logging production with high-energy excitation (well gun, source vehicle, etc.) for deep well section seismic exploration and production, thereby solving the problem that high-energy excitation causes inelastic deformation of shallow formations and low-energy excitation causes seismic wave signals to be unable to be transmitted to the bottom of the well to be measured; the optical cable is spirally arranged in the detection unit, because the optical cable is compressed along the formation direction, and the spatial resolution of the distributed optical fiber vibration demodulator along the axis of the optical cable is constant, that is, the spatial resolution of the distributed optical fiber vibration demodulator for the formation is improved; the detection rod is placed in the well to be measured, and at the same time, the detection rod is parallel to the wall of the well to be measured, which is conducive to matching with the terrain to be measured, and the remaining optical cable is pushed against the casing wall to couple the optical cable and the formation to each other, so as to better receive seismic signals; turning on the distributed optical fiber vibration demodulator, near-surface micro-logging production and deep well seismic exploration and production can be carried out.

[0050] Example 2:

[0051] like Figure 1 As shown, a fiber optic micro-logging device includes: an optical cable 1, a distributed optical fiber vibration demodulator 2 and a detection rod 3; the detection rod 3 is a cylinder; the head end of the optical cable 1 is connected to the distributed optical fiber vibration demodulator 2, and the middle part of the optical cable 1 is spirally and densely wound around the side of the detection rod.

[0052] The structure of the probe rod 3 in this embodiment is as follows Figure 2 As shown, the detection rod A31 is composed of several cylindrical detection units 4;

[0053] The cylindrical detection unit consists of a housing 41, a mass 42, and an elastic body 43. The mass 42 and elastic body 43 are cylindrical, with the upper and lower bases of the mass 42 each connected to an elastic body 43 before being wrapped within the housing 41. A tightly wound portion 5 of the optical cable is provided on the side of the elastic body 43. The mass 42 and elastic body 43 are fixed with an adhesive.

[0054] The shell 41 is made of thin metal, polymer material, or nylon material and is cylindrical in shape. The use of thin metal, polymer material, or nylon material is to reduce the weight of the detection unit and to support the mass block 42 and the elastic body 43 .

[0055] The elastomer 43 is a thermoplastic elastomer, which can be polyurethane elastomer, styrene-butadiene rubber, silicone rubber, etc., so that the elastomer can produce greater deformation for seismic waves of the same size, thereby acting on the optical cable wrapped around the elastomer; the mass block 42 is made of metal, and the material is lead, copper, iron, etc.

[0056] The diameter of the mass block 42 is smaller than the diameter of the elastic body 43 . The length and diameter of the mass block 42 and the elastic body 43 can be adjusted according to the well depth and the bottom structure.

[0057] When the seismic wave signal acts on the detection unit, the mass block 42 remains stationary due to inertia, thereby forcing the elastic body 43 on one side to shorten and the elastic body 43 on the other side to lengthen, causing the optical cable 1 wrapped around the elastic body 43 to change along the length direction, forming a push-pull structure, and converting the relative axial movement between the shell 41 and the mass block 42 into optical fiber tension, that is, it acts as a transducer element; the optical cable is spirally and densely wound around the elastic body of the detection unit; this is to set a longer length of optical fiber in a specific area, so that the longer length of optical fiber can pick up the sound wave signal acting on the detection rod and better receive seismic signals.

[0058] Example 3

[0059] The structure of the probe rod 3 in this embodiment is as follows Figure 3 As shown, the probe rod B32 is constructed from a single cylinder with two alternating diameters on its sides, the difference being twice the diameter of the optical cable 1. The smaller diameter structure is provided with a spirally wound, tightly wound optical cable. The probe rod B32 is made of polyamide or polyethylene. Adhesive is used to fill the gap between the optical cable 1 and the spiral groove. Furthermore, as a preferred embodiment of the present invention, the optical cable 2 utilizes single-mode, tight-buffered optical fiber with a diameter of 0.9 to 2 mm.

[0060] In this embodiment, the probe rod B32 is made of polyamide or polyethylene, which is relatively hard and provides support for the optical cable 1, while also reducing costs. The optical cable 1 is spirally wound around a cylindrical structure with a smaller diameter. Longer lengths of optical cable 1 are installed in specific areas, allowing them to pick up the acoustic wave signals acting on the probe rod, thereby better receiving seismic signals.

[0061] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions based on the principles of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. An optical fiber micro-logging method based on an optical fiber micro-logging device, characterized in that: The optical fiber micro-logging device comprises: an optical cable (1), a distributed optical fiber vibration demodulator (2) and a detection rod (3); the detection rod (3) is a cylinder, and detection units are spaced apart on the side of the detection rod (3), and the optical cable (1) is spirally and densely wound around the detection unit; the head end of the optical cable (1) is connected to the distributed optical fiber vibration demodulator (2), and the tail end of the optical cable is lowered into the well to be measured (6); The spiral dense winding means that there is no gap between the optical cables and the cables are neatly distributed; The detection rod is composed of a plurality of cylindrical detection units (4) spliced ​​together; The cylindrical detection unit is composed of a housing (41), a mass block (42) and an elastic body (43); the mass block (42) and the elastic body (43) are cylindrical; the upper and lower bases of the mass block (42) are each connected to an elastic body (43) and then wrapped in the housing (41); the optical cable (1) is spirally and densely wound around the side of the elastic body (43); The elastic body (43) is a thermoplastic elastomer, and the mass block (42) is made of metal; The diameter of the mass block (42) is smaller than the diameter of the elastic body (43); The optical cable (1) adopts a bare optical fiber or a bend-insensitive optical cable with a diameter of 0.9 mm to 2 mm; The method comprises the following steps: S1: Determine the type of probe, structure and length of the optical cable according to the depth of the well to be measured; S2: The head end of the optical cable is connected to the distributed optical fiber vibration demodulator, and the optical cable is tightly wound spirally around the detection rod; S3: After installation, place the fiber optic cable tail end and the probe rod into the casing and then into the well to be tested. Make sure the probe rod is parallel to the well wall and push the fiber optic cable tail end against the inner wall of the casing. S4: Turn on the distributed optical fiber sensor demodulator, use low energy excitation to perform logging production in the layer where the probe rod is located, and use high energy excitation to perform logging production in the layer below the probe rod at the end of the optical cable.

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