A method for connecting downhole optical cables

Abstract

The present invention relates to a method for splicing downhole optical cables, comprising: splicing and coating the optical fibers of an inner steel pipe; splicing the inner steel pipe; and splicing the sheath steel pipe. After the sheath steel pipe is spliced, fiber break splicing and protection are achieved. The present invention can splice downhole oil well optical cables, eliminating the need for bulky optical cable splicing boxes at the splicing points. Furthermore, the splicing locations have excellent pressure resistance and sealing properties, meeting the high-temperature and high-pressure requirements of downhole use, and are particularly well-suited for installation in confined underground spaces. The present invention can be applied in the field of oilfield wellbore monitoring.

Description

Technical Field

[0001] The present invention relates to the technical field of oilfield wellbore monitoring, in particular to a downhole optical cable connection method. Background Art

[0002] Oil well optical cables are a crucial component of oil and gas well fiber optic sensing and monitoring systems, serving as channels for sensing various parameters and transmitting information downhole. Specialized fixtures are typically used to tie oil well optical cables to the outer wall of the casing or tubing, allowing the cables to be lowered into the well along with the casing or tubing. Due to the harsh downhole construction conditions and the small diameter of the optical cables, they can be easily damaged by equipment, abrasion from rock or casing, or other mechanical forces during construction, leading to breakage of the cables and the internal optical fibers. In these cases, the cables and the internal optical fibers need to be spliced ​​to ensure continuity and integrity, or the broken cables need to be removed and replaced with new ones to meet subsequent fiber optic wellbore monitoring requirements.

[0003] When optical cables are lowered into the well along with the oil pipeline, they are sometimes required to pass through a packer located in a certain area of ​​the well, where they must be cut and spliced. For optical cables laid on the ground, buried directly in the soil, aerially, or underwater, when splicing is required, a splicing box is typically installed at the splicing location. After the optical fibers are spliced, they are protected with heat shrink tubing and placed inside the splicing box. The splicing box is designed to be waterproof and dustproof according to the application environment, providing excellent protection for the fiber splicing points and cable connectors, preventing damage to the optical fibers at the splice location and affecting their normal communication functions. However, commonly used optical cable splice boxes are large in size, exceeding the space that can be accommodated in the wellbore or wellbore, and cannot adapt to the installation environment of the narrow space of the oil and gas well; secondly, as the depth of the oil and gas well increases, the downhole temperature also gradually increases, usually exceeding 100°C or higher. Commonly used splice boxes and internal optical fiber heat shrink tubing are difficult to meet the requirements of long-term tolerance to high temperatures downhole; thirdly, the pressure downhole in oil and gas wells is relatively high, almost exceeding the pressure in all terrestrial and underwater optical cable operating environments. Although commonly used optical cable splice boxes have a certain degree of sealing, they are far from meeting the sealing requirements of the high-pressure environment downhole.

[0004] Therefore, there is an urgent need to study a fiber optic cable splicing method that can adapt to the narrow space underground and meet the sealing performance requirements of the high temperature and high pressure environment underground, so as to make the underground optical cable splicing safe and reliable and ensure that it meets the subsequent optical fiber monitoring applications. Summary of the Invention

[0005] In response to the above problems, the purpose of the present invention is to provide a downhole optical cable splicing method, which can be used to splice downhole oil well optical cables. There is no need to install a bulky optical cable splicing box at the splicing point, and the optical cable splicing part has good pressure resistance and sealing performance, meeting the high temperature and high pressure use environment downhole, and is especially suitable for the construction and installation requirements of the narrow space downhole.

[0006] To achieve the above-mentioned purpose, the present invention adopts the following technical solutions: a downhole optical cable splicing method, which includes: splicing and coating the optical fiber of the inner steel pipe; splicing the inner steel pipe; splicing the sheath steel pipe, and after completing the splicing of the sheath steel pipe, the broken fiber splicing and protection work is realized.

[0007] Furthermore, the optical cable is composed of an optical fiber, an inner steel pipe, a protective steel pipe and an encapsulating sheath from the inside to the outside;

[0008] The optical fiber 1 is a 150°C or 300°C optical fiber;

[0009] The inner steel pipe is a longitudinally welded stainless steel pipe, the sheath steel pipe is a longitudinally welded stainless steel pipe, and the packaging sheath is made of PP or FEP.

[0010] Furthermore, the optical fiber of the inner steel pipe is connected and coated, including:

[0011] The first and second ends of the cut optical cable are stripped of the encapsulating sheath, the protective steel tube and the inner steel tube respectively, the optical fiber is cut out from the inner steel tube and pulled out, and coated with protection, the optical fiber is retained for splicing, and a drawing diameter reducing portion is formed at the cut end of the inner steel tube;

[0012] Insert the pre-prepared first sleeved steel pipe into the inner steel pipe from the second end of the cut length, exposing the optical fiber for standby use;

[0013] The exposed optical fiber is connected and protected by secondary coating, and the optical fiber attenuation test is carried out on the connected and coated connection points. After meeting the use requirements, the optical fiber connection is completed;

[0014] Gently push the first sleeve steel tube over the optical fiber splicing point and sleeve it onto the outside of the splicing point until the first sleeve steel tube reaches the drawing and reducing part of the inner steel tube;

[0015] The contact points of both ends of the first sleeve steel pipe and the inner steel pipe are respectively welded for protection. After welding, the optical fiber attenuation test is performed again. If the test is qualified, the connection protection of the inner steel pipe is completed.

[0016] Furthermore, the cut length of each layer at the first end of the cut optical cable is smaller than the cut length of each layer at the second end.

[0017] Furthermore, the step of stripping the packaging sheath from the first and second ends of the cut optical cable comprises:

[0018] Use a tool to peel off the encapsulating sheath, peel off a length of the first end of the encapsulating sheath, and peel off another length of the second end of the encapsulating sheath without damaging the encapsulating sheath and save it for later use, exposing the sheathed steel pipe, and then use alcohol to clean the oil stains on the surface of the sheathed steel pipe;

[0019] Select a second sleeve steel pipe with the same material and wall thickness as the sheath steel pipe. The inner diameter of the second sleeve steel pipe must be larger than the outer diameter of the sheath steel pipe, and the length of the second sleeve steel pipe must be between the stripping lengths of the first end and the second end.

[0020] Put the prepared second sleeved steel pipe into the sheath steel pipe from the second end of the packaging sheath and set it aside.

[0021] Furthermore, the method of stripping the sheath of the first and second ends of the cut optical cable and then stripping the sheath of the steel tube comprises:

[0022] The sheath steel pipe at the second end is circularly cut from the cut-off point, with the cut-off length being shorter than the cut-off length of the encapsulating sheath at the second end, and the cut sheath steel pipe is pulled out from the inner steel pipe, leaving the inner steel pipe;

[0023] Cutting the sheath steel pipe at the first end from the cutoff point, wherein the cutoff length is less than the cutoff length of the encapsulating sheath at the first end, pulling the cut sheath steel pipe out of the inner steel pipe, and retaining the inner steel pipe;

[0024] A first sleeve steel pipe with the same material, wall thickness and outer diameter as the inner steel pipe is selected for standby use. The length of the first sleeve steel pipe is between the cut length at the first end and the cut length at the second end of the sheath steel pipe.

[0025] Furthermore, the method of stripping the sheath of the first and second ends of the cut optical cable and then stripping the sheath of the steel tube comprises:

[0026] Select a tube drawing die, pre-treat the end of the inner steel tube at the second end, insert the prepared drawing die, and draw and reduce the inner steel tube. After multiple drawing processes, measure the outer diameter, make the outer diameter reach the inner diameter of the first sleeved steel tube, and the difference does not exceed a first preset value, stop drawing, and remove the drawing die;

[0027] The inner steel pipe end at the first end is pre-treated and inserted into the prepared drawing die, and the inner steel pipe is drawn and reduced in diameter. After multiple drawing processes, the outer diameter is measured to make the outer diameter smaller than the inner diameter of the sleeved steel pipe, and the difference does not exceed a second preset value. The drawing is stopped and the drawing die is removed.

[0028] Furthermore, after the encapsulating sheath and the protective steel tube are stripped off the first and second ends of the cut-off optical cable in turn, the method for stripping off the inner steel tube is as follows: the inner steel tube is cut off from the cut-off point respectively, and the first length is cut off from one end of the inner steel tube and the second length is cut off from the other end, the cut inner steel tube is pulled out from the optical fiber, and the optical fiber is retained for optical fiber splicing.

[0029] Furthermore, the connecting of the inner steel pipe includes: gently pushing the pre-prepared second sleeve steel pipe through the first sleeve steel pipe connected to the inner steel pipe to a preset position, welding and protecting the contact points between the two ends of the second sleeve steel pipe and the sheath steel pipe, and performing an optical fiber attenuation test after welding. If the test is qualified, the connection protection of the sheath steel pipe is completed.

[0030] Furthermore, the splicing of the sheathed steel pipe includes: using a material similar to the packaging sheath to encapsulate and protect the splicing portion of the sheathed steel pipe so that the overall size is close to the size of the original optical cable packaging sheath, performing an optical performance test, and completing all splicing protection after the test is qualified.

[0031] The present invention has the following advantages due to the adoption of the above technical solution:

[0032] 1. The optical fiber splice of the present invention is coated with a heat-resistant resin for protection, and there is no need to install a traditional heat shrink tubing, so that the optical fiber splice point is well protected. At the same time, the optical fiber at this part still has good flexibility and is light in weight, and the stress on the optical fiber will not be increased due to the weight of the heat shrink tubing.

[0033] 2. The present invention uses a double-layer stainless steel pipe to protect the optical fiber fusion section, and there is no need to install an optical cable splicing box. The steel pipe has a small diameter and can meet the installation requirements of the narrow space underground; it avoids the huge amount of engineering work and high costs of replacing the optical cable due to cable breakage, thereby improving engineering efficiency.

[0034] 3. The present invention uses a double-layer stainless steel tube to protect the fiber fusion splice section, which has excellent high-temperature and corrosion resistance and can meet the high-temperature and high-corrosion application environment of underground mines. The steel tube is welded to the original steel tube of the optical cable with polarity, which has good sealing performance and high compressive and tensile strength, better meeting the sealing requirements of underground high-pressure environments. This improves the reliability of optical cable splicing in underground high-temperature, high-pressure, and highly corrosive environments.

[0035] 4. The present invention can restore the connection of disconnected special high-temperature resistant optical fibers, allowing them to regain the overall sensing and monitoring functions without affecting the tensile strength or distributed monitoring functions. In addition, the original armored steel pipe protection measure can better protect the internal optical fiber connection and ensure the overall performance of the oil well optical cable. The connected optical fiber and steel pipe optical fiber unit can be used for subsequent production and engineering applications without the need to re-purchase new optical fibers and materials or re-produce the oil well optical cable, thus saving costs and reducing waste.

[0036] 5. In addition to being able to splice and protect special high-temperature resistant optical fibers of the same type, the present invention can also selectively splice and protect optical fibers of different types. For example, it can be used in a combination of applications in which some are conventional optical fibers and some are special optical fibers. This avoids the dilemma of having to use all special optical fibers due to the need for special optical fibers, and can greatly save engineering investment costs.

[0037] 6. In addition to being applied to oil well optical cables in the oil well field, the present invention can also be applied to other special optical cable application fields, such as furnace body monitoring, cable body monitoring, pipeline leakage monitoring, etc., as well as splicing in the production process of special optical cables.

[0038] In summary, the present invention can be widely used in the existing oil field wellbore monitoring field. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a flow chart of a method for connecting downhole optical cables in an embodiment of the present invention;

[0040] Figure 2 is a schematic diagram of the optical cable structure in an embodiment of the present invention;

[0041] Reference numerals:

[0042] 1—optical fiber; 2—inner steel pipe; 3—sheath steel pipe; 4—encapsulating sheath; 5—first connecting steel pipe; 6—second connecting steel pipe. DETAILED DESCRIPTION

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field are within the scope of protection of the present invention.

[0044] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0045] In view of the problem that the existing optical cable splicing box and heat shrink tubing protection method cannot adapt to the high-temperature and high-pressure working environment requirements of the well, and the splicing box is large and cannot adapt to the installation environment of the narrow space underground, the present invention provides a method for splicing downhole optical cables, which belongs to oil well optical cables for oil field wellbore monitoring, including: splicing and coating the optical fiber of the inner steel pipe; splicing the inner steel pipe; splicing the sheath steel pipe. After the splicing of the sheath steel pipe is completed, the special high-temperature resistant optical fiber break splicing and protection work is achieved. The present invention can splice downhole oil well optical cables, and there is no need to install a bulky optical cable splicing box at the splicing point. The splicing part of the optical cable has good pressure resistance and sealing performance, meeting the high-temperature and high-pressure use environment underground, and is particularly suitable for the construction and installation requirements of the narrow space underground.

[0046] In one embodiment of the present invention, a method for connecting downhole optical cables is provided. In this embodiment, the method is to connect the inside out first, such as Figure 1 As shown, the method includes the following steps:

[0047] 1) Splice and coat the optical fiber in the inner tube;

[0048] 2) Connect the inner steel pipe;

[0049] 3) The sheath steel pipe is connected. After the sheath steel pipe connection is completed, the special high-temperature resistant optical fiber broken fiber connection and protection work is achieved.

[0050] In the above embodiment, Figure 2 As shown, the optical cable is composed of optical fiber 1, inner steel tube 2, sheath steel tube 3 and encapsulating sheath 4 from inside to outside.

[0051] Optical fiber 1 is a 150°C or 300°C optical fiber.

[0052] The inner steel pipe 2 is a longitudinally welded stainless steel pipe, which has the characteristics of sealing and withstanding radial high pressure, and provides protection for the optical fiber 1.

[0053] The sheath steel pipe 3 is a longitudinally welded stainless steel pipe that provides mechanical and environmental protection for the optical cable.

[0054] The encapsulating sheath 4 is made of PP or FEP and provides mechanical and friction protection for the sheathed steel pipe 3 (round or square).

[0055] In the above step 1), the optical fiber in the inner tube is connected and coated, including the following steps:

[0056] 1.1) Remove the encapsulating sheath 4, protective steel tube 3, and inner steel tube 2 from the first and second ends of the cut optical cable, cut the optical fiber 1 and pull it out from the inner steel tube 2, apply protective coating, retain the optical fiber 1 for splicing, and form a drawing reduction portion at the cut end of the inner steel tube 2;

[0057] wherein the cut length of each layer on the first end is smaller than the cut length of each layer on the second end;

[0058] 1.2) Insert the pre-prepared first sleeved steel tube 5 from the second end of the cut length into the inner steel tube 2, exposing the optical fiber 1 for later use;

[0059] 1.3) The exposed optical fiber 1 is spliced ​​and protected with secondary coating, and the spliced ​​and coated splice points are tested for optical fiber attenuation. Once the splicing meets the requirements, the splicing of optical fiber 1 is completed.

[0060] 1.4) Gently push the first sleeve steel tube 5 over the optical fiber 1 connection point and sleeve it onto the outside of the connection point until the first sleeve steel tube 5 reaches the drawing and reducing part of the inner steel tube 2;

[0061] 1.5) The contact points of both ends of the first sleeve steel pipe 5 and the inner steel pipe 2 are respectively welded for protection. After welding, the optical fiber attenuation test is performed again. If the test is qualified, the connection protection of the inner steel pipe 2 is completed.

[0062] In the above step 1.1), the encapsulation sheath 4 is stripped from the first and second ends of the cut optical cable, which includes the following steps:

[0063] 1.1.1.1) Use a tool to peel off the encapsulating sheath 4. Peel off a length (e.g., 0.5 m) from the first end A of the encapsulating sheath 4 and another length (e.g., 2 m) from the second end B of the encapsulating sheath 4. Try not to damage the encapsulating sheath 4 and save it for later use. Expose the sheathed steel pipe 3. Then, use alcohol to clean the surface of the sheathed steel pipe 3 from oil stains.

[0064] 1.1.1.2) Select a second sleeve steel pipe 6 of the same material and wall thickness as the sheath steel pipe 3. The inner diameter of the second sleeve steel pipe 6 must be larger than the outer diameter of the sheath steel pipe 3, and the length of the second sleeve steel pipe 6 must be between the stripping lengths of the first and second ends.

[0065] Preferably, the inner diameter of the second sleeve steel pipe 6 is 1-2 mm larger than the outer diameter of the sheath steel pipe 3 ; the length of the second sleeve steel pipe 6 is preferably about 1 m.

[0066] 1.1.1.3) Slip the prepared second sleeved steel pipe 6 into the sheathed steel pipe 3 from the second end B of the packaging sheath 4 with 2 m stripped off, and set aside.

[0067] In the above step 1.1), after the encapsulating sheath 4 is stripped off the first and second ends of the cut optical cable, the method for stripping the sheath steel tube 3 comprises the following steps:

[0068] 1.1.2.1) Cut the sheath steel tube 3 at the second end B from the cutoff point. The cutoff length should be less than the cutoff length of the encapsulating sheath 4 at the second end B. For example, cut the sheath steel tube 3 by 1 m. Carefully pull the cut sheath steel tube 3 out of the inner steel tube 2, leaving the inner steel tube 2 intact.

[0069] In this embodiment, a special steel pipe cutting knife is used to perform circumferential cutting on the sheath steel pipe 3 .

[0070] 1.1.2.2) Repeat the previous step and cut the sheath steel pipe 3 at the first end A from the cut point. The cut length should be less than the cut length of the encapsulating sheath 4 at the first end A. For example, cut the sheath steel pipe 3 by 0.4 m. Carefully pull the cut sheath steel pipe 3 out of the inner steel pipe 2, leaving the inner steel pipe 2 in place.

[0071] 1.1.2.3) Select a first sleeve steel pipe 5 with the same material, wall thickness and outer diameter as the inner steel pipe 2 for standby use. The length of the first sleeve steel pipe 5 is between the cut-off length at the first end A and the cut-off length at the second end B of the sheath steel pipe 3. In this embodiment, the length of the first sleeve steel pipe 5 is preferably about 0.5 m.

[0072] In this embodiment, if there is no suitable sleeve steel pipe, a corresponding pipe drawing die can be selected, the end of the inner steel pipe 2 at the second end B is pre-processed, and the prepared drawing die is inserted. Two people cooperate to draw and reduce the inner steel pipe 2. The processing length is 0.9m. After multiple drawing processes, the outer diameter is measured to make the outer diameter reach the inner diameter of the first sleeve steel pipe 5. The difference does not exceed the first preset value (preferably, the preset value is 0.05mm). At this time, the drawing is stopped and the drawing die is removed;

[0073] The end of the inner steel pipe 2 at the first end A is pre-treated and inserted into the prepared drawing die. Two people work together to draw and reduce the diameter of the inner steel pipe 2. The processing length is 0.3m. After multiple drawing processes, the outer diameter is measured to make the outer diameter smaller than the inner diameter of the sleeve steel pipe 5, and the difference does not exceed the second preset value (preferably, the second preset value is 1~2mm, that is, the outer diameter is 1~2mm smaller than the inner diameter of the sleeve steel pipe 5). At this time, stop drawing and remove the drawing die.

[0074] In the above step 1.1), after the first and second ends of the cut optical cable are stripped of the encapsulating sheath 4 and the protective steel tube 3 in turn, the method for stripping the inner steel tube 2 is as follows: the inner steel tube 2 is cut off from the cut-off point, and one end of the inner steel tube 2 is cut off to a first length (for example, 0.3m), and the other end is cut off to a second length (for example, 0.4m), and the cut inner steel tube 2 is carefully pulled out from the optical fiber 1, and the optical fiber 1 is retained for optical fiber splicing.

[0075] In this embodiment, a special steel pipe cutting knife can be used to cut the inner steel pipe 2.

[0076] In the above step 2), the inner steel pipe 2 is connected, specifically: the pre-prepared second sleeve steel pipe 6 is gently pushed over the first sleeve steel pipe 5 connected to the inner steel pipe 2, pushed to a preset position, and the contact points between the two ends of the second sleeve steel pipe 6 and the sheath steel pipe 3 are welded for protection. After welding, the optical fiber attenuation test is performed again. If the test is qualified, the connection protection of the sheath steel pipe 3 is completed.

[0077] In the above step 3), the sheath steel pipe is connected, specifically: a material similar to the packaging sheath 4 is used to encapsulate and protect the connection part of the sheath steel pipe 3, so that the overall size is close to the size of the original optical cable packaging sheath 4, without affecting the use of supporting accessories, and finally an optical performance test is carried out. If the test is qualified, all connection protection is completed.

[0078] In summary, the present invention can restore the connection of the disconnected special high-temperature resistant optical fiber, and restore the overall sensing and monitoring function, without affecting the tensile strength and distributed monitoring function. In addition, the original armored steel pipe protection measure can better protect the internal optical fiber connection and ensure the performance of the overall oil well optical cable; the connected optical fiber and steel pipe optical fiber unit can be used for subsequent production and engineering applications, without the need to re-purchase new optical fiber and materials and re-produce the oil well optical cable, saving costs and reducing waste.

[0079] Moreover, in addition to being able to splice and protect special high-temperature resistant optical fibers of the same model, the present invention can also selectively splice and protect optical fibers of different models. For example, when used in a combination of applications in which some are conventional optical fibers and some are special optical fibers, the embarrassing situation of having to use all special optical fibers due to the need for special optical fibers is avoided, which can greatly save engineering investment costs.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for connecting downhole optical cables, characterized in that: include: Splice and coat the optical fibers in the inner steel tube; Connect the inner steel pipe; The sheathed steel pipe is connected, and after the connection of the sheathed steel pipe is completed, the broken fiber connection and protection work are realized; The method of splicing and coating the optical fiber of the inner steel pipe includes: The first and second ends of the cut optical cable are stripped of the encapsulating sheath, the protective steel tube and the inner steel tube respectively, the optical fiber is pulled out from the cut portion of the inner steel tube, and coated with a protective coating, the optical fiber is retained for splicing, and a drawing reducing portion is formed at the cut portion of the inner steel tube; Insert the pre-prepared first sleeved steel pipe into the inner steel pipe from the second end with the larger cut length, exposing the optical fiber for standby use; The exposed optical fiber is connected and protected by secondary coating, and the optical fiber attenuation test is carried out on the connected and coated connection points. After meeting the use requirements, the optical fiber connection is completed; Gently push the first sleeve steel tube over the optical fiber splicing point and sleeve it onto the outside of the splicing point until the first sleeve steel tube reaches the drawing and reducing part of the inner steel tube; The contact points of both ends of the first sleeve steel pipe and the inner steel pipe are respectively welded for protection. After welding, the optical fiber attenuation test is performed again. If the test is qualified, the connection protection of the inner steel pipe is completed.

2. The downhole optical cable splicing method according to claim 1, characterized in that: The optical cable is composed of optical fiber, inner steel pipe, protective steel pipe and packaging sheath from inside to outside; The optical fiber is a 150°C or 300°C optical fiber; The inner steel pipe is a longitudinally welded stainless steel pipe, the sheath steel pipe is a longitudinally welded stainless steel pipe, and the packaging sheath is made of PP or FEP.

3. The downhole optical cable splicing method according to claim 1, wherein: The cut length of each layer on the first end of the optical cable is smaller than the cut length of each layer on the second end.

4. The downhole optical cable splicing method according to claim 1, wherein: The method of stripping the packaging sheath from the first and second ends of the cut optical cable comprises: Use a tool to peel off the encapsulating sheath, peel off a length of the first end of the encapsulating sheath, and peel off another length of the second end of the encapsulating sheath without damaging the encapsulating sheath and save it for later use, exposing the sheathed steel pipe, and then use alcohol to clean the oil stains on the surface of the sheathed steel pipe; Select a second sleeve steel pipe with the same material and wall thickness as the sheath steel pipe. The inner diameter of the second sleeve steel pipe must be larger than the outer diameter of the sheath steel pipe, and the length of the second sleeve steel pipe must be between the stripping lengths of the first end and the second end. Put the prepared second sleeved steel pipe into the sheath steel pipe from the second end of the packaging sheath and set it aside.

5. The downhole optical cable splicing method according to claim 1, wherein: The method of stripping the sheath of the first and second ends of the cut optical cable and then stripping the sheath of the steel pipe comprises: The sheath steel pipe at the second end is circularly cut from the cut-off point, with the cut-off length being shorter than the cut-off length of the encapsulating sheath at the second end, and the cut sheath steel pipe is pulled out from the inner steel pipe, leaving the inner steel pipe; Cut the sheath steel pipe at the first end from the cutoff point, with the cutoff length being shorter than the cutoff length of the encapsulating sheath at the first end, and pull the cut sheath steel pipe out of the inner steel pipe, leaving the inner steel pipe; A first sleeve steel pipe with the same material, wall thickness and outer diameter as the inner steel pipe is selected for standby use. The length of the first sleeve steel pipe is between the cut length at the first end and the cut length at the second end of the sheath steel pipe.

6. The downhole optical cable splicing method according to claim 1, characterized in that: The method of stripping the sheath of the first and second ends of the cut optical cable and then stripping the sheath of the steel pipe comprises: Select a tube drawing die, pre-treat the end of the inner steel tube at the second end, insert the prepared drawing die, and draw and reduce the inner steel tube. After multiple drawing processes, measure the outer diameter, make the outer diameter reach the inner diameter of the first sleeved steel tube, and the difference does not exceed a first preset value, stop drawing, and remove the drawing die; The inner steel pipe end at the first end is pre-treated and inserted into the prepared drawing die, and the inner steel pipe is drawn and reduced in diameter. After multiple drawing processes, the outer diameter is measured to make the outer diameter smaller than the inner diameter of the sleeved steel pipe, and the difference does not exceed a second preset value. The drawing is stopped and the drawing die is removed.

7. The downhole optical cable splicing method according to claim 1, wherein: After the encapsulating sheath and the protective steel tube are stripped off the first and second ends of the cut optical cable in turn, the inner steel tube is stripped off by: starting from the cut-off point, one end of the inner steel tube is cut off to a first length, and the other end is cut off to a second length, and the cut inner steel tube is pulled out from the outside of the optical fiber, retaining the optical fiber for optical fiber splicing.

8. The downhole optical cable splicing method according to claim 1, wherein: The connecting of the inner steel pipe includes: gently pushing the pre-prepared second sleeve steel pipe through the first sleeve steel pipe connected to the inner steel pipe to a preset position, welding and protecting the contact points between the two ends of the second sleeve steel pipe and the sheath steel pipe, and performing an optical fiber attenuation test after welding. If the test is passed, the connecting protection of the sheath steel pipe is completed.

9. The downhole optical cable splicing method according to claim 1, wherein: The splicing of the sheathed steel pipe includes: using a packaging sheath material to encapsulate and protect the splicing portion of the sheathed steel pipe so that the overall size is close to the size of the original optical cable packaging sheath, performing an optical performance test, and completing all splicing protection after the test is passed.

Images