Coiled tubing double-layer sheath underground electric heater based on armored distributed temperature measurement optical fiber

Abstract

The invention relates to a coiled tubing double-layer sheath underground electric heater based on armored distributed temperature measurement optical fibers. The heater adopts a double-layer sheath structure, so that the structural stability and durability are enhanced. The underground temperature is monitored in real time through armored distributed temperature measuring optical fibers, the heating process is accurately controlled, the heating efficiency and the crude oil recovery rate are improved, heating units are evenly distributed, it is ensured that heat is evenly transmitted, and an outer continuous pipe sheath is made of high-temperature-resistant and corrosion-resistant materials and adapts to the severe underground environment. And by adopting the excellent characteristics of high technical strength, good toughness, corrosion resistance, high temperature resistance, long fatigue life and the like of the coiled tubing, the service life of the outer sheath in the well can be greatly prolonged. The device can be widely applied to the field of thickened oil recovery, the oil field development efficiency is improved, the operation cost is reduced, efficient utilization of energy is achieved and environmental pollution is reduced by accurately controlling the heating temperature and monitoring the underground temperature, and the device conforms to the green and sustainable energy utilization principle.

Description

Technical Field

[0001] The invention belongs to the field of heavy oil production heating and relates to a heavy oil thermal recovery electric heating device, in particular to a continuous tube double-layer sheathed downhole electric heater based on armored distributed temperature measurement optical fiber. Background Art

[0002] As oilfield development deepens, more and more fields are facing challenges such as high viscosity and low permeability, posing challenges to traditional extraction technologies. To improve crude oil recovery, thermal recovery technologies have emerged. Downhole electric heating, with its advantages of strong controllability and wide adaptability, has become a key means of improving oilfield development efficiency. However, existing downhole electric heating technologies face a number of practical challenges.

[0003] First, existing underground electric heating devices often use heating cables as the heating source, with their outer sheaths connected by welding and other methods. This results in numerous joints and low reliability. In high-temperature environments, the outer sheaths of the heating cables are not sufficiently resistant to pressure and corrosion, making them susceptible to damage, limiting the equipment's reusability and service life.

[0004] Secondly, existing downhole electric heating technology lacks effective temperature monitoring and control methods. In most cases, the heater's operating state is regulated by measuring the temperature of the wellhead or downhole heavy oil. This temperature control method is slow to respond, has low accuracy, and can easily cause the heating temperature to be too high or too low, which not only affects the heating effect but can also adversely affect the wellbore and crude oil.

[0005] For example, Chinese patent CN 210899705 U discloses a downhole oil layer heating cable, which includes a steel tube sheathed cable and a heater fixedly connected to one end of the steel tube sheathed cable and electrically connected thereto; the steel tube sheathed cable includes two or more core wires, an insulation layer, a mineral filler layer and a steel tube sheath, the insulation layer and the mineral filler layer being sequentially coated on the outer surface of each core wire, and the two or more core wires together with the insulation layer and the mineral filler layer being inserted into the steel tube sheath in parallel; the heater includes a metal sheath having the same outer diameter as the steel tube sheath, a conductor which generates heat when energized and is located inside the metal sheath, and a tail end for sealingly connecting the metal sheath and electrically connecting the conductor; the metal sheath is sealed and fixedly connected to the steel tube sheath, and the conductor is electrically connected to the core wire. In the existing technology, the outer sheath of the heating cable is made of a 9-meter seamless steel pipe, which is extended by butt welding. The butt joint poses a serious hidden danger to reliability. The outer sheath has insufficient pressure resistance and corrosion resistance at high temperatures, and the reusability rate is low. The heating cable lacks an effective temperature measurement method. The heater temperature is adjusted by measuring the wellhead temperature or the downhole heavy oil temperature. The temperature control is relatively lagging, and the heating temperature is prone to overshoot, causing heavy oil to form. Or in order to prevent temperature overshoot, the heating temperature is set low, affecting the heating efficiency. Summary of the Invention

[0006] One of the purposes of the present invention is to provide a continuous tube double-sheath downhole electric heater based on armored distributed temperature measurement optical fiber, so as to solve the problems in the prior art of multiple cable outer sheath welding joints, low reliability, insufficient outer sheath pressure resistance and corrosion resistance at high temperatures, and low reuse rate.

[0007] The second purpose of the present invention is to provide a continuous tube double-layer sheathed downhole electric heater based on armored distributed temperature measurement optical fiber to prevent temperature overshoot during the heating process of the heater, and the heating temperature is set too low, which affects the heating efficiency.

[0008] The technical solution of the present invention is: a continuous tubing double-sheathed downhole electric heater based on an armored distributed temperature measurement optical fiber, which is characterized by at least comprising: an outer continuous tubing sheath 1, a heating unit and an armored distributed temperature measurement optical fiber 4, the heating unit and the armored distributed temperature measurement optical fiber 4 being distributed within the outer continuous tubing sheath 1, and there are multiple heating units, which are evenly arranged around the armored distributed temperature measurement optical fiber 4 and are spaced apart from the inner wall of the outer continuous tubing sheath 1.

[0009] The heating unit includes: a cable sheath 2, an internal magnesium oxide filler 3, and a heating core wire 5; wherein, the heating core wire 5 is inside the cable sheath 2 and is filled with the internal magnesium oxide filler 3 at the axial position of the cable sheath 2. The cable sheath 2, the internal magnesium oxide filler 3 and the heating core wire 5 form a concentric structure.

[0010] The number of the heating core wires 3 is 3-5.

[0011] The armored distributed temperature measurement optical fiber 4 includes an optical fiber core, which is covered by a cladding, and the cladding is embedded in a loose tube; the loose tube is surrounded by a waterproof layer, and the outer layer is an armor layer that firmly encapsulates the entire structure. The optical fiber core constitutes an optical fiber temperature sensitive area in the armored distributed temperature measurement optical fiber.

[0012] The armored distributed temperature measurement optical fiber 4 adopts a stainless steel armored outer sheath with a diameter ranging from 3 mm to 5 mm.

[0013] The outer coiled tubing jacket 1 and the inner coiled tubing jacket 2 are both made of stainless steel, and the stainless steel is 316L, 310S or 825.

[0014] The material of the heating core wire 3 is 6J40 alloy or Cr20Ni80 alloy.

[0015] The outer wall diameter of the outer layer continuous pipe sheath 1 ranges from φ31.8 mm to φ88.9 mm.

[0016] The outer layer continuous pipe sheath adopts continuous forming longitudinal welding technology.

[0017] The beneficial effects of the present invention are:

[0018] The present invention relates to a downhole electric heater based on armored distributed temperature measurement optical fiber technology and a double-layer continuous tube sheath structure. Through integrated technical optimization and performance improvement, it provides a more reliable, efficient and economical heating solution for heavy oil thermal recovery in oil fields. First, the present invention uses armored distributed temperature measurement optical fiber to achieve real-time and accurate monitoring of the temperature of the downhole electric heater. Compared with the traditional method that relies on wellhead temperature estimation, it significantly improves the accuracy and response speed of temperature control, effectively avoids the problem of heavy oil coking caused by temperature overshoot, thereby optimizing the heating efficiency and ensuring that the heating process is safer and more effective. Secondly, the use of a double-layer continuous tube sheath design not only simplifies the downhole operation process and reduces the complexity of the operation, but also significantly enhances the structural stability and durability of the electric heater. The outer and inner continuous tube sheaths are both made of high-strength, high-temperature resistant, corrosion-resistant materials such as 316L, 310S or 825 stainless steel, which effectively cope with the harsh environment downhole and extend the service life of the equipment. Furthermore, precise temperature control and the strong anti-interference capabilities of the armored distributed temperature measurement optical fiber ensure accurate and reliable transmission of temperature signals to the wellhead, providing reliable data support for operators, further reducing maintenance costs and downtime caused by equipment failures, and lowering overall operating costs. In summary, this invention significantly enhances the performance and application value of downhole heating cables through technological innovation, providing a new, highly efficient, stable, and environmentally friendly solution for heavy oil thermal recovery in oilfields.

[0019] The present invention will be further described below with reference to the embodiments and accompanying drawings: BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural diagram provided by an embodiment of the present invention.

[0021] In the figure: 1. Continuous tube outer sheath; 2. Cable sheath; 3. Internal magnesium oxide filler; 4. Armored distributed temperature measurement optical fiber; 5. Heating core wire; 6. External magnesium oxide filler. DETAILED DESCRIPTION

[0022] Example 1

[0023] like Figure 1As shown, the device comprises at least: an outer continuous tubing sheath 1, heating units, and an armored distributed temperature measurement optical fiber 4. The heating units and armored distributed temperature measurement optical fiber 4 are distributed within the outer continuous tubing sheath 1. Multiple heating units are evenly distributed around the armored distributed temperature measurement optical fiber 4 and spaced from the inner wall of the outer continuous tubing sheath 1. The heating units comprise: a cable sheath 2, an internal magnesium oxide filler 3, and a heating core 5. The heating core 5 is located within the cable sheath 2 and is filled with magnesium oxide filler 3 at the axial center of the cable sheath 2. The cable sheath 2, internal magnesium oxide filler 3, and heating core 5 form a concentric structure. There are three heating units, evenly distributed at 120 degrees around the outer layer of the armored distributed temperature measurement optical fiber 4.

[0024] Armored distributed temperature measurement optical fiber is placed inside the heating cable during the continuous production process of the heating cable. It is used to achieve temperature measurement during the continuous production process.

[0025] The armored distributed temperature measurement optical fiber includes an optical fiber core, a loose tube surrounding the optical fiber core, a waterproof layer, an armor layer, and an optical fiber temperature sensitive area. The optical fiber core is covered by a cladding, and the combination of the optical fiber core and the cladding is embedded in the loose tube, and the loose tube is surrounded by a waterproof layer. The outer layer is an armor layer that firmly encapsulates the entire structure. The optical fiber core in the armored distributed temperature measurement optical fiber constitutes an optical fiber temperature sensitive area for accurately monitoring changes in ambient temperature. The entire structure is linked layer by layer to ensure the transmission characteristics of the optical fiber and the high efficiency and stability of its temperature measurement function.

[0026] The armored distributed temperature measurement optical fiber 3 uses a stainless steel armored outer sheath with a diameter between 3 and 5 mm, which facilitates integration into the cable.

[0027] The coiled tubing outer sheath 1 is made of stainless steel (316L, 310S, or 825), capable of withstanding long-term underground high temperatures, high pressures, and corrosion from media such as chloride ions and hydrogen sulfide. The heating core 2 is made of 6J40 alloy or Cr20Ni80 alloy. The outer diameter of the coiled tubing outer sheath 1 ranges from φ31.8 mm to φ88.9 mm.

[0028] The outer layer continuous pipe sheath 1 is formed by continuous longitudinal welding technology.

[0029] During the rolling and drawing process of a single-layer coiled tubing-sheathed downhole electric heater based on armored distributed temperature measurement optical fiber, the armored distributed temperature measurement optical fiber maintains its deformation within 30%-35%, and its temperature measurement accuracy meets the national standard Class 1 accuracy requirement. The armored distributed temperature measurement optical fiber can measure temperatures at various points along its length. Its anti-interference properties allow for accurate transmission of downhole temperature signals to the wellhead. The coiled tubing outer sheath is designed to withstand high temperatures, high pressures, and corrosion from media such as chloride ions and hydrogen sulfide during long-term service, enhancing the overall reliability of the cable.

[0030] Example 2

[0031] The outer sheath of the continuous tubing serves as the outermost protective structure of the electric heater, providing physical strength and the ability to withstand the harsh environment downhole;

[0032] The cable sheath is located inside the outer sheath of the continuous tube and is used to further encapsulate and protect the heating core wire and the armored distributed temperature measurement optical fiber to ensure their stable operation in high temperature, high pressure and corrosive environments;

[0033] The internal magnesium oxide filler is filled inside the cable sheath and surrounds the heating core wire to provide electrical insulation and heat conduction, while enhancing the overall structural stability of the heating unit;

[0034] The armored distributed temperature measurement optical fiber is arranged in the cable sheath, parallel to the heating core wire or wrapped around it, and is used to monitor the temperature of the electric heater and its surrounding environment in real time to ensure the safety and efficiency of the heating process;

[0035] The heating core wire, as the core heating element of the electric heater, is made of high-temperature resistant and high-resistance materials and is responsible for converting electrical energy into thermal energy for heating the downhole oil reservoir;

[0036] The external magnesium oxide filler is filled in the space between the outer sheath of the continuous pipe and the cable sheath to enhance the mechanical strength of the entire electric heater and provide additional thermal protection and electrical insulation.

[0037] Example 3

[0038] The difference from Example 1 is that the number of heating units is 4, which are evenly distributed at 90 degrees on the outer layer of the armored distributed temperature measurement optical fiber 4.

[0039] Example 4

[0040] This invention demonstrates a coiled tubing double-jacketed downhole electric heater based on armored distributed temperature-sensing optical fiber and an integrated PLC control system. This design aims to achieve precise management of the downhole electric heating process through automatic, remote, and local control. The core control logic relies on real-time temperature data provided by the armored distributed temperature-sensing optical fiber, enabling the PLC system to dynamically adjust heating power based on actual temperature conditions, ensuring both efficient and safe heating.

[0041] In automatic control mode, the PLC system dynamically adjusts the heating power by analyzing the temperature data monitored by the armored fiber optic sensing area in real time. Specifically, when the monitored temperature difference exceeds a preset safety threshold (such as 80°C), the PLC instructs the power regulator to perform PID adjustment to reduce the input power to prevent damage to the heating element due to overheating. When the temperature difference falls below another safety threshold (such as 10°C), the power is increased to continue heating and ensure the efficiency of reservoir heating. In addition, when approaching the target temperature, the PLC will reduce the power in a timely manner to prevent damage to the reservoir caused by overheating.

[0042] Remote control is enabled through 5G wireless communication technology, connecting the electric heater to the oilfield operation and maintenance center, transmitting heating parameters to the data center in real time. The operation and maintenance team can remotely monitor the heater status and adjust the heating strategy in real time to respond to changes in the downhole environment.

[0043] The local control mode provides on-site operators with a direct intervention option. They can directly set the operating temperature and start or stop the heating process through the touch screen interface. It is suitable for rapid response in emergency situations or immediate control during maintenance.

[0044] The core of this system is an armored distributed temperature-measuring optical fiber that monitors the downhole ambient temperature in real time and feeds this data back to the PLC control system, ensuring the accuracy and responsiveness of the entire heating process. Through optimized design, this invention overcomes several limitations of existing downhole electric heating technology, such as cable connector reliability issues, insufficient pressure and corrosion resistance of the outer sheath, and low cable reuse. This significantly improves the performance, reliability, and economic benefits of downhole electric heaters, providing a more efficient and reliable technical solution for heavy oil thermal recovery in oilfields.

Claims

1. A coiled tube double-sheathed downhole electric heater based on armored distributed temperature measurement optical fiber, comprising at least: An outer continuous tube sheath (1), a heating unit and an armored distributed temperature measurement optical fiber (4), wherein the heating unit and the armored distributed temperature measurement optical fiber (4) are distributed within the outer continuous tube sheath (1), a plurality of heating units are uniformly arranged around the armored distributed temperature measurement optical fiber (4), and are spaced apart from the inner wall of the outer continuous tube sheath (1), wherein the space is filled with an external magnesium oxide filler (6).

2. The coiled tube double-layer sheathed downhole electric heater based on armored distributed temperature measurement optical fiber according to claim 1 is characterized by: The heating unit comprises: a cable sheath (2), an internal magnesium oxide filler (3), and a heating core wire (5); wherein the heating core wire (5) is inside the cable sheath (2) and is filled with the internal magnesium oxide filler (3) at the axial center position of the cable sheath (2); the cable sheath (2), the internal magnesium oxide filler (3) and the heating core wire (5) form a concentric structure.

3. The coiled tube double-sheathed downhole electric heater based on armored distributed temperature measurement optical fiber according to claim 1 is characterized by: The number of the heating core wires (3) is 3-5.

4. The coiled tube double-sheathed downhole electric heater based on armored distributed temperature measurement optical fiber according to claim 1 is characterized by: The armored distributed temperature measurement optical fiber (4) comprises an optical fiber core, which is covered by a cladding, and the cladding is embedded in a loose tube; the loose tube is surrounded by a waterproof layer, and the outer layer is an armor layer that firmly encapsulates the entire structure. The optical fiber core constitutes an optical fiber temperature sensitive area in the armored distributed temperature measurement optical fiber.

5. The coiled tube double-sheathed downhole electric heater based on armored distributed temperature measurement optical fiber according to claim 1 is characterized by: The armored distributed temperature measurement optical fiber (4) adopts a stainless steel armored outer sheath with a diameter ranging from 3 mm to 5 mm.

6. The coiled tube double-sheathed downhole electric heater based on armored distributed temperature measurement optical fiber according to claim 1 is characterized by: The outer layer continuous pipe sheath (1) and the inner layer continuous pipe sheath (2) are both made of stainless steel, and the stainless steel is selected from 316L, 310S or 825.

7. The coiled tube double-sheathed downhole electric heater based on armored distributed temperature measurement optical fiber according to claim 1 is characterized by: The material of the heating core wire (3) is 6J40 alloy or Cr20Ni80 alloy.

8. The coiled tube double-sheathed downhole electric heater based on armored distributed temperature measurement optical fiber according to claim 1 is characterized by: The outer wall diameter of the outer layer continuous pipe sheath (1) ranges from φ31.8 mm to φ88.9 mm.

9. The coiled tube double-sheathed downhole electric heater based on armored distributed temperature measurement optical fiber according to claim 1 is characterized by: The outer layer continuous pipe sheath (1) adopts continuous forming longitudinal welding technology.

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