Wellbore heating apparatus and method of production

Abstract

The application provides a production well wellbore heat tracing device which is installed in combination with an in-use production oil well with a continuous oil production condition, the oil well comprising a production casing, a tubing and an oil production lifting assembly, the tubing is arranged inside the production casing, the oil production lifting assembly is installed in combination with the tubing, and the inner cavity of the tubing constitutes a crude oil exploitation passage; an open perforation for allowing the formation crude oil to flow through is arranged in the production casing production layer section; an oil casing annulus is formed between the tubing and the production casing, a packer which only seals the lower part of the annulus and does not block the perforation is arranged at the bottom of the oil casing annulus, and an annulus sealing end cover which seals the top part is arranged at the wellhead of the top part of the oil casing annulus; the oil casing annulus between the packer and the annulus sealing end cover forms a closed and fixed super-long gravity heat pipe working cavity, and the super-long gravity heat pipe working cavity is filled with liquid working medium and is vacuumized to a preset vacuum degree. The application also provides a heat tracing method using the production well wellbore heat tracing device.

Description

Technical Field

[0001] This invention relates to the field of oil extraction heating technology, and more specifically to a wellbore heating device and method for production wells. Background Technology

[0002] In heavy oil wells, high-pour-point oil wells, and high-wax oil wells in oilfields, during wellbore lifting, the crude oil temperature gradually decreases from bottom to top as heat is dissipated from the tubing to the formation through the casing, with a temperature drop of approximately 3°C per 100 meters. As the temperature decreases, the crude oil viscosity increases exponentially, fluidity decreases, and some of the crude oil precipitates wax, adhering to the sucker rod and tubing walls. In severe cases, this can cause well blockage accidents, hindering normal oil production. To solve this problem, heat tracing technology is needed to supplement heat into the wellbore to counteract the decrease in crude oil temperature, thereby ensuring normal well lifting and production.

[0003] Currently, the two most commonly used wellbore heating methods are the hot fluid circulation method and the electric heating method. The hot fluid circulation method requires the installation of heating fluid on the surface and its circulation within the wellbore to heat the crude oil, but this increases the lifting load on the oil pump, increases the bottom hole pressure, and reduces crude oil production. The electric heating method consumes a lot of electricity, has a high cost, and poses safety hazards such as leakage and pipe bursts.

[0004] In recent years, wellbore heat tracing technology utilizing the principle of gravity heat pipes has attracted attention. Chinese patent applications CN120061759A and CN101298834A disclose wellbore heat tracing systems based on ultra-long gravity heat pipe hollow sucker rods. This scheme constructs a gravity heat pipe inside the hollow sucker rod. Its essential structure is as follows: liquid working fluid is injected into the inner cavity of a slender sucker rod with an inner diameter in the millimeter range (usually less than 30 mm) and a vacuum is drawn, forming a two-phase closed thermosiphon. When the evaporation section at the bottom of the sucker rod is heated, the working fluid vaporizes to form steam. The steam rises along the central channel of the rod under a small pressure difference to the condensation section near the wellhead, where it condenses into liquid and releases latent heat to heat the crude oil. The condensate flows back to the evaporation section along the inner wall of the rod under gravity, completing a self-circulating cycle. Although this scheme achieves zero-energy heat tracing, it has the following fundamental technical defects:

[0005] (1) There is an irreconcilable physical contradiction between the "narrow inner cavity of the sucker rod" and "ultra-long-distance heat transfer". The carrying limit of a gravity heat pipe is directly proportional to the pipe diameter - the smaller the pipe diameter, the higher the rising velocity of the steam, the stronger the shearing effect of the gas-liquid counterflow, and the lower the carrying limit. The inner diameter of the hollow sucker rod is limited by the inner diameter of the oil pipe, usually only 12~30mm (e.g., the inner diameter of a sucker rod with an outer diameter of 34mm and a wall thickness of 6mm is only 22mm). Under such millimeter-level inner diameter, a violent counterflow friction shearing effect is generated between the rising steam and the condensate film flowing back along the wall. The carrying limit may be reached within a length of several hundred meters, resulting in the condensate not being able to flow back smoothly, the evaporation section drying up, and the overall heat transfer capacity of the heat pipe decreasing sharply or even completely failing. This carrying limit problem caused by the extremely small pipe diameter and the ultra-long transmission distance is an inherent physical bottleneck of the sucker rod heat pipe scheme, which cannot be fundamentally overcome by optimizing structural parameters.

[0006] (2) There is a structural conflict between the "fixed heat pipe principle" and the "reciprocating mechanical components". When the sucker rod is in operation, it needs to withstand several alternating tensile, impact and bending loads every minute, and the rod body moves up and down repeatedly. This periodic motion causes the gas-liquid interface of the working fluid in the pipe to be subjected to continuous inertial disturbance, liquid pool sloshing and uneven liquid film distribution, resulting in unstable phase change heat transfer process, large fluctuation in heat transfer efficiency, and further reducing the effective heat transfer capacity that is already limited by the carrying capacity limit.

[0007] (3) The long-term sealing reliability of multi-segment connections is difficult to guarantee. Kilometer-level hollow sucker rods require dozens to hundreds of segmented threaded connections, each of which is both a mechanical bearing surface and a vacuum sealing surface. Under long-term alternating loads, the threaded connection surfaces are at risk of fatigue micro-leakage. Once any connection seal fails, leading to a loss of vacuum, the entire heat pipe will fail. This engineering reliability problem is particularly prominent in rod pump oil production and is one of the main obstacles currently restricting the large-scale application of this technology.

[0008] In summary, how to provide a technical solution that can achieve zero-energy wellbore heating by utilizing geothermal energy without relying on the heat pipe built into the sucker rod, while fundamentally avoiding the carrying capacity bottleneck and sealing reliability issues of the heat pipe, is an unsolved technical problem in this field. Summary of the Invention

[0009] In view of this, the purpose of the present invention is to provide a production wellbore heat tracing device that uses the annulus of the casing as the working chamber of an ultra-long gravity heat pipe, and utilizes geothermal energy to achieve phase change circulation of the working fluid in the working chamber of the ultra-long gravity heat pipe, thereby increasing the temperature of the crude oil at the wellhead and reducing the viscosity of the crude oil.

[0010] Another object of the present invention is to provide a heat tracing method using the aforementioned production wellbore heat tracing device.

[0011] To achieve the above objectives, the present invention provides a wellbore heating device for production wells, which is installed in conjunction with an in-use production oil well capable of continuous oil production. The oil well includes a production casing, tubing, and a production lift assembly. The tubing is disposed inside the production casing, and the production lift assembly is installed in conjunction with the tubing. The inner cavity of the tubing forms an oil extraction channel. The production casing has open perforations in the producing section for the flow of formation crude oil. An annulus is formed between the tubing and the production casing. The bottom of the casing annulus is equipped with a packer that seals only the lower part of the annulus and does not block the perforation. The top of the casing annulus is equipped with an annulus sealing end cap that seals the top. The casing annulus between the packer and the annulus sealing end cap forms a closed and fixed ultra-long gravity heat pipe working chamber. The ultra-long gravity heat pipe working chamber is completely isolated from the crude oil production channel and realizes oil production and wellbore heating simultaneously. The ultra-long gravity heat pipe working chamber is filled with liquid working fluid and evacuated to a preset vacuum level.

[0012] Preferably, the packer is located at the upper end of the high-temperature production zone above the perforation, so that the lower evaporation section of the ultra-long gravity heat pipe working chamber completely corresponds to the downhole high-temperature production zone.

[0013] Preferably, the crude oil extraction channel and the working chamber of the ultra-long gravity heat pipe are independent of each other, and the working chamber of the ultra-long gravity heat pipe is a fixed stationary chamber that does not participate in the movement of the oil extraction lifting assembly.

[0014] Preferably, the annular sealing end cap is an annular flange structure, fitted onto the outer wall of the oil pipe and welded to it for sealing connection, while also being bolted to the top flange of the production casing for sealing connection. A liquid injection valve and a vacuum valve are installed on the annular sealing end cap, penetrating into the working chamber of the ultra-long gravity heat pipe. The liquid injection valve is connected to an external liquid supply device, and the vacuum valve is connected to an external vacuum pumping device.

[0015] Preferably, the working fluid is selected according to the bottom-hole production zone temperature; the liquid working fluid is selected from any one of water, ammonia, methanol, ethanol, acetone, Freon or organic working fluid.

[0016] Preferably, the oil lifting assembly is a rod pump lifting assembly, including a sucker rod disposed inside the tubing and a pump installed at the bottom of the tubing. The pump includes a plunger, a pump barrel, an intake valve, and a discharge valve. The lower end of the sucker rod is connected to the plunger, which reciprocates up and down inside the pump. A polished rod seal is installed at the top of the tubing. The top of the sucker rod passes through the central hole of the annular sealing end cap and the polished rod seal, and the top of the sucker rod is connected to the suspension rope of a beam pumping unit located on the ground.

[0017] Preferably, at least one inner wall of the working chamber of the ultra-long gravity heat pipe is provided with a reflux enhancement structure for accelerating the reflux of the condensing working fluid and reducing the gas-liquid reverse shear resistance. The reflux enhancement structure is a spiral guide groove and / or longitudinal reflux ribs provided on the outer wall of the oil pipe and / or the inner wall of the production casing.

[0018] Preferably, the spiral angle of the spiral guide groove is 15°~45°; the height of the longitudinal return rib is 3~10mm, and the circumferential spacing between adjacent longitudinal return ribs is 20~50mm.

[0019] Preferably, the annular sealing end cap is further provided with a monitoring component, which includes a pressure sensor and / or a temperature transmitter. The sensing end of the pressure sensor and / or temperature transmitter passes through into the working chamber of the ultra-long gravity heat pipe to monitor the vacuum degree and / or working fluid saturation temperature inside the working chamber of the ultra-long gravity heat pipe in real time. The annular sealing end cap is also provided with a pressure relief valve and a liquid injection valve that communicate with the inside of the working chamber of the ultra-long gravity heat pipe. The pressure relief valve is used to release pressure when the pressure inside the working chamber of the ultra-long gravity heat pipe exceeds a preset value, and the liquid injection valve is used to replenish liquid working fluid when the working fluid inside the working chamber of the ultra-long gravity heat pipe is insufficient.

[0020] This invention provides a method for heat tracing a production wellbore, characterized by employing the aforementioned heat tracing device for the production wellbore, comprising the following steps:

[0021] (1) Select production wells with good tubing and production casing sealing as the target for modification;

[0022] (2) Insert the packer into the annulus between the tubing and the production casing to seal the lower part of the annulus;

[0023] (3) Install an annular sealing end cap at the wellhead to seal the top of the annulus of the oil casing, so that the annulus of the oil casing forms a closed fixed ultra-long gravity heat pipe working chamber. The perforation below the packer remains open and connected to the formation throughout the entire process. The oil pipe maintains an independent crude oil extraction channel. The oil extraction operation and the heat pipe heat tracing operate synchronously without interfering with each other.

[0024] (4) Evacuate the working chamber of the ultra-long gravity heat pipe to the preset vacuum level. The preset vacuum level is determined according to the selected liquid working fluid type and the downhole working temperature. When using ammonia / organic working fluid, the partial pressure of non-condensable gas in the chamber is less than 10⁻² Pa.

[0025] (5) Inject liquid working fluid into the working chamber of the ultra-long gravity heat pipe through the injection valve;

[0026] (6) Start the oil production lifting mechanism to extract crude oil. At the same time, the liquid working fluid in the working chamber of the ultra-long gravity heat pipe absorbs heat and vaporizes in the high temperature zone at the bottom of the well and condenses and releases heat in the low temperature zone at the wellhead. The heat is transferred to the crude oil flowing in the pipe through the pipe wall to achieve wellbore heating. The condensed liquid working fluid relies on gravity and the guiding effect of the reflux strengthening structure to flow back to the bottom evaporation section along the inner wall of the chamber.

[0027] (7) The vacuum degree and / or working fluid saturation temperature inside the working chamber of the ultra-long gravity heat pipe are monitored in real time by a pressure sensor and / or a temperature transmitter installed on the annular sealing end cap. When the vacuum degree is found to be lower than the preset threshold or the working fluid temperature is found to be deviated from the preset range, the vacuum is replenished by a vacuum valve and / or the liquid working fluid is replenished by a liquid injection valve.

[0028] Compared with existing technologies, the advantages of the production wellbore heat tracing device and method disclosed in this invention are as follows: the heat pipe working chamber of the production wellbore heat tracing device has a larger cross-sectional area, which can adapt to the high-efficiency heat tracing requirements of kilometer-long wellbores; the heat pipe working chamber of the production wellbore heat tracing device is a fixed static cavity, and the internal working fluid phase change cycle is not affected by inertial disturbances, which can effectively avoid the interference of the reciprocating motion of the sucker rod on the operation of the heat pipe, ensure the stable progress of phase change heat transfer, and effectively guarantee the stability and reliability of the heat pipe operation; the number of sealing points of the production wellbore heat tracing device is greatly reduced, and all of them are static seals, which can effectively reduce the risk of system failure; the production wellbore heat tracing device can be applied to the retrofitting of existing production wells and is suitable for various applications. The lifting method is convenient for modification and has a wider range of applications; the wellbore heating device does not require external power supply or drive, and can complete its own driving working fluid circulation solely by geothermal energy, achieving zero carbon emissions and zero energy consumption; the reflux enhancement structure can gather and guide the condensed liquid working fluid, significantly reducing the gas-liquid reverse flow shear resistance, effectively improving the ultimate heat transfer power and long-term operational stability of the heat pipe under kilometer-deep well conditions; by setting pressure sensors and / or temperature transmitters, the vacuum degree and working fluid saturation temperature in the working chamber of the heat pipe can be monitored online in real time, and pressure relief valves and liquid injection valves can be used to regulate pressure and replenish working fluid, effectively solving maintenance problems such as minor working fluid leakage and vacuum decay during long-term operation, and significantly extending the service life of the device. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 The diagram shown is a structural schematic of a production wellbore heat tracing device according to this application.

[0031] Figure 2 The diagram shown is a schematic diagram of a first preferred embodiment of the reflow reinforcement structure.

[0032] Figure 3 The diagram shown is a schematic diagram of a second preferred embodiment of the reflow reinforcement structure.

[0033] Explanation of reference numerals in the attached drawings: 1-Production casing; 2-Tubing; 3-Sucker rod; 4-Pump; 5-Packer; 6-Annular seal end cap; 7-Working chamber of ultra-long gravity heat pipe; 8-Crude oil flow path; 9-Injection valve; 10-Vacuum valve; 11-Perforation; 12-Walking beam pumping unit; 13-Smooth rod seal; 14-Pressure sensor; 15-Temperature transmitter; 16-Helical guide groove; 17-Longitudinal reflux rib. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] like Figure 1 As shown, this application discloses a wellbore heating device for production wells that is integrated with an oil well. The oil well includes a production casing 1, tubing 2, and a production lift assembly. The tubing 2 is coaxially disposed inside the production casing 1. The production lift assembly is integrated with the tubing 2, and the inner cavity of the tubing 2 forms a crude oil extraction channel. The production casing 1 has an open perforation 11 in the producing section for the flow of formation crude oil. Formation crude oil enters the production casing 1 through the perforation 11. An annulus is formed between the tubing 2 and the production casing 1. The bottom of the annulus is provided with a seal that only seals the lower part of the annulus and does not block the perforation 11. A packer 5 and an annular sealing end cap 6 are installed at the wellhead at the top of the casing annulus. The packer 5 seals the bottom of the casing annulus without obstructing the crude oil entry channel at the perforation 11. The annular sealing end cap 6 seals the top of the casing annulus. The casing annulus between the packer 5 and the annular sealing end cap 6 forms a closed and fixed ultra-long gravity heat pipe working chamber 7. The ultra-long gravity heat pipe working chamber 7 is completely isolated from the crude oil production channel and can simultaneously achieve oil production and wellbore heating. The ultra-long gravity heat pipe working chamber is filled with liquid working fluid and evacuated to a preset vacuum level. The crude oil production channel and the ultra-long gravity heat pipe working chamber 7 are independent of each other. The ultra-long gravity heat pipe working chamber 7 is a fixed, stationary chamber that does not participate in the movement of the oil production lifting components. The packer 5 is located at the upper end of the high-temperature producing layer above the perforation 11, so that the lower evaporation section of the ultra-long gravity heat pipe working chamber 7 completely corresponds to the downhole high-temperature producing layer.

[0036] Compared to existing solutions with built-in heat pipes on sucker rods, the cross-sectional area of ​​the ultra-long gravity heat pipe working chamber 7 is increased by an order of magnitude, effectively reducing steam velocity and fundamentally solving the problem of limited heat transfer distance caused by the extremely small diameter of the heat pipe in existing solutions. This allows the axial length of the ultra-long gravity heat pipe working chamber 7 to adapt to the depth of the oil well, reaching ultra-long dimensions of hundreds to thousands of meters. The ultra-long gravity heat pipe working chamber 7 is a fixed, static cavity, and the internal working fluid phase change cycle is not affected by inertial disturbances, ensuring the stability and reliability of the heat pipe operation. The number of sealing points of the production wellbore heat tracing device is significantly reduced, and all are static seals, which can effectively reduce the risk of system failure. The production wellbore heat tracing device can be applied to the retrofitting of existing production wells without replacing special tubing or sucker rods. Normal oil production operations and heat tracing functions are completely decoupled, and it is applicable to various lifting methods, making retrofitting convenient and with a wider range of applications. The production wellbore heat tracing device does not require external power supply or drive, and can complete its own driving working fluid cycle solely through geothermal energy, achieving zero carbon emissions and zero energy consumption.

[0037] The oil lifting assembly can be a rod pump lifting assembly, including a sucker rod 3 housed inside the tubing 2 and a pump 4 installed at the bottom of the tubing 2. The pump 4 includes a plunger, a pump barrel, a suction valve, and a discharge valve. The lower end of the sucker rod 3 is connected to the plunger, which reciprocates up and down inside the pump 4. A polished rod seal 13 is installed at the top of the tubing 2. The top of the sucker rod 3 passes through the central hole of the annular sealing end cap 6 and the polished rod seal 13, and the top of the sucker rod 3 is connected to the suspension rope of a beam pumping unit 12 installed on the ground. The polished rod seal 13 is used to seal the annular space between the sucker rod 3 and the tubing 2. The beam pumping unit 12 drives the pump 4 to lift crude oil via the sucker rod 3.

[0038] It is worth noting that the oil production lift assembly can also use rodless pump lift assemblies such as electric submersible pumps and screw pumps, and the wellbore heating device can be applied to different oil production wells, with a wider range of applications.

[0039] Packer 5 is a high-temperature and high-pressure resistant packer. The temperature resistance of packer 5 is no less than 1.2 times the highest operating temperature of the lower evaporation section of the ultra-long gravity heat pipe working chamber 7, and it can withstand the temperature and pressure changes generated by the circulation of the working fluid in the ultra-long gravity heat pipe working chamber 7. Packer 5 is seated above the high-temperature producing zone of the oil well, so that the lower evaporation section of the ultra-long gravity heat pipe working chamber 7 is completely within the well depth range corresponding to the high-temperature crude oil at the bottom of the well, ensuring that the liquid working fluid absorbs heat and vaporizes in the high-temperature zone at the bottom of the well.

[0040] The annular sealing end cap 6 is a ring flange structure, fitted onto the outer wall of the tubing 2 and welded to it for sealing. It is also bolted to the top flange of the production casing 1, achieving a seal on the top of the annulus of the tubing. An injection valve 9 and a vacuum valve 10 are installed on the annular sealing end cap 6, penetrating into the working chamber 7 of the ultra-long gravity heat pipe. The injection valve 9 is connected to an external liquid supply device, and the vacuum valve 10 is connected to an external vacuum pumping device. The injection valve 9 is used to inject liquid working fluid into the working chamber 7 of the ultra-long gravity heat pipe, and the vacuum valve 10 is used to evacuate the working chamber 7. The target vacuum level evacuated by the vacuum valve 10 is determined based on the type of liquid working fluid and the downhole operating temperature, ensuring that the liquid working fluid can normally boil and vaporize under the saturated vapor pressure conditions corresponding to the operating temperature of the lower evaporation section of the ultra-long gravity heat pipe working chamber 7.

[0041] The liquid working fluid is selected based on the bottom-hole production zone temperature. The liquid working fluid can be any one of water, ammonia, methanol, ethanol, acetone, Freon, or an organic working fluid. When the bottom-hole temperature of the oil well is in the range of 50~120℃, ammonia or an organic working fluid is selected; when the bottom-hole temperature of the oil well is higher than 100℃, water is selected as the liquid working fluid. Specifically, the filling rate of the ultra-long gravity heat pipe working chamber 7 is 25% of the total volume of the ultra-long gravity heat pipe working chamber 7, and it is evacuated through the vacuum valve 10 until the partial pressure of non-condensable gases is lower than 10⁻² Pa.

[0042] Taking the oil production lifting assembly as a rod pump lifting assembly as an example, the working process of the wellbore heating device is as follows: The walking beam pumping unit 12 drives the sucker rod 3 to move up and down reciprocally, driving the pumping unit 4 to lift the high-temperature crude oil at the bottom of the well to the well; the liquid working fluid in the working chamber 7 of the ultra-long gravity heat pipe absorbs the heat transferred from the high-temperature crude oil at the bottom of the well in the lower evaporation section and undergoes phase change vaporization to form steam. Under the pressure difference, the steam rises along the working chamber 7 of the ultra-long gravity heat pipe to the upper condensation section, where it condenses into liquid and releases the latent heat of phase change. The released heat is transferred to the crude oil flowing in the pipe through the pipe wall of the tubing 2, which increases the temperature of the crude oil at the wellhead and reduces the viscosity of the crude oil; the condensed liquid working fluid flows back to the bottom along the inner wall of the working chamber 7 of the ultra-long gravity heat pipe under the action of gravity, completing the spontaneous circulation.

[0043] The inner wall of the working chamber 7 of the ultra-long gravity heat pipe is provided with a reflux enhancement structure on at least one side for accelerating the reflux of the condensing working fluid and reducing the gas-liquid reverse shear resistance. The reflux enhancement structure is a spiral guide groove and / or longitudinal reflux ribs provided on the outer wall of the oil pipe 2 and / or the inner wall of the production casing 1.

[0044] See Figure 2 The reflux enhancement structure is a spiral guide groove 16 located on the outer wall of the oil pipe 2. The spiral guide groove 16 extends spirally downward along the outer wall of the oil pipe 2, with a spiral angle of 15°~45°. It plays a role in converging and guiding the condensate, reducing the gas-liquid reverse shear resistance. See also Figure 3The reflux enhancement structure consists of longitudinal reflux ribs 17 located on the outer wall of tubing 2. These ribs extend axially along the outer wall of tubing 2 and / or the inner wall of production casing 1, with a height of 3-10 mm and a circumferential spacing of 20-50 mm. They converge the circumferential liquid film into streams, reducing the gas-liquid contact area and increasing the reflux velocity. As an alternative implementation, a porous metal capillary reflux mesh can also be used, driving the condensate downwards through capillary suction, which is particularly suitable for deep wells and low filling rates. These three reflux enhancement structures can be used individually or in any combination.

[0045] The annular sealing end cap 6 is also equipped with a monitoring component, including a pressure sensor 14 and / or a temperature transmitter 15. The sensing ends of the pressure sensor 14 and / or the temperature transmitter 15 are inserted into the working chamber 7 of the ultra-long gravity heat pipe to monitor the vacuum level and / or working fluid saturation temperature inside the working chamber of the ultra-long gravity heat pipe in real time. The annular sealing end cap is also equipped with a pressure relief valve and a liquid injection valve that communicate with the inside of the working chamber 7 of the ultra-long gravity heat pipe. The pressure relief valve is used to release pressure when the pressure inside the working chamber 7 of the ultra-long gravity heat pipe exceeds a preset value, and the liquid injection valve is used to replenish liquid working fluid when the working fluid inside the working chamber 7 of the ultra-long gravity heat pipe is insufficient.

[0046] During long-term operation of the device, pressure sensor 14 and temperature transmitter 15 continuously monitor the vacuum level and working fluid temperature inside the working chamber 7 of the ultra-long gravity heat pipe. When the vacuum level or temperature deviates from the preset range, ground operators replenish the vacuum through vacuum valve 10 and / or replenish the liquid working fluid through liquid injection valve 9 to ensure the continuous and stable operation of the device.

[0047] This application also discloses a method for heat tracing a production wellbore, using the aforementioned heat tracing device for the production wellbore, comprising the following steps:

[0048] (1) Select production wells with good sealing of tubing 2 and production casing 1 as the targets for modification;

[0049] (2) The packer 5 is lowered into the annulus between the tubing 2 and the production casing 1 and set above the perforation 11 to block the lower part of the annulus, so that the perforation 11 is below the packer 5 and crude oil can freely enter the production casing 1.

[0050] (3) Install an annular sealing end cap at the wellhead to seal the top of the annular oil casing, so that the annular oil casing forms a closed fixed ultra-long gravity heat pipe working chamber. The perforation below the packer remains open and connected to the formation throughout the entire process. The oil pipe maintains an independent crude oil extraction channel. The oil extraction operation and the heat pipe heat tracing are operated synchronously and do not interfere with each other.

[0051] (4) The working chamber 7 of the ultra-long gravity heat pipe is evacuated to a preset vacuum level by means of the vacuum valve 10 set on the annular sealing end cap 6. The preset vacuum level is determined according to the selected liquid working fluid type and the downhole working temperature. When ammonia / organic working fluid is used, the partial pressure of non-condensable gas in the chamber is lower than 10⁻² Pa.

[0052] (5) Liquid working fluid is injected into the working chamber 7 of the ultra-long gravity heat pipe through the injection valve 9 set on the annular sealing end cap 6, and the injection valve 9 is closed after the filling is completed.

[0053] (6) Start the oil production lifting mechanism to extract crude oil. At the same time, the liquid working fluid in the working chamber 7 of the ultra-long gravity heat pipe absorbs heat and vaporizes in the high temperature zone at the bottom of the well and condenses and releases heat in the low temperature zone at the wellhead. The heat is transferred to the crude oil flowing in the pipe through the pipe wall of the oil pipe 2 to achieve wellbore heating. The condensed liquid working fluid relies on gravity and the guiding effect of the reflux strengthening structure to flow back to the bottom evaporation section along the inner wall of the chamber.

[0054] (7) The vacuum level and / or working fluid saturation temperature inside the working chamber of the ultra-long gravity heat pipe are monitored in real time by a pressure sensor and / or a temperature transmitter installed on the annular sealing end cap. When the vacuum level is found to be lower than the preset threshold or the working fluid temperature is found to be deviated from the preset range, the vacuum is replenished by a vacuum valve and / or the liquid working fluid is replenished by a replenishment valve.

[0055] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A heat tracing device for a production well shaft, characterized in that, The system is installed in conjunction with an existing production well capable of continuous oil production. The well includes a production casing, tubing, and a production lift assembly. The tubing is located inside the production casing, and the production lift assembly is installed in conjunction with the tubing. The inner cavity of the tubing forms an oil extraction channel. The production casing has open perforations in the producing section for the flow of formation crude oil. An annulus is formed between the tubing and the production casing. A packer is installed at the bottom of the annulus that only seals the lower part of the annulus and does not block the perforations. An annulus sealing cap is installed at the wellhead at the top of the annulus to seal the top. The annulus between the packer and the annulus sealing cap forms a closed and fixed ultra-long gravity heat pipe working chamber. The ultra-long gravity heat pipe working chamber is completely isolated from the crude oil extraction channel and simultaneously achieves oil production and wellbore heating. The ultra-long gravity heat pipe working chamber is filled with liquid working fluid and evacuated to a preset vacuum level.

2. The wellbore heat tracing device as described in claim 1, characterized in that, The packer is located at the upper end of the high-temperature production zone above the perforation, so that the lower evaporation section of the ultra-long gravity heat pipe working chamber completely corresponds to the downhole high-temperature production zone.

3. The wellbore heat tracing device as described in claim 1, characterized in that, The crude oil extraction channel and the working chamber of the ultra-long gravity heat pipe are independent of each other. The working chamber of the ultra-long gravity heat pipe is a fixed, stationary chamber that does not participate in the movement of the oil extraction lifting components.

4. The wellbore heat tracing device as described in claim 1, characterized in that, The annular sealing end cap is an annular flange structure, fitted onto the outer wall of the oil pipe and welded to it for sealing connection. It is also bolted to the top flange of the production casing for sealing connection. An injection valve and a vacuum valve are installed on the annular sealing end cap, penetrating into the working chamber of the ultra-long gravity heat pipe. The injection valve is connected to an external liquid supply device, and the vacuum valve is connected to an external vacuum pumping device.

5. The wellbore heat tracing device as described in claim 1, characterized in that, The working medium is selected according to the temperature of the bottom-hole production formation; the liquid working medium is selected from any one of water, ammonia, methanol, ethanol, acetone, Freon or organic working medium.

6. The wellbore heat tracing device as described in claim 1, characterized in that, The oil production lifting assembly is a rod pump lifting assembly, including a sucker rod disposed inside the tubing and a pump installed at the bottom of the tubing. The pump includes a plunger, a pump barrel, an intake valve, and a discharge valve. The lower end of the sucker rod is connected to the plunger, which reciprocates up and down inside the pump. A polished rod seal is installed at the top of the tubing. The top of the sucker rod passes through the central hole of the annular sealing end cap and the polished rod seal, and the top of the sucker rod is connected to the suspension rope device of a beam pumping unit installed on the ground.

7. The wellbore heat tracing device as described in claim 1, characterized in that, The inner wall of at least one side of the working chamber of the ultra-long gravity heat pipe is provided with a reflux enhancement structure for accelerating the reflux of the condensing working fluid and reducing the gas-liquid reverse shear resistance. The reflux enhancement structure is a spiral guide groove and / or longitudinal reflux ribs provided on the outer wall of the oil pipe and / or the inner wall of the production casing.

8. The wellbore heat tracing device as described in claim 7, characterized in that, The spiral angle of the spiral guide groove is 15°~45°; the height of the longitudinal return rib is 3~10mm, and the circumferential spacing between adjacent longitudinal return ribs is 20~50mm.

9. The wellbore heat tracing device as described in claim 1, characterized in that, The annular sealing end cap is also equipped with a monitoring component, which includes a pressure sensor and / or a temperature transmitter. The sensing end of the pressure sensor and / or temperature transmitter passes through the working chamber of the ultra-long gravity heat pipe and is used to monitor the vacuum degree and / or working fluid saturation temperature inside the working chamber of the ultra-long gravity heat pipe in real time. The annular sealing end cap is also equipped with a pressure relief valve and a liquid injection valve that communicate with the inside of the working chamber of the ultra-long gravity heat pipe. The pressure relief valve is used to release pressure when the pressure inside the working chamber of the ultra-long gravity heat pipe exceeds a preset value, and the liquid injection valve is used to replenish liquid working fluid when the working fluid inside the working chamber of the ultra-long gravity heat pipe is insufficient.

10. A method for heat tracing a production wellbore, characterized in that, The method of using the wellbore heat tracing device as described in any one of claims 1-9 includes the following steps: (1) Select production wells with good tubing and production casing sealing as the target for modification; (2) Insert the packer into the annulus between the tubing and the production casing to seal the lower part of the annulus; (3) Install an annular sealing end cap at the wellhead to seal the top of the annulus of the oil casing, so that the annulus of the oil casing forms a closed fixed ultra-long gravity heat pipe working chamber. The perforation below the packer remains open and connected to the formation throughout the entire process. The oil pipe maintains an independent crude oil extraction channel. The oil extraction operation and the heat pipe heat tracing operate synchronously without interfering with each other. (4) Evacuate the working chamber of the ultra-long gravity heat pipe to the preset vacuum level. The preset vacuum level is determined according to the selected liquid working fluid type and the downhole working temperature. When using ammonia / organic working fluid, the partial pressure of non-condensable gas in the chamber is less than 10⁻² Pa. (5) Inject liquid working fluid into the working chamber of the ultra-long gravity heat pipe through the injection valve; (6) Start the oil production lifting mechanism to extract crude oil. At the same time, the liquid working fluid in the working chamber of the ultra-long gravity heat pipe absorbs heat and vaporizes in the high temperature zone at the bottom of the well and condenses and releases heat in the low temperature zone at the wellhead. The heat is transferred to the crude oil flowing in the pipe through the pipe wall to achieve wellbore heating. The condensed liquid working fluid relies on gravity and the guiding effect of the reflux strengthening structure to flow back to the bottom evaporation section along the inner wall of the chamber. (7) The vacuum degree and / or working fluid saturation temperature inside the working chamber of the ultra-long gravity heat pipe are monitored in real time by a pressure sensor and / or a temperature transmitter installed on the annular sealing end cap. When the vacuum degree is found to be lower than the preset threshold or the working fluid temperature is found to be deviated from the preset range, the vacuum is replenished by a vacuum valve and / or the liquid working fluid is replenished by a liquid injection valve.

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