Heat pump cycle viscosity reduction device based on central tube closed heat exchange and use method

Abstract

The present application relates to the technical field of oil and gas exploitation, and particularly relates to a heat pump circulation viscosity reduction device based on center pipe closed heat exchange and a use method. The technical scheme is that a center pipe heat exchange unit is located in a production oil pipe, and a ground circulation unit is located at one side of a wellhead device; a hollow sucker rod column of the center pipe heat exchange unit is provided with an inner center pipe, a bottom of the inner center pipe is provided with a center pipe bottom head, and a pipe wall of an upper side is provided with more than one center pipe bottom side opening; the beneficial effects are that heat exchange working medium heated by a heat pump is lowered along the inner center pipe to the hollow sucker rod column in a wellbore, and then is raised to a near ground position along the center pipe bottom side opening between the inner center pipe and the hollow sucker rod column, closed heat exchange prevents blockage and circulation, energy consumption is greatly reduced by using the heat pump technology and the geothermal energy, safety is improved, the function of preventing blockage and increasing production is effectively realized, and the number of workover operations is reduced.

Description

Technical Field

[0001] This invention relates to the field of oil and gas extraction technology, and in particular to a heat pump circulation viscosity reduction device based on a central pipe closed-loop heat exchanger and its usage method. Background Technology

[0002] During oil extraction, as oil is brought to the surface from the bottom of the well along the wellbore, especially in the near-surface tubing, paraffin in the oil precipitates below its precipitation point due to temperature and pressure drops. This paraffin then adheres to the wellbore walls, tubing, sucker rods, and other equipment surfaces, forming wax deposits. This wax deposition poses serious risks: first, it blocks oil flow channels, reduces tubing diameter, and increases flow resistance, leading to reduced or even halted well production; second, it increases equipment load, raising the load on the pumping unit's suspension point and increasing the risk of sucker rod breakage or pump jamming; and third, it reduces formation permeability, as wax deposits near the wellbore can clog pores and hinder crude oil inflow.

[0003] Currently, wellbore heating anti-clogging technology mainly adopts electric heating technology, which converts electrical energy into heat energy to directly heat the wellbore fluid. Its core function is to prevent paraffin wax from precipitating or to melt existing deposited wax by raising the wellbore temperature above the wax precipitation point, thereby achieving anti-clogging. Specifically, it includes the following methods: One is the skin effect electric heating rod technology: using industrial frequency AC power to generate a skin effect in the tubing, causing the tubing itself to heat up, concentrating the heat on the tubing wall for efficient wax melting; the second is flat cable heating: a corrosion-resistant, flexible flat cable is lowered into the wellbore along with the tubing, releasing heat after being energized; its advantages are: precise heating, strong controllability, and suitability for remote well sites or wells with high wax content. Its disadvantages are: since most oil wells need to be kept powered on to continuously heat the tubing near the ground, the energy consumption is high. For example, most oil wells require an additional 120,000 to 150,000 yuan in electricity costs per year to continuously heat the tubing, which also increases the number of well workover operations and leads to a continuous increase in oil extraction costs. In addition, the use of electric heating technology also has many safety hazards, such as the risk of short circuits, leakage, overheating causing fires or equipment damage, electric shock to personnel, etc. Summary of the Invention

[0004] The purpose of this invention is to address the aforementioned deficiencies in existing technologies by providing a heat pump circulation viscosity reduction device and its usage method based on a central tube closed-loop heat exchange. On one hand, it combines heat pump technology and geothermal technology, significantly reducing energy consumption to about 30% of the cost of simply using electric heating. On the other hand, it employs an internal central tube added to the hollow sucker rod string to fully utilize geothermal energy and achieve a fully enclosed circulation heat exchange, thereby avoiding blockages during oil extraction and achieving increased production. In addition, it also reduces safety hazards.

[0005] The present invention discloses a heat pump circulation viscosity reduction device based on a central tube closed-loop heat exchanger. The technical solution includes a pumping unit system and a control system, further comprising a surface circulation unit and a central tube heat exchange unit. The central tube heat exchange unit is located inside the production tubing, while the surface circulation unit and control system are located on one side of the wellhead device. The central tube heat exchange unit includes a hollow sucker rod string, an internal central tube, a central tube bottom end cap, and a central tube bottom side opening. The upper end of the hollow sucker rod string is connected to a polished hollow sucker rod. An internal central tube is installed inside the polished hollow sucker rod and the hollow sucker rod string. The bottom of the internal central tube is provided with a central tube bottom end cap, and one or more central tube bottom side openings are provided on the tube wall of the internal central tube above the central tube bottom end cap. The surface circulation unit includes a replenishment tank, a Y-type filter, a surface circulation pump, and a heat pump. The lower outlet of the replenishment tank is connected to the inlet of the surface circulation pump via a pipeline and the Y-type filter. The outlet of the surface circulation pump is connected to the upper end of the built-in central pipe at the wellhead device via a main pipeline. The heat exchange medium flows down along the built-in central pipe to the bottom of the hollow sucker rod string in the wellbore, and then enters the annulus between the built-in central pipe and the hollow sucker rod string through the side opening at the bottom of the central pipe and flows up to the surface. At the wellhead device, it is connected to the inlet of the replenishment tank via the return annulus connection port and the return main pipeline, forming a closed heat exchange anti-clogging circulation. The main pipeline at the outlet end of the ground circulation pump is connected to the heat pump via a control valve and a branch pipeline. The output end of the heat pump is connected to the main pipeline at the outlet end of the ground circulation pump via a first branch pipeline. The heat pump heats and raises the temperature of the heat exchange medium.

[0006] Preferably, the output end of the heat pump is connected to the natural gas heater via a second branch pipeline, and the output end of the natural gas heater is connected to the first branch pipeline of the heat pump output end via a second branch pipeline, so that the heat exchange medium is further heated by the natural gas heater.

[0007] Preferably, the upper part of the hollow sucker rod is connected to the sucker rod suspension rope device, which is connected to the donkey head of the sucker unit via a suspension rope. A sealing diversion short circuit is connected to the upper part of the sucker rod suspension rope device. A central tube connector is installed on the top of the sealing diversion short circuit. The outer end of the central tube connector is connected to the inlet conversion head, and the outer end of the inlet conversion head is connected to the main pipeline, so that the built-in central tube is connected to the main pipeline. A return annular connection port is provided on one side of the sealing diversion short circuit. The outer end of the return annular connection port is connected to the return conversion head, and the outer end of the return conversion head is connected to the return main pipeline.

[0008] Preferably, the lower end of the aforementioned central tube connector is threaded to the upper end of the sealing diversion short circuit. The inner wall of the upper end of the central tube connector has a tapered hole structure, and the outer wall of the upper end of the central tube connector is provided with external threads. The tapered joint at the outer end of the liquid inlet converter is fixed to the upper end of the central tube connector by a locking nut.

[0009] Preferably, the left end of the aforementioned reflux annular connection port is threaded to the side wall of the sealing diversion short circuit, the inner wall of the right end of the reflux annular connection port is a tapered hole structure, and the outer wall of the right end of the reflux annular connection port is provided with external threads. The tapered connector at the outer end of the return liquid conversion head is fixed to the inner wall of the right end of the reflux annular connection port by the second locking nut.

[0010] Preferably, the lower end of the bottom end cap of the aforementioned central tube is equipped with a built-in floating centering base. The upper end of the built-in floating centering base contacts the lower end of the bottom end cap of the central tube, and the lower end of the built-in floating centering base is mounted on the built-in central tube fixed base through a floating centering base spring. The floating centering base spring is located on a spring fixed seat, so that the lower end of the built-in central tube is in a free floating state, eliminating the stress concentration problem caused by thermal expansion and contraction and movement of the built-in central tube.

[0011] Preferably, the aforementioned built-in central tube is made of stainless steel. The outer diameter of the stainless steel tube is smaller than the inner diameter of the hollow sucker rod polish and the hollow sucker rod string, forming an annular channel between the stainless steel tube and the hollow sucker rod polish and the hollow sucker rod string. This achieves a closed-loop heat exchange and anti-clogging circulation in which the heat exchange medium flows downward along the built-in central tube and upward along the annular channel.

[0012] Preferably, the bottom side opening of the central tube is provided in one or more sets and is evenly distributed on the tube wall of the built-in central tube. The edge of the bottom side opening of the central tube is provided with a flow guiding chamfer of 30-60 degrees, so that after the heat exchange medium flows down from the built-in central tube, it smoothly changes direction and enters the annular channel upward, reducing the generation of eddies and reducing flow resistance.

[0013] The method of using the heat pump circulation viscosity reduction device based on a central tube closed-loop heat exchange mentioned in this invention includes the following steps: First, the pump is lowered along the casing to the designed well depth via the production tubing. Then, the internal center tube is inserted into the hollow sucker rod polished rod and the hollow sucker rod string. A center tube bottom end cap is installed at the bottom of the internal center tube, and one or more bottom side openings are machined into the tube wall. Additionally, a floating center tube centering base is installed below the center tube bottom end cap. The lower end of the floating center tube centering base is mounted on a fixed base of the internal center tube via a floating centering base spring, with the spring located on a spring fixing seat. This allows the hollow sucker rod string to move up and down under the influence of the hollow sucker rod polished rod. The lower end of the built-in central tube is in a free-floating state, eliminating stress concentration at the lower end when the built-in central tube moves up and down; then, the hollow sucker rod string with the built-in central tube installed is lowered into the production tubing and connected to the downhole pump; then, a wellhead cross-connector is installed from the wellhead to connect the sucker rod sealing packing box and the main and return main lines of the heat exchange working fluid circulation. The main line is connected to the outlet of the surface circulation pump, and the inlet of the surface circulation pump is connected to the make-up tank through a pipeline and a Y-type filter. The return main line is connected to the upper inlet of the make-up tank to form a closed heat exchange anti-clogging circulation. II. The circulating heat exchange process is as follows: First, start the surface circulation pump and heat pump to heat the heat exchange medium in the replenishment tank. Then, pump it into the built-in central tube through the surface circulation pump and the main pipeline. The heat exchange medium goes down along the built-in central tube to the bottom end cap of the central tube at the bottom of the well. Then, it smoothly changes direction along the side opening at the bottom of the central tube and enters the annulus between the built-in central tube and the hollow sucker rod string and goes up. In the first half of the downward process, the heat exchange medium releases heat outward through the built-in central tube to heat the production tubing. In the second half, the cooled heat exchange medium is heated by the formation in the second half, and its temperature gradually increases. At the bottom, the heat exchange medium smoothly moves upward through the opening at the bottom side of the central tube. In the first half of the upward process, the heat exchange medium continues to be heated by the formation. In the second half, the heated heat exchange medium continues to heat the production tubing until it returns to the surface replenishment tank through the return main pipeline. After being filtered by the Y-type filter, it continues to be heated by the heat pump and pumped into the built-in central tube downhole by the surface circulation pump, achieving continuous heating and circulation of the production tubing. In addition, based on the requirements of reducing crude oil viscosity or the temperature of the ground transportation pipeline, the natural gas heater is started. After the heat exchange medium is further heated by the natural gas heater, it is sent down into the built-in central pipe through the main pipeline for heat exchange, thereby meeting the higher temperature heating requirements.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: First, this invention introduces heat pump technology into the anti-clogging and production enhancement process in oil extraction, and combines it with geothermal technology. By heating the heat exchange medium with a heat pump and then using geothermal energy for supplemental heating, a fully enclosed circulating heat exchange process is achieved, thereby significantly reducing the energy consumption of heating near-ground oil pipelines to about 30% of the cost of simply using electric heating. In addition, when higher temperatures are required, the temperature can be further increased by using a natural gas heater, thus expanding the heat exchange. This invention avoids clogging during oil extraction and significantly improves the effect of increasing oil production. Secondly, this invention employs an internal central tube added inside the hollow sucker rod polished rod and hollow sucker rod string to achieve cyclic heating of the near-ground section of the tubing. Furthermore, a floating centering base and a floating centering base spring are installed below the bottom end cap of the internal central tube. When the internal central tube moves up and down under the drive of the hollow sucker rod polished rod, the lower end of the internal central tube is in a free floating state, eliminating the problem of stress concentration at the lower end when the internal central tube moves up and down, thus improving its service life. Third, in addition, the present invention uses circulating heat exchange medium to avoid the safety hazards that occur when using electric heating alone. Furthermore, the present invention is simple to construct, which can reduce the number and time of well workover operations, significantly increase the production time of oil wells, and improve economic efficiency. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the overall operation of the present invention; Figure 2 This is a connection diagram of the ground circulation unit; Figure 3 This is a schematic diagram of the wellbore cross-section of the central tube heat exchange unit; Figure 4 This is an enlarged schematic diagram of the lower end of the built-in central tube; Figure 5 This is a structural diagram of the bottom end cap of the central tube and the side opening at the bottom of the central tube; Figure 6 This is a three-dimensional structural diagram of the bottom end cap of the central tube and the side opening at the bottom of the central tube; Figure 7 yes Figure 4 Schematic diagram of AA section; Figure 8 This is a schematic diagram of the heat exchange of the central tube heat exchange unit in the wellbore; Figure 9 This is a schematic diagram showing the connection between the wellhead of the central tube heat exchange unit and the surface circulation unit; Figure 10 This is an enlarged schematic diagram of the connection of the dedicated sealed shunt short circuit; Figure 11 This is a schematic diagram showing the connection between the bottom of the built-in central tube and the floating base of the central tube; Figure 12 This is a graph showing the relationship between downhole depth and temperature in a pure circulating pump-driven heat exchange system. Figure 13 This is a graph showing the relationship between downhole depth and temperature when using a 2000kW heat pump unit for heat supplementation. Figure 14 This is a graph showing the relationship between well depth and temperature in a surface associated gas combustion boiler for direct high-temperature heating. In the diagram: Surface circulation unit 100, central tube heat exchange unit 200, pumping unit system 400, control system 500, replenishment tank 101, Y-type filter 102, surface circulation pump 103, heat pump 104, natural gas heater 105, wellhead four-way valve 106, hollow sucker rod polished rod 107, sucker rod sealing packing box 108; Casing 201, production tubing 202, hollow sucker rod string 206, built-in central tube 207, central tube bottom end cap 208, central tube bottom side opening 209, oil pump 210, sealing diversion short connector 212, central tube connector 213, liquid inlet conversion head 214, return annular connection port 215, return liquid conversion head 216, built-in central tube floating centering base 217, floating centering base spring 218, built-in central tube fixed base 219, spring fixing seat 220, heat sink 221, locking nut 213.1, second locking nut 215.1, donkey head 401, suspension rope 402, bare rod suspension rope device 403. Detailed Implementation

[0016] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0017] Example 1, referring to Figures 1-11 The present invention discloses a heat pump circulation viscosity reduction device based on a central tube closed heat exchange, comprising a pumping unit system 400 and a control system 500, wherein it further comprises a surface circulation unit 100 and a central tube heat exchange unit 200, the central tube heat exchange unit 200 being located inside the production tubing 202, and the surface circulation unit 100 and the control system 500 being located on one side of the wellhead device; the central tube heat exchange unit 200 comprises a hollow sucker rod string 206, an internal central tube 207, a central tube bottom end cap 208, and a central tube bottom side opening 209, the upper end of the hollow sucker rod string 206 being connected to a hollow sucker rod polished rod 107, the internal central tube 207 being installed inside the hollow sucker rod polished rod 107 and the hollow sucker rod string 206, the bottom of the internal central tube 207 being provided with a central tube bottom end cap 208, and one or more central tube bottom side openings 209 being provided on the tube wall of the internal central tube 207 above the central tube bottom end cap 208; The surface circulation unit 100 includes a replenishment tank 101, a Y-type filter 102, a surface circulation pump 103, and a heat pump 104. The lower outlet of the replenishment tank 101 is connected to the inlet of the surface circulation pump 103 through a pipeline and the Y-type filter 102. The outlet of the surface circulation pump 103 is connected to the upper end of the built-in central pipe 207 at the wellhead device through a main pipeline. The heat exchange medium flows down along the built-in central pipe 207 to the bottom of the hollow sucker rod string 206 in the wellbore, and then enters the annulus between the built-in central pipe 207 and the hollow sucker rod string 206 through the side opening 209 at the bottom of the central pipe and flows up to the surface. At the wellhead device, it is connected to the inlet of the replenishment tank 101 through the return annulus connection port 215 and the return main pipeline to form a closed heat exchange anti-clogging circulation. The main pipeline at the outlet end of the ground circulation pump 103 is connected to the heat pump 104 via a control valve and a branch pipeline. The output end of the heat pump 104 is connected to the main pipeline at the outlet end of the ground circulation pump 103 via a first branch pipeline. The heat pump 104 heats and raises the temperature of the heat exchange medium.

[0018] In addition, the output end of the heat pump 104 mentioned in this invention is connected to the natural gas heater 105 through a second branch pipeline, and the output end of the natural gas heater 105 is connected to the first branch pipeline of the output end of the heat pump 104 through a second branch pipeline, so that the heat exchange medium is further heated by the natural gas heater 105.

[0019] Reference Figure 9 The upper part of the hollow sucker rod polished rod 107 mentioned in this invention is connected to the polished rod suspension rope 403, and the polished rod suspension rope 403 is connected to the donkey head 401 of the sucker unit through the suspension rope 402; a sealing diversion short connector 212 is connected to the upper part of the polished rod suspension rope 403, a central tube connector 213 is installed on the top of the sealing diversion short connector 212, the outer end of the central tube connector 213 is connected to the liquid inlet conversion head 214, and the outer end of the liquid inlet conversion head 214 is connected to the main pipeline, so that the built-in central tube 207 is connected to the main pipeline; a return annular connection port 215 is provided on one side of the sealing diversion short connector 212, the outer end of the return annular connection port 215 is connected to the return liquid conversion head 216, and the outer end of the return liquid conversion head 216 is connected to the return main pipeline.

[0020] Reference Figure 10 The lower end of the central tube connector 213 mentioned in this invention is connected to the upper end of the sealing diversion short connector 212 by a thread. The inner wall of the upper end of the central tube connector 213 is a tapered hole structure, and the outer wall of the upper end of the central tube connector 213 is provided with an external thread. The tapered connector at the outer end of the liquid inlet conversion head 214 is fixed to the upper end of the central tube connector 213 by a locking nut 213.1.

[0021] The left end of the aforementioned reflux annular connection port 215 is threaded to the side wall of the sealing diversion short connector 212. The inner wall of the right end of the reflux annular connection port 215 has a tapered hole structure, and the outer wall of the right end of the reflux annular connection port 215 is provided with external threads. The tapered connector at the outer end of the return liquid conversion head 216 is fixed to the inner wall of the right end of the reflux annular connection port 215 by the second locking nut 215.1.

[0022] Reference Figure 11 The lower end of the bottom end cap 208 of the central tube mentioned in this invention is equipped with a built-in central tube floating centering base 217. The upper end of the built-in central tube floating centering base 217 is in contact with the lower end of the bottom end cap 208 of the central tube. The lower end of the built-in central tube floating centering base 217 is mounted on the built-in central tube fixed base 219 through a floating centering base spring 218. The floating centering base spring 218 is located on the spring fixed seat 220, so that the lower end of the built-in central tube 207 is in a free floating state, eliminating the stress concentration problem caused by thermal expansion and contraction and movement of the built-in central tube 207.

[0023] The aforementioned built-in central tube 207 is made of stainless steel. The outer diameter of the stainless steel tube is smaller than the inner diameter of the hollow sucker rod polished rod 107 and the hollow sucker rod string 206. It forms an annular channel with the hollow sucker rod polished rod 107 and the hollow sucker rod string 206, realizing a closed heat exchange anti-blocking circulation in which the heat exchange medium flows downward along the built-in central tube 207 and upward along the annular channel.

[0024] Reference Figures 4-7 The central tube bottom side opening 209 mentioned in this invention is provided in one or more sets and is evenly distributed on the tube wall of the built-in central tube 207. The edge of the central tube bottom side opening 209 is provided with a flow guiding chamfer of 30-60 degrees, so that after the heat exchange working medium flows down from the built-in central tube 207, it smoothly changes direction and enters the annular channel upward, reducing the generation of eddies and reducing flow resistance.

[0025] The method of using the heat pump circulation viscosity reduction device based on a central tube closed-loop heat exchanger mentioned in this invention includes the following process: First, the oil pump 210 is lowered along the casing 201 to the designed well depth via the production tubing 202. Then, the built-in center tube 207 is inserted into the hollow sucker rod polished rod 107 and the hollow sucker rod string 206. A center tube bottom end cap 208 is provided at the bottom of the built-in center tube 207, and one or more center tube bottom side openings 209 are machined on the tube wall. In addition, a floating center tube base 217 is installed below the center tube bottom end cap 208. The lower end of the built-in center tube floating center tube base 217 is mounted on the built-in center tube fixed base 219 via a floating center tube base spring 218, and the floating center tube base spring 218 is located on the spring fixing seat 220, so that the hollow sucker rod string 206 is positioned on the hollow sucker rod polished rod 107. When the tube moves up and down, the lower end of the built-in central tube 207 is in a free-floating state, eliminating the stress concentration generated at the lower end when the built-in central tube 207 moves up and down; then, the hollow sucker rod string 206 with the built-in central tube 207 installed is lowered into the inner cavity of the production tubing 202 and connected to the downhole pump 210; then, a wellhead cross-connector 106 is installed from the wellhead on the surface, connecting the sucker rod sealing packing box 108 and the main pipeline and return pipeline of the heat exchange working fluid circulation, and the main pipeline is connected to the outlet of the surface circulation pump 103, the inlet of the surface circulation pump 103 is connected to the replenishment tank 101 through the pipeline and the Y-type filter 102, and the return pipeline is connected to the upper inlet of the replenishment tank 101, forming a closed heat exchange anti-clogging circulation; II. The circulating heat exchange process is as follows: First, the surface circulation pump 103 and heat pump 104 are started to heat the heat exchange medium in the replenishment tank 101. Then, the heat exchange medium is pumped into the built-in central pipe 207 through the surface circulation pump 103 and the main pipeline. The heat exchange medium goes down along the built-in central pipe 207 to the bottom end cap 208 of the central pipe at the bottom of the well, and then smoothly changes direction along the side opening 209 at the bottom of the central pipe and enters the annulus between the built-in central pipe 207 and the hollow sucker rod string 206 and goes up. In the first half of the downward process, the high-temperature heat exchange medium releases heat to the outside through the built-in central tube 207 to heat the production tubing 202. In the second half, the heat exchange medium, after its temperature drops, is heated by the formation in the second half, and its temperature gradually increases. At the bottom, the heat exchange medium smoothly moves upward through the side opening 209 at the bottom of the central tube. In the first half of the upward process, the heat exchange medium continues to be heated by the formation. In the second half, the heated heat exchange medium continues to heat the production tubing 202 until it returns to the replenishment tank 101 on the surface through the return main pipeline. After being filtered by the Y-type filter 102, it continues to be heated by the heat pump 104 and pumped into the built-in central tube 207 downhole by the surface circulation pump 103, thus achieving continuous heating and circulation of the production tubing 202. In addition, based on the requirements of reducing the viscosity of crude oil or the temperature requirements of the ground transportation pipeline, the natural gas heater 105 is started. After the heat exchange medium is further heated by the natural gas heater 105, it is sent down into the built-in central pipe 207 through the main pipeline for heat exchange, thereby meeting the higher temperature heating requirements.

[0026] Reference Figure 12 This system utilizes a single surface circulation pump for extraction of geothermal energy. The wellhead return water design temperature is 50℃, the working fluid velocity is 0.5~0.8 m / s, and the heat exchange method is passive absorption of geothermal energy. The relationship between the inlet water temperature, return water temperature, and formation temperature is as follows: Figure 12 As shown, the downward section absorbs geothermal heat from the strata, while the upward section dissipates heat from the strata.

[0027] Reference Figure 13 To supplement heat using a 2000kW heat pump unit, the wellhead return water design temperature is 60℃. The heat exchange method is a dual heat source of heat pump preheating and geothermal energy. The downward section uses dual absorption of waste heat from the heat pump and geothermal energy from the bottom layer. The upward section has minimal heat loss and closed-loop compensation from the heat pump.

[0028] Reference Figure 14 The surface associated gas combustion boiler directly heats the water at high temperature. The wellhead return water design temperature is 80℃. The heat exchange method is high-temperature forced heat tracing. The downward section dissipates heat to the bottom layer in reverse. The upward section is where the boiler provides real-time heat replenishment, and the temperature continues to rise.

[0029] Example 2: The present invention provides a heat pump circulation viscosity reduction device based on a central tube closed-loop heat exchange, comprising a pumping unit system 400 and a control system 500, further comprising a surface circulation unit 100 and a central tube heat exchange unit 200. The central tube heat exchange unit 200 is located inside the production tubing 202, and the surface circulation unit 100 and the control system 500 are located on one side of the wellhead device. The central tube heat exchange unit 200 comprises a hollow sucker rod string 206, an internal central tube 207, a central tube bottom end cap 208, and a central tube bottom side opening 209. The upper end of the hollow sucker rod string 206 is connected to a hollow sucker rod polished rod 107. The internal central tube 207 is installed inside the hollow sucker rod polished rod 107 and the hollow sucker rod string 206. The bottom of the internal central tube 207 is provided with a central tube bottom end cap 208, and one or more central tube bottom side openings 209 are provided on the tube wall of the internal central tube 207 above the central tube bottom end cap 208.

[0030] The difference from Example 1 is: In this embodiment, a heat sink 221 is installed on the built-in central tube 207 above the bottom side opening 209 of the central tube to achieve better and smoother heat exchange.

[0031] The above description is merely a partial preferred embodiment of the present invention. Any person skilled in the art can modify the above-described technical solutions or modify them into equivalent technical solutions. Therefore, any simple modifications or equivalent transformations made based on the technical solutions of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A heat pump circulation viscosity reduction device based on a central pipe closed-loop heat exchanger, comprising an oil pumping unit system (400) and a control system (500), characterized in that: It also includes a surface circulation unit (100) and a central tube heat exchange unit (200). The central tube heat exchange unit (200) is located inside the production tubing (202). The surface circulation unit (100) and the control system (500) are located on one side of the wellhead device. The central tube heat exchange unit (200) includes a hollow sucker rod string (206), an internal central tube (207), a central tube bottom end cap (208), and a central tube bottom side opening (209). The upper end of the hollow sucker rod string (206) is connected to the hollow sucker rod polished rod (107). The internal central tube (207) is installed inside the hollow sucker rod polished rod (107) and the hollow sucker rod string (206). The bottom of the internal central tube (207) is provided with a central tube bottom end cap (208). One or more central tube bottom side openings (209) are provided on the tube wall of the internal central tube (207) above the central tube bottom end cap (208). The surface circulation unit (100) includes a replenishment tank (101), a Y-type filter (102), a surface circulation pump (103), and a heat pump (104). The lower outlet of the replenishment tank (101) is connected to the inlet of the surface circulation pump (103) through a pipeline and the Y-type filter (102). The outlet of the surface circulation pump (103) is connected to the upper end of the built-in central pipe (207) at the wellhead device through a main pipeline. The heat exchange medium flows down along the built-in central pipe (207) to the bottom of the hollow sucker rod string (206) in the wellbore, and then enters the annulus between the built-in central pipe (207) and the hollow sucker rod string (206) through the side opening (209) at the bottom of the central pipe and flows up to the surface. At the wellhead device, it is connected to the inlet of the replenishment tank (101) through the return annulus connection port (215) and the return main pipeline to form a closed heat exchange anti-clogging circulation. The main pipeline at the outlet end of the ground circulation pump (103) is connected to the heat pump (104) through a control valve and a branch pipeline. The output end of the heat pump (104) is connected to the main pipeline at the outlet end of the ground circulation pump (103) through a first branch pipeline. The heat pump (104) heats and raises the temperature of the heat exchange medium. The lower end of the bottom end cap (208) of the central tube is equipped with a built-in central tube floating centering base (217). The upper end of the built-in central tube floating centering base (217) is in contact with the lower end of the bottom end cap (208) of the central tube. The lower end of the built-in central tube floating centering base (217) is installed on the built-in central tube fixed base (219) through a floating centering base spring (218). The floating centering base spring (218) is located on the spring fixed seat (220), so that the lower end of the built-in central tube (207) is in a free floating state, eliminating the stress concentration problem caused by thermal expansion and contraction and movement of the built-in central tube (207). The bottom side opening (209) of the central tube is provided in one or more sets and is evenly distributed on the tube wall of the built-in central tube (207). The edge of the bottom side opening (209) of the central tube is provided with a flow guide chamfer of 30-60 degrees, so that after the heat exchange medium flows down from the built-in central tube (207), it smoothly changes direction and enters the annular channel to flow up, reducing the generation of eddies and reducing flow resistance.

2. The heat pump circulation viscosity reduction device based on a central tube closed-loop heat exchanger according to claim 1, characterized in that: The output end of the heat pump (104) is connected to the natural gas heater (105) through the second branch pipeline. The output end of the natural gas heater (105) is connected to the first branch pipeline of the output end of the heat pump (104) through the second branch pipeline. The heat exchange medium is further heated by the natural gas heater (105).

3. The heat pump circulation viscosity reduction device based on a central tube closed-loop heat exchanger according to claim 2, characterized in that: The upper part of the hollow sucker rod polished rod (107) is connected to the polished rod suspension rope device (403), and the polished rod suspension rope device (403) is connected to the donkey head (401) of the pumping unit through the suspension rope (402); a sealing diversion short connector (212) is connected to the upper part of the polished rod suspension rope device (403), a central tube connector (213) is installed on the top of the sealing diversion short connector (212), the outer end of the central tube connector (213) is connected to the liquid inlet conversion head (214), and the outer end of the liquid inlet conversion head (214) is connected to the main pipeline, so that the built-in central tube (207) is connected to the main pipeline; a return annular connection port (215) is provided on one side of the sealing diversion short connector (212), the outer end of the return annular connection port (215) is connected to the return liquid conversion head (216), and the outer end of the return liquid conversion head (216) is connected to the return main pipeline.

4. The heat pump circulation viscosity reduction device based on a central tube closed-loop heat exchanger according to claim 3, characterized in that: The lower end of the central tube connector (213) is connected to the upper end of the sealing diversion short connector (212) by a thread. The inner wall of the upper end of the central tube connector (213) is a tapered hole structure, and the outer wall of the upper end of the central tube connector (213) is provided with an external thread. The tapered connector at the outer end of the liquid inlet converter (214) is fixed to the upper end of the central tube connector (213) by a locking nut (213.1).

5. The heat pump circulation viscosity reduction device based on a central tube closed-loop heat exchanger according to claim 4, characterized in that: The left end of the reflux annular connection port (215) is threaded to the side wall of the sealing diversion short connector (212). The inner wall of the right end of the reflux annular connection port (215) is a tapered hole structure. The outer wall of the right end of the reflux annular connection port (215) is provided with external threads. The tapered connector at the outer end of the return liquid conversion head (216) is fixed to the inner wall of the right end of the reflux annular connection port (215) by the second locking nut (215.1).

6. The heat pump circulation viscosity reduction device based on a central tube closed-loop heat exchanger according to claim 5, characterized in that: The built-in central tube (207) is made of stainless steel. The outer diameter of the stainless steel tube is smaller than the inner diameter of the hollow sucker rod polished rod (107) and the hollow sucker rod string (206). It forms an annular channel with the hollow sucker rod polished rod (107) and the hollow sucker rod string (206), realizing a closed heat exchange anti-blocking circulation in which the heat exchange medium flows down along the built-in central tube (207) and up along the annular channel.

7. A method of using the heat pump circulation viscosity reduction device based on a central tube closed-loop heat exchange as described in claim 6, characterized in that: The process includes the following: First, the oil pump (210) is lowered to the designed well depth via the production tubing (202) along the casing (201). Then, the built-in center tube (207) is inserted into the hollow sucker rod polished rod (107) and the hollow sucker rod string (206). A center tube bottom end cap (208) is provided at the bottom of the built-in center tube (207), and one or more center tube bottom side openings (209) are machined on the tube wall. In addition, a built-in center tube floating centering base (217) is installed below the center tube bottom end cap (208). The lower end of the built-in center tube floating centering base (217) is installed on the built-in center tube fixed base (219) via a floating centering base spring (218), and the floating centering base spring (218) is located on the spring fixed seat (220), so that the hollow sucker rod string (206) is in the hollow sucker rod polished rod (107) (208). When the internal central tube (207) moves up and down under the drive of 07), the lower end of the internal central tube (207) is in a free floating state, which eliminates the stress concentration generated at the lower end when the internal central tube (207) moves up and down; then, the hollow sucker rod string (206) with the internal central tube (207) installed above is lowered into the inner cavity of the production tubing (202) and connected to the downhole pump (210); then, a wellhead cross-connector (106) is installed from the wellhead on the surface, connecting the sucker rod sealing packing box (108) and the main pipeline and return pipeline of the heat exchange working fluid circulation, and the main pipeline is connected to the outlet of the surface circulation pump (103), the inlet of the surface circulation pump (103) is connected to the replenishment tank (101) through the pipeline and the Y-type filter (102), and the return pipeline is connected to the upper inlet of the replenishment tank (101) to form a closed heat exchange anti-blocking circulation; II. The circulating heat exchange process is as follows: First, start the surface circulation pump (103) and heat pump (104) to heat the heat exchange medium in the replenishment tank (101), and then pump it into the built-in central pipe (207) through the surface circulation pump (103) and the main pipeline. The heat exchange medium goes down along the built-in central pipe (207) to the bottom end cap (208) of the central pipe at the bottom of the well, and then smoothly changes direction along the side opening (209) at the bottom of the central pipe to enter the annulus between the built-in central pipe (207) and the hollow sucker rod string (206) and goes up. In the first half of the downward process, the heat exchange medium releases heat to the outside through the built-in central tube (207) to heat the production tubing (202). In the second half, the heat exchange medium, after its temperature drops, is heated by the formation in the second half, and the temperature of the heat exchange medium gradually increases. At the bottom, the heat exchange medium smoothly moves upward through the side opening (209) at the bottom of the central tube. In the first half of the upward process, the heat exchange medium continues to be heated by the formation. In the second half, the heated heat exchange medium continues to heat the production tubing (202) until the heat exchange medium returns to the replenishment tank (101) on the surface through the return main pipeline. After being filtered by the Y-type filter (102), it continues to be heated by the heat pump (104) and pumped into the built-in central tube (207) in the well under the action of the surface circulation pump (103) to achieve continuous heating and circulation of the production tubing (202). In addition, according to the viscosity reduction of crude oil or the temperature requirements of the ground transportation pipeline, the natural gas heater (105) is started. After the heat exchange medium is further heated by the natural gas heater (105), it is sent to the built-in central pipe (207) through the main pipeline for heat exchange, thereby meeting the higher temperature heating requirements.

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