A device for preventing cold damage to a carbon dioxide flooding wellbore and a method of using the device

Abstract

The present invention relates to the field of oil production technology, and in particular to a device for preventing cold damage in a carbon dioxide driven wellbore and a method for using the device. The technical solution is: an anti-blocking jet pump is connected through an oil pipe and a small-diameter oil pipe, and the anti-blocking jet pump is installed in the middle of the oil well, the lower end of the anti-blocking jet pump is connected to an underground gas-liquid separator through an oil pipe, the lower part of the underground gas-liquid separator is connected to a fin heat exchanger, the lower part of the fin heat exchanger is connected to a step-down degassing heat exchanger, and the step-down degassing heat exchanger is located below the oil layer. The beneficial effects are: not only can the cooling problem in the oil production wellbore caused by heat absorption during the gasification of carbon dioxide be reduced, and the situation of crude oil waxing and ice blocking the liquid flow channel caused by cooling can be avoided, and the corrosion of carbon dioxide to the pipe column can be greatly reduced due to the incorporation of power fluid; in addition, the present invention can backwash the well to dissolve wax and remove blockage, avoid re-operation, and reduce operating costs.

Description

Technical Field

[0001] The invention relates to the technical field of oil extraction, and in particular to a device for preventing cold damage to a carbon dioxide driven wellbore and a use method thereof. Background Art

[0002] At present, most of my country's oil fields are developed by water injection, and the water drive recovery rate can only reach about 40%. Moreover, long-term large-scale water injection has caused the oil fields to generally enter a high water content stage, so other methods of improving recovery are needed. For example, carbon dioxide recovery technology has huge application potential. Carbon dioxide recovery technology is a technology that injects carbon dioxide into oil layers to increase the oil recovery rate of oil fields. This technology can not only meet the needs of oil field development, but also solve the problem of carbon dioxide storage, protect the atmospheric environment, and inhibit the greenhouse effect. This technology is not only suitable for conventional oil reservoirs, but also for low-permeability, ultra-low-permeability oil reservoirs, deep tight oil reservoirs, shale oil and shale reservoirs, and can significantly improve crude oil recovery.

[0003] However, during the process of CO2 injection and huff-and-puff oil recovery, as the CO2 content in underground oil and water increases, CO2 will depressurize and gasify in the oil production wellbore, and CO2 will absorb heat during the gasification process, resulting in a significant drop in temperature of the oil production wellbore. When the temperature is lower than the wax precipitation temperature of crude oil in the wellbore, the crude oil will wax and freeze in the oil production pipe string and the wellhead, blocking the liquid flow channel, especially the liquid flow in the low-temperature formation section near the ground; in addition, CO2 will also produce carbonate ions, which will cause rapid corrosion of the oil production pipe string, and sometimes cause severe corrosion and fracture of the pipe string at a local depth, which will lead to abnormal production or even shut down of the well.

[0004] The existing solutions are: the first method is the heating technology process in the oil production wellbore, which has the problems of complex construction and uneconomical; the second method is the method of adding chemical agents, which has the problems of cumbersome operation, unstable effect and poor economy; the third method is the drainage and production jet pump lifting system, but the drainage and production jet pump lifting system cannot perform mid-way cleaning, unblocking and anti-corrosion pre-filming treatment on the parts of the oil pipe and casing that are in contact with the oil flow. Therefore, with the increase in gas injection oil wells, it is necessary to invent a carbon dioxide injection wellbore cold damage prevention device and use method. Summary of the invention

[0005] The purpose of the present invention is to provide a carbon dioxide drive wellbore cold damage prevention device and a method of use, which can not only reduce the problem of cooling and freezing in the oil production wellbore and at the wellhead caused by heat absorption during the carbon dioxide gasification process, but also avoid the situation where the crude oil is waxed and frozen and blocks the liquid flow channel due to cooling. When an anti-blocking jet drainage pump is used, the addition of power fluid can greatly reduce the corrosion of carbon dioxide to the pipe column. In addition, the present invention can backwash the well to dissolve wax and remove blockage, avoid re-operation, and reduce operating costs.

[0006] The present invention discloses a device for preventing cold damage to a wellbore in carbon dioxide drive, and the technical scheme thereof is as follows: comprising an oil pipe, a small-diameter oil pipe and an oil pump, the oil pump is connected through the oil pipe and the small-diameter oil pipe, and the oil pump is installed in the middle of the oil well, and the device is characterized in that: it also comprises a downhole gas-liquid separator, a fin heat exchanger, and a pressure-reducing degassing heat exchanger, the lower end of the oil pump is connected to the downhole gas-liquid separator through the oil pipe, the lower part of the downhole gas-liquid separator is connected to the fin heat exchanger, the lower part of the fin heat exchanger is connected to the pressure-reducing degassing heat exchanger, and the pressure-reducing degassing heat exchanger is located below the oil layer;

[0007] The step-down degassing heat exchanger comprises a heat exchange outer tube, a porous throttling umbrella plate, a separation umbrella plate, a fixed nail tube, heat exchange fins and a lower inlet. The heat exchange fins are evenly distributed on the outer wall of the heat exchange outer tube. More than one group of porous throttling umbrella plates are installed in the inner cavity of the heat exchange outer tube. Each group of porous throttling umbrella plates is fixed by a fixed nail tube, and a separation umbrella plate is installed between two groups of porous throttling umbrella plates. A lower inlet is provided at the lower end of the heat exchange outer tube.

[0008] Preferably, the above-mentioned downhole gas-liquid separator includes a separation outer tube, an air outlet, a center tube, a separation inner plate, a liquid flow hole, a lower support seat, and a lower interface. The inner cavity of the separation outer tube is provided with a center tube, and the outer wall of the center tube is connected to the inner wall of the separation outer tube through a plurality of separation inner plates. The lower end of the center tube is mounted on the lower support seat, and the center tube is provided with a plurality of liquid flow holes. The separation outer tube is provided with a plurality of air outlets, and a shut-off hole is provided at the bottom of the center tube, and a lower interface is provided at the lower end of the separation outer tube.

[0009] Preferably, a plurality of groups of gas separation cups are installed on the upper part of the inner cavity of the above-mentioned separation outer tube, and the separation outer tube on the upper side of each group of gas separation cups is provided with a gas outlet hole, and the central tube on the lower side of each group of gas separation cups is provided with a liquid flow hole.

[0010] Preferably, an air outlet is provided on the separation outer tube on the upper side of each set of separation inner plates; the above-mentioned separation inner plate is an inverted umbrella-shaped structure, the upper end of which is connected to the inner wall of the separation outer tube, and the lower end is connected to the outer wall of the central tube.

[0011] Preferably, the gas separation cup comprises an upper connecting portion and a cup body, wherein the upper portion of the cup body is the upper connecting portion, which is connected to the inner wall of the separation outer tube via the outer end surface of the upper connecting portion.

[0012] Preferably, the oil pump is an anti-blocking jet drainage pump or a rod oil pump.

[0013] Preferably, the anti-blocking jet drainage pump comprises a pump body, a throat, a nozzle, a spring, a sleeve switch, a check valve seat, a first power fluid inlet, an outer tube and an inner tube; the inner tube is installed on the upper part of the pump body, the throat is installed in the inner cavity of the inner tube, the nozzle is installed below the throat, and a spring, a sleeve switch and a check valve seat are provided below the nozzle; an outer tube is installed on the outer side of the pump body, a power fluid channel is formed between the outer tube and the inner tube, and the first power fluid inlet is provided on the lower side of the pump body, connecting the power fluid channel with the second power fluid inlet at the lower part of the nozzle.

[0014] Preferably, a valve ball is installed on the upper part of the check valve seat, a check valve lower inlet is provided at the lower part of the check valve seat, and a formation fluid inlet is provided at the lower part of the pump body.

[0015] Preferably, the above-mentioned sleeve switch is located on the outside of the second power fluid inlet, and a spring is installed on the upper part of the sleeve switch. Under the push of the high-pressure power fluid, the sleeve switch moves upward to open the second power fluid inlet. When the injection of power fluid stops, the sleeve switch closes the second power fluid inlet under the action of the spring.

[0016] The method for using the carbon dioxide flooding wellbore cold damage prevention device mentioned in the present invention comprises the following process:

[0017] 1. Inject high-pressure power fluid into the annulus between the oil pipe and the small-diameter oil pipe on the ground. The high-pressure power fluid enters the pump body through the first power fluid inlet of the anti-blocking jet drainage pump. Driven by the high-pressure power fluid, the sleeve switch moves upward to open the second power fluid inlet, and the degassed formation fluid from the bottom of the pump is ejected along the nozzle with a high-speed jet, and then enters the throat pipe together for mixing, and then decelerates through the diffuser and reaches the ground along the small-diameter oil pipe;

[0018] Second, the formation fluid in the oil layer first moves downward in the wellbore, and then moves upward through the pressure-reducing degassing heat exchanger at the bottom of the wellbore. Due to the suction of the anti-blocking jet drainage pump, the pressure in the bottom of the wellbore drops, and carbon dioxide gas and natural gas escape from the formation fluid due to the pressure reduction. The gasification process absorbs heat and causes the surrounding temperature to drop. At this time, the deeper the wellbore, the higher the formation temperature. The heat of the external formation of the pressure-reducing degassing heat exchanger is transferred to the heat exchange outer tube through the heat exchange fins, raising the temperature of carbon dioxide gas, natural gas and formation fluid; carbon dioxide gas, natural gas and formation fluid continue to move upward along the fin heat exchanger and continue to increase in temperature until they reach the downhole gas-liquid separator;

[0019] 3. After passing through the multi-stage and spaced separation inner plates and multiple groups of gas separation cups in the downhole gas-liquid separator, continuous interception, pressure reduction and forced degassing are achieved. The forced degassing gas goes up along the annulus of the oil pipe and casing through the outlet hole. This process continuously absorbs the heat of the casing and the formation. After heating through long-distance heat exchange, the temperature is higher than the freezing point and the ground ambient temperature. The low-gas formation fluid goes up along the central pipe and enters the formation fluid inlet of the anti-blocking jet drainage pump and is sucked and lifted to the ground.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1. The present invention installs a step-down degassing heat exchanger at the bottom of the wellbore, which can forcefully remove a portion of the carbon dioxide gas on the one hand, and fully utilize the heat in the deep formation on the other hand; then, heat exchange is generated with a length of fin heat exchanger to increase the temperature of the gas and formation fluid, and then forced degassing is performed through the downhole gas-liquid separator, and the forcedly removed carbon dioxide gas and natural gas pass through the gas outlet and ascend along the annulus of the oil pipe and casing; in addition, when the formation fluid is pumped out of the ground through the anti-blocking jet drainage pump, wax blockage can be effectively prevented due to the full utilization of the heat of the formation to increase the temperature; at the same time, with the elimination of the low temperature point after centralized degassing in the pipe string, the pre-separation of carbon dioxide and the dilution effect of the power fluid, the corrosion environment in the pipe string is effectively improved and controlled, and the corrosion rate is greatly reduced, which has obvious advantages over the existing conventional rod pump and submersible electric pump oil production;

[0022] 2. The depressurized degassing heat exchanger and the anti-wax plugging and anti-blocking jet pump capable of backwashing wells are novel in structure and unique in function. The liquid circulation in the wellbore is used to exchange the heat energy at the bottom of the well and then send it to the upper low-temperature wellbore section, which ingeniously prevents and removes the blockage of liquid cooling in the low-temperature formation section adjacent to the ground. It is suitable for safe and reliable oil production in wells with high carbon dioxide content, high wax content and heavy oil wells; it can be used as an effective method for increasing the temperature of produced liquid by lengthening the lower tail pipe of the pump for rod pump and rodless pump oil production wells, and is also more suitable for high geothermal deep wells as an effective method for increasing the temperature of produced liquid by lengthening the lower tail pipe of the pump for rod pump and rodless pump oil production wells;

[0023] 3. The present invention can perform physical and chemical beneficial treatments such as cleaning of the surface of the oil pipe and casing by forward well washing at any time, chemical wax dissolution to remove blockage, and pre-filming for corrosion protection, etc. The process is simple, reliable, economical and practical. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the overall principle of embodiment 1 of the present invention;

[0025] Figure 2 It is a structural schematic diagram of an anti-blocking jet drainage pump;

[0026] Figure 3 It is a schematic diagram of the structure of the downhole gas-liquid separator;

[0027] Figure 4 yes Figure 3 An enlarged schematic diagram of the gas separation cup in FIG.

[0028] Figure 5 It is a schematic diagram of the structure of a step-down degassing heat exchanger;

[0029] Figure 6 is a schematic diagram of the overall principle of Embodiment 3 of the present invention;

[0030] In the figure above: oil pipe 1, small diameter oil pipe 2, anti-blocking jet drainage pump 3, downhole gas-liquid separator 4, fin heat exchanger 5, pressure-reducing degassing heat exchanger 6, casing 7, oil layer 8, screen tube 9;

[0031] Pump body 3.1, throat 3.2, nozzle 3.3, spring 3.4, sleeve switch 3.5, check valve seat 3.6, valve ball 3.7, first power fluid inlet 3.8, outer tube 3.9, inner tube 3.10, formation fluid inlet 3.11, check valve lower inlet 3.12, second power fluid inlet 3.13;

[0032] Separation outer tube 4.1, gas separation cup 4.2, gas outlet 4.3, central tube 4.4, separation inner plate 4.5, liquid flow hole 4.6, lower support seat 4.7, lower interface 4.8, intercepting hole 4.9, upper connecting part 4.2.1, cup body 4.2.2;

[0033] Heat exchange outer tube 6.1, porous throttling umbrella plate 6.2, separation umbrella plate 6.3, fixed nail tube 6.4, heat exchange fin 6.5, lower inlet 6.6. DETAILED DESCRIPTION

[0034] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0035] Example 1, reference Figure 1-Figure 5 The present invention mentions a carbon dioxide drive wellbore cold damage prevention device, comprising an oil pipe 1, a small-diameter oil pipe 2, and an anti-blocking jet drainage pump 3, the anti-blocking jet drainage pump 3 is connected through the oil pipe 1 and the small-diameter oil pipe 2, and the anti-blocking jet drainage pump 3 is installed in the middle of the oil well, wherein it also includes a downhole gas-liquid separator 4, a fin heat exchanger 5, and a pressure-reducing degassing heat exchanger 6, the lower end of the anti-blocking jet drainage pump 3 is connected to the downhole gas-liquid separator 4 through the oil pipe 1, the lower part of the downhole gas-liquid separator 4 is connected to the fin heat exchanger 5, the lower part of the fin heat exchanger 5 is connected to the pressure-reducing degassing heat exchanger 6, and the pressure-reducing degassing heat exchanger 6 is located below the oil layer 8;

[0036] Reference Figure 5The step-down degassing heat exchanger 6 comprises a heat exchange outer tube 6.1, a porous throttling umbrella plate 6.2, a separation umbrella plate 6.3, a fixing nail tube 6.4, a heat exchange fin 6.5 and a lower inlet 6.6. The heat exchange fin 6.5 is evenly distributed on the outer wall of the heat exchange outer tube 6.1. More than one group of porous throttling umbrella plates 6.2 are installed in the inner cavity of the heat exchange outer tube 6.1. Each group of porous throttling umbrella plates 6.2 is installed and fixed by a fixing nail tube 6.4. A separation umbrella plate 6.3 is installed between two groups of porous throttling umbrella plates 6.2. A lower inlet 6.6 is provided at the lower end of the heat exchange outer tube 6.1.

[0037] Reference Figure 3 and Figure 4 The downhole gas-liquid separator 4 mentioned in the present invention includes a separation outer tube 4.1, an air outlet 4.3, a central tube 4.4, a separation inner plate 4.5, a liquid flow hole 4.6, a lower support seat 4.7, and a lower interface 4.8. The inner cavity of the separation outer tube 4.1 is provided with a central tube 4.4, and the outer wall of the central tube 4.4 is connected to the inner wall of the separation outer tube 4.1 through a plurality of separation inner plates 4.5. The lower end of the central tube 4.4 is arranged on the lower support seat 4.7, and the central tube 4.4 is provided with a plurality of liquid flow holes 4.6. The separation outer tube 4.1 is provided with a plurality of air outlets 4.3, and a cut-off hole 4.9 is provided at the bottom of the central tube 4.4. A lower interface 4.8 is provided at the lower end of the separation outer tube 4.1.

[0038] Among them, multiple groups of gas separation cups 4.2 are installed on the upper part of the inner cavity of the above-mentioned separation outer tube 4.1, and the separation outer tube 4.1 on the upper side of each group of gas separation cups 4.2 is provided with a gas outlet 4.3, and the central tube 4.4 on the lower side of each group of gas separation cups 4.2 is provided with a liquid flow hole 4.6.

[0039] An air outlet hole 4.3 is provided on the separation outer tube 4.1 on the upper side of each set of separation inner plates 4.5.

[0040] The above-mentioned separation inner plate 4.5 is an inverted umbrella-shaped structure, the upper end of which is connected to the inner wall of the separation outer tube 4.1, and the lower end of which is connected to the outer wall of the central tube 4.4.

[0041] Reference Figure 4 The gas separation cup 4.2 mentioned in the present invention comprises an upper connection part 4.2.1 and a cup body 4.2.2. The upper part of the cup body 4.2.2 is the upper connection part 4.2.1, which is connected to the inner wall of the separation outer tube 4.1 through the outer end surface of the upper connection part 4.2.1.

[0042] Reference Figure 2The anti-blocking jet drainage pump 3 mentioned in the present invention includes a pump body 3.1, a throat 3.2, a nozzle 3.3, a spring 3.4, a sleeve switch 3.5, a check valve seat 3.6, a first power fluid inlet 3.8, an outer tube 3.9, and an inner tube 3.10. The inner tube 3.10 is installed on the upper part of the pump body 3.1, the throat 3.2 is installed in the inner cavity of the inner tube 3.10, the nozzle 3.3 is installed below the throat 3.2, and the spring 3.4, the sleeve switch 3.5 and the check valve seat 3.6 are provided below the nozzle 3.3; the outer tube 3.9 is installed on the outer side of the pump body 3.1, and a power fluid channel is formed between the outer tube 3.9 and the inner tube 3.10. The first power fluid inlet 3.8 is arranged on the lower side of the pump body 3.1, connecting the power fluid channel with the second power fluid inlet 3.13 at the lower part of the nozzle 3.3.

[0043] A valve ball 3.7 is installed on the upper part of the check valve seat 3.6, a check valve lower inlet 3.12 is provided on the lower part of the check valve seat 3.6, and a formation fluid inlet 3.11 is provided on the lower part of the pump body 3.1.

[0044] The above-mentioned sleeve switch 3.5 is located on the outside of the second power fluid inlet 3.13, and a spring 3.4 is installed on the upper part of the sleeve switch 3.5. Under the push of the high-pressure power fluid, the sleeve switch 3.5 moves upward to open the second power fluid inlet 3.13. When the injection of power fluid stops, the sleeve switch 3.5 closes the second power fluid inlet 3.13 under the action of the spring 3.4.

[0045] The method for using the carbon dioxide flooding wellbore cold damage prevention device mentioned in the present invention comprises the following process:

[0046] 1. High-pressure power fluid is injected into the annulus between the oil pipe 1 and the small-diameter oil pipe 2 on the ground. The high-pressure power fluid enters the pump body 3.1 through the first power fluid inlet 3.8 of the anti-blocking jet drainage pump 3. Under the push of the high-pressure power fluid, the sleeve switch 3.5 moves upward to open the second power fluid inlet 3.13, and the degassed formation fluid from the lower part of the pump is ejected along the nozzle 3.3 with a high-speed jet, and then enters the throat pipe 3.2 together for mixing, and then decelerates through the diffuser and reaches the ground along the small-diameter oil pipe 2;

[0047] Second, the formation fluid in the oil layer 8 first moves downward in the wellbore, and then moves upward through the pressure-reducing degassing heat exchanger 6 at the bottom of the wellbore. Due to the suction of the anti-blocking jet drainage pump 3, the pressure in the bottom of the wellbore decreases, and the carbon dioxide gas and natural gas escape from the formation fluid due to the pressure reduction. The gasification process absorbs heat and causes the surrounding temperature to drop. At this time, the deeper the wellbore, the higher the formation temperature. The heat of the external formation of the pressure-reducing degassing heat exchanger 6 is transferred to the heat exchange outer tube 6.1 through the heat exchange fins 6.5, raising the temperature of the carbon dioxide gas, natural gas and formation fluid; the carbon dioxide gas, natural gas and formation fluid continue to move upward along the fin heat exchanger 5 and continue to increase in temperature until they reach the downhole gas-liquid separator 4;

[0048] 3. After passing through the multi-stage and spaced separation inner plates 4.5 and multiple groups of gas separation cups 4.2 in the downhole gas-liquid separator 4, continuous interception, pressure reduction and forced degassing are achieved. The forced degassing gas goes up along the annulus of the oil pipe 1 and the casing 7 through the gas outlet 4.3. This process continuously absorbs the heat of the casing 7 and the formation. After the temperature is raised through long-distance heat exchange, the temperature is higher than the freezing point and the ground ambient temperature; the low-gas formation fluid goes up along the central pipe 4.4 and enters the formation fluid inlet 3.11 of the anti-blocking jet drainage pump 3 to be sucked and lifted to the ground.

[0049] In addition, the present invention can realize reverse well washing, wax dissolving and plugging removal, and the specific operation is as follows:

[0050] On the ground, well-washing fluid of designed temperature is injected into the small-diameter oil pipe 2, and the well-washing fluid flows downward along the inner pipe 3.10 of the anti-blocking jet drainage pump 3. Since the second power fluid inlet 3.13 of the sliding sleeve switch 3.5 is in a closed state under the action of the spring 3.4, and the valve ball 3.7 sits on the check valve seat 3.6, the well-washing fluid flows downward along the formation fluid discharge channel and enters the central pipe 4.4 of the downhole gas-liquid separator 4, continues to flow downward along the central pipe 4.4, enters the fin heat exchanger 5 and the pressure-reducing degassing heat exchanger 6, and is discharged back to the annulus between the oil pipe 1 and the casing 7 through the lower inlet 6.6 of the pressure-reducing degassing heat exchanger 6 until it returns to the ground, thereby completing the cleaning of the entire device.

[0051] Example 2, a carbon dioxide driven wellbore cold damage prevention device mentioned in the present invention includes an oil pipe 1, a small-diameter oil pipe 2, and a rod oil pump. The rod oil pump is connected by the oil pipe 1 and the small-diameter oil pipe 2, and the rod oil pump is installed in the middle of the oil well. It also includes a downhole gas-liquid separator 4, a fin heat exchanger 5, and a pressure-reducing degassing heat exchanger 6. The lower end of the rod oil pump is connected to the downhole gas-liquid separator 4 through the oil pipe 1, the lower part of the downhole gas-liquid separator 4 is connected to the fin heat exchanger 5, the lower part of the fin heat exchanger 5 is connected to the pressure-reducing degassing heat exchanger 6, and the pressure-reducing degassing heat exchanger 6 is located below the oil layer 8.

[0052] The rod pump used in this embodiment is a conventional rod pump, such as a beam pump or a belt pump, which can achieve the above functions.

[0053] Example 3, a carbon dioxide driven wellbore cold damage prevention device mentioned in the present invention includes an oil pipe 1, a small-diameter oil pipe 2, and an oil pump. The oil pump is connected through the oil pipe 1 and the small-diameter oil pipe 2, and the oil pump is installed in the middle of the oil well. It also includes a downhole gas-liquid separator 4, a fin heat exchanger 5, and a pressure-reducing degassing heat exchanger 6. The lower end of the oil pump is connected to the downhole gas-liquid separator 4 through the oil pipe 1, the lower part of the downhole gas-liquid separator 4 is connected to the fin heat exchanger 5, the lower part of the fin heat exchanger 5 is connected to the pressure-reducing degassing heat exchanger 6, and the pressure-reducing degassing heat exchanger 6 is located below the oil layer 8.

[0054] The difference from Example 1 or 2 is:

[0055] Reference Figure 6 A screen pipe 9 is installed below the pressure-reducing degassing heat exchanger 6 to achieve a better sand prevention effect.

[0056] The above are only some preferred embodiments of the present invention. Any person skilled in the art may modify the above technical solutions or modify them into equivalent technical solutions. Therefore, the corresponding simple modifications or equivalent transformations made according to the technical solutions of the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A device for preventing cold damage to a wellbore in a carbon dioxide flooding process, comprising an oil pipe (1), a small-diameter oil pipe (2) and an oil pump, wherein the oil pump is connected to the oil pipe (1) and the small-diameter oil pipe (2), and the oil pump is installed in the middle of the oil well, wherein: It also includes a downhole gas-liquid separator (4), a fin heat exchanger (5), and a pressure-reducing degassing heat exchanger (6); the lower end of the oil pump is connected to the downhole gas-liquid separator (4) via an oil pipe (1); the lower part of the downhole gas-liquid separator (4) is connected to the fin heat exchanger (5); the lower part of the fin heat exchanger (5) is connected to the pressure-reducing degassing heat exchanger (6); and the pressure-reducing degassing heat exchanger (6) is located below the oil layer (8); The pressure-reducing degassing heat exchanger (6) comprises a heat exchange outer tube (6.1), a porous throttling umbrella plate (6.2), a separation umbrella plate (6.3), a fixed nail tube (6.4), heat exchange fins (6.5) and a lower inlet (6.6); the heat exchange fins (6.5) are evenly distributed on the outer wall of the heat exchange outer tube (6.1); more than one group of porous throttling umbrella plates (6.2) are installed in the inner cavity of the heat exchange outer tube (6.1); each group of porous throttling umbrella plates (6.2) is installed and fixed by a fixed nail tube (6.4); a separation umbrella plate (6.3) is installed between two groups of porous throttling umbrella plates (6.2); and a lower inlet (6.6) is provided at the lower end of the heat exchange outer tube (6.1).

2. The device for preventing cold damage in a carbon dioxide flooding wellbore according to claim 1 is characterized in that: The downhole gas-liquid separator (4) comprises a separation outer tube (4.1), an air outlet hole (4.3), a central tube (4.4), a separation inner plate (4.5), a liquid flow hole (4.6), a lower support seat (4.7), and a lower interface (4.8). The inner cavity of the separation outer tube (4.1) is provided with a central tube (4.4). The outer wall of the central tube (4.4) is connected to the inner wall of the separation outer tube (4.1) via a plurality of separation inner plates (4.5). The lower end of the central tube (4.4) is mounted on the lower support seat (4.7). The central tube (4.4) is provided with a plurality of liquid flow holes (4.6). The separation outer tube (4.1) is provided with a plurality of air outlet holes (4.3). The bottom of the central tube (4.4) is provided with a cut-off hole (4.9). The lower end of the separation outer tube (4.1) is provided with a lower interface (4.8).

3. The device for preventing cold damage in a carbon dioxide flooding wellbore according to claim 2 is characterized in that: A plurality of groups of gas separation cups (4.2) are installed on the upper part of the inner cavity of the separation outer tube (4.1), and the separation outer tube (4.1) on the upper side of each group of gas separation cups (4.2) is provided with a gas outlet hole (4.3), and the central tube (4.4) on the lower side of each group of gas separation cups (4.2) is provided with a liquid flow hole (4.6).

4. The device for preventing cold damage to a wellbore in carbon dioxide flooding according to claim 3 is characterized in that: An air outlet hole (4.3) is provided on the separation outer tube (4.1) on the upper side of each set of separation inner plates (4.5); the separation inner plates (4.5) are inverted umbrella-shaped structures, with the upper ends connected to the inner walls of the separation outer tubes (4.1) and the lower ends connected to the outer walls of the central tube (4.4).

5. The device for preventing cold damage to a wellbore in carbon dioxide flooding according to claim 4 is characterized in that: The gas separation cup (4.2) comprises an upper connecting portion (4.2.1) and a cup body (4.2.2); the upper portion of the cup body (4.2.2) is the upper connecting portion (4.2.1), and the outer end surface of the upper connecting portion (4.2.1) is connected to the inner wall of the separation outer tube (4.1).

6. The device for preventing cold damage to a wellbore in carbon dioxide flooding according to claim 5 is characterized in that: The oil pump adopts an anti-blocking jet drainage pump (3) or a rod-type oil pump.

7. The device for preventing cold damage to a wellbore during carbon dioxide flooding according to claim 6 is characterized in that: The anti-blocking jet drainage pump (3) comprises a pump body (3.1), a throat pipe (3.2), a nozzle (3.3), a spring (3.4), a sleeve switch (3.5), a check valve seat (3.6), a first power fluid inlet (3.8), an outer pipe (3.9), and an inner pipe (3.10). The inner pipe (3.10) is installed on the upper part of the pump body (3.1), the throat pipe (3.2) is installed in the inner cavity of the inner pipe (3.10), and the nozzle is installed below the throat pipe (3.2). (3.3), a spring (3.4), a sleeve switch (3.5) and a check valve seat (3.6) are provided below the nozzle (3.3); an outer tube (3.9) is installed outside the pump body (3.1), a power fluid channel is formed between the outer tube (3.9) and the inner tube (3.10), and a first power fluid inlet (3.8) is provided at the lower side of the pump body (3.1), connecting the power fluid channel with a second power fluid inlet (3.13) at the lower part of the nozzle (3.3).

8. The device for preventing cold damage to a wellbore during carbon dioxide flooding according to claim 7 is characterized in that: A valve ball (3.7) is installed on the upper part of the check valve seat (3.6), a check valve lower inlet (3.12) is provided on the lower part of the check valve seat (3.6), and a formation fluid inlet (3.11) is provided on the lower part of the pump body (3.1).

9. The device for preventing cold damage to a wellbore in carbon dioxide flooding according to claim 8 is characterized in that: The sleeve switch (3.5) is located outside the second power fluid inlet (3.13), and a spring (3.4) is installed on the upper part of the sleeve switch (3.5). Under the push of the high-pressure power fluid, the sleeve switch (3.5) moves upward to open the second power fluid inlet (3.13). When the injection of power fluid stops, the sleeve switch (3.5) closes the second power fluid inlet (3.13) under the action of the spring (3.4).

10. The method for using the carbon dioxide flooding wellbore cold damage prevention device according to claim 9, characterized in that The process includes:

1. High-pressure power fluid is injected into the annulus between the oil pipe (1) and the small-diameter oil pipe (2) on the ground. The high-pressure power fluid enters the pump body (3.1) through the first power fluid inlet (3.8) of the anti-blocking jet drainage pump (3). Under the push of the high-pressure power fluid, the sleeve switch (3.5) moves upward to open the second power fluid inlet (3.13), and the degassed formation fluid from the lower part of the pump is ejected along the nozzle (3.3) with a high-speed jet. The fluid then enters the throat pipe (3.2) and mixes with the fluid. The fluid is then decelerated through the diffuser and reaches the ground along the small-diameter oil pipe (2).

2. The formation fluid in the oil layer (8) first moves downward in the wellbore, and then moves upward through the pressure-reducing degassing heat exchanger (6) at the bottom of the wellbore. Due to the suction of the anti-blocking jet drainage pump (3), the pressure at the bottom of the wellbore decreases, and the carbon dioxide gas and natural gas are released from the formation fluid due to the pressure reduction. The gasification process absorbs heat and causes the surrounding temperature to drop. At this time, the deeper the wellbore, the higher the formation temperature. The heat of the external formation of the pressure-reducing degassing heat exchanger (6) is transferred to the heat exchange outer tube (6.1) through the heat exchange fins (6.5), thereby raising the temperature of the carbon dioxide gas, natural gas and formation fluid. The carbon dioxide gas, natural gas and formation fluid continue to move upward along the fin heat exchanger (5) and continue to increase in temperature until they reach the downhole gas-liquid separator (4); 3. After passing through the multi-stage and spaced separation inner plates (4.5) and multiple groups of gas separation cups (4.2) in the downhole gas-liquid separator (4), continuous interception, pressure reduction and forced degassing are achieved. The forced degassing gas passes through the gas outlet (4.3) and ascends along the annulus of the oil pipe (1) and the casing (7). This process continuously absorbs the heat of the casing (7) and the formation. After being heated by long-distance heat exchange, the temperature is higher than the freezing point and the ground environment temperature. The low-gas formation fluid ascends along the central pipe (4.4) and enters the formation fluid inlet (3.11) of the anti-blocking jet drainage pump (3) to be sucked and lifted to the ground.

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