US20170234111A1

US20170234111A1 - Device for Removing and Preventing Paraffin by Using Electric Heating Generated from Skin Effect-based Natural Gas Electricity and Application thereof

Info

Publication number: US20170234111A1
Application number: US15/110,209
Authority: US
Inventors: Binfei Li; Zhaomin LI; Xinjun Zhang; Chao Zhang
Original assignee: China University of Petroleum CUP
Current assignee: China University of Petroleum CUP
Priority date: 2015-08-05
Filing date: 2015-08-15
Publication date: 2017-08-17
Also published as: CN105178913A; WO2017020336A1

Abstract

A device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity and an application thereof are disclosed, and the device comprises a natural gas collection portion, a natural gas electricity generation portion and a device for removing and preventing paraffin by using electric heating powered by the natural gas electricity generation portion; the natural gas collection portion is used to collect and separate natural gases discharged from a wellbore; the natural gas electricity generation portion generates electricity with natural gases. The power source required by the electric heating of the steel armored cable of the present invention comes from the natural gas electricity generation portion, and the air source required by the natural gas electricity generation portion can be obtained directly from the associated gases extracted from an oil well.

Description

This application is the U.S. national phase of International Application No. PCT/CN2015/086777 Filed on 15 Aug. 2015 which designated the U.S. and claims priority to Chinese Application Nos. CN201510475412.5 filed on 5 Aug. 2015, the entire contents of each of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity and an application thereof, and pertains to the technical field of oil-gas field exploitation equipment.

BACKGROUND ART

During oil extraction, due to decrease in formation temperature and pressure and escape of light hydrocarbons in crude oil, paraffin in the crude oil will be separated out and adsorb on the wall of an oil pipe. Paraffin deposition in a wellbore will narrow down an oil flow channel of an oil well, thus preventing crude oil from flowing. Under serious conditions, it even leads to paraffin blocking in the oil well, thus affecting an extraction rate of crude oil and even leading to a production halt of the oil well. To eliminate the effect of paraffin deposition in an oil well, the oil well needs to be closed regularly to remove the paraffin deposited on the pipe wall of the oil well, which affects normal production of the oil well and increases an extraction cost of crude oil.
Currently, there are a variety of processes for removing and preventing paraffin of oil wells, such as a mechanical method, a thermal method, a chemical method or a microbial method; due to a simple operation and a rapid effect, a thermal mechanical paraffin removing process is widely applied in paraffin removing and preventing operations of wellbores in various oil wells. A common thermal mechanical paraffin removing process comprises a thermal washing paraffin removing process injecting thermal fluid into a wellbore, an electric heating paraffin removing and preventing process based on a skin effect or the like. Generally, the electric heating process adopts a sucker rod, an oil pipe and so on as a heating element in a circuit. Depending on a principle of the skin effect, crude oil in the oil pipe is heated continuously during production, which enables paraffin to be removed and prevented without the need to close the oil well and stop production and implements good effects. Generally, the electric heating process adopts a ground power grid as its power source. Its main problem lies in huge power consumption, which may significantly increase power grid load. For a gas-lift well and a flowing well with no power source near the wellhead and an oil wells with limited power grid load, an application of this kind of process will be restricted. Meanwhile, for a conventional sucker rod or a hollow sucker rod heating, a continuous lowering cannot be realized in a lowering process due to a presence of coupling, which increases operation risks during installation.

SUMMARY OF THE INVENTION

Aiming at the drawbacks in the prior art, the present invention provides a device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity.
The present invention also provides a working method of the device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity.
The present invention adopts an oil well associated natural gas for electricity generation to provide power source. A current frequency can be adjusted and heating power can be controlled through a power frequency electric heating control cabinet and continuous heating through a steel armored cable heating, a loop between a cable core wire and a steel armor is formed. The loop is charged with alternating current, thermal energy is generated on an outer wall of the steel armor through the skin effect to remove paraffin of crude oil or prevent paraffin of crude oil from depositing in the oil pipe. This process has advantages of a small investment and a fast installation speed, which can realize continuous lowering of a steel armored cable and paraffin removing and preventing by electric heating during oil extraction, thus ensuring a normal production of an oil well and safety during an installation operation.

Explanations of Terms:

Heat generation principle of skin-effect tracing heat: it is a physical phenomenon that a going and return current in a “heat pipe” is concentrated on a surface of an inner wall of the heat pipe and heat is generated due to an interactive induction effect generated by the going and return current in an insulated conductor and a ferromagnetic carbon steel “heat pipe”. In other words, a skin phenomenon of a current intensely flows on the inner wall of the “heat pipe” to enable the heat pipe to generate heat, whereas a surface of an outer wall of the heat pipe presents no measurable currents.
The heat generation of skin-effect tracing heat comes from three parts:
1. heat generated by impedance of the “heat pipe” during the returning of currents on the inner wall of the ferromagnetic carbon steel “heat pipe”;
2. heat generated by magnetic hysteresis and eddy currents due to an interactive magnetic field produced between the insulated conductor and the “heat pipe”;
3. heat generated by impedance of the insulated conductor I²R.
The technical solution of the present invention is as follows:
A device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity, characterized in that the device comprises a natural gas collection portion, a natural gas electricity generation portion and a device for removing and preventing paraffin by using electric heating powered by the natural gas electricity generation portion;
the natural gas collection portion is used to collect and separate natural gas discharged from a wellbore;
the natural gas electricity generation portion generates electricity with the natural gas.
According to a preferred embodiment in the present invention, the natural gas collection portion comprises an oil-gas metering station, a joint processing station and a natural gas purifying station that are successively connected to the wellbore.
According to a preferred embodiment in the present invention, an oil storage tank is arranged to be connected with the joint processing station.
According to a preferred embodiment in the present invention, a gas storage tank is arranged to be connected with the natural gas purifying station.
According to a preferred embodiment in the present invention, the natural gas electricity generation portion comprises a natural gas generator set and a power frequency electric heating control cabinet that are connected; and the power frequency electric heating control cabinet is used to control the device for removing and preventing paraffin by using electric heating.
According to a preferred embodiment in the present invention, the device for removing and preventing paraffin by using electric heating comprises a steel armored cable extending into the wellbore sealedly through a Christmas tree, and the steel armored cable is connected with the power frequency electric heating control cabinet.
According to a preferred embodiment in the present invention, the steel armored cable comprises a steel armored sheath, an insulating material layer, a polytetrafluoroethylene layer and a cable core wire that are successively arranged from outside to inside. An advantage of the design herein lies in: an effect of using the polytetrafluoroethylene layer in the present invention is to make the cable core wire sealed and temperature resistant. Sealing is used to prevent outside fluid from contacting the cable core wire to cause a short circuit, and temperature resistance is to improve the temperature resistant degree of the cable core wire.
According to a preferred embodiment in the present invention, the steel armored sheath is a continuously seamless steel tube. An advantage of the design herein lies in: when the steel armored cable is supplied with variable-frequency power, thermal energy is produced on the outer wall of the steel armored sheath through the skin effect, with the sealing and tensile strength of the cable guaranteed at the same time.
According to a preferred embodiment in the present invention, the device for removing and preventing paraffin by using electric heating also comprises a wellhead high-pressure sealing system arranged on the top of the Christmas tree; the wellhead high-pressure sealing system comprises a pressing cap, a sealing packing, a spring, a wedge disc and a cable clamping plate that are passed through successively by the steel armored cable. An advantage of the design herein lies in: based on a structure and principle of a steel armored cable, the present invention adopts a pressing cap, a sealing packing, a spring, a wedge disc and a cable clamping plate to form a high-pressure sealing system. When used in combination with the steel armored cable, it can realize the wellhead sealing at the time when the steel armored cable drops into a well accidentally and an operation of lifting the steel armored cable under pressure is performed, wherein the steel armored cable forms the wellhead high-pressure sealing with the pressing cap, the sealing packing, the spring and the wedge disc, which realizes the effect of high-pressure sealing during a lifting/lowering of the steel armored cable from/into a wellbore as well as in the heating process; the cable clamping plate is used to control a position of the steel armored cable in the wellbore. When the steel armored cable lowers into the wellbore, the spring opens the wedge disc; when the steel armored cable is lifted from the wellbore, the spring resets to close the wedge disc to prevent oil-gas liquid from spewing out along the wellhead.
According to a preferred embodiment in the present invention, a suspension connector is further arranged on the top of the pressing cap.
According to a preferred embodiment in the present invention, the device for removing and preventing paraffin by using electric heating further comprises a centralized heater that is arranged on a tail end of the steel armored cable stretching into the well, the centralized heater comprises a resistance wire connected with the steel armored cable, and a thermal conductive insulating layer is arranged outside of the resistance wire.
According to a preferred embodiment in the present invention, the steel armored cable is connected respectively with the resistance wire and the thermal conductive insulating layer through a double-ferrule fitting.
According to a preferred embodiment in the present invention, the thermal conductive insulating layer is a thermal conductive silica gel layer. An advantage of the design herein lies in: to adapt to a complex well body structure under the well, the present invention combines the thermal conductive silica gel layer with the resistance wire, so as to implement a demand-based bending of the cable in the earth formation.
According to a preferred embodiment in the present invention, the natural gas electricity generation portion comprises a natural gas generator set and multiple sets of power frequency electric heating control cabinets; the multiple sets of power frequency electric heating control cabinets are used for correspondingly controlling the devices for removing and preventing paraffin by using electric heating mounted in a plurality of wellbores respectively. An advantage of the design herein lies in: the present invention can realize respective adjustments of power frequency parameters of the power frequency electric heating control cabinets according to different conditions of paraffin deposition of oil wells through electric energy output by the natural gas generator set, thus realizing non-interfering paraffin removing and preventing operations for a plurality of wellbores through a single natural gas generator set.
A working method of the device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity comprises the following steps:
1) the natural gas collection portion collects and separates out the natural gas in the wellbore and transmits the natural gas to the natural gas electricity generation portion for electricity generation;
2) the natural gas electricity generation portion supplies variable-frequency power for the device for removing and preventing paraffin by using electric heating:
the power frequency electric heating control cabinet outputs variable-frequency power, a live line of the power frequency electric heating control cabinet is connected with the cable core wire of the steel armored cable; and
a zero line of the power frequency electric heating control cabinet is connected with the steel armored sheath of the steel armored cable;
so that the cable core wire and the steel armored sheath form a loop, and thermal energy can be generated on an outer wall of the steel armored sheath via the skin effect, so as to remove paraffin or prevent paraffin from forming in the wellbore by crude oil.
According to a preferred embodiment in the present invention, the working method of the device for removing and preventing paraffin by using electric heating further comprises steps of lowering the steel armored cable into the wellbore and lifting the steel armored cable out of the wellbore:
3) when the steel armored cable is lowered into the wellbore, the spring opens the wedge disc, the steel armored cable enters the wellbore, and then the steel armored cable, the pressing cap, the sealing packing, the spring and the wedge disc form a high-pressure wellhead seal, to achieve a high pressure sealing effect in the lowering process and a heating process of the steel armored cable;
4) when the steel armored cable is lifted out of the wellbore, the spring resets to close the wedge disc to prevent oil-gas fluid from spewing out along the wellhead.
According to a preferred embodiment in the present invention, the working method of the device for removing and preventing paraffin by using electric heating further comprises a step for a condition when the steel armored cable accidentally drops into the wellbore:
5) when the steel armored cable accidentally drops into the wellbore, the spring resets to close the wedge disc to prevent oil-gas fluid from spewing out along the wellhead.
Advantages of the present invention are as follows:
(1) the power source required by the electric heating of the steel armored cable in the present invention comes from the natural gas electricity generation portion, and the air source required by the natural gas electricity generation portion can be obtained directly from associated gases extracted from an oil well. This not only can utilize associated gases, but also avoids the dependence of paraffin removing and preventing technology by electric heating method on power grid;
(2) the present invention utilizes a steel armored cable to melt paraffin deposits in a wellbore. And based on the skin effect, thermal energy is generated on an outer wall of the steel armor by using a loop formed by a cable core wire and a steel armor, which can realize continuous lowering of the steel armored cable and paraffin removing and preventing by electric heating during oil extraction, thus ensuring a normal production of an oil well and safety during an installation operation;
(3) the present invention is equipped with a wellhead high-pressure sealing system. In collaboration with the steel armored cable, it solves the problems of dynamic sealing of the steel armored cable and high-pressure spewing in wells;
(4) the present invention adopts a spring sealed-type switch, and a compression spring opens a sealed wedge disc when a cable lowering into a wellbore is loaded; when the steel armored cable is lifted out of the wellbore, the spring resets to close the wedge disc to prevent oil-gas liquid from spewing out; in this manner, it can realize the wellhead sealing at the time when the steel armored cable drops into a well accidentally and an operation of lifting the steel armored cable under pressure is performed;
(5) the present invention can realize respective adjustments of power frequency parameters of the power frequency electric heating control cabinet according to different conditions of paraffin deposition of oil wells through electric energy output by the natural gas generator set, thus realizing non-interfering paraffin removing and preventing operations for a plurality of wellbores through a single natural gas generator set.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structural schematic view of a device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity described in the present invention;

FIG. 2 is a schematic sectional view of a steel armored cable described in the present invention;

FIG. 3 is a structural schematic view of a centralized heater described in the present invention;

FIG. 4 is a structural schematic view of a natural gas power generation device for removing and preventing paraffin by using electric heating based on a skin effect of an embodiment 10 of the invention;

In FIGS. 1 to 4, 1, power transmission line; 2, suspension connector; 3, pressing cap; 4, sealing packing; 5, spring; 6, wedge disc; 7, cable clamping plate; 8, flange; 9, Christmas tree; 10, well cementation cement wall; 11, casing pipe; 12, wellbore; 13, steel armored cable; 14, oil-gas mixing transportation pipeline; 15, oil-gas metering station; 16, oil-gas mixing transportation pipeline; 17, joint processing station; 18, oil transportation pipeline; 19, oil storage tank; 20, natural gas transportation pipeline; 21, natural gas purifying station; 22, natural gas transportation pipeline; 23, gas storage tank; 24, natural gas transportation pipeline; 25, natural gas generator set; 26, power transmission line; 27, power frequency electric heating control cabinet; 28, steel armored sheath; 29, insulating material layer; 30, polytetrafluoroethylene layer; 31, cable core wire; 32, centralized heater; 33, double-ferrule fitting; 34, thermal conductive insulating layer; 35, resistance wire.
In FIG. 4, 27-1, first power frequency electric heating control cabinet; 27-2, second power frequency electric heating control cabinet; 27-3, third power frequency electric heating control cabinet; 27-4, fourth power frequency electric heating control cabinet;
9-1, first Christmas tree; 9-2, second Christmas tree; 9-3, third Christmas tree; 9-4, fourth Christmas tree.

DETAILED DESCRIPTION OF THE INVENTION

The detailed description of the invention is given herein below by combining with the description and the accompanying drawings, but is not limited to it.

Embodiment 1

A device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity comprises a natural gas collection portion, a natural gas electricity generation portion and a device for removing and preventing paraffin by using electric heating powered by the natural gas electricity generation portion;
the natural gas collection portion is used to collect and separate natural gas discharged from of a wellbore 12;
the natural gas electricity generation portion utilizes the natural gas to generate electricity.
The natural gas collection portion comprises an oil-gas metering station 15, a joint processing station 17 and a natural gas purifying station 21 that are successively connected to the wellbore 12.
The natural gas electricity generation portion comprises a natural gas generator set 25 and a power frequency electric heating control cabinet 27 that are connected; and the power frequency electric heating control cabinet 27 is used to control the device for removing and preventing paraffin by using electric heating.
The device for removing and preventing paraffin by using electric heating comprises a steel armored cable 13 extending into the wellbore 12 sealedly through a Christmas tree 9, and the steel armored cable 13 is connected with the power frequency electric heating control cabinet 27.

Embodiment 2

The device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity described in the embodiment 1, characterized in that the steel armored cable 13 comprises a steel armored sheath 28, an insulating material layer 29, a polytetrafluoroethylene layer 30 and a cable core wire 31 that are successively arranged from outside to inside.
The steel armored sheath 28 is a contiguously seamless steel tube.

Embodiment 3

The device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity described in the embodiment 2, characterized in that the device for removing and preventing paraffin by using electric heating further comprises a wellhead high-pressure sealing system arranged on top of the Christmas tree 9; The wellhead high-pressure sealing system comprises a pressing cap 3, a sealing packing 4, a spring 5, a wedge disc 6 and a cable clamping plate 7 that are passed through successively by the steel armored cable 13.
A suspension connector 2 is further arranged on the top of the pressing cap 3.

Embodiment 4

The working method of the device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity described in the embodiments 1, 2 and 3 comprises the following steps:
1) the natural gas collection portion collects and separates out the natural gas in the wellbore and transmits the natural gas to the natural gas electricity generation portion for electricity generation;
2) the natural gas electricity generation portion supplies variable-frequency power for the device for removing and preventing paraffin by using electric heating;
the power frequency electric heating control cabinet 27 outputs variable-frequency power, a live line of the power frequency electric heating control cabinet 27 is connected with the cable core wire 31 of the steel armored cable 13; and
a zero line of the power frequency electric heating control cabinet 27 is connected with the steel armored sheath 28 of the steel armored cable 13;
so that the cable core wire 31 and the steel armored sheath 28 form a loop, and thermal energy can be generated on an outer wall of the steel armored sheath 28 via the skin effect, so as to remove paraffin or prevent paraffin from forming in the wellbore 12 by crude oil.

Embodiment 5

The working method of the device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity described in embodiment 3 differs from embodiment 4 in that the working method further comprises steps of lowering the steel armored cable into the wellbore and lifting the steel armored cable out of the wellbore:
3) when the steel armored cable 13 is lowered into the wellbore 12, the spring 5 opens the wedge disc 6, the steel armored cable 13 enters the wellbore 12, and the steel armored cable 13, the pressing cap 3, the sealing packing 4, the spring 5 and the wedge disc 6 form a high-pressure wellhead seal, to achieve a high pressure sealing effect in the lowering process and a heating process of the steel armored cable;
4) when the steel armored cable 13 is lifted out of the wellbore 12, the spring 5 resets to close the wedge disc 6 to prevent oil-gas fluid from spewing out along the wellhead.

Embodiment 6

The working method of the device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity described in embodiment 3 differs from embodiment 4 in that the working method further comprises a step for a condition when the steel armored cable accidentally drops into the wellbore:
4) when the steel armored cable 13 accidentally drops into the wellbore, the spring 5 resets to close the wedge disc 6 to prevent oil-gas fluid from spewing out along the wellhead.

Embodiment 7

A device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity described in embodiment 1 differs in that an oil storage tank 19 is arranged to be connected with the joint processing station 17; and a gas storage tank 19 is arranged to be connected with the natural gas purifying station 21.

Embodiment 8

When there is severe paraffin precipitation in the wellbore 12 of an oil well and the paraffin cannot be completely removed only by heating of the steel armored cable 13, the device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity differs from embodiments 1, 2 and 3 in that:
the device for removing and preventing paraffin by using electric heating further comprises a centralized heater 32 that is arranged on a tail end of the steel armored cable 13 stretching into the well, the centralized heater 32 comprises a resistance wire 35 connected with the steel armored cable 13, and a thermal conductive insulating layer 34 is arranged outside of the resistance wire 35. The thermal conductive insulating layer 34 is a thermal conductive silica gel layer.
The resistance wire 35 and the thermal conductive insulating layer 34 in the centralized heater 32 are used for centralized heating for those locations where paraffin precipitation is severe, thus realizing paraffin melting at the paraffin blockage locations.

Embodiment 9

A device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity described in embodiment 8 differs in that the steel armored cable 13 is connected respectively with the resistance wire 35 and the thermal conductive insulating layer 34 through a double-ferrule fitting 33.

Embodiment 10

This embodiment is shown in FIG. 4.
For a plurality of relatively concentrated paraffin deposit oil wellbores, a plurality of oil wells need paraffin removal operation simultaneously or alternately, and an electricity generating capacity of the natural gas generator set 25 can be determined according to the quantity of the oil wells.
The natural gas electricity generation portion comprises a natural gas generator set 25 and four sets of power frequency electric heating control cabinets that are connected: a first power frequency electric heating control cabinet 27-1, a second power frequency electric heating control cabinet 27-2, a third power frequency electric heating control cabinet 27-3, a fourth power frequency electric heating control cabinet 27-4; the four sets of power frequency electric heating control cabinets are used to correspondingly control the devices for removing and preventing paraffin by using electric heating mounted in four wellbores respectively.

Claims

What is claimed is:

1. A device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity, characterized in that the device comprises a natural gas collection portion, a natural gas electricity generation portion and a device for removing and preventing paraffin by using electric heating powered by the natural gas electricity generation portion;

the natural gas collection portion is used to collect and separate natural gas discharged from a wellbore; and

the natural gas electricity generation portion generates electricity with the natural gas.

2. The device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity according to claim 1, characterized in that the natural gas collection portion comprises an oil-gas metering station, a joint processing station and a natural gas purifying station that are successively connected to the wellbore.

3. The device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity according to claim 2, characterized in that an oil storage tank is arranged to be connected with the joint processing station.

4. The device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity according to claim 2, characterized in that a gas storage tank is arranged to be connected with the natural gas purifying station.

5. The device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity according to claim 1, characterized in that the natural gas electricity generation portion comprises a natural gas generator set and a power frequency electric heating control cabinet that are connected; and the power frequency electric heating control cabinet is used to control the device for removing and preventing paraffin by using electric heating.

6. The device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity according to claim 5, characterized in that the device for removing and preventing paraffin by using electric heating comprises a steel armored cable extending into the wellbore sealedly through a Christmas tree, and the steel armored cable is connected with the power frequency electric heating control cabinet.

7. The device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity according to claim 6, characterized in that the steel armored cable comprises a steel armored sheath, an insulating material layer, a polytetrafluoroethylene layer and a cable core wire that are successively arranged from outside to inside.

8. The device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity according to claim 7, characterized in that the steel armored sheath is a contiguously seamless steel tube.

9. The device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity according to claim 6, characterized in that the device for removing and preventing paraffin by using electric heating further comprises a wellhead high-pressure sealing system arranged on the top of the Christmas tree; and the wellhead high-pressure sealing system comprises a pressing cap, a sealing packing, a spring, a wedge disc and a cable clamping plate that are passed through successively by the steel armored cable.

10. The device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity according to claim 9, characterized in that a suspension connector is further arranged on the top of the pressing cap.

11. The device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity according to claim 6, characterized in that the device for removing and preventing paraffin by using electric heating further comprises a centralized heater that is arranged on a tail end of the steel armored cable stretching into the well, the centralized heater comprises a resistance wire connected with the steel armored cable, and a thermal conductive insulating layer is arranged outside of the resistance wire.

12. The device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity according to claim 11, characterized in that the steel armored cable is connected respectively with the resistance wire and the thermal conductive insulating layer through a double-ferrule fitting.

13. The device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity according to claim 11, characterized in that the thermal conductive insulating layer is a thermal conductive silica gel layer.

14. The device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity according to claim 1, characterized in that the natural gas electricity generation portion comprises a natural gas generator set and multiple sets of power frequency electric heating control cabinets; the multiple sets of power frequency electric heating control cabinets are used for correspondingly controlling the devices for removing and preventing paraffin by using electric heating mounted in a plurality of wellbores respectively.

15. A working method of the device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity according to claim 7, characterized in that the working method comprises the following steps:

1) the natural gas collection portion collects and separates out the natural gas in the wellbore and transmits the natural gas to the natural gas electricity generation portion for electricity generation;

2) the natural gas electricity generation portion supplies variable-frequency power for the device for removing and preventing paraffin by using electric heating:

the power frequency electric heating control cabinet outputs variable-frequency power, a live line of the power frequency electric heating control cabinet is connected with the cable core wire of the steel armored cable; and

a zero line of the power frequency electric heating control cabinet is connected with the steel armored sheath of the steel armored cable;

so that the cable core wire and the steel armored sheath form a loop, and thermal energy can be generated on an outer wall of the steel armored sheath via the skin effect, so as to remove paraffin or prevent paraffin from forming in the wellbore by crude oil.

16. The working method of the device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity according to claim 15, characterized in that the method further comprises steps of lowering the steel armored cable into the wellbore and lifting the steel armored cable out of the wellbore:

3) when the steel armored cable is lowered into the wellbore, the spring opens the wedge disc, the steel armored cable enters the wellbore, and then the steel armored cable, the pressing cap, the sealing packing, the spring and the wedge disc form a high-pressure wellhead seal, to achieve a high pressure sealing effect in the lowering process and a heating process of the steel armored cable;

4) when the steel armored cable is lifted out of the wellbore, the spring resets to close the wedge disc to prevent oil-gas fluid from spewing out along the wellhead.

17. The working method of the device for removing and preventing paraffin by using electric heating generated from skin effect-based natural gas electricity according to claim 15, characterized in that the method further comprises a step for a condition when the steel armored cable accidentally drops into the wellbore:

5) when the steel armored cable accidentally drops into the wellbore, the spring resets to close the wedge disc to prevent oil-gas fluid from spewing out along the wellhead.