GB2296024A

GB2296024A - Device and method for removing deposits in petroleum and natural gas transport

Info

Publication number: GB2296024A
Application number: GB9525373A
Authority: GB
Inventors: Carsten Loeschen; Alexander Thiel
Original assignee: Tub Tauch und Baggertechnik GmbH
Current assignee: Tub Tauch und Baggertechnik GmbH
Priority date: 1994-12-12
Filing date: 1995-12-12
Publication date: 1996-06-19
Anticipated expiration: 2015-12-12
Also published as: NO305415B1; RU2114981C1; NO955009L; GB9525373D0; NO955009D0; DE19543473A1; GB2296024B; DE19543473C2

Description

1 2296024 DEVICE AND METHOD FOR REMOVING DEPOSITS IN PETROLEUM AND NATURAL

GAS TRANSPORT This invention relates to a device and method for removing deposits such as asphalt, hydrates, and paraffins from petroleum and natural gas production strings and pipelines.

Deposits of asphalt, hydrates and paraffins in production strings and pipelines represent a major process problem for the oil industry. Because the production strings and pipelines are inaccessible from the surrounding formations, it is difficult to remove these deposits so that increasingly time-consuming and expensive methods must be used to remove the deposits, Accordingly, a device and method for removing such deposits in a simple fashion have been sought. It has been the intention that the device be able to work automatically, even at great depths, in such a petroleum or natural gas production string or the like.

Moreover, the device and the method which have been sought were to be such that they enable the deposits to be removed with simple means and hence inexpensively and at a high rate in order to keep downtimes in the oil transport system which are adversely affected by the deposits, as short as possible.

According to one aspect of the invention, there is provided a device for removing deposits such as asphalt, hydrates, and paraffins from petroleum and natural gas production strings and pipelines, which device comprises a tubular housing that is adapted to fit within a production string and is divided into a heating section with a front end zone positioned at the downstream end of the housing and a ballast section at the opposite end, said heating section containing an electrically conducting heating medium and an electrode, a part of the housing defining the heating section being made of an electrically conducting material, and the electrode being connected to one pole of an electrical power supply, and the part of the housing defining the heating section being connected to another pole of the electrical power supply so that the heating section is heated by the electrical power supply.

In a second aspect, this invention provides a method for removing deposits including asphalt, hydrates, and paraffins from petroleum and natural gas production strings and pipelines with a device comprising a tubular housing having a front end zone at the downstream end of the device that is heated, said method comprising heating a heating medium located in the said zone by direct resistance heating by an electrode connected to one pole of an electrical power supply and a metal housing surrounding the electrode connected to an opposite pole of the electrical power supply, said heating medium being heated to a temperature sufficient to evaporate the heating medium whereby the evaporated heating medium rises in the tubular housing, cools and condenses on unheated areas of the housing walls and runs back down housing walls to the end zone, for the heating medium to be once again evaporated by heating, and contacting the deposit with the heated end zone, the housing in said end zone being heated to an extent such that the deposit contacting the end zone of the housing is melted and flows away under gravity.

The method according to the invention is based on melting away the deposits in the petroleum and natural gas production strings and pipelines with the aid of a device embodying this invention. Thus, a front end zone of the housing of the tubular device located at the downstream end of the device is heated. This zone of the housing is heated by direct resistance heating.

The heating medium in this housing zone is heated to a temperature sufficient to evaporate the heating medium by means of an electrode and a voltage applied thereto, with the housing which is electrically conducting, serving as an opposite pole. As a result, the housing is heated in this end zone to the extent that the deposits coming in contact with it are melted away. The heating medium evaporated due to the resistance heating in the tubular housing then rises in the housing and is cooled and condensed on the unheated areas oE the housing walls and runs back down the walls to the zone at the downstream end, to be once again evaporated by the heating of the electrode located therein. During operation, the electrode is continuously energized.

In a particularly advantageous form of device embodying this invention, it is proposed that there be a section of the tubular housing between the heating section and the ballast section which seals these two sections off from each other in a heat-insulating manner. This insulating section separates off the heatable heating section that heats up during operation from the ballast section, so that heat transfer is prevented and the device can be handled at the ballast section without risk of burning, for example, when it is removed from a pipe after the cleaning process.

The ballast section confers a sufficiently high weight on the device according to the invention that it can move on automatically at great depths in a production string by gravity.

The invention proposes use of a heating medium with a sufficiently high specific electrical resistance which is heatable by resistance heating once the voltage is applied to the electrode in the heating up to evaporation of the heating medium whereby the housing in the heating section, particularly at the forwardmost part thereof, is heated to a temperature sufficient to melt away the deposits. This heating medium, which usually is a fluid, can be, for example, an aqueous solution of a natural salt mix such as Carlsbad salt, etc., in distilled water which has high-melting point metals such as titanium and/or tungsten in finely divided form suspended therein.

Na2SC)4 or Na2C03 salt solutions are also useful as the aqueous solution. The heating medium preferably has an electrical resistance of 35 to 45 ohms.

According to a preferred embodiment of the invention, the heating medium is provided at the extreme downstream end zone of the heating section and the remainder of the internal volume of the heating section serves to collect the evaporated heating medium. To produce a sufficient internal volume for collecting the evaporated heating medium, the invention also proposes that the heating medium take up approximately 2 to 10 vol.%- of the total internal volume of the heating section. A sufficient heating of the device according to the invention is achieved if 10 to 50 g distilled water, containing 15 to 30 mg natural salt and 0.01 9 each of titanium and tungsten is used as a heating medium, so that the heating medius has a resistance of 35 to 45 ohms, to achieve a working temperature of 150 to 3500C in the front end zone of the device with an applied voltage of 200 to 800 V.

For achieving electrical connection from the power supply to the device according to the invention, a cable connection may be provided in the ballast section, into which cable connection an electric cable connectable to the power supply and extendable from the ballast section at its free end can be plugged.

In a further advantageous embodiment of the invention, the electrode has a rod shape and is attached to the heat insulating section located between the heating and ballast section and connected to a cable connection located in the ballast section.

It is also preferred that the rod-shaped electrode extends up a point close to the downstream end of the heating section and is guided inside the heating section by means of an electrically insulating spacer, whereby the electrode tip dips into the heating medium in the operating state.

In summary, the present invention provides a device for removing deposits which can be manufactured with the dimensions necessary for the current parameters of the petroleum and natural gas production strings and/or pipelines to be cleaned. Suitable parameters for a device embodying this invention are as follows: a tubular housing with an outside diameter of 20 to 40 mm and a total length of 800 to 1500 mm; a power supply of 200 to 800 V, and a starting current of approximately 15 a. Such a device may be heated in the end zone of the housing to from 150 to 3500C, a temnerature sufficient to melt away deposits in petroleum and natural gas production strings. The device can be inserted down to 7,000 m and even lower in production strings. The device may have an operating rate, i.e. penetration rate, of 5 to 20 m/h depending on the volume of the deposits to be melted away.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:- Figure 1 is a schematic view of a device for removing deposits embodying this invention; Figure 2 is a lengthwise partial section through one end of the device shown in Figure 1 on an enlarged scale; Figure 3 is a lengthwise partial section through is the other end of the device shown in Figure 1 on an enlarged scale; and Figure 4 shows schematically the use of the device according to the invention for removing deposits in a 5 petroleum production string.

According to Figure 1, a device 1 according to the invention comprises a tubular housing divided into a housing part defining a heating section 2 and a housing part defining a ballast section 4, with the heating section 2 and ballast section 4 being separated by a section 3 which seals sections 2, 4 off from one another and thermally insulates sections 2, 4 from one another by means of gaskets 30, 30a (see Figure 3). In operating direction A, the heating section 2 is closed off at one end of the device by a forward-pointing tip 2a. At the opposite end 50 of the device, i.e. at the ballast section 4, a cable 5 for electrical connection of device 1 to a power supply, not shown here in detail, extends out of the housing which is closed, as will be described hereinafter.

In order to heat heating section 2, particularly at its tip 2a, as shown in Figure 2, a device embodying this invention has a rod-shaped electrode 6 which extends along the longitudinal axis of the device within the heating section 2. This rod-shaped electrode 6 is provided at its upper end shown in Figure 3 with a flange ring 61 made of electrically insulating material and is attached by the flange to heat-insulating section 3 which is itself connected to heating section 2, sealing off the latter from the remainder of the device by means of gaskets 30. Section 3 has a threaded portion 31 which engages threads 21 of the housing part defining the heating section. The electrode 6 is electrically insulated from the walls of the sealing section by means of insulating cover 61a (see Figure 3a) made of electrically insulating material, such as ceramic material, in particular. As can also be seen from Figure 3, rod-shaped electrode 6 is connected to the electrical power supply by a cable 5 which passes through a throughhole 50a. Electrical cable 5 is connected inside ballast section 4 with a female connector 42 secured by a ring 41, into which connector 42a connecting pin 62 located at the upper end of electrode 6 and guided in heat-insulating section 3 can be plugged so that electrode 6 can be connected by a plug-in connection 42, 62 to the power supply.

Heat-insulating section 3 which is also made of metal, such as steel, is connected in a sealing fashion in a manner not shown in detail with ballast section 4 and ballast section 4 is closed off at its upstream or rear end by means of end cap 50 and a sealing sleeve 51.

The modes of connection of the various sections of the device of Figures 1 to 3 are not confined to those shown in the illustrated embodiment shown here.

For power supply of alternating current to the device, a multiwire cable 5 is typically used.

Reverting to Figure 2, electrode 6 connected as illustrated to the power supply is guided inside heating section 2 by means of electrically insulating discs 60a, 60b and dips with its end zone pointing in operating direction A into a salt solution SL made of distilled water and Carlsbad salt with small amounts of suspended finely-divided titanium and tungsten, which solution is located in the vicinity of tip 2a of heating section 2. The level 100 of salt solution SL is chosen such that sufficient space within heating section remains above salt solution SL for it to act as an evaporation and condensation chamber. The housing of heating section 2 is made of an electrically conducting material such as a special steel and is -8 connected, by means of the ring 47, or directly, to housing of ballast section. Cable wire 5a supplies to the housing of ballast section 4 electrical current of different polarity to that of rod-shaped electrode 6 which is opposite polarity and supplied with electrical current by means of cable wire 5b. Thus the housing acts as the counter-electrode to the rod-shaped electrode 6. The housing of ballast section 4 is also made of special steel.

If a sufficiently high voltage, which is, for example, in the range between 200 and 900 volts, and which depends on the dimensions of the device according to the invention, and varies according to the depth of the deposits and the operating depth, is applied to rod-shaped electrode 6, the salt solution heats up in known manner by the principle of direct resistance heating. The salt solution is thus a conducting medium positioned between electrode 6 and the housing part of heating section 2 which functions as a counter- electrode. By heating salt solution in this way, the housing part of heating section 2 that surrounds the salt solution also necessarily heats up, primarily in the area filled with salt SL. In this manner, according to the invention, local heating of the device at its forward or downstream end is achieved, which makes it possible for the deposits such as asphalt, hydrates, and paraffins to be removed, i.e. to be melted away.

Heating of salt solution SL by electrode 6 takes place at a temperature such that salt solution SL begins to evaporate. The vapor D from salt solution SL rises from level 100 of salt solution SL (Figure 2) and arrives at the upper area of heating section 2, which is sealed in a gas-tight manner from heat-insulating section 3 by means of gaskets 30. Particularly, the upper areas 2b of the inner walls of heating section 2 -9 r_ and end face 3a of heat-insulating section 3 have a considerably lower temperature than the tip area 2a of heating section 2, heated by the salt solution. This results in the vapor D rising from the salt solution forming drops T on end face 3a of heat-insulating section 3 and condensing on side walls 2b of heating section 2 and running, in the direction of arrows K down side walls 2a back to level 100 of salt solution SL.

As a result of the heating medium in the form of salt solution SL being present so as to occupy only a small proportion of the total space inside heating section 2, not only does local heating of heating section 2 occur within tip 2a, but also the temperature is reliably and automatically regulated. Heating up of the salt solution does not continue without restriction because, as a result of evaporation, level 100 of the salt solution drops continuously, until in the extreme case no salt solution is left in contact with electrode. Then no further heating takes place automatically. In this way, a maximum temperature of tip Sa of heating section 2 can be defined by the Quantity of salt solution, and further heating of tip 2a occurs only when sufficient vapor D from salt solution SL condenses as drops T and flows back into the area of that electrode to form a new level 100 of salt solution SL.

Figure 4 shows how it is thus possible, in a simple manner, to remove deposit 7 in a production string 10, by melting the deposit away. For this purpose, device 1 according to the invention is suspended from a cable 9 and lowered down tube 10 to be cleaned, under gravity G. An electrical voltage is applied to the electrode through wire 5b of cable 5 and to the housing walls via wire 5a so that the tip 2a of heating section 2 heats up to a temperature sufficient r, to melt away deposit 7. When a sufficient weight is provided in ballast section 4, device 1 according to the invention can more easily penetrate deposit 7 by means of its projecting tip 2a whereby deposit 7 is melted away. Small parts 7a of deposit 7 are thereby swept upward by oil stream S while large pieces of deposit 7 settle, once the device according to the invention has passed through ballast section 4. When device 1 according to the invention is pulled up by cable 9, it can be removed once the device according to the invention has been taken out of production string 10. This cleaning process is then repeated until all of the deposit 7 has been removed from production string 10.

In this way, it is possible to rid nearly all petroleum and natural gas production strings and pipelines of deposits such as asphalt, hydrates, and paraffins with a device embodying the invention. Also, a device embodying the invention can be left alone while it is operating, since it descends by gravity to great depths, for example in oil wells, in addition to which the temperature at the tip in the operating direction is regulated by the quantity of salt solution, such regulation being reliable, free of any control elements, and thus being insensitive to outside influences.

For maintenance and cleaning of the device and renewal of the heating fluid. Parts of the device, particularly the heating section, can be removable with respect to the other parts.

Claims

Claims:

1. A device for removing deposits such as asphalt, hydrates, and paraffins from petroleum and natural gas production strings and pipelines, which device comprises a tubular housing that is adapted to fit within a production string and is divided into a heating section with a front end zone positioned at the downstream end of the housing and a ballast section at the opposite end, said heating section containing an electrically conducting heating medium and an electrode, a part of the housing defining the heating section being made of an electrically conducting material, and the electrode being connected to one pole of an electrical power supply, and the part of the housing defining the heating section being connected to another pole of the electrical power supply so that the heating section is heated by the electrical power supply.

2. A device according to claim 1, wherein, between the heating section and the ballast section, is positioned a heat- insulating section that seals the two sections off from each other.

3. A device according to claim 2, wherein the electrode has a portion that is rod-shaped and is adapted for attachment to the heat-insulating section and for connection to a cable connection located in the ballast section.

4. A device according to claim 3, wherein a cable connectable to the power supply and extending from the ballast section at its free end is inserted into the cable connection.

S. A device according to claim 4, wherein the cable connection is designed as a plug-in connection.

6. A device according to any preceding claim, wherein the heating medium is a fluid with an electrical resistance which is sufficiently high that, is when a voltage is applied to the electrode, it is heated by direct resistance heating to cause it to evaporate and thus heat the housing part forming the heating section at said front end zone to a temperature sufficient to melt away a deposit contacted by the said housing part.

7. A device according to claim 6 and any one of claims 2 to 5, wherein the heating medium is provided inside the front end zone of the heating section and a remaining internal zone of the heating section serves to receive evaporated heating medium.

8. A device according to any preceding claim, wherein the heating medium has an electrical resistance of 35 to 45 ohms.

9. A device according to any preceding claim, wherein the heating medium is an aqueous solution of a salt mix in distilled water containing highmelting point finely divided metals dispersed therein.

10. A device according to claim 9, wherein the finely divided metal comprises titanium and/or tungsten.

ii. A device according to any preceding claim, wherein the electrode extends up to a point close to the interior surface heating section of the front end in zone and is guided inside the heating section by means of electrically insulating spacers, whereby the electrode tip dips into the heating medium in the operating state.

12. A device according to any preceding claim, wherein the front end zone of the heating section is formed as a pointed tip of the tubular housing.

13. A device according to any preceding claim, wherein the tubular housing has a cylindrical crosssection and a length of from 1.5 to 3 meters.

14. A device according to any preceding claim 1, wherein at least a part of the tubular housing is made from a special steel. 15. A device according to any preceding claim, wherein the heating section is heatable to temperatures of 150 to 3500C. 5 16. A device for removing deposits from petroleum and natural gas production strings and pipelines, substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings. 17. A method for removing deposits including asphalt, hydrates, and paraffins from petroleum and natural gas production strings and pipelines with a device comprising a tubular housing having a front end zone at the downstream end of the device that is heated, said method comprising heating a heating medium located in the said zone by direct resistance heating by an electrode connected to one pole of an electrical power supply and a metal housing surrounding the electrode connected to an opposite pole of the electrical power supply, said heating medium being heated to a temperature sufficient to evaporate the heating medium whereby the evaporated heating medium rises in the tubular housing, cools and condenses on unheated areas of the housing walls and runs back down housing walls to the end zone, for the heating medium to be once again evaporated by heating, and contacting the deposit with the heated end zone, the housing in said end zone being heated to an extent such that the deposit contacting the end zone of the housing is melted and flows away under gravity. 30 18. A method according to claim 17, wherein an aqueous solution of a salt mix in distilled water is provided as the heating medium, which solution contains high-meltingpoint finely-divided metals dispersed therein. 19. A method according to claim 18, wherein the finely divided metal comprises titanium and/or tungsten.

14- 20. A method according to any one of claims 17 to 19, wherein the electrical power supply provides current at 200 to 900 volts.

21. A method according to claim 18, wherein the heating medium comprises distilled water with each 10 to 50 g of the distilled water containing 15 to 30 mg natural salt and 0.01 g each of titanium and tungsten to achieve heating medium electrical resistance of 35 and a working temperature of 150 to 3500 in front end zone of the device with an applied voltage of 200 to 800 V.

22. A method according to claim 21, wherein the natural salt is Carlsbad salt.

23. A method for removing deposits for petroleum and natural gas production strings and pipelines, substantially as hereinbefore described with reference to the accompanying drawings.

to 45 ohms 10 the