Patent Application
20090057291
The invention relates to a method of operating an electrical heating arrangement of considerable length using a heating line having at least one heating conductor surrounded by an insulation resistant to high temperatures.
Such heating lines are known and are obtainable on the market. Their heating conductors are encased, for example, with mineral or ceramic materials which are resistant at high temperatures. Such heating lines are used in principle where heating at high temperatures of, for example, up to 500° C. is to be effected.
A special field of use of heating lines for very high temperatures is crude oil exploration from oil reserves in which the crude oil is bound, for example, in porous rock, in sand or in shale. Such oil reserves are located in the ground at a depth of approximately 300 m. They extend over a large area at this depth. To deliver the crude oil, therefore, not only are vertically running bores placed, but said bores are continued in the ground over large distances of, for example, 600 m. In order to be able to pump the crude oil out of these reserves as completely as possible with a conventional technique, it must be brought to a sufficiently light-bodied state by heating the surrounding earth or rock.
The object of the invention is to specify a method of operating an electrical heating arrangement with which it is possible to also heat deeper regions of the earth's surface with high efficiency.
This object is achieved according to the invention in a method of the type mentioned at the beginning in that
The expression “air” in this case refers to the gas mixture present at the earth's surface, with 77% nitrogen, about 21% oxygen and about 2% residual quantities.
The outer metallic tube serves to protect the heating line against the oil to be delivered and other aggressive media which could lead to corrosion of the metal tube of the heating line. The heat of up to 1000° C. generated by the heating line is to be transferred as completely as possible to the outer metallic tube so that the desired heating of the oil to be delivered is achieved.
With this method, the heat generated by the heating line is transferred at high efficiency by optimum heat transfer to the outer metallic tube, which in the fitted position is in direct contact with the earth or rock to be heated. This essential advantage is achieved by the gas located in the clearance space and having a low kinematic viscosity, by means of which gas the heat transfer by convection between the metal tube of the heating line and the outer metallic tube is substantially increased. As a result, the metallic tube and thus also its surroundings are heated to a correspondingly more intense degree. Crude oil located in the region of the metallic tube is thereby heated in such a way that it becomes light-bodied and can be pumped out more easily.
The radiation as a further proportion of the heat transfer between the metal tube of the heating line and the outer metallic tube can be increased by roughening the outer surface of the metal tube by the latter being subjected, for example, to sand blasting. This measures leads to further improved transfer of the heat generated by the heating line to the outer metallic tube.
The gas used is preferably an inert gas, such as argon. This results in the further advantage that corrosion cannot occur in the space enclosed by the metallic tube, and therefore the material selection for the metal tube of the heating line is not critical.
The method according to the invention will be explained with reference to the drawings as exemplary embodiment.
In the drawings:
Shown in
A metal tube 4 is placed over the insulation 3 of the heating conductor 2 and bears against the insulation. It is advantageously made of a material that is a good conductor of heat. To improve the transverse stability and the flexibility of the metal tube 4, the same may be corrugated transversely to its longitudinal direction.
The heating line 1 is arranged in an outer metallic tube 5, which has a diameter larger than the diameter of the metal tube 4 and additionally encloses a clearance space 6 relative to the heating line 1. The areas of the outer surface of the metal tube 4 and of the inner surface of the outer metallic tube 5 are preferably to have a ratio of 1:4. The clearance space 6 is large enough so that a sufficient quantity of gas under pressure can be introduced into said clearance space 6 and held therein. The pressure with which the gas is introduced into the clearance space 6 is to be at least 1 bar. The outer metallic tube 5 is tightly closed hermetically at its end 7. It has a wall thickness of preferably 2 to 4 mm and is preferably made of high-grade steel so that rusting can be ruled out in the long run.
The heating arrangement also includes a small metallic tube 8, through which gas can be forced into the clearance space 6. The small tube 8 is fastened to the metal tube 4. It can run rectilinearly, but can also be placed helically around the metal tube 4. To increase its transverse stability and its flexibility, the small tube 8 is advantageously corrugated transversely to its longitudinal direction.
For heating a region located deep in the earth 9, first of all the outer metallic tube 5 is installed in a borehole, through which oil is to be pumped out of an oil reserve located in the ground. The borehole comprises a vertical bore having an approximately horizontally extension of considerable length. The metallic tube is installed as indicated in
As already mentioned, the pressure with which the gas is to be introduced into the small tube 8 and thus into the clearance space 6 is to be at least 1 bar. This pressure is monitored, for example by means of a pressure gauge 13, while the method is being carried out. It is preferably kept constant through the use of a corresponding controller.
The gas forced into the clearance space 6 has a lower kinematic viscosity than air, which is 96.7×10−6 m2/sec at 500C. The gas used is preferably to have a kinematic viscosity of 90×10−6 m2/sec at 500° C.
In an especially advantageous manner, the gas used is an inert gas, such as, for example, and preferably, argon, having a kinematic viscosity of 72.62×10−6 m2/sec. With argon as the gas located in the clearance space 6, the heat transfer by convection between metal tube 4 and outer metallic tube 5 is increased by about 15%. In addition, an inert gas in the clearance space 6 prevents any corrosion at the metal tube 4 and at the inner surface of the metallic tube 5. Therefore any desired metal, such as steel for example, can be used for the metal tube 4.
The heat transfer between the metal tube 4 and the outer metallic tube 5 by radiation can be additionally improved by the outer surface of the metal tube 4 being roughened. This can be advantageously achieved by sand blasting. By means of such a measure, the heat transfer from the metal tube 4 to the outer metallic tube 5 by radiation can be increased by about 25%, which leads to an additional improvement in the efficiency of this method.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102007041983.1 | Sep 2007 | DE | national |
