CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Phase Entry of International Application No. PCT/EP2012/063952, filed on Jul. 17, 2012, which claims priority to French Patent Application Serial No. 1156726, filed on Jul. 25, 2011, both of which are incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to steam generation, and more particularly a device and a method for generating steam.

BACKGROUND

Steam generation is applicable in multiple fields, in particular in the context of hydrocarbon production. For example, the production of viscous oils, whether heavy or not, may require fluidization of the oils (i.e. a reduction in the viscosity of the oils) before they are extracted. This fluidization is even more useful for heavy oils contained in sands, for example asphaltic sands (e.g. like those in Canada or Venezuela). However, the viscosity reduction of an oil is generally obtained by providing heat energy. To that end, steam is often injected into the reservoir.

Various steam injection techniques are used at this time (e.g. CSS, steam drive, or SAGD). Steam generation is generally done on the surface using a dedicated plant or different types of generators. The steam is then conveyed into the reservoir using a pipe partially located on the surface. Such steam generators therefore have a footprint that makes the placement of a production facility complex. It is for example difficult to consider adding steam generators on small offshore platforms. Furthermore, surface steam generation involves heat losses in the parts of the pipe on the surface and in the well. Heat losses in the well can heat the land adjacent to the well, and not only the reservoir (which is generally at the bottom of the well). These heat losses are particularly problematic if the well passes through the permafrost. These heat losses reduce the quality of the steam. These heat losses generally require that the depth of the targets be reduced. The surface generator is generally a fossil energy generator (gas, or recycling part of the oil produced). The aforementioned losses decrease the efficiency of steam injection facilities.

Document WO 1988/000276 A1 discloses a heat generator for oil wells comprising an elongate chamber in which a pair of non-concentric electrodes is located at least partially submerged in water. During operation, the electrodes are supplied with energy and heat the water. However, the generator of this document is not fully satisfactory in light of the aforementioned drawbacks.

Furthermore, certain documents, such as document EP 0 387 125 and document GB 427838, teach the heating of a liquid passing through a pipe that forms the secondary circuit of an electric transformer. These transformers operate using a closed ferromagnetic core. For example, the primary circuit (supplied with electricity) winds around a first branch and the secondary circuit (formed by the pipe) winds around a branch parallel to the first branch. Consequently, two of the three dimensions (height, width and length) of the devices of these documents are too large to be inserted into a well for a given flow rate of steam to be produced. They are therefore not ideally suited to an oil application.

The aim of the present invention is to provide an improved device and method for generating steam, at least partially overcoming the aforementioned drawbacks.

SUMMARY

To that end, the present invention proposes a steam generation device. The device comprises a fluid circulation pipe containing electrically and thermally conductive material, and at least one inductive cable made from an electrically conductive material wound around the pipe. The invention also proposes a method for generating steam using the steam generating device. The method comprises circulating water in the pipe and, simultaneously, electrically supplying the inductive cable. The invention also proposes a hydrocarbon production method, in which the method comprises generating steam according to the steam generation method. The invention also proposes a hydrocarbon production facility, in which the facility comprises the steam generating device.

According to preferred embodiments, the invention comprises one or more of the following features:

- the pipe has at least one protuberance on an inner wall;
- the pipe is cylindrical;
- the protuberance is a helical ramp along the pipe;
- the ramp is continuous or broken;
- the device also comprises a shell made from a ferromagnetic material around the inductive cable;
- the inductive cable forms a solenoid;
- the inductive cable is hollow;
- the pipe has a diameter smaller than 20 cm, preferably smaller than 15 cm;
- the pipe has a length smaller than 30 m, preferably 20 m, and/or larger than 5 m, preferably 10 m;
- the device also comprises an electricity source supplying the cable;
- the electricity source delivers a current with an intensity greater than 500 A, preferably greater than 900 A; and
- the device comprises several water circulation pipes connected to one another.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will appear upon reading the following description of one preferred embodiment of the invention, provided as an example and in reference to the appended drawings.

FIG. 1 shows an example of the steam generation method;

FIGS. 2 and 3 show an example of a steam generating device;

FIG. 4 shows an example of a susceptor; and

FIG. 5 shows an example of magnetic field lines in a steam generating device.

DETAILED DESCRIPTION

A steam generating device is proposed. The device comprises a fluid circulation pipe containing electrically and thermally conductive material, and at least one inductive cable (one or more cables) made from an electrically conductive material wound around the pipe. Such a device improves the steam generation.

The water circulation pipe allows water to circulate from an inlet of the pipe toward an outlet of the pipe. The pipe contains conductive material, for example steel. It may be completely or partially made from said electrically (i.e. capable of conducting electricity) and thermally (i.e. capable of effectively conducting heat) conductive material. The inductive cable is made from electrically conductive material and is therefore an electrical cable, for example made from copper. The inductive cable may assume any form. The inductive cable may for example have a square section. The section of the cable may be larger than 9 mm², preferably 36 mm², and/or less than 144 mm², preferably 64 mm².

Because the inductive cable winds, it has turns. The inductive cable can therefore induce a high magnetic field inside said turns if the inductive cable is supplied with electricity. The conductive material of the pipe makes it possible to generate Foucault currents if it is subjected to such a magnetic field. Thus, subjected to such a magnetic field, the Foucault currents heat the pipe by Joule effect and transfer the heat energy to a fluid that may be present in the pipe, so as to potentially make steam. The inductive cable winds around the pipe and therefore allows the appearance of such a magnetic field where the inductive cable winds around the pipe. One advantage of such an arrangement is also the length of the pipe useful for such heating. In fact, the heating occurs over the entire length on which the inductive cable is wound around the pipe and occurs gradually while the fluid circulates in the pipe. Such a device allows a good efficiency (output), and therefore produces high-quality water vapor (if the fluid is water). The steam quality is the ratio between the amount of water in saturated steam form and the total quantity of water (i.e. liquid+saturated steam). Furthermore, the longitudinal shape of the device makes it particularly suitable for an oil application. Indeed, the device is easy to insert into a well. Such a device also makes it possible to have a rectilinear flux, as well as better preservation of the input pressure.

The inductive cable can form a solenoid. In particular, the inductive cable can form a coil with a length at least two times longer than the diameter of the coil. This ensures a powerful magnetic field at the pipe, and therefore good Joule effect heating. Preferably, the inductive cable winds around the pipe over a length greater than 50 times the diameter of the pipe, preferably greater than 200 times the diameter of the pipe, which ensures heating over a large length of the pipe.

The device can comprise a shell made from a ferromagnetic material around the inductive cable. The shell channels the magnetic field so as to optimize heating. Furthermore, if the device is inserted into a casing (i.e. a metal tube cemented to the wall of the well), the shell protects the casing from the magnetic flux. The ferromagnetic material of the shell may be soft iron or any other material having the characteristics of a soft ferromagnetic material.

The pipe can have at least one protuberance on an inner wall. The term â€œsusceptorâ€ will hereafter be used to designate that protuberance, or all of the protuberances if applicable. The susceptor may be a part of the pipe protruding toward the inside of the pipe. The susceptor increases the inner surface of the pipe and generates hot spots (which may exceed 300Â° C., for example 350 to 400Â° C.). The susceptor therefore improves the heating of a fluid in the pipe. The susceptor also generates turbulence in the circulation of such a fluid. This turbulence forms currents that homogenize the fluid and thereby distribute the heat so as to improve heating. The susceptor also causes pressure losses (i.e. local losses of pressure) that favor steam generation.

Different forms of susceptors may be made. For better heating, the susceptor may form a helical ramp along the pipe that may be cylindrical. The ramp may be continuous or broken. In the event the ramp is broken, the susceptor therefore comprises several protuberances positioned on a helical line virtually drawn inside the pipe.

The inductive cable can be hollow. In that case, the inductive cable comprises an empty passage at the center thereof. This passage allows a cooling liquid to circulate inside the inductive cable, for example water, which makes it possible to avoid damaging the inductive cable. Such cooling of the inductive cable may also serve to preheat the water to be vaporized. For example, the passage in the inductive cable may be connected to the pipe upstream of the pipe. In this way, in any steam generating method using the device, the water can circulate in the inductive cable before arriving, already preheated, in the pipe, where the water can evaporate more easily.

The pipe may have an (outer) diameter smaller than 20 cm, preferably smaller than 15 cm. The casings of the borehole have a diameter of approximately 30 cm. The inner diameter of the pipe may be less than 16 cm, preferably less than 10 cm. In this way, the sizing of the pipe makes it possible to provide space to wind the inductive cable around the pipe. The device is consequently well-suited to the borehole diameters typically used, i.e. between 23 cm and 25 cm.

The pipe may have a length smaller than 13 m, preferably 10 m, and/or greater than 5 m, preferably 8 m, preferably equal to at least approximately 9 m. These dimensions present a good compromise between ease of installation and useful length exploited. In fact, the longer the pipe, the more heating may be done over a large length. However, the length is limited for better adaptation to standard borehole rigs (i.e. borehole facilities).

The device may also comprise an electricity source supplying the inductive cable. The electricity source may be on the surface and transmit electrical energy to the inductive cable(s) winding around the pipe(s) (at the reservoir in the well) by means of one or more transmission cables. Such a generator may not be based on fossil energies. It cannot generate greenhouse gases, in any case in an excessively localized manner. Such a generator is therefore cleaner, and has a good efficiency, since the electricity is easily transportable at low frequencies, with lower losses during transmission. Such a device improves the output, since there are no longer any heat losses. In fact, the steam is generated directly in the well at a distance closer to the formation than the wellhead and not conveyed from the surface.

The electricity supplied to the cable may be a current greater than 500 A, preferably greater than 900 A. For a lower loss with such intensities, the device preferably comprises several transmission cables. The electricity source is then adapted to provide the appropriate voltage. The appropriate voltage may be comprised between 5 and 10 kV.

The pipe may also make up a partially closed enclosure, the pressure inside the tube being little influenced by the pressure of the formation. This makes it possible to control the pressure to which the fluid is subjected when it is heated. In this way, it is possible to know the characteristics of the generated steam (if the fluid is water) easily and to better control the steam generation over time. The invention is sized as a function of the characteristics of the formation; in particular, the steam pressure delivered by the system according to the invention is greater than the pressure of the formation to be exploited.

The device may comprise several water circulation pipes connected to one another. The pipes may be connected in fluid communication using mechanical connections for water circulation inside all of the pipes thereafter. The cables winding around the pipes are connected by electrical connections. It is for example possible to connect three pipes to one another.

The device may be comprised in a hydrocarbon production facility. The device may in particular be located in the well, so that the steam is generated in the well directly at the reservoir. Such a facility is therefore compact and allows exploitation of all highly viscous hydrocarbon reservoirs, owing to the quality of the generated steam, the controlling of the characteristics of the generated steam, and the compactness of the facility, which in particular allows offshore exploitation.

The production facility may comprise a borehole rig. The placement of the device may then comprise:

- positioning a pipe, with winding of at least one electrical cable around it, in the rig,
- lowering the pipe into the well, the top of the pipe remaining accessible from the rig,
- positioning a new pipe in the rig,
- assembling the new pipe, with winding of at least one electrical cable around it, with the previous pipe, including the electrical connection of the cable of the new pipe to the cable of the preceding pipe,
  the above steps being repeated, for example until three pipes are connected.

In reference to FIG. 1, the device may be used in a steam generating method that comprises the circulation (S1) of water in the pipe, and, at the same time, the supply (S2) of electricity to the cable. The electrical power of the cable induces the magnetic field, the heating of the conductive material of the pipe, and the heating to the point of vaporization of water circulating in the pipe at the same time as the electricity supply. Such a device therefore allows vaporization of water with a good efficiency and good quality of the generated steam. As mentioned above, the water may be heated beforehand. To that end, the method may comprise prior circulation of the water in the cable, to cool it.

This method may be comprised in a hydrocarbon production method. The steam may be generated directly at the reservoir and may therefore be directly injected into the reservoir without heat losses. The hydrocarbons can then be extracted more easily, which is particularly advantageous in the case of viscous or heavy oils.

In such a method, the steam may be generated at a flow rate of 100 to 300 tons per day, preferably 200 tons per day. The hydrocarbon production method may be done by H&P (Huff & Puff, i.e. the method comprises the cyclic injection of steam in the reservoir) or by Steam Drive (i.e. the method comprises continuously sweeping the reservoir with steam). The same device can provide these different injection forms. The device is therefore versatile.

Examples of the device will now be described in reference to FIGS. 2 to 5. FIG. 2 shows one example of the steam generating device 10 in longitudinal cross-section. In FIG. 2, the device 10 is shown with its fluid circulation pipe 12 containing electrically and thermally conductive material and the inductive cable 14 made from electrically conductive material that is wound around the pipe 12. FIG. 3 shows a section of the device 10 of FIG. 2, transversely relative to the longitudinal central axis 22 of the device 10, and comprising the portion 29 of the pipe 12 around which the inductive cable 14 winds.

As shown in the figures, liquid water 16 can penetrate the pipe 12, circulate therein, and leave it in steam form (potentially containing liquid as a function of the quality attained). In fact, the cable 14 is electrically supplied with voltage from the electricity source 19 and heats the pipe 12 owing to the magnetic field induced over the entire length of the winding. In this example, the device 10 comprises the transmission cables 24, which convey electricity to the cable 14, and the susceptor 20 on the inner wall of the pipe 12 (protuberances oriented toward the inside of the pipe 12, therefore toward the axis 22). A good thermal efficiency is therefore obtained. This results in vaporizing the water 16. The figures show that the device 10 is compact and in longitudinal form. The length of the device 10 is at least twice as large as its width. The device 10, which is not very bulky, is thus suitable for insertion into a borehole well.

Furthermore, the device may comprise several (three) pipes connected to one another by connections, to form a total length 29 for example of 27 m around which the cable 14 is wound, each pipe 12 around which the cable 14 is wound having a length of 9 m. The device 10 is also shown when it is installed inside a well. The figures in particular show the casing 23 of the well surrounded by cement 13. At the cable 14, the geological ground comprises hydrocarbons and thus constitutes a reservoir 25. Locating the pipes 12 around which a cable 14 is wound at the reservoir thereby makes it possible to avoid heat losses. In this way, the portion 26 of the subsoil closest to the surface 15, which does not contain hydrocarbons, is not needlessly heated. The figure also shows the shell 27 that protects the casing 23 from excessive temperatures.

FIG. 4 shows a susceptor 50 in the form of a helical ramp in the pipe 12 which can be used in the device 10 of FIGS. 2 and 3. FIG. 4 showing a transverse section of the pipe 12, the susceptor 50 assumes the form, in the plane of the section, of regularly spaced protuberances. The susceptor 50 can be made from a thermally and electrically conductive material, and thereby increase the heat exchange surface with the fluid, as shown in the figure.

FIG. 5 diagrammatically shows one example of magnetic field lines 40 in one example of a steam generating device 10. The magnetic field lines 40 were obtained using finite element calculation software. The device is partially shown in longitudinal cross-section. Only half of the device is shown. The device of this example is according to FIG. 2 or 3 and in particular comprises the shell 27 around the cable 14. The figure shows that the shell 27 makes it possible to concentrate the magnetic field at the pipe 12 and protect the casing 23, which is slightly exposed to the magnetic field. In this way, the device 10 allows good Joule effect heating of the pipe 12 with less damage to the casing 23. Of course, the present invention is not limited to the examples described and illustrated, but is open to various alternatives accessible to those skilled in the art.