Patent Application
20100252249
This application is the US National Stage of International Application No. PCT/EP2008/060074 filed Jul. 31, 2008, and claims the benefit thereof. The International Application claims the benefits of German Application No. 10 2007 036 832.3 DE filed Aug. 3, 2007. All of the applications are incorporated by reference herein in their entirety.
The invention relates to a device for in situ extraction of a substance comprising hydrocarbons. The substance comprising hydrocarbons is conveyed from an underground storage site while reducing the viscosity thereof. The device comprises at least one production pipeline leading out of the storage site. Such devices for conveying substances comprising hydrocarbons are for example known from “Steam-Injection Strategy and Energetics of Steam-Assisted Gravity Drainage” by I. D. Gates, 2005, SPE International Thermal Operations and Heavy Oil Symposium, Calgary, Canada, Nov. 1-3, 2005.
Large parts of the world's oil reserves are in the form of oil sands. Oil sand is a mixture of rock, clay, sand, water and bitumen or other heavy oils. In the following, references to bitumen, which occurs with a typical viscosity of API 5° to 15° depending on the storage site, also include heavy and very heavy oils or long-chain hydrocarbons generally. The bitumen can be converted into synthetic crude oil by means of further process steps. Oil sands in some cases are found in geological strata at low depth, which are accessible to open-cast mining. However, large deposits of oil sands also exist which cannot be accessed by open-cast mining. Typically in situ extraction takes place at depths of 60 m or more, since in this situation it no longer seems profitable to remove the overburden.
A method typically used to extract such deposits is “Steam Assisted Gravity Drainage” (SAGD), in which the bitumen occurring in a storage site is heated by hot steam and the storage site is rendered more permeable by the steam pressure. In this way the viscosity of the bitumen is reduced, so that it can be conveyed in liquid form, as well as more quickly, from the storage site. The change in the viscosity of the bitumen is caused by an increase in temperature. For this purpose hot steam is compressed through pipelines into the underground storage site, so that the storage site is heated, and at the same time an overpressure builds up in the storage site. Liquid bitumen is conveyed through a further pipe to the surface by the overpressure prevailing in the storage site (cf. also undergraduate seminar on topics relating to “Unconventional hydrocarbons” on the subject of “Heavy oils and ultra-heavy oils” by J. Seim, Freiberg, Germany, January 2001).
To improve the fluidity of the bitumen the hot steam can be mixed with a solvent. The pipelines for the injection of the hot steam, or of the mixture of hot steam and solvent, are essentially laid in parallel to one another, running horizontally within the storage site. The injection pipeline and production pipeline are typically about 5 m to 10 m apart from one another in the vertical direction. However, the distance between the injection and the production pipeline depends on the thickness of the storage site. In the horizontal direction the pipes extend for a length of between several hundred meters and a few kilometers within the storage site.
Before bitumen actually starts being conveyed out of the storage site, it first has to be heated, in order to reduce the viscosity of the bitumen present in the sand or rock. During the heating phase, to ensure rapid heating of the storage site, hot steam is applied to both the injection pipeline and the production pipeline for a period of approximately 3 months. At the end of the heating phase, the viscosity of the bitumen in the storage site is such that when further hot steam is applied to the injection pipeline, resulting in overpressure in the storage site, liquid bitumen can be conveyed out of the production pipeline to the surface. When sufficient pressure builds up the installation of jacking oil pumps to bring the bitumen/water emulsion up can be dispensed with.
The SAGD procedure currently practiced, as has been roughly outlined, exhibits various technical problems. Firstly, hot steam can escape from the storage site via channels or porous rock strata present in the storage site, thereby reducing the thermal energy introduced into the storage site. Excessive pressures in the storage site can result in soil distortions on the surface (blow-out), especially if the overburden is not very thick. A further problem is “fingering” within the reservoir, whereby steam breakout (steam short-circuit) occurs generally at the start or end of the horizontal part of the parallel steam injection or production pipeline, when the steam seeks out a preferred communicating path between both pipelines and undesired pressure is dissipated, with the injected steam condensing and being conveyed through the production pipeline as water, so that less steam and thus thermal energy is supplied to the storage site and the effectiveness of the process is dramatically reduced. Pressure and temperature within the storage site, for the rapid heating thereof, cannot therefore be increased arbitrarily, depending on the storage site conditions. Large quantities of fresh water are required for the SAGD procedure. The quantity of water required is measured on the basis of the “steam to oil ratio” (SOR). Strict environmental regulations in the production areas call for a reduction in the “steam to oil ratio”, in order to protect the above-ground and underground stores of water.
An object of the present invention is to specify a device for in situ extraction of a substance comprising hydrocarbons, in particular a device for conveying heavy oils or bitumen out of an oil sand storage site, which is an improvement over the prior art at least in that a reduced heating phase prior to the start of the production phase can be achieved.
The object is achieved with a device as claimed in the independent claim. Developments are specified in the dependent claims.
The invention is based on the consideration of using an electric heater, which works both inductively and resistively relative to at least parts of the storage site, for the rapid heating thereof. The storage site itself works as a resistive (non-inductive) resistor relative to the heater's at least two electrodes. At the same time the storage site is also heated inductively by the electric heater.
According to the invention a device is specified for in situ extraction of a substance comprising hydrocarbons while reducing the viscosity thereof from an underground storage site, said device containing at least one production pipeline leading out of the storage site. The device further has at least two electrodes, which work inductively and resistively relative to at least parts of the storage site as an electric heater. Advantageously the heating time for the reservoir containing the substance comprising hydrocarbons can be reduced with the inventive device. Compared to devices as known from the prior art, the “steam to oil ratio” can be reduced.
Advantageous embodiments of the inventive device for in situ extraction of a substance comprising hydrocarbons emerge from the claims dependent on the independent claim, it being possible to combine the embodiment as claimed in the independent claim with the features of one dependent claim, and preferably with those of several dependent claims. Accordingly the inventive device for extraction of a substance comprising hydrocarbons can additionally have the following features:
The two electrodes of the electric heater can be formed by essentially perpendicularly oriented electric conductors running at least in part in the storage site. A perpendicular borehole does not require a great deal of drilling. Thus electric conductors which work inductively and resistively relative to at least parts of the storage site can be introduced into the storage site simply and effectively. This device is especially advantageous if it has to be assumed that the permeability diminishes at increasing depth, or the permeability is non-homogeneous in a horizontal direction, in other words that a non-homogeneous and if appropriate anisotropic storage site is present in respect of permeability and/or porosity.
The at least two electrodes of the electric heater can be formed by essentially horizontally oriented electric conductors running at least in part within the storage site. With electric conductors which run horizontally within the storage site, a large part of the storage site can be heated both resistively and inductively by electricity.
The electrodes can be rod-shaped metal conductors. Rod-shaped metal conductors are especially simple and cheap.
The space between at least segments of the electrodes can decrease as the length of the electrodes increases, from the perspective of a power source. The reduction in distance can in particular be stepless. In particular the distance between the segments of the electrodes can decrease linearly. By changing the distance between the electrodes it is possible to keep the voltage drop constant over the length of the electrodes. This voltage drop is determined by the electrical resistance of the electrodes themselves, plus the electrical resistance of the soil correspondingly present between the electrodes. In this way it is advantageously possible to prevent the entire heat output of the electrodes dropping away at an area in the soil close to the power source.
The electrodes can run coaxially in a guide pipe, said guide pipe being permeable to liquid for the selective deposition of a liquid in parts of the storage site at the corresponding subareas running in the storage site. Thanks to the guide pipe the storage site can be supplied with liquid in selective areas, as a result of which the electrical conductivity of the storage site can be affected. In this way the conductivity of the storage site can be ensured, so that the electric heater will operate fault-free.
The device can have an injection pipeline projecting into the storage site. In that the device has both an injection pipeline and a production pipeline, the storage site can be heated on the one hand by means of the electric heater and on the other hand by for example a steam-assisted heating procedure. Both procedures can interwork in synergy.
The electrodes can be connected to one another electrically at their end regions remote from the power source by a connecting post. Thanks to such an electrical connection the operational reliability of the electric heater can be improved.
The injection pipeline and the production pipeline can have pipe sections running in the storage site essentially parallel to one another, oriented essentially horizontally. Seen in cross-section perpendicular to the injection and production pipeline, the electrodes of the electric heater are disposed on both sides of the injection and production pipeline. Thanks to an arrangement of the electrodes of the electric heater on both sides of the injection and production pipeline, the volume of the storage site, which extends in a horizontal direction between the injection and production pipelines, can in particular be heated by the electric heater. Particularly advantageously, a larger volume of the storage site can be extracted in this way. SAGD procedures known from the prior art achieve an extraction of between 40 and 60% of the bitumen present in the storage site. According to the embodiment described above, extraction levels of over 70% appear possible.
At least two of the electrodes of the electric heater can be formed by at least parts of the injection pipeline or the production pipeline. In that the electric heater is formed by at least parts of the injection or production pipeline, it is possible to cut down on additional material for the electric heater; another borehole is thus likewise dispensed with. Such a design of the electric heater is hence especially advantageous.
Hot steam can be applied to the injection pipeline and the production pipeline. If an underground storage site is exploited in accordance with an SAGD procedure or a similar or related procedure, hot steam is applied to pipelines typically present in the storage site. The combination of such a hot-steam-based procedure with an electric heating procedure is especially advantageous, since as a result of the hot steam additional water is introduced into the storage site, which increases the electrical conductivity of the storage site. A particular electrical conductivity is necessary in order to implement an inductive and resistive electric heating procedure. Thanks to the synergetic combination of a hot steam procedure and an electric heating procedure the efficiency of the combined procedure can be increased over and above that of both individual procedures.
The hot steam can be enriched with an electrolyte, preferably with salt. The electrical conductivity of the steam is increased in this way. The effectiveness of an inductive and resistive electric heater relative to at least parts of a storage site essentially depends on the electrical conductivity of the storage site. In that the hot steam introduced into the storage site by the injection and/or production pipeline is additionally provided with minerals, preferably with salt, the electrical conductivity of the storage site can be selectively adjusted and if appropriate increased.
The electric heater can be an alternating current heater. An alternating current heater prevents ions from migrating within the storage site. Advantageously carbonization or salt encrustation of the injection and/or production pipeline can be prevented in this way.
Further advantageous embodiments of the inventive device emerge from the claims not addressed above and in particular from the drawing explained below. The drawing shows preferred embodiments of the inventive device in a highly diagrammatic illustration. It shows:
and
Corresponding parts in the figures are in each case provided with the same reference characters. Parts not explained in greater detail are generally known prior art.
To be able to extract the substance comprising hydrocarbons from the storage site 100, the viscosity of the substance comprising hydrocarbons present in the storage site 100 must be reduced. For this purpose at least parts of the storage site 100 must be heated. To heat the storage site 100 hot steam is applied to the injection pipeline and the production pipeline 102. After being heated for a period of typically 3 months the viscosity of the substance comprising hydrocarbons present in the storage site 100 has decreased so much as a result of the increased temperature that the substance has become free-flowing. If water steam is now further applied to the injection pipeline 101, then as a result of the overpressure present in the storage site or at least parts of the storage site 100 a substance comprising hydrocarbons can be conveyed through the production pipeline 102 to the surface. To maintain the temperature needed for the substance comprising hydrocarbons to flow freely, hot steam is again applied to the injection pipeline 101. Once the extracted substance comprising hydrocarbons arrives at the surface it can be subjected to further processing steps, so that synthetic crude oil can be obtained.
The device shown in
By heating the storage site 100 or at least parts of the storage site 100 it is possible to reduce the liquid content of the storage site 100 and thus to reduce the electrical conductivity of the storage site 100. A decreasing conductivity of the storage site 100 means that the electric heater, in particular the resistive method of operation, becomes less efficient. To counter this loss of conductivity, hot steam forced into the storage site 100 can be enriched with minerals, in particular with salts. Furthermore, by controlling the enrichment of the hot steam with minerals, in particular with salts, the conductivity of the storage site 100 can be selectively adjusted. The minerals or salts are thereby added to the hot steam after it exits from the steam generator. On the other hand, when the bitumen is extracted at a location, no conductivity is required at this location either. In particular the inductive mode of working means that losses only occur where conductivity exists, in other words the depth of penetration expands accordingly and the bitumen present in the case of natural conductivity is heated and flows down by force of gravity with the naturally occurring reservoir electrolyte. Naturally initially the loss mechanism at the electrode will be at its most effective as a result of resistive as well as inductive working; in other words at the start of extraction the bitumen is made more free-flowing there. If the conductivity at the electrode is low, there is no contact between electrode and reservoir; the inductive mechanism now comes into its own, as it does not rely on the electrical contact between electrode and reservoir.
In that liquid, preferably a liquid which is enriched with an electrolyte to improve the conductivity, is selectively introduced into the storage site 100 or parts of the storage site 100, the electrical conductivity of the storage site 100 can be selectively adjusted. In this way the functional capability of the electric heater can be ensured. As a further measure to ensure the functional capability of the electric heater the ends of the electrodes 301, 301′ which face away from the power source 302 can be short-circuited using an electrical bridge 502.
With the exemplary embodiment illustrated in
The electrodes 301, 301′ can continue to run within the storage site 100 such that the distance between them decreases with the increasing length of the electrodes 301, from the perspective of the power source 302. In particular the distance between the electrodes 301, 301′ can decrease linearly. In this way it is possible to prevent the electric heat output, in particular the resistive electric heat output from the perspective of the power source 302, from being introduced into the storage site 100 at the start of the electrodes 301, 301′ or dropping away into this area. The distance between the electrodes 301, 301′ can in particular be selected such that a continuous heat output over the length of the electrodes 301, 301′, in particular over the length of the subareas of the electrodes 301, 301′ which run within the storage site 100, can be achieved by taking account of the electrical conductivity of the storage site 100.
The distance between the boreholes can in this case be controlled using generally known measures; for example a transmitter can be operated in the first borehole, with the drill head of the second borehole being able to determine the distance from the first borehole on the basis of this transmitted signal.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 036 832.3 | Aug 2007 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP08/60074 | 7/31/2008 | WO | 00 | 1/27/2010 |
