Abstract:
A method to extract bitumen or very heavy oil in situ from oil sand seams close to the Earth&#39;s surface is provided. Energy is introduced via at least two pipes at a given, repeatable distance from the seam, a predefined geometry is maintained in relation to the well pair. The associated apparatus includes at least one additional pipe which is alternatively designed as an electrode or also for feeding vapor and is placed above the injection pipe.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the US National Stage of International Application No. PCT/EP2008/060817, filed Aug. 19, 2008 and claims the benefit thereof. The International Application claims the benefits of German application No. 10 2007 040 606.3 DE filed Aug. 27, 2007. All of the applications are incorporated by reference herein in their entirety. 
     FIELD OF INVENTION 
     The invention relates to a method for the in situ extraction of bitumen or very heavy oil from reservoirs in the faun of oil sand deposits close to the surface, thermal energy being supplied to the reservoir to reduce the viscosity of the bitumen or very heavy oil, to which end elements are used to introduce energy into the reserve and extraction pipes are used to recover the liquefied bitumen or very heavy oil. The invention also relates to the associated apparatus, with at least one element for introducing energy and also an extraction pipe. 
     BACKGROUND OF INVENTION 
     During the in situ breaking down of bitumen from oil sand by means of steam and horizontal bore holes according to the SAGD (Steam Assisted Gravity Drainage) method the problem arises with thin bitumen strata in particular that only an economically limited quantity of bitumen can be tapped. In the most favorable instance this is around 40 to 60% of the bitumen present in the reservoir but much less in the case of thin strata. The reason for this is the limited width of the growing steam chamber, which is typically around twice as wide as it is high. For a high yield in flat reservoirs (20 to 30 m) this means that an injection pipe must be provided to introduce energy every 40 to 60 m above the extraction pipe. The two pipes, one on top of the other, are known in the pertinent prior art as so-called well pairs. 
     A specific SAGD method for extracting very heavy oil is known from U.S. Pat. No. 6,257,334 B1, in which, in addition to a so-called well pair consisting of pipes one on top of the other, further elements are also present, which are intended to improve the heating of the region. Also in WO 03/054351 A1 a facility for the electrical heating of certain regions is described, with which a field is generated between two electrodes, heating the region in between them. 
     In the prior art the well pairs are provided at small intervals, incurring high costs for horizontal boring and piping. Alternatively high yields would have to be sacrificed to save costs. 
     SUMMARY OF INVENTION 
     On this basis the object of the invention is to propose an improved method for extracting bitumen or very heavy oil and to create an associated apparatus. 
     According to the invention the object in respect of the method is achieved by the measures of the claims and in respect of the apparatus by the features of the claims. Developments of the method and the associated apparatus are set out in the subclaims. 
     With the invention the following method steps in particular are implemented: —the energy is introduced in each instance in a predeterminable section of the reservoir by way of at least two separate elements, a predetermined geometry of the elements being maintained in relation to the extraction pipe; —to introduce the energy by way of the separate elements, at least one further pipe is used to introduce steam and/or as an electrode for electrical energization; —the injection pipe and the energization pipe are connected in the manner of an electrical conductor loop; —outer regions of the reservoir are also supplied with thermal energy at least by way of the further pipe. The energy can be introduced in a repeatable manner at predeterminable points of the reservoir. To this end the associated apparatus has at least one extraction pipe per defined unit of the reservoir, the extraction pipe running in a horizontal direction on the bottom of the reservoir, with at least two further energy introduction elements running in a horizontal direction above it at a predetermined upward distance and lateral distance from the extraction pipe. 
     The object of the invention is therefore to introduce thermal energy at precisely defined points of the reservoir, with separate paths being used to introduce the energy. This can be achieved in particular by introducing additional horizontal pipes into the reservoir and further heating the bitumen which would otherwise remain cold. Since only individual pipes are to be used for this rather than pipe pairs, relatively low costs can be anticipated. 
     Based on experience with the inductive heating of oil sand reservoirs, it has shown that bitumen heats up extensively and not only in the discrete environment of the electrodes. It can be deduced from this that bitumen and/or very heavy oil can be extensively melted by means of individual additional electrodes and its viscosity reduced, so that it can then flow into an existing SAGD well pair system with a steam bubble and be extracted. 
     The inventive procedure allows a significantly higher bitumen yield to be achieved. Economic viability calculations promise success. Heating by means of this additional horizontal pipe can take place from the start, continuously at comparatively low power or with a time offset at appropriately higher power. It is important that the conventional SAGD process with the growing steam chamber is not disrupted by early flooding. 
     The later connection of an additional heating unit should in particular also be seen as advantageous as a retrofitting solution for existing SAGD reservoirs, which only promise a low yield. 
     The additional heating pipe does not necessarily have to be electrically operated but can optionally also be an injection pipe operated in steam cycling mode, in other words the hot steam is not released into the reservoir but conveyed back there. This produces a heating process which is propagated into the volume simply by thermal conduction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further details and advantages of the invention will emerge from the description of figures of exemplary embodiments which follows based on the drawing in conjunction with the subclaims, in which drawing: 
         FIG. 1  shows a sectional diagram through a deposit according to the prior art, 
         FIG. 2  shows a three-dimensional diagram of elementary units of the reservoir as an oil sand deposit and 
         FIG. 3  to  FIG. 6  respectively show cross-sections through the deposit according to  FIG. 1  with different arrangements of additional elements for introducing heat. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     In  FIG. 1  a thick line E shows the ground surface, below which an oil sand deposit is located. Generally a superstructure of rock or other material is present below the ground surface, followed by a seam in the form of an oil sand reservoir at a predetermined depth. The seam has a height or thickness h, a length l and a width w. The seam therefore contains the bitumen or very heavy oil and is referred to below as the reservoir  100 . With the known SAGD method an injection pipe  101  for steam and an extraction pipe  102 , also referred to as a production pipe, are routed horizontally on the base of the reservoir  100 . 
       FIG. 1  shows an outline of a method according to the prior art. Externally, i.e. above the ground, means are present for generating steam, which will not be examined in detail in the present context. The steam heats the area around the injection pipe  101  and reduces the viscosity of the bitumen or very heavy oil present in the oil sand. In the extraction pipe  102 , which runs parallel to the injection pipe  101 , the oil is recovered and fed back by way of the perpendicular region through the covering rock. Oil is then separated from the raw bitumen in a method-related installation  4  and further processing, e.g. flotation or the like, takes place. 
       FIG. 2  shows an oil sand deposit, having a longitudinal extension  1  and a height h. A width w is defined, which is used to define an elementary unit  100  as a reservoir for oil sand. In the prior art the injection pipe  101  and the extraction pipe  102  are routed in a parallel manner on top of one another in a horizontal direction in the unit. The section from the oil reservoir is repeated a number of times on both sides. 
       FIGS. 3 to 6  respectively show cross-sections through the deposit according to  FIG. 1  (line IV-IV) or  FIG. 2  (view from front). The dimensions w×h and the arrangement of the extraction pipe  102  on the base of the reservoir  1  are the same. Otherwise alternatives are respectively shown for the injection pipe and/or electrodes. 
       FIG. 3  shows a horizontal pipe pair (well pair), in which the upper of the two pipes, i.e. the injection pipe  101 , can optionally also be configured as an electrode. A further horizontal pipe  106  is also present here, being configured specifically as an electrode. 
     Electrodes  106 ′,  106 ″, . . . are also present in the adjacent sections, so that a regularly repeating structure results. 
     With the arrangement shown inductive energization takes place by means of the electrical connection at the ends of the additional electrode  106  and the injection pipe  101 , resulting in a closed loop. 
     The horizontal distance between the electrode  106  and the extraction pipe is w/h; the vertical distance between the electrodes  106 ,  106 ′, . . . and the well pair, in particular the injection pipe, is 0.1 m to around 0.9 h. In practice distances between 0.1 m and 50 m result. 
     It can be seen from  FIG. 3  that a predetermined region is heated by the well pair with the pipes  101 ,  102 , the thermal distribution at a defined time being outlined roughly by the line A. The additional inductive heating between the pipes  101  and  106  advantageously results in the peripheral region in corresponding thermal distributions in the region outlined by the line B, which is asymmetrical in  FIG. 3 . 
       FIG. 4  is based on an arrangement as in  FIG. 3 , with electrodes  107 ,  107 ′ being respectively disposed above the well pair on a gap between two well pairs. 
       FIG. 2  shows the section of the reservoir, which is repeated a number of times on both sides. The horizontal pair with the injection pipe  101  and production pipe  102  can be seen from the cross-section. The further horizontal pipe  107  is configured as an electrical conductor. Two conductors  107 ,  107 ′ respectively represent the electrodes for inductive energization by means of electrical connection at the ends. The connections here can be made outside the deposit, i.e. above the ground. 
     With the arrangement according to  FIG. 4  the horizontal distance from the electrode  107  to the extraction pipe  102  dl=w/2. The vertical distance corresponds in turn to the one in  FIG. 2  with typical values of around 0.1 m to 50 m. 
     In  FIG. 4  the thermal distribution is similar to the one in  FIG. 3  but this time it is configured symmetrically. 
     In  FIG. 5  the arrangement according to  FIG. 2  is disposed so that there are two injection pipes  108  and  109  present per production pipe  101 , which equally serve as electrodes. It is thus possible to effect an inductive energization between two adjacent electrodes, in so far as a conductor loop is formed. In  FIG. 5  the horizontal distance between the injection pipes  108  and/or  109  and the extraction pipe  102  is around 0.1 w to 0.8 w, signifying values of typically 10 m to 80 m. The vertical distance between the injection pipes  108  and  109  and the extraction pipe  102  is 0.2 h to 0.9 h, corresponding to a value of 5 m to 60 m. 
     The thermal distribution resulting in  FIG. 5  corresponds to the outline A. 
     Finally  FIG. 6  shows an arrangement like the one in  FIG. 2 , in which two injection pipes  111 ,  111 ′ are also positioned above the well pair consisting of the injection pipe  101  and extraction pipe  102  on a gap between two well pairs, with no energization taking place here. The injection pipe is operated so that steam is fed back to the surface. This corresponds essentially to the cycling mode known from the prior art in its preheating phase. 
     The section from the oil reservoir  1  is again shown in detail, being repeated a number of times on both sides. The well pair consists of the injection pipe  101  and the extraction pipe  102  and the additional horizontal pipe  111  or  111 ′ is operated in steam cycling mode. The repeating injection pipe  111 ′ here acts for the adjacent section of the regularly repeating sections. 
     With the arrangement shown in  FIG. 6  the horizontal section of the further injection pipes to the extraction pipe is again w/h; the vertical distance between the additional injection pipes  111 ,  111 ′ and the first injection pipe is roughly between 0.1 m to 0.9 h, which corresponds to values between 0.1 and 50 m. 
     In  FIG. 6  a thermal distribution with the outlines according to  FIG. 4  results with a symmetrical configuration due to the injection pipes positioned on a gap and repeated to the well pair. 
     In the examples described above with reference to  FIGS. 3 to 6  the inventive measures bring about improved thermal distributions over the cross-section, the outlay remaining reasonable. Efficiency improvements generally result, manifesting themselves in a higher oil extraction yield.