VOLUME EQUALIZATION DEVICE

Description

[0001] The invention relates to a system for introducing deep well pumps (also called electric submersible pumps - ESP) into a borehole in geothermal energy, comprising a working oil chamber filled with light oil or a light oil-like fluid and a volume compensation device.

[0002] Deep well drilling in geothermal energy reaches great depths, which, depending on the structure of the Earth's mantle, can be 3,000 m or more. This depends on the depth at which the temperature required for harnessing the geothermal energy exists. The highest possible temperatures are aimed for, as this also increases the energy yield. In the Upper Rhine Graben, for example, temperatures of around 170°C prevail at a depth of 3,000 m. However, these temperatures also bring with them problems, as the pumping device with drive, which is located in the borehole and serves to pump the borehole fluid, also generates heat. In geothermal energy, the borehole fluid is the hot well water. The greatest heat generation occurs in the electric motor, although the highest temperatures can be reached at the axial bearing that supports the drive shaft for the pump. This bearing must absorb forces of 15 to 25 tons.Such a bearing requires lubrication, which is achieved by using oil. However, this oil undergoes volume changes due to temperature fluctuations caused by the heat generated during operation of the device. As a result, well water must not under any circumstances enter the working oil chamber and contaminate the light oil. However, the light oil should not leak into the well water. This risk does not exist with heavy oil, as its consistency and high specific gravity form a reliable barrier even at high temperatures. However, at €600 per liter, heavy oil is far too expensive to be used as a working oil for lubrication of the axial bearing and possibly for filling the electric motor that drives the pump. Light oil, on the other hand, is much less expensive.The problem to be solved is therefore to prevent any penetration of well water into the light oil or any leakage of light oil into the well water despite the change in volume of the working oil.

[0003] Bellows systems are known which separate the working oil from the borehole fluid and, due to their elasticity, enable compensation of the volume change, e.g. DE 1 186 141 (explanatory document), WO 2017 / 096103 A1 and WO 2016 / 032521 A1.

[0004] The disadvantage of this type of volume compensation is, on the one hand, the limitation of this compensation due to the mechanically limited expansion of the bellows, and on the other hand, such a bellows is a heat-sensitive wearing part that would have to be replaced more frequently, which represents a considerable effort due to its arrangement in the borehole.

[0005] PCT / US2017 / 064498 therefore proposes a spring-loaded piston that moves relative to a compressed gas chamber. The disadvantage of this is that the compressibility of the gas limits the volume compensation, and the pressure in the gas would cause a pressure increase in the working oil if the volume to be compensated was large. To compensate for this and maintain the desired pressure in the working oil, a servomotor is provided that moves the piston used for volume compensation, preventing the working oil pressure from rising too much. However, this also requires pressure sensing and control. Such a system is complicated, expensive, and prone to failure, particularly due to the high temperatures involved.

[0006] The document US 3,182,214 A describes a submersible seal for an electric motor driving a pump by means of a shaft passing through the seal in order to protect the motor from the ingress of ambient fluid in which the motor, pump and seal are to be immersed.

[0007] The invention is therefore based on the object of making available a volume compensation device of the type mentioned above which is robust even at high temperatures, is of simple construction and has a high compensation capacity.

[0008] The object is achieved according to the invention in that a separating layer of heavy oil or heavy oil-like fluid is arranged as a volume compensation device between the light oil or the light oil-like fluid of the working oil chamber and the borehole fluid surrounding it, which can be moved in accordance with the change in volume of the light oil or light oil-like fluid.

[0009] In geothermal energy, the borehole fluid is well water, but other possible uses should not be ruled out, for example in oil production, in which case it would be crude oil.

[0010] The basic idea of ​​the invention is to use a layer of heavy oil (this always means a fluid similar to heavy oil, i.e. with a similar specific gravity) to separate the borehole fluid, usually the well water, from the light oil (this always means a fluid similar to light oil with comparable lubricating properties), in order to create a secure barrier that completely prevents well water from penetrating the working oil chamber, mixing with the light oil and thus contaminating it, or leaking into the well water. When implementing this basic idea, account must be taken of the fact that heavy oil is heavier than light oil, collects at the lowest point, and does not mix with water in direct proximity, while the light oil would float on both the heavy oil and the water.It is therefore not possible to insert the heavy oil between the light oil and the water without appropriate measures. The invention proposes various measures to solve this problem.

[0011] In the simplest case, not according to the invention, a piston movable within a cylinder could be arranged on the light oil, on which the heavy oil could be placed above the light oil. However, since the heavy oil is immiscible with water, it can act as a movable separating layer directly adjacent to the well water if it lies below the water.

[0012] However, in the technical implementation of separating light and heavy oil, other options can be used than a movable piston separating these different oils. As an alternative, a multi-chamber system is proposed in which the volume compensation device comprises a volume compensation chamber connected to the working oil chamber, which has a light oil region for volume compensation of the light oil and a heavy oil region containing a heavy oil or a heavy oil-like fluid. The boundary between the light oil region and the heavy oil region is movable, allowing the heavy oil to flow into an expansion chamber, which has another heavy oil region adjacent to a wellbore fluid region. The wellbore fluid can flow in and out of the expansion chamber via a compensation opening.The basic idea of ​​this alternative is that there are two chambers, one for the boundary of light and heavy oil and a separate one for the boundary of heavy oil and well water (or another well fluid that is lighter than heavy oil, for example petroleum).

[0013] This multi-chamber system is then expediently designed in such a way that the volume compensation chamber has a connection from its light oil area to the working oil chamber and from its heavy oil area to another heavy oil area of ​​the expansion chamber.

[0014] Such a multi-chamber system can be constructed in various ways: The working oil chamber can be arranged below the volume compensation chamber and the expansion chamber above the volume compensation chamber. Alternatively, the volume compensation chamber can be arranged below the working oil chamber and the expansion chamber above the working oil chamber, with the connection from the volume compensation chamber to the expansion chamber being a pipe connection bypassing the working oil chamber.

[0015] For the embodiment in which the working oil chamber is arranged below the volume equalization chamber and the expansion chamber is arranged above the volume equalization chamber, it is proposed as a practical further development that a device for collecting any leakage of the heavy oil into the light oil and for returning it to the heavy oil of the volume equalization chamber is arranged on a mechanical seal between the volume equalization chamber and the working oil chamber. A specific implementation for collecting and returning the heavy oil provides that a heavy oil collection basin with a heavy oil sump and a pump is arranged below the mechanical seal to collect any leakage of the heavy oil. This pump transports the collected heavy oil back to the volume equalization chamber via a return line.

[0016] A further advantageous development provides for a heat exchanger that extracts heat from the light oil and transfers it to the wellbore fluid. For this purpose, a pump can be provided that supplies the light oil to be cooled to the heat exchanger via an oil circuit.

[0017] The invention is explained below with reference to exemplary embodiments shown in the drawing. Fig. 1 a first embodiment of the invention with a multi-chamber system Fig. 2 a single-chamber system not according to the invention, Fig. 3 a multi-chamber system not according to the invention and Fig. 4 the use of the invention in a borehole.

[0018] Fig. 1 shows a first embodiment of the invention with a multi-chamber system. The encapsulated volume compensation device 1 is inserted into a borehole 2 in the ground 31, which is usually rock at this depth. This is described in more detail in Fig. 4 presented and described.

[0019] The encapsulated volume compensation device 1 serves to provide volume compensation for a light oil 4 or light oil-like fluid used for lubrication in a working oil chamber 5 when it expands due to heating or contracts again upon cooling. The volume changes are due to three causes: Firstly, the temperature difference between the temperature when the light oil 4 is filled and the temperature when the device 1 is inserted into the hot well water 6 of the borehole 2. This temperature difference is approximately 80 to 150°C. The electric motor 21 then generates heat, resulting in a temperature difference of approximately 50°C. The axial bearing 19 then contributes a further temperature difference of approximately 30°C, but can lead to the highest temperature in its area.All of this takes place in an already hot environment, as geothermal energy is particularly effective when the hottest well water can be extracted.

[0020] In order to ensure volume equalization for the light oil 4 in the working oil chamber 5, which also contains the axial bearing 19, this chamber is connected via a connection 16 to a volume equalization chamber 10, specifically to its light oil region 10'. Below this chamber is a heavy oil region 10", with the light oil 4 and the heavy oil 7 forming a stable boundary 11 due to their different specific gravity. The heavy oil region 10" is connected via a connection 17 to an expansion chamber 12. This expansion chamber 12 has another heavy oil region 13 in its lower region and a borehole fluid region 14 in its upper region. Depending on the change in volume of the light oil 4, which pushes the heavy oil 7 from the volume equalization chamber 10 into the expansion chamber 12 during expansion, the level of the heavy oil 7 there rises or falls when it cools.According to this process, the borehole fluid 6 flows from a compensation opening 15 into the intermediate region of a tube which lines the borehole 2 as a well wall 38 and contains the various functional elements of the conveying device (see . Fig. 4 ). The double arrow 15' shows this entry and exit of the borehole fluid 6 from and into the expansion chamber 13.

[0021] The pump shaft 20 extends through the volume compensation device 1, with the pump 29 with intake port 34 located above and the electric motor 21 below, which is usually also located in an area of ​​the working oil chamber 5 with light oil 4, which must be imagined as being extended downwards in the illustration.

[0022] Also shown is a practical embodiment of the invention, by means of which a leakage 23 of the heavy oil 7 can be collected at a mechanical seal 22 when it passes from the volume compensation chamber 10 into the working oil chamber 5. For this purpose, a heavy oil collecting basin 24 is mounted below the mechanical seal 22, preferably a mechanical seal, which collects the leakage 23 and feeds it to a heavy oil sump 25. A pump 26 then supplies the heavy oil 7 via a return line 27 to the light oil region 10' of the volume compensation chamber 10, where it then sinks to the heavy oil region 10". In this way, it can be avoided that such a leakage 23 causes heavy oil 7 to pass from the volume compensation chamber 10 into the light oil 4 of the working oil chamber 5 and thus be lost for the described function. Furthermore, a heat exchanger 28 is provided, the function of which is to cool the light oil 4.For this purpose, the heat exchanger 28 is arranged between the working oil chamber 5 and the borehole fluid 6 within the well wall 38. To make this cooling as effective as possible, a pump 29 is arranged, for example, on the pump shaft 20. It drives an oil circuit 30 (small arrows), which supplies the oil to the heat exchanger 28. In this way, the strong heat generated by the axial bearing 19 is dissipated, preventing the light oil 4 from overheating and losing some of its lubricating properties.

[0023] Fig. 2shows a single-chamber system not according to the invention, which implements the basic concept of the invention in a simple manner. Here, the axial bearing 19 and the (not shown) electric motor 21 are located in the single chamber and are located in the light oil 4, which is heating up. A piston 9 mounted in a cylinder 8 moves as shown by the double arrow 9'. Due to this displacement - upwards when heated, downwards when cooled - the heavy oil 7, which rests on the piston 9, also moves. Above the heavy oil 7 is the borehole fluid 6, which can enter and exit through the compensation opening 15 according to the arrows 15'. The same reference numerals in the figures indicate functionally identical features. Here, for example, the boundary 11 between the light oil 4 and the heavy oil 7 is formed by the piston 9, and the displacement occurs according to the double arrow 9'.The problem with this arrangement is the seal between the sliding piston and the cylinder wall.

[0024] Fig. 3shows a multi-chamber system not according to the invention, in which the chambers are arranged differently. Here, the working oil chamber 5 is located between the volume compensation chamber 10 and the expansion chamber 12. The axial bearing 19 and the electric motor 21 are arranged in the working oil chamber 5. If the light oil 4 expands in the working oil chamber 5, it is pressed downward through the connection 16 into the volume compensation chamber 10, in which the light oil region 10' and the heavy oil region 10" are located. Here, too, a piston 9 is arranged between the heavy oil 7 and the light oil 4, which moves up and down in a cylinder 8 according to the change in volume of the light oil 4. The piston 9 can also be supported by a spring. The arrangement of piston 9 and cylinder 8 is not necessary, however, since here the light oil 4 and the heavy oil 7 can also come into direct contact with one another, because the heavy oil 7 is always immiscible and located at the bottom.When the light oil 4 expands, the heavy oil 7 is pressed into a connection 17 which, as a pipe connection 18, feeds the heavy oil 7 to the expansion chamber 12, specifically into its heavy oil region 13. There, the borehole fluid 6 is located above the heavy oil 7 in a borehole fluid region 14. This has a compensation opening 15 through which the borehole fluid 6 can flow in and out according to the double arrow 15'.

[0025] Fig. 4shows the use of the invention in a conveying device 39 in a borehole 2. The borehole 2 is separated from the ground 31, i.e. usually the rock, by a well wall 38. The entire conveying device 39 for the well water 6 is located within this well wall 38. This consists of a deep well pump 3, which is driven by an electric motor 21. The conveying pipe 33 serves for conveying. The electric motor 21 is supplied with power via a cable 32. The encapsulated volume compensation device 1 according to the invention with the axial bearing 19 is arranged between the deep well pump 3 with the intake nozzle 34 and the electric motor 21.

[0026] At the lower end of the conveying device 39 there is a sensor 35 and a centering device 36. Above the earth's surface there is an above-ground fitting and pipe 37 for the extracted well water 6 in order to utilize the geothermal heat.

[0027] The illustrated embodiments can of course vary, so the embodiments according to Fig. 2 and Fig. 3 be provided with a device to collect a leak or have a cooling device. Fig. 3 For example, a device for catching a leak could also be arranged between the expansion chamber 12 and the working oil chamber 5. Further variations, such as a system with two chambers, are also possible by transferring features from one example to the other. List of reference symbols

[0028] 1Encapsulated volume equalization device 2Borehole 3Deep well pump 4Light oil or light oil-like fluid 5Working oil chamber (light oil or light oil-like fluid) 6Borehole fluid (well water) 7Heavy oil or heavy oil-like fluid 7'Arrows: Displacement of the heavy oil separating layer 8Cylinder 9Piston 9`Double arrow: Displacement of the piston 10Volume equalization chamber 10'Light oil area of ​​the volume expansion chamber 10"Heavy oil area of ​​the volume expansion chamber 11Boundary between heavy and light oil 12Expansion chamber 13Further heavy oil area (of the expansion chamber) 14Borehole fluid area (of the expansion chamber) 15Equalization opening 15'Inlet and outlet of the borehole fluid 16Connection between the volume equalization chamber and the working oil chamber 17Connection between the volume equalization chamber and the expansion chamber 18Pipe connection 19Thrust bearing 20Pump shaft 21Electric motor 22Mechanical seal 23Heavy oil leakage 24Heavy oil collection tank 25Heavy oil sump 26Pump 27Return line to the volume compensation chamber28Heat exchanger 29Pump 30Oil circuit 31Soil (rock) 32Cable 33Conveyor pipe 34Intake nozzle 35Sensor 36Centering device 37Above-ground fitting and pipe 38Well wall 39Conveying device

Claims

1. System for introduction into a drilled hole (2) for geothermal deep-well pumps (3), having a working-oil chamber (5) which is filled with light oil (4) or a fluid similar to light oil, and having a volume-compensating device (1), characterized in that arranged as a volume-compensating device (1) between the light oil (4) or the fluid similar to light oil of the working-oil chamber (5) and the drilled-hole fluid (6) surrounding said chamber is a separating layer of heavy oil (7) or fluid similar to heavy oil that is displaceable according to the change in volume of the light oil (4) or fluid similar to light oil.

2. System according to Claim 1, characterized in that the volume-compensating device (1) has a volume-compensation chamber (10) which is connected to the working-oil chamber (5) and which has a light-oil region (10') for volume compensation of the light oil (4) and has a heavy-oil region (10'') with a heavy oil (7) or a fluid similar to heavy oil, in that the interface (11) between the light-oil region (10') and the heavy-oil region (10'') is displaceable and the heavy oil (7) can flow into an expansion chamber (12), which has a further heavy-oil region (13) that is adjacent to a drilled-hole-fluid region (14), wherein the drilled-hole fluid (6) can flow into and out of the expansion chamber (12) via a compensation opening (15).

3. System according to Claim 2, characterized in that the volume-compensation chamber (10) has a connection (16) to the working-oil chamber (5) from its light-oil region (10') and has a connection (17) to a further heavy-oil region (13) of the expansion chamber (12) from its heavy-oil region (10'').

4. System according to either of Claims 2 and 3, characterized in that the working-oil chamber (5) is arranged below the volume-compensation chamber (10), and the expansion chamber (12) is arranged above the volume-compensation chamber (10).

5. System according to either of Claims 2 and 3, characterized in that the volume-compensation chamber (10) is arranged below the working-oil chamber (5), and the expansion chamber (12) is arranged above the working-oil chamber (5), wherein the connection (17) from volume-compensation chamber (10) to expansion chamber (12) is a tubular connection (18) which bypasses the working-oil chamber (5).

6. System according to either of Claims 3 and 4, characterized in that, at a mechanical seal (22), preferably a slide-ring seal, between volume-compensation chamber (10) and working-oil chamber (5), there is arranged a device for collecting leakage (23) of the heavy oil (7) into the light oil (4) and for return into the heavy oil (7) of the volume-compensation chamber (10).

7. System according to Claim 6, characterized in that, below the mechanical seal (22), for collecting leakage (23) of the heavy oil (7), there is arranged a heavy-oil-collecting tank (24) with a heavy-oil sump (25) and with a pump (26) which transports the collected heavy oil (7) back into the volume-compensation chamber (10) via a return line (27) .

8. System according to Claim 1 to 7, characterized in that there is arranged a heat exchanger (28) which extracts heat (29) from the light oil (4) and releases said heat to the drilled-hole fluid (6).

9. System according to Claim 8, characterized in that a pump (29) supplies the light oil (4) to be cooled to the heat exchanger (28) by means of an oil circuit (30).