NO319807B1 - Gravity separator device for downhole separation of source fluids, and method for downhole gravity separation of source fluids. - Google Patents

Abstract

Separator device for downhole separation of well fluids comprising at least two separator cells, each separator cell comprising a separator housing. The separator housing has walls (9, 10, 15, 16) which delimit a separator chamber (17) between them. From the separator chamber there is a water outlet (8) and a hydrocarbon outlet (7), and into the separator chamber there is a well stream inlet (13, 14), which communicates with an annulus in the borehole outside the separator housing. A water flow line (21) communicates with the water outlet (8) from the at least two separator cells; and a hydrocarbon flow line (23) communicates with the hydrocarbon outlet (7) to provide parallel operation of said separator cells. There is also described a method for separating well streams from different zones independently of each other.

Description

The present invention relates to a gravity separator device for downhole separation of well fluids and a method for downhole gravity separation of well fluids.

The invention relates particularly, but not exclusively, to countercurrent separation.

When producing hydrocarbons from underground wells, water will be produced in addition to the hydrocarbons. The water usually has a higher density than the hydrocarbons and therefore tends to collect in the lower part of the borehole, and a layered flow pattern will form. Water will also, as a result of gravity, flow at a lower speed than the hydrocarbons in inclined wells. In some sections of the well, it may even flow downwards.

Most wells will see an increase in water production late in their production period. Older fields therefore typically produce more water than hydrocarbons. Consequently, one of the industry's biggest challenges is dealing with these enormous amounts of produced water.

A particularly challenging aspect of this problem is the fact that most of these older wells cannot bear the costs of new drilling or a full well overhaul. Reasonable modifications would therefore be the ideal solution. Most of these wells have no horizontal sections, with the result that downhole horizontal separation based on natural fall cannot be carried out. A separation system that can be used in an awiks well would therefore be of great interest.

There are two important prior art methods for downhole separation:

• the cyclone-based system, which has been known for quite some time, has so far been a limited commercial success due to questionable operational reliability, and • separator systems based on natural fall, where low-flow systems, dual-action pumping systems (DUAL Action Pumping System (DÅPS)) that handle less than 200 m<3>/d, have been tried with mixed results, while high-throughput systems have yet to find commercial application.

Two types of drop separator systems for high throughput are known: The horizontal separator of Norsk Hydro, described in WO 98/41304, and the inclined well separator of Schlumberger, described in GB 2 326 895, in addition to a variant of this associated ABB, described in Norwegian patent application 2000 0900 .

The basic concept behind the downhole separation system described in WO 98/41304 is to regulate the flow rate of formation fluid in a horizontal section of the well to such a level that stratification is achieved. The separated oil is allowed to flow freely to the surface, provided there is sufficient bottomhole pressure (otherwise gas lift or other artificial lifting methods can be used). A well pump is used to inject the secreted water into a suitable area.

The downhole separation systems based on natural fall according to GB 2 326 895 and NO 2000 0900 are suitable for inclined boreholes. The system according to GB 2 326 895 is similar to that of WO 98/41304, with the exception that it proposes two outlet pipes, one taking the oil and the other the separated water. A sensor located near the outlet openings will be used to regulate the outflow amount. Compared to WO 98/41304, it is claimed that this system works at slopes of 0 - 50 degrees. The system according to NO 2000 0900 is also claimed to work in inclined wells where the heavy fluid component (water) is separated from the incoming fluid through openings in a pipe into a second channel formed between the outside of this pipe and the well casing.

Such systems will require layered flow patterns in the separation chamber to work. Oil, which is lighter than water, will flow upwards in the top layer and reach the oil outlet. Water will flow at a lower speed or flow counter-currently inside the separation chamber (depending on the angle and total flow rate) and is captured by the water outlet or drainage openings. The highest allowable slip rate between oil and water is a critical parameter when it comes to determining the total capacity of such a system. When this slip velocity exceeds a certain maximum value, the fluids will mix again at the interface, and the separation will break down.

However, the advantage lies in the ability to operate in an inclined borehole.

US 6080312 represents an example of hydrocyclone separators. This publication shows parallel connected hydrocyclone separators. Such separators are significantly different from gravity separators, as the mode of operation is completely different. In a cyclone separator, the various fluid phases are thrown vigorously. During this process, the phases are first vigorously mixed and then forced to separate. It thus does not matter how the phases exist before they enter the separator. Whether they are already present in a homogeneous mixture or have already been separated to a certain extent has no effect on the function of the cyclone separator.

Cyclone separators also have other disadvantages. They work better the larger the diameter. In a wellbore, the diameter will be strongly limited. The function will also be independent of the orientation of the separator, i.e. whether it is vertical or inclined. A gravity separator can be tilted and thereby separate more efficiently despite its small diameter. The cyclone separator is considerably more complicated. There is therefore a greater risk of a malfunction occurring. Pulling up a separator from the well again to repair or replace it with a new one is very expensive. With a gravity separator, the risk of this is significantly reduced.

A gravity separator can be set for different water cuts (i.e. water to oil ratio). Thereby, the separator can be "tuned" to separate as efficiently as possible for the water cut that exists in the relevant zone where the separator is placed.

In the assembly of hydrocyclone separators as shown in US 6080312, such tuning becomes very difficult. This is because all the inlets from the various zones lead into the same elongated chamber. There is therefore a mixture of fluids from the various zones. In the present invention, the separators are separated from each other as clearly defined cells. There is therefore no mixing of fluids from the various zones after these have flowed into their respective separator cells through the inlets.

The present invention aims to exploit the fact that well fluids are not completely mixed in the well, but are, in a sense, pre-separated by, for example, water and oil being present in pockets. By allowing the well fluids to flow relatively carefully into the separator, the fluids will not mix completely with each other. The separation in the gravity separator will then be able to take place faster and with better results than if the fluids were completely mixed before the separation. This cannot be achieved in a cyclone separator.

During the spring/summer of 2001, the present applicant carried out investigations with the aim of establishing a new downhole separation device which, for example, could

suitable for modification of old wet wells.

The following criteria were used as a basis for a possible downhole separation system for the modification of such old wet wells:

1. No requirement for new drilling.

2. Must fit standard casing dimensions: 7" (approx. 178 mm) and 9 <s>/g" (approx. 229 mm).

3. Must work in inclined wells.

4. If possible, avoid rotating equipment (pump, compressor) in the well.

5. Separated phases (hydrocarbons and water) are led to the surface, alternatively water is led to an underground low-pressure formation without the use of a pump.

6. Minimal monitoring and regulation down in the well (for simplicity).

7. Separated phases are clean enough to pass through the 1st and 2nd stage separators on the surface.

8. Works with all water fractions.

9. Accepts high flow rates (typically over 2000 m<3>/day).

There is currently no downhole separation technology that meets these criteria. Cyclone-based, downhole separation technology will not meet criteria no. 7 and 8. Systems based on natural fall and low flow rate will not meet criteria no. 5 and 9. Downhole horizontal separation (high flow rate) will not meet criterion no. 3. Rotary separators under development will not meet criterion no. 4. Drop-based systems for inclined holes will not meet criterion no. 9 (see below).

Consequently, there is a need to fill these gaps in technology, as feedback from the market indicates that there is a great need for this type of installation.

Based on this, it was decided to carry out a technical evaluation of the counter-current separation (CS) principle (similar to that described in GB 2 326 895 and NO 2000 0900), which depends on an inclined borehole to work . The system is based on separation through natural fall, but differs from WO 98/41304 in that water is directed in the opposite direction to the oil. Gravity will cause the water to collect at the bottom of the well, where an outlet pipe or pump is arranged to deposit it to the surface or in an injection zone. Compared to WO 98/41304, there will be a significant release rate between the oil and water phases. Experiments have shown that this will be a limiting factor for the total capacity of such a system.

The tests showed that to be effective, the flow rate in the borehole would have to be reduced to around 10 - 20% of the discharge rate from a normal high flow well. Consequently, the separators according to GB 2 326 895 and NO 2000 0900 will only be useful for wells with lower throughput.

To overcome this limitation, the present invention prescribes a separator device comprising at least two separator cells, where each separator cell comprises a separator housing, said separator housing having walls which define a separator chamber between them; a water outlet and a hydrocarbon outlet from said separator tank; a well stream inlet to the chamber, which communicates with an annulus in the borehole outside the separator housing; a water flow line communicating with said water outlet from said at least two separator cells; and a hydrocarbon flow line communicating with said hydrocarbon outlet to provide parallel operation of said separator cells.

In a second aspect, a method is proposed for separating well fluids from different zones independently of each other, as hydrocarbon-producing zones in a borehole are blocked off, well fluids are extracted from a respective formation bordering the zones, well fluid that flows into the respective zones is separated into water and hydrocarbons in downhole separators, as the separation of well fluids from the respective zones takes place independently of each other.

The separation can take place in an inclined part of the well and/or a horizontal part of the well.

The invention as stated in the subsequent claims will provide one or more of the following advantages:

• Increased overall throughput capacity.

• The different cells can be set to handle different water fractions (water cut - WC), as the upper cells are likely to handle lower water fractions than the

lower units.

• Increased overall efficiency, since the upper cells will receive more clean oil and less water, while the lower cells have more clean water and less oil to remove. • Can be combined with regulation in the inflow zone to get a better emptying of the reservoir.

• Each cell can be adapted for different inflow pressures along the borehole.

One particularly interesting advantage of such a system is being able to use the control valves in each separation cell for control in the inflow zone. This will require that each section of the well to be emptied separately must be isolated from the others by means of gaskets. The main advantage of such a system is that a combination of both balanced and optimal reservoir emptying and improved separator function is achieved.

To get an indication of the possibilities associated with CS cells, a simple experiment was set up.

A pipe with a length of 7.9 meters and a diameter of 100 mm was designed with an inlet device in the middle part. Collecting pipes for oil and water were included in the main pipe. The tube could be tilted to different angles. A mixture of oil and water was introduced into the central part. Separation and counterflow would take place as described above. The oil/water system consisted of Exxol D80 (a non-aromatized kerosene) and fresh water.

The following parameter was varied during the experiment:

• Separation trials were carried out at angles of between 4 and 47 degrees.

• The flow rates were increased until no separation could occur due to emulsion formation as a result of the dissolution of the interface between

oil and water.

• The water fraction varied from 27 to 79%.

The following observations were made:

• High flow rates gave rise to more emulsions.

• The separation efficiency was lowest at the inversion point (approx. 50% WC).

• A jump in the interface level was detected at surface velocities of between 0.015 and 0.02 m/s. • Addition of emulsion breaker gave an increase in the maximum flow rate that could be achieved before separation ceased.

The experiment showed that:

• A higher separation capacity could be achieved for streams where oil was the base phase (low WC), compared to streams where water was the base phase

(high WC).

• The total separation capacity appeared to be fairly constant for WC above the inversion point (in the region of low WC)

• The separation capacity increased with increasing slope, up to approx. 36 degrees.

• Regulation of the interface between oil and water was more difficult at high angles. • The separation capacity was increased through the use of an emulsion breaker (approximately twice the speed at 7 degrees).

A maximum total flow rate (oil + water) was calculated for

a 9 <5>/g" feed pipe separator (ID 222 mm) on the basis of the separation experiment.

The following conclusions can be drawn from these experiments:

• Separation can be achieved within a wide range of angles, but angles greater than 5-10 degrees and less than 35 -40 degrees appear to be the most favorable for

counterflow separation on.

• Separation efficiency appears to be 50% lower above the inversion point (in the area of high WC) than below. • The total separation capacity is too low to use a stand-alone unit in a well with a large throughput.

• Active level regulation is necessary in order to achieve good product quality.

• The effect of better separation under well conditions can be illustrated through the 100% increase in efficiency at 7 degrees and the use of an emulsion breaker.

The present invention also facilitates the utilization of the pre-separation that has taken place outside the separator chamber before inflow into the separator, as mixing of the separated, countercurrent oil/water flow with the incoming fluid is prevented, which thus reduces flow disturbances to a minimum and increases the efficiency.

Although the present invention is mainly aimed at separators and methods for separation in an inclined well, at least some embodiments of the invention will also be able to be used for horizontal wells.

The invention will be described below in more detail in an embodiment of the invention, with reference to the accompanying drawings, where: Figure 1 shows a section through a borehole with a separator to be used in connection with the present invention; Figures 2a - 2d show the lower part of the separator of Figure 1; Figure 2a shows the lower part in the same cross-section as in Figure 1; Figure 2b shows a cross-section along G - G in Figure 2a; Figure 2c shows the lower part of the separator in a longitudinal cross-section of the longitudinal section on figure 2a, along B - B on figure 2d; Figure 2d shows a cross-section along C - C in Figure 2a; Figures 3a - 3d show the upper part of the separator of Figure 1; Figure 3 a shows the upper part in the same cross-section as in Figure 1; Figure 3b shows a cross-section along F - F in Figure 3a; Figure 3c shows the upper part of the separator in a longitudinal section across the longitudinal section in figure 3a, along B - B in figure 3d; Figure 3d shows a cross-section along H - H in Figure 2a; Figures 4a - 4d show the middle part of the separator of Figure 1; Figure 4a shows the middle section in the same projection as in Figure 1; Figure 4b shows a cross-section along D - D in Figure 4a; Figure 4c shows a longitudinal section along B - B in Figure 4d; Figure 4d shows a cross-section along E - E of Figure 4a;

Figure 5a shows a detailed drawing of the left side of Figure 2c; and

Figure 5b shows a cross-section along C - C in Figure 5a.

Below, the term hydrocarbons is used for the desired fluid from the formation. This includes at least oil, but may also include a smaller amount of gas or condensate.

Figure 1 schematically shows an embodiment of a separator cell according to the present invention for countercurrent separation in an inclined borehole. The well is drilled through a hydrocarbon-bearing layer (production zone 1). As shown in Figure 1, and as is the case in many situations, a casing 2 delimits the well from the production zone 1. Perforations are made through the casing wall (not shown) to allow reservoir fluids to flow into the well. Gaskets 3,4 are placed above and below the production zone 1. The gaskets 3,4 insulate the part of the well that passes through the production zone 1 and can be placed elsewhere than what is shown in Figure 1. Typically several perforation slots are made along the flow pipe 2 between gaskets 3 and 4. The inflow quantity will therefore be distributed over this part. Other parts of the perforated feed pipe can be insulated with gaskets in a similar way.

In cases where the separator is located in an open, unlined well section, gaskets can insulate against the rock surface in the open hole. In some cases, a sand screen can be installed to prevent solids from being carried along with the incoming stream. However, the further description will only deal with the above alternative, since the functional description will be the same.

Since the inflow is distributed over a long section outside the separator, the inflow amount per unit length is small, and there will be a pre-separation of the fluids under the influence of gravity. The lightest fluid, more precisely the hydrocarbon fluid, will move upwards and collect in the upper part of the annulus between the separation chamber and the casing 2 and in the area towards the gasket 4. The heavier fraction, i.e. the water, will move downwards and collect in the lowermost part of the annulus between the separation chamber and the casing 2 and in the area towards the gasket 3.

The separator has a first inlet opening 13 in an upper wall 9 and a second inlet opening 14 in a lower wall 10. The adjustment of the inlet openings 13 and 14 to an upper 13 and a lower 14 opening is important in order to take advantage of the pre-separation of well fluids which takes place in the annulus between the casing 2 and the separator. Hydrocarbon-rich fluid will tend to collect in the upper part of the sealed zone between seals 3 and 4, and water-rich fluid will tend to collect in the lower part of this zone. The hydrocarbon-rich fluid will thus flow in through the upper inlet opening 13, and the water-rich fluid will flow in through the lower inlet opening 14. The separator has a lower end wall 15 and an upper end wall 16 which together with the upper wall 9 and the lower wall 10 enclose the separation chamber 17. In the embodiment shown in Figure 1, an outlet pipe 7 is arranged near the upper wall 9 and the upper end wall 16. The purpose of the outlet pipe 7 is to lead the hydrocarbons out of the separator. Correspondingly, an outlet pipe 8 is arranged near the lower wall 10 and the lower end wall 15. The purpose of the outlet pipe 8 is to lead the water out of the separator. The hydrocarbon outlet pipe 7 is arranged near the upper wall 9 of the separator to capture the hydrocarbons that accumulate near this wall. The water outlet pipe 8 is arranged near the lower wall 10 of the separator to catch the water that accumulates near this wall.

The two outlet pipes 7,8 are preferably designed to capture hydrocarbons and water respectively along a length of the pipe which is provided with openings 11 and 12 respectively. The openings 11 and 12 preferably have an opening area which decreases towards the upper end wall 16 and the lower end wall 15, so that hydrocarbons and water respectively are extracted in smaller and smaller amounts along the length of the outlet pipes 7, 8 to enable coalescence of the smaller droplets in the area towards the end walls 15 and 16. The outlet pipes preferably have a design which is described in detail in Norwegian patent application no. 2000 1954 (corresponds to PCT/NO01/00156) from the present applicant.

The separation of the hydrocarbons and the water will be controlled by gravity and the viscous forces in the fluid. Final coalescence of dispersed oil droplets will take place in the water column above the lower end wall 15. Correspondingly, the dispersed water droplets will coalesce and sink in the oil column near the upper end wall 16.

The separator can be divided (although not necessarily physically) into three parts:

• A lower part 18 which comprises the lower end wall 15, the water outlet pipe 8 and the parts of the upper wall 9 and the lower wall 10 which are located closest to the lower end wall 15; • an upper part 19 which comprises the upper end wall 16, the hydrocarbon outlet pipe 7 and the parts of the upper wall 9 and the lower wall 10 which are located closest to the upper end wall 16; • and a central part 20 which comprises the inlet openings 13,14 and the parts of the upper and lower wall 9,10 which are located close to the inlet openings 13,14.

The separator will now be described in more detail with reference to figures 2a - 2d, 3a

-3d and 4a-4d.

Figures 2a - 2d show the lower part 18 of the separator. In Figure 2a, the lower part 18 is shown in the same cross-section as in Figure 1. This shows the parts of the upper wall 9 and the lower wall 10 which are located closest to the lower end wall IS, containing the water outlet pipe 8. The water outlet pipe 8 is connected to a water flow pipe 21 through a control valve 36 and a transition pipe 22 which puts the water outlet pipe 8 in fluid connection with the water flow pipe 21. The water flow pipe 21 extends through the length of the separator, as shown in, for example, figure 1. Figure 2b shows a cross section along G - G in figure 2a. This cross-section shows the water flow pipe 21 and the water outlet pipe 8, in addition to a hydrocarbon flow pipe 23 which also extends through the length of the separator parallel to the water flow pipe 21.

As can also be seen in Figure 2b, the upper wall 9 and the lower wall 10 together form a cylinder. The upper wall 9 goes down to the water flow pipe 21 and the hydrocarbon flow pipe 23, and the lower wall 10 goes up to the two pipes 21 and 23. In practice, the upper and lower walls 9 and 10 are made completely in the form of pipes.

Figure 2d shows a cross-section along C - C in Figure 2a and shows the water flow pipe 21 and the hydrocarbon flow pipe 23 located in the separator chamber 17.

Figure 2c shows a longitudinal section of the lower part 18 of the separator, across the longitudinal section in Figure 2a, along B - B in Figure 2d. Here, both the water flow pipe 21 and the hydrocarbon flow pipe 23 are visible. Part of the water outlet pipe 8 and the transition pipe 22 is also visible between 21 and 23.

As can be seen in Figures 2a and 2c, the water flow pipe 21 is connected to a connection chamber 24 located behind the end wall IS of the separator. The hydrocarbon flow pipe 23 is connected to a pipe bend 25 that passes through the connection chamber 24. The end of the pipe bend 25 which is farthest from the hydrocarbon flow pipe 23 is located in the middle of the connection chamber 24. The connection chamber 24 and the pipe bend 25 are intended for connection to a connection chamber 24' and a pipe bend 25' in a second separator located below the lower part 18.

The upper part 19 is described with reference to figures 3a - d. The upper part 19 is similar to the lower part 18, with the exception that it is oriented so that the hydrocarbon outlet pipe 7 is located near the upper wall 9, while the water outlet pipe is located near the lower wall 10 in the lower part 18. Figure 3a shows the upper part 19 in the same cross-section as in Figure 1. This shows the parts of the upper wall 9 and the lower wall 10 which are closest to the upper end wall 16, containing the hydrocarbon outlet pipe 7. The hydrocarbon outlet pipe 7 is connected to the hydrocarbon flow pipe 23 through a control valve 37 and a transition pipe 26 which connects the hydrocarbon outlet pipe 7 with the hydrocarbon flow pipe 23. The hydrocarbon flow pipe 23 extends through the length of the separator, as explained earlier. Figure 3b shows a cross-section along F - F in Figure 3a. This cross section shows the water flow pipe 21, the hydrocarbon flow pipe 23 and the hydrocarbon outlet pipe 7. Figure 3d shows a cross section along H - H in Figure 2a, and shows the water flow pipe 21, the hydrocarbon flow pipe 23 and the hydrocarbon outlet pipe 7, in addition to the transition pipe 26, located in the separator chamber 17. Figure 3c shows a longitudinal section through the upper part 19 of the separator across the longitudinal section in Figure 3a, along B - B in Figure 3d. Here, both the water flow pipe 21 and the hydrocarbon flow pipe 23 are visible. The hydrocarbon outlet pipe 7, control valve 37 and transition pipe 26 are also visible, and partly cover pipes 21 and 23.

As can be seen in figures 3a and 3c, the water flow pipe 21 is connected to a connection chamber 27 located behind the upper end wall 16 of the separator. The hydrocarbon flow pipe 23 is connected to a pipe bend 28 which passes through the connection chamber 27. The end of the pipe bend 28 furthest from the upper end wall 16 is located in the middle of the connection chamber 27. The connection chamber 27 and the pipe bend 28 are thought to be connected to a connection chamber 27' and a pipe bend 28' in a second separator located above the upper part 19, in a similar way as described for the connection chamber for the lower part.

With reference to figures 4a - 4d, a description of the middle part 20 will be given.

Figure 4a shows the middle part in the same projection as in Figure 1. The inlet openings 13 and 14 from the well annulus to the separator chamber 17 are shown. Near the inlet openings 13 and

14, guide plates 29, 30, 31 and 32 have been placed. These are intended to prevent the incoming well flow from disturbing the fluids that are already inside the separator, to prevent re-mixing of the already partially separated phases. Figure 4b shows a cross-section along D - D in Figure 4a. The openings 13 and 14, the baffles 30 and 32 and the water and hydrocarbon training tubes 21 and 23 are shown. Figure 4d shows a cross-section along E - E in Figure 4a. The guide plates 30 and 32 and the water and hydrocarbon injection tubes 21 and 23 are also shown here. Figure 4c shows a longitudinal section along B - B in Figure 4d. Water and

the hydrocarbon flow tubes 21 and 23 are shown. In addition, opening 14 and the guide plates 31 and 32 are shown. As can be seen in Figure 4c, the guide plates 31 and 32 are in reality one plate in which an opening corresponding to opening 14 is formed. The inlet arrangement is very simple. During testing, it proved to be very important to include the baffles to protect the countercurrent separated flow from the incoming fluid. The inlet openings 13 and 14 can, however, have different shapes and also consist of several separate openings in the same area.

As shown in Figure 4a, a first level gauge 33 is placed below the inlet openings 13, 14 to measure the water phase's highest level, and a second level gauge 34 is placed above the inlet openings 13, 14 to measure the hydrocarbon phase's lowest level. If the highest level of the water phase exceeds the first level gauge 33, the withdrawal of water through the water outlet pipe 8 (shown in Figure 1) will have to be increased, and/or the withdrawal of hydrocarbons through the hydrocarbon outlet pipe 7 (shown in Figure 1) will have to be reduced. If, on the other hand, the lowest level of the hydrocarbon phase falls below the second level gauge 34, the withdrawal of hydrocarbons through the hydrocarbon outlet pipe will have to be increased and/or the withdrawal of water through the water outlet pipe will have to be reduced.

Regulation of the outflow quantity is preferably carried out by means of the adjustable valves 36,37 at the two outlets, on the basis of the interface level for oil and water in the middle part of the separator chamber. Distributing the flow quantity between the individual separators is preferably done by adjusting the outlet flow from each separator so that it handles a certain proportion of the total inlet quantity.

The connection between two separators according to the present invention will now be described with reference to figures 5 a and 5 b.

As can be seen in Figure 5a, which actually shows the same as the left side of Figure 2c, the water flow pipe 21 in the right separator and the water flow pipe 21' in the left separator are connected to connection chambers 24 and 24' respectively. The connecting chambers have the same inner and outer diameter as the separators, and are in reality an integral part of the respective separator walls 9,10. The two connecting chambers 24 and 24' are connected to each other by means of an external sleeve 35 with right and left threads which engage with corresponding threads on the outside of walls 9, 10, 9', 10'. The connecting chambers 24 and 24' are thus pulled together by turning the sleeve 35. A wedge device (not shown) will ensure that the two separator units are oriented rotationally correctly when fitting. The hydrocarbon flow pipe 23 in the right separator and the hydrocarbon flow pipe 23' in the left separator are connected by pipe bends 25 and 25', respectively. The opposite ends of the pipe bends 25 and 25' are located in the middle of the connecting chamber 24, 24', as shown in the cross-section in Figure 5b along C-C. The pipe bend 25 extends a short distance into the connection chamber 24', so that the pipe bends 25 and 25' overlap each other. The pipe bend 25 also has a larger diameter than the pipe bend 25<*>, so that the pipe bends 25 and 25' fit together in a tight, concentric male/female coupling.

Any number of separators according to the present invention may be interconnected as shown. Thus, the separators can separate well fluids from different zones of the well. The water flow pipes and the hydrocarbon flow pipes will run continuously through the interconnected separators, which will contribute to the flow of the phases by supplying fluid through transition pipes 22 and 26, respectively. In this way, any number of separators can be physically connected one after the other, while the is operationally parallel-connected.

The separator housing is a closed chamber. The inlets are located at the top and bottom along a vertical line. This orientation enables pre-separated hydrocarbons to flow into the separator chamber through the upper inlet opening 13 and pre-separated water to flow into the separator chamber through the lower inlet opening 14. The separator must be equipped with an orientation device to ensure that the hydrocarbon inlet is at the top and the water inlet in the bottom.

In order to be able to use a separator according to the invention in a horizontal part of the well, the inlet opening can be placed at one end of the separator and the outlet openings at the opposite end of the separator. The arrangement would involve a cocurrent arrangement of the phases, as opposed to a countercurrent arrangement.

In order to make the separator practical to install and ensure easy handling on the drill deck, the construction is preferably characterized by the following: Each separator cell (CS cell) is made in a standard size and design (so that

the total capacity will be the sum of the units).

Engineered to match the most common of standard casing diameters. • The maximum length must be kept within the maximum dimensions that are practical to handle (12 -14 m). • Connection types must be used which ensure that the CS cells are connected together with the same rotation orientation; preferably tip union at each separator section,

rotational orientation of each section by means of a wedge device.

• A device for orienting the unit in the borehole in such a way that the oil inlet appears at the top and the water inlet at the bottom; preferably gasket with wedge and

CS cell with orientation slot.

• Robust and simple construction according to common standards for drilling equipment. One-wire system for data transmission for monitoring and control. Chain connection of valves and sensors using connection lines from one unit to the next.

Claims (21)

1. Gravity separator device for downhole separation of well fluids, characterized in that the device comprises: at least two separator cells, where each separator cell comprises a separator housing, since said separator housing has walls (9,10,15,16) which define a separator chamber (17) between them; a water outlet (8) and a hydrocarbon outlet (7) from said separator chamber (17); a well flow inlet (13,14) to the chamber (17), which is connected with an annulus in the borehole outside the separator housing; a water flow line (21) which is in connection with the aforementioned water outlet (8) from said at least two separator cells; and a hydrocarbon flow line (23) connected thereto hydrocarbon outlet (7) to provide parallel operation of said separator cells. 2. Device as specified in claim 1, characterized in that said separator cells are physically connected end to end. 3. Device as stated in claim 2, characterized in that said water flow line (21) and said hydrocarbon flow line (23) are located within said walls (9,10,15,16). 4. Device as stated in any one of claims 1-3, characterized in that the water flow line (21) and the hydrocarbon flow line (23) are in connection with the water outlets (8) and the hydrocarbon outlets (7) through respective control valves (36, 37). 5. Device as specified in one of claims 1-4, characterized in that the separators are counter-flow separators. 6. Device as stated in one of claims 1-5, characterized in that the separator device is placed in a borehole which is divided into at least two zones by blocking off said zones with gaskets (3; 4), said at least two zones transferring well fluid to different separator cells or another set of separator cells. 7. Device as specified in any of the preceding claims, characterized in that the well stream inlet (13,14) is located a good distance from said water outlet (8) and said hydrocarbon outlet (7). 8. Device as stated in any one of the preceding claims, characterized in that the separator is located in an inclined part of the borehole, that the walls of the separator housing comprise a lower end wall (15) and an upper end wall (16), and an upper wall (9 ) and a lower wall (10), said upper wall (9) and said lower wall (10) extending between said lower end wall (15) and said upper end wall (16), where the water outlet (8) is located close to said lower wall (10) and the hydrocarbon outlet (7) are located close to said upper wall (9). 9. Device as stated in claim 8, characterized in that the water outlet (8) is located near said lower end wall (15) and the hydrocarbon outlet (7) is located near said upper end wall (16). 10. Device as stated in any one of claims 8-9, characterized in that an upper well stream inlet (13) is formed in the upper wall (9) and a lower well stream inlet (14) is formed in said lower wall (10). 11. Device as set forth in any one of the preceding claims, characterized in that the well flow inlet includes baffles (29,30, 31,32) to prevent the flow of well fluids flowing into the separator chamber (17) from disturbing the fluids already inside in the separator chamber (17). 12. Device as specified in any of the preceding claims, characterized in that it further comprises at least one level gauge (33, 34) near said well flow inlet (13,14), possibly a first level gauge (33) on a first side of said well flow inlet (13,14) and a second level gauge (34) on a second side of said well flow inlet (13,14), said second side being at a higher level than the first side. 13. Device as specified in any of the preceding claims, characterized in that the separator housing is provided with a first gasket (3) which is located on a first side of said well flow inlet (13,14), and a second gasket (4) which is located on another side of said well flow inlet (13,14), where said gaskets (3,4) block off a zone of the annulus in the area around the separator housing, said zone being connected to the separator chamber (17) through said well flow inlet (13 ,14). 14. Device as stated in any one of the preceding claims, characterized in that the water outlet (8) and the hydrocarbon outlet (7) comprise a series of outlet openings (11,12) distributed along a length of the separator chamber (17) and dimensioned so that they receive a decreasing quantity per unit length towards the downstream end. 15. Device as stated in any one of the preceding claims, characterized in that a water flow line (21) and a hydrocarbon flow line (23) extend through said separator chamber (17), where said water outlet (8) is in connection with said water flow line ( 21) and said hydrocarbon outlet (7) is in connection with said hydrocarbon flow line (23). 16. Device as stated in claim 15, characterized in that said water flow line (21) is a pipe. 17. Device as stated in claim 15, characterized in that said hydrocarbon flow line (23) is a pipe. 18. Device as stated in one of claims 15-17, characterized in that said water flow line (21) and said hydrocarbon flow line (23), at least at one of their ends, end in a connecting part, said connecting part being adapted for connection to a connecting part in a further separator device. 19. Device as stated in claim 18, characterized in that said connection part comprises a connection chamber (24, 24'), one of said water flow line (21) or said hydrocarbon storm line (23) being in connection with said connection chamber (24, 24'); and a pipe part (25, 25'), where the other of said water flow line (21) or said hydrocarbon flow line (23) is in connection with said pipe part (25, 25'). 20. Procedure for downhole gravity separation of well fluids, characterized in that hydrocarbon-producing zones in a borehole are blocked off, well fluids are extracted from a respective formation adjacent to the zones, well fluid that flows into the respective zones is separated into water and hydrocarbons in downhole separators, the separation of well fluids from the respective zones occur independently of each other. 21. Method as stated in claim 20, characterized in that the respective separators are placed in the respective zones and isolated from each other by means of gaskets.