The invention relates generally to emulsion treating, and more particularly to a coalescer for separating emulsified water and solids from oil during longitudinal flow through a horizontally extending tank. More specifically, the invention relates to a method and a device for removing and breaking a stable emulsion layer in an emulsion treating apparatus. The invention applies to all horizontally flowing gas- liquid-liquid gravity separation devices and horizontally flowing liquid-liquid gravity separation devices, comprising devices such as 3 -Phase Separators, FWKOs, Heater- Treaters, Treaters, Electrical Treaters and Desalters.

Background of the Invention

It is well known that petroleum as it is naturally produced from a subterranean formation (commonly referred to as "crude") must be treated so as to separate and remove entrained gas, produced water or solids, in order to render the oil in a condition where it can be further transported (e.g. in a pipeline) and processed. Various techniques and processes have heretofore been employed in order to minimize treatment time and avoid high-energy consumption. The produced water may be either connate water, or water that has been injected for enhanced oil recovery purposes, and can be either fresh or saline (brine) in nature.

The produced water and solids are separated from the oil by gravity. One widely used process is to flow the produced crude though an elongated horizontal separation vessel (commonly referred to as a "treater"), wherein the oil, gas, produced water and solids constituents are separated. In some cases it is necessary to pre-heat the crude prior to separation, and a heater section is then added upstream of the treater. In such case the heater section and the treater are commonly incorporated into one vessel (commonly referred to as a "heater treater").

Gravity separation of oil and water is governed by Stoke's Law, which states that the settling velocity is proportional to the square of the water particle size. In practical design of separation vessels, this principle is used in order to speed up the separation process in the treater and thereby (among other benefits) permitting the use of smaller separation vessels. For example, doubling the size of the water particles to be separated out will increase the settling velocity by 4 times, thus allowing a 75% reduction of treater size. It is known in the art to use mechanical devices (such as matrix packs) and/or electrostatic grids separately or in pairs, in order to grow such larger water particles and thus enhancing the separation process and allowing smaller separation vessels. United States Patent No. 4 329 159, entitled "Energy Saving Heavy Crude Oil Emulsion Treating Method and Apparatus for Use Therewith", describes a method and apparatus comprising an elongated horizontal cylindrical tank, divided by internal partitions, into compartments through which the petroleum will sequentially flow. Burner-fired heaters are normally included in an upstream heater section for heating the emulsion to a desired temperature, during which most of the entrained gas and some of the produced water will separate from the emulsion. The partially de-emulsified produced water then flows into a coalescing section, encountering a series of baffles adapted to encourage even flow of fluids and to avoid the formation of flow channels within the fluid body. Additionally, high-potential electrostatic fields are applied by energizing grids with high voltage potential. The grids are adjacent to each grounded baffle, which creates the fields between each grid and grounded baffle.

Canadian Patent No. 2 329 224, entitled "Energy-Saving Heavy Crude Oil Emulsion-Treating Apparatus", describes a treater for electrostatically separating emulsified produced water from oil during longitudinal flow through a horizontally elongated coalescing section. The treater has a number of baffles with adjacent electrostatic wing grids therein. The electrostatic wing grids are externally connected to one or more transformers so that a higher voltage may be applied to subsequent grids along the coalescing section. Each of the electrostatic wing grids includes a front face and perpendicular side edges and a perpendicular bottom edge to extend the electrostatic field out beyond the front face, so as to enhance the electrostatic action and more efficiently remove water from the emulsion. The baffles preferably extend downwardly to a water/oil interface, so as to increase the coalescing efficiency of the emulsion flowing through the coalescing section and ensure that the electrostatic field is applied to the emulsion.

United States Patent No. 6 207 032, entitled "Electrostatic/Mechanical Emulsion Treating Method and Apparatus", describes a treater for electrostatically and/or mechanically separating emulsified produced water from oil during longitudinal flow through a horizontally elongated metal tank. Adjustable distributor elements are provided for enhancement of the de-emulsification process. The adjustable distributor elements may be externally operated to more closely control the diffusion and distribution of the flowing emulsion across the transverse area of the treater. The emulsion may be first directed through electrical fields, upstream of the distributor elements, where the produced water droplets take on an electrical charge, then move through the distributor elements to electrically grounded coalescing elements. De-emulsified oil is removed in a stream separate from the produced water stream. The treater also operates mechanically, with reduced efficiency, when electrostatic operation is unavailable, and can also be operated if coalescing elements are not used. The externally-adjustable, louvered baffles may be accompanied by fixed, non-adjustable louvers at intermediate spacing between the externally-adjustable louvers to provide additional coalescing and flow direction that will enhance dehydration of the process stream, and become an integral extension component thereof. Equipment for processing oils is subject to a phenomenon referred to as a "rag layer", in some contexts also referred to as a "cuff layer" or a "pad layer", i.e. the formation of a stable oil-water-solids emulsion. The solids components may consist of small sized and oil-wet solids (like clay) and precipitated high mole weight hydrocarbons (like asphaltenes). These are the building blocks for rag. The oil- water-solids rag composition results in a mixture that is heavier than oil but floats on water. It is caused by flow channeling (or stagnant zones) and thermal cooling primarily under process upsets or turn down conditions. The cooling leads to a change in viscosity, as well as a change in the densities of the oil and water preventing separation of the emulsion in these localized areas. This denser emulsion promotes the capture of the solids components creating a very stable oil- water-solids mixture that will continue to increase in density. With horizontal fluid flow, the rag layer migrates in the direction of fluid flow to the outlet end, becoming thicker and thicker with time, in this non-flowing zone.

The rag layer problem is normally experienced with oil having an API gravity below approximately 30. The term "heavy oils" is commonly used for oil having an API gravity of < approximately 20, "extra heavy oil" as having an API gravity < approximately 12, while oil sands bitumen normally has an API gravity < approximately 9. The heavier the oil, the more stable the rag layer will be once it is formed, and thus more difficult to break up. The rag layer build-up is therefore a particular problem in equipment for processing heavy oils, extra heavy oils and oil sands bitumen.

There are a variety of processes for producing bitumen from oil sands. One such process is termed "SAGD" (Steam Assisted Gravity Drainage), in which steam is injected from a pipe above an oil collector pipe. The steam melts the bitumen and it flows by gravity to the oil collection pipe below. Another process is termed "cyclic steam", where steam first is injected into a pipe, and then after a time the produced bitumen and condensed water is pumped out of the same pipe. A third process is "THAI" (or "Toe to Heel Air Injection"), which is a fire flood where air is injected into the reservoir and the bitumen is burnt as fuel. The heat front melts the bitumen which is collected from a separate well. In addition, there are new experimental systems where petroleum solvents are injected into the oil sands with steam to help dissolve the bitumen. Bitumen produced either by the

SAGD, cyclic steam or THAI methods is normally sufficiently hot for separation when it emerges from the reservoir. It may therefore be flowed directly into the treater, and a heater section is not required. With the production of bitumen, as compared to conventional heavy oil, there is often a need to add a diluent (lighter petroleum oils or naphtha), which causes asphaltenes to precipitate out. In addition, the oil sand production also yields a considerable amount of fine clay. This fine clay bonds with the water and asphaltenes and makes the rag layer with the oil sand production very difficult to break down.

In the treatment of conventional heavy oils, generally referred to as Cold Heavy Oil Production (or CHOP's) since the oil is fluid enough to flow naturally out of the well bore, the processing or separation of the oil-water-solids is done using fired equipment or "heater treaters". Here the usual practice is to draw off (blow-down) the rag layer to a slop tank and then recycle it back to the inlet of the treater and reheat it with the normal production fluids.

With the bitumen production associated with the oil sands using the existing thermal extraction technologies (SAGD, Cyclic Steam, THAI) the process heat is input into the reservoir in order to get the bitumen to flow. No additional processing heat is incorporated into the separation equipment. Here, treating the rag layer by conventional recycle from a slop tank, or by direct recycle from the process vessel into the hot well head or inlet production fluids has been unsuccessful.

When using the SAGD process to produce oil sands bitumen, asphaltenes tend to precipitate out of the bitumen and bond with clays suspended in the produced water, thus creating the rag layer. The asphaltenes/clays tend bond or adhere to internal instrumentation surfaces used to control the oil water interface and detect the rag layer. This build up renders the instrumentation ineffective leading to off- specification production in both the oil and water phases, as eventually the rag will be carried over in either or both these product streams.

Therefore, there exists a need for a method and an apparatus for effectively removing and breaking down a rag layer.

Summary of the Invention The present invention meets that need, in that it provides an emulsion treating apparatus for separating an emulsion of emulsified produced water droplets and oil, comprising a generally horizontal and elongate vessel constructed and arranged for longitudinal flow of emulsion therethrough and comprising an emulsion inlet, an oil outlet, a water outlet, and at least one coalescer element supported within the vessel, and an outlet for a stable emulsion forming in the region of an interface between emulsion and water when the apparatus is in use, characterized in that the outlet for the stable emulsion is connected via a fluid line to a separator vessel having an inlet and further comprising an oil outlet and a water outlet and means for breaking the stable emulsion.

In one embodiment, the means for breaking the stable emulsion comprises at least one electrostatic element electrically connected to a power supply and control unit and supported within the separator vessel such that the electrostatic element is immersed in oil and at a distance from an interface between the emulsion or oil and water which occurs when the apparatus is in use, said water providing an electrical ground component whereby an electrostatic field is induced between the electrostatic element and the water. The electrostatic element may comprise a generally horizontal electrostatic grid

In one embodiment, the means for breaking the stable emulsion comprises at least one heating element supported within the separator vessel at or near an interface between the emulsion or oil and water which occurs when the apparatus is in use, whereby the temperature at or near the interface may be controllably increased to a level above the temperature in the surrounding emulsion, oil or water.

The heating element may comprise at least one of a selection of a heating coil, a bare or a finned tube through which a high-temperature heating fluid from an external source is circulated. In one embodiment, the invention comprises a heating fluid re-cycle line for feeding water separated from the emulsion to the heating element, where is circulated though the heating element as a high-temperature heating fluid. The heating element may also comprise an electrically powered heating element.

In one embodiment, the means for breaking the stable emulsion comprises at least one electrostatic element according and at least one heating element in combination. In one embodiment, the separator vessel further comprising a transverse baffle, supported upstream of said means for breaking the stable emulsion.

In one embodiment, the means for breaking the stable emulsion comprises an electrostatic coalescer further comprising an inlet and an oil and water outlet and means for breaking the stable emulsion, being is fluidly connected to a further separation vessel having an oil outlet and a water outlet.

The electrostatic coalescer outlet is in one embodiment fluidly connected to an upstream end of said generally horizontal and elongate vessel, preferably in a region downstream said emulsion inlet and upstream said coalescer element, more preferably in a region upstream of any baffle elements within the vessel. In one embodiment, the electrostatic coalescer outlet is fluidly connected to an inlet line for the emulsion, which in turn is fluidly connected to the emulsion inlet. The electrostatic coalescer may be a compact electrostatic coalescer (CEC ).

It is further provided an apparatus for breaking a stable emulsion, comprising a vessel having an inlet for said stable emulsion, a treated oil outlet, and a water outlet, characterized by means for breaking the stable emulsion arranged within the vessel in a region at or near an interface between emulsion or oil or water when the apparatus is in use.

In one embodiment, the means for breaking the stable emulsion comprises at least one electrostatic element electrically connected to a power supply and control unit and supported within the separator vessel such that the electrostatic element is immersed in oil and at a distance from an interface between the emulsion or oil and water which occurs when the apparatus is in use, said water providing an electrical ground component whereby an electrostatic field is induced between the electrostatic element and the water.

In one embodiment, the electrostatic element comprises a generally horizontal electrostatic grid.

In one embodiment, the means for breaking the stable emulsion comprises at least one heating element supported within the separator vessel at or near an interface between the emulsion or oil and water which occurs when the apparatus is in use, whereby the temperature at or near the interface may be controllably increased to a level above the temperature in the surrounding emulsion, oil or water.

The heating element may comprise at least one of a selection of a heating coil, a bare or a finned tube through which a high-temperature heating fluid from an external source is circulated. One embodiment of the invention comprises a heating fluid re-cycle line for feeding water separated from the emulsion to the heating element, where is circulated though the heating element as a high-temperature heating fluid. The heating element may comprise an electrically powered heating element.

In one embodiment, the means for breaking the stable emulsion comprises at least one electrostatic element and at least one heating element in combination.

Brief description of the drawings

These and other characteristics of the invention will be clear from the following description of embodiment of the invention, given as non-restrictive examples, with reference to the attached drawings, wherein: Fig. 1 is a schematic side elevation view of the coalescing section of a horizontally- extending oil treater vessel in the form of an elongated, horizontally flowing gas- liquid-liquid separation device and a vertical flowing liquid-liquid separator, illustrating a first embodiment of the invention;

Fig. 2 is a schematic side elevation view of a vertical flowing liquid-liquid separator, illustrating a second embodiment of the invention; Fig. 3 is a schematic side elevation view of a vertical flowing liquid-liquid separator, illustrating a third embodiment of the invention;

Fig. 4 is a schematic side elevation view of a vertical flowing liquid-liquid separator, illustrating a fourth embodiment of the invention;

Fig. 5 is a schematic side elevation view of the coalescing section of a horizontally- extending oil treater vessel in the form of an elongated, horizontally flowing gas- liquid-liquid separation device, illustrating a fifth embodiment of the invention; and

Fig. 6 is a schematic side elevation view of the coalescing section of a horizontally- extending oil treater vessel in the form of an elongated, horizontally flowing gas- liquid-liquid separation device, illustrating a sixth embodiment of the invention.

Detailed description of preferred embodiments

First embodiment

Fig. 1 illustrates a first embodiment of the invention, and shows a horizontally extending elongated oil treater vessel 10, having an inlet 12 through which crude (emulsion) to be separated is fed, an oil outlet 22, a water outlet 24, a gas outlet 20, a weir 19 defining an upstream sand dam, and a transverse baffle 15. Crude in this context comprises an emulsion of emulsified produced water droplets, solids and semi-solids and oil, hereinafter referred to as emulsion E. A transverse baffle 15 and a plurality of diffusion baffles 14 are supported at intervals in the treater vessel 10. There is a need to establish a uniform plug flow through the treater; any velocity channelling, resulting in differential cooling of the crude, is undesirable. Thus, the transverse baffle 15 is an initial flow distribution device (or bulk separation device) in which the water W is forced down under the baffle, while the inlet emulsion E is feed through a distribution channel in the transverse baffle in the centre of the oil emulsion layer. The diffusion baffles 14 serve a similar purpose, i.e. providing a uniform flow distribution and thus preventing flow channelling.

Fig. 1 also shows a plurality of matrix packs 18, which are mechanical coalescing devices as described in the Background of the Invention, and well known in the art. Although Fig. 1 shows a plurality of matrix packs, the skilled person knows that only one matrix pack may be sufficient, depending on the specific crude application. When the treater vessel 10 is in operation, emulsion E enters the treater vessel 10 through the inlet 12. The emulsion may have been subjected to pre-heating, either by virtue of the method of extraction from the reservoir (e.g. the SAGD method, as described above) or in a heater section upstream of the treater vessel. In the latter case, the heater section and the treater section are normally integrated into one vessel commonly referred to as a "heater treater", and the emulsion flows into the treater section from the upstream heater section.

As the emulsion flows through the matrix packs 18, water W is separated from the emulsion due to gravity, as explained above. The separated water W is discarded from the vessel 10 via the water outlet 24. Any gas G released from the emulsion is discarded from the vessel via the gas outlet 20, and the treated oil is flowed out of the vessel via the oil outlet 22.

In order to remove the stable emulsion (i.e. the rag layer) R which tends to build up in the oil/water interface as explained above, the vessel 10 also comprises a line 30 arranged to remove the stable emulsion. The fluid line 30 is connected to the inlet of a coalescer unit 32, which in turn is connected to a separator vessel 34 as illustrated in Fig. 1. The stable emulsion may be fed from the vessel 10 to the coalescer unit 32 by means of a pump (not shown). The coalescer unit 32 may be a Compact Electrostatic Coalescer (CRC ^® ), for example of a type described by United States Patent No. 6 136 174, which is a compact device for coalescing finely dispersed droplets of a conductive fluid emulsified in a stream of nonconductive fluid by the use of a high intensity electric field acting on the emulsion as it flows through a narrow flow gap under non-laminar flow conditions. The stable emulsion is drawn from the region of the treater vessel 10 where the rag layer is forming and via the extraction line 30 introduced into the top of the vertically mounted cylindrical coalescer unit 32, where it flows through one or more narrow, annular flow gaps formed between one or more electrodes or an internal wall of the coalescer unit. The broken emulsion is discharged from the outlet 39 of the coalescer unit 32 and into the separator vessel 34 following a short residence time in the high-intensity electrostatic field. From the separator vessel 34, water W is extracted via the water outlet 38 while the treated oil is extracted via the oil outlet 36.

Although not disclosed in Fig. 1 , the skilled person knows that the matrix packs 18 may be supplemented by e.g. one or more conventional electrostatic grid pairs which promote separation by electrostatic coalescing by one grid being energized and controlled e.g. by transformer grid banks, and the other being electrically grounded.

Second embodiment

Fig. 2 illustrates a second embodiment of the invention, and shows a separator vessel 34 arranged to receive stable emulsion via the fluid line 30 which is connected to a treater vessel similar to the vessel 10 illustrated in Fig. 1 and described above with reference to the first embodiment.

The stable emulsion is drawn from the region of the treater vessel 10 where the rag layer is forming (see Fig. 1) and via the extraction line 30 and an inlet 37 introduced into the separator vessel 34. The separator vessel may comprise an initial bulk separation device, such as a transverse baffle 35. Downstream of this baffle, an electrostatic grid 26 is arranged. The electrostatic grid 26 comprises an element supported within the vessel 34 such that it is immersed in the oil and at a distance from the oil/water interface I which occurs when the vessel is in normal operation. The electrostatic grid 26 is supported such that it is substantially parallel with the interface I. Under normal operating conditions, the electrostatic grid 26 is thus substantially horizontal and extends in the separator vessel's 34 horizontal plane. The electrostatic grid 26 is electrically connected to a power supply and control unit 42, whereas the water W provides an electrical ground component, whereby an electrical voltage or electrical potential is induced through the emulsion E and electrostatic coalescing takes place. It is this (intense) electrical field between the high voltage energised grid 26 and ground that performs the coalescing.

The coalescing in the separator vessel 34 is thus controlled by controlling the electrostatic field, the electrostatic grid distance from the interface I, or both. The electrostatic grid must be positioned in the relatively non-conductive oil phase and a distance from the interface I which is sufficient so as to avoid a short circuit. Preferably, the electrostatic grid distance from the interface I is between 4 inches and 12 inches. The skilled person knows, however, that this distance is determined by the voltage applied to the electrostatic grid. The skilled person will understand that in a practical application the power supply and control unit 42 must be mounted such that the high tension electrical cable is immersed in oil and not run through any gas phase.

The skilled individual knows that a process upset could lift the emulsion layer up into the grids 26, creating a dead short situation for the power supply. With the normal power supply system for the conventional electrostatic grids, consisting of a conventional step up transformer, this requires the need for current monitoring devices to shut down the power supply upon detection of a high current draw. Ultimate protection in the event of a failure of the monitoring devices is provided by the power breaker feeding the transformer and the design of the transformer itself to be able handle a short circuit. The latter requires the transformer to be of a 100% reactive type. With this conventional control system the power breaker would have to be manually reset once the process upset is cleared, resulting in additional processing down time. However, the power supply and control unit 42 that would provide power to the rag layer treating grids 26 is a dynamic magnetically controllable transformer unit which is short circuit proof. This is a proprietary system, described by the following patents: US 6 933 822 and US 7 193 495 (basic MCI technology); US 7 026 905 B2 and US 7 256 678 (improved MCI technology); NO 322 439 (MCT power supply); and patent application No. US 2005/076293 Al . This proprietary system is based on the principle that an orthogonal magnetic field can control the relative permeability in a magnetic material such as the coil in a transformer, and hence control the energy (current) transferred to the secondary or output side. By controlling the relative (electric) permeability in the orthogonal direction in the transformer coil material, it controls the amount of flux in the rolling direction. As the magnetic domains in a magnetisable material can only be magnetized in one direction, by magnetizing orthogonally (transverse direction) the domains are not able to be magnetized in the rolling direction and thus the relative permeability in the rolling direction is reduced. This means that more current may flow through the coil main winding as the relative permeability is reduced. Altering, or adjusting the orthogonal magnetic field, controls the transformer coil as a linear electric valve.

This orthogonal magnetic field is controlled by monitoring the current that flows through the main winding. If the current increases due to a very fast load such as in the case of an electric short on the output or secondary side, the driving voltage on the transverse field will collapse until the short is gone. The short will be gone when the voltage collapses. This means that the device is self controlling due to its patented design. The response on a short is almost immediate as this is based on the design and physics of the core, and the relative permeability in the core material at the moment as governed by the transverse magnetic field. Hence the device does not measure the current with an external control system and control loop, the control system simply controls the output voltage that is required in the normal operation mode.

The stable emulsion may be fed from a treater vessel to the separator vessel 34 by means of a pump (not shown). From the separator vessel 34, water W is extracted via the water outlet 38 while the treated oil is extracted via the oil outlet 36.

Third embodiment

Fig. 3 illustrates a third embodiment of the invention, and shows a separator vessel 34 arranged to receive stable emulsion via the fluid line 30 which is connected to a treater vessel similar to the vessel 10 illustrated in Fig. 1 and described above with reference to the first embodiment. The separator vessel 34 illustrated by Fig. 3 has several similar features to the separator vessel illustrated by Fig. 2. Only the differences between the two embodiments will thus be described here. In this third embodiment, the electrostatic grid has been replaced by a heating element 28. The heating element 28 is supported within the separator vessel 34 at or near the interface I. The heating element 28 may be a heating coil, a bare tube or a finned tube or similar heat exchanger connected to a heating source (not shown in Fig. 3) in a closed circuit in a conventional manner. The heating fluid may be externally supplied steam, oil, glycol, or similar. Instead of a separate heating source, the separated water W, taken either from the treater vessel 10 (cf. Fig. 1) or the separator vessel 34 may also be used as heating fluid. Necessary pumps, piping and valves, etc. have been omitted in Fig. 3 for the sake of clarity of illustration. The heating element 28 may also be heated by other means, such as an electrically powered heater, or similar.

With the heating element 28, an amount of heat is added into the emulsion, thus enhancing separation in the separator vessel 34. Only a small temperature difference is required in order to achieve this objective. In one embodiment the temperature difference between the heating element and the surrounding emulsion is in the order of 5 °C. The heating element 28 may be dimensioned both in the horizontal and the vertical plane to extend in a suitable region in or near the interface I.

The stable emulsion may be fed from the vessel 10 to the separator vessel 34 by means of a pump (not shown). From the separator vessel 34, water W is extracted via the water outlet 38 while the treated oil is extracted via the oil outlet 36.

Fourth embodiment

Fig. 4 illustrates a fourth embodiment of the invention, and shows a separator vessel 34 arranged to receive stable emulsion via the fluid line 30 which is connected to a treater vessel similar to the vessel 10 illustrated in Fig. 1 and described above with reference to the first embodiment.. The separator vessel 34 illustrated by Fig. 4 has several similar features to the separator vessel illustrated by Figs. 2 and 3. Only the differences will thus be described here.

This fourth embodiment combines the second and third embodiments, in that the separator vessel 34 comprises the horizontal grid 26 and the heating element 28 in a combined arrangement. The same distance control and electrical field control of the electrostatic grid 26 as that described with reference to Fig. 2 apply to this embodiment, as do the heating means and sources of the hearing element 28 described with reference to fig. 3. The heating element 28 and the electrostatic grid 26 will both contribute to the breaking down the stable emulsion, and the two components may be operated in a manner yielding the optimum control and breaking-down of stable emulsion, such operation depending on the processing situation. Fifth embodiment

Fig. 5 illustrates a fifth embodiment of the invention, and shows a horizontally extending elongated treater vessel 10 similar to the one illustrated in Fig. 1 and described above with reference to the first embodiment. Only changes with respect to the first embodiment will therefore be discussed in the following.

In order to control the thickness of the stable emulsion (i.e. the rag layer) R which tends to build up as explained above, the vessel 10 comprises a line 30 arranged to remove the stable emulsion. The fluid line 30 is connected to the inlet of a coalescer unit 32, which in turn is connected to a region of the inlet end of the vessel 10. The stable emulsion may be fed from the vessel 10 to the coalescer unit 32 by means of a pump 40.

The coalescer unit 32 may be a Compact Electrostatic Coalescer (CRC ), for example of the type described above with reference to Fig. 1. The broken emulsion is discharged from the bottom of the coalescer unit 32 and into the treater vessel 10. Sixth embodiment

Fig. 6 illustrates a sixth embodiment of the invention, and shows a horizontally extending elongated treater vessel 10 similar to the one illustrated in Figs. 1 and 5 and described above with reference to the first embodiment. Only changes with respect to the fifth embodiment will therefore be discussed in the following. In this embodiment, the outlet end of the coalescer 32 is connected to the crude inlet line 12', outside the treater vessel 10, whereby the effluent broken emulsion from the coalescer 32 is introduced into the treater vessel 10 together with the crude.

Common to all embodiments

In some production scenarios, bitumen production is processed without the addition of a diluent. However, depending on how heavy the bitumen is (i.e. how low the

API gravity is) and on the production or processing temperatures, the density of the bitumen may be heavier than that of the produced water. In this case the fluid separation takes place inverted, compared to what is described above. Even though a diluent is not added, as processing temperatures for undiluted bitumen are much higher than those for diluted bitumen asphaltenes still precipitate out. Hence even with this inverted processing scenario there remains a need for a method and an apparatus for effectively preventing and controlling the formation of a rag layer. Therefore, the skilled person will understand that the invention is equally applicable to both processing scenarios described above. Although the invention has been described with reference to a treater vessel employing conventional coalescing means, i.e. matrix packs and/or electrostatic grid pairs, the skilled person will understand that the invention applies equally to all horizontally flowing liquid-liquid gravity separation devices used for emulsion treating, comprising devices such as 3 -Phase Separators, FWKOs, Heater-Treaters, Treaters, Electrical Treaters and Desalters. The skilled person will also understand that although the invention is particularly useful in the treatment of extra heavy oil and bitumen, the invention is also useful in the treatment of other oil/water emulsions, including conventional heavy oil.