WO1992019351A1

WO1992019351A1 - Oil/water separation system

Info

Publication number: WO1992019351A1
Application number: PCT/US1992/001629
Authority: WO
Inventors: Christopher K. Shaw; James R. Roth; Mark F. Schubert; Reimer Z. Hansen; Erick E. Wolfenberger; Mark H. Mamaghani
Original assignee: Conoco Specialty Products Inc
Current assignee: Lubrizol Specialty Products Inc
Priority date: 1991-05-02
Filing date: 1992-02-27
Publication date: 1992-11-12
Anticipated expiration: 1993-11-02
Also published as: WO1992019348A1

Abstract

An oil/water separation system (116) for separating oil and water components of a suspension formed in an oil/water mixture wherein oil coats solid particles in the mixture to form an oil coated nucleus that is neutrally buoyant to form the suspension. A stream (146) of the suspension is passed through a hydrocyclone (147) wherein the oil is removed from the solids. The solids then pass with the water component through an underflow outlet (15) from the hydrocyclone (147) while the oil component is separately passed from an overflow outlet (145). Water may be added to the stream of the suspension prior to passage into the hydrocyclone (147). A pump (152) may be utilized to mix the added water upstream of the hydrocyclone (147).

Description

Description Oil/Water Separation System

Background of The Invention

This invention relates to a liquid/liquid separation system and more particularly to a multi-phase separation process, a common use for which is found in oil field drilling, production, and refining operations, to enhance the gravity separation of immiscible liquids by promoting separation of a fluid suspension such as those having a solids component acting as an emulsion stabilizer or oil coated solids with neutral buoyancy.

Separation systems in any number of other industry applications involving oil and water mixtures may find use for this invention including food processing, animal processing, metals milling, to name but a few. In these applications emulsion layers form in the mixture to provide a difficult separations problem. A variety of separation systems, commonly found in petroleum industry applications are concerned with such an emulsion layer which provides problems as to economical separation of the primarily oil and water components thereof. During the production of petroleum hydrocarbons there is often a substantial amount of water produced. The amount of water will vary depending on many factors, such as: (1) the type of reservoir and formations from which the fluids are produced; (2) the age of the well producing the fluids; (3) the type of enhanced oil recovery (EOR) system that is used, as for example waterflood and steam flooding, both of which will increase the amount of water produced.

As oil is produced it must be separated from the water. The ease of this separation is affected by the fluid properties as well as physical and chemical factors. Some factors which may lead to the formation of emulsion and thus adversely affect separation of oil and water are: 1. Tight reservoirs with low porosity and permeability, where oil droplets will be sheared simply by moving through the reservoir as the oil is produced; 2. The addition of chemicals such as may be used in chemical floods or corrosion inhibitors used in the well;

3. Shearing of fluid droplets due to pumps or any number of devices which may cause high turbulence such as a valve; and

4. Solids particles which can serve to stabilize emulsions as in oil wet colloids.

Again, many of these same factors are found in other industry applications, both petroleum and elsewhere. When drilling petroleum reservoirs the solids being drilled from the underground formations can serve to form an oil wet nucleus about which emulsions can form.

Another petroleum industry situation leading to these problems stems from world crude supplies getting much poorer in quality. Available crudes are getting heavier, more sour, and dirtier. Heavy, viscous crudes hold more particulate matter, and hold it longer. This adverse change in crude oil feedstocks is having significant operating and corrosion implications on refinery units. There are a number of components which may appear in crude oil stocks even in very low quantities which can cause de¬ salting and corrosion complications. Theses components could include solid particulates, oil field producing chemicals and production stimulants. Part of this problem stems from an increase in the use of secondary and tertiary recovery methods which lead to the production of tightly emulsified fluids from water floods, caustic floods, surfactant floods, fire floods and the general use of well stimulant chemicals. Thus, it is seen that a variety of oil industry problems associated with drilling, producing and refining petroleum hydrocarbons, all deal with separating oil and water emulsions. It has also been found that oil/water separation in other industrial environments has similar problems which may be treated accordingly as described herein. Many devices and methods have been used to enhance the effectiveness of such oil/water separation. Such devices and methods may involve the use of chemicals to facilitate phase separation, the addition of heat to reduce viscosity of the fluids, the use of structured packing, specially designed flow paths, filters and other such mechanical devices to structure flow that produces contact of the components in a mixture to promote coalescence, or the use of electrostatic devices to create electric fields and charges that promote coalescence and separation of mixture components. Centrifugal separators have often been employed to remove solids in such systems. Desalting

A speci ic petroleum process which typi ies this problem has to do with crude oil distillation. Crude stills are the first major processing units in a refinery. They are used to separate the crude oils by distillation into fractions according to boiling point. If the salt content of the crude oil is greater than 10 lb/1,000 bbl, the crude requires desalting to minimize fouling and corrosion caused by salt deposition on heat transfer surfaces and acids formed by decomposition of the chloride salts. In addition, some metals which can cause catalyst deactivation in catalytic processing units are partially rejected in the desalting process.

The trend toward running heavier crude oils has increased the importance of efficient desalting of crude. The salt in the crude is in the form of dissolved or suspended salt crystals in water emulsified with the crude oil. It is important to note that while the term de¬ salting is used to describe the process, sediment or solids other than salts are of similar importance. These impurities in the crude oil may be natural or induced. The water in crude oil is usually in the form of a water in oil emulsion or oil external emulsion where the oil phase is external to the water phase. The emulsion is stabilized by surface active agents in the oil. Emulsion stabilizers such as asphalts, resins, waxes, solids and organic acids add to the problem of desalting modern crude.

Impurities are often categorized as those which are water soluble and are removable by washing and those which are water insoluble and not readily removable by washing. The oil insoluble impurities are sometimes referred to as the oleophobic or oil-hating impurities. These include water, salt, and some solids.

Among the more common impurities found in crude oil are silt, sand, iron oxide, iron sulfide, arsenic and strontium, sediments, the chlorides of sodium, potassium, calcium and magnesium; the sulfates of potassium, magnesium, calcium and sodium; crystalline salt, carbon, sulfur, salts and water.

In addition to the naturally occurring impurities in crude oils, there are induced impurities. Induced impurities might be described as those things that become mixed into the crude oil during the process of extracting it from its natural habitat and producing, transporting and processing it on its way to the consumer end uses. The de¬ salting process which is involved in removing these contaminants and separating the oil and water components of a mixture is based on two premises: (1) oil is lighter than water, and (2) emulsions which are temporarily stabilized by surface active materials can be destabilized by the action of electric field or chemical demulsifiers. In the simplest form, the desalter is a washing device for oil, with a mix valve providing the scrubbing and the desalter vessel itself being the gravity, settling or separation tank. The mixing that takes place across the valve allows the water to wash the salt out of the crude oil. This mixing also tends to generate an emulsion. In the presence of finely dispersed polar solids, this emulsion is very stable and has its own characteristic physical properties. Its density being in between that of the two pure components, the emulsion will accumulate at the interface of the components and may eventually contaminate both oil and water discharge streams. Solids are a powerful emulsion stabilizer and a tremendous consumer of demulsifier or any surface active/adsorptive material. One of the problems in desalting is being able to take the demulsifier to the water and solids interface within the mixture since it is the solids that provide the nucleus for the emulsion. Oil is normally external in these emulsions and thus the water/solids interface is hidden under oil. One solid which is found to be a particular problem in this situation is iron which shows up eventually downstream in the hydrocarbon products of the oil refinery processes.

Prior art devices for solving de-salting problems utilize conventional horizontal or vertical gravity separation vessels. Several methods have been used to promote coalescence in these vessels, however, these methods usually involve treating the entire fluid stream rather them a side stream of the suspension or emulsified layer. The use of chemicals is the most common practice to break the interfacial tension between droplets and to promote separation. Desalting vessels often incorporate structured packings which allow the fluids to move along corrugated parallel plates or through narrow openings and contact other droplets which coalesce into larger particles. These particles can then be more easily separated by gravity forces due to increase in buoyancy and reduction in surface area.

Addition of heat is often used to reduce the viscosity of the fluids which will significantly increase the droplets ability to migrate through the continuous phase liquid. Increasing temperature may also increase the density difference between the fluids. The use of an electrostatic potential across the fluids can be used to create a polarity field to charge the liquid droplets much like magnetic poles and thus promote separation. The use of heat or electrostatic potential is typically very energy intensive and costly.

Prilling Fluids Another example of an industry problem which may be treated by the present separation system concerns the separation of hydrocarbon fluids from drilling fluids. One particular situation that exemplifies the problem in this area involves the separation of components in a drilling fluids system associated with drilling horizontal wells in a chalk formation where hydrocarbon fluids are produced from the formations being drilled, during the drilling operation. The separation problem associated with such drilling is set forth in detail in copending U.S. patent application serial no. 649,382 titled "Method and Apparatus for Separating Drilling and Production Fluids". However, to briefly address the issue set forth in that application, the drilling fluids system is designed to run in an underbalanced condition to allow formation fluids into the wellbore. Pressure on the system at th* surface is reduced to let formation fluids flow under reservoir pressures into the borehold. These formation fluids become entrained in the drilling fluids and are brought to the surface. At the surface the hydrocarbon fluids are separated rom the water in the system as well as solids such as the drill cuttings. Because hydrocarbon fluids tend to decrease the density of the drilling fluids system, it is desirable to remove those low density fluids from the system in order to maintain a proper .pressure balance on the formations being drilled. One of the problems that is encountered in this situation is that produced oil tends to coat fine particles of formation materials such as chalk. These oil coated particles become neutrally buoyant and form a suspension layer in the fluid system and therefore do not readily separate out due to density differences. As a result, they tend to carry over into the recirculated drilling fluids where they may cause problems associated with weight of the system. In addition, such carry over prevents the cuttings from being removed from the system to provide a further burden on the drilling fluids system.

Prior art separation schemes for dealing with the problems described above have disadvantages in that they are space intensive because of their reliance to a great extent on time to eventually permit gravity separation of the components of the mixture. The operational efficiency of prior devices and systems for adequately separating the components has been hampered by the presence of the oil coated particles forming an oil in water suspension as described above, with such prior art systems either not adequately addressing the problem or addressing the problem at an undesirable economic level. Typically, the addition of heat, chemicals, greater residence time, etc. have been the solution to these problems, with the inherent undesirable characteristics described above.

It is therefore an object of the present invention to provide a simpler, more efficient and less costly method and apparatus for the problem of separating oil and water components of a fluid mixture, particularly where an oil external emulsion exists and where particulate matter is a component of the mixture and combines with the other components in such a manner as to compound the separation problem.

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With this and other objects in view the present invention provides a separation system for a fluid mixture that includes oil and water components with particles suspended therein as a result of oil in the mixture coating the particles to form an oil coated nucleus. The oil coated nucleus is neutrally buoyant and forms a suspension with the water component. The present separation system utilizes a hydrocyclone for separating oil from the oil coated solids particle nucleus present in the mixture inletted to the hydrocyclone. This removal of oil from the solids particle renders the solids particle non-buoyant and thereby permits the solids particle to separate from the mixture due to its difference in density. The oil thus removed is coalesced into a component that separates out as a less dense phase in the hydrocyclone. The water and solids particles are then discharged from the underflow of the hydrocyclone and the oil is discharged from the overflow. Additionally, the oil emulsion may be urged to reverse by adding water to the emulsion before it is inletted into the hydrocyclone. Also by passing the emulsion mixture with the added water through a pump upstream of the hydrocyclone, this reversal of the emulsion is further facilitated. All of these factors then enhance coalescence of the components as they pass through the hydrocyclone. Means are also provided for adding chemicals to the process streams before and after passage through the hydrocyclone.

Another separator may be provided downstream of the hydrocyclone underflow for receiving the more dense components and to permit further separation of the water and solids. Provisions are then made to remove the solids from the system and discharge the water for disposal or further us*. Said further use of the water might include recycle of the water to the vessel from which the fluid is initially taken. Alternatively, solids may be outletted from the hydrocyclone through a separate solids outlet or the solids may be recycled with the underflow to the vessel from which the fluid mixture is initially taken, for further separation such as by gravity. Also, a coalescing hydrocyclone having only an underflow outlet may be used in such a system wherein all components are passed to a downstream separation vessel to separate the coalesced components.

Brief Description of the Drawings

Figure 1 is a schematic drawing of a separation system in accordance with the present invention for separating a suspension layer formed in a separation process;

Figure 2 is a schematic drawing of a separation system in accordance with the present invention for processing drilling fluids in a well drilling operation;

Figure 3 is a schematic drawing of. a separation system for separating a suspension layer in a desalting operation; and

Figure 4 is a schematic drawing of a separation system for separating components of a suspension layer wherein water is added to the suspension layer and pumped into the inlet of a hydrocyclone.

Description of the Preferred Embodiment Referring first to Figure l of the drawings, a desalting operation is shown for treating crude oil to remove excess solids therefrom prior to their being further processed as in a refining operation. A source of crude oil 12 is shown being passed through a pump 14 having an outlet passing through a mixing valve 20 into an inlet 22 of a two-phase separation vessel 23. Water is provided by an inlet line 16 from a pump 18 for mixing water into the crude to thereby wash the salts or other dissolved materials from the crude. Mixing valve 20 provides a means for mixing the water with the crude to ensure that the washing process takes place. The mixture emerging from the mixing valve 20 is then passed by means of inlet 22 into the separating vessel 23 wherein by gravity separation, the more dense water phase migrates towards the bottom of the vessel into a layer 30 with the less dense oil phase migrating to the top of the vessel into a layer 26. A mid- layer or interface layer 32 is formed in the vessel and is comprised of a suspension or emulsion of oil and water which is sometimes referred to as a "rag" layer. This may be an oil in water or water in oil suspension or emulsion and even have changing characteristics in this respect. This interface or "rag" layer becomes a relatively large part of the fluid mixture in the vessel and substantially decreases the residence times of fluid in the separating vessel due to the increased volume of this emulsion layer. Prior art systems often treat this layer by the use of chemicals in addition to increased residence time in order to separate the suspension or emulsion and recover the constituent fluids. In addition to chemical treatment of these fluids, mechanical devices, as well as the use of heat and electrical potential are used for breaking the emulsion and promoting coalescence of the constituent fluids, in the process of trying to find a solution to the problems involved in the separation process described, it has been found that solids particles which are a constituent part of the fluids being treated, serve to form a nucleus about which oil forms to envelope the solid particle and thereby create a neutrally buoyant particle which is a combination of the more dense solid and the less dense oil coating. This neutrally buoyant component is an integral part of the rag layer which typifies this process and generates the problems of separation associated therewith. In order to better treat this rag layer in a more efficient and simplified manner, an outlet line 34 from the separator vessel 23 feeds the rag layer to a hydrocyclone 40. If necessary this may be facilitated by use of a pump 36 provided in the line 34 between the separation vessel 23 and hydrocyclone 40. The rag layer is admitted to the hydrocyclone by means of an inlet 38. These fluids are admitted tangentially into the hydrocyclone wherein they are caused to separate by the centrifugal action imposed upon the fluids as a result of the geometrical design of the hydrocyclone. The centrifugal forces in the hydrocyclone are increased to the point that the oil coating the particulate matter becomes dislodged therefrom and the particulate matter is forced to the outer wall of the hydrocyclone while the oil component migrates to the centerline of the hydrocyclone for discharge from an overflow outlet 44. The solid particulate matter thus joins the water component in the system at the outer wall of the hydrocyclone for discharge at an underflow outlet 42. This more dense component of the mixture which is comprised of the solids and water is passed through a control valve 46 into an outlet line 48 and thence into a separation vessel 50. Separation vessel 50 provides a means for separating out the solids from the liquid constituents which have exited the hydrocyclone through the underflow. The solids will have now had the oil coating removed therefrom to provide a sufficient density differential with respect to the liquids accompanying them to effect gravity separation therefrom in the separation vessel 50. The solids are removed by means of a dump outlet 51 on the bottom of the vessel. Liquids in the vessel are passed over a weir 53 to an outlet line 52. The water component which now predominates the effluent into line 52 can be discharged from the system by means of a line 59 by operation of valve 61, or alternatively, may be passed by operation of valves 57 or 58 respectively into return lines 56 and 60 which eventually return the water component to the separation vessel 23. Alternative line 60 passes such a water component into the fluids inletting into the separator 23. Again, alternate routes are provided so that such water can be inletted either before or after the crude passes through the mixing valve 20. Line 64 provides a flow path into the inlet stream ahead of the mixing valve so that this water may be used to remix and thereby wash the crudes. Operation of a valve 66 permits an alternative route for supplying the water to the inletting fluids downstream of the mixing valve. In some situations the mixing valve may be creating more of an emulsion problem for the mixture than is solved by the mixing of the water and crude. Also, the recycle stream from the hydrocyclone underflow 42 may be too contaminated to provide wash water for the desalter. In those situations, the alternative flow path 62 could be used to introduce the water downstream of the mixing valve. In certain situations it may be desirable to introduce the water into the separator near the lower level of the rag layer to thereby provide for its entry into the vessel 23 separate from the oil and/or solid components of the mixture. This might be necessary in a situation where it is desirable to continuously remove water from the system such as when the inletting fluid has a substantially large water component in the beginning. In such a situation, it may not be necessary to add wash water to the inletting mixture.

These various alternative schemes for dealing with the water leg being discharged from the hydrocyclone are provided to show that there are any number of separation schemes which may be treated by the system described herein when the basic problem being attacked is that of removing the oil layer from a solid particle to enhance its separation from a fluid mixture. In this respect, another alternative flow arrangement is shown in Figure 3 for a classic desalting operation wherein the system is similar to Figure 1 up to the point of discharge of fluids from hydrocyclone 40. However, instead of passing the underflow stream of the hydrocyclone 40 through a downstream separator for removing solids, the underflow stream is recycled, directly to the input of the vessel 23, which in this case would be a desalting device. Often in a desalting operation, the makeup of the rag layer is such that it will not be separated in one pass through the hydrocyclone and therefore the streams outletting the hydrocyclone will not be pure enough components for discharge from the separation system. Thus, these hydrocyclone outlet streams will be returned to the separation vessel 23. The solid particles which become separated from the oil coating in the hydrocyclone will pass with the underflow stream into the inlet 22 of the separator wherein they will separate such as by gravity for removal through the outlet 28 on the bottom of vessel 23. In this desalting system of Figure 3, the pump 36 provides the necessary to move the solids in the more dense underflow stream back to the vessel 23 for separation and subsequent disposal. Likewise, the overflow stream is carried by way of line 70 back to vessel 23. In the Figure 1 embodiment, the oil or less dense component emerging at the overflow outlet 44 of the hydrocyclone is passed by means of a flowline through alternate flow paths. Alternate flow path 74 serves to discharge the oil component from the system either for further processing of the oil or for its disposal in some manner. Alternatively, by operation of the valve 72 the oil component may be passed back to the separation vessel 23 by means of inlet 70 at or near the upper level of the rag layer to thereby promote its further separation from the incoming mixture. In this case, the oil would be discharged by means of outlet 24 for whatever further processing or disposal would be desirable.

In Figures 1 and 3, inlet lines 68, 54 and 35 are shown for providing a means of injecting chemicals into the various fluid streams. Chemical injection line 54 is provided for inletting a chemical into the water leg 52 exiting from the separator vessel 50. This would provide further treatment of the water leg to separate any remaining oil components and/or facilitate separation of solids therefrom either before its disposal from the system or prior to recirculating the water leg into the separation system. Injection of chemicals at this point would have the advantage of providing more intense treatment of the fluids in the line 52 prior to recombination of the water leg in line 52 with the inletted fluids to the primary separation vessel 23. In addition, a chemical injection line 68 is shown for injecting chemicals into the oil component shown exiting the hydrocyclone at outlet 44 prior to the readmission of the oil stream into the inlet 70 of the separation vessel 23. Again, introduction of chemicals at this point in the system will provide for more concentrated treatment of that component by the chemical prior to its being remixed with the other fluids in the separation vessel 23. In addition, a chemical injection line 35 is shown feeding into the outlet line 34 from separation vessel 23 to provide a means for injecting chemicals into the mixture passing to the hydrocyclone 40, upstream of the pump 36.

In the operation of this system just described with respect to Figures 1 and 3, as for example, in a desalting operation, the crude oil being treated likely contains a concentration of solids particles in the form of salts or heavy metals which provide downstream problems as to either corrosion of the refining and process systems or in the products derived from the crude. To remove these solids, such fluids are inletted by means of inlet line 12 and pump 14 to the separation vessel 23. In the case of a classical desalting operation, water would be added by means of inlet lines 16 and pump 18 to mix with the crude and by means of mixing valve 20 wash the salts from the crude for subsequent separation in the tank or separating vessel 23. In other operations, there may be sufficient water in the incoming oil line such as in a production separation situation, wherein it would be undesirable to utilize the mixing valve 20 or to add additional water to the system. In any event, the fluids are inletted by means of inlet 22 into the separation vessel 23. Vessel 23 serves as a residence vessel for permitting fluid components of the mixture to separate by density into more dense and less dense layers. The more dense layer, which in this typical system is water, will fall to the bottom of the separation vessel 23 for removal therefrom by means of line 28. The lighter phase of the system will migrate to the upper level 26 for removal therefrom by means of the exit line 24. Typical of the fluids being treated by the system of the present invention is that such fluids have the common problem of developing a suspension or emulsion layer that is stabilized by the effect of solids particles in the fluid mixture. These solid particles act as a nucleus about which oil collects to form a neutrally buoyant component layer described as a rag layer. This emulsion component 32 is taken by line 34 into the inlet 38 of the hydrocyclone 40. An inlet line 35 provides means to inject treating materials into the line 34 prior to the mixture entering the hydrocyclone. Such materials might be demulsifying chemicals or other such chemicals to aid in the separation process by enhancing separation in the hydrocyclone or with the chemical being enhanced by the hydrocyclone for aiding in further separation in or downstream of the hydrocyclone.

The fluids inletted to the hydrocyclone 40 are separated within the hydrocyclone to form a less dense component exiting the overflow outlet 44 and a more dense component which is comprised of water and solids particles which outlet through the underflow outlet 42 into a discharge line 48. A control valve 46 is provided in the line 48 to control the outlet flow from the underflow of the hydrocyclone. The more dense component of the mixture which is comprised of the water and solids particles is passed into a separation vessel 50 for removing the solids and passing the water component by means of a line 52 for further processing in the system. In the case of a desalting operation such more dense underflow stream would likely be returned directly to the input line 22 to vessel 23 as shown in Figure 3 of the drawings.

When the underflow stream of the Figure 3 embodiment is returned directly to the separation vessel 23, such recycled materials being predominately water with solids may be introduced into the vessel 23 in the water layer itself as shown in Figure 2 to avoid mixing these now separated components with the oil component. -The same rationale may also be applied to the return of the oil component from the hydrocyclone to the vessel 23, wherein as shown in Figure 2 the overflow stream is recycled into the oil layer 96 in vessel 116 via the overflow line 145. In other systems where it is desirable to remove net water from the system, the water outletting from the separation vessel 50 (Figures 1 and 2) may be discharged to an outside disposal line, by means of an outlet line 59 and valve 61. Alternatively, water outlet 52 can be recycled into the separation vessel 23 by means of valve 57 and recycle line 56. The route returns the water into the vessel 23 near the interface of the suspension/emulsion layer 32 and water layer 30 so that the water returns to water. Again alternatively, the water output from line 52 may be recycled into the emulsion layer 32 by introducing the water stream into the inletting mixture either upstream or downstream of the mixing valve 20. This latter route is chosen by use of valve 58 and line 60, in conjunction with lines 62, 64 and valve 66. The embodiment of Figure 4 is similar in many aspects to that of Figures l and 3 wherein a desalting application serves as a typical process for describing the alternative scheme. Figure 4 shows a crude oil/water mixture inletting to a gravity separation vessel 23 wherein an emulsion layer 32 forms between on upper oil layer 26 and a lower water layer 30. In a desalting operation, water may be added into the inlet stream by means of pump 18 and line 16 to wash the mixture passing through mixing valve 20 into the vessel 23. As with the system of Figures l and 3, the suspension or emulsion layer is typically formed of an oil external emulsion which is taken from the vessel by means of line 34 for further treatment. In the Figure 4 embodiment, water- is added to the suspension stream in line 34 by means of a water inlet line 31 which may receive its water supply from the same source as wash water for the desalter. Valve 19 controls this flow of water through line 31. Water may alternatively be supplied by line 33 taking water from the lower layer 30 in vessel 23. Valve 21 controls the flow in supply line 33. One reason for taking water from inlet line 31 is that this water will be under a higher pressure than that available through line 33 from the separator. The higher pressure water can be more precisely regulated to provide a known quantity of added water to the mixture inletting the hydrocyclone. The suspension stream with water added may also be passed through pump 36 into inlet 38 of hydrocyclone 40. The overflow outlet 44 passes a heavy component of the mixture back to the vessel 23, into communication with the upper less dense component layer 26. The hydrocyclone underflow 42 passes the heavier components including water and any solids through choke valve 46 into line 48. This underflow stream may be recycled directly to the vessel 23 up way of line 29 where it is introduced into the water layer 30.

Alternatively the underflow may be routed through an alternative flowline 39 by means of valves 41, 43, to pass the underflow stream through a desanding centrifuge 47 or the like, to remove any solids that might be entrained in the underflow stream. Any solids which are returned to the vessel 23 may separate out in the vessel or may be collected in a solids sump 49 which is provided with means to remove solids from the sump, thereby preventing reintrainment in the emulsion layer. The overflow stream from the hydrocyclone 40 is recycled to the oil layer 26 of the vessel 23.

In any of the embodiments described herein, a coalescing hydrocyclone may be employed for the hydrocyclone 40, wherein only an underflow outlet is provided so that all components are passed through the one outlet to a downstream separation device such as vessel 23 in Figures 1, 3 and 4 and vessel 116 in Figure 2, to separate the coalesced components. Such a coalescing hydrocyclone is shown in U.S. Patent 4,995,989.

In the operation of the system described with respect to Figure 4, water is added to the emulsion stream coming from the layer 32 in the vessel 23 to enhance the separation process. Based on laboratory investigation of the emulsion or suspension layer in a typical desalting separator, this layer contained approximately 40% oil, 55% water and 5% solids. This mixture of fluids in this so called "rag" layer 32 formed an oil external emulsion with a very high viscosity. It was found that by adding approximately 15% water to the emulsion mixture, with some agitation, the emulsion could be changed to a water external emulsion whereby the viscosity of the fluid was greatly reduced. Further tests showed that when using a laboratory centrifuge to simulate hydrocyclone performance, separation was dramatically increased by having a water external emulsion. Therefore in the Figure 4 embodiment, water is added to the emulsion stream in line 34 by means of water supply lines 31 and/or 33 and this water enriched mixture is then pumped into the hydrocyclone 40 by means of pump 36, with the pump providing additional mixing of the two streams.

It is possible of course that sufficient pressure could prevail in the inletting mixture to the hydrocyclone to preclude the need for a pump in the system. This is particularly true if the additional water is taken from supply line 31. If additional mixing or agitation is needed to reverse the emulsion, a mixing valve could be utilized.

In the feed lines from the desalter vessel 23 to the hydrocyclone 40, it may be appropriate to take a mixture of approximately 80% from the rag layer 32 and 20% from the water layer 30. The appropriate mixture will of course depend on a number of factors which affect the dynamics of such a process. In simulated laboratory centrifuge separations, it was found that 2 to 3% solids were separated from the emulsion stream into the water phase exiting the hydrocyclone underflow. These solids were apparently rendered non-buoyant in the hydrocyclone thus separating out with the more dense water phase. These solids are recycled to the vessel 23 where residence time in the vessel 23 permits their settling to the sump 49. Alternatively solids can be diverted through line 39 into a solids separator or desander 47. Next referring to Figure 2 of the drawings, a system is described for solving similar problems in a different environment which involves the use of separation equipment for separating fluid components of a drilling fluid system for use in drilling oil wells. Referring now to Figure 2 of the drawings a drilling fluids separation system is shown having a choke manifold 82 which provides for ultimate control over pressure between the wellbore and the separation system. A separator 84 receives fluids from the circulation system of the conventional drilling system and in the drilling operation described herein the pressure from the well being drilled is fully or partially passed into the separator 84 which then serves as a choke on the system. Such a separator vessel is capable of withstanding relatively higher pressure. As an example, the Ansi Class 600 vessels will accommodate pressures up to 1,480 psi. In the separator 84 most of the gas which is produced is liberated from the fluids, which gas can be flared or passed to a gas receiving system for subsequent disposal through the line 86. Also, in the separator 84, solids which may be in the form of a fine paste of drilling cuttings or the like, such as when drilling is performed in a chalk formation, may gravity separate from the fluids to the bottom of the separator. The bottom of the separator is periodically drained through line 88 to allow the solids to pass to a pit for disposal of the solid fines. A level control 90 opens and closes the valves 92 to maintain a liquid level in the separator 84 to keep gas above the lower level of the separator and thus prevent gas as much as possible from moving out into the remainder of the separator system. If the liquid level of separator 84 should fall below a desired level, the liquid level control 90 will close the valves 92 to permit a buildup of fluids within the separator and thereby keep the gas level at a sufficiently high position in the separator.

The fluids exiting separator 84 are passed through valves 92 to a holding tank 116 which typically is a large portable tank that can be moved easily. The tank

116 is not a pressure vessel normally but is enclosed and has a fan to draw off gas through a stack 117 for venting to the atmosphere. The tank 116 provides a first quiet zone 110 so that the solids or fines in the fluids at this point may gravity separate to the bottom of tank 116. A major portion of the solids may be removed from the drilling fluids in the tank 116. These solids are then pumped or drained from the bottom of tank 116 through line 124 to a solid/liquid centrifuge separator 118 which separates solids from liquids therein, with the solid components from the separator 118 passing to a pit, not shown, through underflow outlet 122. Water and oil from the centrifuge 118 are then passed back to an overflow chamber 119 in the tank 116 where they join the oil and water components that spill over the baffle 121 into chamber 119.

Tank 116 is arranged to control the level of oil and water layers 96, 98 respectively in the tank, using a level control 143. The top of the oil layer 96 in chamber 119 of tank 116 is passed through a line 140 to a settling tank 142 for further separation before pumping to sales represented by the tank 141. Any water taken from the surge tank 142 is passed back to the water layer 98 of tank 116 by way of line 141.

It has been found that particulate matter in the drill cuttings such as particles of chalk become wetted by the produced oil which passes from the formations being drilled into the drilling fluids stream. These solid particles thus form a nucleus which when covered with oil becomes a neutrally buoyant particle that forms the basis of a suspension or emulsion layer in the fluid mixture. Thus, the water phase that is taken from tank 116 which passes through line 146 into the inlet 134 of a hydrocyclone 147, has such neutrally buoyant oil coated particles as a part of the makeup of the mixture which is inletted to the hydrocyclone. An oil phase exits through the reject or overflow outlet 45 of the hydrocyclone and is passed back to the oil layer 96 of the tank 116 to enter the tank at the top edge of the suspension layer 97. This suspension layer 97 being separated by the hydrocyclone 147 may be for example in the range of 65% oil and 35% water but at this point the oil phase portion of the stream represents only 1 1/2 to 2% of the total fluid volume of the system. A pump 152 may be provided in the line 146 in the system to provide sufficient inlet pressure of fluids entering the hydrocyclone to effect proper separation of the oil and water phases in the mixture passing into the hydrocyclone. The underflow outlet 151 from the hydrocyclone 147 connects with alternate flow paths. One such path passes the water leg to a residence vessel 162 which serves as a means for separating solids from the primarily water component exiting from the underflow (151) of the hydrocyclone. This residence vessel has a weir 163 therein for trapping solids in a first portion of the vessel which may be removed by means of a drain outlet 164. The water component passes over the weir into the remainder of the vessel 162 and is outletted through a flow line 165 to a drilling fluid pit at the drill site to await recirculation in the drilling fluids system. If the level control 143 on tank 116 is calling for recycle of the water stream, then this water stream passes by way of a line 166 through valve 144 back to tank 116 where it enters the tank at or below the interface of the water layer 98 and the emulsion layer 97. The outlet line 165 to the drilling fluid pit is closed by means of control valve 168 likewise operated by the level control 143.

The level control 143 on tank 116 operates as follows: as the level of water in tank 116 rises to a predetermined level, the level control closes the recycle valve 144 and opens valve 168, since enough water is being received with the incoming fluids from the well. Thus, the water passing from the tank 116 and separated by hydrocyclone 147 and residence vessel 162, is passed to the drilling fluids tank or pit through line 165. Alternatively, when the water level in tank 116 drops to a predetermined level, the level control 143 opens valves 144, closes valve 168, and thereby maintains the oil/water interface within a predetermined limit range. In theory, valves 144, 168 will be opened and closed in a throttling fashion, attempting to maintain a relatively constant level within the predetermined range.

An alternative arrangement is shown in Figure 2 for treating fluids emanating from the underflow outlet 151 or hydrocyclone 147. A valve 149 may be opened to permit fluids from the underflow to pass through a flowline 150 to a centrifugal separator 153 for separating solids from the underflow component. The solids would leave the centrifugal separator 153 by means of an underflow 155 for further disposal wherein the water component therein would pass by means of an overflow outlet 154 for recirculation in the drilling fluids system. A still further alternative arrangement might include a hydrocyclone in place of or in addition to centrifuge 153 for separating the underflow stream into solid and liquid components.

In the operation of the apparatus just described fluids are circulated from a borehole drilling operation into the present system by means of a flowline passing such fluids from the borehole annulus through a choke manifold 82. These fluids are typically comprised of drilling fluids such as brine, water, or the like; drill cuttings; and petroleum fluids which have produced from underground formations being traversed by the borehole. These fluids comprising the makeup of the drilling fluid system, are then passed into a separator 84 where a substantial portion of any gas present in the fluids is liberated. This equipment is sometimes called a "gas buster". This liberation of gas from the fluids substantially reduces the pressure on the fluids system so that further processing is done at a reduced pressure. Some of the drill cuttings in the fluid system may also separate out in the separator 84 and are then removed for subsequent disposal through a line 88 at the bottom of the separator. A level control 90 is operatively connected to an output line from the separator 84 to pass liquids therefrom a valve system 92. These valves are operated by the level control. These dirty fluids which have now been depleted of most gas and some solids (drill cuttings) are next passed into a large tank 116 where they are received in a first sump or quiet zone 110 separated by a baffle 121 from the main chamber portion 119 of the tank. This first quiet zone serves to separate out a substantial portion of the solids in the form of drill cuttings in the fluids. These solids are then discharged by way of a line 124 to the inlet of a centrifuge 118 which is effective to separate any fluids in the materials discharging through line 124 from solids therein. The solids are passed to a pit, or the like (not shown) for subsequent disposal. Water or other liquids which are separated in the centrifuge 118 are discharged through the overflow 123 into chamber 119 in the tank 116. Here they are treated with the other fluid components of the fluid system which spill over the baffle 121 into chamber 119. These system fluids are permitted to gravity separate in this chamber so that a predominantly water layer 98 develops in the bottom of chamber 119 with an oil layer 96 on top. An intermediate layer 97 forms between the oil and water layers and is principally comprised of a suspension or emulsion of oil and water which is stabilized by the presence of solid particles. These solid particles act as a nucleus about which oil collects to thereby form a neutrally buoyant particle in the fluid system.

The oil layer 96 in the tank 116 passes through an overflow line 140 exiting from the upper portion of chamber 119 which directs the oil component of the fluids to a settling tank 142. The settling tank permits further separation which can be assisted by the additions of chemicals such as demulsifiers. Any water which accumulates in tank 142 may be returned by way of a line 41 to the chamber 119 in tank 116 for further processing or alternatively, may be passed back to the drilling fluid system for reuse therein. An upper outlet of tank 142 is fed to a pump for transferring the oil to a tank 161 for sale thereof.

The suspension component 97 in chamber 119 is taken from the tank by way of a line 146 and is thus passed to a hydrocyclone 147. A pump 152 may be used to increase pressure on the inlet fluids to the hydrocyclone in order to provide sufficient swirl to effect separation therein. Such a pump can be constructed in accordance with the low shear type pump disclosed in U.S. Patent 4,844,817.

These fluids passing through the hydrocyclone 147 are typically comprised of droplets forming a disperse oil or water phase in a continuous oil or water phase which separate within the hydrocyclone into the respective phases. In addition, as described above, solids particles which are present in the drilling fluids system and which have been coated by oil become neutrally buoyant because of the combined composition of a more dense solids particle and a less dense oil coating to provide a combined substance that is neutrally buoyant. This neutrally buoyant substance then passes with the continuous phase having the droplets dispersed therein. In the hydrocyclone the oil coating about the solids particles is forcibly removed by the excessive gravity orces that are present in the hydrocyclone which liberates the solids particle thus providing a less dense oil component and a more dense solids particle. The solid particles then combine with the more dense water phase and exit the hydrocyclone through the underflow outlet 151. This underflow stream which comprises the water phase and the solid particles is passed into the residence vessel 162 to remove the solids therefrom so that the water phase can be recirculated into the drilling fluids system for reuse in the drilling operation. The less dense oil phase is passed through the overflow outlet for return to the tank 119 or alternatively, could be passed directly to sales if the oil phase therein were sufficiently dry. However, if the oil phase is returned to the tank 116 the oil therein will readily deploy to the oil layer 96 within the chamber 119 for subsequent processing of the oil phase passing therefrom.

The hydrocyclone 147 which is shown in this system would typically be a dewatering hydrocyclone or a deoiling hydrocyclone which is arranged to handle a substantial amount of water, and which are described more particularly in United States Patent 4,749,490 and United States Patent Application Serial No. 415,316. In an alternative arrangement the hydrocyclone 40 of Figures 1 and 3 and hydrocyclone 147 shown in Figure 2, may be of the type disclosed in U.S. Patent 4,810,382 which is incorporated herein by reference and which shows a circumferential slotted outlet in the outer wall of the hydrocyclone which is effective to outlet solids into an annular gallery for separate removal from the hydrocyclone. other arrangements for solids removal from a hydrocyclone outlet are, of course, not precluded.

It is readily appreciated from the disclosure herein, which applies a unique process to two diverse separation problems, that the invention herein has application to a wide variety of industrial applications wherein water and oil components of a fluid mixture create an emulsion that is difficult to separate. Therefore, while particular embodiments of the present invention have been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects, and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

Claims

I claim:

Claim l. A fluid separation system for processing a fluid mixture including oil and water . components and having an intermediate component in the mixture comprised of an oil emulsion, comprising; a vessel for gravity separating components of the mixture wherein an intermediate zone is formed between an overlying oil layer and underlying layer of heavier components including water; hydrocyclone means having an inlet for receiving a portion of the mixture from the intermediate zone of the vessel; first flowline means for passing a portion of the mixture from the intermediate zone of the vessel to the hydrocyclone; water injection means for injecting a predetermined amount of water into the mixture in said first flowline means upstream of the hydrocyclone inlet to enhance separation of oil and water components of the mixture in said hydrocyclone.

Claim 2. The separation system of claim 1 and further including means in said first flowline upstream of said hydrocyclone inlet for enhancing the mixing of water being injected into the mixture in said first flowline to facilitate reversing the oil emulsion in the mixture.

Claim 3. The separation system of claim 1 wherein said hydrocyclone has at least one outlet for outletting materials separated within said hydrocyclone and further including second flowline means for recycling outletted materials from said hydrocyclone to said vessel.

Claim 4. The separation system of claim 1 and further including pump means in said first flowline for increasing the pressure of the fluid mixture entering the inlet of said hydrocyclone and for enhancing the mixing of water being injected into said mixture in said first flowline.

Claim 5. The separation system of claim 3 wherein solids are present in the intermediate zone and further including means downstream of said hydrocyclone outlet for receiving any solids component which is separated from the other components of the mixture in the hydrocyclone.

Claim 6. A method for separating components of a fluid mixture including oil, water and some solids components and having an intermediate component comprised of an oil emulsion, comprising the steps of; passing the fluid mixture into a vessel for gravity separating lighter and more dense components into upper and lower layers respectively and wherein an intermediate layer including an oil emulsion is formed between the upper and lower layers; passing components of the mixture from the vessel including portions of the oil emulsion into a first flowline; injecting and mixing water into the components in said first flowline to facilitate reversing the oil emulsion; and passing the mixture of components and injected water into the inlet of a hydrocyclone to enhance separation of the components of the mixture.

Claim 7. The method of claim 6 and further including pumping the mixture in said first flowline into the hydrocyclone in order to increase the pressure of the mixture in the hydrocyclone and to enhance mixing of the injected water to thereby further facilitate reversal of the oil emulsion.

Claim 8. The method of claim 7 wherein said hydrocyclone has an overflow outlet for outletting more dense components of the mixture including the water component and any solids component present in the inletted mixture to the hydrocyclone; and passing a more dense components stream from the underflow outlet to a downstream separation device for removal of solids in the underflow stream.

Claim 9. The method of claim 8 wherein said underflow stream is recycled to said vessel.

Claim 10. The method of claim 9 wherein said underflow stream is recycled to said lower layer in said vessel.

Claim 11. A fluid separation system for processing a fluid mixture including oil and water components with solid particles suspended therein and wherein oil in the mixture has coated solid particles to form an oil coated particle that is substantially neutrally buoyant, comprising; gravity separation means for receiving the mixture and for gravity separating the fluids into an oil layer and a water layer, with such oil coated particles collecting in a suspension layer between the oil and water layers; hydrocyclone means comprised of a hydrocyclone designed, constructed and arranged for separating oil and water components of a fluid mixture and for separating oil from the oil coated particles present in the fluid mixture, said hydrocyclone having an inlet means for inlet of a fluid mixture to be separated, an underflow outlet for outletting more dense materials in the mixture comprised substantially of water and non-buoyant solid particles and an overflow outlet for outletting a less dense oil component of the mixture; and flowline means for passing fluids from the suspension layer and inletting such fluids into said hydrocyclone inlet means.

Claim 12. The separation system of claim 11 and further including second flowline means for passing more dense materials from the hydrocyclone underflow outlet into said gravity separation means.

Claim 13. The separation system of claim 12 wherein said more dense materials are passed via said second flowline means into the water layer of said gravity separation means.

Claim 14. The separation system of claim 11 and further including third flowline means for passing the less dense oil component from the hydrocyclone overflow outlet into said gravity separation means.

Claim 15. The separation system of claim 14 wherein said less dense oil component is passed via said third flowline means into the oil layer of said gravity separation means.

Claim 16. The separation system of claim 12 and further including deβanding separation means positioned in said second flowline between said hydrocyclone underflow outlet and said gravity separation means.

Claim 17. The method of claim 10 wherein the fluid mixture has a gas component and further including separating at least a portion of the gas component from the fluid mixture before passing the suspension containing the oil coated solids and water into the inlet of said hydrocyclone.

Claim 18. A fluid separation system for processing a fluid mixture including multiple liquid components and having an intermediate component in the mixture comprised of an emulsion, comprising; a vessel for graving separating components of the mixture wherein an intermediate zone is formed between an overlying less dense layer and underlying layer of heavier components; hydrocyclone means having an inlet for receiving a portion of the mixture from the intermediate zone of the vessel; first flowline means for passing a portion of the mixture from the intermediate zone of the vessel to the hydrocyclone; injection means for injecting a predetermined amount of one of the less dense or heavier components into the mixture in said first flowline means upstream of the hydrocyclone inlet to enhance separation of the multiple liquid components of the mixture in said hydrocyclone.

Claim 19. A method for separating components of a fluid mixture having multiple liquid components and some solids and having an intermediate component comprised of a liquid emulsion, comprising the steps of; passing the fluid mixture into a vessel for gravity separating lighter and more dense components into upper and lower layers respectively and wherein an intermediate layer including the emulsion is formed between the upper and lower layers; passing a portion of the emulsion from the intermediate layer in the vessel into a first flowline; injecting and mixing one of the lighter or more dense components into the emulsion in said first flowline to facilitate reversing the emulsion; and passing the mixture of emulsion and injected components into the inlet of a hydrocyclone to enhance separation of the components of the mixture.

Claim 20. A fluid separation system for processing a fluid mixture including multiple liquid components with solid particles suspended therein and wherein a liquid component in the mixture has coated solid particles to form a liquid coated particle that is substantially neutrally buoyant, comprising; gravity separation means for receiving the mixture and for gravity separating the fluid mixture into a less dense layer and a more dense layer, with such liquid coated particles collecting in a suspension layer between the less and more dense layers; hydrocyclone means comprised of a hydrocyclone designed, constructed and arranged for separating liquid/liquid components of a fluid mixture and for separating a portion of the liquid component from the liquid coated particles present in the mixture, said hydrocyclone having an inlet means for inlet of a fluid mixture to be separated, an underflow outlet for outletting more dense materials in the mixture comprised substantially of a liquid component and non-buoyant solid particles and an overflow outlet for outletting a less dense component of the mixture; and flowline means for passing fluids from the suspension layer and inletting such fluids into said hydrocyclone inlet means.