US20070193739A1

US20070193739A1 - Scale-inhibited water reduction in solutions and slurries

Info

Publication number: US20070193739A1
Application number: US11/705,300
Authority: US
Inventors: Kevin Smith; Robert Sloan; Harry Smith
Original assignee: Total Separation Solutions LLC
Current assignee: TOTAL SEPARATION SOLUTIONS HOLDINGS LLC
Priority date: 2005-02-14
Filing date: 2007-02-12
Publication date: 2007-08-23

Abstract

A cavitation device is used to reduce the water content of used or wastep solutions and slurries, including oil well fluids and muds, solution mining fluids, industrial oil/water emulsions, and other used or wastep aqueous industrial fluids. A main reason for reducing the water content of such fluids is to facilitate their disposal or reuse. Thermal energy from the steam and vapor produced by the non-scaling cavitation device is recycled in steam turbines or piston expander engines, or otherwise facilitates evaporation through a membrane or condensation to useful fresh water; the efficiency of the process can be enhanced by mechanical vapor recompression.

Description

RELATED APPLICATION

This application claims the full benefit of copending application Ser. No. 11/352,889, filed Feb. 13, 2006, which in turn claims the benefit of provisional application 60/652,549 filed Feb. 14, 2005 and 60/652,711 filed Feb. 14, 2005.

TECHNICAL FIELD

A cavitation device is used to reduce the water content of used or wastep solutions and slurries, including oil well fluids and muds, solution mining fluids, industrial oil/water emulsions, and other used or wastep aqueous industrial fluids. A main reason for reducing the water content of such fluids is to facilitate their disposal or reuse. Thermal energy from the steam and vapor produced by the non-scaling cavitation device is recycled in steam turbines or piston expander engines, or otherwise facilitates evaporation or condensation to useful fresh water.

BACKGROUND OF THE INVENTION

In oil and other hydrocarbon production, drilling, completion and workover, fluids are typically circulated down the string of tubes and upwards around the outside of the tubes, contacting the formation surface of the wellbore from which the hydrocarbons are to be produced. In the case of a completion, drilling, or workover fluids an original clear brine is typically prescribed to have a density which is a function of the formation pressure. Oil well fluids may include calcium, zinc, ammonium and/or cesium as cations, and chloride, formate and particularly bromide as anions from any source. Typical sources include cesium chloride or formate, calcium chloride, sodium chloride, sodium bromide, calcium bromide, zinc chloride, zinc bromide, ammonium chloride, and mixtures thereof as well as their cation and anion forming moieties from other sources. The salts and other additives in the completion, drilling, or workover fluid may be partially diluted by the formation water, as a result of contact with the formation. The brines can also become diluted deliberately by the well operator, who may add water to replace fluid lost into the formation, or to reduce the density following a decision that it is too high. Oil field fluids commonly include as ingredients not only various salts but also polymers, corrosion inhibitors, densifying agents such as barium compounds, biocides, solids such as mud additives, and other compounds. Whether or not they are diluted, the oil field operator is ultimately faced with the problem of disposal or reuse. Frequently, finding a permissible site for disposal of such solutions and slurries is difficult and very expensive Disposal is also difficult for other common oil well fluids such as water/oil (or oil/water) emulsions of widely varying composition, including muds. A related point is that if the excess water in dilute fluids is not eliminated or recovered for various purposes, the volume of fluid at the wellsite continues to increase. The cost of trucking to an approved disposal or processing site can be prohibitive in many instances, and accordingly a significant reduction in the volume of such materials is needed in the art. All such fluids originating in the hydrocarbon production industry—the oil and gas fields—may be referred to herein collectively as “oil well fluids.” All such fluids for which our invention is useful, including oil well fluids, may be referred to herein collectively as “industrial fluids.” They will all include at least some water which is to be removed.
Conventional methods of dewatering such fluids, such as distillation or simple evaporation, are very susceptible to scale formation on the heat exchange surfaces, which soon renders the distillation or evaporation equipment inoperable. Conventional methods tend also to be energy inefficient, and do not lend themselves to the use of thermal and electrical energy commonly available at the well site.
Production of hydrocarbons from underground formations generally includes water from the same formations. In 2007 the ratio of water produced to oil produced worldwide is about 5 barrels of water for every barrel of oil produced. As oilfields mature the produced water volumes typically increase. Unfortunately the water produced with oil is not fresh water and is typically highly contaminated with both dissolved salts and suspended solids that include very hard to remove oil droplets. It typically comes from much greater depths than the fresh water aquifers.
At the same time there is only a small amount of chloride-free, fresh water in the world compared to the amount of sea water. It has been logical and common practice to extract fresh water from sea water or other “brackish” waters. One can simply boil sea water and then condense the steam as fresh water. Today desalination of sea water into fresh water is a commonly accepted technology in wide use around the world. Units range from a few gallons per day to 1,000,000's gallons per day. The technology for desalination is evolving with several dominate technologies generally defined as either evaporation or reverse osmosis and as of 2007 the two technologies represent about 50% of the new plants built; although, with the current rate of new membrane technology development it is generally expected that the use of reverse osmosis will grow relative to evaporation. Each has its advantages and there are numerous methods defined in the literature to describe both technologies in detail.
Like seawater, the water produced from hydrocarbon extraction contains chlorides, and it seems logical that technology from desalination could apply to such produced water. In some produced water applications desalination technology does work and is being used successfully. Unfortunately there are some key differences between seawater and produced water. Seawater can be considered a consistent feedstock; therefore, you can design for the most efficient operation based on a number of choices and then amortize the cost of the plant over a long life. You can control the flow into the plant and assume the feedstock will never change. Furthermore, generally size is not an issue and size can improve efficiency particularly with heat exchangers, membranes etc.
Unfortunately, water obtained in hydrocarbon production is not a consistent feedstock. It can vary even in the same field, and composition can change over time. Harsh chemicals are often used in the production of hydrocarbons and the well treatment chemicals contaminate the associated produced water. Typically, produced water contains significant dissolved and suspended organics. Produced water is reactive and changes over time. The water in the formation is in a reduced state; whereas, seawater is fully oxidized and non reactive. Surface handling of produced water often adds oxygen that oxidizes the components of the produced water. Changes in temperature and pressure cause significant scale deposition. Unlike a seawater desalination plant where you control the flow into the plant, with produced water, you must cope with the flow from the formation. Not only does the produced water volume from a well typically increase with time, there are upsets that change everything. An example of an upset might be where oil overwhelms an oil/water separator and the oil intrudes into the desalination process. Typically a desalination plant requires pretreatment of the seawater feedstock. Given the variability of the produced oilfield water it has been very difficult to design the pretreatment system particularly for reverse osmosis membranes.
To evaporate produced water there are some major issues. One is economics. Generally most produced water is re-injected into the same or similar formations. Downhole disposal is an environmentally acceptable alternative to evaporation and it is one of the least expensive alternatives; however, it often requires trucking or piping that adds considerable cost. The other major problem is scale. Scale is inversely soluble with heat. As temperature increases the scaling salts are less soluble. Scale is detrimental to an evaporation process that uses heat. The scale will form first on hot surfaces and that includes heat exchanger surfaces. First there is loss of efficiency. as the scale starts to insulate the hot heat exchanger surface from the fluid. Scale buildup also plugs the heat exchanger. Unfortunately, corrosion must also be considered. Heat can speed the corrosion process and since most produced waters contain chlorides, one must consider chloride stress cracking of metals.
While evaporation in the oilfield is not as simple as desalination, it can be accomplished with a careful process design and it is a proven effective way to dispose of brine. Evaporation is a key technology in numerous industries, including food, chemicals and minerals processing. There are a wide variety of processes and many variations. Different evaporation processes and components were considered in developing this technology. Generally the methods to design such systems are to work out the mass and heat balances of the system and then each component. Components generally include a flash tank where steam vapor separates from the liquid, a source of heat, pumps to add fluid to the process and remove fluid, crystallizers to remove dry solids, solids handling equipment, heat exchangers, mixers, calandrias, evaporative cooling towers, condensers, vacuum pumps, compressors, piping, heat-transfer fluids, vents, packing trays, mist eliminators, economizers, and combinations of all these components. Furthermore the chemistry of the water must be considered as part of the design process. Typically with seawater desalination there is a pretreatment to remove hardness, or to mitigate its effect in the process. Unfortunately oilfield waters typically contain an order of magnitude greater concentration of hardness. Furthermore the hardness can vary from a relatively benign calcium carbonate compound to a nuisance calcium sulfate, but there is also hazardous barium sulfate scale and even radioactive strontium sulfate scaling. In designing a plant a chemical balance must be considered along with the heat and mass balance. Oilfield water chemistry is well defined in various reference books such as the classic textbook by Dr. Charles Patten entitled “Oilfield Water Chemistry” available through DA Campbell and Associates. There are many text books on water chemistry, but Patten is different because it deals with oilfield waters. There are graphs to predict scale formation based on water analysis, pressures and temperatures that are proven reliable and universal for oilfield waters. The scaling indexes have since been refined and reduced to computer programs.
Many evaporation technologies and system layouts are well known and have been practiced for at least 100 years, if not longer.
For example, a simple system might be a source of heat and a flash tank.
One could use any number of components to improve the design and function of a flash tank. For example there is natural circulation and forced circulation to consider. Fluid to be evaporated can be pumped into the tank to turn it into a simple continuous process. For example if you pump the same weight of water into the evaporation tank to equal the pounds of steam vapor being removed then you would have a continuous process. If you consider the mass balance and heat balance you need to know that it takes 1 BTU of heat to raise the temperature of one pound of water one degree. Unfortunately it then takes 970.4 BTU per pound of water to vaporize that water into steam. To evaporate water using this method, you must add heat, generally know as sensible heat, to raise the temperature of the base fluid from the starting point to the boiling point. Then you must add the latent heat of vaporization to run the evaporation. The mass and heat balance are simple equations and for one pound of water evaporated, you need to add the sensible heat to the latent heat and then you can decide how much you want to process per hour and you will know how much energy is required and then you can design your system around your requirements using standard chemical engineering texts, vendor input, handbooks, etc. It is typical to start with a proposed Process and Instrumentation Diagram or P&ID and then work though the mass balance and heat balance. In doing such work it becomes obvious that this simple design is not efficient. If steam is the ultimate goal, or if steam is required in another process then this simple flash tank evaporator works, and one can continue through the design to size the unit and then specify components to build the system. These types of units are typically called steam boilers. They are packaged readily available for purchase, lease or rental in a multitude of sizes and configurations from a variety of sources. Steam drove the industrial revolution and again the technology is very well known and has evolved over time. A conventional steam boiler is not an ideal evaporator of oilfield waters because scale and corrosion rapidly foul the unit and can even cause serious injury.
If you do not need the steam, then it becomes a cost. With desalination, you need fresh water for civilizations to survive. You can afford to pay for fresh water. Oilfield water is a cost that you want to minimize since it offsets the revenue from the hydrocarbons. It is not only a cost, but often an environmental hazard. Using a conventional steam boiler is a very inefficient way to evaporate oilfield waters. The first law of thermodynamics is the conservation of energy. If you make steam, the energy in the steam goes somewhere. If you evaporate produced oilfield waters, the steam in the simple evaporation design goes to global warming. That is both costly and not environmentally sound. If you take advantage of the first law of thermodynamics and “recycle” the steam into the evaporation process, you become far more efficient. That is it takes less energy. For example you could run a simple evaporation process but use the steam to further evaporation with a simple evaporative cooling tower.
If you add a cooling tower to your process essentially you can double the evaporation of the system. One could term this multiple-effect evaporation. There are numerous multiple effect evaporators and generally to be economical you need at least five effects. Simply you must utilize the 2^ndlaw of thermodynamics which says heat moves from hot to cold. Steam at atmospheric pressure cannot boil water at atmospheric. It can only provide sensible heat—that is heat the water to the vaporization point. It cannot boil the water because heat will not move between two bodies that are the same temperature. As you compress steam it goes up in temperature. With some compression you can get more heat in the steam and then take advantage of the second law of thermodynamics. With a multiple-effect arrangement generally the first evaporation tank is at the highest pressure. High pressure steam goes to the next flash tank that is operating at lower pressure and the heat boils that liquid. That steam moves to the third, tank that is lower pressure than the second tank and so on. Systems have been built with 20 or 30 effects. It still takes 970 BTU/pound of water evaporated, but by recycling the steam through multiple effects; you can divide the 970 BTU/pound by the number of effects to get the actual number of BTU's used for pound evaporated. For example, if you have 5 effects essentially you can evaporate water 5 times more efficiently or put another way use only 200 BTU per pound.
Another well known method to enhance evaporation is by using compression. You can use one flash tank, but compress the steam and use a heat exchanger to condense the steam into fresh water. The fluid circulates from the flash tank through a heat exchanger where you condense high pressure steam on the outside of the same heat exchanger. By condensing the steam you get back the latent heat of vaporization and fresh water as a by product. The steam must be hotter than the evaporative fluid. By compressing the steam the temperature goes up and heat moves from the hot to cold or from the hot steam into the lower temperature (although still hot) fluid being evaporated. Vapor compression can either be by thermocompressor or by mechanical vapor recompression (MVR). A thermocompressor simply mixes high pressure steam with low-pressure steam to raise the temperature of the steam. The MVR system relies on an engine driving compressor. MVR can be a very efficient process. There are numerous references in the literature to the efficiency of compression. Systems can equal 50-effect evaporators. If you have high pressure steam, or another high pressure gas thermocompression makes the most sense; otherwise, MVR would be the choice.
All of the above systems use, and require, one thing in common: heat exchangers that are prone to fouling in oilfield environments. Heat exchangers by definition have a hot surface. Again heat moves from hot to cold; therefore, heat moves from the hottest fluid to the heat exchange surface (usually metal) and then to the colder fluid. That means the heated surface is hotter than the fluid and scale is inversely soluble with temperature. That means scale starts to form on the heat transfer surface. As scale forms heat transfer efficiency decreases. There are numerous designs to minimize scale build up on heat transfer surfaces. There are mechanical devices to even scrape the surfaces to prevent scale buildup. A crystallizer is simply a heat exchanger designed to handle very high solids, and is often used in the situations were scale can be a problem. There are a multitude of heat exchanger designs and patented systems to improve heat transfer and to prevent scale buildup. Chemicals can also be used to treat for scale and are often utilized in the oilfield since scale even builds up downhole; however, chemicals add to the cost of systems and an important goal is to minimize costs.
One method to evaporate produced water is to remove the scale-forming chemicals first and then further process the water with the steam into a crystallizer or conventional MVR system. If you remove the hardness, any of the conventional evaporation systems will work. It is common practice to precipitate scale with chemicals or by other means. One method is to seed liquid as you heat it to precipitate the scale in the “fluid” instead of on the heat transfer surfaces. You can also keep the fluid below the scaling index by selecting systems that run at lower temperatures, or by using vacuum, among other methods. Seeding compounds and techniques are selected according to the composition of the concentrate and the type of scale likely to deposit under the circumstances.
The present method avoids the use of conventional heat exchangers in the dirty fluids to a great extent, recycles thermal energy wherever feasible, and promotes scale-free evaporation to obtain useful fresh water without undue energy use. As will be seen below, a cavitation device, or SPR, is a versatile device for converting shaft horsepower into heat without using a conventional heat exchange surface. The SPR can be used in various heat and energy saving systems to realize cost savings in many ways while making copious amounts of useful fresh water and concentrating otherwise used wastep fluids so they can be economically reused or disposed of.

SUMMARY OF THE INVENTION

This invention dewaters dilute and contaminated solutions and slurries—industrial fluids—by passing them through a cavitation device which generates shock waves to heat the fluid and facilitate the removal of moisture, thereby reducing the volume of wastep material for disposal. Preferably the cavitation device is one manufactured and sold by Hydro Dynamics, Inc., of Rome, Ga., most preferably the device described in U.S. Pat. Nos. 5,385,298, 5,957,122 6,627,784 and particularly 5,188,090, all of which are incorporated herein by reference in their entireties. In recent years, Hydro Dynamics, Inc. has adopted the trademark “Shockwave Power Reactor” for its cavitation devices, and we use the term SPR herein to describe the products of this company and other cavitation devices that can be used in our invention. The cavitation device will heat the fluid without accumulating any scale. The reason is that the generation of thermal energy takes place within the fluid and not on a heat exchange surface.
Definition: We use the term “cavitation device,” or “SPR,” to mean and include any device which will impart thermal energy to flowing liquid by causing bubbles or pockets of partial vacuum to form within the liquid it processes, the bubbles or pockets of partial vacuum being quickly imploded and filled by the flowing liquid. The bubbles or pockets of partial vacuum have also been described as areas within the liquid which have reached the vapor pressure of the liquid. The turbulence and/or impact, which may be called a shock wave, caused by the implosion imparts thermal energy to the liquid, which, in the case of water, may readily reach boiling temperatures. The bubbles or pockets of partial vacuum are typically created by flowing the liquid through narrow passages which present side depressions, cavities, pockets, apertures, or dead-end holes to the flowing liquid; hence the term “cavitation effect” is frequently applied, and devices known as “cavitation pumps” or “cavitation regenerators” are included in our definition. Steam generated in the cavitation device can be separated from the remaining, now concentrated, water and/or other liquid which frequently will include significant quantities of solids small enough to pass through the reactor.
The term “cavitation device” includes not only all the devices described in the above itemized U.S. Pat. Nos. 5,385,298, 5,957,122 6,627,784 and 5,188,090 but also any of the devices described by Sajewski in U.S. Pat. Nos. 5,183,513, 5,184,576, and 5,239,948, Wyszomirski in U.S. Pat. No. 3,198,191, Selivanov in U.S. Pat. No. 6,016,798, Thoma in U.S. Pat. Nos. 7,089,886, 6,976,486, 6,959,669, 6,910,448, and 6,823,820, Crosta et al in U.S. Pat. No. 6,595,759, Giebeler et al in U.S. Pat. Nos. 5,931,153 and 6,164,274, Huffman in U.S. Pat. No. 5,419,306, Archibald et al in U.S. Pat. No. 6,596,178 and other similar devices which employ a shearing effect between two close surfaces, at least one of which is moving, such as a rotor, and/or at least one of which has cavities of various designs in its surface as explained above.
The solution or slurry is increased in temperature in the SPR and then passed to a next step either for utilizing the heat energy of the fluid or to enhance the efficiency of its vaporization. The vapor or steam associated with the heated fluid can be used, for example, to operate a steam turbine or steam engine, or it can be subjected to recompression to make its heat energy readily available for reuse, or it can be passed through a membrane to enhance the efficiency of vaporization, or simply passed to a cooling tower.
The fluid heated by the SPR, or a portion of it, can be immediately recycled to the SPR to heat it further. Vapor or steam generated in the SPR can be separated to be passed to one of the above-mentioned steps, before, after, or at the same time as the remaining fluid.
Our invention includes the optional step of filtering the fluid before it enters the SPR, or after it is concentrated by the SPR. Because the SPR is able to handle large proportions of solids in the fluid it processes, our invention enables the postponement of filtration until after the fluid is reduced in water content by passing through the SPR to heat it and facilitate removal of vapor; filters and the filtration process can therefore be engineered to handle smaller volumes of liquid with higher concentrations of solids.
In another aspect, our invention includes a method of processing a used oil well fluid comprising optionally filtering the used oil well fluid, passing the used oil well fluid through a heat exchanger utilizing wastep heat from a power source such as the exhaust of a Diesel engine, powering a cavitation device with the power source, passing the oil well fluid through the cavitation device to increase the temperature thereof, optionally recycling at least some of the used oil well fluid through the cavitation device to further increase the temperature of the used oil well fluid, passing the used oil well fluid into a flash tank to separate steam and vapor from the used oil well fluid and to obtain a concentrated fluid, removing at least a portion of the concentrated fluid from the flash tank, and reusing the at least a portion of the concentrated fluid in an oil well. The use of a Diesel engine is not essential; the cavitation device may be powered by any more or less equivalent source of mechanical energy, such as a common internal combustion engine, a steam engine, an electric motor, or the like. Wastep heat from any of these, either in an exhaust gas or otherwise, may be utilized in a known manner to warm the oil well fluid before or after passing it through the SPR.
While the SPR is quite capable of elevating the temperature of an aqueous solution or slurry to the boiling point of water (at atmospheric pressure) or higher, it is not essential in our process for it to do so, as the flash tank, membrane, or other vapor recovery device may be operated under a vacuum to draw off vapors at temperatures below the boiling point at atmospheric pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a and 1 b show variations of a cavitation device as utilized in our invention.
FIGS. 2A-2D are flow sheets illustrating our process made more efficient by utilizing steam from the heated fluid to operate a steam turbine or a steam engine for assisting in operating the SPR.
FIG. 3 shows a recompression loop in which steam or vapor originating in the SPR is recompressed to conserve energy.
In FIGS. 4 a and 4 b, a membrane distillation step is combined with our SPR system; two different configurations are shown.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 a and 1 b show two slightly different variations, and views, of the cavitation devices sometimes known as a cavitation pump, or a cavitation regenerator, and sometimes referred to herein as an SPR, which we use in our invention to regenerate solutions comprising heavy brine components.
FIGS. 1 a and 1 b are taken from FIGS. 1 and 2 of Griggs U.S. Pat. No. 5,188,090, which is incorporated herein by reference along with related U.S. Pat. Nos. 5,385,298, 5,957,122, and 6,627,784. As explained in the 5,188,090 patent and elsewhere in the referenced patents, liquid is heated in the device without the use of a heat transfer surface, thus avoiding the usual scaling problems common to boilers and distillation apparatus.
A housing 10 in FIGS. 1 a and 1 b encloses cylindrical rotor 11 leaving only a small clearance 12 around its curved surface and clearance 13 at the ends. The rotor 11 is mounted on a shaft 14 turned by motor 15. Cavities 17 are drilled or otherwise cut into the surface of rotor 11. As explained in the Griggs patents, other irregularities, such as shallow lips around the cavities 17, may be placed on the surface of the rotor 11. Some of the cavities 17 may be drilled at an angle other than perpendicular to the surface of rotor 11—for example, at a 15 degree angle. Liquid (fluid)—in the case of the present invention, a solution containing heavy brine components, or a used mud emulsion, or a used workover fluid, or other industrial fluid which may or may not contain solid particulates,—is introduced through port 16 under pressure and enters clearances 13 and 12. As the fluid passes from port 16 to clearance 13 to clearance 12 and out exit 18 while the rotor 11 is turning, areas of vacuum are generated and heat is generated within the fluid from its own turbulence, expansion and compression (shock waves). As explained at column 2 lines 61 et seq in the 5,188,090 patent, “(T)he depth, diameter and orientation of (the cavities) may be adjusted in dimension to optimize efficiency and effectiveness of (the cavitation device) for heating various fluids, and to optimize operation, efficiency, and effectiveness . . . with respect to particular fluid temperatures, pressures and flow rates, as they relate to rotational speed of (the rotor 11).” Smaller or larger clearances may be provided (col. 3, lines 9-14). Also the interior surface of the housing 10 may be smooth with no irregularities or may be serrated, feature holes or bores or other irregularities as desired to increase efficiency and effectiveness for particular fluids, flow rates and rotational speeds of the rotor 11. (col. 3, lines 23-29) Rotational velocity may be on the order of 5000 rpm (col 4 line 13). The diameter of the exhaust ports 18 may be varied also depending on the fluid treated. Pressure at entrance port 16 may be 75 psi, for example, and the temperature at exit port 18 may be 300° F. Thus the heavy brine components containing solution may be flashed or otherwise treated in the cavitation device to remove excess water as steam or water vapor. Note that the position of exit port 18 is somewhat different in FIGS. 1 a and 1 b; likewise the position of entrance port 16 differs in the two versions and may also be varied to achieve different effects in the flow pattern within the SPR.
Another variation which can lend versatility to the SPR is to design the opposing surfaces of housing 10 and rotor 11 to be somewhat conical, and to provide a means for adjusting the position of the rotor within the housing so as to increase or decrease the width of the clearance 12. This can allow for different sizes of solids present in the fluid, to reduce the shearing effect if desired (by increasing the width of clearance 12), to vary the velocity of the rotor as a function of the fluid's viscosity, or for any other reason.
Operation of the SPR (cavitation device) is as follows. A shearing stress is created in the solution as it passes into the narrow clearance 12 between the rotor 11 and the housing 10. This shearing stress causes an increase in temperature. The solution quickly encounters the cavities 17 in the rotor 11, and tends to fill the cavities, but the centrifugal force of the rotation tends to throw the liquid back out of the cavity, which creates a vacuum. The vacuum in the cavities 17 draws liquid back into them, and accordingly “shock waves” are formed as the cavities are constantly filled, emptied and filled again. Small bubbles, some of them microscopic, are formed and imploded. All of this stress on the liquid generates heat which increases the temperature of the liquid dramatically. The design of the SPR ensures that, since the bubble collapse and most of the other stress takes place in the cavities, little or no erosion of the working surfaces of the rotor 11 takes place, and virtually all of the heat generated remains within the liquid.
Temperatures within the cavitation device—of the rotor 11, the housing 10, and the fluid within the clearance spaces 12 between the rotor and the housing—remain substantially constant after the process is begun and while the feed rate and other variables are maintained at the desired values. There is no outside heat source; it is the mechanical energy of the spinning rotor—to some extent friction, as well as the above described cavitation effect—that is converted to heat taken up by the solution and soon removed along with the solution when it is passes through exit 18. The rotor and housing 10, particularly in its interior 20, indeed tend to be lower in temperature than the liquid in clearances 12 and 13. There is little danger of scale formation even with high concentrations of heavy brine components in the solution being processed.
Any solids present in the solution, having dimensions small enough to pass through the clearances 12 and 13 may pass through the SPR unchanged. This may be taken into account when using the reconstituted solution in for oil well purposes. On the other hand, subjecting the water-soluble polymers to the localized cavitation process and heating may break them down, shear them, or otherwise completely destroy them, a favorable outcome for many purposes. The condition known as “fish-eyes,” sometimes caused by the gelling of water-soluble polymers, can be cured by the SPR. These effects will take place in spite of the possible presence of significant amounts of solids.
Concentrated and heavy or dense brines are more liable to crystallize in use than dilute brines, and accordingly their crystallization temperatures are of concern. The crystallization point of a highly salt-laden solution does not imply merely that a small portion of the salts may crystallize out, but that the entire solution will tend to gel or actually solidify, a phenomenon of great concern during the transportation of such solutions or in storage, for example. The ability to concentrate heavy brine components and their ratios to each other in a solution using a cavitation device leads to better control over crystallization temperature and the ability to achieve a good balance between crystallization temperature and density. Complex relationships between the concentrations and ratios of heavy brine component ions and other constituents in the solution rather precisely obtained by our invention means that the crystallization temperature of a completion or workover fluid can be more readily controlled while conserving substantially all of the components available to be saved.
The ability to concentrate heavy brine components content in a solution using a cavitation device also leads to better control over solution density. Relationships between the rather precisely obtained concentrations of heavy brine component ions and other constituents in the solution means that the density of a completion or workover fluid can be more readily matched with the density of the drilling fluid.
Where the fluid treated is a heavy brine containing cesium, it will commonly contain at least 2.5% cesium by weight. Our invention includes a method of treating a hydrocarbon producing formation comprising introducing into the formation through a well an oil well fluid containing at least 2.5% by weight cesium, whereby the fluid becomes diluted so that it contains less than 2.5% cesium by weight, circulating the fluid from the well, and passing at least a portion of the fluid through a cavitation device to remove moisture therefrom and produce a regenerated fluid containing at least 2.5% cesium by weight in the fluid.
Similar percentages may be found in cesium solutions used in mining cesium, and our invention may be quite useful for concentrating cesium solutions in cesium mining.
In FIGS. 2A-D, a dilute solution, slurry or emulsion (hereafter sometimes a fluid) enters in line 32 from the lower left, as depicted. It may come directly from a well, from a hold tank, or indirectly from another industrial fluid source. The SPR (cavitation device) 30 requires a motor or engine to rotate it. Here, a Diesel engine or other power source, designated Mech. Power 40, powers the SPR through shaft 41 and generates hot exhaust gases or other wastep heat, which is/are passed to heat exchanger 42, where the thermal energy of the exhaust gas or other wastep heat is used to heat the incoming fluid in line 32 through a heat exchange surface or other conventional or expedient manner. Optionally the heat exchanger may be bypassed in a line not shown. The incoming fluid continues through line 31 to the SPR 30 which may be any cavitation device described above; for illustrative purposes, it may be substantially as shown in FIGS. 1 a and 1 b. A supplemental pump, not shown, may assist the passage of the fluid. In the SPR 30, the fluid is heated as described with reference to FIGS. 1 a and 1 b, and the heated fluid is passed through line 33 to a flash tank 44, where steam and vapor is separated and removed in line 34. Alternatively or supplementally, steam or vapor may be vented through a separate vent, not shown, from the SPR to the atmosphere or drawn off directly from or in a similar vent associated with exit port 18 (FIGS. 1 a and 1 b). The steam may be recycled in a known manner for thermal energy preservation, for condensing to make substantially pure water, put to other useful purposes, or simply flashed to the atmosphere. Optionally a vacuum may be drawn on the flash tank to assist in removing the vapor and steam. It is not essential that the temperature of the fluid exiting from the SPR exceed the boiling point of water, as a vacuum assist can facilitate the withdrawal of vapors. Concentrated fluid from the flash tank, in line 35, can be recycled to the well, or analyzed on-line or after removal in order to determine the best way to re-establish the ratios of ingredients, a desired crystallization temperature, a desired density, or other property; it can also be recycled to line 32 to join with the input to the SPR to become further concentrated and for further water removal. In FIGS. 2A-2D, the concentrated fluid in line 35 is shown passing through heat exchanger 42 where it will contribute its excess thermal energy to the elevation of the temperature of the incoming fluid in line 32. For this purpose, line 35 may have its own heat exchanger separate from one such as depicted deriving its thermal energy from mechanical power source 40.
FIGS. 2A and 2B show the steam or vapor in line 34 going to a steam turbine 36, where the thermal energy is used to rotate the turbine, generating mechanical rotational power for supplementing the mechanical power source 40 in the operation of the SPR, through shaft 45. In FIG. 2B, the turbine 36 is connected to an electrical generator 37 which generates power sent through wire 49 to electric motor 39 for rotating shaft 45. Fluid discharged from the turbine 36 in line 38 is condensed by passing through turbine 36 and may be used as a source of fresh water.
FIG. 2C is similar to FIG. 2A except that a steam cylinder engine 43, such as a Spilling engine, is substituted for the steam turbine 36 in FIG. 2A. Steam and vapor from line 34 is sent to the steam engine 43, which turns shaft 45 for supplementing the mechanical power input of power source 40. In FIG. 2D, the steam engine 43 is coupled to an electric generator 46, generating electricity sent through wire 49 to motor 39 for rotating shaft 45. The steam and vapor entering steam cylinder engine 43 of FIGS. 2C and 2D is condensed while its thermal energy is converted to mechanical energy, and the condensate may be collected in a discharge line not shown for any convenient use as fresh water.
Supplemental pumps, and various filters, meters and valves, not shown, may be deployed throughout the system of FIGS. 2A-D, as in any of the other system configurations described herein to assure the desired flow rates and pressures, and to direct the fluids in the system to and through the various options described; automatic or manual controls for the valves pumps and other components may also be installed. Likewise, the system may utilize various electric and mechanical power and thermal energy sources available on site to drive pumps and/or assure the evaporation of water from the incoming fluid in line 32. It should be understood that any electric power generated by the system will result in savings in commercial power otherwise available at the site.
Referring now to FIG. 3, the SPR is shown in use with mechanical vapor recompression. An incoming solution or slurry is passed through line 80 to heat exchanger 81 where it picks up heat from the condensate in line 82, then passes through line 84 to heat exchanger 85 to absorb heat from hot concentrated liquid or slurry in line 86 from flash tank 87, and on through line 88 to the SPR 89. SPR 89 receives rotational power from mechanical power source 62 through shaft 68. The SPR 89 further heats the incoming slurry or solution and forwards the heated fluid through line 50, optionally through a devolatilizer 51 and further through line 52 to flash tank 87. The SPR may have a vent not shown for venting vapor or steam to the atmosphere or for carrying the vapor or steam to any device in the system that could use the heat or steam power therefrom. In flash tank 87, steam or vapor is removed through line 56 and sent to compressor 57, which compresses it, at the same time elevating its temperature because of the increased pressure. Compressor 57 receives rotational mechanical power from power source 62 through shaft 69 or from a different power source not shown, for example an electrical motor which in turn may be powered by a steam turbine using steam from the system (see FIGS. 2A-2D). Because the SPR heats the fluid without employing a solid heat exchange surface, it is virtually scale free; therefore the relatively high temperatures of the fluid in line 56 are achieved in a relatively scale-free manner. On the other hand, because the SPR is able to handle not only highly concentrated brines and other oilfield fluids containing solids as well as dissolved solids, the liquid accumulating in flash tank 87 may contain significant amounts of both dissolved and undissolved solids. The concentrated fluid can be removed through line 86 and filtered if desired. Condensation in condenser 83 of the high-temperature compressed steam from compressor 57 provides a condensed fluid in line 82 having considerable thermal energy for heating the incoming fluid in incoming line 80 through heat exchanger 81. Additional mechanical vapor recompression loops can be installed as is known in the art of mechanical vapor recompression. Some of the steam or vapor in line 56 may optionally be diverted through line 65 to heat exchanger 66 designed to capture wastep heat from power source 62, such as from exhaust gases or a thermal jacket, not shown in detail; this diverted steam or vapor can be isolated in line 70 for use as an optional steam or vapor, or, after it gives up its heat elsewhere, as condensate that can be used separately as a source of fresh water or combined with the distilled water in line 59. Note also that concentrate from line 86 or line 71 is desirably recycled to the SPR in lines 63 or 64, or both, to further elevate its temperature and/or remove additional water from it and/or further concentrate the fluid in lines 86 and 71.
FIGS. 4 a and 4 b are flow diagrams showing the use of membranes to enhance evaporation of water in an SPR system. In FIG. 4 a, an industrial or oilfield fluid enters the SPR 96 in line 108, is heated in the SPR as described above and continues in line 108. After passing through an optional heat exchanger 97, the fluid output from the SPR 96 in line 90 goes directly to the retentate side 98 of a membrane 94 selected for its ability to permit heated water to pass, leaving salts and solids behind. FIG. 4 a is adapted from U.S. Pat. No. 6,656,361, which is expressly incorporated herein by reference in its entirety. The membrane in FIG. 4 a is hydrophilic, which permits liquid water to pass through its pores. The fluid introduced from line 90 continues to flow while it contacts the surface of membrane 94. It may be recirculated in line 91, showing the now concentrated fluid leaving the membrane housing 95 and reentering it after passing through an optional heat exchanger 99 to increase its temperature, and joining line 90. Heat exchanger 99 and other heat exchangers shown herein may utilize wastep heat from any of numerous sources normally available in an industrial setting and especially in an oilfield site. On the permeate side 100 of the membrane 94, a slightly negative pressure may be drawn, leading vapor and/or aqueous droplets into space 92, where the cooler conditions bring about condensation of vapor to fresh liquid water. The condensate is removed in line 101 for use in an associated system such as for makeup of a new oilfield fluid, or it may be simply collected for use as fresh water. As disclosed in U.S. Pat. No. 6,656,361, an air blower may assist in moving and condensing the vapor in space 92. Additional or optional cooling devices or circulating coolant 103 may be employed on the permeate side of the membrane also to assist in the condensation process. The fluid passing through the membrane housing 95, now containing less water in line 91 may be further recycled through line 102 and optionally through another heat exchanger 104 to further increase its temperature, to the SPR 96 for additional heating before being returned to the membrane. A continuous or intermittent blowdown may be conducted, for example through line 107 to maintain desired concentrations of constituents in the circulating fluid; this may be accomplished by monitoring and controlling the conductivity of the fluid in line 102, for example.
In the configuration of FIG. 4 b, a hydrophobic membrane is used to enhance the evaporation of water from the fluid heated in the SPR 110. The oilfield or other industrial fluid from input line 121 is heated in the SPR 110 and goes through line 111 to flash tank 112 where it is separated more or less like the fluid in flash tank 44 of FIGS. 2A-D—that is, part of it remains in the flash tank as liquid, including undissolved solids or not, and part of it is given off as vapor or steam. The vapor or steam is directed (possibly with the aid of a slight negative pressure) to the retentate side 114 of the membrane 113. Water vapor passes from the retentate side 114 of the membrane 113 into the air gap 115 defined by wall 116 more or less parallel to membrane 113. Wall 116 is cooler than the heated fluid on the retentate side 114, and accordingly the vapor tends to condense in air gap 115, resulting in a fresh water condensate which is removed in line 117 for use as fresh water in any of numerous possible applications. The retentate may be recycled in line 118 to the retentate side 114 of the membrane, or in line 119 to the SPR for reheating. A concentrate stream is removed from the flash tank 112 continuously or intermittently in line 120 either for use as a source of its components or for disposal. If it is to be discarded, a considerable advantage of the process, as with all the methods disclosed herein, is that it will include far less volume to be transported or stored. In either case, the fluid in line 120 may be passed through a heat exchanger not shown to conserve its heat energy for other purposes, for example to preheat the incoming fluid in line 121. Because the SPR 110 is able to generate relatively high temperatures in the original fluid without using a scale-forming surface, the system is essentially scale-free. As in FIGS. 2 and 3, various valves, filters, meters, monitors, controls, heat exchangers and the like may be deployed through out the systems of FIGS. 4 a and 4 b as desired or as may be indicated by the circumstances. In almost all oilfield areas, wastep heat sources are available and can be adapted to heat exchangers of various kinds as are known in the art; the heat energy can be used as illustrated in FIGS. 2A-D to elevate temperatures of fluids, or for conversion to electrical or mechanical power which also can be used wherever desirable in the system. Heat exchangers using wastep heat from any source may be of particular use on the incoming fluids in line 108 of FIGS. 4 a and 121 of FIG. 4 b, but of course may be applied wherever heat will be beneficial. Generally, hydrophobic membranes are preferred, as by definition they permit only water vapor, and not water droplets, to pass. If water droplets pass through the membrane, they may carry dissolved salts with them, which is counterproductive. However, we do not intend to disclaim the use of hydrophilic membranes, particularly as their properties may be improved in the future to reject dissolved salts more completely. It is a notable advantage of the SPR that it is able to heat the dirty or salts-laden water without significant scale formation, while retaining scale-forming salts in the concentrate, and the vapor or steam that is delivered to the membrane, whether the membrane is hydrophobic or hydrophilic, presents little danger of fouling. Both types of membranes are well known in the art of desalination, medical applications, and for other purposes. Any membranes which will perform as described with respect to FIGS. 4 a and 4 b are contemplated in our invention.

Claims

1-20. (canceled)

21. Method of evaporating water from a water-containing industrial fluid comprising passing said fluid through a cavitation device to increase its temperature, said cavitation device being driven by a mechanical power source, and converting thermal energy from said fluid having an elevated temperature to mechanical energy.

22. Method of claim 21 wherein said converting of thermal energy to mechanical energy is performed in a steam turbine.

23. Method of claim 22 wherein mechanical energy from said steam turbine is used to supplement the mechanical power source for said cavitation device.

24. Method of claim 22 wherein mechanical energy from said steam turbine is used to generate electricity.

25. Method of claim 24 wherein said electricity is used to power an electric motor.

26. Method of claim 25 wherein said electric motor is used to supplement the mechanical power source for said cavitation device.

27. Method of claim 21 wherein said converting of thermal energy to mechanical energy is performed in a steam cylinder engine.

28. Method of claim 22 wherein mechanical energy from said steam cylinder engine is used to supplement the mechanical power source for said cavitation device.

29. Method of claim 22 wherein mechanical energy from said steam cylinder engine is used to generate electricity.

30. Method of claim 24 wherein said electricity is used to power an electric motor.

31. Method of claim 25 wherein said electric motor is used to supplement the mechanical power source for said cavitation device.

32. Method of removing water from a water-containing industrial fluid comprising passing fluid through a cavitation device to increase its temperature, said cavitation device being driven by a mechanical power source, passing said fluid at said increased temperature to a flash tank to separate vapor and steam from said fluid, passing said vapor and steam to a compressor and compressing said vapor and steam to further elevate its temperature, condensing said vapor and steam so compressed at its elevated temperature to obtain distilled water, and optionally passing said distilled water through a heat exchanger to conserve its heat energy

33. Method of claim 32 wherein said heat exchanger is used to heat said water-containing industrial fluid before entering said cavitation device.

34. Method of claim 32 including removing fluid remaining in said flash tank from said flash tank and recycling it to said cavitation device.

35. Method of claim 32 including using at least one component of said fluid remaining in said flash tank as an ingredient in another industrial fluid.

36. Method of evaporating water from an industrial fluid comprising heating said fluid in a cavitation device and contacting the heated fluid so obtained on the retentate side of a membrane capable of passing water vapor.

37. Method of claim 36 wherein said membrane is a hydrophilic membrane.

38. Method of claim 36 wherein said membrane is hydrophobic membrane.

39. Method of claim 38 including recycling at least a portion of said fluid into contact with said membrane.

40. Method of claim 38 wherein said heated fluid from said cavitation device is passed to a flash tank and wherein vapors from said flash tank are passed into contact with said retentate side of said membrane.