Water, water, everywhere,
Nor any drop to drink
Samuel Taylor Coleridge, The Rime of the Ancient Mariner
In all, the world contains approximately 1.4 million cubic kilometers of water. Despite this abundance, however, all life on Earth depends on less than one percent of the total volume of water on the planet. The problem lies in quality, not just quantity. Most of earth’s water is salty, leaving only about 2.5 percent as fresh water.
Most of this is frozen in polar ice caps or glaciers. Much of the rest lies essentially beyond human reach deep underground in aquifers.
Energy Quest, Inc. (“NrgQst”) exists to provide environmentally friendly, non-destructive technologies to the oil and gas industry, with an emphasis to this industry and as well as other market sectors, for the purpose of recycling and reuse of contaminated water supplies. Typically these water supplies would not be usable but technologies are now available that mitigate solids, totally dissolved solids, microbial bacteria and other harmful micro-organisms in water supplies and recycle non-potable water to clean water that is introduced into the environment. These solutions use technology that is Green – friendly to the environment.
Oil and gas exploration always associated with production of water
Produced water contains contaminants from underground rock structures and chemical additives
Due to rising oil prices, natural gas emerging as a major source of energy worldwide
Many large reserves were untapped as gas is trapped within shale rock structures
Gas produced from these structures called Shale Gas
Now possible to tap those reserves with advanced technology (horizontal drilling and fracking)
Releasing shale gas during production requires fracturing the rock structures that trap the gas
Hydrofracture (frac) water” consists of water, sand (or another “proppant”) and a small quantity of chemicals (anti-scalants, friction reducers and biocides), injected under high pressure.
Frac water that returns during fracing (anywhere from 5-50%) is called flowback water. Flowback water contains dissolved solids from the reservoir and chemicals used in fracing.
Produced water” is water from the reservoir that flows to the surface with oil or gas production during the life of the well.
Produced Water” is water trapped in or injected into underground formations that is brought to the surface along with oil or gas. Even without the added volumes resulting from hydraulic fracturing, produced water is the largest volume byproduct associated with oil & gas production.
Early in the life of an oil well, the oil production is high and water production is low. Over time the oil production decreases and the water production increases. Another way of looking at this is to examine the ratio of water-to-oil:
U.S. average estimate – 7:1, because many U.S. fields are mature and past their peak production
Many older U.S. wells have ratios > 50:1
In excess of 20 billion bbl (barrels; 1 bbl = 42 U.S. gallons) of produced water are generated each year in the United States from nearly a million wells (Source: NETL)
Currently most produced water is disposed of in injection wells or evaporation pits, usually located distant from the production well
Industry is aggressively seeking alternatives to reduce costs and environmental impacts of Produced Waters and Frac Water.
$1.25–$1.50/bbl raw water cost
$1.75–$2.25/bbl concentrated brine water cost
$0.75–$3.50/bbl transportation cost
$0.75–$3.50/bbl transportation cost
$0.75–$1.25/bbl disposal via deep well injection
$2.00–$8.75/bbl fresh water and disposal
$4.00–$10.50/bbl brine water and disposal
Organics removal (oil / grease, polymers, etc.) – Oily Water Separator
Particulate removal (filtration)
Efficient management (removal of dissolved hardness and metals (scale formers by brine softening)
Bacteria control (incorporated in brine softening step along with salt removal)
The major problem with use of flowback water for makeup of hydrofracture water is the total organic carbons and very high content of scale forming constituents present (hard water contaminants).
The high levels of barium, calcium, iron, magnesium, manganese, and strontium common in flowback water will readily form precipitates, scale, which would rapidly block the fractures in gas bearing formations required for economic gas production.
Removal of these constituents to much lower levels is thus required for recycle of flowback water, or use of production water, as frac water.
Two methods of contaminant removal used by NrgQst are caustic soda softening and/or ion exchange resins if warranted.
Example flowback treatment levels for recycling purposes per industry standards:
Total organic carbon <10 parts per million (ppm) range
Total cations 10 – 2,000 ppm range
Acceptable levels range from company to company
Primary focus on Barium (Ba) and Strontium (Sr), but Calcium (Ca) also a concern
Ba, Sr , Iron (Fe), Manganese (Mn), Magnesium (Mg) <10 ppm
Ca <1,000 ppm
Hardness <2,500 ppm
Processed water sulfates levels <30 ppm
Total Suspended Solids (TSS) <30 ppm
Total Dissolved Solids (TDS) is variable, >50,000 ppm can be acceptable
Barium, beryllium, calcium, magnesium and strontium belong to a group of chemicals called the “alkaline earth metals.” Although these chemicals belong to the same chemical group, they vary widely in their abundance and behavior in ground water and in their potential health effects.
Calcium and magnesium are abundant in rocks and soil, particularly limestones and dolomites. They are relatively soluble.
Strontium and barium are also abundant in earth materials, although their concentrations are one to two orders of magnitude lower than those of calcium and magnesium.
Strontium and barium are less soluble than calcium and magnesium, but are found in appreciable quantities in aquifers consisting of sandstone and igneous rocks.
Step #1 Oily Water Separator – The first step comprises a method of effectively extracting organic carbons (oil) from the frac water by means of the Crystal Oily-Water Separator (102) operating in conjunction with the Crystalline Polishing Unit (103).
Crystal Oily-Water Separator (102) is an innovative apparatus capable of reducing the oil content in the effluent to less than 5 ppm (mg/l) in five stages of separation. Crystal Oily-Water Separator (102) does not require any consumables and is virtually maintenance free resulting in important savings in manpower and downtime costs.
ØCrystalline Polishing Unit (103) is designed to eliminate any traces of oil and reduce the oil content to zero ppm (mg/l). Similarly to Crystal unit, the polisher does not necessitate filters or other consumables and is designed for unattended operation. Crystalline is the only polishing unit worldwide that can achieve this type of decontamination in terms of effluent purity and without consumables.
Oil reclaimed by Crystal separator contains up to 6% water and needs to be dehydrated in order to meet pipeline specs, i.e. 0.5% BS&W (basic sediment and water).
65°C, do not necessitate chemicals and have few moving parts being far more economical than centrifuges, which operate at 90°C with emulsion breakers and produce pollutant sludge.
Therefore, Coalescing Dehydrator (104) will assist Vacuum Dehydrator (105) to attain the required oil dryness in one pass or could even eliminate it altogether. The tests will indicate whether Coalescing Dehydrator (104) will be able to achieve pipeline specifications without the Vacuum Dehydrator (105). In any case, it will be very useful in reducing energy consumption and capital costs of the Vacuum Dehydrator (105).
Step #2 Filtration – Water is then passed through a Conventional Filter Press (201) for solids-water separation designed to retain solids up to 20 microns. Contaminated fluid is injected into the center of the press and the pressure inside the system will increase due to the gradual formation of sludge. Then, the liquid is filtered out through the filter clothes by adding a stream of water. The process is fully automated, the unit having larger plates and frames filter presses with mechanical “plate shifter”. The function of the plate shifter is to move the plates and allow rapid discharge of the filter cakes accumulated in between the plates.
The Filter Press (201) will be temporarily bypassed during automatic discharge in order to ensure the continuous operation of the system. The filtration system downstream will then handle the fluid during the self-cleaning sequence of the filter press.
Whereas the Filter Press (201) is very effective in removing solids it cannot accomplish a satisfactory clarification of the water. In some situations the water turbidity can be quite high and further steps are provided for dealing with such turbidity.
The filtered water is introduced into a Mixing Tank (301) and then a Settling Tank (302) for reducing the turbidity of the water by means of coagulation and sedimentation. Multimedia Filter (303) removes the remaining suspended solids and colloids whereas the Activated Carbon Filter (305) removes chlorine, odor, volatile organic compounds etc. Clarified water with a turbidity comparable to that of tap water is temporarily kept in Surge Tank (401).
For the full scale plant an Anjan Unit will be used. The filtration system described above will be used in place of an Anjan Unit because it is not feasible to miniaturize an Anjan Unit. Information is provided on the Anjan Unit.
Whereas the pilot plant filtering system will not be as effective as Anjan it can provide nonetheless a satisfactory alternative to it especially when the brine is further clarified by the softening step downstream.
Strontium , 90% of which can removed by Anjan, will remain in solution. However, as will be shown in the softening step, strontium will form non- toxic compounds which can safely disposed of as sludge. Furthermore natural strontium is non radioactive contrary to the public perception.
In effect, strontium commonly occurs in nature being the 15th most abundant element on Earth, estimated to average approximately 360 parts per million in the Earth’s crust. Frac water contains natural strontium which is dissolved when brine is injected into the formation.
Step #3 – Brine Softening – In general lime is used for precipitation softening but some problems such as handling difficulties, health problems including chemical bronchitis and also some operating upsets, including blocking the lines and injection equipment, arise during handling it.
The use of caustic soda as a superior alkaline reagent in water softening is well known and discussed in many references which found caustic soda as an efficient alkaline reagent in water softening compared to lime. The
precipitation reactions of caustic soda with hardness are shown below:
magnesium chloride + caustic soda = magnesium hydroxide + salt
magnesium sulphate + caustic soda = magnesium hydroxide + sodium sulphate
For precipitating calcium chloride (CaCl2) and calcium sulphate (CaSO4) the following reaction with soda ash occur:
calcium chloride + soda ash = calcium carbonate + salt
calcium sulphate + soda ash = calcium carbonate + sodium sulphate
The above reactions indicate that the amount of sludge resulting from the precipitation of calcium and magnesium compounds is far lower than that generated by lime treatment. Thus, caustic soda produces salt and sodium sulphate which remain in solution.
The water analysis indicates that the amount of carbonate hardness in negligible. Traces amounts of bicarbonate will react with caustic soda and from soda ash and magnesium hydroxide. Soda ash will then be used up for removing calcium compounds.
The barium and strontium content in the feed is unknown at this time. However data from similar operations suggest that they are present in small amounts.
Barium reacts with sodium sulphate (Na2SO4) which is produced during the reaction of caustic soda with magnesium hydroxide as was shown previously.
Barium sulfate is non toxic and is frequently used clinically as a radio-contrast agent for X-ray imaging and other diagnostic procedures. It is most often used in imaging of the GI tract during what is colloquially known as a ‘barium meal’. It is therefore obvious that barium sulphate is non toxic.
Strontium hydroxide, resulted from the reaction between caustic soda and strontium ions is used chiefly in the refining of beet sugar and as a stabilizer in plastic and is also non toxic.
Strontium carbonate is produced from the reaction with soda ash is non toxic and is used for manufacturing CTV to absorb electrons resulting from the cathode, in the preparation of iridescent glass, luminous paints, strontium oxide or strontium salts and in refining sugar and certain drugs.
It should be noted that strontium has physical and chemical properties similar to those of its two neighbors calcium and barium. While natural strontium is stable, the synthetic 90Sr isotope is present in radioactive
fallout and has a half-life of 28.90 years. Natural strontium is NON-
RADIOACTIVE and NON-TOXIC, a fact that eludes the public that confuses it with synthetic Strontium 90 which is mainly generated by nuclear power plants. This confusion is exploited by the media and politicians to further their interests at the expense of the truth.
In most applications lime treatment is preferred to caustic soda treatment due to the fact that the use of caustic soda is limited by the carbonated hardness of the water. Thus carbonates reacting with caustic soda increase the amount of soda ash which in turn would increase the alkalinity of water. As a result, sources of water have significant carbonated hardness render softening by lime treatment more suitable.
In this application carbonated hardness is negligible as can be seen from CO3 and HCO3 content. Consequently, the water treatment needs to deal with non carbonated hardness given by calcium and magnesium compounds which are in significant amount and render the caustic soda very effective in softening the water without the risk of increasing the alkalinity.
Another reason for opting for lime is the higher price of caustic soda. However, this cost is only apparently higher and needs a careful analysis. Thus, comparison of the lime-sodium carbonate system with caustic
softening system shows that the amount of produced CaCO3, in case of using caustic soda, is significantly less than the other case. Decrease in produced CaCO3 significantly reduces the disposal costs. Additionally, the caustic softening process produces 0.5 mole sodium carbonate per mole of consumed caustic soda which can be considered as an economical alternative for water softening, compared to lime and sodium carbonate thus savings in disposal costs and soda ash compensate the higher price of caustic soda.
Furthermore, a caustic soda plant with a total annual production of 5,000 metric tons, which costs in the order of tens of thousands of dollars can be added to the full size water treatment plant. The plant would use salt (NaCl) brine and electricity for producing caustic soda, chlorine and hydrogen. The excess caustic soda could be sold, fetching three times higher prices than pure salt and its commercialization would be obviously far more lucrative.
The salt mine in Romania where the brine composition is similar to that in this application has used caustic soda since 2001, thus successfully replacing lime and precluding the problems associated with it.
With reference to the Treatment Flow Diagram, clear brine drawn from Surge Tank (401) is introduced into Mixing Tank (402) where caustic soda and soda ash react with calcium and magnesium compounds which precipitate of calcium carbonate and magnesium hydroxide.
Barium and strontium form the non toxic compounds which were described above and also precipitate in Sedimentation Tank (403).
The sludge is extracted periodically from the bottom of Sedimentation Tank (403), may be dewatered by gravity in a decanter or by means of a dewatering screw (not shown) and disposed of at a landfill. It should be noted that some operators use calcium carbonate and magnesium hydroxide as additives to fertilizers or for the remediation of acidic soils.
Softened brine is then filtered through Multimedia Filter (404) and discharged into Surge Tank (501).
Caustic soda also destroys bacteria and viruses very effectively therefore no additional means need to be provided for bacteria elimination.For example, caustic soda used for clearing sewage piping destroys bacteria in septic tanks and renders them useless so it cannot be used in households
that have septic tanks.
A refinement of the softening method used in the salt mine would be the selective removal of magnesium compounds with caustic soda and that of the calcium compounds with soda ash. Magnesium hydroxide and calcium carbonate could thus be separated . Magnesium hydroxide could then be treated with sulfuric acid to obtain Epsom salt.
Precipitated calcium carbonate (PCC), pre-dispersed in slurry form, is a common filler material for latex gloves with the aim of achieving maximum saving in material and production costs. Therefore it would be beneficial to depart from the conventional design and introduce this novel method.
It should be noted, another advantage is that barium could be also precipitated with caustic soda and then neutralized with sulfuric acid in order to obtain completely harmless barium sulfate . This proposed method would have to be discussed with a reputable chemist in order to asses its feasibility and advantages. However, in principle the reactions described above should occur having the expected results mentioned above.
In order to obtain higher purity Epsom salt barium would have to be extracted prior to using caustic soda. Chelating resins may be able to extract barium that but most of them also have affinity with calcium and magnesium, which defeats the purpose. Selective barium removal with chelating resins needs more investigation and will be one of the objectives of the pilot plant .
However, if a satisfactory solution cannot be found, barium can be precipitated and neutralized with caustic soda and sulfuric acid. In this case the purity of the Epsom salt will depend on the amount of barium in the frac water.
Step #4 – Evaporation (Mechanical Vapor Recompressor)
The last stage of the process comprises Surge Tank (501), Evaporator (502), Crystallizer (503) and Centrifuge (504).
Evaporator (501) is an MVR (mechanical vapor recompression) type evaporator which comprises a compressor for increasing the pressure of the vapor produced from the brine.
The pressure increase of the vapor also generates an increase in the condensation temperature. As a result, same vapor can serve as the heating medium for its "mother" liquid i.e. the brine in order to evaporate the brine . Consequently, MVR evaporators are more energy efficient than any other type of evaporator.
Furthermore, due to the fact that the brine is condensing the vapors, there is no need for condensing them with cooling water. This feature renders the MVR evaporator uniquely suitable for this project since no river water is available in the regions where it will operate. In effect, no other type of evaporator could be utilized in this application.
For the pilot plant the evaporator capacity will be 0.1 m3/h, which is significantly lower than the capacity of the plant. This is due to the fact that the evaporator and crystallizer need to be portable. The dimensions of an evaporator that has larger capacity would not permit its installation in a
The system provided by this method is flexible, thus both brine and salt can be produced simultaneously. NaCl brine from Surge Tank (501) can be separated into two streams. A stream will be supplied to the MVR Evaporator (502), Crystallizer (503) and Centrifuge (504). The salt produced in this manner, having a humidity between 2 and 3 % will be sufficient for determining its properties and value on the market.
The other stream of NaCl brine will not contain Ca and Mg ions and its composition will permit its recycling in fracing operations with important profits.
Also, the water treatment plant can be operated intermittently for treating the feed and clean brine can be stored in Tank (501). In this situation the evaporator would operate continuously in order to obtain exclusively salt.
Distilled water (fresh water) is a valuable by-product that can generate important revenues. The income from distilled water and salt will be higher than that generated by the sale of brine therefore a full size unit would be more profitable when the evaporator is used at its maximum capacity. After a preliminary market study is done an ultrapure water system may further process distilled water in order to generate another highly priced by-product, which can be sold to hospitals, semiconductor industry, pharmaceutics, etc. (Has limited use in Texas)
The heartbeat of the system is the
Crystal Oily Water Separator.
Low power consumption with highly efficient design.
No costly filters required.
Handles a wide range of densities with no limitation
on oil particle size.
Unaffected by chemicals or detergents.
Coast Guard and ABS Certified IMO MEPC 107 (49)
compliant. Did not exceed 5ppm even with 100% oil influent.
Extremely compact, front side access for ease of installation. Easily transported.
Designed for continuous automated predictable operation.
The lowest maintenance and operating costs in the industry. 30 units currently operating trouble free for years in various locations.
Outstanding reliability. Has no internal moving parts & does not require internal maintenance or cleaning
Crystalline Polishing Units have been devised to remove oil particles to zero ppm. The most advanced polishing units currently in use cannot reduce the oil content below 50 mg/l. Furthermore, there is a limitation on oil particles size, which must be above 20 microns. The performance of older units is even more unsatisfactory, with oil content in the effluent exceeding 200 mg/l.
The importance of minimizing the oil content cannot be emphasized enough.
As produced water is pumped into the formation, oil prematurely plugs the well with significant economic losses.
MVR is very energy efficient, since the latent heat of vaporization is fully utilized through vapor recompression and condensation.
The major advantage of MVR is the energy economy.
ØTypical MVR energy requirement is 0.05 to 0.15 kWh per kg of water evaporated.
For the removal of the hardness ions Ca2+, Mg2+, Sr2+ and Ba2+, there exist two types of ion exchange resins: The first has aminomethylphosphonic (AMP) functional groups while the second has iminodiacetic (IDA) type functional groups. Both types can form stable complexes with alkaline earth ions with the following selectivity preference:
Ba2+< Sr2+< Ca2+< Mg2+
The difference between the two types lies in the different selectivity for the various alkaline earth elements. The AMP types have more pronounced affinity for Ca2+ and Mg2+ than the IDA types. On the other hand, the IDA types have more pronounced affinities for Sr2+ and Ba2+ than the AMP types. Consequently, the choice of the resin depends on the feed
brine composition and on the criterion for the end-point of the loading cycle. If the end-point is based on Ca2+ and Mg2+ breakthrough then the AMP type of resin is recommended. If it is based on Sr2+ breakthrough, then the IDA type of resin gives a longer cycle.
Water effluent quality can be saturated brine for frac water makeup or can be near potable for fresh water needs
Perfect water to re-use in all oil and gas needs
Secondary uses in irrigation and industrial needs
Does not use current freshwater drinking supplies
Low cost to operate and maintain