Scale barium sulfate

The produced fluids from all of the producing wells in the field are gathered into a larger stream prior to separation. These fluids contain gas, oil, water and other impurities such as iron sulfide, sulfate scales (barium sulfate, calcium sulfate), sand and other insoluble particulates. While the natural gas is generally easy to separate for the other components, the oil and water that are produced usually exist as an emulsion. It is through the action of the separators (usually with the aid of chemicals) that the emulsion is broken into oil and water. A description of the separation process is as follows. 

Chemical scaling is another form of fouling that occurs in NF and RO plants. The thermodynamic solubility of salts such as calcium carbonate and calcium and barium sulfate imposes an upper boundary on the system recovery. Thus, it is essential to operate systems at recoveries lower than this critical value to avoid chemical scaling, unless the water chemistry is adjusted to prevent precipitation. It is possible to increase system recovery by either adjusting the pH or adding an antisealant, or both. 

The scale may consist of calcium carbonate, barium sulfate, gypsum, strontium sulfate, iron carbonate, iron oxides, iron sulfides, and magnesium salts [943]. There are monographs (e.g.. Corrosion and Scale Handbook [159]) and reviews [414] on scale depositions available in the literature. 

Thennodynamic inhibitors are complexing and chelating agents, suitable for specific scales. For example, for scale inhibition of barium sulfate, common chemicals are ethylenediaminetetraacetic acid (EDTA) andnitrilotriacetic acid. The solubility of calcium carbonate can be influenced by varying the pH or the partial pressure of carbon dioxide (CO2). The solubility increases with decreasing pH and increasing partial pressure of CO2, and it decreases with temperature. 

The formation of calcium carbonate (CaCOs), calcium sulfate, and barium sulfate scales in brine may create problems with permeability. Therefore it is advantageous that newly made fractures have a scale inhibitor in place in the fracture to help prevent the formation of scale. Formulations of hydraulic fracturing fluids containing a scale inhibitor have been described in the literature [1828]. 

Y. B. Zeng and S. B. Fu. The inhibiting property of phosphoric acid esters of rice bran extract for barium sulfate scaling. Oilfield Chem, 15(4) 333-335,365, December 1998. 

There is considerable potential, therefore, for mineral scale, such as barium sulfate (see the next section), to form during these procedures. The scale may be deposited in the formation, the wellbore, or in production tubing. Scale that forms in the formation near wells, known as formation damage, can dramatically lower permeability and throttle production. When it forms in the wellbore and production tubing, mineral scale is costly to remove and may lead to safety problems if it blocks release valves. 

Nitro substituents and heterocyclic nitrogen influence not only the yield of fluorodediazoniation but also the rate of decomposition which, in these cases, is too high to perform the reaction on a multigram scale. Some explosions have been reported. Thus, the decomposition of nitro-substituted or heterocyclic diazonium tetrafluoroborates is usually controlled by three-to fivefold dilution of these substrates in inert solids, such as acid-washed sand,113 218 Kiesel-guhr,3 sodium carbonate,3 barium sulfate,217 sodium fluoride,216 or sodium tetrafluoroborate.3 This modified technique has been generalized to the decomposition of all kinds of diazonium tetrafluoroborates under safe conditions, even on rather large scales. 

Acid cleaning agents such as hydrochloric, phosphoric, or citric acids effectively remove common scaling compounds. With cellulose acetate membranes the pH of the solution should not go below 2.0 or else hydrolysis of the membrane will occur. Oxalic acid is particularly effective for removing iron deposits. Acids such as citric acid are not very effective with calcium, magnesium, or barium sulfate scale in this case a chelatant such as ethylene diamine tetraacetic acid (EDTA) may be used. 

A positive LSI means that scaling is favored a negative LSI means that corrosion is favored. It is desirable to keep the LSI near zero (or below) in the RO concentrate to minimize calcium carbonate scaling. This is usually accomplished by feeding acid to lower the pH or feeding an antisealant (see Chapter 8.2.3). Care must be given if sulfuric acid is used to adjust the pH, as this may exacerbate sulfate-based scales, such as calcium sulfate, barium sulfate, and strontium sulfate. 

Barium and strontium form sulfate scales that are not readily soluble. In fact, barium is the least soluble of all the alkaline-earth sulfates. It can act as a catalyst for strontium and calcium sulfates scale.4 Analyses of the ion product with the solubility constants for barium and strontium sulfates is necessary to determine the potential for scaling with these species. If the ion product (IP) for barium sulfate exceeds the solubility constant, scale will form. Note that in the case of strontium sulfate, if IP > 0.8Ksp, scaling is likely. However, the induction period (the time it takes for scale to form) is longer for these sulfate-based scales than it is for calcium carbonate scale. 

Calcium phosphate has become a common problem with the increase in treatment of municipal waste-water for reuse. Surface waters can also contain phosphate. Calcium phosphate compounds can contain hydroxyl, chloride, fluoride, aluminum, and/ or iron. Several calcium phosphate compounds have low solubility, as shown in Table 7.2. Solubility for calcium carbonate and barium sulfate are also shown by comparison. The potential for scaling RO membranes with the calcium phosphate compounds listed in Table 7.2 is high and will occur when the ion product exceeds the solubility constant. This can occur at orthophosphate concentrations as low as 0.5 ppm. Sodium softening or antisealants together with low pH help to control phosphate-based scaling. 

Table 15.2 lists the saturation indexes for the untreated feed water, feed water with 10.2 ppm antisealant, and 4.2 ppm of antisealant plus 3.4 ppm sulfuric acid for pH reduction form 8.1 to 7.5. As the untreated water shows, the major species of concern are the calcium carbonate, barium sulfate, and calcium phosphate. The antisealant does a good job with all but the calcium phosphate. To address this potential scale, acid must be added. This reduces the antisealant demand by 60%. 

Another commercial aldehyde synthesis is the catalytic dehydrogenation of primary alcohols at high temperature in the presence of a copper or a copper-chromite catalyst. Although there are several other synthetic processes employed, these tend to be smaller scale reactions. For example, acyl halides can be reduced to the aldehyde (Rosemnund reaction) using a palladium-on-barium sulfate catalyst. Formylation of aryl compounds, similar to hydrofomiylation, using HCN and HQ (Gatterman reaction) or carbon monoxide and HQ (Gatterman-Koch reaction) can be used to produce aromatic aldehydes. 

Barium sulf ate scales form in situations where production of reservoir fluids causes mixing of incompatible aqueous fluids. For example, in North Sea (UK) offshore hydrocarbon production, seawater is injected into reservoirs to displace oil, and maintain reservoir pressure. When seawater, high in sulfate, contacts reservoir fluids that have high concentrations of Ba +, BaS04 scales result. Barium sulfate is an especially intractable scale mineral because of its physical hardness and very low solubility (i-6). 

Laboratory Screening Test to Determine the Ability of Scale Inhibitors to Prevent the Precipitation of Barium Sulfate and/or Strontium Sulfate from Solution (For Oil and Gas Production Systems)... 

Scale Salts that have precipitated out of water. Calcium carbonate, barium sulfate, and calcium sulfate are common in oil fields. 

Problems in the separation system. There are several problems that oilfield operators and service companies address in production system of an oilfield. These problems may involve solids that inhibit or reduce the efficiency of the separation process, or they may be microbiological in nature. The solids that present the most problems in the separation system are either sulfate-based scale, namely calcium or barium sulfate, or iron sulfide. 

There are several gas-well fields that produce hydrocarbon gas associated with very high TDS connate waters. Classical oilfield scale problems (e.g., calcium carbonate, barium sulfate, and calcium sulfate) are minimal in these fields. Halite (NaCl), however, can be precipitated to such an extent that production is lost in hours. As a result, a bottom-hole fluid sample is retrieved from all new wells. Unstable components are "fixed" immediately after sampling, and pH is determined under pressure. A full ionic and physical analysis is also carried out in the laboratory. 

Lithopone is formed through co-precipitation of zinc sulfide and barium sulfate. Lithopones are intimate mixtures of the components rather than solid solutions. It is said to have been discovered by G.R de Doubet around 1850 and first produced on a large scale by J.B. Orr in 1874, hence the alternative name of Orr s zinc white q.v.). Other synonyms include Griffith s White, Griffith s Patent Zinc White and Oleum White. The Colour Index (1971) designation is Cl 77115. 

Deposition of inorganic scale may occur during well production. Depending on well conditions and produced water characteristics, different scale types may form. Often, scale formation is associated with a breakthrough of water production. Common scales include calcium carbonate, iron carbonate, calcium sulfate, barium sulfate, strontium sulfate, andiron sulfide. Combinations may also form. Figures 3-2 and 3-3 show well samples of calcium carbonate and iron scale, respectively. 

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