Iron control agent

Iron control agents. Citric acid, acetic acid and organophosphorus compounds complex iron and prevent the formation and precipitation of ferric hydroxide. 

Iron control agents such as citric acid and organophosphorus compounds form iron complexes and prevent the formation of ferric hydroxide precipitate. 

As outlined above, surfactants are added to acids to perform one or more of several needed functions. However, other chemicals are also added to the acid. These additives inclnde corrosion inhibitors [IS], iron control agents [J9, 20], hydrogen sulfide scavengers [21], scale inhibitor [22] and clay stabilizers [23], It is very important to perform compatibility tests of the selected surfactant with the acid formnla, especially in this complex environment. Also, some of the snrfactants are nsed in high temperature and high salinity applications. Therefore, it is necessary to ensure thermal stability of these surfactants nnder these harsh conditions. 

Another common problem is the use of multiple additives, two or more of which may be incompatible. Although service companies have guidelines for additive use, it is reasonable to accept that on occasion, they will not be consulted properly and consequently that incompatible additives will be included in a treatment design. Remember that service company guidelines for the use of certain additives are not alwaj readily available to tbeir representatives, especially those located outside the United States and in remote locations. As a result, errors in the mixing of additives can be made. A common error is to mix together cationic and anionic siurfactants or polymers. Another error is the use of an iron control agent in an add in which its solubility is low. 

Iron control agents react with dissolved iron and other dissolved metal ions to inhibit solids precipitation as acid spends and pH increases. Iron control agents do not reduce the amount of iron dissolved, nor do they reduce or prevent acid reaction with iron compounds. They do prevent repredpitation of iron compounds by maintaining iron cations in solution. 

Iron control is critical in the acidizing of injection wells, because iron rust and scale are deposited in the wellbore and at the formation face. Produdng-well tubulars typically contain layers of iron oxide or iron sulfide. Add will dissolve rust very easily and redeposit the iron in the formation if an iron control agent is not used. 

Table 6-8 gives examples of common iron control agents and concentration ranges in applicable add mixtures. Notably, some iron control agents are available in their acid states or as sodium salts. 

Table 6-8. Properties of common iron control agents...

Iron Control Agent Temperature Limit Appllcatlon(s) Conoentration Range (pptg )... 

Note Liquid concentrate forms of these iron control agents also exist. Pounds per thousand gallons of acid. 

Concentrations differ depending on whether the iron control agents are in the free acid form (e.g., ethylenediaminetetraaectic acid [EDTA]) or in one of the sodium salt forms. Service company guidelines must be consulted for proper additive loading. Sodium salt forms preclude use in HF mixtures, as spent HF will form insoluble precipitates with sodium ions. 

In addition to the common iron control agents listed in table 6-8, service companies provide other iron control systems. Citric acid combined with acetic anhydride has been a common system in the past. Special iron control add mixtures (blends of acetic, formic, and citric acids) are commercially available. 

Newer iron control agents and combinations thereof have been introduced in recent years. There are also proprietary iron stabiHzers, which are typically combinations of iron control agents and organic adds. Iron reducers from the same family as erythorbic acid are often included... 

Fortunately, certain surfactants are quite effective in preventing the formation of sludge. As mentioned earlier, a proper iron control agent (reducing agent) may help to prevent or reduce sludge formation when included in combination with the proper antisludge surfactant. 

Acid/crude oil fluid-compatibility tests should be conducted to demonstrate whether an antisludging agent will be needed. This testing should also be used to determine the surfactant and iron control agent types and concentrations required. 

Note The following acid additives are required corrosion inhibitor and iron control agent. 

Calcite scales can be easily dissolved with HCl. In most cases, these scales can be removed, at least temporarily, with a conventional acid treatment. The standard scale-dissolving solution is 15% HCl containing a corrosion inhibitor and an iron control agent. At high temperatures, organic acids, such as acetic acid, have application as well. 

Most iron scales can be treated with acid with varpng degrees of success. Greater care must be taken to maintain soluble material in solution. A properly selected iron control agent is imperative. Iron sulfide is partially soluble or slowly soluble in HCl, but that is the only viable treatment option. It may be safer to remove iron scales mechanically by drill-out, milling, or high-pressure jetting operations. 

H EDTA (acid form) 2.0 Low Iron control agent in acid not a treating fluid... 

Na EDTA (tetrasodium EDTA) 10.6 High Sultate scale removal, also used as an iron control agent... 

Note The following acid additives are required corrasian inhibitor, iron control agent, water-wetting surfactant, and 5% mutual solvent nonemulsifier is optional. 

Preflush 7,5% HCI + corrosion inhibitor-e iron control agent + surfactant -i- 5% EGMBE 100... 

Note Stages are pumped at maximum matrix rate, without diversion, even in long zones. Acid must first be spotted with coiled tubing, then pumped through the annulus at a high rate.The following acid additives are required corrosion inhibitor, iron control agent, and surfactant. 

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