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→Corrosion
==Corrosion==
==Corrosion==
[[file:production-problems_fig3.png|thumb|{{figure number|3}}Effects of corrosion on metal pipe.]]
The potential for corrosion must be recognized and diagnosed early in the producing life of a field. Otherwise, expensive [[workovers]] and repairs may be necessary. Corrosion within the wellbore can occur in various forms and is often accompanied by the formation of scale (discussed previously). Corrosion can be divided into three categories:
The potential for corrosion must be recognized and diagnosed early in the producing life of a field. Otherwise, expensive [[workovers]] and repairs may be necessary. Corrosion within the wellbore can occur in various forms and is often accompanied by the formation of scale (discussed previously). Corrosion can be divided into three categories:
''Electrical corrosion'' is caused by the natural flow of an electrical current from the metal pipe (anode) into the formation (electrolyte) or into another metal that is lower in the electromotive series (cathode). As current flows, the anode will corrode. To prevent this type of corrosion, the expected anode can be insulated or coated. Cathodic protection can also be installed to slow down the flow of current.
''Electrical corrosion'' is caused by the natural flow of an electrical current from the metal pipe (anode) into the formation (electrolyte) or into another metal that is lower in the electromotive series (cathode). As current flows, the anode will corrode. To prevent this type of corrosion, the expected anode can be insulated or coated. Cathodic protection can also be installed to slow down the flow of current.
''Chemical corrosion'' is caused by soluble organic acids within the produced formation water or carbon dioxide within gas in the reservoir. These agents react with the metal and cause severe pitting (Figure 3). The incidence and severity of this type of corrosion is increased with higher bottomhole temperatures.
''Chemical corrosion'' is caused by soluble organic acids within the produced formation water or carbon dioxide within gas in the reservoir. These agents react with the metal and cause severe pitting ([[:file:production-problems_fig3.png|Figure 3]]). The incidence and severity of this type of corrosion is increased with higher bottomhole temperatures.
Another form of corrosion is that from hydrogen sulfide (H<sub>2</sub>S), which is a combination of electrical and chemical corrosion. The severity and potential danger of this type of corrosion makes it worth special mention (see “[[Wellsite safety]]”). Hydrogen sulfide causes damage to rubulars by several different mechanisms. First, a sulfide scale forms and causes pitting as the steel acts as an anode and transmits current to the sulfide scale. As a result of formation of the sulfide scale, hydrogen is liberated, which is absorbed by the steel. The hydrogen combines with the carbon compounds in the steel, reducing its strength and causing it to blister and crack. Since hydrogen sulfide is a poisonous gas, its production should be considered dangerous because of the potential for damage to surface and downhole equipment. Special corrosion inhibitors are commercially available to help protect the metal equipment from these types of corrosion.
Another form of corrosion is that from hydrogen sulfide (H<sub>2</sub>S), which is a combination of electrical and chemical corrosion. The severity and potential danger of this type of corrosion makes it worth special mention (see “[[Wellsite safety]]”). Hydrogen sulfide causes damage to rubulars by several different mechanisms. First, a sulfide scale forms and causes pitting as the steel acts as an anode and transmits current to the sulfide scale. As a result of formation of the sulfide scale, hydrogen is liberated, which is absorbed by the steel. The hydrogen combines with the carbon compounds in the steel, reducing its strength and causing it to blister and crack. Since hydrogen sulfide is a poisonous gas, its production should be considered dangerous because of the potential for damage to surface and downhole equipment. Special corrosion inhibitors are commercially available to help protect the metal equipment from these types of corrosion.