Drill string corrosion

Establish corrosion rate and identify type of corrosion attack with drill string corrosion coupons prior to treatment. Each well should be evaluated individually and inhibitor treatments based on evaluation of the corrosion coupons. 

Drilling Muds in the Petroleum and Natural Gas Industry. Since 1941, chromium chemicals have been used in the drilling of wells to combat fatigue corrosion cracking of drill strings, with about one metric ton of sodium chromate being used aimuaHy for an average West Texas well. Other early uses were in gas-condensate wells in Louisiana and East Texas. 

Corrosion inhibitors are used to reduce the corrosion of surface equipment, surface casing, and the drill string by drilling and well treatment fluids. Many different corrosion inhibitors have been used. These include amine salts such as ammonium sulfite -bisulfite blends, zinc carbonate, zinc chromate, hydrated lime, fatty amine salts of alkylphosphates, cationic polar amines, ethoxylated amines, and tertiary cyclic amines. Commercial products are usually proprietary blends of chemicals. 

Drill-string and casing in continuous contact with drilling fluid may cause a form of corrosion. 

To maintain the BSR at less than 5.5, the string of drill collars must frequently be composed of different sizes. For severe drilling conditions (hole enlargement, corrosive environment, hard formations), reduction of the BSR to 3.5 helps to reduce frequency of drill pipe failure. 

Microencapsulated Cl fixed on the surfaces of metal parts forming immovable joints have found application in various industrial sectors. The interior of the shells is liberated when the parts are brought into contact and the capsules become squashed. This technique is used for antirust protection of rivet joints of the skin of airplanes. Microcapsules with Cl are carried, with minimum outlay, to the demanding corrosion sites of casing and drilling pipe strings at excavation sites of oil and gas deposits. The effective use of inhibited microcapsules has not been fully realized due to a number of reasons, including technical and economic ones. 

Corrosion due to mechanical and metallurgical problems also exist. Metal tools used in drilling wells are often softer than the formation being penetrated. The abrasiveness of formation solids can easily erode protective films from drilling equipment, leaving metal exposed to corrosion-erosion attack. Mechanical and chemical separation of abrasive solids helps control this attack. It is difficult, however, to control stress concentrations in a string of driU pipe that may reach many kilometers into the earth. 

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