Corrosion Control of Drilling Tools Through Chemical Treatments
- Karen Bybee (JPT Assistant Technology Editor)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- June 2011
- Document Type
- Journal Paper
- 76 - 78
- 2011. Society of Petroleum Engineers
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- 99 since 2007
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This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 130515, "Corrosion Control of Drilling Tools Through Chemical Treatments - Effectiveness and Challenges," by Nausha Asrar, SPE, Schlumberger, originally prepared for the 2010 SPE International Conference on Oilfield Corrosion, Aberdeen, 24-25 May. The paper has not been peer reviewed.
Increasing production is challenging because the wellbore fluids in many new fields are typically multiphase with harsh chemical compositions and conditions, such as high hydrogen sulfide (H2S), carbon dioxide (CO2), and occasionally dissolved oxygen, in a high-temperature/high-pressure environment. All this makes corrosion control a major concern, especially in the present challenging economic climate, where the risks and cost associated with corrosion may have significant impact on health, safety and the environment; on capital expenditure; and on operation expenditure.
Domestic oil and gas production is considered a mature industry in the USA because most of the significant available reserves have been identified and are being exploited. Direct corrosion costs associated with this activity are estimated to be approximately USD 1.4 billion, with USD 0.6 billion attributed to surface-piping and facility cost, USD 0.5 billion to downhole tubing, and USD 0.3 billion to capital expenditures related to corrosion.
Corrosion is defined formally as the destruction of metal by direct chemical reaction or by an electrochemical reaction of a metal with its environment. Chemical corrosion is the direct combining of a metal with another material, and it usually occurs at higher temperatures. Corrosion of this type seldom occurs in drilling, except in very-high-temperature wells. The second, more common type of corrosion electrochemical, occurs at a solid/liquid interface. This arises in nearly every instance where water or brine contacts metal/alloy equipment. Therefore, electrochemical corrosion is the principal concern in drilling operations.
Drillpipe probably is the most harshly treated of all equipment at the rigsite. While a well is being drilled, the drillpipe is exposed to high stresses, and it is exposed to both formation fluids and drilling mud. Thick-walled drillpipes are called drill collars. They contain electronic chassis and other measurement tools on the annular side and provide weight to the bit for drilling. These drillpipes are made of hardened high-strength steel and are likely to suffer from fatigue and different types of corrosion started from deep corrosion pits caused by corrosives, either from the mud itself or from being stacked wet. Also, the high hardness and strength of the drill-collar materials makes such collars more susceptible to stress corrosion cracking (SCC).
Corrosion encountered in drilling operations involves several mechanisms that have been grouped into (1) electrochemical corrosion, and (2) mechanical/corrosive effects.
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