CO2 Corrosion in the Anadarko Basin

Abstract

Member SPE-AIME Abstract Some high pressure, temperature and volume gas wells located in the Anadarko Basin area of Washita, Beckham, and Roger Mills counties of Oklahoma have demonstrated in several cases severe corrosion rates which has led to surface equipment and tubular failures. This paper deals primarily with the El Paso Exploration Company's approach to the corrosion problem in producing gas wells. A basic theory on the mechanism of CO 2 corrosion and the identification of this type of corrosion will be presented to insure a general understanding of this type of corrosion. A discussion on the detection and monitoring system used with comparison of water and gas analysis, visual inspections, ultrasonic thickness measurements and coupon installation. The procedures which determines whether or not a well may require corrosion treating, along with the method by which the wells are treated, and the amount of protection which can be expected from individual treatments. Some specific problems and personal observations will be presented on the corrosion that has been found in the field which may be utilized as a guide or a better indication that a corrosive environment exists. A discussion on corrosion and a corrosion program as it affects economic, environmental and personal safety aspects should a failure occur is also presented. presented. Carbon Dioxide Corrosion Carbon dioxide corrosion is commonly called sweet corrosion. This corrosion of steel is a localized corrosion which appears as pits and gutters of various sizes and shapes. It is caused by carbon dioxide dissolving in water to form carbonic acid as water must be present to have corrosion.(1) (2) Some of the factors which affect the solubility of carbon dioxide are pressure which increases solubility to lower the pH, temperature which decrease the solubility to raise the pH and certain minerals in the water which may act as a buffer preventing pH reduction. Tn gas wells both water and condensate pH reduction. Tn gas wells both water and condensate will condense when their respective dew points are reached. Therefore, the extent of corrosion depends on many variables. A few are temperature, pressure, CO2 content, water content and flowing pressure, CO2 content, water content and flowing conditions. An excellent and more in-depth discussion of corrosion can be found in publications by the National Association of Corrosion Engineers and Production Operations, Volume 2. Production Operations, Volume 2.Detection and Monitoring Monitoring and detection of corrosion is essential for any corrosion control program. The more data you collect on your wells, the better chance you have to predict and fight corrosion. El Paso Exploration has compiled a large amount of information on their high pressure, deep gas wells located in western Oklahoma, since recognition of severe CO corrosion occurring in some wells. The program continues to expand as more information is gathered. Our detection and monitoring consists of the following steps in which a graph of each well's monthly iron count is plotted along with a posting by well of each water and gas analysis. – Water analysis is run once a month. – The gas is analyzed periodically for mol% CO2 and ppm H2S. – Corrosion coupons are installed in the flow-lines between the wellhead and production separators, however, some problems with determining the actual loss have been incurred with the coupons but a good representation is visually evident. coupons are normally installed on high volume, temperature wells and inspected annually. Figure 1 shows the coupon design. P. 27