ABSTRACT

This paper presents a methodology for designing field tests to assess the relative performance of inhibitors and other chemical products, which are used to control corrosion associated with crude oil production. The same corrosion inhibitor injection points and corrosion monitoring points can be used for (1) routine operations, and for (2) field performance tests of candidate products. Field tests, which assess the performance of individual products for three phase fluids or wet gas production, require precise step changes in the chemical treatments rates in order to accurately determine the minimum quantity of inhibitor for attaining a pre-established level of performance. The approach to field-testing is applicable to all production fields. However, the candidate products must be selected, based on the chemistry of the produced fluids, including the concentration of CO2.

Downhole corrosion inhibitor treatments were also discussed. Although downhole monitoring evidenced extremely short treatment lifetimes at one field, the results cannot be construed to mean that treatments elsewhere would be ineffective. An approach was provided to enable monitoring at the wellhead to be able to assess the performance of downhole tubing displacement treatments. The use of corrosion modeling software was discussed, and comparisons were made with previously published measurements of downhole corrosion rates. Reasonable agreement was observed. However, better comparisons could be obtained with more precise and more current measurements of the process parameters and the compositions of the produced fluid and gas.

This paper also emphasized the need to quantify the concentration of biocide treatment, which arrive at the remote locations in the produced water or seawater injection systems. The concentration must be sufficient as to be effective. The application of downhole scale inhibitors was also discussed. The chemistry of the produced water, natural gas, and the injected seawater must be known in order to properly select the best candidate products, since the dissolved carbon dioxide can make a tremendous impact upon the pH, and the ability of the products to properly adsorb and slowly desorb, thereby providing scale inhibition. This paper also emphasizes the selection of the candidate chemical products, based on measured cost-performance.

INTRODUCTION

The number of papers and symposium at the annual NACE Corrosion conferences dedicated to corrosion control of crude oil production attest to the diversity of challenges, which corrosion engineers face. The challenges associated with internal corrosion are typically addressed by the use of alternate materials, coatings, or the application of chemical - corrosion inhibitors.

The first option is the use of alternate materials, such as corrosion resistant alloys (CRAs), and should be used when it is the most cost-effective option, and is practical, i.e., it can be implemented without major interruptions to production. It's used frequently for new construction or when materials must be replaced. Consider, for example, deepwater production in the Gulf of Mexico (GOM), where CO2 and HzS may be encountered. Many of the new production wells and downhole tubulars are constructed from CRAs. However, carbon steel piping is used for the crude oil and gas gathering systems on the bottom of the C~M, since it wouldn't be economical to run CRA pipelines for stretches up to 32-48 km (20-30 miles) between production facilities. This arrangement necessitates the use of corrosion inhibitors to protect the subsea pipelines, and they are applied at the subsea wellheads, through umbilicals.

The second option for controlling corrosion is throu

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