Introduction

ABSTRACT

Carbon dioxide corrosion models, including empirical, semi-empirical, and mechanistic ones, have been developed to predict corrosion of carbon steel for the past several decades. Although the mechanisms of carbon dioxide corrosion are well understood through laboratory investigations, it is still challenging to apply corrosion models to predict corrosion in actual oil and gas fields. This paper will discuss the applications of corrosion models in oil and gas production, which include calculating corrosion allowance and making prediction of facilities life in the design phase, providing guidance in corrosion management in the production phase, understanding the results obtained from in-line pipeline inspection tools, determining inspection frequency, and serving as a tool for improvement, trouble-shooting, and failure analysis.

The internal corrosion of carbon steel represents a significant problem for the oil and gas industry. Although high cost corrosion resistance alloys (CRAs) were developed to resist internal corrosion, carbon steel is still the most cost effective material used in oil and gas production. It is very important to develop an integrated corrosion prediction approach for optimizing the use of carbon steel in corrosive service while ensuring the operational integrity of equipment and facilities.

Both corrosion models and laboratory testing are frequently used in this industry to make lifetime predictions of facilities using carbon steel and further to make decisions on materials selection. Corrosion models, including empirical, semi-empirical, and mechanistic ones, have been developed to predict corrosion of carbon steel for the past several decades1-6. Corrosion models can provide engineers quick and economical corrosion predictions. Most of the models were validated by either certain laboratory data or field data. Empirical and semi-empirical models usually provide reasonable predictions in their validation range and poor predictions out of their range. Mechanistic models generally can extrapolate the conditions out of the validation range and remain accurate to a certain degree. Consequently, one should always understand the validation range and limitations of the models to not misuse them. Although part of corrosion mechanisms are well understood in lab investigations, it is still challenging to apply lab short-term testing results and corrosion models to predict corrosion of facilities for twenty to thirty years of service due to the complexity in production operations.

A reliable corrosion model validated by laboratory and field data was developed by ExxonMobil* to apply for corrosion predictions in the oil and gas production. This paper discusses the corrosion prediction model and how to apply this model to oil and gas production.

Model Overview

Corrosion prediction model is one of the key components of an integrated approach for corrosion prediction. This integrated approach enables the optimal use of carbon steel in corrosive service for downhole, pipeline, and facilities applications. The approach is increasingly important, due to increasing production from unconventional resources, such as highly sour gas fields, and the need to effectively manage the integrity of existing resources. The software implementation of this corrosion prediction model, named CorrCast (referred as the software in this paper).

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