The corrosion and erosion predictions involve verification or derivation from the parameters in the Basis of Design for new oil and gas developments. The field design and operating data are partly developed from reservoir analyses, flow simulations, and thermodynamic models. These models provide necessary data to obtain the parameters controlling corrosion and erosion. One responsibility of a materials or corrosion engineer is to assure that engineers in the other disciplines develop the field specific information that is required for materials selection and corrosion control.
With the current development of corrosion models the limitations in the accuracy of the corrosion prediction is often due to the limitation in accuracy of the input data, rather than the accuracy of the corrosion models themselves. This paper will discuss the types of operational and environmental parameters that are used for development of the corrosion/erosion control philosophy. It will discuss variations in these parameters from field to field and the common pitfalls in developing this data. The corrosion models are not expert systems and their use requires a sound understanding of the corrosion risks and the common pitfalls.
The field operating history sometimes provides effective performance and field parameters that do not agree with laboratory testing. Since most corrosion prediction techniques are based on laboratory test results, they may miss these cases in predicting field performance.
The paper will discuss corrosion control of production, process, and transportation facilities. The information required for internal corrosion control of multiphase gas pipelines is described.
The proliferation of corrosion prediction models with user friendly software has produced a new breed of corrosion engineers, some who have little formal training or experience in corrosion. While corrosion prediction has become simpler, the complexity of the corrosion related issues and the magnitude of the corrosion related economic impact have continued to increase. Each oil and gas field presents unique circumstances that must be understood and incorporated into the corrosion prediction, materials selection, and corrosion control systems. Applying the same corrosion control solution universally will not produce reliable, low-cost oil and gas production facilities.
CORROSION/EROSION PREDICTION
The Water Production Rate
Oil Production Water production rate (water cut) is an important parameter that controls corrosion rates. It must be included to predict corrosion rates in oil and gas production. In oil service, the water cut invariably increases with time. In the design phase, water cut profiles are predicted as part of the reservoir modeling. Predictions consider production of both formation waters and injected waters. During operations, the water cut predictions are refined with empirical information received as part of production data. While these predictions or extrapolations are adequate for an entire field, they have larger variability for single wells.
Below a critical water cut in oil production, the corrosion is mild but increases at higher water cuts. No corrosion control (addition of corrosion inhibitors) is often practiced in oil fields until the water cut exceeds this critical value. Inhibition may be delayed until after corrosion has been detected (e.g. penetrated 10% of the wall). However, after corrosion occurs, inhibition is much more difficult to achieve, probably because of the exclusion of the inhibitor by the corrosion products, or because of the presence of localized corrosion, or because of increased surface area.
Reliance on oi
