Socrates-B
also assists in determining the viability of carbon steels versus
CRAs through a rigorous evaluation of general corrosion susceptibility
of steels, with or without inhibition in the operating environment.
This evaluation is, however, not applicable to stimulation acids,
since all steel utilization in acidizing environments inherently
involves use of corrosion inhibitors. The system determines a
steel corrosion severity index, a measure of the overall corrosive
severity of the environment. The Steel corrosivity model employed
in Socrates-B is a subset of a more comprehensive prediction program
(Predict™) developed at
InterCorr.
In
material selection it should be realized that conventional steels
can be significantly more economical than CRAs in low severity
environments or in greater severity environments when used with
proper chemical inhibition. Therefore, before considering CRAs,
it is important to first evaluate whether steels can be used in
oilfield environments without being susceptible to sulfide stress
cracking.
Socrates-B
uses a large number of parameters to determine the steel corrosion
severity index. The system uses the de Waard - Milliams' CO2-based
corrosion prediction model to obtain an initial assessment of
corrosion severity in carbon steels in injected water environments
without aeration. This estimate is modified to account for the
effects of other factors such as temperature, H2S, chlorides,
velocity, oxygen and inhibition. Relevant parameters in steel
evaluation include:
Environmental
severity, a measure of general corrosivity of the operating
system, is computed for completion fluids and injected waters
as a function of applicable parameters, such as:
- Acid gas
partial pressures
- Chlorides
- Maximum
operating temperature
- pH
- Fluid velocity
- Aeration/chlorination
- Flow type
- Inhibition
methods and efficiency
