Background
Internal corrosion of oil and gas wells and pipelines made form carbon steel is always associated
with the presence of water, and the likelihood of corrosion generally increases with the volume
fraction of water. When the walls of the pipeline are wetted with oil, no corrosion is possible. In
addition, it has been suggested that some components in the crude oil could have inhibitive
properties, as well as help in obtaining more protective films. When the pipe wall becomes water
wet corrosion is possible. Other main factors which are important for water wetting and
corrosion are:
- Water chemistry
- Crude oil composition
- Additives (corrosion/scaling inhibitor, DRA, etc.)
- Pipe wall surface state (scales, films, etc.)
- Flow regime and velocity, etc.
In the past, the effect of these parameters on water wetting has been considered only in a
qualitative sense. Understanding of water wetting is one of the most important missing links in
our current overall understanding of internal corrosion of oil gas production and transportation
facilities made from carbon steel.
Water Wetting in Oil-Water Flows
A project sponsored by Saudi Aramco is under way since 2004, which includes an experimental
investigation and numerical modeling of water wetting and CO2 corrosion in large diameter,
horizontal and inclined oil-water flow, by using various crude oils.
The aim is to investigate the effects of crude oil type, water cut, pipe inclination and flow
velocity on water wetting. Five different techniques are used:
- traversing high frequency impedance probe
- flush mounted wall conductance probes
- fluid sampling
- visual recording
- corrosion monitoring by using ER and iron counts
The five different measurement techniques have already been successfully tested and used with
LVT200 oil and different crude oils in our current water wetting project sponsored by Saudi
Aramco. As an illustration, Figure 1 shows the phase wetting map for the LVT200 oil-water twophase
horizontal flow. Three types of phase wetting regimes were detected: stable water wetting,
intermittent wetting and stable oil wetting. It is interesting to observe that for this oil and for this
inclination the transition from intermittent wetting to oil wetting is approximately 1.5 m/s. No
corrosion was observed for an oil-wet regime while corrosion rates measured in intermittent flow
regime were half those measured in for stable water wetting. With different inclinations and
different oils this behavior changes. These preliminary results confirm that water wetting is a
complex phenomenon which has a large influence on the corrosion rate; however they also
demonstrate that we have already developed the necessary tools to conduct successful water
wetting experiments under realistic flow conditions with real crude oils.
A 3 year, multi-company JIP was initiated in 2006.
Deliverables
- Improved understanding of water wetting and the key factors affecting it
- A small scale benchtop apparatus for testing of water wetting
- Full reports (every six months) documenting the results, analysis and outlining future
work
- A database of water wetting and multiphase flow data which can be made available to
other software developers under by special agreement
- An updated generic model of water wetting in oil/water two- and gas/oil/water threephase
flows be implemented into MULTICORP shared by all the sponsors
- A plug-in water wetting module particular for each crude oil, compatible with
MULTICORP and available exclusively to the individual sponsors
