A pilot scale study into the
feasibility of applying magnesium anodes to the cathodic
protection of well platforms and well casings, was carried out
by Saudi Aramco in the offshore Safaniya field in the period of
1998-2000. There are currently 200 production platforms,
covering area of 750 sq km, in which there is no power supply
available for impressed current cathodic protection (ICCP).
The well platforms are protected
by aluminum galvanic anodes. These galvanic anode systems are
designed with a 25-year life expectancy, providing a minimum
structure-to-water potential of -0.90 Volts with reference to a
Ag/AgCI electrode.
Down-hole logs conducted with a
Corrosion Protection Evaluation Tool (CPETTM) were run on
several wells. This revealed influence of cathodic protection
from the aluminum anodes through the shallow corrosive
formations, down to an average depth of approximately 760 m
(2,500 feet).
Thirty percent of the well
casings have experienced leakages due to the presence of
corrosive formations at depths between 760-1220m (2500-4000
feet). It was considered that the higher driving potential of
1.7 volts magnesium anodes might provide protective current down
to these depths, resulting in cathodic protection of the well
casing and preventing further failures.
