Autor(es):
Nóbrega, Ana Cecilia Vieira da 
; Rocha, L. A. ; Avila, E. A. ; Martinelli, A. E. ; Melo, D. M. A. ; Sá, Maria das Vitórias Vieira Almeida de
Data: 2013
Identificador Persistente: http://hdl.handle.net/1822/25223
Origem: RepositóriUM - Universidade do Minho
Assunto(s): Oilwell; Cementing; Casing; Acidizing; Corrosion; SAE 1045
Descrição
External corrosion is one of the most common causes of oilwell casing failure. Hostile
environments can be due to acidizing treatments. Although it is common to add corrosion inhibitors
and oxygen scavengers in acidic solutions to control external casing corrosion, their real efficiency
is unknown yet. Therefore, it is important to establish how aggressive to steel are the different
hostile environments to help decide which acidic systems can be used. A comparative evaluation of
the corrosion of steel immersed in hardened cement slurries submitted to commonly acidizing
agents is suggested. The performance of Special Class Portland Cement Slurries reinforced with
polished SAE 1045 steel was evaluated by electrochemical measurements as a function of time.
Open circuit potential, polarization curves and electrochemical impedance spectroscopy were
studied. 15.0 wt% HCl, 12.0 wt% HCl + 3.0 wt% HF (regular mud acid), 10.0 wt% HAc + 1.5 wt%
HF and a simulated hardened cement slurry pore solution were used as electrolytes. The most
aggressive acid solution to plain Portland hardened cement slurries was the regular mud acid. 10.0
wt% HAc + 1.5 wt% HF electrolytes were the least aggressive ones, showing open circuit
potentials around +250 mV compared to -130 mV of the simulated hardened cement slurry pore
solution after the first 24 hours of immersion. This behavior was observed during two months at
least. Similar corrosion rates were shown between both electrolytes, around 0.01 μA.cm-2. Total
impedance values, insipient arcs and large polarization resistance capacitive arcs on the Nyquist
plots, indicating passivity process, confirmed the behaviour of the system in the 10.0 wt% HAc +
1.5 wt% HF electrolyte.
