developed to retard the acid corrosion of low carbon steel coiled tubing ..... The authors would like to thank Anthony Pearson (SGR), Dmitry Eskin (DBR) and Tim ...
Paper No.
4114
Effect of surface roughness and flow on corrosion inhibition of coiled tubing steel under matrix acidizing conditions
Evgeny Barmatov, Trevor Hughes, Michaela Nagl Schlumberger Gould Research High Cross, Madingley Road Cambridge, CB3 OEL, UK
ABSTRACT The effect of surface roughness on the corrosion behavior of low carbon steel in 4M hydrochloric acid at 80°C in the presence of corrosion inhibitor molecules has been examined using rotating cylinder electrodes under laminar (5 rpm) and turbulent (6000 rpm) flowing conditions. Glass bead blasted (BB) metal coupons as well as samples with P240 or P1200 grit surface finishes were studied. Rotating cylinder electrodes were used to simulate the effect of flow velocity on pipe corrosion. The corrosion rate and cathodic current density were determined by potentiodynamic polarization, linear polarization resistance, and electrochemical impedance spectroscopy. A commercially available corrosion inhibitor “A” comprising a mixture of polymerizable molecules (acetylenic alcohols), an oily phase and nonionic surfactants was used. Under laminar and turbulent flow conditions, the inhibited corrosion rate decreases in the following order: Bead blasted > P240 > P1200. The lowest corrosion rate is established on smooth surfaces (Ra =0.14m and 0.63m) and the highest rate on the rougher surface (Ra=5.26m). Turbulent flow has different effects on smooth and rough surfaces. On smooth surfaces (Ra≤0.63m), the corrosion rate slightly increases with flow velocity which may be attributed to a decrease in the density of hydrogen bubbles formed on the surface of the metal and corrosion occurs in the diffusion sublayer. However, when the surface roughness (Ra=5.26m) is sufficient to interfere with the diffusion boundary layer (~2m at 6000 rpm), turbulent eddies enhance the flow-induced erosion of the inhibitor film and an increase in flow velocity results in a stronger increase in corrosion rate. For both flow regimes, the effect of exposure time on corrosion rate, open-circuit corrosion potential and the value of electrochemical double layer capacitance were studied. Key words: corrosion, surface roughness, laminar and turbulent flow, flow induced corrosion, corrosion inhibitors, hydrochloric acid, matrix acidizing, Oil & Gas industry
©2014 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084. The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.
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INTRODUCTION Matrix acidizing of oil and gas reservoirs is a widely established technique to increase hydrocarbon production by the partial dissolution of reservoir rocks and fine particles which may have been introduced during drilling1. Either organic acids such as acetic acid or mineral acids such as HCl or HCl/HF mixtures are injected into the well at high concentrations. For this application, corrosion inhibitors are enabling because uninhibited matrix acidizing treatment fluids would induce severe corrosion of downhole equipment. A broad range of organic film-forming corrosion inhibitors have been developed to retard the acid corrosion of low carbon steel coiled tubing through which the acidizing fluids are injected. Depending on the injection rate, flow velocity and surface texture parameters may have a profound effect on the rate of material corrosion. In this paper we discuss the effect of surface roughness on the corrosion behavior of low carbon steel exposed to 4M hydrochloric acid at 80°C in the presence of corrosion inhibitor molecules under laminar and turbulent flow conditions. EXPERIMENTAL PART Materials All electrodes for electrochemical testing were prepared from field grade tubular goods. Coiled tubing HS80 low carbon steel was used. The composition of this steel is 0.1-0.15% C, 0.6-0.9% Mn,
