Investigation of the electrochemical phenomena associated with a corroding oil well and the effects of insulated couplings

Abstract

The purpose of this investigation was to obtain a correlation of the internal electrochemical corrosion occurring a producing oil well with other measurable electrical phenomena and to construct and evaluate insulated couplings and their effect in reducing corrosion failures. Insulated couplings were constructed at Texas A&M University however, commercially available insulated couplings were installed in a field test well. Laboratory tests to show the effect of the interior surface condition of the tubing on the electric logs obtained are described and correlated with the field tests. The SP (Spontaneous Potential) curve was found to provide a reliable method of locating anodic areas. The potential profile was shown to be unaffected by external currents but such currents may raise or lower the gross potential of the profile. The theory of corrosion and its control are reviewed. The theory of electric well logging and the possibility of its application for detection and control of corrosion are discussed. Insulated sucker rod and tubing couplings were installed in a field test well. The frequency of tubing and rod failures before and after installation of the couplings is compared to the failure history of adjacent wells in the area. The presence of insulated couplings appeared to reduce the tubing and rod failures, although the time of observation has been too short for conclusive results. The internal currents as indicated by the SP curve were also reduced. Initially, the location of the insulators could be determined by the SP curve. Commercially available logging methods known as the Lateral Log and the Dia-Log were also able to locate the insulated couplings, the former by the electrical resistivity of the coupling, the latter by internal profile detail.