Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.
A simple procedure is described for measuring instantaneous corrosion rates in brines under conditions simulating those encountered in the field. Rates of adsorption and desorption of n-dodecylamine inhibitor in mildly acidic, anaerobic brine saturated with carbon dioxide were inferred from corrosion rate measurements. Adsorption rates were also studied in brine saturated with hydrogen sulfide.
Both adsorption and desorption rates appear to be strongly dependent on concentration of the inhibitor during the adsorption period. Where adsorption equilibrium is approached slowly desorption rates in uninhibited brine appear to be very slow.
The results lead to suggested methods of improving field application of inhibitors.
Almost twenty-five years ago it was discovered that the very severe corrosion problems occurring in petroleum production and refining equipment could be petroleum production and refining equipment could be mitigated by adding small concentrations of certain classes of cationic, surface-active compounds to the fluids involved. With suitable formulation and application these products have been found broadly effective in most typical oxygen-free systems containing hydrocarbons.
Large volumes of corrosive anaerobic brine are now handled in the oil fields, especially in the United States. Somewhat surprisingly, the use of the familiar cationic inhibitors in such brines has been generally disappointing. The degree of inhibition has been limited or costly concentrations have had to be used continuously.
A principal aim of the present work was to study the behavior of cationic inhibitors in mildly acidic brines with the aim of elucidating their behavior and, hopefully, finding means to improve their effectiveness. A special aim of this work was to devise a means of studying rates of adsorption and desorption of inhibitor films.
Earlier work with oil and brine fluids from oil wells indicated that organic inhibitors function in such systems by adsorbing on the exposed metal surfaces to form very thin — possibly monomolecular — films which present a barrier to corrosion reactions.
