Novel Method to Quantify the Concentration of Corrosion Inhibitors in Produced Water

摘要

Production chemicals are injected downhole, at the wellhead or between the wellhead and the oil/water separation facilities. Typically, the injected fluid is a complex mixture of chemicals designed to impart several functions including (ⅰ) inhibition of asphaltene, wax and/or organic scale deposition, (ⅱ) inhibition of inorganic scale deposition, (ⅲ) inhibition of gas hydrates, (ⅳ) inhibition of corrosion, (ⅴ) scavenging of unwanted species such as H_2S and (ⅵ) enhancement of the efficiency of oil/water separation. Most production chemicals are soluble in the produced water, in the liquid hydrocarbon phase or they partition between the water and oil phases. Produced waters are either reinjected or they are treated to minimize the concentration of residual oil and production chemicals prior to discharge. There is a need for methods to monitor the concentration of production chemicals in produced water in order to optimize their process efficiency and for environmental reasons. We have developed a method, based on Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFTS), to quantify the concentration of production chemicals such as the corrosion inhibitor component in produced brines. Methods development followed three successive phases. In phase I, a procedure was evaluated in which the produced water sample is mixed with a concentrated aqueous solution of potassium bromide before drying to remove the water and DRIFTS analysis of the dried residue. The spectrum comprises absorbance bands due to infrared active salts in the brine and organic constituents including various components of the production chemicals mixture. Calibrations were constructed for a specific production chemicals mixture and a particular produced brine composition. Several absorbance bands were used to construct calibrations relating the absorbance to the concentration of the production chemicals mixture and its corrosion inhibitor component. In phase II, the effect of sample volume on determination limits was investigated. In phase III, an organic solvent extraction procedure which reduces determination limits was developed. Examples are given wherein the corrosion inhibitor is part of a production chemicals mixture which also contains a scale inhibitor and a corrosion inhibitor synergist added to a North Sea produced brine.