Manual and Automated Turbidimetric Methods for the Determination of Polyacrylamides in the Presence of Sulfonates
- D.L. Kuehne (Chevron Oil Field Research Co.) | D.W. Shaw (Chevron Oil Field Research Co.)
- Document ID
- Society of Petroleum Engineers
- Society of Petroleum Engineers Journal
- Publication Date
- October 1985
- Document Type
- Journal Paper
- 687 - 692
- 1985. Society of Petroleum Engineers
- 4.1.5 Processing Equipment, 4.3.4 Scale, 4.2 Pipelines, Flowlines and Risers, 5.5.11 Formation Testing (e.g., Wireline, LWD), 4.1.2 Separation and Treating
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Polymers and sulfonates are often part of the multicomponent chemical systems designed to increase oil recovery from depleted reservoirs. The objective of this work was to develop reliable, analytical methods for measuring polyacrylamide concentration in the presence of sulfonates. The need for new or improved methods arose because petroleum sulfonates caused interference with the standard turbidimetric method for determining polyacrylamides. This interference was eliminated by the addition of a butanol-extraction step to remove sulfonates.
Based on the new manual procedure, an automated method was developed for use with a Technicon AutoAnalyzer™ to reduce analysis time. The automated method was designed with four modes of operation to cover high and low polymer concentrations with and without sulfonates present in the samples. Polymer concentrations ranging from 10 to a maximum of 1,200 wt ppm [10 to 1200 mg/kg] can be measured. A unique feature of the automated method is the continuous-flow solvent extraction. Depending on the mode, AutoAnalyzer throughput is 20 or 30 samples per hour. The accuracy of the results is 5% with extraction and 1% without extraction.
Polyacrylamide polymers are used for mobility control and profile modification in EOR processes. Rapid and accurate analytical methods are needed for laboratory studies of polymer behavior and for the determination of polymer concentration in field samples. Procedures1,2 based on the turbidimetric reaction of polyacrylamide with bleach (sodium hypochlorite) are commonly used to measure the concentration of polyacrylamide in aqueous samples. In the attempt to apply these procedures to micellar solutions containing polymer, it was found that petroleum sulfonates cause interference because of both their inherent color and unknown reactions with bleach.
Two different analytical methods were examined briefly. The starch-triiodide method developed by Scoggins and Miller3 also suffered from petroleum sulfonate interference. An automated method4 involving polymer hydrolysis followed by colorimetric determination of the liberated ammonia worked well with low concentrations of sulfonates. However, any free ammonia or ammonium ions in solution caused a substantial background response. For some of the emulsion-type polyacrylamides, the background response from ammonia in the product was much greater than the polymer response.
Efforts to eliminate interferences were focused on the turbidimetric method because it was the easiest to use. Solvent extraction was selected as the best approach to remove petroleum sulfonates and oil from aqueous polymer samples. The requirements for a good solvent were that it remove the interfering components, separate rapidly from the aqueous phase, and have low water solubility. A series of alcohols and other solvents were tested; 1-butanol was found to be the most effective. Therefore, a butanol-extraction step was added to the standard turbidimetric method. Based on this new manual procedure, an automated method was developed for use with an AutoAnalyzer II (Technicon Industrial Systems). Both the manual and automated methods can be run with or without butanol extraction, depending on the type of samples.
In the turbidimetric method, polyacrylamide polymer reacts with sodium hypochlorite in acetic acid to form an insoluble chloroamide. The resulting turbidity is proportional to polymer concentration and can be measured with a spectrophotometer or turbidimeter. If petroleum sulfonates are present in the samples, they are extracted with 1-butanol that is acidified with HCl. The HCl is necessary to change the sulfonates into sulfonic acids, so that they can be extracted easily. To prevent excess HCl from interfering with the polyacrylamide reaction, the glacial acetic acid is buffered with sodium acetate.
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