Interrelationship of Weak Organic Acids, Bases, pH and HPLC Analysis Method in Produced Waters

Abstract

Weak Organic acids, such as acetic or formic acid, are ubiquitous in produced waters from petroleumproducing basins. Although the absolute concentrations of individual short-chain acids vary over many orders of magnitude the concentration can reach up to 1000 mg/L or more. It is known that weak organic acids influence the pH and alkalinity of a given water significantly, because they act as a buffer. Therefore the hydration and gelation of Guar based fracturing fluids could be affected. As the industry trend is to use more produced water as a base fluid for fracturing fluids, it is of interest to measure the concentration of different weak organic acids in produced waters and determine their influence on the hydration and gelation of fracturing fluids. The chosen measurement system was a HPLC system with a standard hydrophobic C18 column and sodium dihydrogen phosphate as mobile phase. The method was calibrated for formic acid, acetic acid, propionic acid and butyric acid, as these for weak organic acids are the most common naturally occurring species. With this analytical method we were able to detect and determine the weak organic acid concentration in different produced waters up to a few mg/L. The high concentration of sodium and chloride ions could cause a matrix problem and hinder the correct analysis. In order to eliminate this influence the reversed-phase method was chosen. By this it was possible to detect also low concentrations of organic acids in high salinity produced waters.