Organic acids, such as acetic or formic acid, are ubiquitous in produced waters from petroleum-producing basins. The chosen measurement system was a reversed-phase mode High Pressure Liquid Chromatography (HPLC). This method can overcome the matrix problem of high inorganic ion concentration in produced waters. This is possible due to the usage of a highly hydrophobic stationary phase, which is not interacting with the high amount of inorganic ions present in produced waters.
In extension to the initial publication the influence of organic acids on the hydration and gelation for zirconium and borate cross-linked fracturing systems was determined in detail. This was done with the original brine samples from different locations and with artificial brines which were doped with different organic acids at different concentrations. It could be shown that in the presence of organic acids the usage of borate cross-linked fracturing gels, which requires a high pH of 9 to 11, is impossible due to a hindered crosslinking. Only with economically meaningless loadings of basic buffers the pH could be increased high enough to achieve a weak crosslinking.
As the natural pH of produced waters in the presence of organic acids is around 4, tests were carried out with zirconium cross-linked systems. These fracturing systems, which require a low pH of 4.5 to 5, were tested in both artificial brines and the actual produced waters with organic acids. It could be shown that in the presence of 600 mg/L or 1200 mg/L organic acids a stable cross-linked gel could be achieved. This is possible even in the presence of high salt concentrations up to 250,000 mg/L.
The conclusion of this work is that in the presence of a higher concentration (from around 500 mg/L) of organic acids like formic or acetic acid the substitution of a common borate cross-linked fracturing system with a zirconium cross-linked fracturing system should be considered.