RESEARCH OF THE SODIUM FORMATE INFLUENCE ON THERMOSTABILITY OF STARCH-CONTAINING CLAY DRILLING MUD

Abstract

The relevance of the work is caused by the need to preserve the properties of drilling fluids containing starchy reagents, in conditions of high salinity and prolonged exposure to elevated temperatures. The main aim of the study is to determine experimentally the temperature range and optimal concentrations of the effective use of sodium formate in drilling fluids containing starch reagents. The objects: starch-containing clay mud with different concentrations of sodium salts (sodium chloride and sodium formate). Methods: determination of filtration and rheological parameters according to GOST 33213-2014 (ISO 10414-1: 2008) after drilling fluids aging at elevated temperatures using thermal cells; conducting experiments by constructing a matrix of central compositional planning and mathematical processing of the results of experimental data. Results. The authors have carried out thecomparative analysis of the properties of clay drilling fluids containing starch reagent, using sodium chloride NaCl and sodium formate HCOONa, after a long stay of the system at high temperatures. It is shown that the nature of the salt has a significant effect on the heat resistance of starch-containing drilling fluid: sodium chloride does not provide thermostability of the solution; sodium formate allows providing heat resistance starch-containing drilling fluid to 140–160 °C. The second-order regression equations were obtained. They describe the dependence of the filtration rate and rheological parameters of starch-containing clay mud on the temperature and concentration of sodium formate. It was found that the heat resistance of starch reagent when combined with sodium formate increases due to the high solubility of the salt, which inhibits the polysaccharide hydration, and, accordingly, slows down its hydrolysis when exposed to high temperatures. It was revealed that the effective concentration of sodium salt of formic acid as a heat stabilizer in the composition of starch-containing drilling fluid depends on the temperature of application of the system: at low salt concentrations, heat resistance is ensured in the range of 100–133 °C due to good starch activity; at high salt concentrations – in the range 133–160 °C – due to the low content of free water in the system due to the high solubility of sodium formate. It was shown that sodium formate does not prevent clay swelling, but, on the contrary, is capable of exerting a peptizing effect on them.

Keywords

• polysaccharide
• destruction
• heat resistance
• mineralization
• formate
• drilling mud
• salt
• starch