Interaction between Polymer-Based Drilling Fluids Containing Ordinary Salts and Clay Rocks

Abstract

The study of the interaction processes between polymer-based drilling fluids and clay rocks is essential. Careful selection of drilling fluid composition will allow you to avoid such complications during drilling as the bridge over, clogging of the bottom-hole zone with cuttings, reduction of the mechanical drilling speed, differential wall sticking, a fluid wash of the wellbore walls and core plugs, and drilling fluid losses. Various salts of alkali and alkaline earth metals are often used as clay swelling inhibitors, which can cause changes in the rheological properties of the drilling fluid on their addition at high concentrations. The paper presents the experimental results of determining the swelling value of the clay mineral illite in drilling fluids prepared on the basis of cationic (K-6729) and anionic (EZ-MUDDP) polymers with the addition of inorganic salts – potassium chloride, sodium chloride and sodium silicate. The rheology of the tested samples deteriorates when salts are added to polymer solutions. This fact is explained by the hydration of salts and water molecules binding to the hydration shells of electrolyte ions, as well as the destruction of hydrogen bonds in water's structure with an increase in its molecular mobility. The paper demonstrates that in a sodium silicate solution, the hydration and swelling of illite are significantly inhibited. Thus, the change in the linear dimensions of pressed clay powder tablets with different permeabilities in distilled water, potassium, and sodium chloride solutions amounted to 30%, while in sodium silicate solution it did not exceed 6.3%. However, compared to potassium and sodium chlorides, when sodium silicate as a clay inhibitor, then the rheological characteristics of the drilling fluid decrease less significantly.