Dynamics of changes in static secondary filtration of drilling muds depending on the content of acrylic reagents

Abstract

The cause of hydration and swelling of clay minerals in the rock massif is most often the filtrate of water-based drilling fluids. The volume of the filtrate depends on the pressure drop in the well, porosity and permeability of the rocks. In such cases, there is a need to create a dense impermeable barrier on the walls of the well, and the filtration crust can well serve as such a barrier if its permeability to the filtrate is lower than the permeability of the rock massif. During the circulation of the drilling fluid, favorable conditions arise for the formation of a filtration screen, and to ensure its low hydrodynamic characteristics, reagents are added to the drilling fluid to reduce the filtration index. The article considers the effect of reagents based on acrylic polymers, which serve as flocculants, regulators of rheological parameters, stabilizers of filtration and thixotropic properties, in particular POLYPLUS, SYPAN and POLYGUM. Laboratory studies were conducted to determine the dependence of the filtration index under static conditions and the thickness of the filtration crust on the content of these reagents and it was found that SYPAN at a concentration of 0.8–1.0% best reduces the filtration index to 3 cm3/30 min, with the addition of POLYGUM at a concentration of 0.8–1.0% and POLYPLUS at a concentration of 0.07–0.1% the filtration index decreased only to 4–7 cm3/30 min. To study the influence of the studied polymeric chemical reagents on the formation of the properties of the filtration crust, in particular, thickness, permeability, porosity, density, experimental studies were performed on models of filtrates of fresh, mineralized and salt-saturated drilling fluids, during which the efficiency of the reagents was evaluated by the secondary filtration index of the crust. The addition of POLYPLUS contributed to a decrease in secondary filtration by approximately 1.5 times and, characteristically, for the salt-saturated solution model this indicator is almost three times lower compared to the models of fresh and mineralized solutions. Similar laboratory studies of the influence of SYPAN and POLYGUM confirmed the regularity of the previous experiments. Based on the obtained values ​​of secondary filtration, calculations of the permeability of the filtration crust were performed, which allow choosing a reagent that ensures the formation of its quality indicators and significantly reduces the intensity of the filtration process.