Researches On Synthesis And Mechanism Of Calcium/Magnesium-Tolerant Polymer Filtration Reducer

This paper mainly aims at reducing the filtration loss of water-based drilling fluid and improving the deficiency of water-based drilling fluids in anti-calcium,magnesium,and other high-valent metal cations.We proposed a new method to prepare a novel polymeric fluid-loss control agent through optimizing the polymer molecular structure.With the aqueous solution polymerization method and 2-vinyl acrylamide-2-methylpropane sulfonic acid,acrylamide and 4-vinylpyridine with protonation effect as the raw materials,a polymeric additive agent PAAV for water-based drilling fluid was synthesized,which had a good anti-calcium and magnesium performance.Single-factor analysis and orthogonal test were performed to determine the optimal experimental conditions.The API fluid loss of drilling fluid in the composite brine were selected as the main evaluation index,combined with the change of viscosity retention and intrinsic viscosity during the aging test in the drilling fluid system.The molecular structure was characterized using nuclear magnetic resonance spectroscopy,infrared spectroscopy,elemental analysis and other analytical methods.Intrinsic viscosity analysis determined the viscosity average molecular weight of PAAV.In this way,the comprehensive performance of PAAV in water-based drilling fluids was tested and its mechanism was discussed using instrumental analysis method.The experimental results showed that PAAV has an approximate viscosity average molecular weight of 1.15 million g/mol and it has good ability in reducing filtration loss under high temperature and high salinity.Even under the condition of up to 1.5% calcium chloride and magnesium chloride,2.0% PAAV in composite brine did not delaminate after being aged at 150-180°C.This indicates that PAAV offers a good protection to the colloid under high temperature.This is due to the fact that PAAV can adsorb on the surface of clay particle through both van der Waals forces between pyridine rings and electrostatic force after the protonation of the pyridyl group.The adsorption of the polymer on the surface of the clay particles can effectively prevent the coalescence of clay particles under high-temperature,promising a more reasonable particle size distribution.At the same time,PAAV can effectively increase the Zeta potential of the drilling fluid system to stabilize the colloidal dispersion system,and finally achieve the goal of lowering the filtration loss under high temperature and salt concentration.