Ionic effects on silica precipitation in acidic solutions

Abstract

In the upstream petroleum industry, silica precipitation during the matrix acidization of sandstone reservoirs has become a serious problem that potentially causes significant losses in the permeability of reservoirs and oil productivity. This research has aimed to study the influence of salts and ionic strength on the precipitation behavior of silica in highly acidic circumstances. A number of salts were used to investigate the growth of silica particles and the aggregation phenomena. The ICP/MS and Light Scattering results indicated that the presence of salts can accelerate silica particle growth and that the different salts promote particle growth rate in the following order: AICI₃ > CaCl₂ > MgCl₂ > NaCl > CsCl for chloride salts and Nal > NaBr > NaCl ~ NaNO₃ for sodium salts. The silica particles undergo exponential growth with time, and the evolution of particle sizes can be well-simulated by using the reaction-limited aggregation (RLA) model under the framework of a geometric population balance equations. From UV-Vis experiments, it was found that the monosilicic acid disappears very rapidly from the solution and the disappearance rate is third order with respect to the molar concentration of monosilicic acid. It was also found that disappearance rate constants, particle growth rate constants, and collision efficiency increase exponentially as a function of ionic strength.