Evaluation of Scale Dissolver Products for Near-Wellbore Applications

Abstract Scale dissolvers have been widely used to remove mineral scales from flowlines, tubing, wellbores, and near-wellbore formation regions. When developing a scale dissolver product, several aspects—such as the product's corrosivity, application temperatures, compatibility with brines and other production chemicals, and the byproducts formed following scale dissolution—must be considered in addition to the product's effectiveness in dissolving mineral scales. The use of scale dissolver products in near-wellbore regions to remove scale and repair formation damage caused by scale deposition and the combined use of a scale dissolver and a scale inhibitor squeeze treatment are reported in the literature and have shown success in field applications. The success of such applications relies not only on the selected scale dissolver's dissolution performance but also on its formation damage potential. This paper presents two-phase coreflood studies that were conducted using reservoir conditions for two newly developed scale dissolver products (a carbonate dissolver and a sulfate dissolver) that specifically target near-wellbore reservoir applications are presented. The potential formation damage capacity of these scale dissolver products was evaluated by studying brine and oil permeability and injectivity before and after injection of the dissolver package and various effluents from the core flood tests during different stages. The effluent pH profile and the concentration profiles of calcium (Ca2+), magnesium (Mg2+), barium (Ba2+), strontium (Sr2+), and iron (Fe2+) ions were examined to understand the interaction between the formation rock and the scale dissolvers. The corrosivity of the dissolvers on various metals was also evaluated. The dissolution performance of the carbonate dissolver and the sulfate dissolver in removing, respectively, calcium carbonate and barium sulfate was evaluated. The results showed that neither dissolver product caused formation damage to the sandstone core under the conditions tested. The dissolution capacity tests suggested that the carbonate dissolver can dissolve approximately 123 g of calcium carbonate per liter, and the sulfate dissolver can dissolve approximately 30 g of barium sulfate per liter of a 25% diluted product.