Applications and Laboratory Studies of a New Class of Silica Polymerization Inhibitors of Bio-renewable Origin

Abstract

Silica precipitation during a sandstone acidizing treatment or its subsequent deposition post-treatment can negate the effectiveness of said acid treatment. Moreover, the removal of tenacious silica scale from a wellbore can sometimes result in matrix damage as a result of injecting the dissolved silicon into the formation. While this problem is well-known, effective solutions continue to be sought to sustain mature, hydrothermal, and siliceous wells that suffer from fines migration. Geochemical reactions operative in siliceous formations can induce various processes, such as silica migration, diagenesis, or hard scale. Laboratory investigations focused on preventing the formation of silica have identified a new class of silica polymerization inhibitor (SPI). The SPI mechanism is disruption or retardation of the condensation and polymerization of silicic acid monomers and oligomers and the ultimate growth of amorphous silica. Aluminum, commonly present in clay and feldspar minerals, can interfere with the SPI, so its effect has been studied. Dissolved Al 3+ in the fluid must be regulated with the use of chelating agents to prevent precipitation, along with the silicon-SPI complex, at pH levels of interest in acidizing operations, namely <4. Most effective acidizing treatments employ HF formulations, with HCl or organic acids, to dissolve the silicate minerals or scale in the near-wellbore region; hence, these studies are directed toward this application.The SPI described in this work is a naturally occurring material of low molecular weight (MW) that effectively maintains in solution total dissolved silicon concentrations of up to 3,000 mg/L (0.12 M) below 2 pH, where minimal precipitation has been observed. Minimization of silica precipitation with typical concentrations of 1,000 to 2,000 mg/L of SPI was attained at <4 pH. At this and lower pH levels, nearly constant silicon concentrations of 2,400 mg/L were maintained. These findings are significant to maximizing resource recovery because they allow the operator to consider alternatives for treatment processes geared toward higher-temperature wells, fracture acidizing, and expansion of the pH range of treatment fluids.