An Efficient, Safe, and Practical Chemical Method for Barium Sulfate Scale Removal

Abstract Wells for the production or storage of subsurface minerals, geothermal heat, CO2 gas, or produced waters are subject to scale generation by mixing two or more incompatible components that form deposits known as scales. Prevention (inhibition) of these scales is possible in some cases. Still, unplanned and unavoidable upsets in dynamic flowing systems of produced or injected fluids will often produce solid scales obstructing flow passages in pipes and formations. The development of a novel converter or dissolver is needed to effectively return wells to operation and minimize the need for mechanical removal that involves opening the well. Initial work into highly effective scale converters has identified chemical materials and methods that significantly improve the barium sulfate scale removal process. Low-cost removal of flow-obstructing barium sulfate scales is a high priority in unconventional and conventional wells, especially when the scale contains natural radioactive ions. Our development's alpha version delivers 4 to 5 times more removal capacity while reducing treatment costs by 80% to 90%. Removal of scales is a significant expenditure for geothermal, hydrocarbon, and mining industries. Among the most troublesome scales to remove are near-pure barium sulfate scales that are resistant to most chemical removers and often contain radionuclides, usually radium ions, that are substituted into the BaSO4 scale matrix to produce a naturally occurring radioactive material (NORM). By chemical removal of barium and strontium sulfate scales, the contaminating radium ions are dispersed in the aqueous flush solution, returning the NORM activity to near-background levels of connate fluids. Mechanical removal of NORM scales requires the collection and disposal of large amounts of solids that often must be handled as radioactive waste. Development testing has centered on using environmentally safe components, mostly food-grade additives with dispersants and surface-treating chemicals with low impact based on available toxicity information. Over six hundred laboratory tests have refined the technology to a nearly ready state of being scaled up to field application. Initial laboratory comparison tests using non-stirred exposure of BaSO4 removal chemicals with mined and near-pure BaSO4 field samples (identical area-to-volume ratio) at 400 psi and 121oC (250oF). The active treating solution converts barium sulfate into fine mesh (sub 100 to 300 microns) particles dispersed by water flush or produced fluids. If the particle size is bigger a dilute acid solution is needed. The pure barium sulfate crystalline deposits before and after reaction with the invented solution. In these tests, averages of 80% of near-pure BaSO4 scale containing NORM is converted and can be dispersed and removed with water flushing, compared to 9% removal with well-known commercial competitors’ solution (DTPA) under the same conditions. Advantages of this aqueous solution include lower cost, better efficiency, applicability in broader pH and temperature ranges, limited or no toxicity, and no corrosivity to common tubular materials.