One of the challenges in operating oil & gas wells with production of very saline formation water is preventing and controlling the onset of scale precipitation and deposition. The reason is that operators often face scale deposits of not only common minerals such as carbonates and sulfates, but also much more significantly sodium chloride (halite). Halite scales in oil and gas wells can significantly reduce production and generate severe safety issues. Current industry practice includes fresh water injection for halite control and application of classical inhibitors aimed for reducing common scales independently. The operation cost of fresh water injection is getting higher, which makes the halite inhibitor more attractive. Poor stability and brine incompatibility, however, have made viability of such inhibitors to be fairly limited. Need for a multifunctional scale inhibitor to combat both halite and common scales is of paramount significance in optimizing operational costs.
Multiple methods had been involved in the development and investigation of the multifunctional inhibitor for controlling both halite and common scales. The static jar tests were used to evaluate the halite inhibition performance of the polymer component of the multifunctional product. Thermal stability was examined for the new polymer by thermogravimetric analysis and assessment of the thermally aged polymer. Divalent ion tolerance was also checked for the new polymer during the development of the multifunctional product. For the developed multifunctional scale inhibitor, kinetic turbidity test was undertaken to investigate its kinetic behavior to prevent halite formation at different concentrations, temperatures, and brine compositions. Meanwhile, dynamic scale loop was adopted for evaluation of the product to prevent formation of the common carbonate and sulfate scales.
A unique polymeric scale inhibitor was developed based on a carboxylate-sulfonate copolymer which exhibited excellent hydrolytic and thermal stability up to 350°F (177°C) and was tolerant to waters containing high levels of divalent metal ions. The development was targeted on inhibition of multiple types of scales particularly halite. The product showed successful performance on halite control in both lab experiments and the field trial. Besides, the product exhibited efficiency to mitigate the regular carbonate and sulfate scales in lab experiments and field monitoring. In this paper, we will present and discuss benefits and limitations of new chemistry in comparison to other known methods.
This work provides an in-depth overview of challenges in managing halite and regular carbonate and sulfate scales in salt-saturated formation brines. It will also present a novel multifunctional polymeric scale inhibitor that is effective in managing such mineral scales. Impacts on reducing fresh water injection and improving production efficacy will be discussed for the benefits of operators and engineers.