Chemical solutions for restoring scaling-induced injectivity impairment in offshore produced water re-injection

Produced water re-injection (PWRI) is a promising and sustainable strategy to manage substantial quantities of produced water for subsurface energy production systems. This approach offers an alternative to the environmentally harmful practice of marine disposal. Nonetheless, produced water re-injection may lead to considerable reductions in the injectivity. The injectivity loss can be attributed to several factors, including inorganic scaling, which can obstruct the flow pathway through porous media near the wellbore as well as subsurface facilities (e.g., tubing). Scaling can also contribute to the formation of mixed organic-inorganic schmoo-like complexes. Iron-containing (Fe_xS_y, Fe_xO_y-Fe_xO_yH_z), carbonate-, and sulfate-based scales (e.g., BaSO₄, SrSO₄, and CaCO₃) are the primary precipitates that have disruptive effects during PWRI scheme, especially in reservoirs suffering from microbial souring activities. In this work, we first screened the mineral scales that may form under the relevant re-injection conditions using the composition of produced water and seawater samples from the Danish North Sea. Subsequently, we assessed the efficiency of a commercial scale inhibitor against the scaling of targeted mineral phases through a series of batch experiments, followed by the development of a model to simulate its inhibitory performance. To reduce the precipitation or deposition of different minerals in water injection applications, we evaluated the combined effect of adding other chemicals (i.e., an acid, an oxidizer, and a chelating agent) to the injection water along with the scale inhibitor. To do this, we described the relevant mineral-aqueous interactions (dissolution, precipitation, and solution complexation) in PHREEQC. This predictive model represents an alternative to time- and resource-intensive experiments and may aid in achieving optimized chemical recipes required to mitigate mineral scaling in water injection systems under various physiochemical conditions. This work can contribute to the development of more sustainable and efficient strategies for managing produced water, ultimately helping to reduce the environmental impacts of hydrocarbon production.