Laboratory evaluation of synergistic effect of transition metals with mineral scale inhibitor in controlling halite scale deposition

Highlights

• Combined effect of transition metals with halite inhibitors was evaluated.

• FCN is superior than PAA with a prolonged halite induction time.

• Pb²⁺ ion demonstrates a synergistic effect with both FCN and PAA inhibitors.

• Calculated inhibition efficiency is the highest for Pb²⁺ with FCN inhibitor.

Abstract

Sodium chloride (halite) has been traditionally regarded as an unconventional oilfield mineral scale, compared with more prevalent carbonate and sulfate scales. However, with the increasing productions from offshore deepwater and shale gas fields, halite scale occurrence becomes more frequent, leading to significant technical and financial challenges to productions. Although low-salinity water dilution remains the primary approach in controlling halite scale threat, chemical inhibition has been evaluated as an alternative halite control strategy due to the intrinsic issues associated with low-salinity water availability and water quality. There are limited studies concerning the combined effect of metals, especially transition metals with scale inhibitors in halite control. In this study, the combined effect of a number of transition metal ions with two common halite scale inhibitors was evaluated in a laboratory setup. It was found that among the transition metals studied, Pb²⁺ ion demonstrates a synergistic effect with the scale inhibitors evaluated by considerably extending the halite induction time. The calculated inhibition efficiency also indicates that the presence of Pb²⁺ improves inhibitor performance. Although Pb²⁺ is an environmental pollutant, an aqueous Pb²⁺ concentration of up to 10 mg L⁻¹ can naturally occur in both natural gas produced water and oilfield produced water. The operators can take advantage of the reported synergistic effect of Pb²⁺ with scale inhibitors in this study while designing field halite control strategy. The enhanced inhibition efficiency elaborated in this study can be useful in designing the halite scale control strategy, if a decent amount of Pb²⁺ is present in the produced water.