Advanced carbonate ladder inhibition in the North Sea via mixtures of synergistic inhibitor molecules

Fouling control of inorganic sulfates and carbonates with polymer, phosphonate, and phosphate ester scale inhibitors is common in the oilfield services industry. It is well known in which environments individual inhibitor types work best; for example, sulfonates are very effective for sulfate fouling control at low temperatures (SPE 80229) while phosphonates are much less effective under the same conditions but improve at higher temperatures (SPE 179889).

Less well understood is the potential of scale inhibitors that use synergistic interactions with blends of polymers, phosphonates, and phosphate esters to reduce chemical costs, treatment rates, and transportation logistics, resulting in a more effective scale management program with a small operational footprint.

To evaluate the performance of a selected range of blended inhibitors, ChampionX ran a trial on a water system manufactured in the North Sea, which was applying a monoethanolamine phosphonate (MEA)-type scale inhibitor and new cleaning schedules to counter a high carbonate saturation ratio in the heater (SPE 204365). The goal was to find an improved scale inhibitor formulation that outperformed MEA phosphonate in controlling the high saturation ratio of brine calcite. In this application, the fluids produced pass through a heater with a skin temperature between 90°C and 105°C.

Identify the challenge of the ladder

Studies of the synergistic properties of phosphonates and polymer ladder inhibitors show that there is potential to create blends of existing chemicals to create a formulation that exhibits superior performance over either inhibitor component alone. Four general scale inhibitors were considered that could effectively prevent scale at 105°C.

1. A polyaspartate acid, generally found thermally stable at 120°C

2. The current MEA phosphonate chemical, widely used for this kind of high temperature fouling inhibition

3. A phosphoric ester, found thermally stable at temperatures of 90°C

4. Phosphonate-functionalized biopolymer, which has shown good carbonate inhibition properties and excellent environmental properties

The objective was to develop a synergistic blend that would mitigate the legislative (cost of REACH registration) and economic (cost of new raw material product set up within the supply chain system) problems associated with the development of new classes of scale inhibitors for a relatively small market.

There are two main methods of inhibiting scale in product water.

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