Calcium carbonate scale control during Alkaline Surfactant Polymer (ASP) flooding is a recognised challenge due to mixing of the high-pH ASP waters with reservoir brine. In most cases ASP flooding is aimed towards reservoirs containing low-calcium and magnesium formation waters, and previous reports have concluded that in such cases production well scaling can be effectively treated with conventional scale inhibitors. For reservoirs containing moderate to high levels of alkaline-earth metal ions in the produced waters, such as reservoirs that have been flooded with sea water, the scaling risk is considerably exacerbated, with the result that conventional scale inhibitors are essentially ineffective except at very low sea-water fractions in the produced water mixture following ASP breakthrough.

This paper presents the results for an extensive research and development project firstly to examine alternative inhibitor chemistries and then to develop more complex formulations containing synergistic additives to improve calcium carbonate scale control in high sea-water content produced waters in ASP floods. The developed formulations are shown to control the scales effectively with water chemistries that were previously shown to be beyond the efficacy of conventional inhibitors (negligible effect at 500 mg/l).

The paper will present and discuss the different types of scale inhibitor chemistries examined, the nature of other chemistries and additives examined in combination with the scale inhibitors, and will describe the synergistic effects observed between the different chemicals.

Results from this extensive series of laboratory tests will then be presented showing the considerable benefits of the new formulations and demonstrating how scale inhibition can now be achieved under these extreme and previously uncontrollable producer well conditions. The paper will also introduce the challenges and present an overview of the case study that initiated this development program.

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