The Influence of Maleic Acid Co-polymers on the Growth and Microstructure of Calcite Scale

Abstract

AbstractAdditive-mediated crystal growth has been a large area of scientific research over many generations. In oil and gas production crystal growth modifiers (scale inhibitors) are used routinely, although their impact on the structure and morphology of the scale is often overlooked. This work presents results for the inhibition of calcite using specially prepared maleic acid – acrylic acid and maleic acid – acrylamide co-polymers. Performance tests show that the inhibitors provide effective performance against CaCO3 in both static and dynamic conditions. Additive-mediated crystallisation was then progressed at concentrations below the MIC’s. The results show significant changes in the microstructure and morphology of the crystals formed, from typical calcite rhombs in the absence of additives towards needles and aragonite structures as well the formation of almost perfectly formed "micro-rosettes". The trends in the microstructure are tracked as a function of temperature and chemical concentration and are related to the inhibitors ability to influence different crystal growth surfaces under different conditions. More significantly, dramatic differences are recorded under dynamic and static test conditions, indicating that the structures which lead to adherence and blocking of pipework during flow may be different than those which dominate under bulk conditions. The indication is that the most effective inhibitors are those which inhibit crystal morphologies which lend themselves towards adhesion and growth from metal surfaces.The synthesis and characterisation of the polymers together with calcium carbonate inhibition performance results and crystal microstructures formed in static and dynamic conditions are presented, together with conclusions on their importance when attempting to inhibit scale formation on pipeline walls in dynamic oil production systems. Previous published works in this area will be included to support the conclusions made.