Advances in Inorganic Scale Prediction – Development and Validation of a Kinetic Model

Abstract Understanding and predicting the impact of chemical kinetics and metastability on inorganic scaling in oil and gas production systems has been a significant challenge, particularly in many Arabian Gulf production environments where many systems are only moderately scaling. Development of a kinetic model can lead to significant improvements in predicting risk, occurrence and location of inorganic scaling in oil and gas production systems, resulting in significant cost savings when designing scale mitigation treatments. A combination of fluid flow dynamics (FFD) modelling and laboratory tests were used to understand the influence of kinetics and metastability on the location and propensity of scale formation in oil and gas production systems. Extensive laboratory works were conducted using small scale high shear laboratory experiments and larger scale "pilot rig" tests under field representative conditions designed using CFD (computational fluid dynamics) modelling to recreate field flow environments using conditions prevalent in both Arabian Gulf and North Sea production environments. Subsequent validation of results was obtained by comparison with field experience. In moderate or low scaling environments, under conventional (lower shear/lower turbulence) flow conditions mineral scale often either isn’t seen in the production system or forms high up in the production tubulars even though the produced fluids are oversaturated further upstream. However, if the well inflow patterns are modified (e.g. by the introduction of ICDs, ICVs and / or slotted liners), this can change the local fluid flow dynamics such that the location of inorganic scaling moves further downhole, often leading to scale formation in the most undesirable places – such as around SSSVs, ICDs/ICVs, ESPs etc. The impact of increases in shear and turbulence can also have important consequences for chemical scale inhibitor treatments or other remedial treatments, which now may have to be applied further downhole in the wells as opposed to in the production tubulars or topside equipment. The impact of kinetics and fluid flow dynamics on inorganic scaling can also require increased volumes of inhibitor to prevent scaling. This paper focuses on the development of the first truly kinetic model for scale prediction, including fluid flow dynamics considerations and the concept of the Critical Saturation Ratio. The results presented here demonstrate how careful understanding of FFD, and use of a kinetic model can lead to significant improvements in predicting the risk, occurrence and location of inorganic scaling in oil and gas production systems, resulting in significant cost savings when designing scale mitigation treatments.