One of the critical approaches for scale control is the proper selection and use of scale inhibitors. Laboratory tests help to select the appropriate scale inhibitor with the most common testing methods, including static bottle test and dynamic scaling loop test. Recently, Kinetic Turbidity Test (KTT) has gained increased recognition as a new testing method for scale inhibitor evaluation due to short testing time, simple sample preparation, and good reproducibility. There has been a good deal of research and studies on KTT as a technique for multifunctional scales, including calcium carbonate and barium sulfate (especially low scaling brines), halite and silicates. In addition, KTT can examine dispersant effects of polymers and surfactants on scale and other solids and can work under anaerobic conditions to give mechanistic understanding in the presence of iron. This paper discusses an alternative and efficient scale inhibitor testing method and gives insight for scale treatment chemistry and dosage by comparing and contrasting the different evaluation methods for scale inhibitors.
Scale formation during oil and gas operation is problematic. Scale deposits that build up on pipeline or heat exchanger tubes reduce flow velocities inside pipes and heat transfer. They can also cause overheating of equipment and accelerate corrosion, which may lead to equipment failure to cause expensive downtime for cleaning or repair. One of the most common and effective scale control approaches can be achieved by using chemicals.1–10 Different types of scales require different types of scale inhibitor chemistry, at varying dosages. Therefore, laboratory scale inhibitor testing is a powerful approach for screening products and determining effective dosages for the treatment.
Traditional testing methods for scale testing are dynamic scaling loop (dynamic tube block) and static bottle tests. For static bottle tests, it is easy to prepare and obtain acceptable accurate results. However, visual observation during the bottle test is subjective, and using titration or ICP (Inductively coupled plasma) for obtaining scaling ion concentration, to calculate inhibition efficiency, is time-consuming. For scaling loop tests, pressure differences across a scaling coil to indicate scale formation is utilized, which introduces many uncertainty factors to the testing results, including cleaning of coils, flow rate control, brine mixing in coils, etc. The maintenance of scaling loop equipment is also time-consuming. In recent years, the KTT method has been applied for more and more scale testing.11–15 Compared with the conventional static bottle and dynamic scaling loop tests, KTT provides information on absorbance changes with time and temperature, with up to 12 samples, in one round of testing. This provides an effective and rapid way of differentiating the performance of scale inhibitors. For unconventional type scale testing, e.g. halite and silicate, KTT can be especially helpful for obtaining good operational and reproducible data, compared with other testing methods. KTT data can also provide information on scale formation rate, in the presence of a scale inhibitor, under given testing conditions. Since dispersancy is related to turbidity, studies on the dispersancy of scale inhibitors can be performed with KTT, as this is an indicator of the capability of a chemical to disperse particles and suspend them in solutions.
