Barium sulphate surface deposition kinetics and inhibition in dynamic flow systems

This research work focuses on scale kinetics in real field complex brines using two complementary laboratory techniques; static bulk precipitation tests and dynamic surface deposition capillary cell tests. All experimental results are backed up by theoretical scale predictions. This study focuses on the barium sulphate system in complex solutions. It explores the effect of temperature (25 °C, 50 °C and 75 °C), and the resulting saturation ratio (SR) of barium species active concentration on the barium sulphate formation. The effect involves both static bulk precipitation and surface deposition using a dynamic flow system. This work systematically shows that the predicted saturation ratios, at different temperatures, do not seem to control the surface crystallization in a barium sulphate system once heat is applied. At room temperature, the saturation ratio was predicted to be the highest while the observed bulk and surface induction periods are largest. On the other hand, at 75 °C when the saturation ratio was predicted to be the lowest, the observed bulk and surface crystallization induction periods were shortest. The surface morphology of scale crystals is also affected by the saturation ratios resulting from temperature differences rather than the smaller differences in SR due to mixing ratios within each temperature applied. The novelty of this research work is primarily around the detailed investigation of the surface nucleation/scaling period, and the mechanism of growth. In addition, the barite/scale surface kinetic investigations supported by thermodynamic theoretical calculations and static bulk tests to explain surface kinetics. The advantage of this setup facilitates a uniform development of scale thickness along a test capillary with respect to the differential pressure drop across it. A mathematical relation (Hagen–Poiseuille) which links the average flow velocity in the pipe (Q) to the pressure drop Δp across a circular pipe of length (L) was used. The results show the scale thickness increase rate. In addition to assessing the barium content, this work is also focused on the effect of other different variables (saturation ratio (SR), mixing ratio, temperature, flow rate, residence time, and surface condition) on the scaling kinetics and final crystal surface conformations. As the main precipitate, on stainless steel surface substrate, the effect of free active barium cations was successfully studied across a wide range of saturation ratios using the dynamic flow loop rig. In this regard, the barium content was varied from 0 ppm - 150 ppm through 20 ppm, 50 ppm, 80 ppm and 100 ppm at 75 ᵒC. The surface induction period and the total cell blockage time were used to assess the effect of barium ions in real field brines. The data analysis show that the surface induction time is proportional to barium content (SR); it increases with the increase of barium species activities. The surface growth factor was also found to be proportional to the saturation ratio which results from the increase of barium content in the brine mixture. The figures were used as a reference when similar brine formulation mixtures were used to scale chemically manipulated steel surfaces with a water soluble anti-nucleation phosphonate scale inhibitor called diethylene tri amine penta phosphonic acid (DETPMP). Almost all of the scaled surfaces (resulting from the dynamic tests) were analysed using different surface integration techniques; surface topography and chemical composition using SEM and EDX respectively. Multiphase crystal composition and alignments were investigated using ex-situ X-Ray diffraction apparatus.