Abstract
In several HT/HP production environments severe downhole carbonate scale is often anticipated. Moreover, the high temperature means that reaction kinetics are very rapid and therefore the propensity for scale formation remains high even at moderate levels of oversaturation. However, a number of limitations are recognised when assessing the scale risks associated with such production conditions. This includes; uncertainties regarding the initial FW composition, accuracy of scale prediction tools and the application of conventional laboratory test procedures under these conditions. This paper describes the use of a novel HT/HP stirred reactor test rig (400F & 5,000 psi) designed to conduct in situ scaling experiments and allow equilibrium conditions to be established. The equipment is specially designed for the extraction and stabilisation of samples at or near tested conditions allowing the equilibrium brine composition to be determined under more representative HT/HP conditions. Initial results presented in this paper describe the commissioning and validation of the experimental design including the use of tracers to ensure effective transfer and collection of fluids from the reaction vessel. Results are then presented to determine the equilibrium saturation state of a particular field brine starting from the supplied water composition. In summary equilibrium saturation tests conducted at 340F and pressures between 200 psi and 5,000 psi showed significant quantities of carbonate scale (both barium and calcium carbonate) precipitating from solution, indicating a potential uncertainty in the original brine composition.
In summary, the data generated allows equilibrium saturation levels to be determined under HT/HP conditions allowing uncertainties in the water composition to be assessed. The determined saturation levels are also directly correlated with dynamic tube blocking tests and scale prediction tools. The data can therefore be used to further tune predictive modelling capabilities under these more extreme (HT/HP and high salinity) conditions.
