Abstract
Halite scaling has caused serious issues in oil/gas field with high TDS and low water cut due to temperature drop and evaporation of the produced water. Simulation of such field condition is very hard. Analytical error for high concentrations of Na+and Cl- is large in the brine making accurate assessment of solubility and Saturation Index (SI) calculation difficult. We have developed the testing capability and methods to understand and control halite problems. We have developed testing methods that can create halite super saturation by incorporating (i) additional chloride from CaCl2 to the reaction mix at equilibrium and/or (ii) utilizing the change in temperature (∆T) as a driving force. These methods are optimized to assess the halite problem from 25-150 °C using mass analyses techniques, mixing of incompatible brines and temperature drop. The composition of salt, dilution volume and saturation index have been calculated using BCC ScaleSoftPitzer software. The induction time (tind) and mass of precipitated salts are considered for data analyses. Various experimentations to simulate the water dilution at ∆T were conducted and data suggest that in some cases 5 % dilution of the brine could drop halite saturation index (SI) to the equilibrium. Similarly, solubility of halite was analyzed in the presence of high calcium concentration in the brine up to 80,000 mg/L. Inhibitors with different functionalities were tested at various ranges of brine condition at saturation index of up to 0.15. Some inhibitors like polymers were found to prolong the induction time for several hours and reduce the halite precipitation mass up to 95%. Overall, the methods are robust yet simple and economic that can simulate field conditions in oil/gas production system to assess the halite scaling risk at higher extremes.
