Investigation of the Centrifugal Effect in Calcite Scale Deposition

Calcium carbonate scale formation is one of the most critical challenges of the oil and gas industry in Brazil. The high content of CO₂, the formation brine and the types of rock reservoir observed in the Brazilian Pre-salt favor the occurrence of inorganic scaling throughout the production, from the bottom hole to upstream primary oil processing facilities. In particular, de-oiling cyclones used in the final stages of water treatment may suffer from loss of performance or complete blockage due to inorganic scaling. Cyclones benefit from centrifugal forces to promote an efficient and cost-effective gas-liquid or liquid-liquid separation. The flow inside the cyclonic body, with its characteristic inner and outer vortex, may interact with the precipitated solid particles from the bulk flow directing them towards the wall and favoring particle adhesion and growth. In addition, the pressure drop across the separator inlet and outlets and along the conic cross section may influence CO₂ equilibrium, which may also imply in local precipitation. In order to model the influence of the cyclonic effect on scaling properties, laboratory tests have been conducted under experimental conditions very similar to real field applications. Solutions of calcium chloride and sodium bicarbonate were mixed at a one-inch diameter stainless steel pipe that was used to feed an encapsulated hydrocyclone prototype. In order to isolate the contribution of the centrifugal effect, results were compared with the scaling formed across a straight T-shaped tube under the same experimental conditions, including the same internal area and the same initial pressure drop. During the experiments, liquid samples were collected at the inlet and at both exits for characterization of pH, conductivity, temperature and particle counts. The solid samples were analyzed through scanning electron microscopy for identification of the calcium carbonate crystalline structure and measurement of its layer thickness. The deposited mass, temporal evolution of the pressure drop and crystalline structure of the deposited material were also analyzed. Results for total deposited mass and scaling rate indicate that the centrifugal force exerts a small effect on the scaling rate inside the cyclonic separator.