Inorganic scales are a significant production issue with extensive inorganic scales observed in many Brazilian offshore fields and is also a worldwide phenomenon resulting in considerable productivity impairment. With the intervention of more sophisticated downhole tools such as inflow control devices (ICDs) and inflow control valves (ICVs), increased shear stresses are experienced in the wellbores near these devices resulting in an increased risk of scale formation and adherence even under very mild levels of oversaturation. The impact of scaling on or near ICDs or ICVs will have a dramatic impact on productivity since scaling would form in the wellbore itself.
In this work we have focused on downhole carbonate scaling under Petrobras new deepwater field conditions where the drawdown in the near wellbore area results in oversaturated brine systems. Downhole conditions have been modeled and closely simulated in the laboratory to ensure that laboratory conditions closely match the mild level of over saturation expected due to drawdown such as the ones present in ICV orifices.
The work initially examines the relationship between increased shear and scaling examining both bulk scaling (homogeneous precipitation) as well as the relationship between shear and surface scaling. The results show that there is interdependence between bulk and surface precipitation as a function of increased shear. In addition the work examines a range of different materials of construction commonly used in ICVs including different metallurgies, and different surface finishes as well as coatings specifically designed to minimise the potential for scaling.
Work at a variety of shear conditions clearly shows the potential to minimise surface scaling by careful material selection and / or by the use of specially formulated surface coatings. A mock valve has also been designed and commissioned to allow testing of the potential for scaling under realistic downhole flow conditions at representative downhole temperatures and pressures. Preliminary work using this more representative " pilot" test design is also discussed.