Minimizing Scale Deposition Through Surface Enhancement in Downhole Tools
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.