Evaluating Chemical-Injection Packages for Downhole Continual Injection in High-Rate HP/HT Gas Production Systems

摘要

Downhole chemical deployment via continuous injection capillaries is becoming a more common method for protecting SSSV's or other downhole equipment from inorganic scaling. For new start up wells, especially for very expensive and HPHT subsea production systems with CaCO3 risk from Formation Water, common practice is often to continually inject treatment chemicals from day #1 in order to ensure that sufficient chemical is present when water eventually produces. In such instances the additional costs associated with chemical injection are generally outweighed by the costs associated with downhole scaling, which may potentially form predominantly near SSSV's following early or unexpected water breakthrough. The work presented in this paper describes a novel laboratory test rig designed to replicate flowing conditions near the injection ports in a new HPHT gas production system in the Norwegian North Sea. The equipment allowed a range of novel scale inhibitor chemicals, formulated in low vapour pressure / high boiling point solvents to be assessed with special emphasis focused on the re-dissolution of ‘gunked out' product. The results demonstrate that under the proposed application conditions (160°C / 320F) significant solvent loss was recorded leading to rapid gunking and eventual blocking of the flow lines. The work therefore demonstrated a relatively significant risk existed for continuous chemical injection in these wells prior to water production and led to the decision to adjust normal start up procedures for this field delaying chemical injection until water breakthrough is detected.