Inhibition of Lead and Zinc Sulphide Scale Deposits Formed during Production from High Temperature Oil and Condensate Reservoirs.

Abstract Carbonate and sulphate scales are the most common types of mineral deposit associated with the recovery and processing of hydrocarbon and associated produced water. In three high temperature fields (>140C) within the North Sea more usual scale types have been observed namely zinc and lead sulphide. Conventional inhibitors cannot control these scale types and their removal by chemical means can result in the generation of toxic gas (H2S). The conditions for the formation of these unusual scale types is described and well as the economic impact these deposit had on hydrocarbon production of these fields. In this paper the development of a novel scale inhibitor package and its successful application in these fields is described. Field evaluation of the inhibitor types used to control sulphide scale is described in this paper as well as the details on how the field trials were planned, carried out and evaluated. Mechanical and chemical removal are also discussed as an alternative to inhibition. The finding of this paper significantly increase the industries understanding of sulphide scale deposits in terms of mode of formation and mechanism of inhibition. The paper stresses the critical factors to be evaluated within produced water at the early stage of field appraisal/development that can aid in the assessment of the risk of sulphide scale deposition. The development of a novel zinc and lead sulphide inhibitor gives a cost effective, environment friendly alternative to chemical or mechanical removal of such deposits.