Sulphide scale (PbS/ZnS) formation and inhibition tests for a gas condensate field with severe scaling conditions

Identifying effective sulphide scale squeeze inhibitors has been a major challenge in the production of oil and gas from deeper, higher temperature reservoirs. Managing sulphide scales of zinc and lead (ZnS and PbS) that commonly occurs in deep, hot reservoirs poses a significant challenge because of their very low solubilities. In general, for scaling problems applying chemical scale inhibitors or dispersants is the preferred solution to most challenges. However, to date no effective sulphide inhibitors/dispersants have been available which can deal with severe lead, zinc and iron sulphide problems at high salinity (HS >200, 000TDS) and high temperature (HT >180°C) conditions. It is a particularly difficult task to find sulphide inhibitors which can also be "squeezed" successfully since they must return to the wellbore at relatively high concentrations. This paper describes various sulphide inhibitor testing techniques which have been applied to many candidate products for the management of ZnS and PbS in a gas condensate field with a known relatively severe ZnS/PbS scaling problem. The paper presents sulphide static and dynamic test measurements along with thermal ageing results that show some encouraging results in terms of ZnS/PbS sulphide inhibition. The paper extends our knowledge and ability to test effective sulphide inhibitors for severe ZnS/PbS scaling conditions in high pressure/high temperature (HPHT) reservoirs.