Sulphide Scale (PbS/ZnS) Formation and Inhibition Tests for a Gas Condensate Field with Severe Scaling Conditions

Abstract

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 Ͼ200, 000TDS) and high temperature (HT Ͼ180°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.

Deposition of Inorganic Carbonate, Sulfate, and Sulfide Scales on Antifouling Surfaces in Multiphase Flow

“…The procedure more closely reflects mechanisms and conditions during production within a sour production well, where pressure-volume-temper- ature (PVT) studies have shown that aqueous H 2 S concentrations reach up to approximately 55 ppm at equilibrium, and turbulent, two-phase flow conditions are generated in an anaerobic environment. 7 Further experiments, contrasting the precipitation and deposition mechanisms of "conventional" carbonate and sulfate scales onto antifouling surfaces, supplant current notions within the oil and gas industry that metal sulfides nucleate directly onto surfaces, 6,8 instead highlighting the role of the light oil phase on homogeneous scale adhesion. The design and development of an airtight delivery vessel allowed introduction of incompatible seawater and formation water brines under anaerobic conditions.…”

“…In this study, a new method and apparatus whereby H 2 S gas is introduced into the air-space of an anaerobic reaction vessel, gradually diffusing into the aqueous phase before reaching equilibrium and dissociating into reactive bisulfide (HS − ) species, is employed. The procedure more closely reflects mechanisms and conditions during production within a sour production well, where pressure-volume-temperature (PVT) studies have shown that aqueous H 2 S concentrations reach up to approximately 55 ppm at equilibrium, and turbulent, two-phase flow conditions are generated in an anaerobic environment . Further experiments, contrasting the precipitation and deposition mechanisms of “conventional” carbonate and sulfate scales onto antifouling surfaces, supplant current notions within the oil and gas industry that metal sulfides nucleate directly onto surfaces, , instead highlighting the role of the light oil phase on homogeneous scale adhesion.…”

“…In this study, a new method and apparatus whereby H2S gas introduced into the air-space of an anaerobic reaction vessel, gradually diffusing into the aqueous phase before reaching equilibrium and dissociating into reactive bisulfide species, is employed. The procedure more closely reflects mechanisms and conditions during production within a sour production well, where PVT studies have shown that aqueous H2S concentrations reach up to approximately 55 ppm at equilibrium; and turbulent, two-phase flow conditions are generated in an anaerobic environment 7 .…”