Lead Sulfide (PbS) Scale Behavior and Deposition as a Function of Polymeric Sulfide Inhibitor Concentration in Multiphase

Deposition of inorganic mineral scale on downhole completion equipment contributes to significant downtime and loss of production within the oil and gas industry. High temperature/high pressure (HT/HP) fields have reported build-up of lead sulfide (PbS) scale as a consequence of reservoir souring; and the resultant reaction between dissociated sulfide anions from hydrogen sulfide (H2S) and heavy metal cations. In this work, laboratory apparatus enabled simulation of scale precipitation under turbulent emulsion-forming multiphase conditions, with behavior of PbS particles at the oil/water interface and subsequent adhesion onto anti-fouling surfaces measured at a range of polymer concentrations. Introduction of polymer sulfide inhibitor (PSI) product to the formation brine at concentrations of 500mg/L reduced overall PbS deposition whilst addition of 5000mg/L further reduced scale crystallisation but resulted in complete emulsification of the light oil phase. The tendency of soluble polymers to act as surfactants led to increased stabilisation of the formed oil in water (o/w) emulsion with heightened PSI concentration. Optical microscope, gravimetric and rheological measurements explained depositional behaviour; whereby enhanced o/w emulsion viscosity and stability due to amphiphilic polymer adsorption onto both PbS scale and oil droplet interfaces resulted in uniform deposition upon all surfaces.