Sulphide scales have low solubility and are mostly observed in deep high temperature/high pressure (HTHP) reservoirs. Particularly, squeeze treatment for HTHP wells in sandstone reservoir, has always been challenging due to the thermal degradation of polymeric scale inhibitors followed by poor retention properties. To this date, identifying a squeezable scale inhibitor for sulphide scale deposition that compiles with these conditions is an ongoing research topic. A thermally stable Polyaniline-Co-Polymer based scale inhibitor (PANI-Co-Polymer SI) has been developed, characterised, and tested. Adsorption isotherms analysis, thermogravimetric analysis (TGA), dynamic tube blocking tests (TBT) and scanning electron microscopy (SEM) analysis have been carried out in order to assess the efficiency against zinc sulphide (ZnS) scale as well as adsorption and desorption properties of the newly formulated product. Based on adsorption isotherms analyses, PANI- Co-Polymer SI shows high adsorption on sand particles that follows the Freundlich adsorption model. Product performance was also evaluated by TBT and TGA. Monitored differential pressure values over a one-hour period, shows a minimum effective dose (MED) of <5mg/L for ZnS and thermal stability up to 385° C, respectively. For a better interpretation of the inhibition mechanism by PANI-Co-Polymer SI, transmission electron microscopy (TEM) images and selected area electron diffraction (SAED) were implemented. Results indicate secondary crystal nucleation and growth disruption for ZnS. These results show that PANI-Co-Polymer SI could be a successful candidate to be used as a squeeze treatment for preventing ZnS scaling issues under HTHP conditions.