Development of Geothermal reservoirs targeting steam production for electricity generation requires to implement specific subsurface infrastructure able to withstand aggressive conditions for extended number of years. Elevated temperature from 150°C to above 300°C are systematically encountered and the presence corrosive gases (carbon dioxide or hydrogen sulfide) brings on another challenge for the zonal isolation and asset integrity.

In order to ensure wells integrity cement sheath shall seal tightly rock and steel casing. As many studies demonstrated in the past, ordinary Portland cement would lose its mechanical performance and barrier properties when exposed to high temperatures and acidic environments. Thus, modified cements with adapted mineral compositions have been promoted for the specific use in Geothermal wells construction.

As based on different mineralogy, these blends present better chemical resistance and mechanical durability when compared to ordinary Portland cement. Therefore, organic additives such as retarder, fluid loss or gas migration control additives as well as suspension aids would have to be appropriately selected from their working mechanism to be used in Geothermal blends.

The scope of this study is investigate a set of additives, which would be "compatible" with Geothermal jobs and ensure good cement placement.

This paper summarizes first some key aspects of the Geothermal blends versus ordinary Portland cement in terms of physico-chemical behavior as well as a few primary additives instrumental to a successful cementing job.

Based on this background information, performance of the most promising candidates were assessed within our equipment temperature limitations with Geothermal blends using conventional API performance test protocols.

From this study, it was concluded that some fluid loss additives with working mechanism based on adsorption on mineral particles could suffer from competitive adsorption from high temperature retarders. On the other hand, structured copolymer with strongly adsorbing moieties show consistently satisfactory performance. In addition, styrene butadiene latexes with adapted stabilization packages can also represent good option to run HPHT cementing jobs in corrosive environments.

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