High-density formate brine-based drilling fluid systems have emerged as viable reservoir drilling and completion fluid options for deep high-temperature wells. Upon their commercialization in the early 1990's, these systems were shown to possess a unique combination of properties that could be exploited to engineer high-density fluids that would comprise minimal solids, maintain rheological stability at high temperatures, minimize reservoir damage and satisfy environmental requirements.

This paper describes the evolution of these systems and their recent application in the drilling of deep wells in Northern Germany and other areas. Not only did the formate-based systems exhibit faster penetration rates than the water-based fluids used previously; they also eliminated the solids sag problems experienced with water-based drilling fluids used in technically and economically demanding high-temperature environments. Furthermore, the formate brine-based systems were shown to improve well productivity.

Through an examination of 15 deep gas wells in Germany and other formate-based applications, the authors review the performance of formate brines as reservoir drilling, completion and workover fluids. Particular attention is given to drilling and eventual well performance, as compared to offset wells drilled and/or completed with alternative systems.

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