Optimizing High-Temperature Kill Pills: The Åsgard Experience

Abstract

Abstract Historically, the survival rate for conventional non-damaging polymer/carbonate kill pills under elevated temperatures was limited. Accordingly, a development program was instituted to develop a new high-temperature kill pill that would possess superb bridging characteristics on a high permeability proppant while remaining thermally stable at temperatures exceeding 165ºC. This paper describes the development of a sodium formate kill pill geared specifically for the demanding Åsgard Development in the Norwegian North Sea. The pill was engineered and successfully applied in a high-temperature application to seal a high permeability (400-500 Darcys) frac pack sand in the Smørbukk field. In the field, the newly engineered formate-base pill proved to be thermally stable, while providing sufficient leak-off control. Furthermore, the development reinforced the critical role of proper particle size distribution in minimizing fluid invasion and formation damage. With emphasis on particle size distribution, the authors will review the formation damage testing procedure of the new formulation on simulated frac packs. In the laboratory, the fluids demonstrated excellent thermal stability after long-term exposure to temperatures exceeding 150°C. After the pills were aged for 16 and 72 hours, leak-off tests were performed on 16/30 proppant at 165ºC, resulting in minimal filtration. The authors also will examine the unusually demanding conditions at Åsgard relative to other Norwegian fields and will detail the application and performance of the new kill pill in this hostile downhole environment.