Optimizing High-Temperature Kill Pills: The Åsgard Experience

Abstract

Summary Historically, the survival rate for conventional, nondamaging 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 165°C (329°F). 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 to 500 darcys) frac-pack sand in the Smørbukk field. In the field, the newly engineered formate-based pill proved to be thermally stable while providing sufficient leakoff control. Furthermore, the development reinforced the critical role of proper particle-size distribution (PSD) in minimizing fluid invasion. With an emphasis on the PSD, this paper reviews the relative formation-damage potential testing procedure of the new formulation on simulated fracture packs. In the laboratory, the fluids demonstrated excellent thermal stability after long-term exposure to temperatures exceeding 150°C (300°F). The aging process was started simultaneously with two samples of each pill and concluded at the end of 16 and 72 hours, respectively. Leakoff tests were performed on 16/30 proppant at 165°C (329°F), resulting in minimal filtration. This paper also examines the unusually demanding conditions at Åsgard relative to other Norwegian fields and details the application and performance of the new kill pill in this hostile downhole environment.