Formate Drilling and Completion Fluids: Evaluation of Potential Well-Productivity Impact, Valemon

Summary Valemon, operated by Statoil, is a high-pressure/high-temperature (HP/HT) gas/condensate field on the Norwegian Continental Shelf. Production started at the beginning of 2015 from a development consisting initially of cased-and-perforated wells. However, during early field development, the orginal concept was for a standalone-screen (SAS) lower completion. A potassium/cesium (K/Cs) formate water-based system with a density of 2.02 specific gravity (sg) was considered as a candidate drilling-and-completion fluid for the wells completed with screens, one of which could potentially be suspended in formate brine for up to 10 months before the arrival of the platform and before cleanup and the onset of production. An unknown was the possibility for any near-wellbore interaction with these fluids during extended contact and the possible detrimental impact on productivity. Computational-fluid-dynamics (CFD) modeling was performed to determine the length of time formate would be in contact with the near wellbore, demonstrating that, especially for the lower-permeability intervals, a contact time of approximately 45 days was a possibility. In light of this, a sequence of corefloods was performed that involved extended soaks in formate along with pre- and post-test analyses to identify potential damage mechanisms. Those identified included kaolinite dissolution, precipitation of barium and cesium silicate, and swelling of kaolinite because of the incorporation of potassium and cesium into the kaolinite lattice. To confirm the findings from the CFD and coreflood modeling, a field review was made of Statoil’s experiences with suspending wells for extended time in formate before cleanup and production. The field review demonstrated positive experiences in the use of formates in suspended wells with respect to productivity. Lower than expected productivity was experienced for some wells, but this could not be related conclusively to the use of formates. This paper provides an overview of lessons learned from coreflooding, CFD modeling, and actual field data on wells suspended in formate before cleanup and production.