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

Abstract

Abstract Valemon, operated by Statoil, is a HPHT gas/condensate field on the Norwegian Continental Shelf. Production started at the end of 2014 from a development consisting initially of cased & perforated wells. However, during early field development the orginal concept had been for stand alone screens (SAS) lower completion. K/Cs formate water based system with a density of 2.02sg. 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 prior to the arrival of the platform and before clean up 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 that this could have. Computational fluid dynamic (CFD) modelling was performed to determine how long formate would be in contact with the near wellbore and this demonstrated 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 involving extended soaks in formate along with pre- and post test analyses to identify potential damage mechanisms. Those identified included kaolinite dissolution, precipitation of Barsium and cesium silicate, and swelling of kaolinite due to the incorporation of potassium and cesium into the kaolinite lattice. To confirm the findings from the CFD and coreflood modelling, a field review was made of Statoil's experiences with suspending wells for extended time in formate prior to clean up and production. The field review demonstrated positive experiences in using formates in suspended wells with respect to productivity. Lower than expected productivity was experienced for some wells but this could not be conclusively related to use of formates. The paper provides an overview of lessons learned from coreflooding, CFD modelling and actual field data on wells suspended in formate prior to clean-up and production.