This paper describes the development of a low-solids oil-based fluid and its successful application as a kill pill in long, perforated horizontal wells in the Norwegian North Sea. The authors detail the investigative process that resulted in the development of the heavy, brine-based, internal-phase fluid system.
Simulated perforation formation-damage tests with and without zinc perforating debris were conducted on conventional brine-and oil-based fluid systems. The tests showed that the chemical reaction of the brine-based system to zinc debris significantly increased fluid loss. With the conventional oil-based mud, return flow efficiencies dropped by 10 to 15% when the zinc debris was added.
The newly developed low-solids, oil-based kill-pill system was engineered with a high content of heavy brine for fluid density and minimal solids content. The only solids in the system are calcium carbonate, which is used for bridging, and minimal amounts of clay and lime for rheology control and alkalinity, respectively. In perforation tests, it exhibited more than 80% return flow efficiency.