This paper describes the development of a low-solids oil-based fluid and its successful application as a kill pill in long horizontal well perforations in the Norwegian North Sea. The authors detail the investigative process that resulted in the development of the cesium formate-based internal phase fluid system.
Simulated perforation formation damage tests with and without zinc debris were conducted on conventional brine-based and oil-based fluid systems. The tests showed the chemical reaction of the brine-based system to zinc debris had little effect on return flow efficiency, but significantly increased fluid loss. With the conventional oil-based mud, returns dropped to 10-15% 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.