Knut Taugbol

Particulate-Based Loss-Prevention Material--The Secrets of Fracture Sealing Revealed!

Owing to the narrow drilling margin that exists between th e pore pressure and fracture pressure gradients, drilling in depleted reservoir, HPHT and deep water environments is univer sally recognized as being technically challenging. A number of field techniques are available for mitigating against many of the drilling problems encountered. Included amongst these are specialized fluid engineering that involve use of chemical- and particulate-based treatments for minimi zing or preventing losses. In many instances these techniques can be used to strengthen or stabilize the wellbore when drillin g on or near the fracture gradient thereby potentially eliminating the need for intermediate casing strings. This paper discusses particulate-based treatment design for sealing fractures. Substantial experience gained from innovative laboratory testing has highlighted the mechanisms and many factors that determine the effectiveness of the fracture seal. The particle size distribution relative to the fr acture aperture, particle morphology, volumetric concentration, fluid rheology and fluid-loss-control influence whether the seal is established within the fracture or at the fracture mo uth. Understanding this distinction is important with respect to selecting the optimum treatment and its application for giv en field conditions. Parameters critical for optimizing the treatment h ave been identified and are discussed in the context of laboratory and field experience.

New low-solids oil-based mud demonstrates improved returns as a perforating kill pill

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.