Use of Silicate Mud to Control Borehole Stability and Overpressured Gas Formations in Northeastern British Columbia

Abstract A freshwater silicate based drilling fluid, containing 20-30% sodium silicate by volume, was successfully used to drill a gas well in northeastern British Columbia. Major drilling issues in the area include borehole instability in 500 plus meters of highly dispersible Ft. Simpson shale, high pressure gas zones and potential moderate-severe lost circulation. Despite problems of severe lost circulation and high mud weights, the caliper log on the silicate well showed <1% hole enlargement over the Ft. Simpson shale and 12% enlargement over the entire intermediate section. Typical offset calipers with other water-based muds average 48% and 31% enlargement over the Ft. Simpson and entire well section, respectively. Rates of penetration with silicate mud were generally better than offset wells. Uphole formations drilled to 1060 meters with a low solids, lower density silicate fluid (1195 kg/m3 mud density) drilled at an average of 19.2 m/hr. Offsets drilled with gel-chemical or gel-PHPA systems over the same interval normally averaged 12.6 m/hr. This paper describes the planning and drilling of the first well with a drilling fluid containing silicates up to 30% concentration. Topics discussed include borehole stability, rates-of-penetration, motor performance, drilling fluid stability and properties, and environmental aspects of silicate disposal.