Coiled-tubing drilling of horizontal sidetrack in House Mountain Field, Alberta

In 1995, the first horizontal sidetrack successfully drilled using coiled t ubing (CT) was carried out at Shell's House Mountain 7. oilfield. The objec tive was to drill underbalanced a 3 7/8-in. diam by 300-m-long horizontal h ole section from an existing vertical, cased oil well. The existing well wa s re-entered using a conventional drilling rig; a window milled in the casi ng, and the build section drilled to an inclination of 90 degrees. 2 3/8-in . CT was then used to directionally drill the horizontal section underbalan ced with nitrified water. The zone of interest was a Devonian-age reef-edge and limestone structure, at a depth of about 2200 m, called the Slave Poin t. A case history of directionally drilling the horizontal sidetrack using 2 3 /8-in. OD. CT is provided. Coiled-tubing drilling proved to be a cost-effec tive alternative to drilling the horizontal sidetrack without using a conve ntional drilling rig. Shorter trip times, underbalanced drilling, enhanced rates of penetration (ROP), and the ability to maintain weight an bit were all achieved. ROPs increased by up to three-fold while drilling underbalanc ed.