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An operator experienced severe seepage losses and hole instability issues in offset wells in the Liard Basin in Canada. While drilling the mechanically weak shale sequence with a managed pressure drilling (MPD) system, wellbore instability was a challenge in the main hole interval. The narrow pore pressure/frac gradients of these wells made it difficult to maintain sufficient mud weight to prevent influx and wellbore instability problems without encountering whole losses while drilling to total depth (TD).
The operator pre-treated the active mud system with STAR SHIELD to minimize fluid and pressure invasion in the problematic formation. While drilling out the second intermediate casing string at 12.106-ft. (3,620 m) a formation integrity test (FIT) was performed with a 15.4 lb/gal (1850 kg/m3) invert emulsion-based mud. The test showed an equivalent mud weight (EMW) of 19 lb/gal. With this in mind, the operator was confident to continue STAR SHIELD treatment of 5 lb/bbl in the 8½-in. section.
The operator drilled the problematic interval, and casing was successfully set at programmed TD for two wells using STAR SHIELD. The incorporation of STAR SHIELD prevented whole mud losses, despite drilling fluid densities as high as 16.8 lb/gal (2020 kg/ m3) and EMW up to 18.2 lb/gal (2191 kg/m3). On one well, the horizontal section was drilled to target depth at an average rate of 55 ft/hr (17 m/hr), reportedly making it one of the fastest laterals ever drilled in the field, which combined with a reduction in overall non-productive time (NPT).