In the main hole interval of offset wells in the Liard Basin, an operator experienced severe seepage losses and hole instability issues while drilling the mechanically weak shale sequence with a managed pressure drilling (MPD) system. 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).
Upon drilling out the second intermediate casing of its latest horizontal MPD well at 12,106 ft (3,690 m), the operator pre-treated the active mud system with STAR SHIELD® ultra-low invasion additive at a concentration of 5 lb/bbl (15 kg/m3). The wellbore shielding technology minimizes fluid and pressure invasion by quickly depositing an impenetrable barrier across highly permeable formations and micro-fractures (natural or induced) up to 3,000 microns (μm). A formation integrity test (FIT) performed with a 15.4 lb/gal (1850 kg/m3) invert emulsion mud prior to drilling the 8 ½-in. section showed an equivalent mud weight (EMW) 19 lb/gal.
The operator drilled the 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) saved the operator in drilling costs compared to offsets.