Case History

Wellbore Shielding® Additive Deepens Intermediate Casing Point Through Coal Formations


The problematic Belly River coal and Edmonton formations in the Kakwa Field are
known for wellbore instability issues that have led to catastrophic whole mud
losses in offset wells. Offset data also showed operators experienced mud
losses and hole instability issues in the Belly River coal and Edmonton formations
when higher mud weights were needed to manage an influx in pressure while
drilling into the Notikewin formation. Narrow pore pressure / fracture gradient
windows can make these wells challenging while trying to maintain enough mud
weight to prevent a gas influx or hole collapse without encountering mud losses
while drilling to the intermediate casing point. Impact Fluids was given the
opportunity to provide a solution allowing the operator to deepen their intermediate
casing point and enable drilling the vertical and curve sections together,
limiting wellbore instability issues including whole mud losses. By deepening this
intermediate casing point through these coal formations, and successfully
cementing the casing on bottom, the operator displaced to a brine water-based
system and drilled the horizontal section of these wells with brine water instead
of the traditional invert oil-based mud systems, therefore substantially increasing
their rate of penetration (ROP) and reducing the overall bit trips in this interval of the well.


Impact pre-treated the invert-based mud system with 25kg/m3 (8 lb/bbl) of the
wellbore shielding additive prior to displacing the sodium silicate mud out of the
well at 2160m (7,087-ft.). Maintenance additions of this wellbore shielding
additive were added to the circulating system while drilling ahead to the top of
the Doe Creek formation (Est. 2554m (8,380-ft.)). An open-hole FIT was performed
to determine if the wellbore shielding additive provided enough stability
to prevent catastrophic mud losses to the Belly River coal formation above. Upon
completing a successful FIT, the 251mm (9 7/8-in.) hole would be drilled through
the Notikewin and Falher coal formations to landing point while maintaining this
25 kg/m3 concentration in the system.


Solids control equipment was fitted with API 70 mesh screens prior to displacing
the sodium silicate mud from the well with the wellbore shielding treated invert
system. The circulating system was maintained with a 25 kg/m3 concentration to
the top of the Doe Creek formation (2,554m). An open hole FIT was performed to a
1355 kg/m3 (11.3 lb/gal) EMW providing the operator with confidence to continue
drilling the 251mm hole through the vertical and curve section of the intermediate
interval from 2160m – 3,404m (7,087-11,168-ft.). The over-all mud losses and hole
instability in the coal formations were minimized throughout and the intermediate
casing was run and cemented on bottom with full returns. The wellbore
shielding® technology was successful in minimizing instability issues while
drilling through the Notikewin and Falher coal formations to reach landing point
while also preventing catastrophic mud losses in the mechanically weak Belly
River and Edmonton formations above.