Well positioning and design
Wintershall Noordzee BV planned to drill a near-horizontal development
sidetrack offshore the Netherlands. The objective was to redevelop a number of
variably depleted reservoir zones that were no longer producing due to water
influx. The consideration for positioning, designing the well, and selecting
the target entry point was the optimal penetration of all zones at highest
possible position to reduce the risk of early water breakthrough. Effective
hydraulic isolation was more critical than ever, considering the planned
sequential production from the variably depletedhorizontal reservoir zones.
Advanced, customized cement solution
Schlumberger cement sheath stress analysis software was used to model
the mechanical performance of the set cement under changing well conditions.
The software predicted the required set-cement properties. Furthermore, because
of the very small margin between drilling fluid and slurry densities,
equivalent circulating density simulation strongly indicated that lightweight
slurry was required to prevent losses. This analysis led to the selection of
FlexSTONE advanced flexible cement technology. The 11.5-lbm/galUS customized
cement system designed was the lightest ever pumped in the North Sea.
FlexSTONE advanced flexible cement technology represents a fundamental
change to oil- and gas-well cementing. This sealant system has mechanical
properties that are matched to the downhole stress environment. By enabling the
set cement to conform to the changes that occur during the drilling,
production, and abandonment cycles of the well, the FlexSTONE system can offer
lifelong zonal isolation.
Each FlexSTONE slurry is individually designed for a specific well
application. First, the stresses that the cement sheath will experience over
the wells life are predicted by numerical analysis modeling. Then the
systems mechanical properties are customized using the FlexSTONE trimodal
particle-size distribution technology to accommodate the predicted
Robust, production-quality zonal isolation
The team used the ultralightweight expandable FlexSTONE flexible cement
system, shown to be robust through a 5,000-psi pressure test and subsequent
1,400-psi in-flow test. Sonic bond logs have shown that the cement job achieved
its primary objectives by minimizing losses and achieving production-quality
zonal isolation across the zones of interest.