Published: 09/04/2001
Published: 09/04/2001
In May 2001, Schlumberger Well Services utilized DeepCRETE slurry to cement the 30-in conductor string on Norsk Hydro's Well 31/2-K-21 H.
DeepCRETE slurry is designed to reduce waiting-on-cement (WOC) time without complicating deepwater operations.
In this case, DeepCRETE was used to combat the long WOC times that normally result from the cool temperatures found at the seabed in the Troll field in the Norwegian North Sea.
DeepCRETE was deployed from the West Venture, a state-of-the-art, fifth generation semisubmersible drilling and production rig. Drilling efficiency from these rigs has increased significantly in comparison to fourth generation units.
One of the key features providing the efficiency gains is the availability of two independent derricks for simultaneous operations.
The superior speed of DeepCRETE in generating compressive strength resulted in the WOC time being reduced to five hours, which is a record in cold, deepwater well construction. This allowed the West Venture to take advantage of the second derrick and begin drilling much sooner than would have been possible with a conventional tail slurry.
Comparing this to similar jobs using a conventional tail slurry, savings of approximately nine hours, or $80,000, in rig time were made. This value includes accounting for cost difference between the slurries.
The DeepCRETE cementing slurry system is a member of the CemCRETE family of products, which are in turn based on Advanced Cement Technology from Schlumberger. DeepCRETE makes use of engineered-particle-size-distribution, whereby smaller particles fill the void space between larger particles, resulting in a slurry requiring less water. The smaller particles within the cement are further engineered to contribute to both the slurry and the set-cement properties, leaving water as a reactant and carrying agent. This is all achieved whilst retaining the cement properties most valued in hydrocarbon exploration application—density that is disconnected from rheology, lower permeability, higher and faster compressive strength, improved mechanical durability, improved injectibility for remediation, and improved field operations.
Drilling the shallow strings in deepwater environments usually means cool seafloor temperatures. Normal density slurries can require more than 24 hours to develop adequate strength in these conditions. Even then they may suffer losses and require top-out jobs that further delay operations. In some cases they may never develop sufficient compressive strength.
DeepCRETE is designed to isolate deepwater zones and allow drilling to resume sooner through reducing the WOC time.
DeepCRETE sets fast, even in extremes of low temperature. CemCADE cementing design software was used in this case to aid in temperature modeling, thereby optimizing the slurry properties for the job.
For well 31/2-K-21 H the borehole static temperature was 8 degC. The conductor was set to a depth of 413 m in water depth of 370 m. The open hole size was 36-in. with 200% annular excess considered for slurry volume calculations. A conventional lead slurry (1.44 sg) was pumped ahead of 20 m3 of DeepCRETE tail slurry (2.1 sg). The job was performed with a 5.5-in drillpipe inner string secured into the 30-in casing shoe. Total pump time for the job was approximately 1.5 hours. The successful use of DeepCRETE in this instance resulted in a saving of approximately 9 hours of rig time.
Location: Troll Field, Norwegian North Sea
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