Plug cementing is still considered to be a critical operation, and cases of
failure eventually happen. A large annular gap and eccentricity, typical of
these operations, are factors that may promote unstable flows, resulting in
cement-slurry contamination. Deepwater conditions enhance chances of free fall,
and, consequently, low displacement velocities can occur in the annulus.
This article presents a parametric study of the role of rheological
properties of fluids (drilling fluid, spacers, and cements slurries), string
rotation, and flow rates (including free-fall effects) in the displacement
quality of cement plugs. Analyses are based on two different simulation tools.
Conventional cement-pumping software defines flow-rate profiles at the annulus
entrance, accounting for free-fall effects, and computational fluid dynamics
(CFD) simulates the interface propagation and contamination levels.
The main issues addressed by the simulations are
- What are the maximum yield stresses that guarantee nonstagnation regions
while circulating the drilling fluid?
- How can one optimize density and rheology hierarchy, which minimizes
contamination and avoids channeling?
- What is the role of string rotation on the displacement efficiency?
The compilation of simulation results into useful guidelines and procedures
for displacing cement plugs in vertical, inclined, and horizontal offshore
wells is presented.
© 2011. Society of Petroleum Engineers
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- Original manuscript received:
23 November 2010
- Meeting paper published:
2 March 2011
- Revised manuscript received:
27 April 2011
- Manuscript approved:
14 June 2011
- Published online:
1 September 2011
- Version of record:
15 September 2011