Rheology Flashcards
Advantages of Generalized Hershel Bulkley
- Can be easily reduced to more conventional methods
- Flexibility to characterize viscocity functions
- provides framework for developing friction prediction.
What does Bingham plastic assume
It assumes a yield point at zero shear stress.
GHB combined with BP
It includes a yield point like BP but also assumes a non linear shear stress to shear rate relationship.
Why would rheo models be inaccurate
Casing Centralization
narrow annulus
deviated wells
Why do deviated wells pose problems predicting friction
fluids want to flow on the high side of the annulus causing channeling.
Disadvantage of Bingham plastic
overestimates shear stress at low shear rates. Assumes a yield point at zero shear stress.
Non Newtonian fluids behave:
fluid flow does not kick in with a relatively small stress
non linear shear stress to shear rate. (continued stress does not necessarily keep a afluid in motion. the friction pressure will be higher at lower rates than higher rates.
Is a higher rate a good thing
not necessarily. You want to pump at a rate in which your friction pressures are in hierarchy between fluids.
Friction Loss is a function of
Geometry
flow rate
density
rheological properties.
What sets GHB apart
incorporates all models and assumes that shear stress is not a direct function of shear rate.
Key driver for developing GHB
realtime evaluation of ECD. Requires accurate prediction of friction pressure
Why use GHB
Provides flexibility to accomidate non Newtonian fluids
provides flexibility for more complex fluids in the future that include shear thickening.
Friction is a function of
Rheo, density, flow rate, geometry
GHB transition
GHB accurately predicts when the fluid will make the transition to turbulent flow and the increase in friction pressure that goes along with it.
Rheo hierarchy importance
at defined pump rates the friction pressure is greater than the fluid ahead of it.
