Hydraulics Flashcards
(37 cards)
What are the 3 situations which subsurface fluid pressures become critical?
- Static Condition
- Circulating operation
- tripping operation
What are examples of a static condition
connection time prior to running casing flow checks rig problems wireline operations
what does ECD stand for?
Equivalent Circulating Density (effective fluid density exerted on the formation at a particular depth).
ECD equation?
ECD= density + P/0.00981xD
= kg/m3
What are examples of dynamic conditions?
drilling fluid in motion
drill string in motion
Why is it important to know dynamic conditions?
to determine the ECD’s while drilling/cementing/tripping as well as calculating optimum size of drill string and bit nozzles.
Where do system pressure losses occur?
Surface system
Drillstring
Bit
Annulus
What parameters are required to determine the true bit nozzle optimization?
Penetration Rate Operational cost Bit wear Potential hole problems (ie. washout) Drilling fluid carrying capacity
What are the factors effecting the drill bit performance?
Over balance pressure/ drilling fluid properties Formation characteristics WOB rotary speed Bit Design Hydraulic efficiency
What is overbalance pressure?
Excess of base hole pressure over formation fluid pressure.
What does over balance pressure do?
- creates a hole down effect on the chips which hinders removal.
- Increases effective compressive strength of the rock
How is ROP related to overbalance pressure?
It is inversely proportional to the overbalance pressure.
List the formation characteristics
Compressive strength
Porosity
Permeability
Swelling of Clay
What are the characteristics to take into consideration when selecting a bit?
Tooth protrusion
Tooth Shape
Number of teeth
Skew
What is Skew?
When original triangle shape from brand new bit begins to skew away from center after use.
What are the most common parameters to optimize bit hydraulics?
Flow Rate
Pressure drop
Hydraulic horsepower
Formation characteristics, bit type and rig capabilities are used to calculate what?
Hydraulics
Equation for HIS (hydraulic horsepower)?
HIS= (change in P x Q)/(35140xdiameter^2)
NOTE: typical HIS values range from 2 to 5
Why is pressure drop critical?
Bit cleaning, especially in sticky formations
Why is flow rate critical?
Hole cleaning
(minimum flow rate is required for adequate bit cleaning)
(influenced by hole size and formation properties).
what is DOT?
Drill off test
What does a DOT do?
Helps optimize WOB and RPM
Drill off test process
one parameter is held constant while the other is varied, then parameters are reversed.
Parameter may need to be changed if formations change
Why is water used to soak bits and not diesel?
To protect the seals from degradation.
