¶ Overpull
The Overpull load case is defined as the scenario where the casing string becomes stuck after it has been run in the wellbore and additional tension is applied to pull the string free. This load case is usually defined as a Pre-Installation Load Case. If it is used as an installation load, the sticking point should be set to the packer depth.
¶ Inputs
By default, this load case utilizes the Undisturbed Temperature Profile.
The inputs include:
- Description
- Pressure at Hanger
- Sticking Point
- Coefficient of Friction (String to String)
- Coefficient of Friction (String to Open Hole)
The Description is nothing more than the load’s name, which can be edited by the well designer.
The Pressure at Hanger is the hydrostatic pressure of the annulus fluid at the wellhead. The default value is the pressure resulting from the mud density in which the string was run. While this field can be edited, it will rarely need to be.
The Sticking Point is the point in the wellbore where the string hypothetically becomes stuck. The default is the shoe depth, but this can be changed by the well designer to any point along the string’s length.
The Coefficient of Friction (String to String) is the steel on steel friction used by StrinGnosis®. The default is 0.12, but any number between 0.00 and 1.00 is valid.
The Coefficient of Friction (String to Open Hole) is the steel on rock friction used by StrinGnosis®. The default is 0.30, but any number between 0.00 and 1.00 is valid.
This load case assumes Undisturbed Temperature by default, but other temperature profiles, including Custom, can be selected.
There is one more field shown on the input window, the Running Fluids. This field is grayed out and for well designer reference only. This is the density used for both the internal and external pressure profiles for this load.
¶ Internal and External Pressure Profiles
Both internal and external pressure profiles are calculated using the same run-in fluid density and is defined as following - p(z) = Cρz where,
- C = conversion factor, 0.051948 psi/(ppg×ft)
- ρ = internal and external fluid density, ppg
- p(z) = internal and external hydrostatic pressures at depth z, psi
- z = true vertical depth of interest, ft TVD
¶ Temperature profile
Undisturbed temperature is assumed as the default temperature profile.