Gas Tubing Performance
PetroSimple
1.2 Varies with device
This app computes the flowing and static bottomhole OR wellhead pressures in a wellbore in field units using the Cullender-Smith method. The user can select if they want to compute the bottomhole pressure (BHP) from the wellhead pressure (WHP) or if they want to calculate the WHP from BHP.

This app requires the gas Specific Gravity (γ), tubing diameter (d), tubing roughness (ε), Well depth (D), hole deviation (θ), gas flow rate (q), WHP or BHP (Pwh OR Pbh) and the wellhead and bottom hole temperatures (Twh and Tbh).

The user also has the option of inputting the data from an offset well to compare its performace with this well. The offset data is plotted on pressure traverse and inflow performance curves.

This app will compute the flowing bottom hole pressures at various depths for different gas flow rates. The resulting curves are plotted as pressure traverse curves. One calculation is also made for zero gas flow rate, yielding the static pressure traverse curves. The bottom hole pressures are also plotted versus flow rate to generate the tubing performance curves.

Finally a report of the calculation is also available in copyable tab delimited text form to copy to clipboard to paste into email or a mobile word processor.

Technical Description
The app uses the Cullender-Smith method to calculate the flowing bottom hole pressures. Temperatures are assumed to be linearly distrubuted along the depth. Z-factors are calculated with the Hall-Yarborough method.

Note: A non-physical solution may result while computing wellhead pressures from the given bottom hole pressures. This happens because a low BHP value will yeild a lower WHP value or in extreme cases negative values of pressure might result. The app handles it by substitiuting zeros for negative pressure and it should be understood that a non-physical situation has occured and that a higher value of BHP must be chosen OR the flow rate should be reduced to get a physical value for WHPs.

References
1. Cullender, M.H. and Smith, R.V. 1956. Practical Solution of Gas-Flow Equations for Wells and Pipelines with Large Temperature Gradients. Trans., AIME 207: 281.