Gas Well Deliverability
Run a full nodal analysis on a gas well: fit inflow from a back-pressure test, integrate the tubing pressure with Ode45, find the operating point and decide whether a tubing change is worth a workover.
The brief
You are the production engineer, well performance
Gas well GW-7 has just finished a four-point back-pressure test. The gas sales contract needs a firm rate forecast, and the workover team is asking whether replacing the 2⅞-inch tubing with a larger string is worth a rig.
A well produces where the reservoir's ability to deliver gas (inflow) meets the pressure the tubing needs to lift it to surface (outflow). Finding that point is nodal analysis, the core calculation of production engineering.
You will fit the inflow from the test, integrate pressure up the tubing with an ODE solver, find the operating point, and run the tubing sensitivity that answers the workover question. The finished engine drives a 3D deliverability surface over reservoir and wellhead pressure.
- Reservoir pressure
- 3,000 psia
- Test: pwf (psia) → q (Mscf/d)
- 2,700 → 1,214 · 2,400 → 2,076 · 2,000 → 2,942 · 1,500 → 3,798
- Well
- 8,000 ft vertical, 2.441 in tubing ID
- Gas and temperature
- γ = 0.70, 80 °F at surface, +0.015 °F/ft
- Wellhead pressure
- 500 psia (sales line)
What you will be able to do
- Analyse a back-pressure test to get the inflow performance relationship
- Write the pressure gradient of flowing gas, with real-gas density and friction
- Integrate pressure along the tubing with Ode45
- Find the operating point where inflow meets outflow
- Run a tubing-size sensitivity and support a workover decision