Production Engineering and Well Performance
Production Engineering and Well Performance tests how reservoir inflow, tubular flow, and lift systems combine to set rate. Expect inflow performance relationships, Vogel, productivity index, nodal analysis, skin, artificial lift, and water or gas coning.
Core rules
- Productivity index J = q/(Pr-Pwf) applies to single-phase liquid flow. Below bubble point, use a composite or Vogel IPR.
- Vogel: q/qmax = 1 - 0.2(Pwf/Pr) - 0.8(Pwf/Pr)^2.
- Nodal analysis matches inflow (IPR) with outflow (tubing and lift). The intersection is the operating rate.
- Positive skin increases drawdown for a given rate; negative skin from stimulation improves inflow. Partial penetration and perforation add pseudo-skin.
- ESPs suit high-volume wells, gas lift tolerates sand and deviated geometry but needs gas supply, and rod pumps suit lower-rate wells.
- Water coning is controlled by limiting drawdown and keeping perforations away from the water contact.
Worked example
A well has Pr = 3,000 psi, qmax = 1,000 STB/d, and Pwf = 1,500 psi. The pressure ratio is 0.5. Vogel gives q = 1,000[1 - 0.2(0.5) - 0.8(0.5)^2] = 1,000(1 - 0.1 - 0.2) = 700 STB/d. A linear PI model would overpredict because the well is below bubble point and the inflow curve is nonlinear.
Traps
Applying a constant PI below bubble point is a major source of error. Ignoring skin, using gauge instead of absolute pressure, or mixing STB/d with reservoir barrels will also fail unit checks. Do not assume qmax is fixed when reservoir pressure declines, and do not ignore outflow backpressure when comparing lift options.
Key points
- PI is valid only for single-phase liquid inflow.
- Vogel captures nonlinear inflow below bubble point.
- Nodal analysis intersects IPR and outflow curves.
- Positive skin raises drawdown and lowers rate.
- Limit drawdown to control water coning.