Defining the Optimum Tubing Diameter
The tubing of 3.859'' ID has been selected for the casing diameter of 6.969" ID and Total Depth of the well, the following factors have been considered:
- The significant
favorable effect of tubing size on the reduction of the injection pressure
(tubular flow) for tubing sizes less than 5 in (figure 1).
- Insignificant
(unfavorable) effect of tubing sizes on the frictional losses of single phase
gas flow (annular flow) for tubing sizes less than 5 in (figure 2).
-
The
clearance required for placement of the gas lift valves (more than 1 inch).
Selecting Depth
of & Volume of Gas Injection
After choosing the proper tubing size, 3 depths of contentious injection have been selected to assess the gas lift performance
- total well depth
- half of well depth
3/4 of well depth
Considering the capital and running costs (figure 3 and figure 4), it have been decided to inject the gas at 3/4 of the depth (6220ft/8293ft).
The valves pacing design was then conducted using the graphical method (figure 5).
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| Figure 1: Contribution of Pressure Terms in Annular Flow |
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| Figure 2: Effect of Tubing Diameter on BHFP Requirments |
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| Figure 3: Incremental Oil Production for Unit Change in Compressor Horse-Power |
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| Figure 4: ΔQo/ΔHHP for Various Injection Depths at Optimum Conditions
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| Figure 5: Valve Spacing Using the Graphical Approach |
