API RP 11V8:2003 pdf download.Recommended Practice for Gas Lift System Design and Performance Prediction.
• Obtain a flowing temperature profile to serve in valve temperature estimates for the lower valves (the upper unloading valves will have a cooler, transient temperaturi during initial unloading).
iiuperature prediction is important in the design calculations of gas lift valves with nitrogen charged bellows. It is much less important ftw spring loaded valves. The flowing temperature profile measured in conjunction with a pressure survey represents the producing well. The survey does not give the coolcr wellbore temperatures that exist at the start of the unloading process.
• Use the flowing temperature survey for analysis by stopping at (or slightly above and below each gas lift valve. A cooling effect indicates gas passage. A tubing hole can also be located with numerous stops through the interval of the suspected problem.
• The temperature prolile can be used to set the lower valves that are subjected to hot reservoir fluid. The temperatures for the upper valves are not based on the flowing temperature survey. These upper temperatures tor the design calculations) must be estimated from
unloading conditions. Section 4.1 recommends temperatwe models for unloading valves.
3.3 PRODUCTION TESTS
Production tests, which are also known as well tests, are essential for effective gas lift analysis and design. These tests are used to gauge or measure the oil, water, and total gas production rates. The water fraction, and coupled with measured gas injection rates, the IGLR can be calculated.
• Steady non-slugging flow.
• Intermittent well testing should be conducted for a sufficient number of cycles to obtain a good average production rate.
• (las, oil, and water meters (and their associated outlet control valves downstream of’ the rneter sized to operale at the mid-point of their full-scale range. Dual meters (and control valves) should be used when the test vessel will be used for both very high rate and very low rate tests, The piping between the separator and the meter shoukl be short with no restrictions.
• Separator purge time. linked to the well’s rate, which eliminates the initial instability and diminishes the eflects of the prior well’s test.
• Test flowline purge time (for wells linked to the station via a test line) that establishes new equilibrium gas, oil, and water flow regimes and liquid holdup in the pipeline.
• Test duration that permits the rate to stahiliie at the test separator pressure (which should give the same flowing wellhead pressure as created by the production separator pressure).
• Shrinkage factor (reciprocal of volume factor at separator pressure and temperature) based on PVT data applied to obtain stock tank barrels.
• Meter temperature compensation (either in the meter or with the shrinkage factor).
• Gas samples and chromatograph analysis for specifIc gravity applied to gas measurement.
Test accuracy in low rate wells is usually poor. The biggest problem is the low rate (relative to tubular size) and slugging. The gas and liquid rates are not repeatable and the true rate is difficult to determine.
If severe slugging cannot be controlled by injection rate variation or by adjustments on controls, then a station inlet choke may be necessary to dampen the slugs. This will raise the well head pressure and reduce the test production rate, but it may be the only technique that will yield repeatable tests.
API RP 11V8:2003 pdf download
