API RP 19G5 pdf free download
API RP 19G5 pdf free download.Operation, Maintenance, Surveillance, and Troubleshooting of Gas-lift Installations.
4.2 Under-lifted and Over-lifted Wells 4.2.1 General A gas-lift well is under-lifted when the depth of gas injection is shallower than necessary for optimum lift or the rate of gas injection is too low, or both. Both of these conditions can lead to ineffective lift gas utilization and lower than desired production. A gas-lift well is over-lifted when the rate of gas injection is too high or the gas injection pressure is too high, or both. These conditions can lead to ineffective lift gas utilization. Less than optimum gas-lift exists when a large increase in injection gas rate results in a small gain or even a loss in production. The objective is to use the total available injection gas in an optimum way to maximize the total oil production rate. Over-lifting can also cause high casing pressures and reopening of upper unloading valves resulting in much less efficient use of lift gas and wear on unloading valves. When the compressor capacity exceeds optimum injection gas required for the group of wells, the criteria of flow stability can be applied. Stability requires a velocity of about 6 ft/sec (1.83 m/sec) in the gas-lifted mixture in the tubing string above the injection point. 4.2.2 Practices for Under-lifted and Over-lifted wells The following practices are recommended and should be followed for under-lifted and over-lifted wells. — Monitor the performance of each gas-lift well using flowing pressure and temperature surveys, and static pressure surveys, in conjunction with accurate well test and injection information, to determine (or estimate) the current producing gradients, depth(s) of gas-lift injection, FBHP(s), and inflow performance. Use this data to create a calibrated computer model for use in surveillance and troubleshooting. Apply the same procedures to natural flow wells that will eventually be artificially lifted. — As an alternative to a flowing pressure and temperature surveys, a CO 2 tracer survey method may be used to determine the depth(s) of gas-lift injection. Here, a small amount of CO 2 is injected along with the injected gas-lift gas. The return production is monitored and the time for the return of the CO 2 is determined. The time of the CO 2 return is correlated to the depth(s) of injection from the casing annulus into the tubing. This method can be used on both single and dual string gas-lift wells. — Use a calibrated computer model, with current operating conditions, to detect a well that is being under-lifted, and to predict the optimum gas-lift injection rate, pressure, depth, and expected increase in production from solving the problem.An excessive gas-lift injection rate can also limit production. Excess gas can also increase friction in the surface flowline. This can cause a higher FBHP resulting in less drawdown and a lower production rate. The gas rate can become so high that the effect of friction loss exceeds the reduction in fluid density and the pressure gradient begins to increase, the FBHP rises, and the liquid rate decreases. When gas is injected into a continuous gas-lift well, it mixes with the liquid in the production stream (usually the tubing). Gas is less dense than liquid, thus it lightens the pressure gradient (reduces the mixture density), allowing the well to produce with lower production pressure drops. As gas injection is increased, the production pressure continues to drop, up to a point. This point is called the minimum pressure gradient (see Figure 4). The point labeled “Ideal Operation” is considered to be on the minimum practical pressure gradient. The injection gas rate for a continuous gas-lift well should be less than the rate required to reach the minimum gradient, which can increase challenges.API RP 19G5 pdf download.
