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API RP 19G5-2019 pdf free download

API RP 19G5-2019 pdf free download.Operation, Maintenance, Surveillance, and Troubleshooting of Gas-lift Installations.
5.3 Gas Dehydration Facility 5.3.1 General Most gas-lift systems use dehydrated gas; however, in some fields wet un-dehydrated gas is used. This can lead to corrosion or formation of hydrates and plugging of piping if temperatures fall below the hydrate formation temperature for the system pressure. Hydrates are solid crystals that form when gas molecules are trapped within a cage of water molecules. If free water is present, hydrates can form at 80 °F (26.67 °C) in high-pressure systems. A large temperature drop accompanies a large pressure drop, due to the Joule-Thomson effect; this can cause hydrates to form in the gas. Hydrate formation at the chokes or in the distribution lines causes increased pressure drops, which makes the freezing problem worse. The blockage can rapidly diminish the flow of gas and cause the well to be shut down. Figure 8 (courtesy GPSA, Engineering Data Book) shows potential hydrate conditions. Liquid in the gas-lift distribution system can also cause problems with measurement or control. Liquid tends to collect in any low spot in the distribution system; when a sufficient quantity has collected, it moves as a slug. Liquid slugging significantly affects or damages gas meters, controllers, and gas-lift valves or orifices, or a combination thereof. Inaccurate measurement, ineffective gas control, permanent damage to equipment, or severe production heading in the tubing, or a combination thereof can result from slugging.
5.3.2 Gas Dehydration Practices The following practices are recommended for a gas dehydration facility. Dehydrate all gas that enters a gas-lift distribution system. The objective is to lower the dew point below the lowest expected temperature to prevent hydrate formation. In many fields, this can be achieved by dehydrating to 7 lb (3.18 kg) of water per million standard ft 3 (28,317 m 3 ) of gas. Even drier gas may be needed in very cold weather or when CO 2 is present, where the guide is 3 lb (1.36 kg) per million standard ft 3 (28,317 m 3 ). Figure 9 (courtesy GPSA, Engineering Data Book) shows water content versus dew point temperature with gas pressure as the parametric lines; design gas-lift systems to avoid excessive pressure drops in the surface piping distribution system. Minimize the pressure drop across the surface control choke or control valve by using a gas-lift valve (rather than an orifice) as the operating valve on low PI wells so that casing pressure will be higher. Note that it is desired to take the largest pressure drop downhole where temperatures are higher, and the added benefit of an IPO valve is that it minimizes downtime after start-up. If an IPO valve is selected, it should be flagged with a lower set pressure to provide adequate gas passage and prevent multi-point injection.
— Design gas-lift systems with liquid traps at low spots where liquid can accumulate, especially upstream of gas flow rate meters or control devices. Install blow down valves in the traps so any accumulated liquid can be periodically removed from the system. Large piping distribution systems, particularly offshore, should have pig launchers and receivers to remove liquid and debris by periodic pigging. — If the presence of liquid cannot be avoided, periodically purge the distribution system to remove accumulated liquid. Purge orifice meter pressure and differential pressure taps periodically. — Use seal pots (liquid traps) on orifice meter pressure and differential pressure taps and purge periodically. Install the meter recorders or transmitters at higher elevation above the orifice tube and ensure the connecting instrument piping has no traps; and is of sufficient diameter to allow drainage (example 3 / 8 in./12 mm). — Use methanol to avoid temporary freezing problems. Also insulate control valves or chokes where large pressure drops can occur. Methanol is a hydrate point depressant that lowers the dew point. The best approach is to avoid the problems by using effective dehydration. Note that methanol is flammable and a neurotoxin. Refer to the safety data sheet (SDS) before use. Inhibitors should not be injected into the manifold as the liquids do not split flow in the same proportion as the gas. This is the route preferential flow phenomenon. Inhibitors should be injected into individual well lift gas injection lines. — Use a heater (line, gas, or catalytic) as an alternative to reduce the tendency for hydrate formation if effective dehydration is not an option.

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