Taitel (1986) provided with a theoretical explanation for the success of choking to stabilize the flow as described by Schmidt et al. (1980) noted that the severe slugging in a pipeline-riser system could be eliminated or minimized by choking at the riser top, causing little or no changes in flow rates and pipeline pressure. Contrary to Yocum's claim, Schmidt et al. Yocum observed that increased backpressure could eliminate severe slugging but would severely reduce the flow capacity. Topside chocking was one of the first methods proposed for the control of severe slugging phenomenon ( Yocum, 1973). This is a low-cost slug-mitigation option, but its application might be associated with considerable production deferment. While, a topsides choke can keep liquids from overwhelming the system, it cannot provide required control of the gas surges that might be difficult for the downstream system to manage. This method induces bubble flow or normal slug flow in the riser by increasing the effective backpressure at the riser outlet. Mak, in Handbook of Natural Gas Transmission and Processing (Third Edition), 2015 Topside choking They experimentally made three observations (1) large amounts of injected gas were needed to stabilize the flow with the gas-lifting technique, (2) careful chocking was needed to stabilize the flow with minimal backpressure increase, and (3) gas-lifting and chocking combination were the best elimination method reducing the amount of injected gas and the degree of choking to stabilize the flow. They proposed the stability and the quasi-equilibrium models for the analysis of the above elimination methods. (1996) investigated different elimination methods such as gas lifting, chocking, and gas lifting and chocking combination. Taitel (1986) provided a theoretical explanation for the success of choking to stabilize the flow as described by Schmidt et al. While, a topside choke can keep liquids from overwhelming the system, it cannot provide required control of the gas surges that might be difficult for the downstream system to manage. Mak, in Handbook of Natural Gas Transmission and Processing (Fourth Edition), 2019 3.8.4.3.3.2 Topside Choking It is also possible for the well to continue to flow for a long period in a loaded condition, producing gas up through the liquids with no liquids coming to the surface. If corrective action is not taken, the well will continue to decline and eventually log off. This occurs when the gas rate is too low to carry liquids to surface and simply bubbles up through a stagnant liquid column. Note that the flow regime further downhole may be in bubble or slug flow, even though the surface production is in stable mist flow.Įventually, the unstable slug flow at surface will transition to a stable, fairly steady production rate again as the gas rate declines still further.
This will often be accompanied by a marked increase in the decline rate. At this point, the well production becomes somewhat erratic, progressing to slug flow as gas rate continues to decline. Liquid production may also increase as the gas production declines.įlow at the surface will remain in mist flow until the conditions change sufficiently at the surface to force the flow regime into transition flow. As time increases and production declines, the flow regimes from perforations to surface will change as the gas velocity decreases. The well may initially have a high gas rate so that the flow regime is in mist flow in the tubing but may be in bubble, transition, or slug flow below the tubing end to the mid-perforations.
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