Abstract

In the oil and gas industry a large portion of the compressor feed streams are characterised as wet gas, with a liquid volume content of between zero and five percent. Typically, this liquid is separated upstream of the compressor and handled separately. Such compressor systems have a large footprint, high weight, and high cost. In addition, if the liquid separation is not sufficiently good, trace amounts of liquid will enter the compressor and eventually cause fouling and performance degradation and possibly mechanical damage. The promising technology of wet gas compression is attractive to the oil and gas producers as it attempts to simplify the compressor systems thus reducing the footprint, weight, and cost. Furthermore, if the liquid amount is always sufficient to allow for liquid at the compressor discharge, fouling will not occur as the machine is continuously washed. This can allow for wet gas compressors continuously operating for years without any interventions. Installing such a wet gas compressor near the well head will provide increased recovery from the reservoirs.

Wet gas compressors are designed and used in a variety of operating conditions. Dependent on reservoir depletion, well stream compressors experience a gradual shift in inlet pressure and fluid behaviour. A major challenge both to designers and operators of wet gas compressors, is related to the impact of changing fluid conditions, such as gas mass fraction and density ratio, on performance.

Several single stage, two stage and multistage wet gas compressor test campaigns have been conducted at K-Lab. A large range of inlet conditions has been tested, i.e. inlet pressure ranging from 12 to 110 bar, gas mass fraction between 0.7 and 1.0, and combinations of hydrocarbon gas, hydrocarbon liquid, and water have been used as test fluids.

Performance test results from one of these wet gas test campaigns are presented in order to expose the impact of variables such as the fluid density ratio. The reference full-scale tests were conducted in real conditions i.e. realistic hydrocarbon composition, pressures, and temperatures. A large range of suction pressures were investigated, with a gas mass fraction ranging from 0.7 to 1.0. The density ratio between gas and liquid is of great importance as it relates to the flow regime, phase segregation and phase slip. Special emphasis is made to relate the performance shift between dry and wet conditions to the density ratio and other wet gas parameters, and a model is proposed that will incorporate these parameters to this shift.

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