Introduction

The transport of untreated hydrocarbons and its associates through one single pipeline is called multiphase flow. It is governed by a mostly unpredictable scenario of the different fractions of oil, gas and water occurring. The fractions tend to separate from one each other not only directly in the well, but also in the surface flow lines causing more or less severe slug flow. The reservoir energy or any artificial lift method drives the flow to a field separation station. There energy is added to the different phases for further transport to the final destination. Quite often gas and associated condensate are just flared at such locations. Besides the economical impact this can hardly be tolerated due to environmental issues.

Additionally flowline pressure losses cause backpressure onto the wellhead influencing production of the wells in a negative way.

In order to add energy to the untreated wellstream and to cut-off pressure losses from wells, a multiphase pump may be installed, thus giving incremental production and avoiding intermediate separation with gas flaring or even separated flowlines for liquid and gas. The pump may serve only one well, on a manifold or even a complete cluster. Its location is governed by many different aspects to be carefully evaluated.

Challenges

In contradiction to the transfer of pure liquid or gas, the equipment in question has to be able to handle totally transient flow conditions. Nevertheless the expression "pump" or "booster" has become very popular. In detail it has to be considered that the different fractions unpredictably change for an uncertain timeslot. A standard pump or compressor cannot cope with this scenario. Especially during a period of only gas running to the pump, i.e. the gas volume fraction is 100%, it has to be guaranteed that this is moved onwards and no overheating or "gas-lock" occurs. Aside of this the required discharge pressure has to be maintained at all times.

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