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Multiphase Pumping Multiphase pumping, often also referred to as multiphase boosting, is the transport of liquids and gas as one common mixture. The mixture may also contain a certain amount of particulate, mainly from the reservoir. This technology, today predominantly installed at surface, aims to increase the pressure of the mixture to allow for constant and increased flow in pipelines over longer distances. Subsequently the untreated flow from a single or multiple wells is picked up right by the well head or at a manifold, which brings together several wells at one location. Surface facilities for the production of hydrocarbons usually are sized according to the estimated plateau production, i.e. the amount of oil, gas, and water over a reasonable long period that allows for the recovery of more than the investment. However, with the removal of the fluid from the reservoir, not only the mixture will change, but also will the reservoir pressure. This in turn may require substantial changes in the facilities, if the production shall further contribute to the benefit of the operator and/or owner. Additionally a vast number of oil fields are equipped with 1st-stage processing facilities, usually separating the gas from the liquids in the field. Since the value of the oil compared to that of the gas is much higher, very often the gas is either vented or flared – and even its lower value is lost forever. Since the technology will enable all the produced fluids to be transported further, in-field separation deems not to ne necessary. The gathering of gas at a more distant location, potentially suitable for the entire production, will enable power generation for either the field operations, and/or an adjacent power grid. As such the gas value is not lost, and the environment is protected from pollution. The two main ideas behind multiphase pumping are 1. Unload the well head/manifold from its downstream pressure needs, which will lead to a higher differential pressure at bottom hole, which in turn may result in prolonged and incremental production, and 2. At the same time still satisfy the pressure requirement at the receiving facility, as the separator pressure should be maintained to serve its downstream scenario.
The rotating machinery used is known as a “multiphase pump”, in short often MPP. Two different technologies are commonly used, the positive displacement, as well as the roto-dynamic one. The challenge for both these technologies is the entirely transient flow at the pump inlet. Because of separation effects already in the well bore, as well as in the flowlines to the pump, the gas volume fraction (GVF) of the current fluid flow nearly is unpredictable. It will vary between 100% liquid and 100 % gas – the typical quasi-static inlet scenarios of either a liquid pump or a gas compressor. However, neither is able to take an uncertain mixture. As such the MPP, which basically is a pump, and its package need to be adopted to meet that challenge. While the general package design follows industry’s best practise, the GVF at MPP inlet needs to be controlled to suit the technology selected. For positive displacement pumps the pump characteristic is independent of the fluid’s specific gravity. However, a certain amount of liquid at pump inlet is needed, at least to carry over the heat generated by friction and gas compression. This is achieved by catching liquid downstream of the MPP. This liquid then is recycled to inlet. A cooler in the recycle line may be used. For the roto-dynamic technology, a vessel with the manufacturer’s proprietary design may be used. For this it is advisable to know the maximum length of a gas slug to enter the MPP.
SPE 109785 Operating Multiphase Helicoaxial Pump in Series to Develop a Satellite Oil Field in a Remote Desert Location
SPE 81504 Application of Multiphase Pumps in a Remote Oil Field Onshore Abu Dhabi
Papers to be continued… (There is a large number of papers available in One Petro).