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Abstract

Two-phase pipelines offer the potential for substantial cost savings in the offshore transport of hydrocarbons. Their design has been hampered by uncertainties in two-phase pressure drop relations, in flow regime determination, and in liquid slug length prediction. This uncertainty makes difficult the choice of pipe size and the design of downstream separation facilities. In order to reduce the uncertainty in two-phase flow pipeline design, Esso, Statoil, Mobil, Texaco, and Getty have sponsored the construction of the Norwegian Two-Phase Flow Laboratory now being operated by SINTEF. A large pipeline-riser experimental facility has been pipeline-riser experimental facility has been constructed to obtain laboratory quality data in a field scale apparatus. In addition, analytical modeling o two-phase flow is proceeding to provide a framework for interpretation of the experimental measurements. The experimental facility, results of experimental measurements, and analytical modeling techniques are described. The two-phase flow data and analysis resulting from this project promise to reduce substantially the uncertainty in the design of two-phase pipelines and downstream separation facilities.

Summary of the Significance of the Research Program at the Norwegian Two-Phase Flow Laboratory

1. Inadequate understanding of the pressure drop flow rate behavior and the slugging behavior of multiphase pipelines has been recognized as a major impediment to the realization of the cost saving potential of multiphase pipelines in offshore hydrocarbon production.

2. A large scale facility capable of taking laboratory quality data has been constructed. Data from this facility greatly aid in the determination of scale-up effects in multiphase flow.

3. Extensive measurements not only of pressure drop flow rate behavior, but also of instantaneous liquid holdup fraction have been made. The extensive use of multiple gamma densitometers has made possible the detailed description of liquid distribution effects, particularly in slug flow.

4. Combined experimental, analytical, and numerical developments have been carried out simultaneously. By use of this three-pronged approach, the experimental results will be more generally useful for commercial facilities design.

5. One of the outputs of the research program will be OLGA, a polished, calibrated, and tested transient flow multiphase pipeline simulator of direct applicability to commercial facilities.

6. The Norwegian technical community will have been strengthened by the development of expertise in a commercially important and technically sophisticated topic.

Cost Saving Potential of Multiphase Flow in the Off shore Environment

Two characteristics of the offshore environment make multiphase pipelines potentially attractive. First, pipe laying is expensive. If both liquid and vapor must be transported offshore, their simultaneous transport in a single pipe will save the cost of laying separate liquid and vapor lines. Second, offshore processing facilities are exceedingly expensive. Both the facilities themselves and the platform to support the facilities are very high platform to support the facilities are very high cost items. If offshore vapor-liquid separation can be avoided, considerable facility and platform cost savings may be realized. The avoidance of vapor-liquid separation offshore implies multiphase pipelines to shore. pipelines to shore.