ABSTRACT:

The Aquila field is the deepest offshore field in Europe and was selected by Eni-Agip for a data collection campaign during transient operations. The field is placed in 850 m deep water, and it is developed by two wells connected to an FPSO by two independent flexible risers. The main goal of this data collection was the set-up of a database for the validation and qualification of computer codes for multiphase transient hydraulic analysis. Production data were collected every day, and the mean production values are reported in daily sheet. Moreover four operational transient were completely monitored by collecting data with high frequency, respectively in April 98, October 98, December 98 and August 99. From April 98 to August 99, the reservoir depletion have caused a general pressure decrease in the system, so the same scenario was analysed in different pressure conditions, with difference code response. Multiphase transient codes are used in ENI-Agip in an extensive way in design, production optimisation and safety analysis (like blow-out prevention and mitigation). In particular, the OLGA code is an R&D product developed for the analysis of three phase flows in pipelines and networks in transient conditions. It is very important to evaluate the error performance of the computer code, in fact during the multiphase production analysis, the knowledge of multiphase flow parameters like pressure drops, liquid hold-up, temperature and single phase (oil, gas and water) flow rates both in steady state and in transient conditions it is a necessary information for a correct system design and production optimisation. Starting from the wells and risers geometry, and from the PVT studies performed in Agip, the simulation of the five, collected transient scenario has been performed. The comparison between measured and calculated trends of the main system parameter permit the evaluation of the code capabilities in the prediction of this kind of scenarios and the accuracy associated to the calculated data. The most significant results have been selected and reported in this paper

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