Abstract
The Pyrenees development, operated by BHP Billiton, comprises the concurrent development of three oil and gas fields: Ravensworth, Crosby and Stickle. The fields are located in production licenses WA-42-L and WA-43-L, offshore Western Australia, in the Exmouth Sub-basin. Seventeen subsea wells, including 13 horizontal producers, 3 vertical water disposal wells and 1 gas injection well have been constructed to date. The project is presently on production with first oil achieved during February 2010.
Due to the normally pressured reservoir conditions, reliable kick-off and clean-up of the long horizontal development wells to the FPSO was heavily dependent upon gas lift. As a result of uncertainty of gas compression availability at field start-up, detailed contingency plans were developed to reduce the reliance on gas lift during field start-up. Identification of feasible contingencies required a thorough understanding of the dynamic flow behaviour of the wells and flowlines during the start-up process.
This paper summarises how a commercial transient multiphase flow simulator was utilised to model well kick-off and clean-up for a number of cases with and without gas lift against initial flowline contents of seawater, diesel or gas. The approach employed to modelling the lateral well sections completed with inflow control devices (ICDs) allowed for an accurate representation of initial and residual drilling mud volumes, annular flow and the impact of the ICDs on the inflow profile.
The primary objective of the dynamic simulation was to identify the requirement for invoking contingency options and to confirm the feasibility of the various options in ensuring a reliable and successful well kick-off without gas lift. A comprehensive analysis of the results contributed to a thorough understanding of the dynamic flow behaviour of the clean-up process. Secondary objectives of the simulation included an estimate of the reservoir drilling fluid (RDF), diesel and flowline contents return rates and volumes to the test separator and an estimate of the time required for each well to clean-up. Conclusions from this work were crucial to contingency planning and proved to be invaluable in successfully executing and optimising well clean-up operations, the field start-up planning and the production ramp-up.
