Production system analysis for Woollybutt mature oil field using dynamic simulation

Abstract

This paper describes how multi-phase flow dynamic simulation techniques were applied to support and optimise the day to day production operations for the Woollybutt oil field on the North West Shelf, Australia. Eni Australia is the operator of the: Woollybutt oil project, which consists of two separate fields; Woollybutt North, which has three production wells; and Woollybutt South, which has one production well– Woollybutt–4H (WBT–4H). WBT–4H is located about 7 km from the floating production storage and offloading (FPSO) facilities and shares the production flowline with two other production wells from the Woollybutt North field. Production from WBT-4H accounts for more than 60% of the total production. For this reason, achieving steady production from this well is the highest priority for the operations. To understand the hydrodynamic behaviour and to maximise production from WBT–4H, the production system for the Woollybutt South field was modelled from WBT–4H reservoir inflow points to the FPSO using a commercial dynamic simulation software package. The model successfully matched the pressures measured at the permanent down hole gauge (PDHG) and upstream production subsea choke dynamically, using the arrival pressure at the FPSO and the measured gas lift rate at the FPSO as input data. The model was used to identify the reason for slugging , to locate where the slugging conditions were originating, as well as to investigate optimum gas lift rate and the impact of bringing other wells on production from the Woollybutt South field. Furthermore, the model was used to identify the cause of sudden severe slugging, which forced to reduce the subsea production choke opening. The simulation work concluded that an unstable gas injection at the gas lift orifice valve (GLOV) induced severe slugging. This conclusion was validated operationally in the field soon after. Results of the multi-phase flow dynamic simulation provided good understanding of the hydrodynamic behaviour in the production system and are used to make informed decisions to support and optimise the day to day production operations.