The Chevron-operated Gorgon asset is the largest single resource project in Australia, with a portfolio of offshore gas fields to supply gas via two trunklines (Gorgon and Jansz-Io) to a three-train, 15.6 MTPA LNG plant and a 300 TJ/D domestic gas plant on Barrow Island. Gorgon will be a legacy project, with decades of production anticipated from the development of backfill fields gas resources. To realise the value of the asset, it is critical to select the right projects and execute them at the right time. Greater Gorgon Integrated Production Modelling (IPM) has been developed by Chevron Australia's gas supply team on behalf of the Gorgon Joint Venture (Australian Subsidiaries of Chevron, ExxonMobil, Shell, Osaka Gas, Tokyo Gas and JERA) to specifically enable optimisation of both the subsurface and surface value chain. It integrates reservoirs, wells, and subsea production networks to enable rigorous assessment of various portfolio-level development and planning scenarios.

The focus of this paper is on the Jansz-Io trunkline, which is initially supplied by the massive depletion drive Jansz-Io field, and the key decision of how to maintain production post development of the Gorgon Stage 2 (GS2) project. To inform this key decision, extensive evaluation was conducted using coupled INTERSECT (IX) IPM model to assess Jansz-Io Compression (J-IC) concepts (floating platform vs subsea compression). The IX-IPM model includes either detailed IX dynamic simulation or simplified material balance (MBAL) reservoirs, and a detailed production system that captures the full pressure hydraulics and their complex interactions. Using this IX-IPM model, a systematic staircase approach was applied, starting with a minimum facility concept, before sequentially adding more functionalities (power, capacity, phasing and backfill fields tie-in) and quantifying their incremental benefits. This enabled comprehensive understanding of the compression model's pressure hydraulic performance and various value trade-offs at each step. A fit-for-purpose, fixed power compression model was implemented to commence the staircase assessment. Once subsea compression was selected, and as the assessment matured, vendor compressor performance curves were adopted for more rigorous modelling.

Overall, the Greater Gorgon coupled IX-IPM model has proved to be invaluable in the assessment of the J-IC concept select and supported the Final Investment Decision (FID) on J-IC in 2021. The coupled IX-IPM model is continually refined with greater engineering resolution and additional production history to support the wider Gorgon asset decisions.

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