Integrated Sub-Surface and Surface Modelling for Gas Field Planning and Refinery Feedstock Evaluation

Abstract A gas field is producing condensate with higher density than typical due to its higher napthene and aromatic content. Several future gas fields to be developed also have condensate with similar properties as this single field. The changes in future condensate properties and increasing amount of this atypical condensate will have major impact on existing refinery. It was necessary to create an integrated reservoir and surface facilities model and characterised fluids that can produce prediction of future feedstock including these aromatic condensate to the refinery. The model also produced the usual outputs such as gas quality and condensate quantities forecast over the life of the gas fields. A compositional network model consists of fluid modelling, reservoir, well, topside facilities and pipeline modelling through to the onshore terminal process modelling were developed in order to model the export gas and condensate network. Steady state models were developed and validated against operating condition for each system and an integrator was utilized in order to integrate the subsurface and process simulator together. For the fluid modelling, a compositional model suitable to produce assays was used instead of black oil model in order to predict the quality of both the gas and condensate delivered. The fluid models for fields with aromatic condensate used True Boiling Point (TBP) assay instead of a standard gas chromatograph composition from a Pressure, Volume and Temperature (PVT) laboratory test report. Several characterisation methods were developed and tested in order to obtain representative and relevant properties for refinery design. Other gas fields which had a more common chemical characteristic of paraffinic dominant condensate used standard characterisation method. The model enables representative prediction of condensate properties relevant for refinery design and evaluate options to develop the fields. The work will show that an integrated sub-surface-surface network model is essential in order to define the impact for a development throughout the value chain, specifically the changes to the products and downstream facilities. It will also provide an insight on the impact of fluid characterization methods of different types of condensate.