--> The Most Complex Structure Ever to be Dynamically Modelled? State-of-the-Art Workflows Allow New Insights Into North Rankin, a Producing Giant Gas Field on Australia's NW Shelf

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The Most Complex Structure Ever to be Dynamically Modelled? State-of-the-Art Workflows Allow New Insights Into North Rankin, a Producing Giant Gas Field on Australia's NW Shelf

Abstract

The North Rankin giant gas field has been supplying Australia's North-West Shelf Gas Project since 1984, and is expected to continue for many years. The field comprises an elevated horst block containing complex internal faulting, with styles including top truncation, multiple stacked antithetic and crossing faults. Until now it was not possible to fully understand intra-field flow and the influence of the aquifer, as pillar gridding techniques cannot produce geocellular models of the required complexity. Intensive seismic interpretation effort allowed a detailed structural framework to be built. Its complexity could be captured for the first time in a static reservoir model, using a new volume-based approach. The dynamic simulation version of this model, with appropriate global fault transmissibility applied to the stair-step fault representations, provided an impressive history match to field performance at the first attempt. Significantly, an alternative model based on simplified structure gave an inferior match. The new structure modeling also permitted seismic horizon interpretation to follow a tiered approach, keeping the time and effort involved within acceptable limits. After defining the structural framework using three meticulously picked horizons, relatively quick picks were accurately extrapolated across the entire complex structure for four additional horizons. With ongoing dynamic calibration of the model, including aquifer size and connectivity, excellent history matches to production, pressures and contact movements have led to revision of the field's Gas Initially In Place and range of forward production profiles. Furthermore, new insights have arisen concerning undrilled blocks and pressures encountered in an offset well.