Integated Reservior and Surface Network Simulation in Reservoir Management of Southern North Sea Gas Reservoirs
Authors: Tingas John , Frimpong Robert , Liou James 
Published: December 2007

Abstract
Integrated reservoir and surface network simulation is used to improve reservoir management in southern North Sea gas production systems where multi-branch surface facilities networks, reservoir compatuentalization and differential depletion play an important role. The integration of a 3D reservoir and surface network simulation into a single model provides an advanced approach for efficient reservoir management and production optimization from existing fields at different depletion stages and for planning of future field developments. It provides a tool for evaluating the remaining capacity of the surface network, for new field developments and the commercial opportunities presented by evacuating third party gas fields. The integrated simulation approach is also used to evaluate the negative impact of differential system pressures in situations where multiple well streams at various pressures from new field developments and/or third party gas fields are commingled. Significant pressure imbalance in gas producing systems require earlier startup of gas compression and low gas compression suction pressures to flow low pressure wells.
A coupled surface network and reservoir optimization software was identified as a critical technology element for studies of gas reservoirs at different depletion stages sharing the same surface network. For this purpose, a surface facility network programme, PIPEPHASE, proprietary of SIMSCI, integrated into Amoco's proprietary advanced reservoir simulation package GCOMP. GCOMP/PIPEPHASE was chosen for a fully integrated 3D reservoir and surface facility network simulation. The GCOMP/PIPEPHASE model replaced the Carter/RAISEGAS mainframe simulator, an older single phase 2D simulator, with a surface facility option. Carter/RAISEGAS has been used extensively in integrated surface network simulation of the Leman and Indefatigable gas fields, and up until recently it was the prime tool for reservoir performance evaluation, At this time, fully integrated GCOMP/PIPEPHASE models had been developed for the Leman and Indefatigable systems, as well as standalone Eclipse models of the three Indefatigable satellites, Davy, Bessemer and Beaufort.
Leman and Indefatigable are mature dry gas fields, extensively depleted after nearly thirty years of production. Production data have provided some evidence of differential depletion within the producing fields due primarily to comparmentalization of the reservoirs and regions of lower reservoir rock quality. The three new Indefatigable satellite gas fields commenced production in the winter season 1995-96. New high pressure field developments are planned to be evacuated via the Leman and Indefatigable gas field infrastructures. Simulation cases have included production optimization, evaluation of infill wells or adjacent reservoir developments at different pressures, the effect of reservoir differential depletion, identification of bottlenecks in surface facility layout, pipe size design and compressor capacities, evacuating new field developments and third party gas fields via the infrastructure with minimum gas back-out effect. Simulation results obtained from the integrated models provide optimized reservoir management leading to incremental production; a production strategy to maximize hydrocarbon recovery; rigorous technical analysis upon which economic performance and commercial value can be assessed; and a methodology to evaluate production enhancement projects.
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