In the central North Sea ‘Gannet‐A’ field, a 50 ft oil rim is overlain by a gas cap of variable thickness. Oil is produced from horizontal wells which initially produced dry oil, but as the field became more mature, a significant water cut was seen in several wells. A dedicated 4D seismic monitor survey was acquired in order to assess the remaining distribution of oil reserves. By forward modelling the synthetic seismic response to parameters such as contact movement and residual saturations (using 2D and 3D wedge models), and comparing the results with real seismic data, we are able to decipher the contact movements across the field. It is shown that, in one part of the field, the increased water cut is caused primarily by the vertical displacement of the entire oil rim into the initial gas cap. This oil‐rim displacement produces a very different 4D seismic response from the case of a static gas–oil contact and rising oil–water contact (normal production). As a result of these observations, we are able to optimize field production by both re‐perforation of existing wells and by drilling sidetracks into the displaced rim: a brown‐field development opportunity that might otherwise be missed.
Gas Field Planning Tool (GFPT) was developed in 1990 by the Shell Group of Companies to fill the need for a tool for gas field planning and development using deterministic subsurface and surface models. Main initiators were Shell Canada, NAM (the Netherlands), Shell Expro (UK) and BSP (Shell Brunei), as these companies are major gas producers.Shell Companies now have several years experience with using the GFPT. Application ranges from simple single field models to corporate-level models with a large number of gas reservoirs and wells. Shell companies now using GFPT models are Shell Expro (UK), BSP (Brunei), SSB (Malaysia), Shell Canada, SPDC (Nigeria), SDA (Australia), Woodside (Australia), PDO (Oman), NAM (the Netherlands), New Business Development (e.g. Lunar Project) and in future also Shell Egypt.NAM currently has a GFPT model for the Anjum field in Friesland and for the Ten Arlo field in the north of Holland.GFPT is currently being migrated to an HFPT (Hydrocarbon Field Planning Tool), which can also be used for planning of condensate, oil and water developments and for control of hydrocarbon compositions in the network using PVT de-lumping at the well head (e.g. for LNG plants) and optimisation techniques (linear, non-linear or based on bean-back lists).
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