Predicting water in the crest of a giant gas field: Ormen Lange Hydrodynamic Aquifer Model

Abstract

Abstract Hydrodynamic aquifer conditions have been described in many basins around the world since first introduced by Hubbert1 in 1953. The hydrodynamic aquifer concept in Ormen Lange has been assessed using iso-potential mapping1 and dynamic simulation of the fluid fill development (i.e. imbibition) over geological time. Simulation shows2,3 the hydro-dynamically tilted/stepping contacts depend on rate of water flow across the aquifer, stratigraphic baffling and faulting, effective aquifer area and reservoir quality (NTG and effective permeability). The role of sealing faults over geological time scale is downplayed in terms of justifying the fluid distribution. Baffling during production is, however, expected. In Ormen Lange the hydrodynamic aquifer has pushed the gas from the crest of the structure into the south of the field leaving behind a northward-thickening prism of residual gas which is imaged by a seismic DHI. Confirmation of the hydrodynamic aquifer scenario in this field was achieved after drilling an appraisal well in the north of the structure that corroborated fluids (water with residual gas) and pressures as prognosed by the hydrodynamic aquifer model.