The Solaris upper Jurassic prospect in the Norwegian Central Graben has been classified as ultra HPHT (>1200 bar and ~200 degC). The pore pressure prediction for this prospect was challenged as standard methods for prediction cannot be applied in the Central Graben for mineralogical and lithological reasons. The prediction was based on a gas event in the upper Jurassic shale of a neighboring well. The equivalent mud weight pressure was adopted as the reservoir aquifer pressure. Assumptions on the water and hydrocarbon densities based on regional knowledge built further the pore pressure prediction. The drilling commitment case was based on a seal breach scenario. The Fracture Closure Pressure at top structure was the anchor point for the aquifer pressure. Seal breach was considered as the main risk for the Solaris prospect. The seal retention analysis remained positive at both BCU and even base Chalk, using an average fracture gradient based on pressure integrity test of surrounding wells. The well was drilled successfully, using Managed Pressure Drilling. The pressures were found in line with the prediction. The PIT of the well, however, fell far below the fracture gradient. The structure suffered most likely from seal breach along the main fault.


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