Geomechanical integrity of sealing faults during depressurisation of the Statfjord Field

In this paper the results of geomechanical analyses of fault behaviour at the Statfjord Field carried out as part of Statfjord Late Life Project are presented. The objective was to assess the sealing integrity of the horst structure between the Statfjord and Snorre fields during final depressurisation of the Statfjord Field. According to field pressure observations the Brent Fault is to date still acting as a pressure seal between the Brent Field and the Statfjord Field, despite the large present-day depressurisation of the Brent Field. These observations were used as a calibration and verification of the stress conditions that can be sustained without modifying the seal integrity of the fault. Based on the calculated stress changes in the horst structure which are equal to or less critical than the calculated present stress changes on the Brent Fault, it is concluded that the mechanical effects associated with the planned depressurisation of the Statfjord Field during its late life phase will not affect significantly the hydraulic resistance of the horst structure. A parametric study was conducted to investigate the sensitivity of the calculated stress changes to various input parameters for fault geometry and properties. The largest uncertainty relates to the peak shear strength of the fault (core) zone.