Fault slip or bed-parallel shear- – A multi-scenario modeling approach to investigating well deformation in the deep overburden of a compacting reservoir in the North Sea

摘要

A multi-scenario geomechanical modeling approach is presented to investigate the potential mechanisms that lead to a series of observed well deformation incidents in the deep overburden overlying a depleting and compacting chalk reservoir in the North Sea. Complementary to the commonly pursued approach of building a full-field geomechanical model, a suite of detailed ideal geomechanical models is developed based on data and evidence driven scenarios that take into considerations fault population and juxtaposition, contrasting mechanical stratigraphy, intra-bedding contact conditions, and lateral persistence of thin stringer beds. The simulation results of extensive runs suggest that as the majority of faults in the overburden mudstones would remain stable under the pre-production stress state, however, the contrasting mechanical stratigraphy consisting of thick compliant mudstone and thin stiff carbonate stringers facilitates “domino” or “bookshelf” style intra-bedded shear slippage in response to the developing dominant shear zone around the periphery of the active compacting region. This multi-scenario approach provides new and accelerated insights into the diagnosis of compaction-induced well failure and allows mapping of competing mechanisms potentially responsible for the problem, which helps to steer further modeling efforts, and guides future data acquisition.