The Value of Geomechanical Modeling of Fault Properties for Trap Analysis

Abstract

Geomechanical and kinematic modelling techniques were applied to support the trap integrity risking process for a North Sea appraisal project in faulted Carboniferous clastic strata. A key issue here is whether clay smearing has the potential to provide a valid seal across reservoir compartmentalizing faults. Standard fault seal analysis workflows use the critical clay smear factor (CCSF) to assess the potential for fault sealing. However in a mechanically layered sequence, the CCSF will vary between layers depending on the position of the layer within the overall stratigraphy and the rate of fault propagation. We use a combination of mechanical and kinematic models to predict (a) where the faults will nucleate in a mechanically layered sequence and how fast they will propagate through it, and (b) the resultant fault propagation folding in shale layers and hence the CCSF for each shale layer. We show that the development of clay smears is dependent on both the surrounding stratigraphy, the depth of burial at the time of faulting, and the rate of fault propagation.