Petroleum geomechanics modelling in the Eastern Mediterranean basin: analysis and application of fault stress mechanics

Abstract

A fault stress analysis of a typical gas field in the Eastern Mediterranean is presented. The objective of this study is to provide estimates of the in situ stresses and pore pressure for populating a regional Mechanical Earth Model and to characterize the stability of faults under current and changing reservoir conditions. The fault stability analysis is based on the Mohr-Coulomb frictional faulting theory. The vertical in situ stress is estimated using seismic and density data and the bounds of the horizontal stresses were determined for different fault regimes. The pore pressure for determining the effective in situ stresses is estimated using the Bowers pore pressure prediction method. Fault stress analysis is performed in a series of calculations and the results are plotted on Mohr diagrams for shear failure. The fault stress analysis is performed on a wide range of alternative azimuth orientations for SHmax in order to capture the uncertainty on the actual orientation. Sensitivity with respect to reservoir pore pressure change suggests that pressure reduction in the reservoir improves the fault stress stability, ignoring in the current analysis any stress arching effects. Pore pressure increase decreases the normal stress on the fault leading to increasing risk of shear failure of the critically stressed faults. The case study examines eight faults on the Aphrodite gas field with the objective to characterize if the faults are active or remain dormant under current stress conditions and how the stability may change in reservoir injection or depletion conditions.