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.

3D Geomechanical Finite Element Analysis for a Deepwater Faulted Reservoir in the Eastern Mediterranean

“…Structural geometry of faults is constructed using the interpretation of available seismic data while the 3D representation of fault blocks and their mechanical reactions can create technical modeling challenges in meshing and shear failure (Healy et al 2015;Markou and Papanastasiou 2020b) Fault displacement and slip tendency can support the estimation of stress state in a faulted system and Alpak et al (2019) presented a model for structural connectivity of faults in a reservoir. Markou and Papanastasiou (2018) supported that the existing structural geometry of the fault blocks in reservoirs can indicate that the deformations occurred in the reservoir through the geological time driven by paleostresses. The 3D geometry includes interaction between multiple fault blocks providing improved model visibility, so one can appreciate the evolved stress-strain impacts in a dynamic stress environment.…”

“…The geometry of faults is related to the dip angle of the fault slip surface, which is affected by the applied principal stresses relationship. Markou and Papanastasiou (2018) examined how the stress field related to the faulting regimes are related to field stresses, while Haimson and Rudnicki (2010) presented that the fault dip angle increases with intermediate stress. The faulting regimes are primarily classified as normal faults, strike-slipping, and reserve faults; however, in actual conditions, a combination of the primary classes exists.…”

“…A geological section is shown in Fig. 1c, as part of the 1D Mechanical Earth Model (MEM) constructed by Markou and Papanastasiou (2018) for the Aphrodite field, where it presents the complexity of the faulted blocks of the compartmentalized reservoir.…”

“…The significance of geomechanics lies in its ability to provide solutions for the challenges of reservoir production and well stability. The benefits of applying geomechanics encounter in the efficient coupling of rock mechanics with reservoir fluid flow simulators to produce dynamic earth representation models (Markou and Papanastasiou 2018). The integration of rock physics with porous fluids can enhance the accuracy of reservoir models.…”

Economic and fault stability analysis of geothermal field development in direct-use hydrothermal reservoirs

“…Therefore, failure in this case does not take place on the σ 1 -σ 3 plane, but rather on the σ 2 -σ 3 plane that defines the angle of the vertical fault plane with respect to the horizontal components of the stress tensor (Fig. 3b) resulting in strike-slip failure Markou and Papanastasiou (2018). Thermal stresses can cause significant changes in the stress tensor, especially around the injector well where the largest temperature differences occur.…”