A methodology for incorporating geomechanically-based fault damage zones models into reservoir simulation

In the fault damage zone modeling study for a field in the Timor Sea, I present a methodology to incorporate geomechanically-based fault damage zones into reservoir simulation. In the studied field, production history suggests that the mismatch between actual production and model prediction is due to preferential fluid flow through the damage zones associated with the reservoir scale faults, which is not included in the baseline petrophysical model. I analyzed well data to estimate stress heterogeneity and fracture distributions in the reservoir. Image logs show that stress orientations are homogenous at the field scale with a strike-slip/normal faulting stress regime and maximum horizontal stress oriented in NE-SW direction. Observed fracture zones in wells are mostly associated with well scale fault and bed boundaries. These zones do not show any anomalies in production logs or well test data, because most of the fractures are not optimally oriented to the present day stress state, and matrix permeability is high enough to mask any small anomalies from the fracture zones. However, I found that fracture density increases towards the reservoir scale faults, indicating high fracture density zones or damage zones close to these faults, which is consistent with the preferred flow direction indicated by interference and tracer test done between the wells.; It is well known from geologic studies that there is a concentration of secondary fractures and faults in a damage zone adjacent to larger faults. Because there is usually inadequate data to incorporate damage zone fractures and faults into reservoir simulation models, in this study I utilized the principles of dynamic rupture propagation from earthquake seismology to predict the nature of fractured/damage zones associated with reservoir scale faults. The implemented workflow can be used to more routinely incorporate damage zones into reservoir simulation models. Applying this methodology to a real reservoir utilizing both field and well scale observations, I found that damage intensity gradually decreases away from faults, and if the secondary features associated with the damage zones are optimally oriented for shear failure in the present day stress state, they may affect the permeability of the reservoir in both the horizontal and vertical directions. I verified the modeling results with both field (outcrop) scale and well scale observations from a number of studies and show that dynamic rupture propagation gives a reasonable first order approximation of damage zones and can be incorporated into reservoir simulation models. Using fluid simulation in a fine-scale model that included the discrete secondary features of a damage zone, I demonstrated that the permeability anisotropy due to a damage zone exists due to increased permeability along the strike of the fault and in the vertical direction. However, there is no significant change in the permeability of the damage zone in a direction perpendicular to the strike of the parent faults in the studied field.; Faults are generally curved and oriented in multiple directions in a reservoir, so often they are not aligned with the simulation grid. Based on the complexity of fault geometry, a simulation grid may have complex cell geometry adjacent to the faults. I present a methodology to implement the effects of damage zones in the simulation grid, which are generally located in fault adjacent grid blocks. To incorporate the fault-related effects of permeability anisotropy in the simulation grid, I used the strike and dip of faults with reference to the grid axes. The relative effects of the dimension of the damage zone are incorporated using the normalized damage zone width with respect to cell volume and surface area. The absolute value of permeability anisotropy is then defined by several iterations of history matching with the observed production data of the studied field. Inclusion of damage zones into simulation model shows a...