The prediction of stress and strain changes in and around reservoir using numerical simulators is often based on assumption of linear elasticity before reaching yield point. However, it is known that rocks are generally behaving non-linearly and a deviation from purely elastic response begins already at micro-strain level. In this work, we performed multi-scenario numerical modelling of hydrocarbon reservoir depletion using a non-linear elastic model. The model has been calibrated based on the laboratory test results with both sandstone and shale. The non-linear elastic modelling is then compared to purely linear-elastic cases. We found that assumption of pure elasticity could lead to a strong underestimation of stress and strain changes in and around the reservoir. In addition, stress path (direction of stress changes) may significantly deviate when non-linear elasticity is not accounted for.
It is well-established within the petroleum industry that reservoir depletion and associated stress changes have an essential impact on field performance. Reservoir pore pressure depletion results in various stress paths in and around the reservoir. The stress path affects the geomechanical behavior, i.e. the reservoir compaction and the associated surface subsidence. Additionally, the stress changes may also cause seismic velocities alterations affecting time-lapse seismic response and providing options to monitor reservoir performance. Furthermore, the stress paths of the reservoir and the overburden are affecting the stability of boreholes during drilling and hydrocarbon production, as well as sand production.
When the stress changes in the subsurface are estimated using numerical simulators, one of the common assumptions is linear elasticity prior to the plastic yield point. Such simplification may have strong consequences on the output since it is known that rocks are not linear elastic media and a deviation from purely elastic response begins already at micro-strain level (Lozovyi et al., 2017; Winkler et al., 1979). Assumption of linear elasticity could lead to inaccurate prediction of stress-strain changes and stress path in the subsurface during e.g. hydrocarbon reservoir depletion or injection.
