A 3D reservoir geomechanics study was conducted in the Lower Cretaceous Minagish Oolite reservoir, Umm-Gudair field, West Kuwait, using coupled modelling. A series of parametric studies was performed to understand the impact of permeability changes on pressure, water production, and oil production at a selection of key wells. The evolution of fieldwide water saturation during more than 40 years of production was examined. The anisotropy between vertical and horizontal permeabilities was investigated. The coupled modelling demonstrated the impact of geomechanics changes (alterations in stress and strain) on both well and overall field performance.
A 3D geomechanical model was developed based on an existing dynamic reservoir model and static geological model. The 3D model consisted of 3,993,134 grid-cells and included the reservoir, its surrounding formations, and 10 seismically interpreted faults. Mechanical properties derived from well data, in situ measurements, and triaxial test data were populated within the 3D model. A preproduction stress calculation was performed to obtain a representative initial stress state before production, with calibration against measurements along various wells. The effective stress changes caused by depletion were simulated at various intervals over the production time; the reservoir displacements, both horizontally and vertically, were computed. To simulate the impact of reservoir rock deformation on reservoir performance, permeability updating was simulated considering the pore volume change of intact rock, the induced plastic shear strain of formed microcracks, and the dilation/opening of preexisting nonconductive fractures. This resulted in the variation of well performance in terms of pressure, water production, and oil production.
Four permeability updating scenarios were tested to understand the impact of dynamic permeability updating on well performance and field behaviour. The results show (a) an improved history matching of well pressure at almost all examined wells, (b) an improved history matching of water and oil productions at most of the examined wells, and (c) an insignificant impact on those wells along the flanks, despite significant improvements at the core of the anticlines. The results of this study provided guidance for optimal field development planning.