The evolution of the reservoir stress state throughout the history of production

Based on principle stress theorem, the effective stress changes in the reservoir and its surrounding formation tightly coupled with pore pressure changes due to reservoir fluid withdraw or injection. Rock mechanical deformation induced by evolution of effective stress would be controlled through paths in which the reservoir stress follows during pore pressure alterations. The stress path that the reservoir conforms all over history of production undoubtedly affects the mechanical behaviour of the reservoir and fluid flow characteristics and could be one of the key factors in measurements and calculations of geomechanical instabilities related to pressure depletion/injection. The stress path additionally, has a considerable influence on recovery drive mechanism, straightly through compaction drive, and indirectly through permeability variation. Furthermore, the stress modifications in the reservoir and bounding formation possibly lead to changes in seismic attributes and consequently disturbing time-lapse (4D) seismic response. Other associated geomechanical problems include wellbore instability, casing collapse and solid production are strongly related to the stress path that reservoir and its burdens follow during production. Reservoir stress path and its changes throughout reservoir depletion are strongly dependent on several geological and mechanical factors such as reservoir boundary, reservoir dimension and its shape, constitutive behavior of reservoir rock and surrounding formations, and so on. A coupled hydromechanical model that includes above mentioned parameters was extended to more precisely forecast the reservoir stress state changes and to investigate the influences of these factors on reservoir behaviour. The main goals of this Paper are to explore which factors have the significant impact on the stress path, and to consider the effects of stress path on hydromechanical behaviour of a depleting reservoir. Numerical modelling results confirm that reservoir stress path is associated with the dimension and geometry of the reservoir and on poroelastic properties of the reservoir rock and bounding formations. Also we have shown that permeability reduction of the reservoir through fluid withdraw strongly depend on magnitude of the reservoir stress path.