Dynamics of Stresses and Fractures in Reservoir and Cap Rock under Production and Injection

Production of hydrocarbons from geological reservoirs, and injection of fluids such as water or CO2 into geological strata are accompanied with stress changes in the reservoir and in the cap rock. If the stress changes are large enough, they may reactivate faults or pre-existing natural fractures, or induce new fractures in the reservoir and/or the cap rock. Fractures in the cap rock caused by stress changes during CO2 injection may threaten the cap rock integrity. Fractures within the reservoir may increase its injectivity, improve hydraulic communication and thereby facilitate spreading of the injected fluid. The objective of this work was to classify possible stress dynamics and fracturing scenarios that may take place under geological storage of CO2. A compendium of stress regimes and expected fracture patterns is compiled that can be used as a quick guide when evaluating the risk of fracturing under CO2 injection into deep saline aquifers or depleted fields as well as when estimating geomechanical effects of reservoir stimulation.