Modelling of the undrained pore pressure changes around (an inflating) reservoir

The sealing efficiency and fault stability of the reservoir's overburden are essential in both CO2 storage and hydrocarbon production. This elevates the importance of induced stress and pore pressure change prediction in the proximity of the production or injection zones. The low-permeability nature of the overburden makes it necessary to quantify undrained pore pressure response from stress changes. The primary objective of our work is to model and comprehensively visualize the undrained pore pressure response of low permeability surroundings (typically shales) of various geological bodies in multiple scenarios of inflation or depletion. We perform each scenario in two steps: First, we perform finite element simulations of stress and strain evolution. Then, we post-process the modelling results to compute the undrained pore pressure change. In order to permit parametric sensitivity studies and provide an understanding of mechanisms that may act in the field, we model isolated geo-features, e.g., disk- and dome-shaped reservoir surroundings, tilted layers, and fault zones. This may serve as a basis for subsequent studies of real-life reservoirs with their excessive complexity and ambiguity of result interpretation. Moreover, we aim to demonstrate the consequences of using different geomechanical finite-element modelling approaches on the predicted pore pressure distribution trends and values. Our study investigates the impact of factors such as boundary conditions of the model, properties assigned to the modelled deposits, relations between all three principal stresses, and the choice of pore pressure prediction model. The impact of anisotropy assigned to reservoir surroundings during geomechanical modelling on the estimated pore pressure response is shown in Figure 1. We compare the approaches in terms of the complexity of their application and the results their produce. Finally, we identify the most important factors, which should be taken into consideration during a full-scale reservoir modelling.