Modeling of Fluid Pressure and Overburden Response Caused by Activation of a Dormant Fracture in Caprock

Successful sequestration projects require substantial volume of CO2 to be injected into the reservoir and store it for a long period of time. Any leakage of CO2 from the reservoir through the caprock seal would be undesirable. When a large volume of CO2 is sequestered in a reservoir, the fluid pressure is influenced by the presence of any leakage pathway in the caprock seal. Existing dormant fractures may become active in the caprock due to stress changes that can lead to potential leakage. Fluid pressure response in an overburden monitoring layer can be used to identify such possible scenarios of leakage in the caprock. In this paper, the fluid pressure and geomechanical response of the overburden caused by the activation of a fault/fracture is presented. The influence of the fracture location on the overburden pressure response is also presented in the paper. A finite element approach was used to model the changes in the fluid pressure and subsequent overburden response during and after the injection of CO2. Two-dimensional and three-dimensional finite element analyses were performed to simulate the activation of an existing dormant fracture after the initiation of CO2 injection. The pressure response in the overburden formations was studied by performing coupled flow-deformation calculations. Results show significantly different pressure distribution in the overburden monitoring layer due to presence of a fracture. Pressure response is different at different locations in the monitoring zone, which could be used as a monitoring method in identifying the possible locations of a caprock fracture. Results show that the activation of a simulated fault causes a sudden change in the pressure signature at different locations in the overburden monitoring layer. Such changes in the pressure signatures at monitoring locations can be useful in identifying the possible breaks in the caprock seal during the injection of CO2.