A Numerical Study of the Effect of Fluid Pressure on Smeared Cracking Behavior in the Caprock of Underground Gas Storage Reservoirs

The injection or extraction of gas can change the pore pressure within the reservoir, which in turn results in redistribution of the stress field. Consequently, the induced deformations within the reservoir and the sealing caprock can potentially prompt a damage zone in the caprock.The main objective of this paper is to develop a model to estimate the growth and extension of cracks in the caprock. In order to achieve this aim, the smeared crack approach is used to model the process of cracking in the caprock. To do this, we will employ smeared crack approach to study the initiation and propagation of cracks in caprock of subsurface reservoir. There are generally three approaches in solid mechanics when modelling cracks: discrete crack, interface elements and smeared crack. Although, discrete crack approach reflects the fracture development phenomenon most closely, it does not fit the nature of numerical methods and it can computationally expensive with development of cracks, each node is replaced by more nodes, which entails re-definition of finite element mesh and hence more computational resources are needed. On the other hand, smeared crack approach assumes that the cracked solid is a continuum and permits the description of the medium in terms of conventional stress-strain equations. Within the smeared crack framework, small cracks are formed in the band are gradually connected to each other and one or more cracks may be defined for each gauss point of each element. As one of the important innovations of this paper, the study of the effect of fluid pressure on the smeared crack propagation, has been done, which is based on coding in FORTRAN programming environment. Due to the results obtained by the flow of fluid into the crack, the crack opening increased significantly.