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Ground deformation, commonly observed in storage projects, carries useful information about processes occurring in the injection formation. The Krechba gas field at In Salah (Algeria) is one of the best-known sites for studying ground surface deformation during geological carbon storage. At this first industrial-scale on-shore CO 2 demonstration project, satellite-based ground-deformation monitoring data of high quality are available and used to study the large-scale hydrological and geomechanical response of the system to injection. In this work, we carry out coupled fluid flow and geomechanical simulations to understand the uplift at three different CO 2 injection wells (KB-501, KB-502, KB-503). Previous numerical studies focused on the KB-502 injection well, where a double-lobe uplift pattern has been observed in the ground-deformation data. The observed uplift patterns at KB-501 and KB-503 have single-lobe patterns, but they can also indicate a deep fracture zone mechanical response to the injection. The current study improves the previous modeling approach by introducing an injection reservoir and a fracture zone, both responding to a Mohr-Coulomb failure criterion. In addition, we model a stress-dependent permeability and bulk modulus, according to a dual continuum model. Mechanical and hydraulic properties are determined through inverse modeling by matching the simulated spatial and temporal evolution of uplift to InSAR observations as well as by matching simulated and measured pressures. The numerical simulations are in agreement with both spatial and temporal observations. The estimated values for the parameterized mechanical and hydraulic properties are in good agreement with previous numerical results. In addition, the formal joint inversion of hydrogeological and geomechanical data provides measures of the estimation uncertainty. [ABSTRACT FROM AUTHOR]

Abstract: The interaction between multiple fractures (e.g., hydraulic fractures and pre-existing natural fractures) is important in the analysis of a number of geoengineering applications, such as in the evaluation of the stability and integrity of caprock during underground CO2 sequestration. Here, we present new developments and applications of a model for analyzing coupled multiphase fluid flow and geomechanical processes during fracturing involving multiple fractures and their interactions. Based on a numerical code, i.e., rock discontinuous cellular automaton (RDCA), we introduce a discontinuous displacement function for representing multiple discontinuities, and develop an algorithm to deal with a propagating fracture that interacts with other discontinuities. By applying multiphase fluid pressure to fracture surfaces, the RDCA has the ability to simulate multiphase fluid flow-driven fracturing. The RDCA technique incorporates the discontinuity of the crack independently of the mesh, such that the cracks can be arbitrarily located within an element. This method does not require any remeshing for multiple cracks growth, an aspect that greatly reduces the complexity and improves efficiency in modeling multiple-fracture propagation. The RDCA is integrated with the TOUGH2 multiphase flow and heat-transport simulator by a sequential coupling algorithm, using mixed FORTRAN and C++ programming. The coupled TOUGH2 and RDCA code is applied to simulate the multiple fracture interaction in caprock induced by CO2 injection into a deep brine aquifer. The simulation results show hydraulic fracture trajectory, fracture aperture, and pressures as a function of injection time. Fluid flow (driven by CO2 injection) into natural fractures and their transition to hydraulic fractures is simulated. The injection pressure profile shows the complexity of the fracturing and its impact on CO2 migration and caprock integrity. [Copyright &y& Elsevier]