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This article reports and describes the data related to the paper “Conforming, non-conforming and non-matching discretization couplings in discrete fracture network simulations” (Fumagalli et al., 2019). The data provided include a set of geometrical input data of Discrete Fracture Networks (DFNs) and a set of simulation results. The geometrical data describe the geometry of fracture networks of increasing complexity. These data also include the geometry of a DFN extruded from a real fracture outcrop in Western Norway. Simulation results are obtained using several different numerical schemes and provide convergence history, plots over line and upscaled output quantities related to the various considered geometries.

Various phenomena in the subsurface are characterised by the interplay between deforming structures such as fractures and coupled thermal, hydraulic and mechanical processes. Simulation of subsurface dynamics can provide valuable phenomenological understanding, but requires models which faithfully represent the dynamics involved; these models therefore are themselves highly complex. This paper presents a mixed-dimensional thermo-hydro-mechanical model designed to capture the process–structure interplay using a discrete–fracture–matrix framework. It incorporates tightly coupled thermo-hydro-mechanical processes based on balance laws for momentum, mass and energy in subdomains representing the matrix and the lower-dimensional fractures and fracture intersections. The deformation of explicitly represented fractures is modelled by contact mechanics relations and a Coulomb friction law, with a novel formulation consistently integrating fracture dilation in the governing equations. The model is discretised using multi-point finite volume methods for the balance equations and a semismooth Newton scheme for the contact conditions and is implemented in the open-source fracture simulation toolbox PorePy. Finally, simulation studies demonstrate the model’s convergence, investigate process–structure coupling effects, explore different fracture dilation models and show an application of the model to stimulation and long-term cooling of a three-dimensional geothermal reservoir. publishedVersion

The hydraulic stimulation of the well RN-34 at the Reykjanes geothermal field in Iceland caused increased seismic activity near the well. Here, we use this as a case study for investigation on how seismic analysis can be combined with physics-based simulation studies to further understand injection-induced fault reactivation. The work presents new analysis of the seismic data combined with application of a recent simulation software for modeling of coupled hydromechanical processes and fault deformation caused by fluid injection. The simulation model incorporates an explicit model of the fault network based on geological characterization combined with insights from seismic analysis. The 3D faulted reservoir model is then calibrated based on injection data. Despite limited data, the work shows how seismic interpretations can be used in developing simulation models and, reciprocally, how the modeling can add to the seismic interpretations in analysis of dynamics.

To address the engineering questions on security issues of geological carbon sequestration (GCS), a broad range of computational models with different levels of complexity have been developed - from multiphase multicomponent fully coupled three-dimensional models to simplified analytical solutions. Within this wide range of models, a family of so-called vertical equilibrium (VE) models has been developed. These models assume that CO2 and brine have segregated due to buoyancy and reached a hydrostatic pressure distribution in the vertical direction. Such VE models are computationally efficient due to the dimensional reduction in the vertical, and accurate as long as the VE assumption is satisfied. However, a study comparing results from a VE model to results from a full three- dimensional model found that there are realistic conditions for which the VE assumption is not justified, especially for geological formations that have low vertical permeability, on the order of 10 milliDarcy or lower [1] . In an attempt to overcome the VE limitation of the vertically-integrated models, a new type of vertically-integrated model which relaxes the VE assumption while still using a vertically-integrated framework has been developed [2] . The new vertically-integrated model is cast into a multiscale framework, where the coarse scale is the horizontal domain and the fine scale is the vertical domain corresponding to the thickness of a geologic formation. This type of model maintains much of the computational advantages of the VE models, while allowing a much wider range of problem to be modelled. In this paper, we extend the model in [2] to include horizontally layered geologic heterogeneities and develop a new dynamic reconstruction model, which we refer to as a “multi-layer dynamic reconstruction” model. The model in [2] is called “single-layer dynamic reconstruction” model to distinguish the modelling approaches. We apply both dynamic reconstruction models to field injection sites, including a hypothetical injection scenario into the Mount Simon formation in the Illinois Basin, USA and the well-known industrial-scale injection into the Utsira formation at the Sleipner site in Norway. The modelling results show that the multi-layer dynamic reconstruction model is capable of dealing with horizontally layered heterogeneities and gives results that agree reasonably well with results from the full multi-dimensional model, although in geologic layers with high permeability the reconstruction algorithm is not able to fully capture the horizontal driving forces due to buoyancy. This could be important over long time scales for highly permeable geologic layers. The single- layer dynamic reconstruction model was shown be to the right model choice for homogeneous formations with relatively low permeability where it takes a long time for CO2 and brine to reach vertical equilibrium [2] . In this study, we found that for homogeneous formations with high permeability and steep capillary pressure curves, the single-layer dynamic reconstruction model gives results that are analogous to vertical equilibrium models, with the fast segregation dynamics requiring small time steps in the dynamic reconstruction algorithm. As such vertical equilibrium models are the appropriate choice for systems with high permeability, although we also note that the behaviour of the brine relative permeability curve at low brine saturations is an additional important consideration and must be included in the overall analysis.

When injected in deep saline aquifers, CO2 moves radially away from the injection well and progressively higher in the formation because of buoyancy forces. Analyzes have shown that after the injection period, CO2 will potentially migrate over several kilometers in the horizontal direction but only tens of meters in the vertical direction, limited by the aquifer caprock [1, 2]. Because of the large horizontal plume dimensions, three-dimensional numerical simulations of the plume migration over long periods of time are computationally intensive. Thus, to get results within a reasonable time frame, one is typically forced to use coarse meshes and long time steps which result in inaccurate results because of numerical errors in resolving the plume tip. Given the large aspect ratio between the vertical and horizontal plume dimensions, it is reasonable to approximate the CO2 migration using vertically averaged models. Such models can, in many cases, be more accurate than coarse three-dimensional computations. In particular, models based on vertical equilibrium (VE) [3] are attractive to simulate the long-term fate of CO2 sequestered into deep saline aquifers. The reduced spatial dimensionality resulting from the vertical integration ensures that the computational performance of VE models exceeds the performance of standard three-dimensional models. Thus, VE models are suitable to study the long-time and large-scale behavior of plumes in real large-scale CO2-injection projects [4, 1, 2, 5]. We investigate the use of VE models to simulate CO2 migration in a real large-scale eld case based on data from the Sleipner site in the North Sea. We discuss the potential and limitations of VE models and show how VE models can be used to give reliable estimates of long-term CO2 migration. In particular, we focus on a VE formulation that incorporates the aquifer geometry and heterogeneity, and that considers the eects of hydrodynamic and residual trapping. We compare the results of VE simulations with standard reservoir simulation tools on test cases and discuss their advantages and limitations and show how, provided that certain conditions are met, they can be used to give reliable estimates of long-term CO2 migration.