3D thermo-poroelastic analysis of fracture network deformation and induced micro-seismicity in enhanced geothermal systems

Geothermics ◽  
2015 ◽  
Vol 58 ◽  
pp. 1-14 ◽  
Author(s):  
Reza Safari ◽  
Ahmad Ghassemi
Keyword(s):  
Fracture Network ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems

Modeling fluid flow through complex fracture network in geological media by using hierarchical hydraulic properties

2020 ◽  
Author(s):  
Kyung Won Chang ◽  
Gungor Beskardes ◽  
Chester Weiss
Keyword(s):  
Fluid Flow ◽  
Surrounding Medium ◽  
Computational Cost ◽  
Energy Resource ◽  
Fracture Network ◽  
Fractured Media ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Hydraulic Stimulation ◽  
Complex Fracture

<p>Hydraulic stimulation is the process of initiating fractures in a target reservoir for subsurface energy resource management with applications in unconventional oil/gas and enhanced geothermal systems. The fracture characteristics (i.e., number, size and orientation with respect to the wellbore) determines the modified permeability field of the host rock and thus, numerical simulations of flow in fractured media are essential for estimating the anticipated change in reservoir productivity. However, numerical modeling of fluid flow in highly fractured media is challenging due to the explosive computational cost imposed by the explicit discretization of fractures at multiple length scales. A common strategy for mitigating this extreme cost is to crudely simplify the geometry of fracture network, thereby neglecting the important contributions made by all elements of the complex fracture system.</p><p>The proposed “Hierarchical Finite Element Method” (Hi-FEM; Weiss, Geophysics, 2017) reduces the comparatively insignificant dimensions of planar- and curvilinear-like features by translating them into integrated hydraulic conductivities, thus enabling cost-effective simulations with requisite solutions at material discontinuities without defining ad-hoc, heuristic, or empirically-estimated boundary conditions between fractures and the surrounding formation. By representing geometrical and geostatistical features of a given fracture network through the Hi-FEM computational framework, geometrically- and geomechanically-dependent fluid flow properly can now be modeled economically both within fractures as well as the surrounding medium, with a natural “physics-informed” coupling between the two.</p><p>SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.</p>

scholarly journals Hydraulic Fracturing in Enhanced Geothermal Systems—Field, Tectonic and Rock Mechanics Conditions—A Review

Energies ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5725
Author(s):  
Rafał Moska ◽  
Krzysztof Labus ◽  
Piotr Kasza
Keyword(s):  
Hydraulic Fracturing ◽  
Fracture Network ◽  
Hydraulic Fractures ◽  
Enhanced Geothermal Systems ◽  
Seismic Velocities ◽  
Geothermal Systems ◽  
Principal Stresses ◽  
Pumping Rate ◽  
Work Related ◽  
Stimulation Method

Hydraulic fracturing (HF) is a well-known stimulation method used to increase production from conventional and unconventional hydrocarbon reservoirs. In recent years, HF has been widely used in Enhanced Geothermal Systems (EGS). HF in EGS is used to create a geothermal collector in impermeable or poor-permeable hot rocks (HDR) at a depth formation. Artificially created fracture network in the collector allows for force the flow of technological fluid in a loop between at least two wells (injector and producer). Fluid heats up in the collector, then is pumped to the surface. Thermal energy is used to drive turbines generating electricity. This paper is a compilation of selected data from 10 major world’s EGS projects and provides an overview of the basic elements needed to design HF. Authors were focused on two types of data: geological, i.e., stratigraphy, lithology, target zone deposition depth and temperature; geophysical, i.e., the tectonic regime at the site, magnitudes of the principal stresses, elastic parameters of rocks and the seismic velocities. For each of the EGS areas, the scope of work related to HF processes was briefly presented. The most important HF parameters are cited, i.e., fracturing pressure, pumping rate and used fracking fluids and proppants. In a few cases, the dimensions of the modeled or created hydraulic fractures are also provided. Additionally, the current state of the conceptual work of EGS projects in Poland is also briefly presented.

Tracking the development of seismic fracture network by considering the fault rupture method

2020 ◽  
Author(s):  
Taghi Shirzad ◽  
Stanisław Lasocki ◽  
Beata Orlecka‐Sikora
Keyword(s):  
Maximum Amplitude ◽  
Clean Energy ◽  
Velocity Model ◽  
Fracture Network ◽  
P Wave ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
The European Union ◽  
Fault Rupture ◽  
Horizon 2020

<p> In Enhanced Geothermal Systems pressurized injections play a role in developing fracture networks and enhancing the water transmissivity. However, the fractures may also coalesce into undesired pathways for fluid migration to enable the fluids to reach pre-existing faults. The properties of observed seismicity can shed some light on the fracture network development and from the standpoint of the possibility to form such undesired pathways. However, to reach this goal the seismic events should be well parameterized. In particular, the information on fault plane mechanisms is essential, which is often not readily accessible. In this study, we use the rupturing process with an accurate P-wave velocity model, which is obtained by the first arrival P-wave tomography approach, to compensate for an eventual lack of source mechanisms of micro-events. For this purpose, four characteristics of the sources (final/average displacement on the fault, the dimension of fault, rupture velocity and particle velocity) can be considered. A 3D model is defined around the hypocenter of each event, so that the size of this model directly depends on the event magnitude. After calculating the arrival time of the selected phase (e.g., P, S, p or s) for each station, all waveforms are then aligned, and stacked by different stacking (e.g., phase weight, N<sup>th</sup>-root) methods. By considering the maximum amplitude of the stacked waveform which is stimulated by each grid, the rupturing plane and the average velocity of rupturing can be obtained. This information of source can be replaced by the double-couple mechanism to investigate the fractures linking and tracking.</p><p>This work was supported under the <em>S4CE</em>: "Science for Clean Energy" project, which has received funding from the European Union’s Horizon 2020 research and innovation program, under grant agreement No 764810.</p>

Stress-based tomography: potential, open-questions and future developments

2020 ◽  
Author(s):  
Peter Bayer ◽  
Mohammad Javad Afshari Moein ◽  
Márk Somogyvári ◽  
Lisa Ringel ◽  
Mohammadreza Jalali
Keyword(s):  
Rock Mass ◽  
Imaging Techniques ◽  
Fracture Network ◽  
Great Depth ◽  
Heterogeneous Structure ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Fracture Networks ◽  
Future Developments ◽  
Open Questions

<p>Fracture network characterization is critical for many subsurface engineering problems in petroleum, mining, nuclear waste disposal and Enhanced Geothermal Systems (EGS). Due to limited exposure, direct measurement of fracture network properties at great depth is not possible and geophysical imaging techniques cannot resolve the fractures. Therefore, tomographic imaging techniques have been proposed and applied to reconstruct the structural discontinuities of rock mass. Stress-based tomography is a novel concept aiming at probabilistic imaging of the fracture network using the stress perturbations along deep boreholes. Currently, this approach has only been successfully tested on two-dimensional fracture networks. However, its great potential to unravel the heterogeneous structure of fractured rocks at great depth motivates further scientific effort. Here, we present the potential, open questions, current challenges and necessary future developments in order to apply this methodology to image three-dimensional multiscale structure of the rock mass in the field. Other tomographic approaches such as tracer and hydraulic tomography invert tracer breakthrough curves (BTCs) and pressure response in an observational well. We suggest a joint and comparative tomographic analysis in a Bayesian inversion framework to reconstruct Discrete Fracture Networks (DFN). This is expected to provide a new view of the strengths of each tomographic variant.</p>

scholarly journals Numerical simulation of fluid injection in faulted and fractured rocks based on a fully-coupled hydro-mechanical model

2021 ◽  
Author(s):  
Lei Qinghua ◽  
Chin-Fu Tsang
Keyword(s):  
Fractured Rocks ◽  
Network Connectivity ◽  
Fracture Network ◽  
Elastic Response ◽  
Fluid Injection ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Stress Dependent ◽  
Strong Control ◽  
Fully Coupled

<p>We present a fully-coupled hydro-mechanical simulation of fluid injection-induced activation of pre-existing discontinuities, propagation of new damages, development of seismic activities, and alteration of network connectivity in naturally faulted and fractured rocks, which are represented using the discrete fracture network approach. We use the finite element method to compute the multiphysical fields including stress, strain, damage, displacement, and pressure by solving governing and constitutive equations of coupled solid and fluid domains. Essential hydro-mechanical coupling mechanisms are honoured such as pore pressure-induced shear slip of natural discontinuities, poro-elastic response of rock matrix, and stress-dependent permeability/storativity of both fractures and rocks. We use the numerical model developed to investigate the hydro-mechanical behaviour of deeply buried fractured rocks and fault zones in response to high-pressure fluid injection, with a specific focus on the system either below or above the percolation threshold. We observe a strong control of fracture network connectivity on the damage emergence, seismicity occurrence and connectivity change in the rock mass subject to hydraulic stimulation. We highlight the strong poro-elastic effect that tends to drive heterogeneous connectivity evolution of fracture systems during fluid injection. The results of our research and insights obtained have important implications for injection-related geoengineering activities such as the development of enhanced geothermal systems and extraction of hydrocarbon resources.</p>

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