scholarly journals Investigations of fluid flow through fractures in Enhanced Geothermal Systems

2020 ◽  
Author(s):  
Jiawei Li
Keyword(s):  
Fluid Flow ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Flow Through

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>

Anisotropic permeability and fluid dispersion in pervasively fractured lavas, Rotokawa Geothermal System, New Zealand.

2021 ◽  
Author(s):  
Warwick Kissling ◽  
Cecile Massiot
Keyword(s):  
Fluid Flow ◽  
New Zealand ◽  
Geothermal Field ◽  
Geothermal System ◽  
Geothermal Systems ◽  
Fracture Density ◽  
Tracer Transport ◽  
Fracture Models ◽  
Flow Through ◽  
Permeability Anisotropy

<p>Geothermal provides nearly 20% of New Zealand’s electricity as well as increasing opportunities for direct use. In New Zealand’s ~20 high temperature geothermal systems, fluids flow dominantly through fractured rocks with low matrix permeability. It is important to understand the nature of these fracture systems, and how fluids flow through them, so that the geothermal systems may be more efficiently and sustainably used. Here we present fluid flow calculations in several distinct discrete fracture models, each of which is broadly consistent with the fracture density and high dip magnitude angle distributions directly observed in borehole image logs at the Rotokawa Geothermal Field (>300°C, 175 MWe installed capacity). This reservoir is hosted in fractured andesites. In general, fractures are steeply dipping, and the reservoir is known to be compartmentalized.</p><p>Our new code describes fluid flow through large numbers (e.g., thousands) of stochastic fracture networks to provide statistical distributions of permeability, permeability anisotropy and fluid dispersion at reservoir scale (e.g., 1 km<sup>2</sup>). Calculations can be based on both the cubic flow law for smooth-walled fractures and the Forchheimer flow model, which includes an additional term to describe the nonlinear drag (i.e. friction) in real fractures caused by surface roughness of the fracture walls.</p><p>Models with fracture density consistent with borehole observations show pervasive connectivity at reservoir scales, with fluid flow (hence permeability) and tracer transport predominantly along the mean fracture orientation. As the fracture density is varied, we find a linear relationship between permeability which holds above a well-defined percolation threshold. Permeability anisotropy is in general high (~10 to 15), because of the steeply dipping fractures. As fracture density decreases, mean anisotropy decreases while its variability increases. Significant dispersion of fluid occurs as it is transported through the reservoir. These fracture models will inform more traditional continuum models of fractured geothermal reservoirs hosted in volcanic rocks, to provide a better description of fluid flow within reservoirs and aid the responsible and sustainable use of that resource in the future.</p>

Investigation of injection-induced seismicity using a coupled fluid flow and rate/state friction model

Geophysics ◽  
2011 ◽  
Vol 76 (6) ◽  
pp. WC181-WC198 ◽  
Author(s):  
Mark W. McClure ◽  
Roland N. Horne
Keyword(s):  
Fluid Flow ◽  
Induced Seismicity ◽  
Large Scale ◽  
Injection Pressure ◽  
Friction Model ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Isolated Fracture ◽  
Lower Magnitude ◽  
Event Magnitude

We describe a numerical investigation of seismicity induced by injection into a single isolated fracture. Injection into a single isolated fracture is a simple analog for shear stimulation in enhanced geothermal systems (EGS) during which water is injected into fractured, low permeability rock, triggering slip on preexisting large scale fracture zones. A model was developed and used that couples (1) fluid flow, (2) rate and state friction, and (3) mechanical stress interaction between fracture elements. Based on the results of this model, we propose a mechanism to describe the process by which the stimulated region grows during shear stimulation, which we refer to as the sequential stimulation (SS) mechanism. If the SS mechanism is realistic, it would undermine assumptions that are made for the estimation of the minimum principal stress and unstimulated hydraulic diffusivity. We investigated the effect of injection pressure on induced seismicity. For injection at constant pressure, there was not a significant dependence of maximum event magnitude on injection pressure, but there were more relatively large events for higher injection pressure. Decreasing injection pressure over time significantly reduced the maximum event magnitude. Significant seismicity occurred after shut-in, which was consistent with observations from EGS stimulations. Production of fluid from the well immediately after injection inhibited shut-in seismic events. The results of the model in this study were found to be broadly consistent with results from prior work using a simpler treatment of friction that we refer to as static/dynamic. We investigated the effect of shear-induced pore volume dilation and the rate and state characteristic length scale, [Formula: see text]. Shear-induced pore dilation resulted in a larger number of lower magnitude events. A larger value of [Formula: see text] caused slip to occur aseismically.

Fluid Flow Through Branched Channels in a Fracture Plane in an Enhanced Geothermal System

2012 ◽  
Author(s):  
Rosemarie Mohais ◽  
Chaoshui Xu ◽  
Peter A. Dowd
Keyword(s):  
Fluid Flow ◽  
Fractal Theory ◽  
Maximum Flow ◽  
Constructal Theory ◽  
Fracture Plane ◽  
Geothermal System ◽  
Enhanced Geothermal Systems ◽  
Simple Relationship ◽  
Geothermal Systems ◽  
Heterogeneous Rock

Fluid flow in Enhanced Geothermal Systems (EGS) occurs primarily through fractures which are embedded in an almost impermeable granite rock matrix. Experimental and numerical studies have shown that flow in fractures exhibits channeling effects; this means that flow occurs along preferred pathways, most likely the paths of least resistance. There has been evidence to date of dendritic and star-like patterns in granite and as a result, authors have used fractal theory in order to address flow phenomena in these patterns. The application of Bejan’s Constructal theory to this problem however has never been attempted. We base our model on dendritic patterns of flow paths in heterogeneous rock fractures. Flow enters into a main channel which bifurcates into daughter channels of unique dimensions of length and height. We study these parameters for consecutive channels in the flow path and show that for minimization of resistance to flow within a plane using area and volume constraints for a T-shaped channel, a simple relationship holds for the ratios of lengths and heights which will enable maximum flow for this configuration.

Fluid flow distribution in fractures for a doublet system in Enhanced Geothermal Systems (EGS)

Geothermics ◽  
2018 ◽  
Vol 75 ◽  
pp. 171-179 ◽  
Author(s):  
Pranay Asai ◽  
Palash Panja ◽  
Raul Velasco ◽  
John McLennan ◽  
Joseph Moore
Keyword(s):  
Fluid Flow ◽  
Flow Distribution ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems

scholarly journals Fossil vs. Active Geothermal Systems: A Field and Laboratory Method to Disclose the Relationships between Geothermal Fluid Flow and Geological Structures at Depth

Energies ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 933
Author(s):  
Domenico Liotta ◽  
Andrea Brogi ◽  
Giovanni Ruggieri ◽  
Martina Zucchi
Keyword(s):  
Fluid Flow ◽  
Fluid Inclusions ◽  
Laboratory Method ◽  
Geothermal Systems ◽  
Active System ◽  
Geological Structures ◽  
Deep Roots ◽  
Kinematic Data ◽  
Length Width ◽  
Flow Through

Comparison between fossil and analogue active geothermal systems permit to obtain key-parameters to define a conceptual model of the area under exploration. The approach is based on structural, kinematic, and fluid inclusions analyses. The fossil system is investigated to describe the distribution of the hydrothermal mineralization as witness of the fluid flow through geological structures and bodies, at depth. Structural and kinematic data (to define the preferential direction of fluid flow) are collected in structural stations and by scan lines and scan boxes on key outcrops. Distribution, length, width of fractures, and hydrothermal veins bring to evaluate permeability in the fossil system and, by analogy, in the deep roots of the active system. Fluid inclusions analysis shed light on density, viscosity, and temperature of the paleo-fluids. Data integration provides the hydraulic conductivity. In active geothermal systems, fieldwork is addressed to paleo-stress analysis with data from recent faults (<2 Ma), to compare with local focal mechanisms. By this, indications on the present fluid pathways are given. The main advantage resides in obtaining parameters normally got after drilling, thus contributing to strengthen the strategy of exploration, de-risking unsuccessful boreholes.

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