Fractured Rock Formations Research Articles

Impact of earthquake on the communities of bacteria and archaea in groundwater ecosystems

In this study, the possible changes in microbial communities after the occurrence of an earthquake were investigated. To this end, the effects of the 2016 Gyeongju earthquake (ML 5.8) on the microbial communities in nearby aquifers were analyzed together with associated hydrochemistry data. Fourteen water samples were collected from two types of wells (alluvial and fractured rock formation); hydrogeochemical parameters, groundwater level, radon concentration, strontium isotopes, and microbiological features were monitored. The results obtained for microbial compositions and special bacteria were consistent with the hydrochemical results. Distinctive microbial communities in groundwater samples taken adjacent to the earthquake epicenter were also observed. The predominant bacteria in most samples were Pseudomonas and Flavobacterium. Radon concentrations, helium isotopes, and the helium/neon ratio showed anomalies in one well (KW8) compared to microbial composition data. Strontium data indicated that the study site may have been affected by seawater intrusion; this was corroborated by the microbiological features of archaea. The results indicate that an earthquake can change the number of species or their abundance in groundwater ecosystems. Therefore, microbial features might be a good additional indicator for analyzing the effects of earthquakes on groundwater, together with major chemical parameters such as radon, strontium, and helium. The microbiological features indicate that levels of bacteria such as Pseudomonas and Flavobacterium in the groundwater were highly correlated with the Gyeongju earthquake and the associated hydrochemical data.

Effective Correlation of Stress and Thermal Effects on Porosity and Permeability of Naturally Fractured Formations by a Modified Power Law

SummaryEffective theory and methodology are proposed and validated for accurate correlation of stress–dependent petrophysical properties of naturally fractured or induced–fractured reservoir formations by means of a matrix/fracture dual–compressibility treatment. Inspection of various experimental data indicates a sudden change in trends at a certain critical net effective stress in the stress dependence of petrophysical properties of porous rocks as a result of a stress shock caused by the opening or closing of fractures. The variation of petrophysical properties in fractured–rock formations subjected to stress loading/unloading and thermally induced stress occurs mainly by deformation of the fractures below the critical effective stress and the deformation of the matrix above the critical effective stress. The alteration of petrophysical properties and a slope discontinuity might also be experienced when the stress exceeds the onset of other rock–alteration/damaging processes, such as pore collapsing and grain crushing. Proper formulations of the relevant processes and special correlation methods are presented in a manner to capture this nature of the petrophysical experimental data obtained by testing of cores extracted from naturally fractured or induced–fractured reservoir–rock formations. The dependency of porosity and permeability of fractured–rock samples under stress because of thermal, hydraulic, and mechanical effects is represented accurately by a modified–power–law equation derived from a kinetics model as confirmed by effective correlations of various experimental data. It is shown that this new model represents the thermal effect better than the frequently used Arrhenius (1889) equation and Vogel–Tammann–Fulcher (VTF) equation (Vogel 1921; Fulcher 1925; Tammann and Hesse 1926).

3D Numerical Simulation of Elastic Wave Propagation in Discrete Fracture Network Rocks

Fractures play an important role in controlling rock block stability and the hydraulic properties of fractured rock formations. Understanding elastic wave propagation in fractured media can result in significant advances for the geophysical prediction of fracture parameters from seismic data. However, most natural fracture characteristics, such as fracture length, aperture, angle and location are random; therefore, fracture models must be built discretely and follow some stochastic principles. We construct stochastic models of fractured rock samples using a random fracture network rather than a single fracture. Three-dimensional (3D) wave field computation is a computationally complex problem. Here, the 3D fourth-order in space, second-order in time, displacement-stress staggered-grid finite-difference scheme is used for accurate simulations. Our numerical examples demonstrate the effects of varying fracture number, aperture, and length distribution of the fracture network on the seismic response. The wave field scattering caused by the contrast between fractures and background media is one of the key features, and the resulting scattering is more obvious for S-waves than for P-waves. Such an approach can be applied to any fracture network model that provides a link between fracture parameters and seismic attributes.

Assessment of the Nonlinear Flow Characteristic of Water Inrush Based on the Brinkman and Forchheimer Seepage Model

Underground fault water inrush is a hydrogeological disaster that frequently occurs in underground mining and tunnel construction projects. Groundwater may pour from an aquifer when disasters occur, and aquifers are typically associated with fractured rock formations. Water inrush accidents are likely to occur when fractured rock masses are encountered during excavation. In this study, Comsol Multiphysics, cross-platform multiphysics field coupling software, was used to simulate the evolution characteristics of water flow in different flow fields of faults and aquifers when water inrush from underground faults occurs. First, the Darcy and Brinkman flow field nonlinear seepage models were used to model the seepage law of water flow in aquifers and faults. Second, the Forchheimer flow field was used to modify the seepage of fluid in fault-broken rocks in the Brinkman flow field. In general, this phenomenon does not meet the applicable conditions of Darcy’s formula. Therefore, the Darcy and Forchheimer flow models were coupled in this study. Simulation results show that flow behavior in an aquifer varies depending on fault permeability. An aquifer near a fault is likely to be affected by non-Darcy flow. That is, the non-Darcy effect zone will either increase or decrease as fault permeability increases or decreases. The fault rupture zone that connects the aquifer and upper roadway of the fault leads to fault water inrush due to the considerably improved permeability of the fractured rock mass.

Delineation of fracture zone for groundwater using combined inversion technique

This paper deals with severe issue of groundwater crisis over a part of hard rock terrain in the premises of Central Institute of Mining and Fuel Research (CIMFR), Dhanbad, Jharkhand, India. The goal of this study is delineation and mapping of fractured rock mass for groundwater exploration. Generally, fractured rock formation is the only source of groundwater in hard rock terrain. Electrical resistivity tomography (ERT) survey was conducted along three profiles over different parts of CIMFR premises using Wenner–Schlumberger and dipole–dipole arrays. Combined inversion of both arrays has been carried out during data analysis for better delineation of fracture rock masses in the complex geological environment. Two water-saturated fracture zones have been identified for the availability of groundwater, which has been confirmed by direct borehole drilling. This proves the effectiveness of ERT survey by combined inversion of both arrays for delineation of fracture zones.

Quantitative estimations of aquifer properties from resistivity in the Bolivian highlands

Abstract Resistivity data constitute the largest part of the available information to assess the hydrogeological characteristics of the aquifer system near Oruro, in the central part of the Bolivian Altiplano. Two aquifers are part of this system; top unconsolidated sediments storing fresh water in their granular voids, overlying fractured hard rock formations where saline water was detected in connection to some faults. This study proposes an indirect and cost-effective way to estimate aquifer hydraulic properties for the groundwater management in the region. Hydraulic conductivity and transmissivity in the top aquifer were estimated using an empirical linear relationship between hydraulic conductivity and resistivity. This latter parameter, as well as the aquifer thickness, were obtained from the inverted models corresponding to the geoelectrical tests performed in the study area (electrical resistivity tomography, transient electromagnetic soundings and vertical electrical soundings). The highest estimated transmissivity values are ∼4.0 × 10−2 m2/s located in the centre of the study area, the lowest values are ∼3.4 × 10−3 m2/s, located around thermal intrusions to the south and where the top of the bedrock is shallow (∼20 m depth) to the west. The methodology presented in this study makes wider use of resistivity measurements to identify promising groundwater production sites.

Numerical modeling and analysis of induced thermal stress for a non-isothermal wellbore strengthening process

Wellbore strengthening (WBS) methods are broadly applied in the field to combat lost circulation by plugging drilling induced fractures using wellbore strengthening materials (WSM). While changes in formation temperature during drilling have been identified as an important factor in wellbore stability considerations, the performance of WBS in a non-isothermal setting is unclear and remains as a barrier to successful designs of the types and sizes of WSMs. To understand the problem, a 3D finite element analysis was conducted to investigate the state of stresses in near-wellbore region from the interaction between induced thermal stresses and fractures based on different WBS plugging mechanisms. The model developed in this study coupled fluid and heat flow in fractured thermal-poroelastic rock formations and enabled flow restrictions in the fracture for simulating wellbore strengthening processes. By implementing different WBS mechanisms in the simulations, the induced thermal stresses from fluid leakage into the formations were analyzed, and the effectiveness of different WBS strategies in preventing fracture propagation under thermal effects was evaluated.The results disclosed how stresses redistribute around a fractured wellbore as non-isothermal mud invasion and WSM plugging take places. They show that temperature decreases of formation rock due to mud invasion can significantly facilitate fracture propagation and diminish the effectiveness of WBS. Such information is important to the successful management of lost circulation by taking thermal effects into consideration for better WSM design and WBS implementations.

Numerical Investigation into the Effect of Natural Fracture Density on Hydraulic Fracture Network Propagation

Hydraulic fracturing is an important method to enhance permeability in oil and gas exploitation projects and weaken hard roofs of coal seams to reduce dynamic disasters, for example, rock burst. It is necessary to fully understand the mechanism of the initiation, propagation, and coalescence of hydraulic fracture network (HFN) caused by fluid flow in rock formations. In this study, a coupled hydro-mechanical model was built based on synthetic rock mass (SRM) method to investigate the effects of natural fracture (NF) density on HFN propagation. Firstly, the geometrical structures of NF obtained from borehole images at the field scale were applied to the model. Secondly, the micro-parameters of the proposed model were validated against the interaction between NF and hydraulic fracture (HF) in physical experiments. Finally, a series of numerical simulations were performed to study the mechanism of HFN propagation. In addition, confining pressure ratio (CPR) and injection rate were also taken into consideration. The results suggested that the increase of NF density drives the growth of stimulated reservoir volume (SRV), concentration area of injection pressure (CAIP), and the number of cracks caused by NF. The number of tensile cracks caused by rock matrix decrease gradually with the increase of NF density, and the number of shear cracks caused by rock matrix are almost immune to the change of NF density. The propagation orientation of HFN and the breakdown pressure in rock formations are mainly controlled by CPR. Different injection rates would result in a relatively big difference in the gradient of injection pressure, but this difference would be gradually narrowed with the increase of NF density. Natural fracture density is the key factor that influences the percentages of different crack types in HFN, regardless of the value of CPR and injection rate. The proposed model may help predict HFN propagation and optimize fracturing treatment designs in fractured rock formations.

Fracture connectivity can reduce the velocity anisotropy of seismic waves

Abstract The degree of connectivity of fracture networks is a key parameter that controls the hydraulic properties of fractured rock formations. The current understanding is that this parameter does not alter the effective elastic properties of the probed medium and, hence, cannot be inferred from seismic data. However, this reasoning is based on static elasticity, which neglects dynamic effects related to wave-induced fluid pressure diffusion (FPD). Using a numerical upscaling procedure based on the theory of quasi-static poroelasticity, we provide the first evidence to suggest that fracture connectivity can reduce significantly velocity anisotropy in the seismic frequency band. Analyses of fluid pressure fields in response to the propagation of seismic waves demonstrate that this reduction of velocity anisotropy is not due to changes of the geometrical characteristics of the probed fracture networks, but rather related to variations of the stiffening effect of the fracture fluid in response to FPD. These results suggest that accounting for FPD effects may not only allow for improving estimations of geometrical and mechanical properties of fracture networks, but may also provide information with regard to the effective hydraulic properties.

Hydro-mechanically coupled FDEM framework to investigate near–wellbore hydraulic fracturing in homogeneous and fractured rock formations

This paper reports on a numerical study that was conducted to investigate near–wellbore behaviour of Hydraulic Fracture (HF) growth using a Finite–Discrete Element Modelling (FDEM) approach. In particular we consider the effect on fracture propagation of pre–existing defects (joints) within the rock medium, as well as physical mechanisms that induce microseismic events. Initial modelling was conducted for an isotropic and homogeneous rock mass subject to isotropic and anisotropic far–field stress states. The introduction of single isolated joints for a rock mass subject to anisotropic far–field stresses that did not intersect the wellbore, such as those created by previous fracturing stages, were seen to impose a lateral stress gradient. The presence of stress gradients leads to asymmetric fracture initiation and growth, generally away from the pre–existing joint, accompanied by an increase in the fluid pressure required to initiate fractures. However, the influence of pre–existing joints diminishes with distance from the wellbore. Due to the high permeability of pre–existing rock joints, fractures prefer to initiate at joint tips after the joint is intersected by a fluid–driven fracture. Based on our simulations, a set of pre–existing, randomly distributed joints around the wellbore leads to microseismic events that are primarily induced by shear slippage on critically stressed joints. For a given injection energy, the presence of multiple joints around a wellbore increases the extent to which fluid–driven fractures can grow. Finally, comparison of our simulation with measured results from low–volume injection test confirms that our approach appears to capture salient aspects of elastic deformation and breakdown pressures in the field.

River-spring connectivity and hydrogeochemical interactions in a shallow fractured rock formation. The case study of Fuensanta river valley (Southern Spain)

In upland catchments, the hydrology and hydrochemistry of streams are largely influenced by groundwater inflows, at both regional and local scale. However, reverse conditions (groundwater dynamics conditioned by surface water interferences), although less described, may also occur. In this research, the local river-spring connectivity and induced hydrogeochemical interactions in intensely folded, fractured and layered Cretaceous marls and marly-limestones (Fuensanta river valley, S Spain) are discussed based on field observations, tracer tests and hydrodynamic and hydrochemical data. The differential flow measurements and tracing experiments performed in the Fuensanta river permitted us to quantify the surface water losses and to verify its direct hydraulic connection with the Fuensanta spring. The numerical simulations of tracer breakthrough curves suggest the existence of a groundwater flow system through well-connected master and tributary fractures, with fast and multi-source flow components. Furthermore, the multivariate statistical analysis conducted using chemical data from the sampled waters, the geochemical study of water-rock interactions and the proposed water mixing approach allowed the spatial characterization of the chemistry of the springs and river/stream waters draining low permeable Cretaceous formations. Results corroborated that the mixing of surface waters, as well as calcite dissolution and CO2 dissolution/exsolution, are the main geochemical processes constraining Fuensanta spring hydrochemistry. The estimated contribution of the tributary surface waters to the spring flow during the research period was approximately 26–53% (Fuensanta river) and 47–74% (Convento stream), being predominant the first component during high flow and the second one during the dry season. The identification of secondary geochemical processes (dolomite and gypsum dissolution and dedolomitization) in Fuensanta spring waters evidences the induced hydrogeochemical changes resulting from the allogenic recharge. This research highlights the usefulness of an integrated approach based on river and spring flow examination, dye tracing interpretation and regression and multivariate statistical analysis using hydrochemical data for surface water-groundwater interaction assessment in fractured complex environments worldwide, whose implementation becomes critical for an appropriate groundwater policy.

Implications of Grain-Scale Mineralogical Heterogeneity for Radionuclide Transport in Fractured Media

The geological disposal of nuclear waste is based on the multi-barrier concept, comprising various engineered and natural barriers, to confine the radioactive waste and isolate it from the biosphere. Some of the planned repositories for high-level nuclear waste will be hosted in fractured crystalline rock formations. The potential of these formations to act as natural transport barriers is related to two coupled processes: diffusion into the rock matrix and sorption onto the mineral surfaces available in the rock matrix. Different in situ and laboratory experiments have pointed out the ubiquitous heterogeneous nature of the rock matrix: mineral surfaces and pore space are distributed in complex microstructures and their distribution is far from being homogeneous (as typically assumed by Darcy-scale coarse reactive transport models). In this work, we use a synthetically generated fracture–matrix system to assess the implications of grain-scale physical and mineralogical heterogeneity on cesium transport and retention. The resulting grain-scale reactive transport model is solved using high-performance computing technologies, and the results are compared with those derived from two alternative models, denoted as upscaled models, where mineral abundance is averaged over the matrix volume. In the grain-scale model, the penetration of cesium into the matrix is faster and the penetration front is uneven and finger-shaped. The analysis of the cesium breakthrough curves computed at two different points in the fracture shows that the upscaled models provide later first-arrival time estimates compared to the grain-scale model. The breakthrough curves computed with the three models converge at late times. These results suggest that spatially averaged upscaled parameters of sorption site distribution can be used to predict the late-time behavior of breakthrough curves but could be inadequate to simulate the early behavior.

Probe Drilling Ahead of Two TBMs in Difficult Ground Conditions in Turkey

This paper summarizes the results of probe drilling carried out ahead of TBMs in two difficult tunneling projects in Turkey. The tunnels have completely different geological characteristics which necessitated two different methods of data analysis. Melen Water Tunnel was excavated under Istanbul Bosphorus within sedimentary rocks which are cut frequently by andesitic dykes, fracturing the surrounding rocks and creating a potential risk for water ingress into the tunnel. At the beginning of Melen Project, pioneering probe drillings with petrographic analysis and strength tests were performed on samples collected from TBM muck. This analysis allowed identifying some critical normalized probe drilling rate values for predicting potential weak zones created by andesitic dykes. These studies gave a sound basis for further interpretation of TBM and geologic data for the same tunnel. The second set of probe drilling analysis was from Kargi Tunnel. The North Anatolian Fault highly affected the tunnel excavation by fractured rock formations. Although the change in normalized probe drilling data was a good indicator of fractured zones, the diversity of rock formations made it difficult to interpret the data.

Hydrogeophysical characterization of transport processes in fractured rock by combining push‐pull and single‐hole ground penetrating radar experiments

AbstractThe in situ characterization of transport processes in fractured media is particularly challenging due to the considerable spatial uncertainty on tracer pathways and dominant controlling processes, such as dispersion, channeling, trapping, matrix diffusion, ambient and density driven flows. We attempted to reduce this uncertainty by coupling push‐pull tracer experiments with single‐hole ground penetrating radar (GPR) time‐lapse imaging. The experiments involved different injection fractures, chaser volumes and resting times, and were performed at the fractured rock research site of Ploemeur in France (H+ network, hplus.ore.fr/en). For the GPR acquisitions, we used both fixed and moving antenna setups in a borehole that was isolated with a flexible liner. During the fixed‐antenna experiment, time‐varying GPR reflections allowed us to track the spatial and temporal dynamics of the tracer during the push‐pull experiment. During the moving antenna experiments, we clearly imaged the dominant fractures in which tracer transport took place, fractures in which the tracer was trapped for longer time periods, and the spatial extent of the tracer distribution (up to 8 m) at different times. This demonstrated the existence of strongly channelized flow in the first few meters and radial flow at greater distances. By varying the resting time of a given experiment, we identified regions affected by density‐driven and ambient flow. These experiments open up new perspectives for coupled hydrogeophysical inversion aimed at understanding transport phenomena in fractured rock formations.

Development of Water Resources for Micro Watershed at Chinamushidiwada Village in Visakhapatnam, Andhra Pradesh, India

An attempt made to develop water resource for micro watershed of Visakhapatnam Urban Area. The study area extends from 17° 47’ 02’’ N to 17° 48’ 38’’ N latitudes and 83° 11’ 51’’ E to 83° 14’ 45’’ E longitudes, covering an aerial extent of 9.18 km2. A detailed examination of the existing three tanks in the study area is carried out using both spatial technology and ground based observations. The alteration of the terrain topography is studied from the survey of India toposheets and Total Station survey conducted in the study area. The 3-Dimensional terrain model is generated and the drainage network is simulated to study its interaction with the results of the change detection analysis. For the quantification of surface water bodies, Total Station survey is carried out for the tanks. Geophysical explorations are carried out, which identifies the thicknesses of top soil, weathered rock, fractured rock, hard fractured rock and hard rock formations, to assess the volume of the groundwater that can be stored in the aquifer system.

Thermo-hydro-mechanical processes in fractured rock formations during a glacial advance

Abstract. The paper examines the coupled thermo-hydro-mechanical (THM) processes that develop in a fractured rock region within a fluid-saturated rock mass due to loads imposed by an advancing glacier. This scenario needs to be examined in order to assess the suitability of potential sites for the location of deep geologic repositories for the storage of high-level nuclear waste. The THM processes are examined using a computational multiphysics approach that takes into account thermo-poroelasticity of the intact geological formation and the presence of a system of sessile but hydraulically interacting fractures (fracture zones). The modelling considers coupled thermo-hydro-mechanical effects in both the intact rock and the fracture zones due to contact normal stresses and fluid pressure at the base of the advancing glacier. Computational modelling provides an assessment of the role of fractures in modifying the pore pressure generation within the entire rock mass.

Characterizing borehole fluid flow and formation permeability in the ocean crust using linked analytic models and Markov chain Monte Carlo analysis

Thermal records from boreholes in young oceanic crust, in which water is flowing up or down, are used to assess formation and borehole flow properties using three analytic equations that describe the transient thermal and barometric influence of downhole or uphole flow. We link these calculations with an iterative model and apply Markov chain Monte Carlo (MCMC) analysis to quantify ranges of possible values. The model is applied to two data sets interpreted in previous studies, from Deep Sea Drilling Project Hole 504B on the southern flank of the Costa Rica Rift and Ocean Drilling Program Hole 1026B on the eastern flank of the Juan de Fuca Ridge, and to two new records collected in Integrated Ocean Drilling Program Holes U1301A and U1301B, also on the eastern flank of the Juan de Fuca Ridge. Our calculations indicate that fluid flow rates when thermal logs were collected were ∼2 L/s in Holes 504B, 1026B, and U1301A, and >20 L/s in Hole U1301B. The median bulk permeabilities determined with MCMC analyses are 4 to 7 × 10−12 m2 around the uppermost parts of Holes 504B, 1026B, and U1301A, and 1.5 × 10−11 m2 around a deeper section of Hole U1301B, with a standard deviation of 0.2 to 0.3 log cycles at each borehole. The consistency of permeability values inferred from these four holes is surprising, given the range of values determined globally and the tendency for permeability to be highly variable in fractured crystalline rock formations such as the upper oceanic crust.

A smoothed particle hydrodynamics model for droplet and film flow on smooth and rough fracture surfaces

Flow on fracture surfaces has been identified by many authors as an important flow process in unsaturated fractured rock formations. Given the complexity of flow dynamics on such small scales, robust numerical methods have to be employed in order to capture the highly dynamic interfaces and flow intermittency. In this work we use a three-dimensional multiphase Smoothed Particle Hydrodynamics (SPH) model to simulate surface tension dominated flow on smooth fracture surfaces. We model droplet and film flow over a wide range of contact angles and Reynolds numbers encountered in such flows on rock surfaces. We validate our model via comparison with existing empirical and semi-analytical solutions for droplet flow. We use the SPH model to investigate the occurrence of adsorbed trailing films left behind droplets under various flow conditions and its importance for the flow dynamics when films and droplets coexist. It is shown that flow velocities are higher on prewetted surfaces covered by a thin film which is qualitatively attributed to the enhanced dynamic wetting and dewetting at the trailing and advancing contact lines. Finally, we demonstrate that the SPH model can be used to study flow on rough surfaces.

Influence of Flow Velocity on Conservative Solute Transport in Sets of Parallel Fractures with Fracture Skin

Abstract Analysis of contaminant transport through fractured crystalline rocks has received considerable attention, particularly with regard to subsurface nuclear waste repositories. Most of the studies have employed the dual continuum approach, with the fractures and the rock matrix as the two continuums, assuming that fractures control the overall conductivity of the rock and the porous matrix just provides storage. However, field observations of rock fractures have shown that the real situation can be very complex. Based on some recent investigations, it has been reported that the portion of the rock matrix adjacent to many open fractures is physically and chemically altered. These alterations, referred to as the fracture skin, can have different sorption and diffusion properties compared to those of the undisturbed rock matrix and this may influence the transport of solutes through such formations. In the present study, a numerical model is developed to simulate conservative solute transport in a fractured crystalline rock formation using the triple continuum approach - with the fracture, fracture skin and the rock matrix as the three continuums. The model is solved using a fully implicit finite difference scheme. Contaminant migration in the fractured formation with and without skin has been simulated. It is observed that contaminant penetration along the fracture is enhanced at large flow velocities. The effect of flow velocity on conservative solute transport is investigated for different fracture apertures and fracture skin thicknesses. The influence of flow velocity on contaminant transport is demonstrated to be more with change in fracture aperture than with change in skin thickness.

Bench scale laboratory tests to analyze non-linear flow in fractured media

Abstract. The knowledge of flow phenomena in fractured rocks is very important for groundwater resources management in hydrogeological engineering. A critical emerging issue for fractured aquifers is the validity of the Darcian-type "local cubic law", which assumes a linear relationship between flow rate and pressure gradient to accurately describe flow patterns. Experimental data obtained under controlled conditions such as in a laboratory increase our understanding of the fundamental physics of fracture flow and allow us to investigate the presence of non-linear flow inside fractures that generates a substantial deviation from Darcy's law. In this study the presence of non-linear flow in a fractured rock formation has been analyzed at bench scale in laboratory tests. The effects of non-linearity in flow have been investigated by analyzing hydraulic tests on an artificially created fractured rock sample of parallelepiped (0.60 × 0.40 × 0.8 m) shape. The volumes of water passing through different paths across the fractured sample for various hydraulic head differences have been measured, and the results of the experiments have been reported as specific flow rate vs. head gradient. The experimental results closely match the Forchheimer equation and describe a strong inertial regime. The results of the test have been interpreted by means of numerical simulations. For each pair of ports, several steady-state simulations have been carried out varying the hydraulic head difference between the inlet and outlet ports. The estimated linear and non-linear Forchheimer coefficients have been correlated to each other and respectively to the tortuosity of the flow paths. A correlation among the linear and non-linear Forchheimer coefficients is evident. Moreover, a tortuosity factor that influences flow dynamics has been determined.