Simulation of brine migration along geological fault zones using a consistent mesh approach

2020 ◽  
Author(s):  
Falko Vehling ◽  
Firdovsi Gasanzade ◽  
Jens-Olaf Delfs ◽  
Sebastian Bauer
Keyword(s):  
Fluid Flow ◽  
Corner Point ◽  
Fault Plane ◽  
Damage Zone ◽  
Gas Injection ◽  
Gas Storage ◽  
Fault Zones ◽  
Formation Pressure ◽  
Brine Migration ◽  
Fault Damage Zone

<p>Upward brine migration through permeable fault damage zones could endanger near-surface drinking water resources. Deep porous rock formations offer a large potential for gas storage, like e.g. methane or CO<sub>2</sub>. But gas injection induces formation pressure build up, that can potentially lead to vertical or horizontal brine displacement. Here fault zones play an important role as they can act either as lateral no-flow boundaries or as permeable pathways, that allow for fluid flow and pressure dissipation. Numerical reservoir simulations, which have become an important tool for investigating these effects quantitatively, have to be performed on a regional scale, in order to include the large-scale geological faults zones. Fault zones have to be implemented into the model in a geometrically and hydraulically flexible way, to account for the variety of natural conditions encountered, as e.g. open or closed fault zone.</p><p>In order to model that complexity, the corner point grid approach has been applied by geologists for decades. The corner point grid utilizes a set of hexahedral blocks to represent geological formations. At the fault plane, where geological layers are vertically shifted, hanging nodes appear and the corner point grid cannot be used directly, if permeable fault zones have to be represented in the model. In this study we present an extension of a mesh converter, which removes hanging nodes at the fault plane by point combination, thus providing a consistent finite element mesh. Our numerical model can account for heterogeneous hydraulic properties of the fault damage zone and the enclosed fault core. The fault core is represented by one layer of 3D finite elements on each side of the fault plane. The fault damage zone consists of a continuous layer of quadrangular 2D finite elements, which are attached at the outer face of the 3D fault core elements. This model allows for fluid flow along the fault plane while fluid flow through the fault core could be adjusted by element permeability. This concept was implemented into a workflow using the FEM-simulator OpenGeoSys in combination with a mesh converter.</p><p>The concept and workflow are shown to run stable using dedicated test cases for method validation, accounting for the coupled transport of water, heat and salt mass for different fault zone setups in a synthetic multi-layered subsurface. Here we focused on brine displacement and uprising due to formation pressure increase after gas injection, which is numerically realized by Dirichlet pressure boundary conditions. Further, we will investigate the relation between computational efficiency and flow solution differences by comparing this concept with the approach of fully discretized faults. Additionally, we will apply our workflow on a real geological case in the Northern German Basin, where a fault system is close to a potential gas storage side.  </p>

scholarly journals Fault reactivation by gas injection at an underground gas storage off the east coast of Spain

2019 ◽  
Author(s):  
Antonio Villaseñor ◽  
Robert B. Herrmann ◽  
Beatriz Gaite ◽  
Arantza Ugalde
Keyword(s):  
East Coast ◽  
Fault Plane ◽  
Source Parameters ◽  
Gas Injection ◽  
Focal Depth ◽  
Gas Storage ◽  
Fault Reactivation ◽  
Underground Gas Storage ◽  
Waveform Modeling ◽  
Valencia Trough

Abstract. During September–October of 2013 an intense swarm of earthquakes occurred off the east coast of Spain associated with the injection of the base gas in an offshore underground gas storage. Two weeks after the end of the injection operations, three moderate-sized earthquakes (Mw 4.0–4.1) occurred near the storage. These events were widely felt by the nearby population, leading to the indefinite shut-down of the facility. Here we investigate the source parameters (focal depth and mechanism) of the largest earthquakes in the sequence in order to identify the faults reactivated by the gas injection, and to help understand the processes that caused the earthquakes. Our waveform modeling results indicate that the largest earthquakes occurred at depths of 6–8 km beneath the sea floor, significantly deeper than the injection depth (~ 1800 m). Although we cannot undoubtedly discriminate the fault plane from the two nodal planes of the mechanisms, most evidence seems to favor a NW-SE striking fault plane. We propose that the gas injection reactivated unmapped faults in the Paleozoic basement, with regional orientation possibly inherited from the opening of the Valencia Trough.

Deformation band populations in fault damage zone—impact on fluid flow

2009 ◽  
Vol 14 (2) ◽  
pp. 231-248 ◽  
Author(s):  
Dmitry Kolyukhin ◽  
Sylvie Schueller ◽  
Magne S. Espedal ◽  
Haakon Fossen
Keyword(s):  
Fluid Flow ◽  
Deformation Band ◽  
Damage Zone ◽  
Fault Damage Zone

scholarly journals Fault reactivation by gas injection at an underground gas storage off the east coast of Spain

Solid Earth ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 63-74
Author(s):  
Antonio Villaseñor ◽  
Robert B. Herrmann ◽  
Beatriz Gaite ◽  
Arantza Ugalde
Keyword(s):  
East Coast ◽  
Fault Plane ◽  
Source Parameters ◽  
Gas Injection ◽  
Focal Depth ◽  
Gas Storage ◽  
Fault Reactivation ◽  
Underground Gas Storage ◽  
Waveform Modeling ◽  
Valencia Trough

Abstract. During September–October of 2013 an intense swarm of earthquakes occurred off the east coast of Spain associated with the injection of the base gas in an offshore underground gas storage. Two weeks after the end of the injection operations, three moderate-sized earthquakes (Mw 4.0–4.1) occurred near the storage. These events were widely felt by the nearby population, leading to the indefinite shut-down of the facility. Here we investigate the source parameters (focal depth and mechanism) of the largest earthquakes in the sequence in order to identify the faults reactivated by the gas injection and to help understand the processes that caused the earthquakes. Our waveform modeling results indicate that the largest earthquakes occurred at depths of 6–8 km beneath the sea floor, significantly deeper than the injection depth (∼1800 m). Although we cannot undoubtedly discriminate the fault plane from the two nodal planes of the mechanisms, most evidence seems to favor a NW–SE-striking fault plane. We propose that the gas injection reactivated faults in the Paleozoic basement, with regional orientation possibly inherited from the opening of the Valencia Trough.

Single-event throw distribution along the Delta fault (Baikal rift) from geomorphological and ground-penetrating radar investigations

2020 ◽  
Author(s):  
Oksana Lunina ◽  
Ivan Denisenko
Keyword(s):  
Ground Penetrating Radar ◽  
Fault Plane ◽  
Damage Zone ◽  
Fault Scarp ◽  
Unconsolidated Sediments ◽  
Normal Faults ◽  
Single Event ◽  
Fault Damage Zone ◽  
Ductile Component ◽  
Ground Penetrating

<div> <p>Tectonic displacement is one of the important parameters in determining the seismic potential of an active fault. Its distribution along the fault strike is highly variable; therefore, when assessing seismic hazard, both the quality and the number of measurements of single-event throws are essential. We reconstructed and studied peculiarities of distribution of vertical displacements, which occurred on the land-based part of the Delta fault during the devasting M~7.5 Thagan earthquake of 12 January 1862. Morphologically, the seismogenic structure is expressed by the fault scarp in unconslolidated Holocene sediments, which underwent significant liquefaction and fluidization during the seismic event. In space, the fault scarp coincides with the lacustrine-deltoid and alluvial-deltoid terraces of Lake Baikal and the Selenga river and complicated by eolian deposits.</p> <p>As a basic method, we used ground-penetrating radar (GPR) in combination with data from shallow drilling, trenching and analysis of seven topographic profiles. By measuring near-field displacements at the fault planes (brittle component) and far-field displacement at a distance from the fault plane (sum of brittle and ductile components according to Homberg et al. (2017)) on GPR sections, we subtracted folding component of the total throw. Besides, we considered a number of other parameters in relation with the value of the last single-event offset in the upper sedimentary layer at a depth of the first meters. As a result, it was found that the displacement during the Tsagan earthquake occurred under NW-SE extension as motion on a stepped system of normal faults with a dip of the major plane to the NW at angles 56–77°. The total throws from GPR data on each of seven profiles were 3.83 m, 9.59 m, 2.4 m, 4.27 m, 9.28 m, 5.23 m, and 1.81 m, which are aligned with vertical fault displacements H1 with an error from 0.03 to 0.47 m. H1 was defined as a vertical distance between the intersections of the fault plane, and planes formed by the displaced original geomorphic surfaces (McCalpin, 2009). The brittle components were 2.32 m, 5.54 m, 1.93 m, 3.0 m, 6.07 m, 3.2 m, and 1.58 m, respectively. The contribution of the ductile component to the total displacement varies from 13% to 42%, the visible fault damage zone widths are from 2.55 m to 20 m. The maximal contributions of the ductile component correspond to minimal fault dips of the major fault plane and, as a whole, to the largest fault damage zone widths, which also correlate well with the offset values.</p> <p>The structural features of the rupture zones and peculiarities of throw distribution in unconsolidated sediments should be taken into account in order to avoid underestimating the magnitudes of the normal fault earthquakes and their seismic effect. In the case of soft sediments of mixed rheology (competent and incompetent), obviously, one should expect large values of total displacements and wider zones of deformations, in comparison with homogeneous sections. Acknowledgments: The reported study was partly funded by RFBR, project number 19-35-90003.</p> </div>

Permeability of carbonate fault rocks: a case study from Malta

2019 ◽  
Vol 26 (3) ◽  
pp. 418-433 ◽  
Author(s):  
Andy P. Cooke ◽  
Quentin J. Fisher ◽  
Emma A. H. Michie ◽  
Graham Yielding
Keyword(s):  
Fluid Flow ◽  
Host Rock ◽  
Damage Zone ◽  
Fault Zones ◽  
High Porosity ◽  
Rock Permeability ◽  
Fault Rock ◽  
Fault Rocks ◽  
Diagenetic Alteration ◽  
Hydraulic Behaviour

The inherent heterogeneity of carbonate rocks suggests that carbonate-hosted fault zones are also likely to be heterogeneous. Coupled with a lack of host–fault petrophysical relationships, this makes the hydraulic behaviour of carbonate-hosted fault zones difficult to predict. Here we investigate the link between host rock and fault rock porosity, permeability and texture, by presenting data from series of host rock, damage zone and fault rock samples from normally faulted, shallowly buried limestones from Malta. Core plug X-ray tomography indicates that texturally heterogeneous host rocks lead to greater variability in the porosity and permeability of fault rocks. Fault rocks derived from moderate- to high-porosity (>20%) formations experience permeability reductions of up to six orders of magnitude relative to the host; >30% of these fault rocks could act as baffles or barriers to fluid flow over production timescales. Fault rocks derived from lower-porosity (<20%) algal packstones have permeabilities that are lower than their hosts by up to three orders of magnitude, which is unlikely to impact fluid flow on production timescales. The variability of fault rock permeability is controlled by a number of factors, including the initial host rock texture and porosity, the magnitude of strain localization, and the extent of post-deformation diagenetic alteration. Fault displacement has no obvious control over fault rock permeability. The results enable better predictions of fault rock permeability in similar lithotypes and tectonic regimes. This may enable predictions of across-fault fluid flow potential when combined with data on fault zone architecture.

scholarly journals Episodic fluid flow in an active fault

Geology ◽  
2019 ◽  
Vol 47 (10) ◽  
pp. 938-942 ◽  
Author(s):  
Sarah Louis ◽  
Elco Luijendijk ◽  
István Dunkl ◽  
Mark Person
Keyword(s):  
Fluid Flow ◽  
Numerical Models ◽  
Damage Zone ◽  
Normal Fault ◽  
Geothermal Gradient ◽  
Hydrothermal Activity ◽  
The Past ◽  
Discharge Rates ◽  
Fault Damage Zone ◽  
Wide Zone

Abstract We present a reconstruction of episodic fluid flow over the past ∼250 k.y. along the Malpais normal fault, which hosts the Beowawe hydrothermal system (Nevada, USA), using a novel combination of the apatite (U-Th)/He (AHe) thermochronometer and a model of the thermal effects of fluid flow. Samples show partial resetting of the AHe thermochronometer in a 40-m-wide zone around the fault. Numerical models using current fluid temperatures and discharge rates indicate that fluid flow events lasting 2 k.y. or more lead to fully reset samples. Episodic fluid pulses lasting 1 k.y. result in partially reset samples, with 30–40 individual fluid pulses required to match the data. Episodic fluid flow is also supported by an overturned geothermal gradient in a borehole that crosses the fault, and by breaks in stable isotope trends in hydrothermal sinter deposits that coincide with two independently dated earthquakes in the past 20 k.y. This suggests a system where fluid flow is triggered by repeated seismic activity, and that seals itself over ∼1 k.y. due to the formation of clays and silicates in the fault damage zone. Hydrothermal activity is younger than the 6–10 Ma age of the fault, which means that deep (∼5 km) fluid flow was initiated only after a large part of the 230 m of fault offset had taken place.

scholarly journals Fault damage zone volume and initial salinity distribution determine intensity of shallow aquifer salinisation in subsurface storage

2016 ◽  
Vol 20 (3) ◽  
pp. 1049-1067 ◽  
Author(s):  
Elena Tillner ◽  
Maria Langer ◽  
Thomas Kempka ◽  
Michael Kühn
Keyword(s):  
Fluid Flow ◽  
Boundary Conditions ◽  
Groundwater Resources ◽  
Damage Zone ◽  
Shallow Aquifer ◽  
Scale Model ◽  
Exclusion Criterion ◽  
Salinity Distribution ◽  
Fluid Displacement ◽  
Fault Damage Zone

Abstract. Injection of fluids into deep saline aquifers causes a pore pressure increase in the storage formation, and thus displacement of resident brine. Via hydraulically conductive faults, brine may migrate upwards into shallower aquifers and lead to unwanted salinisation of potable groundwater resources. In the present study, we investigated different scenarios for a potential storage site in the Northeast German Basin using a three-dimensional (3-D) regional-scale model that includes four major fault zones. The focus was on assessing the impact of fault length and the effect of a secondary reservoir above the storage formation, as well as model boundary conditions and initial salinity distribution on the potential salinisation of shallow groundwater resources. We employed numerical simulations of brine injection as a representative fluid. Our simulation results demonstrate that the lateral model boundary settings and the effective fault damage zone volume have the greatest influence on pressure build-up and development within the reservoir, and thus intensity and duration of fluid flow through the faults. Higher vertical pressure gradients for short fault segments or a small effective fault damage zone volume result in the highest salinisation potential due to a larger vertical fault height affected by fluid displacement. Consequently, it has a strong impact on the degree of shallow aquifer salinisation, whether a gradient in salinity exists or the saltwater–freshwater interface lies below the fluid displacement depth in the faults. A small effective fault damage zone volume or low fault permeability further extend the duration of fluid flow, which can persist for several tens to hundreds of years, if the reservoir is laterally confined. Laterally open reservoir boundaries, large effective fault damage zone volumes and intermediate reservoirs significantly reduce vertical brine migration and the potential of freshwater salinisation because the origin depth of displaced brine is located only a few decametres below the shallow aquifer in maximum. The present study demonstrates that the existence of hydraulically conductive faults is not necessarily an exclusion criterion for potential injection sites, because salinisation of shallower aquifers strongly depends on initial salinity distribution, location of hydraulically conductive faults and their effective damage zone volumes as well as geological boundary conditions.

Permeability contrasts of fault zones - from conceptual model to numerical simulation

2020 ◽  
Author(s):  
Ulrich Kelka ◽  
Thomas Poulet ◽  
Luk Peeters
Keyword(s):  
Fluid Flow ◽  
Fault Zone ◽  
Large Scale ◽  
Regional Scale ◽  
Damage Zone ◽  
Fluid Pressure ◽  
Fault Zones ◽  
Strong Impact ◽  
Fault Zone Architecture ◽  
The Impact

&lt;p&gt;Fault and fracture networks can govern fluid flow patterns in the subsurface and predicting fluid flow on a regional scale is of interest in a variety of fields like groundwater management, mining engineering, energy, and mineral resources. Especially the pore fluid pressure can have a strong impact on the strength of fault zones and might be one of the drivers for fault reactivation. Reliable simulations of the transient changes in fluid pressure need to account for the generic architecture of fault zones that comprises strong permeability contrast between the fault core and damage zone.&lt;/p&gt;&lt;p&gt;Particularly, the distribution and connectivity of large-scale fault zones can have a strong impact on the flow field. Yet, modelling numerically such features in their full complexity remains challenging. Often faults zones are conceptualized as forming exclusively either barriers or conduits to fluid flow. However, a generic architecture of fault zones often comprises a discrete fault core surrounded by a diffuse damage zone and conceptualizing large scale discontinuities simply as a barrier or conduit is unlikely to capture the regional scale fluid flow dynamics. It is known that if the fault zone is hosted in low-permeability strata, such as clays or crystalline rocks, a transversal flow barrier can form along the fault core whereas the fracture-rich fault damage zone represents a longitudinal conduit. In more permeable host-rocks (i.e. sandstones or carbonates) the reverse situation can occur, and the permeability distributions in the damage zones can be governed by the abundance of low-permeability deformation features. A reliable numerical model needs to account for the difference and strong contrasts in fluid flow properties of the core and the damage zone, both transversally and longitudinally, in order to make prediction about the regional fluid flow pattern.&lt;/p&gt;&lt;p&gt;Here, we present a numerical method that accounts for the generic fault zone architecture as lower dimensional interfaces in conforming meshes during fluid flow simulations in fault networks. With this method we aim to decipher the impact of fault zone architecture on subsurface flow pattern and fluid pressure evolution in fractures and faulted porous media. The method is implemented in a finite element framework for Multiphysics simulations. We demonstrate the impact of considering the more generic geological structure of individual faults on the flow field by conceptualizing discontinuities either as barriers, conduits or as a conduit-barrier system and show were these conceptualizations are applicable in natural systems. We further show that a reliable regional scale fluid flow simulation in faulted porous media needs to account for the generic fault zone architecture. The approach is finally used to evaluate the fluid flow response of statistically parameterised faulted media, in order to investigate the impact and sensitivity of each variable parameter.&lt;/p&gt;

scholarly journals Petrophysical Properties and Microstructural Analysis of Faulted Heterolithic Packages: A Case Study from Miocene Turbidite Successions, Italy

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-23 ◽  
Author(s):  
Hannah Riegel ◽  
Miller Zambrano ◽  
Fabrizio Balsamo ◽  
Luca Mattioni ◽  
Emanuele Tondi
Keyword(s):  
Fluid Flow ◽  
Host Rock ◽  
Damage Zone ◽  
Microstructural Analysis ◽  
Fault Zones ◽  
Clay Material ◽  
Fault Rock ◽  
Matrix Permeability ◽  
The Matrix ◽  
The Individual

Geofluid reservoirs located in heterolithic successions (e.g., turbidites) can be affected by vertical and lateral compartmentalization due to interbedded fine-grained facies (i.e., shale, siltstones) and the presence of faults, respectively. A fault can behave as a conduit or barrier to fluid flow depending on its architecture and the individual hydraulic behavior of its components (i.e., fault core, damage zone). The fault core, normally composed by fault rock or smeared clay material, commonly acts as a flow inhibitor across the fault. Fault-related fractures (macro- and microscopic) in the damage zone generally increase the permeability parallel to the fault, except when they are cemented or filled with gouge material. Although macrofractures (which define the fracture porosity) dominate fluid flow, the matrix porosity (including microfractures) begins to have a more important role in fluid flow as the aperture of macrofractures is occluded, particularly at greater depth. This study investigates the variation in matrix permeability in fault zones hosted in heterolithic successions due to fault architecture and stratigraphy of host rock (i.e., sand-rich turbidites). Two key areas of well-exposed, faulted Miocene turbidites located in central and southern Italy were selected. For this study, six separate fault zones of varying offset were chosen. Each impacts heterolithic successions that formed under similar tectonic conditions and burial depths. Across the selected fault zones, an extensive petrophysical analysis was done in the field and laboratory, through air permeameter measurements, thin section, and synchrotron analysis in both host rock, damage zone, and fault core. Results suggest that the amount and distribution of clay layers in a heterolithic sequence affects fluid flow across the fault, regardless of fault offset.

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