"uuid","repository link","title","author","contributor","publication year","abstract","subject topic","language","publication type","publisher","isbn","issn","patent","patent status","bibliographic note","access restriction","embargo date","faculty","department","research group","programme","project","coordinates"
"uuid:fe5da713-59d9-4baa-850f-ea9934df510b","http://resolver.tudelft.nl/uuid:fe5da713-59d9-4baa-850f-ea9934df510b","Pressure transient analysis to investigate a coupled fracture corridor and a fault damage zone causing an early thermal breakthrough in the North Alpine Foreland Basin","M Fadel, M. (TU Delft Applied Geology; Leibniz Institute for Applied Geophysics; Georg-August-University); Meneses Rioseco, Ernesto (Leibniz Institute for Applied Geophysics; Georg-August-University); Bruna, P.B.R. (TU Delft Applied Geology); Moeck, Inga (Leibniz Institute for Applied Geophysics; Georg-August-University)","","2023","The heterogeneity of the Upper Jurassic carbonate reservoir (Malm reservoir) beneath the North Alpine Foreland Basin has a significant influence on the mass and heat flow processes during geothermal exploitation. Geophysical borehole data revealed that sub-seismic scale fractures and karstified fractures occur at the inflow zones of deep geothermal wells. However, pressure transient analysis (PTA) in some previous studies concluded that it is difficult to detect the influence of sub-seismic scale features, suggesting that radial flow regime is dominant. Accordingly, a regional thermal-hydraulic model adopted the equivalent porous medium (EPM) approach, homogenizing the sub-seismic scale reservoir heterogeneities; however, unable to detect an early thermal breakthrough (ETB) in a geothermal doublet located SE of Munich. We apply PTA on three buildup tests belonging to that doublet following a deterministic approach to constrain the reservoir type by interpreting the pressure derivative (PD) plots constrained by geophysical and geological data. We derive the magnitudes of the reservoir hydraulic parameters by matching the PD plots with the selected interpretation models. We find that clustered fractures have a significant influence on the reservoir hydraulics, evidenced by trough-shaped curves in the PD plots. Linear flow regime interpreted from the interference test between the two wells indicates permeability anisotropy, which may have caused the ETB. Geophysical data interpretations indicate that these fractures correspond to a coupled fault damage zone and a fracture corridor. Finally, we present a fit-for-purpose 2D discrete fracture network model utilizing the PTA results to match our analytically calibrated model. Our study offers a potential hydraulic explanation to the cause of the ETB highlighting the importance of integrating multi-scale/disciplinary data sets to improve the reliability of dynamic reservoir models, based on which, economic-related decisions are made.","Double porosity models and discreet fracture network; Fracture corridors; North Alpine foreland Basin; Premature thermal breakthrough; Pressure transient analysis; Upper Jurassic carbonates","en","journal article","","","","","","","","","","","Applied Geology","","",""
"uuid:37464633-9480-4726-9034-f55f9f6e1b16","http://resolver.tudelft.nl/uuid:37464633-9480-4726-9034-f55f9f6e1b16","Towards the Uncertainty Quantification of Fractured Karst Systems: Reactive Transport and Fracture Networks: Where Numerical Modeling Meets Outcrop Observations","de Hoop, S. (TU Delft Applied Geology)","Voskov, D.V. (promotor); Bertotti, G. (promotor); Barnhoorn, A. (promotor); Delft University of Technology (degree granting institution)","2022","Society relies on large amounts of energy to progress and allow for a high standard of living. The recent severe climate changes require advanced technologies related to cleaner energy resources. One such technology beneficial for accelerating this current energy transition is geothermal energy. This type of energy is often found in fractured and karstified carbonate aquifers. Understanding the reservoir properties and reducing the risks of such subsurface-related activities is vital. This thesis attempts to understand the complex fractured carbonate reservoirs better and improve the numerical simulation capabilities toward large-scale uncertainty quantification.","Reactive transport; Multiphase flow; Operator-Based Linearization; Fracture networks; Karst; Uncertainty Quantification","en","doctoral thesis","","978-94-6469-044-6","","","","","","","","","Applied Geology","","",""
"uuid:49827786-deb7-4417-ba3d-67d1660471d8","http://resolver.tudelft.nl/uuid:49827786-deb7-4417-ba3d-67d1660471d8","Fracture characterisation in carbonate reservoirs for geothermal production","Barreiros Jorge, Sofia (TU Delft Civil Engineering and Geosciences)","Bruna, P.B.R. (mentor); Delft University of Technology (degree granting institution)","2022","Subsurface energy projects carry high risk due to the lack of data available to accurately model reservoir characteristics. There is a need for high level analysis to extrapolate subsurface data from a single point (i.e. a well). The focus of this study will be on fracture characterisation in a carbonate reservoir located within the Geneva Basin for the purposes of geothermal exploration. The goal is to use fracture characterisation techniques in the form of an OBI analysis and the use of a fracture growth model with a focus on geomechanics to predict the possible fracture growth patterns. This work will allow for a better understanding of fluid flow and permeability throughout the reservoir. As well as explore the benefits and limitations of this approach. The case study is a fractured carbonate reservoir made up of limestone and marlstone packages. To calculate the paleo stress environment, the fracture data is used to back calculate the possible magnitude of the stress field during fracture formation. This choice was made after careful consideration and comparison of the fracture data with the fault data. The output of this modelling will be a DFN with multiple layers controlled by the fracture density. This model can hopefully be used in the future for dynamic simulation to understand the impacts of these assumptions and validate with production data from the well.
2 sequestration). Fractured reservoirs often have a very complex structure, making modeling flow and transport in such networks slow and unstable. Consequently, this limits our ability to perform uncertainty quantification and increases development costs and environmental risks. This study provides an advanced methodology for simulation based on Discrete Fracture Model approach. The preprocessing framework results in a fully conformal, uniformly distributed grid for realistic 2D fracture networks at a required level of precision. The simplified geometry and topology of the resulting network are compared with input (i.e., unchanged) data to evaluate the preprocessing influence. The resulting mesh-related parameters, such as volume distributions and orthogonality of control volume connections, are analyzed. Furthermore, changes in fluid-flow response related to preprocessing are evaluated using a high-enthalpy two-phase flow geothermal simulator. The simplified topology directly improves meshing results and, consequently, the accuracy and efficiency of numerical simulation. The main novelty of this work is the introduction of an automatic preprocessing framework allowing us to simplify the fracture network down to required level of complexity and addition of a fracture aperture correction capable of handling heterogeneous aperture distributions, low connectivity fracture networks, and sealing fractures. The graph-based framework is fully open-source and explicitly resolves small-angle intersections within the fracture network. A rigorous analysis of changes in the static and dynamic impact of the preprocessing algorithm demonstrates that explicit fracture representation can be computationally efficient, enabling their use in large-scale uncertainty quantification studies.","complex fracture networks; efficient discrete fracture methodology; geothermal energy; topology; two-phase flow; uncertainty","en","journal article","","","","","","","","","","","Reservoir Engineering","","",""
"uuid:5858480a-e689-4166-81f5-3c40b3a4d471","http://resolver.tudelft.nl/uuid:5858480a-e689-4166-81f5-3c40b3a4d471","Fracture Network Prediction in the Geneva Basin: A Geothermal Case Study","Alhamad Mahmood Abdulaziz M, Mahmood (TU Delft Civil Engineering and Geosciences)","Bruna, P.B.R. (mentor); Bertotti, G. (mentor); Delft University of Technology (degree granting institution)","2021","The aim of this study is to reduce the risk of the ongoing Geothermal exploration effort in Geneva Basin by estimating the influence of the natural fracture on the reservoir properties. A Discrete Fracture Network (DFN) was generated to resemble the fracture network in the Lower Cretaceous carbonate reservoir. The DFN modelling approach is using a novel workflow that is based on a geomechanical forward modelling simulation approach. Two 2D seismic lines and well data, including interpreted fractures using Borehole Image (BHI) log, were used to prepare the model inputs. Some results were derived from the fracture data that were also used to prepare the model inputs. In general, the fracture data have fairly constant orientation along the Lower Cretaceous interval. In this study the fractures are assumed to be formed under a single tectonic regime. However, when partitioning the fractures in different stratigraphic formations, a change in the direction of the fractures with depth is observed. This observation could be explained by the variation in rock's stiffness between different stratigraphic formations.
Two techniques were used to model the subsurface fracture network: paleo-tectonic stress inversion and fracture network forward modelling techniques. The modelled DFN resembles the fractures geometry at the well location whereas away from the well the model is constrained by the subsurface fault geometry and far-field tectonic stress. Moreover, the modelled DFN consists of multiple 2 meters thick layers where each layer include a layer-bound fracture network. One of the main limitations of this approach is that it can not consider multiple tectonic regimes to simulate the fracture network. In addition, this approach requires large computational power.","Geothermal Exploration; Natural Fracture Networks; discrete fracture network; Geomechanical Modelling; Geneva Basin; Lower Cretaceous Carbonates","en","master thesis","","","","","","","","","","","","Applied Earth Sciences","",""
"uuid:ba848fe2-50d5-4ac8-8462-090b5f4a4b5f","http://resolver.tudelft.nl/uuid:ba848fe2-50d5-4ac8-8462-090b5f4a4b5f","The impact of natural fractures on heat extraction from tight Triassic sandstones in the West Netherlands Basin: A case study combining well, seismic and numerical data","Boersma, Q.D. (TU Delft Applied Geology); Bruna, P.B.R. (TU Delft Applied Geology); de Hoop, S. (TU Delft Applied Geology); Vinci, Francesco (PanTerra Geoconsultants B.V.); Moradi Tehrani, Ali (CGG); Bertotti, G. (TU Delft Applied Geology)","","2021","The positive impact that natural fractures can have on geothermal heat production from low-permeability reservoirs has become increasingly recognised and proven by subsurface case studies. In this study, we assess the potential impact of natural fractures on heat extraction from the tight Lower Buntsandstein Subgroup targeted by the recently drilled NLW-GT-01 well (West Netherlands Basin (WNB)). We integrate: (1) reservoir property characterisation using petrophysical analysis and geostatistical inversion, (2) image-log and core interpretation, (3) large-scale seismic fault extraction and characterisation, (4) Discrete Fracture Network (DFN) modelling and permeability upscaling, and (5) fluid-flow and temperature modelling. First, the results of the petrophysical analysis and geostatistical inversion indicate that the Volpriehausen has almost no intrinsic porosity or permeability in the rock volume surrounding the NLW-GT-01 well. The Detfurth and Hardegsen sandstones show better reservoir properties. Second, the image-log interpretation shows predominately NW-SE-orientated fractures, which are hydraulically conductive and show log-normal and negative-power-law behaviour for their length and aperture, respectively. Third, the faults extracted from the seismic data have four different orientations: NW-SE, N-S, NE-SW and E-W, with faults in proximity to the NLW-GT-01 having a similar strike to the observed fractures. Fourth, inspection of the reservoir-scale 2D DFNs, upscaled permeability models and fluid-flow/temperature simulations indicates that these potentially open natural fractures significantly enhance the effective permeability and heat production of the normally tight reservoir volume. However, our modelling results also show that when the natural fractures are closed, production values are negligible. Furthermore, because active well tests were not performed prior to the abandonment of the Triassic formations targeted by the NLW-GT-01, no conclusive data exist on whether the observed natural fractures are connected and hydraulically conductive under subsurface conditions. Therefore, based on the presented findings and remaining uncertainties, we propose that measures which can test the potential of fracture-enhanced permeability under subsurface conditions should become standard procedure in projects targeting deep and potentially fractured geothermal reservoirs.","fracture networks; geothermal energy; temperature modelling; West Netherlands Basin","en","journal article","","","","","","","","","","","Applied Geology","","",""
"uuid:818adf34-98d9-4aa4-a36f-a10b03a4a1b2","http://resolver.tudelft.nl/uuid:818adf34-98d9-4aa4-a36f-a10b03a4a1b2","Large-scale natural fracture network patterns: Insights from automated mapping in the Lilstock (Bristol Channel) limestone outcrops","Prabhakaran, R. (TU Delft Applied Geology; Eindhoven University of Technology); Urai, J. L. (Rheinisch-Westfälische Technische Hochschule); Bertotti, G. (TU Delft Applied Geology); Weismüller, C. (Rheinisch-Westfälische Technische Hochschule); Smeulders, D.M.J. (Eindhoven University of Technology)","","2021","The Lilstock outcrop in the southern Bristol Channel provides exceptional exposures of several limestone beds displaying stratabound fracture networks, providing the opportunity to create a very large, complete, and ground-truthed fracture model. Here we present the result of automated fracture extraction of high-resolution photogrammetric images (0.9 cm/pixel) of the full outcrop, obtained using an unmanned aerial vehicle, to obtain a spatially extensive, full-resolution map of the complete fracture network with nearly 350,000 ground-truthed fractures. We developed graph-based functions to resolve some common issues that arise in automatic fracture tracing such as incomplete traces, incorrect topology, artificial fragmentation, and linking of fracture segments to generate geologically significant trace interpretations. The fracture networks corresponding to different regions within the outcrop are compared using several network metrics and the results indicate both inter- and intra-network (layer to layer) structural variabilities. The dataset is a valuable benchmark in the study of large-scale natural fracture networks and its extension to stochastic network generation in geomodelling. The dataset also highlights the intrinsic spatial variation in natural fracture networks that can occur even in weakly-deformed rocks over relatively short length scales of tens of metres.","Carbonates; Discrete fracture networks; Fractured pavements; Graph theory; Natural fracture networks; Spatial graphs","en","journal article","","","","","","","","","","","Applied Geology","","",""
"uuid:e81bdc6b-5d42-49ce-b4ba-4dc76e5d369a","http://resolver.tudelft.nl/uuid:e81bdc6b-5d42-49ce-b4ba-4dc76e5d369a","Fast and robust scheme for uncertainty quantification in naturally fractured reservoirs","de Hoop, S. (TU Delft Applied Geology); Voskov, D.V. (TU Delft Reservoir Engineering; Stanford University)","","2021","The main objective of this study is to perform Uncertainty Quantification (UQ) using a detailed representation of fractured reservoirs. This is achieved by creating a simplified representation of the fracture network while preserving the main characteristics of the high-fidelity model. We include information at different scales in the UQ workflow which allows for a large reduction in the computational time while converging to the high-fidelity full ensemble statistics. Ultimately, it allows us to make accurate predictions on geothermal energy production in highly heterogeneous fractured porous media. The numerical reservoir simulation tool we use in this work is the Delft Advanced Research Terra Simulator (DARTS). It is based on Finite Volume approximation in space, fully coupled explicit approximation in time, and uses the novel linearization technique called Operator-Based Linearization (OBL) for the system of discretized nonlinear governing equations. We use a fracture network generation algorithm that uses distributions for length, angles, size of fracture sets, and connectivity as its main input. This allows us to generate a large number of complex fracture networks at the reservoir scale. We developed a pre-processing algorithm to simplify the fracture network and use graph theory to analyze the connectivity before and after pre-processing. Furthermore, we use metric space modeling methods for statistical analysis. A robust coarsening method for the Discrete Fracture Matrix model (DFM) is developed which allows for great control over the degree of simplification of the network’s topology and connectivity. We apply the framework to modeling of geothermal energy extraction. The pre-processing algorithm allows for a hierarchical representation of the fracture network, which in turn is utilized in the reduced UQ methodology. The reduced UQ workflow uses the coarser representation of the fracture networks to partition/rank the high-fidelity parameter space. Then a small subset of high-fidelity models is chosen to represent the full ensemble statistics. Hereby, the computational time of the UQ is reduced by two/three orders of magnitude, while converging to similar statistics as the high-fidelity full ensemble statistics. The methods developed in this study are part of a larger project on a prediction of energy production from carboniferous carbonates. The final goal is to perform UQ in pre-salt reservoirs which are characterized by complex reservoir architecture (i.e., large karstification and fracture networks). The UQ of fractured reservoirs is typically done in the petroleum industry using effective media models. We present a methodology that can efficiently handle a large ensemble of DFM models, which represent complex fracture networks and allow for making decisions under uncertainty using more detailed high-resolution numerical models.","machine learning; upstream oil & gas; intersection; reservoir simulation; fracture network; complex reservoir; voskov; workflow; high-fidelity model; connectivity","en","conference paper","Society of Petroleum Engineers","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2022-04-19","","","Applied Geology","","",""
"uuid:0b7c48fa-657b-407a-a56d-e6718671cd99","http://resolver.tudelft.nl/uuid:0b7c48fa-657b-407a-a56d-e6718671cd99","Regional Geology and Fracture Network Characterisation of the Southern Chotts and Jeffara Basins, Central Tunisia: Implications for Petroleum Reservoirs","Smith, Ruaridh (TU Delft Civil Engineering and Geosciences)","Bertotti, G. (mentor); Bruna, P.B.R. (mentor); Martinius, A.W. (graduation committee); Barnhoorn, A. (graduation committee); Delft University of Technology (degree granting institution)","2020","The Southern Chotts and Jeffara Basins are situated within the Saharan Domain of Central Tunisia, North Africa. The Southern Chotts Basin hosts reservoirs within the Triassic, Permian and Ordovician units that contain significant hydrocarbon accumulations whilst the Jeffara Basin contains outcrop analogues of the same hydrocarbonbearing formations. The basins experienced a late Hercynian shortening phase which involved the uplift of a major topographic high (Tebaga de Medenine). This high, in conjunction with a older regional high, the Telemzane Arch influenced the deposition and geometry of the Permian and Triassic units across both basins. This shortening event is characterised at the scale of hundreds of meters by EW striking folds into which the midlate Triassic and early Jurassic units are deposited. The folding is also observed at field scale (10’s meters) through small faultrelated folds in the Permian deposits of the Tebaga de Medenine. This late Hercynian phase occurs between the late Permian and early Jurassic in the basins. Fracture data collected from the upper Permian and lower Triassic units (Jeffara Basin) provides an analogue to the fracture networks at depth (Southern Chotts Basin) in the Paleozoic reservoirs. A conjugate fracture system observed in the field (from fracture pavements) corroborates with the interpretation of regional shortening in the basins. Seismic attribute analysis on depth slices in the Paleozoic reservoirs also shows the conjugate system at depth. This analysis is integrated with outcrop fracture data and FMI data from wells to create an open fold distributed fracture model of the system in the basins. This model indicates the main driver for fracture generation in the region is folding and is used to predict the fracture networks at depth. This is undertaken using discrete fracture network (DFN) modelling of the subsurface. This model is integrated with a deterministic model from the seismic time slices to create a hybrid predictive fracture model of the early Paleozoic reservoirs. Analytical aperture modelling of the fracture model demonstrates the fractures varied in openness depending on orientation and fracture length. The conjugate set orientated at 240∘and longer joints detected from seismic attributes presented the widest aperture size. These fractures in the subsurface at implications on the transmissibility of the reservoirs, especially Permian units which have low bulk rock permeability and the lower Triassic (TAGI) sequences which are susceptible to compartmentalisation.","Structural Geology; Tebaga de Medenine; Shortening; Natural Fractures; Fracture Network Characterisation; Fracture Network Modelling","en","master thesis","","","","","","","","2021-11-12","","","","","","33.422350, 10.221321"
"uuid:8c8e04ec-b697-4ebd-aee4-46a01434021c","http://resolver.tudelft.nl/uuid:8c8e04ec-b697-4ebd-aee4-46a01434021c","Characterization of a Fracture-Controlled Enhanced Geothermal System (EGS) in the Trans-Mexican-Volcanic-Belt (TMVB): Predictive Mechanical Model for Fracture Stimulation in an Enhanced Geothermal System Context (EGS)","Lepillier, B.P. (TU Delft Reservoir Engineering)","Bruhn, D.F. (promotor); Bertotti, G. (promotor); Delft University of Technology (degree granting institution)","2020","In 2020, as the world Energy demand keeps on rising (International Energy Agency (IEA), 2019), and with the global climate warming a reality (The Organisation for Economic Co-operation and Development (OECD), 2020), reducing our societal impact on Earth is of utmost importance. Energy and Climate have always been intrinsically related. Therefore, solving the Energy-Climate problem is a challenge where not one but several solutions should come together. Part of this global solution is the potential of geothermal resources. Geothermal energy is a renewable energy resource which has large potential to reduce the dependency on fossil fuels. Within the several uses of geothermal resources, a promising technique is titled Enhanced Geothermal Systems. More than renewable, this method has the potential to be sustainable. EGS consists of an originally low permeability reservoir rock that is artificially enhanced. The enhancement can be achieved by different stimulation techniques, such as mechanical, chemical, thermal or a combination of all. This thesis focuses on the mechanical EGS stimulation, where opening of existing fractures and creation of new ones is achieved by injecting a pressurized fluid in the reservoir rock formation. Such a process results in propagating a hydraulic fracture. The complexity of the EGS technique stands in predicting the hydraulic fracture propagation phenomena. EGS research and development is part of the GEMex goals. The GEMex project is a collaboration between Mexican institutions and the European Commission, dedicated to the development of non-conventional geothermal techniques. The Acoculco geothermal field, located in Puebla, is foreseen as a potential EGS. Because this field has been explored with two geothermal wells, and because an analogue exhumed system is available nearby, in the LasMinas area, this systemconstitutes a great research site for developing knowledge on EGS.","Geothermal reservoir; Enhanced Geothermal System; Natural fractures; Discrete fracture network; thermo-hydro-mechanical modelling; hydraulic fracture modelling; phase-field; Finite Element Method","en","doctoral thesis","","978-94-6384-168-9","","","","","","","","","Reservoir Engineering","","",""
"uuid:2093ca04-337b-425e-952c-74d59b7a0174","http://resolver.tudelft.nl/uuid:2093ca04-337b-425e-952c-74d59b7a0174","Morphology and topology of dolostone lithons in the regional Carboneras Fault Zone, Southern Spain","Igbokwe, Onyedika A. (Ruhr-Universität Bochum; Alex Ekwueme Federal University Ndufu-Alike); Mueller, Mathias (Ruhr-Universität Bochum); Bertotti, G. (TU Delft Applied Geology); Timothy, Jithender J. (Ruhr-Universität Bochum); Abah, Obinna (Queen's University Belfast); Immenhauser, Adrian (Ruhr-Universität Bochum)","","2020","Dolostones in a Neogene strike-slip fault zone are described. Two main types of structural features are recognised: (i) Background deformation in the form of a network of bedding-perpendicular and hybrid conjugate fractures, barren fractures and bedding-parallel stylolites. (ii) Fault-related features include breccias and cataclasites. Orthorhombic rock lithons are generated from the intersection of fracture sets with bedding and/or joints. Lithon size and morphology change across the dolostone fault block gradually producing a tetragonal or isometric shape. The lithons are 1–2 cm in dimension (only ~ 20% outside this range) and have an average cross-sectional aspect ratio of 1.6, irrespective of size or structural position. Topology is analysed using nodes and branches, ranging from isolated (I- node and I-I branch) to connected (Y- and X-nodes, and I-C to C-C branches) respectively. The quantitative description of the geometrical and topological analysis of the dolostone lithons suggest that they become more connected and interact within the dolostone fault blocks. Assessing the change in topology and lithons connectivity have important implications for subsurface reservoirs and aquifers hosted in dolostone-fault zones.","Background deformation; Carboneras Fault Zone; Dolostone; Fracture network connectivity; Lithons; Topology","en","journal article","","","","","","Accepted Author Manuscript","","2022-05-11","","","Applied Geology","","",""
"uuid:db40b161-89d0-4848-a95a-a1ce61d499ee","http://resolver.tudelft.nl/uuid:db40b161-89d0-4848-a95a-a1ce61d499ee","A Computational Workflow for Flow and Transport in Fractured Porous Media Based on a Hierarchical Nonlinear Discrete Fracture Modeling Approach","Zhang, Wenjuan (Khalifa University of Science and Technology); Diab, Waleeb (Khalifa University of Science and Technology); Hajibeygi, H. (TU Delft Reservoir Engineering); Al Kobaisi, Mohammed (Petroleum Institute; Khalifa University of Science and Technology)","","2020","Modeling flow and transport in fractured porous media has been a topic of intensive research for a number of energy- and environment-related industries. The presence of multiscale fractures makes it an extremely challenging task to resolve accurately and efficiently the flow dynamics at both the local and global scales. To tackle this challenge, we developed a computational workflow that adopts a two-level hierarchical strategy based on fracture length partitioning. This was achieved by specifying a partition length to split the discrete fracture network (DFN) into small-scale fractures and large-scale fractures. Flow-based numerical upscaling was then employed to homogenize the small-scale fractures and the porous matrix into an equivalent/effective single medium, whereas the large-scale fractures were modeled explicitly. As the effective medium properties can be fully tensorial, the developed hierarchical framework constructed the discrete systems for the explicit fracture–matrix sub-domains using the nonlinear two-point flux approximation (NTPFA) scheme. This led to a significant reduction of grid orientation effects, thus developing a robust, applicable, and field-relevant framework. To assess the efficacy of the proposed hierarchical workflow, several numerical simulations were carried out to systematically analyze the effects of the homogenized explicit cutoff length scale, as well as the fracture length and orientation distributions. The effect of different boundary conditions, namely, the constant pressure drop boundary condition and the linear pressure boundary condition, for the numerical upscaling on the accuracy of the workflow was investigated. The results show that when the partition length is much larger than the characteristic length of the grid block, and when the DFN has a predominant orientation that is often the case in practical simulations, the workflow employing linear pressure boundary conditions for numerical upscaling give closer results to the full-model reference solutions. Our findings shed new light on the development of meaningful computational frameworks for highly fractured, heterogeneous geological media where fractures are present at multiple scales.","Discrete fracture network (DFN); Embedded discrete fracture–matrix (EDFM); Fractures; Hierarchical modeling; Nonlinear two-point flux approximation (NTPFA); Simulation; Upscaling","en","journal article","","","","","","","","","","","Reservoir Engineering","","",""
"uuid:b151f41d-400f-4197-9b93-5b93bcc1e7c5","http://resolver.tudelft.nl/uuid:b151f41d-400f-4197-9b93-5b93bcc1e7c5","An integrated workflow for stress and flow modelling using outcrop-derived discrete fracture networks","Bisdom, K. (TU Delft Applied Geology); Nick, H.M. (TU Delft Reservoir Engineering; Technical University of Denmark); Bertotti, G. (TU Delft Applied Geology)","","2017","Fluid flow in naturally fractured reservoirs is often controlled by subseismic-scale fracture networks. Although the fracture network can be partly sampled in the direct vicinity of wells, the inter-well scale network is poorly constrained in fractured reservoir models. Outcrop analogues can provide data for populating domains of the reservoir model where no direct measurements are available. However, extracting relevant statistics from large outcrops representative of inter-well scale fracture networks remains challenging. Recent advances in outcrop imaging provide high-resolution datasets that can cover areas of several hundred by several hundred meters, i.e. the domain between adjacent wells, but even then, data from the high-resolution models is often upscaled to reservoir flow grids, resulting in loss of accuracy. We present a workflow that uses photorealistic georeferenced outcrop models to construct geomechanical and fluid flow models containing thousands of discrete fractures covering sufficiently large areas, that does not require upscaling to model permeability. This workflow seamlessly integrates geomechanical Finite Element models with flow models that take into account stress-sensitive fracture permeability and matrix flow to determine the full permeability tensor. The applicability of this workflow is illustrated using an outcropping carbonate pavement in the Potiguar basin in Brazil, from which 1082 fractures are digitised. The permeability tensor for a range of matrix permeabilities shows that conventional upscaling to effective grid properties leads to potential underestimation of the true permeability and the orientation of principal permeabilities. The presented workflow yields the full permeability tensor model of discrete fracture networks with stress-induced apertures, instead of relying on effective properties as most conventional flow models do.","Aperture; Brazil; Discrete fracture matrix; Fracture mechanics; Fracture networks; Fracture permeability; Outcrop analogue modelling; Permeability tensor","en","journal article","","","","","","","","2019-04-01","","","Applied Geology","","",""
"uuid:298b9ef8-7f21-47eb-8a32-8f0f811203d9","http://resolver.tudelft.nl/uuid:298b9ef8-7f21-47eb-8a32-8f0f811203d9","Fluid flow from matrix to fractures in Early Jurassic shales","Houben, M. E. (Universiteit Utrecht); Hardebol, N.J. (TU Delft Applied Geology); Barnhoorn, A. (TU Delft Applied Geophysics and Petrophysics); Boersma, Q.D. (TU Delft Applied Geology; Universiteit Utrecht); Carone, A. (Universiteit Utrecht); Liu, Y. (Universiteit Utrecht); de Winter, D. A.M. (Universiteit Utrecht); Peach, C. J. (Universiteit Utrecht); Drury, M. R. (Universiteit Utrecht)","","2017","The potential of shale reservoirs for gas extraction is largely determined by the permeability of the rock. Typical pore diameters in shales range from the μm down to the nm scale. The permeability of shale reservoirs is a function of the interconnectivity between the pore space and the natural fracture network present. We have measured the permeability of the Whitby Mudstone, the exposed counterpart of the Posidonia Shales buried in the Dutch subsurface and a possible target for unconventional gas, using different methods and established a correlation with the microstructures and pore networks present down to the nanometer scale. Whitby Mudstone is a clay rich rock with a low porosity. The permeability of the Whitby Mudstone is in the range of 10−18m2–10−21m2. 2D microstructures of the Whitby Mudstone show no connected pore networks, but isolated pore bodies mainly situated in the clay matrix, whereas 3D data shows that connected pore networks are present in less compacted parts of the rock. A closely spaced interconnected fracture network is often required to speed up transport of fluids from the matrix into a producing well. For fluids within the matrix the nearest natural fracture is on average at a distance of approximately 10cm in the Whitby Mudstone. The combination of the permeability data and the porosity data with natural fracture spacing of the fractures present in outcrops along the Yorkshire coast (UK) resulted in new insights into possible fluid pathways from reservoir to well.","Fracture network; Jurassic shales; Multi-scale flow; Permeability; Whitby Mudstone","en","journal article","","","","","","","","","","","Applied Geology","","",""
"uuid:050335b1-ca2d-43c3-9058-6b61705c072b","http://resolver.tudelft.nl/uuid:050335b1-ca2d-43c3-9058-6b61705c072b","Inter-well scale natural fracture geometry and permeability variations in low-deformation carbonate rocks","Bisdom, K. (TU Delft Applied Geology); Bertotti, G. (TU Delft Applied Geology); Bezerra, F. H. (Universidade Federal do Rio Grande do Norte)","","2017","Regional natural fracture networks often show variations on a scale below that captured by seismic reflection data. This variability is not considered in most reservoir models, but likely impacts uncertainties in permeability. We quantify this uncertainty using a database of 13,000 fractures in nine outcrops digitised in the carbonate Jandaíra Formation (Potiguar basin, Brazil). Distance between outcrops is on average 11 km, with a minimum of 300 m, which is comparable to the distance between wells in naturally fractured reservoirs. In between outcrops, significant variations exist in orientation, intensity, length and topology. Using discrete fracture-matrix flow models, we model the permeability of each deterministic pattern and find that small changes in geometry and topology result in permeability variations that are not captured by connectivity-based analyses such as percolation probabilities, particularly when the matrix is permeable. The permeability variations associated with subseismic-scale fracture variability are not captured in conventional stochastic models, but can be captured using deterministic outcrop models with flow through discrete fractures. The deterministic models provide a permeability range associated with subseismic fracture variability, that can be assigned to grid cells of fractured reservoir flow models, as an alternative to assuming constant permeability in the absence of subseismic-scale deformation.","Aperture; Discrete fracture networks; Equivalent permeability; Natural fractures; Potiguar basin; Shallow-water carbonates","en","journal article","","","","","","","","2019-05-01","","","Applied Geology","","",""
"uuid:5a6113f5-04ca-4da3-b147-d32af7b58852","http://resolver.tudelft.nl/uuid:5a6113f5-04ca-4da3-b147-d32af7b58852","Statistical analysis of 2D trace-line maps of fracture networks in carbonate rocks of the Jandeíra Formation in Brazil","Paulides, C.A.M.","Bertotti, G. (mentor)","2013","The fracture network of the Jandeíra Formation in the northeastern part of Brazil is controlled by two main (paleo-) stress fields. The first stress field, characterized by a NS-oriented compression, occurred from the Campanian to the Miocene. The second occurred from the Miocene to the Quaternary as an EW-oriented compression. In the western and central part of the Potiguar Basin it shifts to a NW-SE-oriented compression and a NE-SW-oriented extension. Both stress fields resulted in a heterogeneous fracture network throughout the whole basin. This system has been analyzed with imagery from around 50 meters above the ground with a resolution of 1.5 cm/pixel. Three main fracture sets are found in the studied outcrop, though in the outcrop itself the sets are highly heterogeneous spread; which supports the conventional outcrop studies. The length distribution of EW fractures are strongly influenced by abutment i.e. earlier fractures have restricted the propagation of succeeding fractures. This study shows that fracture length distributions and spatial distribution are exponentially distributed. Although this study is limited by its resolution, it gives a good first impression of fracture behavior in the Jandeíra Formation, but composite analysis of different scale ranges would improve the value of this study considerably.","fracture network analysis; carbonate rocks; ArcGIS; georeferenced imagery","en","bachelor thesis","","","","","","","","","Civil Engineering and Geosciences","Geoscience & Engineering","","Applied Geology","",""
"uuid:9a70ef3f-aff5-4007-8728-cbda5d82481a","http://resolver.tudelft.nl/uuid:9a70ef3f-aff5-4007-8728-cbda5d82481a","Analysis of fracture network geometries and orientations within a fold-and-thrust structure in the Northern Apennines, Italy","De Vries, H.C.; Benthem, M.","Bertotti, G. (mentor)","2013","This research focuses on fracture networks in sedimentary rocks within the Umbria-Marche fold-and-thrust belt in the Northern Apennines, Italy. The aim of this research is twofold, namely to correlate the geometry of fracture networks with tectonic position and lithology and to correlate the orientation of fracture networks with the origination of a fold-and-thrust structure. The fold-and-thrust belt within the area strikes about N160° and developed in the Miocene within a compressional regime as the result of the collision between the European Corsica-Sardinia Margin and the Adriatic plate, accompanied by back-arc extension due to rollback. In order to analyze geometries of fracture networks software named DigiFract is used to digitize outcrops in the field. Fracture orientation, density, spacing, height and termination are analysed for different lithologies within the Umbria-Marche succession. Orientations of fracture sets are correlated to different structural stages during the development of the fold-and-trust structure. The first stage in which fractures develop is layer parallel shortening, during which bedding-normal pressure-solution surfaces develop, striking parallel to the hinge line. Subsequently, longitudinal joints striking parallel to the hinge line develop during fold initiation. This is followed by amplification and tightening of the fold, causing development of transversal joints, striking perpendicular to the hinge line. In theory, fold limbs are preferred sites for deformation within an active-hinge fault-related anticline, rather than the corresponding anticlinal crests (Salvini and Storti, 2001; Salvini and Storti, 2004). Our data is not substantial to proof this theory, but is in accordance to it. Chert, primarily present in the Maiolica Fm and the Diasprini Fm, and marl, present in the Bisciaro Fm, act as non-fractured or very low density-boundary between fractured beddings. Siliclastic turbidites are less fractured than carbonates at similar tectonic positions.","fracture network geometry; DigiFract software; fracture orientation; fold-and-thrust structure","en","bachelor thesis","","","","","","","","2013-07-12","Civil Engineering and Geosciences","Geoscience & Engineering","","Applied Geology","",""
"uuid:fb9515dd-ffee-441f-a104-b29079d72a3f","http://resolver.tudelft.nl/uuid:fb9515dd-ffee-441f-a104-b29079d72a3f","Multi-scale Fracture Analysis from an Outcrop Analogue: A Case Study from the Cambro-Ordovician Sequence in Petra, Jordan","Strijker, G.","Luthi, S.M. (promotor); Bertotti, G. (promotor)","2013","Natural fractures occur over several orders of size magnitude. Accurately predicting the three-dimensional and multi-scale distribution of fractures in subsurface reservoirs is very difficult. Direct observations are limited to large-scale faults visible on seismic data and high-resolution, mostly small-scale, measurements of fractures intersecting the well, valid only in the direct vicinity of the wellbore. Analogue outcrop studies can be used to help fill in the gaps. The multi-scale properties of the natural fracture network exposed in the Cambro-Ordovician siliciclastic sequence in Petra, Jordan, are captured and it is investigated how these properties can be applied for the characterization of subsurface fractured reservoirs. The thesis consists of a series of chapters describing the geology of the study area, the results of the multi-scale fracture study in Jordan, followed by an analysis of the network connectivity using percolation theory and discrete fracture network models. The thesis is concluded by the results of numerical experiments where the influence of stress rotation on the re-activation of pre-existing fractures is investigated to help understand the evolution of complex networks consisting of multiple fracture sets.","fracture network; Jordan; outcrop analogue; finite-element model; percolation theory","en","doctoral thesis","","","","","","","","","Civil Engineering and Geosciences","Geoscience & Engineering","","","",""
"uuid:4c621d54-7484-447a-a46a-3d47e8a5bca3","http://resolver.tudelft.nl/uuid:4c621d54-7484-447a-a46a-3d47e8a5bca3","The Sensitivity of the 3D Connectivity in a Multi-Scale Fracture Network to Variations in Distribution Parameters: A Case Study from Petra, Jordan","Hürxkens, C.C.M.J.","Luthi, S.M. (mentor); Strijker, G. (mentor)","2011","The behavior of naturally fractured reservoirs is very different from that of conventional reservoirs. In order to develop a successful production strategy it is important to understand this behavior. Golder Associates developed a software package to model heterogeneous and fractured rock masses. FracMan generates three-dimensional fracture networks based on fracture parameters that are specified by the user. The fracture network exposed in the Cambro-Ordovician sedimentary succession in southwestern Jordan was modeled with this software. Parameters from the multi-scale data set that Strijker et al. (subm) acquired from high-resolution satellite imagery and field measurements were used to generate a stochastic fracture network. With a special feature in FracMan the connectivity of the network was analyzed. The sensitivity of the fracture connectivity to variations in parameters was tested as well. The results were embedded in the context of percolation theory. The two- and three-dimensional percolation thresholds were determined after constructing cumulative distributions for the probability of percolation as a function of the fracture intensity. The results are consistent with the theoretical Nc,2d ? 0.5 and Nc,3d ? 0.249 (Stauffer, 1985). The probabilities of percolation for the stochastically generated fracture networks are N2d ? 1 and N3d ? 0.99, which are both far above the percolation threshold. This means the connectivity of the fracture network is good and therefore fluid flow in reservoirs with a comparable network to the Petra succession should be possible. The sensitivity of the fracture connectivity was tested by varying three different pa- rameters: fracture orientation, fracture polygon shape, and the aspect ratio of these polygons. A standard deviation was introduced for the orientation. This had a positive influence on the fracture network connectivity; the probability of percolation increased. The greater the number of sides of a polygon, the lower the probability of percolation. The probability of percolation and the total number of polygon sides are negatively correlated. The aspect ratio had the greatest impact on the percolation probability. With an increasing aspect ratio the two-dimensional percolation probability grows (? +0.30), while the three- dimensional probability declines (? -0.33). It is therefore an important parameter with a great impact on the fracture network connectivity.","percolation theory; fracture network; fracman; fracture connectivity","en","bachelor thesis","","","","","","","","","Civil Engineering and Geosciences","Applied Geology","","","",""