Download or read book Fractal Characterization of Subsurface Fracture Network for Geothermal Energy Extraction System written by and published by . This book was released on 1993 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: As a new modeling procedure of geothermal energy extraction systems, the authors present two dimensional and three dimensional modeling techniques of subsurface fracture network, based on fractal geometry. Fluid flow in fractured rock occurs primarily through a connected network of discrete fractures. The fracture network approach, therefore, seeks to model fluid flow and heat transfer through such rocks directly. Recent geophysical investigations have revealed that subsurface fracture networks can be described by "fractal geometry". In this paper, a modeling procedure of subsurface fracture network is proposed based on fractal geometry. Models of fracture networks are generated by distributing fractures randomly, following the fractal relation between fracture length r and the number of fractures N expressed with fractal dimension D as N =C·r-D, where C is a constant to signify the fracture density of the rock mass. This procedure makes it possible to characterize geothermal reservoirs by the parameters measured from field data, such as core sampling. In this characterization, the fractal dimension D and the fracture density parameter C of a geothermal reservoir are used as parameters to model the subsurface fracture network. Using this model, the transmissivities between boreholes are also obtained as a function of the fracture density parameter C, and a parameter study of system performances, such as heat extraction, is performed. The results show the dependence of thermal recovery of geothermal reservoir on fracture density parameter C.

Download or read book Fracture Characterization in Geothermal Reservoirs Using Time lapse Electric Potential Data written by Lilja Magnúsdóttir and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The configuration of fractures in a geothermal reservoir is central to the performance of the system. The interconnected fractures control the heat and mass transport in the reservoir and if the fluid reaches production wells before it is fully heated, unfavorable effects on energy production may result due to decreasing fluid enthalpies. Consequently, inappropriate placing of injection or production wells can lead to premature thermal breakthrough. Thus, fracture characterization in geothermal reservoirs is an important task in order to design the recovery strategy appropriately and increase the overall efficiency of the power production. This is true both in naturally fractured geothermal systems as well as in Enhanced Geothermal Systems (EGS) with man-made fractures produced by hydraulic stimulation. In this study, the aim was to estimate fracture connectivity in geothermal reservoirs using a conductive fluid injection and an inversion of time-lapse electric potential data. Discrete fracture networks were modeled and a flow simulator was used first to simulate the flow of a conductive tracer through the reservoirs. Then, the simulator was applied to solve the electric fields at each time step by utilizing the analogy between Ohm's law and Darcy's law. The electric potential difference between well-pairs drops as a conductive fluid fills fracture paths from the injector towards the producer. Therefore, the time-lapse electric potential data can be representative of the connectivity of the fracture network. Flow and electric simulations were performed on models of various fracture networks and inverse modeling was used to match reservoir models to other fracture networks in a library of networks by comparing the time-histories of the electric potential. Two fracture characterization indices were investigated for describing the character of the fractured reservoirs; the fractional connected area and the spatial fractal dimension. In most cases, the electrical potential approach was used successfully to estimate both the fractional connected area of the reservoirs and the spatial fractal dimension. The locations of the linked fracture sets were also predicted correctly. Next, the electric method was compared to using only the simple tracer return curves at the producers in the inverse analysis. The study showed that the fracture characterization indices were estimated somewhat better using the electric approach. The locations of connected areas in the predicted network were also in many cases incorrect when only the tracer return curves were used. The use of the electric approach to predict thermal return was investigated and compared to using just the simple tracer return curves. The electric approach predicted the thermal return curves relatively accurately. However, in some cases the tracer return gave a better estimation of the thermal behavior. The electric measurements are affected by both the time it takes for the conductive tracer to reach the production well, as well as the overall location of the connected areas. When only the tracer return curves are used in the inverse analysis, only the concentration of tracer at the producer is measured but there is a good correlation between the tracer breakthrough time and the thermal breakthrough times. Thus, the tracer return curves can predict the thermal return accurately but the overall location of fractures might not be predicted correctly. The electric data and the tracer return data were also used together in an inverse analysis to predict the thermal returns. The results were in some cases somewhat better than using only the tracer return curves or only the electric data. A different injection scheme was also tested for both approaches. The electric data characterized the overall fracture network better than the tracer return curves so when the well pattern was changed from what was used during the tracer and electric measurements, the electric approach predicted the new thermal return better. In addition, the thermal return was predicted considerably better using the electric approach when measurements over a shorter period of time were used in the inverse analysis. In addition to characterizing the fracture distribution better, the electric approach can give information about the conductive fluid flowing through the fracture network even before it has reached the production wells.

Download or read book Workshop Report written by and published by . This book was released on with total page 328 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Hydraulic fracturing and geothermal energy written by S. Nemat-Nassar and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 519 pages. Available in PDF, EPUB and Kindle. Book excerpt: Hydraulic fracturing has been and continues to be a major techno logical tool in oil and gas recovery, nuclear and other waste disposal, mining and particularly in-situ coal gasification, and, more recently, in geothermal heat recovery, particularly extracting heat from hot dry rock masses. The understanding of the fracture process under the ac tion of pressurized fluid at various temperatures is of fundamental scientific importance, which requires an adequate description of thermomechanical properties of subsurface rock, fluid-solid interaction effects, as well as degradation of the host rock due to temperature gradients introduced by heat extraction. Considerable progress has been made over the past several years in laboratory experiments, analytical and numerical modeling, and in-situ field studies in various aspects of hydraulic fracturing and geothermal energy extraction, by researchers in the United States and Japan and also elsewhere. However, the results have been scattered throughout the literature. Therefore, the time seemed ripe for bringing together selected researchers from the two countries, as well as observers from other countries, in order to survey the state of the art, exchange scientific information, and establish closer collaboration for further, better coordinated scientific effort in this important area of research and exploration.

Download or read book Thermomechanical Analysis of Rock Asperity in Fractures of Enhanced Geothermal Systems written by Chao Zeng and published by . This book was released on 2019 with total page 229 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Enhanced Geothermal Systems (EGS) offer great potential for dramatically expanding the use of geothermal energy and become a promising supplement for fossil energy. The EGS is to extract heat by creating a subsurface system to which cold water can be added through injection wells. Injected water is heated by contact with rock and returns to the surface through production well. Fracture provides the primary conduit for fluid flow and heat transfer in natural rock. Fracture is propped by fracture roughness with varying heights which is called asperity. The stability of asperity determines fracture aperture and hence imposes substantial effect on hydraulic conductivity and heat transfer efficiency in EGS. Firstly, two rough fracture surfaces are characterized by statistical method and fractal analysis. The asperity heights and enclosed aperture heights are described by probability density function before cold water is pumped into fracture. Secondly, when water injection and induced cooling occurs, the thermomechanical analysis of single asperity is studied by establishing an un-symmetric damage mechanics model. The deformation curve of asperity under thermal stress is determined. Thirdly, deformation of fracture with various asperities on it in response to thermal stress is analyzed by a new stratified continuum percolation model. This model incorporates the fracture surface characteristics and preceding deformation curve of asperity. The fracture closure and fracture stiffness can be accurately quantified by this model. In addition, the scaling invariance and multifractal parameters in this process are identified and validated with Monte Carlo simulation"--Abstract, page iii.

Download or read book An Experimental Study of Creation of Optimal Fracture Network for Heat Extraction from Engineered Geothermal Reservoirs written by Banambar Singh and published by . This book was released on 2015 with total page 290 pages. Available in PDF, EPUB and Kindle. Book excerpt: Enhanced geothermal system has been successfully able to increase the permeability of the reservoir and hydro-fracturing is the conventional method of creating artificial fracture system. But more precise technique is required to reduce the cost of the geothermal energy extraction and this will require proper understanding of the thermo-mechanical behaviour of the reservoir rocks i.e. Granites. Current research work has focused on the thermo-mechanical properties of granites under various temperature and strain rate condition. Granites of two different areas i.e. Bundelkhand granite, India and Harcourt granite, Australia have been investigated for the research work. 4 different strain rates i.e. 0.05 mm/min, 0.5 mm/min, 5.0 mm/min and 50 mm/min at 3 different temperatures i.e. room temperature (25 °C), 200 °C and 400 °C were considered for experimental analysis. It was observed that at room temperature, with increasing strain rate the uniaxial compressive strength of the rock increases and the same trend is also observed at higher temperatures conditions. Whereas at low strain rate the compressive strength decreases with increase in temperature, while the trend is irregular at higher strain rates. Bundelkhand granites have thermal conductivity values between 3.1 to 3.6 W/m.K whereas that of Harcourt granite is 2.4 W/m.K. Sieve analysis of the fragmented particles due to UCS test suggested that there is no effect of strain rate on particle size distribution whereas higher temperatures produces more finer particles. It was observed that more than 75% of the fragmented particles are having diameter of greater than 11.3 mm. Effective size i.e. D10 was analysed and found that at room temperature (25 °C) 10% of fragmented particles are finer than 3.0 mm whereas at 200 °C and 400 °C 10% of finer particles are finer than 1.9 mm and 1.5 mm respectively. Numerical simulation results of the numerical simulation are quite analogous to the lab experimental data.

Download or read book Fractal Analysis for Natural Hazards written by Giuseppe Cello and published by Geological Society of London. This book was released on 2006 with total page 190 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the Earth Sciences, the concept of fractals and scale invariance is well-recognized in many natural objects. However, the use of fractals for spatial and temporal analyses of natural hazards has been less used (and accepted) in the Earth Sciences. This book brings together twelve contributions that emphasize the role of fractal analyses in natural hazard research, including landslides, wildfires, floods, catastrophic rock fractures and earthquakes. A wide variety of spatial and temporal fractal-related approaches and techniques are applied to 'natural' data, experimental data, and computer simulations. These approaches include probabilistic hazard analysis, cellular-automata models, spatial analyses, temporal variability, prediction, and self-organizing behaviour. The main aims of this volume are to present current research on fractal analyses as applied to natural hazards, and to stimulate the curiosity of advanced Earth Science students and researchers in the use of fractals analyses for the better understanding of natural hazards.

Download or read book Fractals in the Earth Sciences written by C.C. Barton and published by Springer Science & Business Media. This book was released on 2013-06-29 with total page 277 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fractals have changed the way we understand and study nature. This change has been brought about mainly by the work of B. B. Mandelbrot and his book The Fractal Geometry of Nature. Now here is a book that collects articles treating fractals in the earth sciences. The themes chosen span, as is appropriate for a discourse on fractals, many orders of magnitude; including earthquakes, ocean floor topography, fractures, faults, mineral crystallinity, gold and silver deposition. There are also chapters on dynamical processes that are fractal, such as rivers, earthquakes, and a paper on self-organized criticality. Many of the chapters discuss how to estimate fractal dimensions, Hurst exponents, and other scaling exponents. This book, in a way, represents a snapshot of a field in which fractals has brought inspiration and a fresh look at familiar subjects. New ideas and attempts to quantify the world we see around us are found throughout. Many of these ideas will grow and inspire further work, others will be superseded by new observations and insights, most probably with future contributions by the authors of these chapters.

Download or read book Fractal Geometry of Two dimensional Fracture Networks at Yucca Mountain Southwestern Nevada written by and published by . This book was released on 1985 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fracture traces exposed on three 214- to 260-m2 pavements in the same Miocene ash-flow tuff at Yucca Mountain, southwestern Nevada, have been mapped at a scale of 1:50. The maps are two-dimensional sections through the three-dimensional network of strata-bound fractures. All fractures with trace lengths greater than 0.20 m were mapped. The distribution of fracture-trace lengths is log-normal. The fractures do not exhibit well-defined sets based on orientation. Since fractal characterization of such complex fracture-trace networks may prove useful for modeling fracture flow and mechanical responses of fractured rock, an analysis of each of the three maps was done to test whether such networks are fractal. These networks proved to be fractal and the fractal dimensions (D) are tightly clustered (1.12, 1.14, 1.16) for three laterally separated pavements, even though visually the fracture networks appear quite different. The fractal analysis also indicates that the network patterns are scale independent over two orders of magnitude for trace lengths ranging from 0.20 to 25 m. 7 refs., 7 figs.

Download or read book Fractal Modeling of Natural Fracture Networks written by and published by . This book was released on 1995 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt: West Virginia University will implement procedures for a fractal analysis of fractures in reservoirs. This procedure will be applied to fracture networks in outcrops and to fractures intersecting horizontal boreholes. The parameters resulting from this analysis will be used to generate synthetic fracture networks with the same fractal characteristics as the real networks. Recovery from naturally fractured, tight-gas reservoirs is controlled by the fracture network. Reliable characterization of the actual fracture network in the reservoir is severely limited. The location and orientation of fractures intersecting the borehole can be determined, but the length of these fractures cannot be unambiguously determined. Because of the lack of detailed information about the actual fracture network, modeling methods must represent the porosity and permeability associated with the fracture network, as accurately as possible with very little a priori information. In the sections following, the authors will (1) present fractal analysis of the MWX site, using the box-counting procedure; (2) review evidence testing the fractal nature of fracture distributions and discuss the advantages of using the fractal analysis over a stochastic analysis; and (3) present an efficient algorithm for producing a self-similar fracture networks which mimic the real MWX outcrop fracture network.

Download or read book Discrete Fracture Network Modeling and Simulation Using EDFM written by Joseph Alexander Leines Artieda and published by . This book was released on 2020 with total page 280 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recent advances in fracture network characterization have identified high degrees of heterogeneity and permeability anisotropy in conventional reservoirs and complex fracture network generation after well stimulation in unconventional reservoirs. Traditional methods to model such complex systems may not capture the key role of fracture network geometry, spatial distribution, and connectivity on well performance. Because of the ubiquitous presence of natural fractures in conventional and unconventional reservoirs, it is key to provide efficient tools to model them accurately. We extend the application of the embedded discrete fracture model (EDFM) to study the influence of natural fractures represented by discrete fracture network (DFN) models on well performance. Current state-of-the-art modeling technologies have been able to describe natural fracture systems as a whole, without providing flexibility to extract, vary, and group fracture network properties. Our developed implementations analyze fracture network topology and provide advanced mechanisms to model and understand fracture network properties. The first application features a numerical model in combination with EDFM to study water intrusion in a naturally fractured carbonate reservoir. We developed a workflow that overcomes conventional methods limitations by modeling the fracture network as a graph. This representation allowed to identify the shortest paths that connect the nearby water zone with the well perforations, providing the mechanisms to obtain a satisfactory history match of the reservoir. Additionally, we modeled a critically-stressed carbonate field by modeling faults interactions with natural fractures. Our workflow allowed to discretize the hydraulic backbone of the field and assess its influence on the entire field gas production. Our next application applies a connectivity analysis using an efficient and robust collision detection algorithm capable of identifying groups of connected or isolated natural fractures in an unconventional reservoir. This study uses numerical models in combination with EDFM to analyze the effect of fracture network connectivity on well production using fractal DFN models. We concluded that fracture network connectivity plays a key role on the behavior of fractured reservoirs with negligible effect of non-connected fractures. Finally, we performed assisted history matching (AHM) using fractal methods to characterize in a probabilistic manner the reservoir properties and to offer key insights regarding spatial distribution, number, and geometry of both hydraulic and natural fractures in unconventional reservoirs. In this work, we provided computational tools that constitute the foundations to conduct advanced modeling using DFN models in conjunction with EDFM in several reservoir engineering areas such as well-interference, water intrusion, water breakthrough, enhanced oil recovery (EOR) efficiency characterization, and fracture network connectivity assessments. The benefits of our work extend to conventional, unconventional, and geothermal reservoirs

Download or read book Modeling Flow in Fractured Geologic Media written by Tawfik Rajeh and published by . This book was released on 2019 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fractures constitute major pathways for flow and transport in fractured porous rocks. These types of rocks are encountered in a wide range of applications like for example gas and petroleum engineering, CO2 sequestration and geothermal energy extraction. The present thesis presents a framework to analyze geometrical, topological and hydraulic properties of 3D planar fracture networks with focus on upscaling these properties to obtain an equivalent continuum, in view of application to simulations of geothermal reservoir exploitation. The description of fractures and discrete fracture networks (DFN), their statistical properties and their generation procedures are studied. As permeability plays a key role in flow and transport in fractured porous rocks, we have developed a fast upscaling approach for determining the equivalent permeability tensor of 3D fractured porous media. This new approach is based on the superposition principle improved by empirical connectivity factors in order to take into account the connectivity and percolation properties of the fracture network. Although efficient in predicting permeability, the proposed method presents a major limitation due mainly to the difficulty in assessing the percolation and connectivity properties of the network. To overcome these limitations and for further insightful analyses of DFN composed of planar fractures, an original framework of geometrical and topological analysis of 3D fracture networks has been developed. In this framework, all the geometrical and topological attributes (intersections, areas, trace lengths, clusters, percolating clusters, etc.) of a DFN are explicitly calculated by a set of algorithms. These algorithms are validated in detail by comparison to commercial softwares, and their computational efficiency is highlighted. The final purpose of this framework is to give a graph representation of the DFN. Given the newly developed tools, our capabilities of treating fracture networks have drastically increased. Hence, using a graph representation of the DFN, new approaches have been developed concerning two main issues with fracture networks: (i) percolation, (ii) clustering phenomenon (i.e., the formation of clusters by groups of fractures) and (iii) permeability upscaling. A large scale thermo-hydraulic simulator has therefore been developed with the finite volume open source code “OpenFoam”. The purpose is to apply the upscaling techniques to large scale reservoir configurations with a full coupling with heat transfer. A typical example of injectionproduction wells in a 3D geothermal reservoir is presented, and other cases are being developed within the GEOTREF project ( www.geotref.com ).

Download or read book Numerical Construction and Flow Simulation in Networks of Fractures Using Fractals written by Y. C. Yortsos and published by . This book was released on 1991 with total page 40 pages. Available in PDF, EPUB and Kindle. Book excerpt: Present models for the representation of naturally fractured systems rely on the double-porosity Warren-Root model or on random arrays of fractures. However, field observation in outcrops has demonstrated the existence of multiple length scales in many naturally fractured media. The existing models fail to capture this important fractal property. In this paper, we use concepts from the theory of fragmentation and from fractal geometry for the numerical construction of networks of fractures that have fractal characteristics. The method is based mainly on the work of Barnsley (1) and allows for great flexibility in the development of patterns. Numerical techniques are developed for the simulation of unsteady single phase flow in such networks. It is found that the pressure transient response of finite fractals behaves according to the analytical predictions of Chang and Yortsos (6), provided that there exists a power law in the mass-radius relationship around the test well location. Otherwise, the finite size effects become significant and interfere severely with the identification of the underlying fractal structure. 21 refs., 13 figs.

Download or read book Detection and Characterization of Natural and Induced Fractures for the Development of Enhanced Geothermal Systems written by and published by . This book was released on 2013 with total page 35 pages. Available in PDF, EPUB and Kindle. Book excerpt: The objective of this 3-year project is to use various geophysical methods for reservoir and fracture characterization. The targeted field is the Cove Fort-Sulphurdale Geothermal Field in Utah operated by ENEL North America (ENA). Our effort has been focused on 1) understanding the regional and local geological settings around the geothermal field; 2) collecting and assembling various geophysical data sets including heat flow, gravity, magnetotelluric (MT) and seismic surface and body wave data; 3) installing the local temporary seismic network around the geothermal site; 4) imaging the regional and local seismic velocity structure around the geothermal field using seismic travel time tomography; and (5) determining the fracture direction using the shear-wave splitting analysis and focal mechanism analysis. Various geophysical data sets indicate that beneath the Cove Fort-Sulphurdale Geothermal Field, there is a strong anomaly of low seismic velocity, low gravity, high heat flow and high electrical conductivity. These suggest that there is a heat source in the crust beneath the geothermal field. The high-temperature body is on average 150 °C - 200 °C hotter than the surrounding rock. The local seismic velocity and attenuation tomography gives a detailed velocity and attenuation model around the geothermal site, which shows that the major geothermal development target is a high velocity body near surface, composed mainly of monzonite. The major fracture direction points to NNE. The detailed velocity model along with the fracture direction will be helpful for guiding the geothermal development in the Cove Fort area.

Download or read book Fractures in Geothermal Reservoirs written by Geothermal Resources Council and published by . This book was released on 1982 with total page 352 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Crustal Rock Fracture Mechanics for Design and Control of Artificial Subsurface Cracks in Geothermal Energy Extraction Engineering Gamma Project written by and published by . This book was released on 1983 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Recently a significant role of artificial and/or natural cracks in the geothermal reservoir has been demonstrated in the literatures (Abe, H., et al., 1983, Nielson, D.L. and Hullen, J.B., 1983), where the cracks behave as fluid paths and/or heat exchanging surfaces. Until now, however, there are several problems such as a design procedure of hydraulic fracturing, and a quantitative estimate of fluid and heat transfer for reservoir design. In order to develop a design methodology of geothermal reservoir cracks, a special distinguished research project, named as ''[Lambda]-Project'', started at Tohoku University (5 years project, 1983-1988). In this project a basic fracture mechanics model of geothermal reservoir cracks is being demonstrated and its validation is being discussed both theoretically and experimentally. This paper descibes an outline of ''[Lambda]-Project''.

Download or read book Characterization of Natural Fracture Networks Using Fractal Methods written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: