Parametric Analysis of Factors Affecting Injection and Production in Geothermal Reservoirs PDF Download
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Languages : en
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A program was designed to allow the study of the effects of several parameters on the injection of water into and production of fluid from a fractured low porosity geothermal reservoir with properties similar to those at The Geysers. Fractures were modeled explicitly with low porosity, high permeability blocks rather than with a dual-porosity formulation to gain insight into the effects of single fractures. A portion of a geothermal reservoir with physical characteristics similar to those at the Geysers geothermal field was constructed by simulating a single fracture bounded by porous matrix. A series of simulation runs were made.using this system as a basis. Reservoir superheat prior to injection, injection temperature, angle of fracture inclination, fracture/matrix permeability contrast, fracture and matrix relative permeability, and the capillary pressure curves in both fracture and matrix were varied and the effects on production were compared. Analysis of the effects of these parameter variations led to qualitative conclusions about injection and production characteristics at the Geysers. The degree of superheat prior to water injection was found to significantly affect the production from geothermal reservoirs. A high degree of superheat prior to injection increases the enthalpy of the produced fluid and causes the cumulative produced energy to nearly equal that from a reservoir which began injection much earlier. Injection temperature was found to have very little effect on production characteristics. Angle of fracture inclination affects the enthalpy of the produced fluid. Fractures dipping toward the production well allow greater flow of water toward the producer resulting in lower enthalpies of produced fluid. The fracture/matrix permeability contrast was shown to influence the production in an expected way: The lower the contrast, the lower the production rate, and the lower the enthalpy of the produced fluid at a given time. Results obtained by varying relative permeability show that the relative permeability curves used have little effect on the production from the reservoir. This indicates that the transfer between the matrix and the fracture is dominated by capillary forces, thus reducing the importance of the shape of the relative permeability curve. Capillary pressure curves were shown to have a strong effect on production characteristics, further emphasizing the importance of capillary forces in Geysers-type geothermal reservoirs.
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Languages : en
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Book Description
A program was designed to allow the study of the effects of several parameters on the injection of water into and production of fluid from a fractured low porosity geothermal reservoir with properties similar to those at The Geysers. Fractures were modeled explicitly with low porosity, high permeability blocks rather than with a dual-porosity formulation to gain insight into the effects of single fractures. A portion of a geothermal reservoir with physical characteristics similar to those at the Geysers geothermal field was constructed by simulating a single fracture bounded by porous matrix. A series of simulation runs were made.using this system as a basis. Reservoir superheat prior to injection, injection temperature, angle of fracture inclination, fracture/matrix permeability contrast, fracture and matrix relative permeability, and the capillary pressure curves in both fracture and matrix were varied and the effects on production were compared. Analysis of the effects of these parameter variations led to qualitative conclusions about injection and production characteristics at the Geysers. The degree of superheat prior to water injection was found to significantly affect the production from geothermal reservoirs. A high degree of superheat prior to injection increases the enthalpy of the produced fluid and causes the cumulative produced energy to nearly equal that from a reservoir which began injection much earlier. Injection temperature was found to have very little effect on production characteristics. Angle of fracture inclination affects the enthalpy of the produced fluid. Fractures dipping toward the production well allow greater flow of water toward the producer resulting in lower enthalpies of produced fluid. The fracture/matrix permeability contrast was shown to influence the production in an expected way: The lower the contrast, the lower the production rate, and the lower the enthalpy of the produced fluid at a given time. Results obtained by varying relative permeability show that the relative permeability curves used have little effect on the production from the reservoir. This indicates that the transfer between the matrix and the fracture is dominated by capillary forces, thus reducing the importance of the shape of the relative permeability curve. Capillary pressure curves were shown to have a strong effect on production characteristics, further emphasizing the importance of capillary forces in Geysers-type geothermal reservoirs.
Author:
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Category : Geothermal engineering
Languages : en
Pages : 382
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Languages : en
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The response of a liquid-dominated geothermal reservoir to injection and production from a single well is studied. Different injection-production schemes are analyzed to explore how to minimize temporary cooling around the injection well and to optimize thermal recovery. The pressure response is also calculated, and found to be affected significantly by temperature-dependent viscosity variations. This will have implications on well-test methods for geothermal reservoirs. Vertical consolidation of the geothermal system during fluid withdrawal is also discussed, showing the need to establish previous stress history before attempting to predict the reservoir deformation. The transport of heat and fluid through a porous reservoir is computed using a numerical model. The one-dimensional consolidation theory of Terzaghi has been coupled to the heat and fluid flow to calculate reservoir compaction. No attempt is made of model chemical reactions or precipitation that might occur when waters of a different temperature and salinity are injected into the reservoir.
Author: Lawrence Berkeley Laboratory
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Category : Geothermal reservoirs
Languages : en
Pages : 111
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Languages : en
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Geothermal energy constitutes an important energy resource worldwide. Effective management of such a resource requires an understanding of a complex set of physical phenomena, including interphase mass transfer, convective transport of mass, and conduction and convection of energy. The coupled nature of these processes frequently requires that numerical simulation be used to investigate reservoir response to different management strategies. The first stage of designing a simulation study of a particular reservoir involves defining the boundaries of the reservoir itself. We must determine the reservoir structure, the ''edges'' of the field, select the appropriate boundary conditions to be used, i.e., whether pressure support from an adjacent aquifer is present, values of heat flux, etc. Having determined the three-dimensional extent and shape of the reservoir, we must identify the relevant fluid and petrophysical properties to be used in the simulation. In fractured geothermal systems, this data includes absolute and relative permeabilities for the fractures and rock matrix, fracture spacing and orientation, capillary pressure-saturation relationships, thermal conductivities, and others. While it is fairly straightforward to identify the data required for accurate simulation of a geothermal reservoir, data acquisition is a different matter. Reservoir engineering is unique in the engineering disciplines in that much of the data is inferred by indirect means rather than being collected or measured. The data that can be measured (relative permeability, for example) can be of questionable reliability, in that the rock is removed from its native state, and conditions altered. Much of the data is also fit to empirical relationships; some is even estimated from these relationships. Due to the inherent uncertainties is this data, results of simulation studies using these data must be used with caution. Of course, each of the variables noted above do not impact simulation results in the same way. In fact, errors in some of the data may exert little or no effect on our results. If that is the case, little effort need be expended by the geothermal operator to obtain this data. The problem is knowing which data exerts the most influence on simulation results, and therefore which should receive highest priority in acquisition efforts. The study presented in this paper seeks to answer this question by quantifying the effect changes in various parameters have on reservoir response to injection in a vapor-dominated reservoir. From a base case reservoir dataset we will examine differences in injectate recovery and steam energy produced as input data is varied. Parameters that are examined include relative permeability and capillary pressure relationships, fracture spacing, initial liquid saturations, and geologic structure.
Author: Marcelo J. Lippman
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Category : Geothermal reservoirs
Languages : en
Pages :
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Category :
Languages : en
Pages :
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By introducing a similarity variable r/.sqrt.t a quasi-analytical method can be used to calculate the flow induced by the injection of cold water into a hot water or boiling geothermal reservoir. The results obtained are compared with those produced by the reservoir simulator SHAFT79 and show good agreement.
Author: UNU Geothermal Training Programme (Iceland).
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Category :
Languages : en
Pages : 106
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Author: Craig M. Bethke
Publisher: Cambridge University Press
ISBN: 1139468324
Category : Science
Languages : en
Pages : 564
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This book provides a comprehensive overview of reaction processes in the Earth's crust and on its surface, both in the laboratory and in the field. A clear exposition of the underlying equations and calculation techniques is balanced by a large number of fully worked examples. The book uses The Geochemist's Workbench® modeling software, developed by the author and already installed at over 1000 universities and research facilities worldwide. Since publication of the first edition, the field of reaction modeling has continued to grow and find increasingly broad application. In particular, the description of microbial activity, surface chemistry, and redox chemistry within reaction models has become broader and more rigorous. These areas are covered in detail in this new edition, which was originally published in 2007. This text is written for graduate students and academic researchers in the fields of geochemistry, environmental engineering, contaminant hydrology, geomicrobiology, and numerical modeling.
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Languages : en
Pages : 12
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System modeling supports the design and long-term, commercially successful operation of geothermal reservoirs. Modeling guides in the placement of the injection and production wells, in the stimulation of the reservoir, and in the operational strategies used to ensure continuing production. Without an understanding of the reservoir, it is possible to harm the reservoir by inappropriate operation (especially break-through of cold injection fluid) and the desired profitable lifetimes will not be reached. In this project the authors have continued to develop models for predicting the life of geothermal reservoirs. One of the goals has been to maintain and transfer existing Hot Dry Rock two-dimensional fractured reservoir analysis capability to the geothermal industry and to begin the extension of the analysis concepts to three dimensions. Primary focus has been on interaction with industry, maintenance of Geocrack2D, and development of the Geocrack3D model. It is important to emphasize that the modeling is complementary to current industry modeling, in that they focus on flow in fractured rock and on the coupled effect of thermal cooling. In the following sections the authors document activities as part of this research project: industry interaction; national and international collaboration; and model development.
