Fracture Network Modeling of a Hot Dry Rock Geothermal Reservoir PDF Download

Author: Bruce A. Robinson
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Category : Hot dry rock systems
Languages : en
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Languages : en
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Fluid flow and tracer transport in a fractured Hot Dry Rock (HDR) geothermal reservoir are modeled using fracture network modeling techniques. The steady state pressure and flow fields are solved for a two-dimensional, interconnected network of fractures with no-flow outer boundaries and constant-pressure source and sink points to simulate wellbore-fracture intersections. The tracer response is simulated by particle tracking, which follows the progress of a representative sample of individual tracer molecules traveling through the network. Solute retardation due to matrix diffusion and sorption is handled easily with these particle tracking methods. Matrix diffusion is shown to have an important effect in many fractured geothermal reservoirs, including those in crystalline formations of relatively low matrix porosity. Pressure drop and tracer behavior are matched for a fractured HDR reservoir tested at Fenton Hill, NM.

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Languages : en
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Discrete fracture and continuum models are being developed to simulate Hot Dry Rock (HDR) geothermal reservoirs. The discrete fracture model is a two-dimensional steady state simulator of fluid flow and tracer transport in a fracture network which is generated from assumed statistical properties of the fractures. The model's strength lies in its ability to compute the steady state pressure drop and tracer response in a realistic network of interconnected fractures. The continuum approach models fracture behavior by treating permeability and porosity as functions of temperature and effective stress. With this model it is practical to model transient behavior as well as the coupled processes of fluid flow, heat transfer, and stress effects in a three-dimensional system. The model capabilities being developed will also have applications in conventional geothermal systems undergoing reinjection and in fractured geothermal reservoirs in general. 15 refs., 7 figs.

Author: Bruce A. Robinson
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Category : Hot dry rock systems
Languages : en
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Languages : en
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Modeling results are presented for the Fenton Hill Phase II reservoir using a two-dimensional steady state simulator of fluid flow and solute transport in fractured porous media. Fluid flow and tracer response data are simulated using a fracture flow model in which the fracture apertures are string functions of pressure. The model is used to match the available steady state data of pressure drop versus flow rate and the tracer data. Various schemes for improving reservoir performance, such as high backpressure, chemical etching, stimulation using a viscous fluid, and the drilling of a second production wellbore, are then examined. 15 refs., 7 figs., 4 tabs.

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Languages : en
Pages : 6

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A conceptual model is developed for fluid flow in the Fenton Hill, New Mexico Hot Dry Rock (HDR) geothermal reservoir. The model consists of discrete fractures whose apertures, and hence permeabilities, are strong functions of pressure. Fluid storage occurs within the main fracture system and in the surrounding country rock. Using a fracture network simulator, the reservoir model has been calibrated using reservoir test data obtained at a variety of pressures and flow rates with the system undergoing either circulation or injection with no production. Model results indicate that operating the reservoir with the production well at a higher pressure than is usually used could improve the performance by reducing the pressure difference between the injection and production wells required for circulation. An experiment is designed using numerical simulations to address the following issues: (1) the operating conditions we should employ for the test, (2) the test duration, and (3) the possibility of inducing unwanted reservoir extension. This test is scheduled to be carried out in the late summer of this year. 13 refs., 9 figs.

Author: Bruce A. Robinson
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Category : Geothermal reservoirs
Languages : en
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Languages : en
Pages : 8

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A fracture network model has been developed to simulate transient fluid flow behavior in a fractured rock mass. Included is a pressure-dependent aperture submodel to simulate behavior often seen in fractured systems. The model is used to simulate data from the Fenton Hill Hot Dry Rock (HDR) geothermal reservoir. Both low-pressure/low-flow-rate and high-pressure/high-flow-rate transient data are adequately simulated. The model parameters obtained suggest ways in which the model can be refined to achieve even more realistic fits to the data. The model is then used to demonstrate more efficient operating modes than the two-well circulating mode usually proposed for HDR reservoirs. 11 refs., 9 figs., 1 tab.

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Languages : en
Pages : 145

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In geothermal energy technology, the hydrothermal systems rely on volcanic hot rocks being fortuitously co-located with an adequate supply of natural ground water, usually at some considerable depth within the earth. This represents essentially two accidents in the same place, and the occurrence is relatively rare. Yellowstone Park and the desert valley of southern California are the most noteworthy US. examples. Since the heat is the energy needed, if we could just get the water down to it and back. Well, that's what is being done with the hot dry rock program. A well is drilled down to where there is adequate heat in the rocks. The well is then pressurized until the rock fractures creating what amounts to a reservoir full of hot, shattered rock. Finally, a well is drilled into the reservoir and water is pumped in one well, heated by the rock, and taken out through the other well at useful temperatures and pressures. We are getting ready to run significant long-term flow tests at the Fenton Hill Hot Dry Rock site west of Los Alamos, New Mexico. We expect the operational information to provide the data to forecast the energy life of the wells as a production facility. This kind of resource is much more common than regular geothermal resources. Robert H. Hendron described the Long Term Flow Test and reservoir studies for which the project is preparing. A shortfall of available funding has slowed preparations, delaying the start of that test. The test is planning to gather data for more definitive reservoir modeling with energy availability or reservoir lifetime of primary interest. Other interests include geochemistry and tracer studies, microseismic response, water requirements and flow impedance which relates directly to the pumping power required. Progress has been made in modeling studies, chemically reactive tracer techniques, and in improvements in acoustic or microseismic event analysis. Donald W. Brown discussed reservoir modeling as it relates to production management of the HDR well. For wells which are fracture dominated rather than matrix-permeability controlled, a knowledge of the pressure-dependent permeability of the interconnected system of natural joints (or pre-existing fractures is critical to long-term power production from the wells) through optimized pressure management. It was mentioned that a knowledge of the pressure-dependent joint permeability could aid in designing more appropriate secondary recovery strategies in petroleum reservoirs, or reinjection I procedures of geothermal reservoirs. Dr. Bruce A. Robinson discussed the development of fluid flow and transport models for simulation of HDR geothermal reservoirs. These models are also expected to provide accurate predictions of long-term behavior and help in the development of strategies for reservoir improvement and operation. Two approaches were discussed. The discrete fracture approach is based on a random fracture network subject to prescribed statistical properties of the fracture set. It is used to simulate steady state fluid flow and solute transport. The other approach used the continuum approximation. This type of model is appropriate when the reservoir consists of many interconnected fractures, as is the case at Fenton Hill.

Author: G. W. Lanyon
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Category : Fracture mechanics
Languages : en
Pages : 10

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