Paul Kruger

Electric power requirement for large-scale production of hydrogen fuel for the world vehicle fleet

Abstract Replacement of fossil fuels by hydrogen in motor vehicles throughout the world is postulated to occur over the next 50 years as mass production of fuel-cell engines accelerates. For the estimated size of the world vehicle fleet by 2050, large-scale electrolysis of water may become the primary means to produce hydrogen in sufficient quantity. Unlike petroleum production, which is concentrated in only a few well-endowed countries in the world, electrolytic production of hydrogen can be carried out in all countries as an indigenous supply of fuel. However, each nation will require a significant increase in the rate of electric energy consumption and a concomitant increase in electric power generating facilities. A dynamic model was used to estimate the annual total electric energy requirement to sustain long-term growth of hydrogen fuel production in two time sequences. In the first sequence, from 2000 to 2010, when a fuel-cell engine industry is likely to expand rapidly, extrapolation of historic data on world population, vehicle, traffic, and energy statistics from official agencies provides the initial conditions in year 2010 for the second time sequence. In the second sequence, the model examines a range of growth scenarios to the year 2050, when a significant fraction of the total world vehicle fleet could be operated with hydrogen fuel. The model calculations show that even with improved energy consumption efficiency of electrolytic production facilities, the additional electric energy demand to sustain growth of hydrogen fuel production will require installation of significant additional electric power generating capacity throughout the world.

Fluid circulation and heat extraction from engineered geothermal reservoirs

Abstract A large amount of fluid circulation and heat extraction (i.e., thermal power production) research and testing has been conducted on engineered geothermal reservoirs in the past 15 years. In confined reservoirs, which best represent the original Hot Dry Rock concept, the flow distribution at any given time is primarily determined by three parameters: (1) the nature of the interconnected network of pressure-stimulated joints and open fractures within the flow-accessible reservoir region, (2) the mean pressure in the reservoir, and (3) the cumulative amount of fluid circulation—and therefore reservoir cooling—that has occurred. For an initial reservoir rock temperature distribution and mean fluid outlet temperature, the rate of heat extraction (i.e., thermal power) is at first only a function of the production flow rate, since the production temperature can be expected to remain essentially constant for some time (months, or even years). However, as reservoir circulation proceeds, the production temperature will eventually start to decline, as determined by the mean effective joint spacing and the total flow-accessible (i.e., heat-transfer) volume of the reservoir. The rate of heat extraction, which depends on the production flow rate, can also vary with time as a result of continuing changes in the flow distribution arising from reservoir cooling. The thermal power of engineered reservoirs can most readily be increased by increasing the production flow rate, as long as this does not lead to premature cooldown, the development of short-circuit flow paths, or excessive water losses. Generally, an increase in flow rate can be accomplished by increasing the injection pressure within limits. This strategy increases the driving pressure drop across the reservoir and the mean reservoir pressure, which in turn reduces the reservoir flow impedance by increasing the amount of joint dilation. However, the usefulness of this strategy is limited to reservoir operating pressures below the fracture extension pressure, and may lead to excessive water losses, particularly in less-confined reservoirs. Under such conditions, a downhole production-well pump may be employed to increase productivity by recovering more of the injected fluid at lower mean reservoir operating pressures.

Electric power requirement in the United States for large-scale production of hydrogen fuel

Long-term growth in substitution of hydrogen for fossil fuels in motor vehicles will require a significant increase in the rate of adding electric power generating facilities in the United States, where the number of vehicles is estimated to reach about 250 million by 2010. Electrolysis of water may become the primary means to produce hydrogen in sufficient quantity for so large a vehicle fleet. Estimation of the increased annual electric energy requirement to sustain long-term growth of adequate hydrogen fuel production was made in two time sequences with the use of a dynamic model. In the first sequence, from 1995 to 2010, when a fuel-cell engine vehicle industry is likely to expand rapidly, extrapolation of historic data on US population, vehicle, and energy statistics from Federal agencies provides the initial conditions for the year 2010 for the second time sequence. In the second sequence, the model examines a range of growth scenarios to the year 2050, when a significant fraction of the total United States vehicle fleet could be operated with hydrogen fuel. The results of the model calculations show that even with improved energy consumption efficiency of electrolytic production facilities, the additional electric energy demand to sustain replacement growth of hydrogen fuel in the fleet will require installation of significant additional electric power generating capacity.

Radon in geothermal reservoir engineering

Two general types of information related to transit time are amenable to radon measurement experiments. Under steady flow conditions, changes in the radon source will result in changes in the radon concentration in produced geofluids. And under steady emanation conditions, changes in the flow regime will also result in changes in the radon concentration. Current interest has focused on the relationship between radon concentration and the flow regime in producing geothermal reservoirs. The paper describes actual and planned experiments using radon as a tracer at The Geysers and other reservoirs. 1 tab., 4 refs., 2 figs.

Electric power requirement in California for large-scale production of hydrogen fuel

Abstract Substitution of hydrogen for fossil fuels in motor vehicles will require a significant growth of electric energy consumption, especially in high growth rate states such as California. A major concern is the magnitude of the additional electric power capacity necessary to build a large-scale hydrogen fuel industry in California to accommodate the fuel demand of a 30-million vehicle fleet. Electrolysis of water may be the only practical means to produce hydrogen in sufficient quantity without use of fossil fuels for so large a vehicle fleet. A dynamic model was used to estimate the increasing annual electric energy requirement to sustain long-term growth of adequate hydrogen fuel production in two time sequences. The first extrapolates historic data on population, vehicle, and energy statistics from California State agencies to the year 2010 when a fuel-cell engine vehicle industry could begin to expand rapidly. The second time sequence uses the 2010 values as the initial conditions to examine a range of growth scenarios to the year 2050 when a significant fraction of the total California vehicle fleet could be operated with hydrogen fuel. The results of the model calculations show that even with improved energy consumption efficiency of electrolytic production facilities, the additional electric energy demand to sustain replacement growth of hydrogen fuel in the fleet will require installation of additional generating capacity.

Relationship of radon concentration to spatial and temporal variations of reservoir thermodynamic conditions in the Cerro Prieto geothermal field

Abstract Measurements of radon concentration in geothermal fluids at Cerro Prieto are evaluated with respect to spatial and temporal variations in reservoir thermodynamic conditions and the rock — fluid mass ratio for radon emanation. Higher concentration of radon observed at wells with higher fluid enthalpy can be attributed to the higher steam fraction in the reservoir fluid. Regression analysis of radon concentration with specific volume of pore fluid shows a significant degree of correlation, resulting from the dependence of specific volume on both two-phase conditions and reservoir temperature. Temporal variations in radon concentration reflect changing phase conditions in the reservoir. Observations over a 2-year interval show significant changes in the producing zones. The constant low concentration along the western edge of the field indicates a fluid of low steam saturation. In the eastern area, radon concentrations have increased significantly suggesting an increase in the steam saturation in this part of the reservoir due to exploitation. Other areas, e.g. the southeast area, show decreased radon concentration indicating a decrease in steam saturation. Concurrent measurements of ammonia, a soluble component of the noncondensable gases, support the observations of partitioning of gas components, with wellhead concentration dependent on spatial variations in steam saturation over the field.

Analysis of the stanford geothermal reservoir model experiments using the LBL reservoir simulator

Abstract This paper describes the results of an analysis of data obtained from a series of heat-sweep experiments performed in the Stanford Geothermal Reservoir Model using the Lawrence Berkeley Laboratory reservoir simulator. The physical reservoir model is an experimental system consisting of a pressure vessel which contains a granite rock matrix with production and recharge capabilities to simulate the heat-sweep process in a fractured hydrothermal reservoir under liquid-phase conditions. Arrangements were made with the Lawrence Berkeley Laboratory to test their geothermal reservoir simulator on the physical model data. The objectives were to provide insight into the detailed physical processes occurring in the relatively complex physical system and to provide feedback to LBL on the capability and possible improvements to the LBL reservoir simulator to model a complex physical system. The overall conclusion of this work is that the LBL simulator does an excellent job of predicting the physical processes in the Stanford Geothermal Reservoir Model experiments for extreme thermal gradient conditions and for a system with very complex boundary conditions. The analysis demonstrates the importance of specifying relevant parameters accurately to provide adequate modeling for the important physical processes.

Investigation of soluble indium chelates for groundwater and hydrothermal fluid tracing

Abstract Indium is an excellent tracer with a unique combination of good activation analysis sensitivity retaining most of the advantages of radioactive tracers without creating health or environemental risk, and low background concentration in surface and subsurface fluids. The organic chelating agents ethylenediaminetetraacetic acid (EDTA) and nitrilotriacetic acid (NTA) were selected to enhance the solubility of In as a tracer within the pH range of groundwater and hydrothermal fluids. The thermal stability of indium chelates of EDTA and NTA was investigated at temperatures from 22 to 240°C. Degradation of In(III)-EDTA, observed at and above 200°C, is attributed to metal dissociation followed by thermal decomposition of the organic ligand. Degradation of In(III)-NTA, observed at temperatures greater than 150°C, is probably due to significant decrease of the thermodynamic formation constant. The results suggest that soluble indium chelates can be used effectively as tracers for surface and groundwater flow and transport studies. The applicability of In(III)-EDTA as a conservative tracer can be extended to low-temperature geothermal reservoirs where ionic chemical tracers are not fully conservative.

Experimental Studies on Heat Extraction from Fractured Geothermal Reservoirs

Most of the available energy in hydrothermal systems and all of the available energy in hot igneous rock systems is present in the formation rock. Long-term commercial development of geothermal resources for electric power production will depend on optimum heat extraction from such systems. Studies underway in the Stanford Geothermal Program since 1972 to improve the efficiency of energy extraction from geothermal resources involve a combination of physical and mathematical models. Results of these studies include the development of a simple, lumped parameter heat extraction model to evaluate the potential for recharge-sweep production. Incorporated into the model are results from a series of tests on several rock loadings in a large physical model of a rechargeable hydrothermal reservoir, experiments on shape factor correlations for single, irregular-shaped rocks and assemblies of reservoir-shaped rocks, and experiments on the effect of thermal stressing on rock heat transfer properties. Current efforts involve the improvement of the model to include distributed-parameter analysis of heat extraction using a rock loading of known geometric shape and spacing.

Stanford Geothermal Program, reservoir and injection technology

This annual report of the Stanford Geothermal Program presents major projects in reservoir and injection technology. The four include: (1) an application of the boundary element method to front tracking and pressure transient testing; (2) determination of fracture aperture, a multi-tracer approach; (3) an analysis of tracer and thermal transients during reinjection; and, (4) pressure transient modeling of a non-uniformly fractured reservoir. (BN)