We have measured the spectra of gamma rays from approximately 14 MeV to the endpoint in the {sup 89}Y({rvec p},{gamma}) reaction with 19.6 MeV polarized protons from the TUNL tandem accelerator. Gamma spectra were measured with a pair of 25.4 cm {times} 25.4 cm anticoincidence shielded NaI detectors at angles of 30, 55, 90, 125, and 150{degrees} with respect to the incident beam. The {gamma}-ray spectra show significant analyzing powers and forward peaking of the angular distributions. These features allow for the discrimination between compound processes which do not exhibit interference between different channels, and direct processes. The observed interference effects indicate that multistep-direct processes are important at {gamma}-ray energies lower than those for which direct-semidirect capture is the dominant mechanism.

Many emergency response dispersion modeling systems provide simple Gaussian models driven by single meteorological tower inputs to estimate the downwind consequences from accidental spills or stack releases. Complex meteorological or terrain settings demand more sophisticated resolution of the three-dimensional structure of the atmosphere to reliably calculate plume dispersion. Mountain valleys and sea breeze flows are two common examples of such settings. To address these complexities, the authors have implemented the three-dimensional diagnostic MATHEW mass-adjusted wind field and ADPIC particle-in-cell dispersion models on a workstation for use in real-time emergency response modeling. MATHEW/ADPIC have shown their utility in a variety of complex settings over the last 15 years within the Department of Energy`s Atmospheric Release Advisory Capability (ARAC) project. The models are initialized using an array of surface wind measurements from meteorological towers coupled with vertical profiles from an acoustic sounder (sodar). The workstation automatically acquires the meteorological data every 15 minutes. A source term is generated using either defaults or a real-time stack monitor. Model outputs include contoured isopleths displayed on site geography or plume densities shown over 3-D color shaded terrain. The models are automatically updated every 15 minutes to provide the emergency response manager with a continuous display …

Training new users of complex machines is often an expensive and time-consuming process. This is particularly true for special purpose systems, such as those frequently encountered in DOE applications. This paper presents a computer-based training system intended as a partial solution to this problem. The system extends the basic virtual reality (VR) training paradigm by adding a multimedia component which may be accessed during interaction with the virtual environment: The 3D model used to create the virtual reality is also used as the primary navigation tool through the associated multimedia. This method exploits the natural mapping between a virtual world and the real world that it represents to provide a more intuitive way for the student to interact with all forms of information about the system.

Estimates of temperatures, past and present, in geothermal reservoirs can be made by using now standard mineralogical techniques, including fluid inclusion geothermometry, vitrinite reflectance, calc-silicate and clay occurrence, the extent of clay interlayering, and measuring clay crystallinity. Recent studies of clays in 60 drillcores from 6 wells at Wairakei, for example, show an inverse relationship between reservoir temperatures and crystallinities from 90&deg; to 225&deg;C (195 to 435°F) (K&uuml;bler Indices: 1.40 to 0.44 <FONT FACE="Symbol">D</FONT>&deg;2<FONT FACE="Symbol">q</FONT>). Fluid inclusion geothermometry results require careful interpretation but the method need not be calibrated with respect to the reservoir, as do other geothermometric methods.

This paper presents a theoretical study of the discharge characteristics of slim holes compared to production wells. Assuming that (1) the boreholes feed from an all-liquid zone, and (2) the feedzone pressure and temperature are independent of borehole diameter, calculations have been carried out for a variety of borehole diameters. The wellhead pressure/flowrate relationships for the various borehole diameters do not collapse to a single curve, even when flow rates are adjusted to account for differences in cross-sectional area. The area-scaled discharge rate declines with a decrease in borehole diameter. Both frictional pressure gradient and heat loss effects are more significant for the smaller-diameter slim holes than for the larger-diameter wells. The difference in heat loss effects is probably responsible, at least in some cases, for the difficulty encountered in inducing deep slim holes (depths >> 300 m) to discharge. Scaling up the discharge capacity of slim holes to those of production wells by the cross-section area ratio provides a conservative estimate of production-size hole discharge.

The data from flow tests which employed two different production zones in a well at Fenton Hill indicates the flow impedance of a wellbore zone damaged by rapid depressurization was altered, possibly by pressure spallation, which appears to have mechanically propped the joint apertures of outlet flow paths intersecting the altered wellbore. The rapid depressurization and subsequent flow test data derived from the damaged well has led to the hypothesis that pressure spallation and the resultant mechanical propping of outlet flow paths reduced the outlet flow impedance of the damaged wellbore. Furthermore, transient pressure data shows the largest pressure drop between the injection and production wellheads occurs near the production wellbore, so lowering the outlet impedance by increasing the apertures of outlet flow paths will have the greatest effect on reducing the overall reservoir impedance. Fenton Hill data also reveals that increasing the overall reservoir pressure dilates the apertures of flow paths, which likewise serves to reduce the reservoir impedance. Data suggests that either pressure dilating the wellbore connected joints with high production wellhead pressure, or mechanically propping open the outlet flow paths will increase the near-wellbore permeability. Finally, a new method for calculating and comparing near-wellbore outlet impedances has …

The Bulalo geothermal field, located in Laguna province, Philippines, supplies 12% of the electricity on the island of Luzon. The first 110 MWe power plant was on line May 1979; current 330 MWe (gross) installed capacity was reached in 1984. Since then, the field has operated at an average plant factor of 76%. The National Power Corporation plans to add 40 MWe base load and 40 MWe standby in 1995. A numerical simulation model for the Bulalo field has been created that matches historic pressure changes, enthalpy and steam flash trends and cumulative steam production. Gravity modeling provided independent verification of mass balances and time rate of change of liquid desaturation in the rock matrix. Gravity modeling, in conjunction with reservoir simulation provides a means of predicting matrix dry out and the time to limiting conditions for sustainable levelized steam deliverability and power generation.

The work described represents a move towards better representations of the natural fracture system. The discrete fracture network model used during the study was the NAPSAC code (Grindrod et al, 1992). The goals of the work were to investigate the application of discrete fracture network models to Hot Dry Rock systems, increase the understanding of the basic thermal extraction process and more specifically the understanding of the Rosemanowes Phase 2B system. The aim in applying the work to the Rosemanowes site was to use the discrete fracture network approach to integrate a diverse set of field measurements into as simple a model as possible.

A single-box-model numerical simulator for personal computer analysis was developed in order to estimate macroscopic parameter values for exploited geothermal reservoirs and essential fluids coming from the depth. The simulator was designed to compute history data concerning total production and reinjection fluids at geothermal power plants from the assumed parameter values, based on conservation laws for water mass, heat energy and masses of conservative chemical constituents of geothermal fluids. Using two kinds of forward analysis techniques, i.e. the cast-net and pursuit methods, programs containing the simulator can semiautomatically select the optimum combination of the unknown parameter values by minimizing the differences between the simulated and measured history data for specific enthalpy and chemical compositions of the production fluids. The forward analysis programs were applied to the history data from the Onuma geothermal power plant (production capacity, 10MWe) where waste hot water reinjection, chemical monitoring and artificial tracer tests have been conducted since 1970, almost the beginning of the geothermal exploitation. Using the history data, enthalpy and iodine concentrations of the total production fluids with the amounts of KI tracer injected as spikes, the macroscopic parameter values for the exploited reservoir and the essential hot water from the depth were uniquely …

Gas chemistry from 28 wells complement water chemistry and physical data in developing a reservoir model for the Bacon-Manito geothermal project (BMGP), Philippines. Reservoir temperature, T_HSH, and steam fraction, y, are calculated or extrapolated from the grid defined by the Fischer-Tropsch (FT) and H₂-H₂S (HSH) gas equilibria reactions. A correction is made for H₂ that is lost due to preferential partitioning into the vapor phase and the reequilibration of H₂S after steam loss.

A new technique has been developed for the measurement of steam mass flowrate, water mass flowrate and total enthalpy of two-phase fluids produced from geothermal wells. The method involves precisely metered injection of liquid and vapor phase tracers into the two-phase production pipeline and concurrent sampling of each phase downstream of the injection point. Subsequent chemical analysis of the steam and water samples for tracer content enables the calculation of mass flowrate for each phase given the known mass injection rates of tracer. This technique has now been used extensively at the Coso geothermal project, owned and operated by California Energy Company. Initial validation of the method was performed at the Roosevelt Hot Springs geothermal project on wells producing to individual production separators equipped with orificeplate flowmeters for each phase.

A vapor-dominated two-phase zone would be formed in a geothermal reservoir under fissured caprock, if the permeability of the fissure is much smaller than a critical permeability which is estimated by an energy balance. If the permeability of the fissure is large, then the rule of minimum mass input would be applied.

A new equation-of-state module has been developed for the TOUGH2 simulator, belonging to the MULKOM family of computer codes developed at LBL. This EOS module is able to handle three-component mixtures of water, sodium chloride, and a non-condensible gas. It can describe liquid and gas phases, and includes precipitation and dissolution of solid salt. The dependence of density, viscosity, enthalpy, and vapor pressure of brine on salt concentration is taken into account, as well as the effects of salinity on gas solubility in the liquid phase and related heat of solution. The main assumptions made in developing this EOS module are discussed, together with the correlations employed to calculate the thermophysical properties of multiphase multicomponent mixtures. At present the non-condensible gas can be chosen to be air, CO₂, CH₄, H₂, or N₂. This paper focuses on H₂O-NaCI-CO₂ mixtures and describes new correlations obtained from fitting of published experimental data. Illustrative results for geothermal reservoir depletion in the presence of salinity and non-condensible gas are presented. We demonstrate and analyze effects of vapor pressure lowering and gas solubility decrease from salinity, and loss of reservoir porosity and permeability from salt precipitation during boiling of brines.

A new type of dual-porosity model is being developed to simulate two-phase flow processes in fractured geothermal reservoirs. At this time it is assumed that the liquid phase in the matrix blocks remains immobile. By utilizing the effective compressibility of a two-phase water/steam mixture in a porous rock, flow within the matrix blocks can be modeled by a single diffusion equation. This equation in turn is replaced by a nonlinear ordinary differential equation that utilizes the mean pressure and mean saturation in the matrix blocks to calculate the rate of fluid flow between the matrix blocks and fractures. This equation has been incorporated into the numerical simulator TOUGH to serve as a source/sink term for computational gridblocks that represent the fracture system. The new method has been compared with solutions obtained using fully-discretized matrix blocks, on a problem involving a three-dimensional vapor-dominated reservoir containing an injection and a production well, and has been found to be quite accurate.

When liquid is injected into a geothermal reservoir, a fraction of the liquid may vaporise if the reservoir is sufficiently hot. The vapour forms at an approximately planar liquid-vapour interface and diffuses towards the far boundary of the reservoir. If vapour is extracted from the far boundary, then once the new vapour has diffused across the reservoir, the rate of production of vapour at the liquid-vapour interface approximately balances the rate of extraction. We find that if the pressure at the injection pump and extraction well is fixed, then the fraction of the liquid which vaporises and the rate of extraction of vapour from the reservoir increase with time. However, the rate at which liquid is pumped into the reservoir inay initially decrease but subsequently increases with time, if a sufficient fraction of the liquid vaporises. If the mass flux of liquid injected into the reservoir is fixed, then again both the fraction of the liquid which vaporises and the mass flux of vapour which may be extracted increase with time. In this case, the pressure at the injection pump may increase but subsequently decreases with time, again if a sufficient fraction of the liquid vaporises.

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&middot;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 …

It presents a systematic methodology to evaluate the reservoir characteristics of Chipilapa- Ahuachapan geothermal field through the highly diluted natural manifestations (springs and domestic wells) in its surroundings. The manifestations are classified in three main groups according to their mechanism of formation: high salinity water (HSW), medium salinity water (MSW), and Sulfated Water (SW). The reservoir temperature at Chipilapa geothermal field is around 220°C which is estimated with application of various chemical geothermometers. The isotopic studies indicate that the heating of local meteoric water with the separated steam of deep reservoir fluids is a dominating process in the formation of springs and domestic wells fluids. The process of formation of primary and secondary vapor explains the isotopic composition of fumaroles.

There are two reservoirs with different temperature and permeability in the Kakkonda hydrothermal system. The shallow reservoir is permeable and 230 to 260&deg;C, while the deep reservoir is less permeable and 350 to 360&deg;C. However, they are hydraulically connected each other. Recent drilling of deep wells revealed existence of Pre- Tertiary formation below Tertiary formations and neogranitic pluton younger than 5Ma. This pluton is a heat source of metamorphism found in Pre-Tertiary and Tertiary formations. There is a permeable horizon at the top of the pluton, and is very productive. To date, 4 production wells have been completed in this deep reservoir.

Using thermodynamic gas equilibria to calculate temperature and steam fraction in the reservoir, three main physical phenomena due to exploitation of Palinpinon field are identified. 1) Pressure drawdown producing a local increase in the computed steam fraction, with the fluid maintaining high temperature values (close to 300°C). Strong decline in flow rate is observed. 2) Irreversible steam losses from the original high temperature liquid phase during its ascent through fractures in upper zones of the reservoir. Steam is generally lost at temperatures (e.g. 240°C) lower then those of the original aquifer. 3) Dilution and cooling effects due to reinjection fluid returns. These are function of the local geostructural conditions linking through fractures the injectors and production wells. The computed fraction of the recovered reinjected brine can in some case exceed 80% of the total produced fluid. At the same time the computed gas equilibration temperatures can decline from 280-300°C to as low as 215-220°C. Comparing these values with the well bottom measured temperatures, the proposed methodology based on gas chemistry gives more reliable temperature estimate than water chemistry based geothermometers for fluids with high fractions of injected brine.

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 …

This paper summarizes an ongoing numerical modeling effort aimed at describing some of the thermodynamic conditions observed in vapor-dominated reservoirs, including the formation of a high temperature reservoir (HTR) beneath the "typical" reservoir. The modeled system begins as a hot water geothermal reservoir, and evolves through time into a vapor-dominated reservoir with a HTR at depth. This approach taken here to develop a vapor-dominated system is similar to that of Pruess (1985), and involves induced boiling through venting. The reservoir description is intentionally generic, but serves to describe a means of evolution of conditions observed (in particular) at The Geysers. This study addresses the question of HTR formation numerically. The reservoir model and approach used is similar to that of Pruess (1985); however, vapor pressure lowering effects were included for the rock matrix. Results of this study indicate that a high temperature reservoir may occur as a steady state component of a "typical" vapor-dominated reservoir. Fractures within the HTR are dry; however, saturated conditions exists in the rock matrix. Pressures at depth follow a vapor pressure with depth relationship. Temperatures at depth are large (relative to saturated conditions) because of superheat in the fractures and vapor pressure lowering in the …

Experimental isotherms of water vapor adsorption/desorption on three geothermal reservoir rock samples have been measured at temperatures of 80, 100, 120 and 140°C. Initial surface status of the sample was found to influence the amount of water adsorbed. At low relative pressures, adsorption is the dominant process of water retention onto the rock samples. Adsorption/desorption hysteresis was observed to exist over the whole pressure range at all temperatures. Similar observations were made for all three samples. The results of this study suggest that adsorption is important in storing water in geothermal reservoir rocks not only in itself, but also in inducing capillary condensation.

Methods of tracing reservoir processes will be discussed and applied to the NCPA Geysers steam field. The gas and isotope chemistry of produced steam is far from uniform even in a restricted volume of the reservoir. The composition is affected by many factors. Differences in permeability, local existence of gas pockets or perched liquid and the pattern of fracture connection can cause neighboring wells to produce steam of different compositions. This study attempts to separate local effects from general influences by viewing the data across the field and over a period of time. The fits of the trend lines to the data are far from perfect but present a reasonably consistent picture.

Three chemical tracer experiments and one extended injection of fluid low in concentration of dissolved species have been carried out during the Long Term Flow Test (LTFT) of the Fenton Hill Hot Dry Rock (HDR) reservoir. The tracer tests results illustrate the dynamic nature of the flow system, with more fluid traveling through longer residence time paths as heat is extracted. The total fracture volumes calculated from these tests allow us to determine the fate of unrecovered injection fluid, examine the pressure-dependence of fracture volume, and, through a comparison to the hydraulic performance, postulate a model for the nature of the pressure drops through the system. The Fresh Water Flush (FWF) test showed that while no dissolved specie behavior is truly conservative (no sources or sinks), several breakthrough curves are well explained with a pore fluid displacement model. Other dissolved components are clearly influenced by dissolution or precipitation reactions. Finally, the transient response of the chemistry during the FWF to an increase in production well pressure showed that some fractures connected to the production well preferentially open when pressure is raised.