The development of reliable spinner tools may help avoid much of the ambiquity which often accompanies well tests in geothermal wells, due to interlayer flows through the well bore. However, the use of both pressure and flow rate changes requires new methods of well test interpretation. The Stanford Geothermal Program has been developing microcomputer-based techniques for the simultaneous analysis of pressure and flow rate measurements. There are two key steps in the procedure. Firstly, the non-linear regression is achieved by calculating the gradients of the response (with respect to the unknown reservoir parameters) in Laplace space, and inverting numerically. Secondly, the variable flow rate is represented in terms of a superposition of many step changes - this was found to work better than a spline fit to the data. One problem was encountered when attempting to analyze data in which the spinner "stalled", causing a jump to zero flow rate. The method shows great promise in that the degrees of freedom on the interpretation are greatly reduced, the well bore storage effect disappears, and inter-feed flows do not affect the results.

The Krafla geothermal field in northeastern Iceland consists of several zones, which contain fluids of different composition and thermodynamic state (Stefansson, 1981). In this paper they examine production data from wells which are completed in two-phase zones. Transient changes in flow rate and flowing enthalpy are analyzed to obtain insight into relative (liquid and gas phase) permeabilities, and other reservoir parameters. Numerous studies have shown that predictions of geothermal reservoir behavior are strongly dependent upon the choice of relative permeability functions. There is an extensive literature on gas-oil and oil-water relative permeabilities, but steam-water relative permeabilities which are needed for geothermal reservoir analysis are poorly known. Laboratory experiments by Chen et al. (1978) and Counsil and Ramey (1979) have provided some data which, however, seem to be at variance with relative permeability characteristics deduced from field data by Grant (1977) and Horne and Ramey (1978). The differences may reflect uncertainties in the analysis methods used, or they may reflect ''real'' differences in relative permeability behavior of fractured reservoirs from that of porous medium-type laboratory cores. Recent theoretical work by Menzies (1982) and Gudmundsson et al. (1983) has substantiated the relative permeability characteristics obtained by Horne and Ramey (1978) for Wairakei …

A basic concept of the geothermal reservoir as a set of cracks is first presented. Extensions of subsurface cracks during well stimulation treatments at Nigorikawa(Mori) and closure operations of production well-head valves at Kakkonda are analysed and their behaviors are demonstrated based on results of long-distance AE Measurements.

Complementary broad-band instruments have been developed to measure time dependent, absolute soft x-ray spectra at the Lawrence Livermore National Laboratory (LLNL) Nd glass laser irradiation facilities. Absolute flux measurements of x rays emitted from laser-produced plasmas are important for understanding laser absorption and energy transport. We will describe two new 10-channel XRD systems that have been installed at the LLNL Novette facility for use in the 0.15- to 1.5-keV range. Since XRD channel time response is limited by available oscilloscope performance to 120 ps, a soft x-ray streak camera has been developed for better time resolution (20 ps) and greater dynamic range (approx.10/sup 3/) in the same x-ray energy region. Using suitable filters, grazing incidence mirrors, and a gold or cesium-iodide transmission cathode, this streak camera instrument has been installed at Novette to provide one broad and four relatively narrow channels. It can also be used in a single channel, spatially discriminating mode by means of pinhole imaging. The complementary nature of these instruments has been enhanced by locating them in close proximity and matching their channel energy responses. As an example of the use of these instruments, we present results from Novette 2..omega..(0.53 ..mu..m) gold disk irradiations at 1 …

The Advanced Test Accelerator (ATA) is a recent development in the field of charged particle beam research at Lawrence Livermore National Laboratory. With this experimental apparatus, researchers will characterize intense pulses of electron beams propagated through air. Inherent with the ATA concept was the potential for exposure to hazards, such as high radiation levels and hostile breathing atmospheres. The need for a comprehensive safety program was mandated; a formal system safety program was implemented during the project's conceptual phase. A project staff position was created for a safety analyst who would act as a liaison between the project staff and the safety department. Additionally, the safety analyst would be responsible for compiling various hazards analyses reports, which formed the basis of th project's Safety Analysis Report. Recommendations for safety features from the hazards analysis reports were incorporated as necessary at appropriate phases in project development rather than adding features afterwards. The safety program established for the ATA project faciliated in controlling losses and in achieving a low-level of acceptable risk.

The cost effectiveness of fracture stimulation at The Geysers, the Imperial Valley, and other geothermal resource areas in the United States vas studied using GEOCOM, a computer code for analyzing the impact of completion activities on the life-cycle costs of geothermal wells. Technologies for fracturing the reservoir near the wellbore involve the creation of a pressure pulse in the wellbore by means of either hydraulic or explosive force. The cost of a single fracture stimulation job can vary from $50,000 to over $500,000, with a typical cost of around $300,000. The code shows that additional flow achieved by fracture stimulation must exceed 10,000 pounds per hour for each $100,000 invested in stimulation in order for a fracture treatment to be cost effective. In some reservoirs, this additional flow must be as great as 30,000 pounds per hour. The cost effectiveness of fracturing has not yet been demonstrated in the field. The Geothermal Well Stimulation Program achieved an overall average of about 10,000 pounds per hour for each $100,000 invested.

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''.

The 400{degree}F liquid dominated Desert Peak geothermal reservoir produces from fractures associated with intersecting north-northeast and east-northeast trending normal faults. Fractures occur in intrusive basement rocks, pre-Tertiary metasedimentary and metavolcanic rocks, and Tertiary volcanic rocks. Static temperature surveys from six deep wells indicate that the reservoir has both recharge and discharge in the vicinity of wells B21-1 and 86-21. Interference data, from a 30-day flow test of 86-21 show high reservoir connectivity. the calculated transmissivity is an order of magnitude higher in a north-south direction than in an east-west direction. A reservoir thickness on the order of thousands of feet and disturbed reserves in excess of 7 billion barrels are estimated. A conceptual model of the Desert Peak system contains meteric water derived from the Carson and Fernley Sinks. Heated at depth, water rises up along normal faults into highly fractured rocks between the depths of 3000 and 9000 feet, forming a geothermal reservoir. the thermal water naturally rises or leaks out of the reservoir up normal faults to within a few hundred feet of the surface until it has reached hydrostatic equilibrium or is blocked by discontinuous impermeable lacustrine sedimentary rocks. In the latter case it spreads out laterally …

The concept of relative permeability is the key concept in extending Darcy's law for single phase flow through porous media to the two-phase flow regime. Relative permeability functions are needed for simulation studies of two-phase geothermal reservoirs. These are poorly known inspite of considerable theoretical and experimental investigations during the last decade. Since no conclusive results exist, many investigators use ad hoc parametrization, or adopt results obtined from flow of oil and gas (Corey, 1954). It has been shown by Reda and Eaton (1980) that this can lead to serious deficiencies. Sensitivity of the relative permeability curves for prediction of mass flow rate and flowing enthalpy into geothermal wells has been studied by many investigators (e.g. Eaton and Reda (1980), Bodvarsson et al (1980), Sun and Ershagi (1979) etc.). It can be concluded from these studies that the beehavior of a two-phase steam/water reservoir depends greatly on the relative permeability curves used. Hence, there exists a need for obtaining reliable relative permeability functions.

This paper discusses the development and use of a high temperature (300{degrees}C) downhole flowmeter for geothermal well logging. The availability of the instrument gives the reservoir engineer a powerful tool for formation evaluation and studying wellbore dynamics. The instrument components, their function, and temperature limitations are discussed in detail. Several field examples of spinner log interpretation are also presented.

A freshly flashed geothermal liquid, previously dosed with inhibitor and super-saturated with calcite was injected into another well where it displaced an unflashed counterpart of itself around the wellbore. Back-production of the injectate, and subsequently the native fluid, has yielded data for the rate that a scale inhibitor is degraded after injection. The circumstance also displays a novel mechanism whereby two fluids that do not physically mix never the less reactive with one another through the reservoir rock's serving a role of intermediary. The results have been further interpretated to conclude that in some circumstances a short lifetime for the scale inhibitor is not necessarily a problem for long-term injection.

DOE's geothermal program continues to emphasize a range of reservoir-related programs in reservoir definition, brine injection, stimulation, hot dry rock, geopressured resources and, now, magma resources. These programs are described briefly. Programs in international cooperation between the U.S. and 23 other countries on hydrothermal research have produced important gains in knowledge over the past ten years. Although the activity has diminished, a resurgence is anticipated.

A tracer test was carried out in a geothermal doublet system to study the injection behavior of a developed reservoir known to be fractured. The doublet produces about 320 gpm of 160 F water that is used for space heating and then injected; the wells are spaced 250 ft apart. Tracer breakthrough was observed in 2 hours and 45 minutes in the production well, indicating fracture flow. However, the tracer concentrations were low and indicated porous media flow; the tracers mixed with a reservoir volume much larger than a fracture.

Test data from several wells where scale either formed in the wellbore or in the reservoir have been observed. Some generalizations can be made about the behavior of downhole and wellhead pressure during drawdown and build-up. In addition, estimates of the size of the obstruction can be made in the field. Reservoir parameters can be calculated from pressure build-ups, after the problem of downhole scaling has been identified.

A study of the temporal behaviour of gas compsition in the Larderello-Castelnuovo area shows that this behaviour varies, depending on whether the wells are affected or not by natural recharge. Where no natural recharge exists, gas composition seems to be governed by chemical equilibria. The recharge water, and the steam it produces, mix with the fluid already existing in the reservoir. At Larderello (far from absorption areas) the gas composition resulting from this mixing does not undergo further changes by chemical reaction. This is due either to a lack of reactivity where there is no liquid phase or to an ineffective fluid-rock interaction. At Castelnuovo (close to absorption areas) the H{sub 2}S and CH{sub 4} contents in the gas have gradually decreased with the increase in recharge effects. The decrease in H{sub 2}S can be attributed to dissolution in liquid water and oxidation. Various hypotheses have been forwarded for the methane. The correlation existing between CH{sub 4} and N{sub 2} concentrations, even when methane decreases in the areas affected by recharge, suggests that CH{sub 4} may be governed by more than just the Fisher-Tropsch reaction.

In order to evaluate geothermal reserves, it is necessary to estimate the porosity-thickness product of the reservoir. This paper deals with the method for estimating the porosity-thickness product of geothermal reservoirs by means of combining well interference and pressure buildup tests. A field study from the Chingshui geothermal area in Taiwan is given to illustrate the application of the method.

MCR Geothermal Corporation pioneered successful exploratiory drilling the Bottle Rock area of the Geysers Steam Field in 1976. The wellfield is characterized by a deep reservoir with varied flowrates, temperatures, pressures, and stem chemistries being quite acceptable. More detailed reservoir engineering tests will follow as production commences.

Fracture systems may be generalized in terms of number and orientation of sets of parallel fractures and the distribution of length, width, thickness and separation. Borehole measurements may be used to particularize these parameters for a specific site. Global flow and dispersion in an aquifer occur in the interconnected fractures and may be related to specific fracture elements. A fluid dynamics code named SALE has been used to solve the Navier-Stokes equations for laminar flow in these elemental geometries. A marker particle calculation has been added to characterize longitudinal dispersion due to the velocity profile across the fracture and lateral dispersion due to flow disturbances at junctions. Local flow and dispersion in the matrix occur in the finer fracture structure and are evaluated using porous media approaches. These results or models are integrated in a 2D isothermal reservoir simulator named FRACSL. Discrete fractures are superimposed on the edges or diagnoals of rectangular grid elements. Water may flow from node to node through the matrix or through the fracture. The heads are found by iterating for the distribution which conserves the appropriate local mass. Marker particles are used to monitor the tracer dispersion due to motion in the fractures, in the …

Five new gas geothermometers are introduced. They are useful for predicting subsurface temperatures in water dominated geothermal systems. The geothermometers use data on CO{sub 2}, H{sub 2}S and H{sub 2} concentrations in fumarole steam as well as CO{sub 2}/H{sub 2} and H{sub 2}S/H{sub 2} ratios. It is demonstrated that the gas composition of fumarole steam may be used with or withour drillhole data to evaluate steam condensation in the upflow zones of geothermal systems. Uncertainty exists, however, in distinguishing between the effects of steam condensation and phase separation at elevated pressures. The gas content in steam from discharging wells and the solute content of the water phase can be used to evaluate which boiling processes lead to "excess steam" in the discharge and at which temperature this "excess steam" is added to the fluid moving through the aquifer and into the well. Examples, using field data, are given to demonstrate all the mentioned applications of geothermal chemistry.

Using numerical simulation techniques and the radial model developed for the study of the natural state of the Heber field (Lippmann and Bodvarsson, 1983b), the response of this geothermal system to exploitation is analyzed. In this study the generation rate in the field is allowed to build up over a period of 10 years; after that, 30 years of constant power production is assumed. Full (100%) injection of the spent brines is considered, the fluids being injected 2250 m ("near injection") or 4250 m ("far injection") from the center of the system. The study shows that a maximum of 6000 kg/s (equivalent to approximately 300 MWe) of fluids may be produced for the near injection case, but only 3000 kg/s (eqivalent to approximately 150 MWe) for the far injection case. The results indicate that the possible extraction rates (generating capacity) generally are limited by the pressure drop in the reservoir. The average temperature of the produced fluids will decline 10-18{degrees}C over the 40-year period.

The caldera environment represents a complex interaction of volcanic, structural, and often, hydrothermal processes. As a result calderas are often targets for geothermal exploration and development. From the standpoint of the reservoir engineer, such geothermal systems would be hosted by rocks that display a complex interplay of stratigrphic permeability, structural permeability, and changing permeability which results from the process of hydrothermal alteration and new fracture generation. The purpose of this paper is to present a geolgic model of the Baca geothermal reservoir which is situated in New Mexico. The geologic history of the Valles caldera is presented in Smith and Bailey (1968). The data we present is largely based on our studies of subsurface samples from Union Oil Company's Baca project area. Additional results of our work have been published previously (Hulen and Nielson, 1982, 1983; Nielson and Hulen, in press).

China's geothermal resources are mainly of low - medium temperature. More than 30 geothermal areas have been or are being explorated. According to the geology, economy and technology of geothermal energy development main efforts are concentrated in some places with better conditions and can be exploited effectively in the near future, such as low temperature geothermal fields in Beijing and Tianjin, Yangbajain and Dengchong high temperature geothermal fields respectively in Tibet and Ynnan province. In Beijing and Tianjin the geothermal water is used for space heating, bathing, medical treatment, greenhouse, raising tropical fish, industry and so on. In Beijing now more than 200 thousand sq. m. of indoor floor is being heated with geothermal water and about 50 thousand persons per day use it to take bath. In future, the low temperature geothermal water utilization in these big citites would flourish. In 1970 the first experimental geothermal power plant using the flashing method was built in Dengwu, Guangdong province. In 1977 one MW experimental wet steam power plant was built in Yangbajain, Tibet, a 6 MW power plant in 1981, and another 3 MW generator is expected to complete in 1985. This paper is intended to summarize some important results …

Mexico is a Country characterized by its diversified means of Power Gerneration. Actual installed capacity is almost 19000 MW, of which 205 MW corresponds to Geothermal Plants, that is, 180 MW in Cerro Prieto and 25 MW of Portable Plants in Los Azufres. To date, 346 area with exploitation possibilites, are known. They are mainly distributed along the Volcanic Belt where the most prominent are, Los Azufres, La Primavera, Los Humeros, Ixtlan De Los Hervores and Los Negritos, among others. Proved reserves are 920 MW, and the accessible resource base are 4600 MW identified and 6000 MW undiscovered. The long range construction studies intends to achieve a total installed capacity of 100000 MW, by the end of this century, including 2000 MW Geothermal, through conventional and Portable Plants. It is not a definite program but a development strategy. The carrying out of a definite program, will depend upon the confirmation of Hypothesis made in previous studies, and the economic decisions related to the financial sources availability, and techologies to be used in the future as well.

Achievements and problem areas are reviewed with respect to various engineering implications of geothermal field development in the European Community (EC). Current and furture development goals address three resource settings. (a) low enthalpy sources (30-150{degrees}C), an outlook common to all Member states as a result of hot water aquifers flowing in large sedimentary units with normal heat flow, widespread thoughout the EC; (b) high enthalpy sources (<150{degrees}C) in areas of high heat flow which, as a consequence of the geodynamics of the Eurasian plate, are limited to Central and South-West Italy and to Eastern Greece; (c) hot dry rocks (HDR), whose potential for Europe, and also the difficulties in implementing the heat mining concept, are enormous. A large scale experiment conducted at medium depth in Cornwall (UK) proves encouraging though. It has provided the right sort of scientific inputs to the understanding of the mechanics of anisotropic brittle basement rocks.