As suggested by the discusssion of Barker, 1988, on the influence of flow dimension on the late-time behaviour of the generalized line source solution, it was inferred that observed long term reservoir pressure decline was an outcome of the 1D (linear) flow geometry, indicated by well tests. The detrimental effects of the reservoir pressure decline can be partly mitigated by taking advantage of the two-phase flow which occurs when methane, originally dissolved in the geothermal brine, is released within the well bore. Sustainable artesiar withdrawal scenarios for existing geothermal fields are devised, based on an accurate prediction of bottomhole pressure decline trends and an adequate selection of the diameter and length of the production tubing. Overall analysis and forecast are performed by an integrated reservoir & well bore simulator.

The problem of free convection in a thin porous contour, placed in uniform impermeable massif is considered. The approximate analitical solution of conjugate problem is obtained. The critical Rayleigh number is determined, by exceeding of which the steady fluid circulation in an annulus is established. The computations of abnormal heat flow near surface are carried out, stipulated by thermoconvection in a contour.

The results of the study on the possibilities of geothermal power in West Lithuania are presented. Three approaches to supplying thermal power to a settlement were studied a) no heat pump, extended heating surfaces in individual houses, b) a heat pump in each individual house, c) a central heat pump power plant for the settlement. It was concluded that heat carriers of low potential heat can be applied in standard houses of the Construction Plant in Alytus (panel walls and floors) only after improving the thermal insulation of the houses. The project of a central heat pump power plant requires minor reconstruction of the houses. It is more expensive than approuch a), but cheaper than approach b). The settlement Venckai can consume just 1/10 of the power of such thermal plant. Consequently, a project for the township Priekulé should be considered.

An early injection experiment has been conducted in attempt to evaluate of possibilities of waste disposal and of influence degree of reinjection on thermo and hydro regime of field. Changing of temperature profiles, fluid enthalpy, pressure, well’s output and chemical test data in more than 30 injection, exploitation and observation wells has been analyzed and interpreted. Results have allowed to define of structure and resources of geothermal field more accurately, to determine of rational reinjection strategy and to restart of reinjection in 1994.

The ORNL high temperature isopiestic apparatus was adapted for adsorption measurements. The quantity of water retained by rock samples taken from three different wells of The Geysers was measured at 150 °C and at 200 °C as a function of pressure in the range 0.00 ≤ p/p₀ ≤ 0.98, where p₀ is the saturated water vapor pressure. The rocks were crushed and sieved into three fractions of different grain sizes (with different specific surface areas). Both adsorption (increasing pressure) and desorption (decreasing pressure) runs were made in order to investigate the nature and extent of the hysteresis. Additionally, BET surface area analyses were performed by Porous Materials Inc. on the same rock samples using nitrogen or krypton adsorption measurements at 77 K. Specific surface areas and pore volumes were determined. These parameters are important in estimating water retention capability of a porous material. The same laboratory also determined the densities of the samples by helium pycnometry. Their results were then compared with our own density values obtained by measuring the effect of buoyancy in compressed argon. One of the goals of this project is to determine the dependence of the water retention capacity of the rocks as a function of …

It is a well known fact that a liquid flowing through a microporous media creates a potential difference between entry and exit of the sample. This phenomenon is known as streaming potential. In an other hand, when a potential difference is applied through an impregnate rock sample, a flow is induced, this is called electroosmosis effect. In this paper, we examine electroosmosis experiments made in a percolation cell in which two gold electrodes are placed in the inner and in the outer chamber. The temperature, the pressure and potential difference, the flow, the current and the chemical composition of water in chambers may be recorded. Experiment consist to the application of electric field through the sample and to observe the evolution of the flow, the electrical current and the chemical dissolution.

I/S and C/S mixed layers from the geothermal field of Chipilapa (El Salvador) have been studied in details in order to reevaluate their potential use as indicator of the thermodynamic conditions in which they were formed. It is funded that overprinting of clay bearing alteration stages is common. For a given alteration stage, the spatial variation of I/S and C/S mixed layer ininerals is controlled by kinetics of mixed layer transformation and not only by temperature. Clay geo-thermometers cannot give reliable results because the present crystal-chemical states of the I/S and C/S mixed layers is not their initial state, it was aquired during the overall hydrothermal history which post dated the nucleation of smectitic clay material at high temperature. Occurrences of smectites or smectite-rich mixed layers at high temperature in reservoirs is a promising guide for reconstruct the zones in which boiling or mixing of non isotherinal fluids occurred very recently or still presently.

The solubility of boehmite, AlO(OH), has been measured as a function of pH (2 - 10, depending on ionic strength), temperature (100 - 250&deg;C) and ionic strength (0.03 - 1 molal, NaCl) in a hydrogen-electrode concentration cell, HECC, which provided in situ measurement of hydrogen ion molality. Samples of the solution were withdrawn after the pH reading stabilized for analysis of total aluminum content by ion chromatography. Acidic or basic titrant could then be metered into the cell to affect a change in the pH of the solution. The direction of approach to the equilibrium saturated state could be readily varied to ensure that the system was reversible thermodynamically. This represents our second application of direct pH measurement to high temperature solubility studies. The results at low ionic strength are compared with those from two recently-reported high-temperature studies of boehmite solubility, which relied on the conventional batch technique. Comparisons are also made with the low temperature (<90&deg;C) hydrolysis constants for aluminum garnered from solubility measurements with gibbsite as the stable phase. Based on these preliminary results, it is possible to draw some general conclusions concerning the relative importance of the aluminum species in solution and to reduce significantly the number …

The thermal conductivities of most major rock-forming minerals vary with both temperature and confining pressure, leading to substantial changes in the thermal properties of some rocks at the high temperatures characteristic of geothermal systems. In areas with large geothermal gradients, the successful use of near-surface heat flow measurements to predict temperatures at depth depends upon accurate corrections for varying thermal conductivity. Previous measurements of the thermal conductivity of dry rock samples as a function of temperature were inadequate for porous rocks and susceptible to thermal cracking effects in nonporous rocks. We have developed an instrument for measuring the thermal conductivity of water-saturated rocks at temperatures from 20 to 350 &deg;C and confining pressures up to 100 MPa. A transient line-source of heat is applied through a needle probe centered within the rock sample, which in turn is enclosed within a heated pressure vessel with independent controls on pore and confining pressure. Application of this technique to samples of Franciscan graywacke from The Geysers reveals a significant change in thermal conductivity with temperature. At reservoir-equivalent temperatures of 250 &deg;C, the conductivity of the graywacke decreases by approximately 25% relative to the room temperature value. Where heat flow is constant with depth …

A variety of hydrocarbons, C₁ - C₁₂, have been found in volcanic gases (fumarolic) and in geothermal waters and gases. The hydrocarbons are thought to have come from products of pyrolysis of kerogen in sedimentary rocks or they could be fed into the geothermal system by the recharging waters which may contain dissolved hydrocarbons or hydrocarbons extracted by the waters from the rocks. In the hot geothermal zone, 300°+ C, many of these hydrocarbons are in their critical state. It is thought that they move upwards due to buoyancy and flux up with the upflowing geothermal fluids in the upflow zones together with the magmatic gases. Permeability which could be provided by faults, fissures, mini and micro fractures are thought to provide pathways for the upward flux. A sensitive technique (Petrex) utilizing passive integrative adsorption of the hydrocarbons in soil gas on activated charcoal followed by desorption and analysis of the hydrocarbons by direct introduction mass spectrometry allows mapping of the anomalous areas. Surveys for geothermal resources conducted in Japan and in Indonesia show that the hydrocarbon anomaly occur over known fields and over areas strongly suspected of geothermal potential. The hydrocarbons found and identified were n-paraffins (C₇-C₉) and aromatics …

The Fiji Department of Energy (DOE) has a comprehensive resource assessment programme which assesses and promotes the use of local renewable energy resources where they are economically viable. DOE is currently involved in the investigation of the extent of geothermal resources for future energy planning and supply purposes. The aim is to determine (a) whether exploitable geothermal fields exist in the Savusavu or Labasa areas. the two geothermal fields with the greatest potential, (b) the cost of exploiting these fields for electricity generation/process heat on Vanua Levu. (c) the comparative cost per mega-watt-hour (MWh) of geothermal electricity generation with other generating options on Vanua Levu, and. (d) to promote the development of the geothermal resource by inviting BOO/BOOT schemes. Results to date have indicated that prospects for using geothermal resource for generating electricity lies in Savusavu only - whereas the Labasa resource can only provide process heat. All geophysical surveys have been completed and the next stage is deep drilling to verify the theoretical findings and subsequent development.

Adsorption phenomena are a rich and rather new field of study in geothermal research, in particular at very high temperature. ENEL is interested in the exploitation of geothermal regions with superheated steam, and it is important to understand the behavior of water-rock interaction. We have analyzed in the 170-200 &deg;C temperature range four samples of Monteverdi cuttings; the next experimental effort will be at 220 &deg;C and over in 1996. The first results of the 1995 runs are collected in this paper. We can highlight four main items: 1. At relative pressures over 0.6 the capillarity forces are very important. 2. There is no significant temperature effect. 3. Adsorbed water can be present, and it is able to multiply by a factor of 15 the estimated reserve of super-heated steam only. 4. Pores smaller than 15 &Aring; do not contribute to the adsorbed mass.

Numerical simulations were carried out to predict pressure transients in a hypothetical deep geothermal well which penetrates a reservoir at super-critical conditions. Production at about 4000 m depth was assumed. In many cases, two-phase conditions develop due to high temperature and production-induced pressure decrease. Several cases in which single-phase conditions are maintained were studied in detail. Pressure transients are influenced by the reservoir temperature distribution - in particular, a temperature distribution with subcritical conditions at the well but supercritical conditions farther away causes a characteristic nonlinear pressure response whlch is influenced by the large compressibility and small kinematic viscosity near the critical point.

Most geothermal reservoirs are extensively fractured and injected fluids usually enter the reservoir formation at distinct feed points. As the cold water passes through the hot rock, it is heated, and may be recovered at production wells for power production. The influence of fractures is two-fold. Firstly, preferential pathways exist along major faults and the general motion of fluids away from injection wells is controlled by the effective permeability structure. Secondly, since fractures can be spaced several metres or more apart and the flow rates within each fracture can be relatively high, the injected fluid does not necessarily attain thermal equilibrium will all of the host rock at a given distance from the injection well. It is important that sufficient heat transfer between the fluid and rock occurs before the injected fluid is recovered at an injection well in order to prevent thermal breakthrough. In this paper we present preliminary results of an experimental research program examining the effects of injection into fractures. We build upon previous theoretical work by seeking to confirm the results and then discuss the initial results of injection into superheated reservoirs.

Source mechanisms of 985 microearthquakes at the Southeast Geysers geothermal field, are investigated using a moment tensor formulation. P- and S-wave amplitude and polarity are utilized to estimate the full, second-order moment tensor, which is then decomposed into isotropic, double-couple, and compensated linear vector dipole components. The moment tensor principal axes are used to infer the directions of principal stress associated with the double-couple component of the source mechanism. Most of the events can be modeled as primarily double-couple; however, a small but significant isotropic component, which can be either positive or negative, is also needed to explain the observed waveforms. Events with positive isotropic components and events with negative isotropic components both occur in areas of steam extraction and in areas of fluid injection. Principal axes of moment tensors with negative isotropic components are aligned with the regional stress field, while those of moment tensors with positive isotropic components differ significantly from the regional stress field. This suggests that two differing inducing mechanisms are required: negative-type events involve local stress perturbations that are small compared to the regional stress, while positive-type events involve stress perturbations which locally dominate over the regional stress.

X-ray attenuation, electrical conductivity, and ultrasonic velocity are reported for a segment of preserved core from SB-15D, 918 ft. X-ray tomography and ultrasonic measurements change as the core dries, providing information regarding handling and disturbance of the core. Electrical conductivity measurements at reservoir conditions indicate that pore fluid properties and pore microstructure control bulk conductivity. These data are useful for calibration and interpretation of field geophysical measurements.

This paper reports on a continuing experimental effort to characterize the adsorption behavior of rocks from The Geysers steam field in California. We show adsorption results obtained for 36 rock samples. All of the adsorption isotherms plotted on the same graph exhibit an envelope of isotherms. The minimum and the maximum values of the slope (or rate of adsorption) and of the magnitude within this envelope of isotherms belonged to the UOC-1 (felsite) and NCPA B-5 (serpentine) samples. The values of surface area and porosity, and pore size distribution for 19 of the samples indicated a very weak correlation with adsorption. An interpretation of the pore size distributions and the liquid saturation isotherms suggests that the change in the slope and the magnitude of the adsorption isotherms within the envelope is controlled primarily by the physical adsorption mechanism instead of capillary condensation. Grain-size and framework grain to matrix ratio are found to be insufficient to characterize this adsorption behavior. An accurate identification of the mineralogy of the samples will be essential to complete this analysis.

The understanding of transport processes that occur in naturally fractured geothermal systems is far from being complete. Often, evaluation and numerical simulations of fractured geothermal reservoirs, are carried out by assuming equivalent porous media and homogeneous petrophysical properties within big matrix blocks. The purpose of this paper, is to present a comparison between results obtained from numerical studies of a naturally fractured reservoir treated as a simple porous medium and the simulation of some real aspects of the fractured reservoir. A general conclusion outlines the great practical importance of considering even approximately, the true nature of such systems. Our results show that the homogeneous simplified evaluation of the energy resource in a fractured system, could result in unrealistic estimates of the reservoir capacity to generate electricity.

The paper describes the plan of the town Altheim in Upper Austria to produce electricity by an Organic Rankine Cycle-turbogenerator in the field of utilization of low temperatured thermal water. The aim of the project is to improve the technical and economic situation of the geothermal plant.

A vapor-dominated reservoir is modelled as a uniform porous medium containing immobile water and mobile steam. Changes in concentrations of different gas species are used to determine the porosity and liquid saturation of the reservoir. The “grid" method provides an incomplete analysis of this type of reservoir, either for water content or reservoir temperature. It is conjectured that the reservoirs of Kamojang and Darajat in Indonesia are significantly wetter than The Geysers, and consequently have greater fluid reserves per cubic kilometre.

By February 1995 the European HDR project at Soultz was operating 6 boreholes: 2 deep hydraulic test wells (GPK-1, 3590 m & GPK-2, 3876 m) and 4 seismic observation wells with depths between 1500 and 2200 m. In 1993 the first section of a deep underground exchanger had been created through massive stimulation (injection of some 45000 m&sup3; of water). Between November 1994 until January 1995 a second deep well, GPK-2, was drilled at the periphery of this exchanger. A complex test programme involving the stimulation of GPK-2 (connecting it to the existing exchanger) and various circulation experiments with different production techniques (flash throttled and unthrottled, submersible pump) and varying injection rates was performed between June and August 1995.

We discuss fluid flow and heat transfer processes during water injection into hot, fluid-depleted vapor zones. Numerical simulations of injection plumes in fractures, modeled as two-dimensional heterogeneous porous media, indicate complex behavior. Under certain conditions it is possible to make detailed quantitative predictions of vaporization behavior. However, when effects of reservoir heterogeneity are dominant it will only be possible to predict the behavior of injection plumes in general terms.

This paper presents a case study of pressure build-up in some geothermal re-injection wells in Sweden. The geothermal heat plant, in which the re-injection wells are used, has been in operation since the beginning of 1985. Each day since the start of the geothermal plant registration of the injection pressure has been done. The paper describes how a stimulation of the gravel pack outside the well screen can improve the hydraulic performance of the well. The stimulation is done by reversing the flow direction in the well. It is also shown how important it is to have a good well completion in order to receive a positive effect of well stimulation. The paper give example of recordings from two different re-injection wells. The recordings from one of the re-injection wells show that there are serious problems in the well, while the other one shows "normal" hydraulic behavior.

The Tatapani Geothermal field, located on the Son-Narmada mega lineament is one of the most intense geothermal manifestation, with hot spring temperature of 98&deg;c. in Central India. 21 Exploratory and thermal gradient boreholes followed by 5 production wells for proposed 300 KWe binary cycle power plant, have revealed specific reservoir parameters of shallow geothermal reservoir of 110&deg;c in upper 350 m of geothermal system and their possible continuation to deeper reservoir of anticipated temperature of 160 &plusmn; 10&deg;c. Testing of five production wells done by Oil and Natural Gas Corporation concurrently with drilling at different depths and also on completion of drilling, have established feeder zones of thermal water at depth of 175-200 m, 280-300 m, maximum temperature of 112.5&deg;c and bottom hole pressure of 42 kg/cm&sup2;. Further interpretation of temperature and pressure profiles, injection test, well head discharges and chemical analysis data has revealed thermal characteristics of individual production wells and overall configuration of .thermal production zones with their permeability, temperature, and discharge characteristics in the shallow thermal reservoir area. Well testing data and interpretation of reservoir parameters therefrom, for upper 350 m part of geothermal system and possible model of deeper geothermal reservoir at Tatapani have been presented …