Well SN-12 in the Seltjarnarnes low-temperature field in SW-Iceland was drilled to a depth of 2714 m in the fall of 1994. The well appeared to be almost non-productive at the end of drilling. A comprehensive ten day stimulation program was, therefore, initiated. The program involved, firstly, high-pressure wellhead injection and, secondly, high-pressure injection below a packer placed at 1412 m depth. After about twelve hours of wellhead stimulation the pressure dropped suddenly, indicating that the well had been stimulated. At the same time the water level response increased suddenly in two near-by monitoring wells. During the second stimulation phase (packer at 1412 m) the well appeared to be stimulated even further. The well eventually produced about 35 l/s with a drawdown of roughly 60 m, and the stimulation had increased the yield of the well by a factor of nearly 60. Thus well SN-12, which appeared to be almost non-productive at the completion of drilling, had turned into a good production well. It is believed that during the stimulation some previously closed fractures, or interbed contacts, reopened connecting well SN-12 to the main fracture system of the geothermal reservoir.

Well AH-4_bis, at the Ahuachapan Geothermal Field is planned to be drilled on the same pad as the former AH-4. A simulation study was carried out for two casing dameters 13 5/8 and 9 5/8” in order to estimate its production and to know its economic feasibility. The simulation results indcate a high probability of production in the range of 7 Mwe, equivalent to 120 kg/s total mass flow rate, 1250 kJ/kg at 6 bar-a for the new well AH-4_bis. Well AH- 17 is good producer, during 1991 after ten years of production, the well was shut-in due to silica scaling problems. A wellbore simulation was carried out in order to predict the new production conditions after the work-over, mainly to estimate the water flow rate in order to reduce the silica scaling. The results indicate a very low water flow rate. The match between the simulated and measured production curves after the work-over was successful. The well AH-18 is located at the southern part of the actual bore field. CEL is planning to expand the borefield at this area and it is neccessary to estimate the possible production condtions at that zone. The results indicate a high probabilty of …

Downhole temperature and pressure, mass flow, and enthalpy measurements on three production wells at Kawerau geothermal field are interpretted to illustrate interference effects between these wells. Feed zone locations within the wells, together with geology and chemistry are discussed. Downhole measurements are made in one well while production flow changes are made on another well to monitor pressure transient effects. The interference effects have implications for planning future production drilling.

A numerical model for geothermal reservoir has been developed. The model used is based on an idealized, two-dimensional case, where the porous medium is isotropic, nonhomogeneous, filled with saturated liquid. The fluids are assumed to have constant and temperature dependent viscosity. A Boussinesq approximation and Darcy’s law are used. The model will utilize a simple hypothetical geothermal system, i.e. graben within horsts structure, with three layers of different permeabilities. Vorticity plays an importance roles in the natural convection process, and its generation and development do not depend only on the buoyancy, but also on the magnitude and direction relation between the flow velocity and the local gradient of permeability to viscosity ratio. This model is currently used together with a physical, scaled-down reservoir model to help conceptual modeling.

The Kakkonda geothermal field is known as a unique field such that a new reservoir was found at about 2500 m in depth after the shallow reservoir ranging from 1000 m to 1500 m had been produced for about eight years. The shallow reservoir is composed of sedimentary rock with igneous rock intrusions, while the deep reservoir is a fractured thin zone located at the top of a large granite intrusion. Between the two, there exist thermally metamorphosed zones. This study aims at integrated interpretation of the top structural surface of the deep reservoir. The data used include well data, microearthquakes, and several metamorphic minerals. Microearthquakes, which are continuously observed at surface, reflect the structural surface of the granite intrusion of the deep reservoir. The metamorphic minerals such as biotite and cordierite caused by strong heat conduction out of the granite also give an image of the structure. Based on the spacings of acoustic emission data, images of the structural surface are extracted statistically. The degree of uncertainty is evaluated. The isograds of the metamorphic mineral distributions are reproduced by a regional heat conduction model.

Kamojang Geothermal Field is one of the best geothermal field in the world, explored since 1918. The field lies 33 km south-east Bandung, West Java. It is located in the centre of a volcanic chain which has progressively grown from WSW to ENE. Three tectonic activities have created current Kamojang structures. Firstly, the circular collapse of Pangkalan, 2 km in diameter whch occupies the central part of the Kamojang field; secondly, NE -SW flults of tensional and lateral origin, are parallel to the magmatic axis; and last, 5 km wide graben is a major expression of NW-SE tensional faults. The faults, having N60 strike in the southeastern part of the field have been identified as a very important structures related to the main target of reservoir Kamojang field. Even if the faults and fractures have been altered in the upper part of the surface and form non permeable seals, the bottom sections may still be highly permeable. Therefore for development drilling one must consider the deep structures instead of just shallow expressions and alteration. Geological correlations between the several wells drilled up to date shows evidence that the structures correspond to the surface features as described above. Case study of …

A preliminary investigation on the propagation of compression waves through a radial system of porous medium filled with steam has been conducted for the case of uniform and non-uniform basic temperature distributions. When a relatively weak pressure disturbance is introduced as a signal source in a uniform temperature system, it is found that the pressure disturbance decays away and smears out as time progresses. However, for the case of a nonuniform basic temperature distribution, the temperature gradient and fluid viscosity give significant effects on the reduction of pressure signal attenuation. The attenuation of the compression waves depends on the wave frequencies. For higher frequencies the strength of the signal decays rapidly, and for lower frequencies the signal could propagate farther away. It is found also that porosity and permeability distributions gives significant effects on the amplitude and the wave profiles.

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.

There are four long-term exploited geothermal fields in Kamchatka: one steam-water field Pauzhetka (south of Kamchatka peninsula) and three hot water fields: Paratunka (near by town of Petropavlovsk-Kamchatsky) and Esso and Anavgay (center of peninsula). Pauzhetka and Paratunka fields are exploited during almost 28 years. Esso and Anavgay fields are exploited during 25 years. In Pauzhetka 11 MWe geothermal power plant work and on the other fields thermal energy of hot water is directly used. Kamchatka region satisfies energetic demands mainly by organic imported fuels. At the same time electricity produced by geothermal fluids constitutes less than 2 per cent of total region electricity production, and thermal energy produced by geothermal fluids constitutes less than 3 per cent of total region thermal energy production. The main reasons of small geothermal portion in the energy production balance of Kamchatka are briefly discussed. The geothermal development reserves and perspectives of geothermal energy use increase in Kamchatka are outlined.

As a part of a full scale production test, a long term tracer test was performed in the Thelamork low temperature geothermal system, in N-Iceland. The tracer test was aimed at recovering the transport properties of fractures connecting the injection and production wells. Hence, the estimated parameters might be used in determining the performance of the system under various injection schemes. A qualitative evaluation the tracer return profile showed the presence of strong recirculation effects. In addition, the return profile indicated that the medium appears to be highly dispersive. Earlier modelling studies employed a one-dimensional two path model to match the return profile and substituted the properties of the major path in the Lauwerier model to estimate the thermal breakthrough time. However, the two path model estimates a very large dispersive tiansport almost equal to the convective transport. This large dispersivity necessitates adding a dispersive heat transport term in the Lauwerier model and as a result reduces the Lauwerier thermal breakthrough time almost to half. Considering the injection and production rates, we used a more accurate one-dimensional five-path model in this work. This model infers a smaller dispersivity and leads to a greater breakthrough time than the two path model, …

Until recently, geothermal reservoir simulators use flat interface thermodynamics to determine the thermodynamic state of the reservoir. Development of new simulators and the modification of existing ones has now incorporated the physics of curved interface thermodynamics. These simulators account for the effects of sorption and capillary forces. The simulators GSS and TETRAD were used to simulate the performance of a hypothetical vapordominated geothermal reservoir. GSS is a simulator specifically developed to account for adsorption by using adsorption isotherms. On the other hand, TETRAD is a commercial simulator that was modified to account for vapor pressure lowering by using capillary pressure relations. GSS and TETRAD yielded similar results. Thus, the two formulations being used to account for curved interface thermodynamics are practically equivalent. Areas for improvement of both GSS and TETRAD were identified. The hysteresis and temperature dependence of sorption and capillary properties are issues that are needed to be addressed.