Geothermal Production Research Articles

Material Balance Depletion Models For Two-Phase Geothermal Reservoirs

Summary Material balance calculations, often referred to as "zero-dimensional" or "lumped element" reservoir evaluations, have been used extensively in petroleum and geothermal engineering. This paper presents a Havlena and Odeh-type material balance depletion model for two-phase reservoirs incorporating adsorption phenomena. A straight line formed between groups of thermodynamic and adsorption properties of water and the cumulative production history provides the initial fluid in place production history provides the initial fluid in place and the size of the vapor-dominated "steam cap." Adsorption phenomena were found to be the controlling mechanism phenomena were found to be the controlling mechanism in the depletion of vapor-dominated geothermal reservoirs. A material balance for vapor-dominated geothermal reservoirs, demonstrating the importance of adsorption phenomena, is presented also. A straight line provides the initial fluid in place. provides the initial fluid in place. Introduction The general approach to the material balance depletion model was first suggested by Schilthuis. The equation provides a volumetric balance between the expansion of provides a volumetric balance between the expansion of reservoir fluids as a result of the cumulative production. Havlena and Odeh, using the Schilthuis approach, developed linear expressions of the material balance equation for a variety of cases including undersaturated, gas-cap-drive and solution-gas-drive reservoirs. I present a similar development for the two-phase geothermal reservoir. Studies of reservoir and production behavior of vapor-dominated geothermal systems have focused on estimates of resource size. Whiting and Ramey presented an application of material and energy balances to geothermal steam production. Ramey applying conventional techniques for natural gas reservoirs, attempted to estimate the reserves of steam in place. Economides and Miller using the experimental results of Hsieh, in which the importance and magnitude of adsorption were demonstrated, introduced a new approach for material balance calculation of vapor-dominated systems. As I will show, desorption is the controlling mechanism in the depletion of vapor-dominated geothermal systems and the major variable in their material balance calculations. The Form of the Material Balance Equation for a Two-Phase Geothermal Reservoir As in the Havlena and Odeh approach, a volume balance in reservoir cubic feet [m3] may be written (in their work they used res bbl [res m3]): underground withdrawal equals expansion of liquid water, plus boiled-off water, plus expansion of steam cap, plus expansion of desorbed water, plus reduction in the PV. The reduction in PV will be neglected in the case of two-phase and vapor-dominated systems, as has been demonstrated for saturated reservoirs. Fig. 1 is a schematic of the two-phase geothermal model used in this analysis. Expansion of Liquid Water and Boiled-Off Water This term contains two components:liquid water expansion andboiled-off steam expansion. suppose that Wi lbm [kg] were present originally; then WiVli would be the initial volume while Wivl would be the volume at a lower pressure. Hence, the difference would provide the liquid expansion W i (vl-vli)................................(1) The boiled-off steam is taken here as the difference between the product of the initial liquid in place and the corresponding evaporation specific volumes at the given pressure interval. This is analogous to the product of the pressure interval. This is analogous to the product of the initial oil in place, the solution GOR, and the gas FVF in the Havlena and Odeh analysis. In both cases the difference depicts the expansion of the evolved gas. Wi (vlg-vlgi)...............................(2) Expansion of Steam Cap The total mass in the steam cap is taken as mWi, where m is expressed as the ratio of the mass of water in the vapor-dominated zone to the mass in the liquid-dominated zone. Then the expansion of the steam is given by mWi(vg-vgj).................................(3) Expansion of Desorbed Steam As presented by Economides and Miller, the volume occupied by desorbed fluid is given by mrM(Xi-X)vg.................................(4) where mr is the mass of rock, M is the molecular weight (18 in the case that no noncondensable gases exist in appreciable quantities), and Xj and X are the masses of adsorbed water in lbm-mol/lbm [gmol/g] of rock in the pressure increment. pressure increment. JPT P. 1305

Long-distance acoustic emission monitoring of hydraulically induced subsurface cracks in nigorikawa geothermal field, Japan

Acoustic emissions (AE) during a massive hydraulic fracturing experiment in a geothermal production well in Nigorikawa field, Hokkaido, Japan, were measured using an acceleration sensitive downhole AE sonde installed in a 30 m well. Crack extensions at a depth of 1500 m were detected and characterized by long-distance AE measurements. The mechanism by which productivity was increased in the geothermal well through hydraulic fracturing has been represented by a model based on AE data and geological considerations.

Section 3 Fluid production technology: state-of-the-art, potentialities and limitations

This report deals with fluid production technology based on the drilling of geothermal wells to depths of 1000-2000m. Present technology is essentially that used in oil-drilling. It is only in exceptional cases, involving the exploitation of water deposits close to the surface, that well-drilling technology in any way resembles the drilling of wells for water. The author points out the differences in geothermal well drilling, well completion and production technology as compared to oil technology.

Induced seismicity in The Geysers Geothermal Area, California

A simultaneous inversion for hypocenters, velocities, and station delays was performed from the P arrival times of 55 microearthquakes and four explosions distributed throughout a 90‐ by 100‐km region centered at The Geysers geothermal area in northern California. The resulting one‐dimensional layered model shows velocity increasing with depth from 4.4 km/s at the surface to 5.9 km/s at 8 km and deeper. We relocated 7215 earthquakes which occurred between May 1975 and February 1982, using the new velocity model. These relocations show a significant spatial clustering near production wells in the steam field that was not apparent in earlier studies. We infer from the spatial and temporal pattern of seismicity that the seismicity at The Geysers is induced by geothermal production activities. With the expansion of power production by approximately 70% in 1979–1980, seismic activity has developed near the new production areas. Seismicity has also expanded northwestward of the present production area, although there are no active steam wells in this area. Statistical cross correlations between the number of earthquakes per month and both steam withdrawal per month and injection volume per month were calculated. For the wells studied, we find no consistent pattern of correlation between injection and seismicity. Likewise, we find little or no correlation between steam withdrawal and seismicity for steam wells in production longer than 7 years. Two mechanisms remain plausible for inducing seismicity at The Geysers. Volumetric contraction due to mass withdrawal may perturb the stress field and cause faulting in reservoir rock already near failure due to the regional stress field. Alternatively, aseismic deformation due to regional tectonic stress may be converted to stick‐slip(seismic) deformation due to an increase of coefficient of friction along fault surfaces, such as could occur from exsolution of dissolved silica into fractures. Neither mechanism would be likely to show strong correlation between production and seismicity rates. However, we expect seismicity to continue in The Geysers and for seismicity to appear in areas where new production occurs.

Geologic and Geothermal Fluid Flow Models of Cerro Prieto Field: ABSTRACT

A detailed hydrogeologic model of the liquid-dominated Cerro Prieto geothermal field in Mexico (located in Baja California about 35 km [22 mi] south of the U.S. border) has been developed to identify subsurface geothermal fluid flow paths. This was accomplished by integrating downhole temperature profiles and depth of production intervals with a geologic model derived from the interpretation of geophysical and lithologic well logs. Two different methods were used to define the geologic model of the Cerro Prieto field. In the first, the lithology was divided into seven different formations based on correlatable groups of beds having distinct lithologic, structural, and fluid production characteristics. In the second method, the lithology was classified into three basic types of lithofacies: shales, sandy shales, and sands. Faults identified by the first method were incorporated into lithofacies sections. Figure Geothermal fluid flow paths were identified by integrating well temperature profiles and the depths of geothermal well production intervals with the lithofacies cross sections. Hot fluids are believed to enter the field at depths greater than 3,000 m (10,000 ft) from the east through a thick, porous sand unit, called Sand Unit Z, which dips gently to the east. This unit underlies a 450 to 600 m (1,500 to 2,000 ft) thick low porosity shale unit, named Shale Unit O, which acts as a local caprock. The fluids flow westward until they encounter a normal fault, Fault H, with downthrow to the southeast. The fluids then move up along this fault until they again encounter Sand Unit Z along the upthrown side of Fault H. Whereas most of the fluids continue to flow westward through Sand Unit Z, a small portion rise along Fault H, as evidenced by high temperatures found at shallow depths in the faulted region. The westward flow continues until it reaches a gap in the overlying Shale Unit O. There, some of the flow rises up and into the western Shale Unit O, which is sandier in this region, while the rest continues to flow westward through Sand Unit Z. Eventually, some of the geothermal fluids leak to the surface, whereas the rest mix with colder waters that surround the geothermal system. A number of cross sections detailing the subsurface movement of the geothermal fluids are shown. This hydrogeologic model is consistent with other geologic, geophysical, geochemical, and reservoir engineering studies carried out at this field. End_of_Article - Last_Page 477------------

Chemical Characterization Problems of Water-Soluble Polymers

Abstract Water-soluble polymers are being used increasingly in oil, gas, and geothermal production. Applications include drilling, stimulation, workover and completion, and reservoir flooding fluids. The development of polymers and their application has been mostly empirical. Such a course of development was suitable in the past. However, empirical techniques do not satisfy present and future needs which include (1) the cost/performance relationship and (2) environmental effects associated with expanding polymer application. Therefore, a more thorough understanding of the polymer chemistry is required. The first step in doing this is to develop laboratory methods to characterize these complex materials and their degradation products. The problems are (1) understanding polymer chemistry under field conditions and (2) developing analytical procedures. These problems emerged dramatically during analysis of recent fracture stimulation of some geothermal wells. An involved study of the potential analytical methods was conducted. Polysaccharides were used for the actual field fracture jobs as well as for the analytical procedures. Correlations were made between the total organic content and carbohydrate content of the return waters as a function of residence time under simulated reservoir conditions. Preliminary indications are that more sophisticated information can be obtained by the use of emerging analytical techniques such as high pressure liquid chromatography (HPLC). Advantages gained from use of these methods and others are discussed.

Drilling Fluid Disposal

Summary A maze of U.S. regulations and regulatory agencies coupled with uncertainty in interpretation of environmental data and an evolving system of disposal engineering will require industry action to monitor the area and derive a solid engineering basis for disposal of spent drilling fluid. A set of disposal methods with approximate costs is presented to serve as an initial guide for disposal. Introduction In the past 10 years, regulatory practice for waste disposal has changed radically because of the imposition of environmental legislation at the federal level; the Clean Water Act (CWA), Resource Conservation and Recovery Act (RCRA), and the Toxic Substance Control Ant (TSCA) all bear on this new industrial problem. The drilling industry has been exempted temporarily from direct application of part of this regulatory action by the 1980 Solid Waste Disposal Act Amendments. This exemption may end in Oct. 1982, at which time the U.S. Environmental Protection Agency (EPA) administrator is to have determined whether hazardous waste classification is appropriate for any drilling fluids. Within 6 months, Congress would have to pass additional legislation to place the recommendations into appropriate actions. In spite of the federal moratorium on regulatory control, another phase of the RCRA is intended to transfer federal management of the hazardous waste program to state agencies. Following EPA approval, program to state agencies. Following EPA approval, the states will assume prime responsibility for RCRA management and enforcement. This transfer process and the degree to which it already has been accomplished has been reviewed in Ref. 1. This review includes a list of the states whose RCRA programs have been approved by EPA. Once its state plan is approved, each state becomes eligible for federal money that EPA has allocated to manage and implement RCRA. This amounts to $30 million in fiscal 1981; EPA has requested $41.7 million for fiscal 1982 for this state program. The state agencies, thus, are assuming the regulatory and enforcement procedures initiated by EPA and will have considerable autonomy in selection of EPA's guidelines for enforcement. Variations in state programs undoubtedly will complicate drilling operations, although local agencies will understand the local situations better than federal rule makers. This paper reviews the background of waste management for drilling fluid disposal. It presents a brief outline of suggested disposal methods, their approximate costs, rig safety and fluid management suggestions, and a suggestion to build an API data base on state agency waste management as it applies to drilling fluid disposal. Disposal methods considered are (1) fluid ejection, (2) pit and solids encapsulation, (3) injection into safe formations, (4) removal to disposal sites off location, (5) separation into clean solids and clean fluid, (6) incineration, (7) microorganism processing, (8) distillation, liquid extraction, and chemical fixation, and (9) traditional solids control. Discussion Laws Forming Basis of Regulatory Actions Federal. Federal laws include the CWA, RCRA, and TSCA. Miscellaneous State and Local Agency Laws. Currently, disposal of drilling fluids has been exempted from the direct application of the federal RCRA rules by the 1980 Solid Waste Disposal Act Amendments Some quotes from this amendment may help explain a continuing obligation of regulatory control that essentially has been transferred from the EPA to state agencies for enforcement. Sec. 7 of the 1980 amendment states, "Drilling fluids, produced waters, and other wastes associated with the exploration, development, or production of crude oil or natural gas or geothermal production of crude oil or natural gas or geothermal energy shall be subject only to existing State or Federal regulatory programs in lieu of subtitle C until at least 24 months after the date of enactment of the Solid Waste Disposal Act Amendments of 1980 and after promulgation of the regulations in accordance with subparagraphs (B) and (C) of this paragraph." paragraph." JPT P. 2377

A Comprehensive Wellbore Steam/Water Flow Model for Steam Injection and Geothermal Applications

Abstract A comprehensive mathematical model was developed to simulate the downward or upward flow of a steam/water mixture in a well. Comparisons of model predictions with actual field data for both steam injection for oil recovery and geothermal production showed the validity of the model. The proposed model is based on mass and momentum balances in the wellbore and on heat balance in the wellbore and the surrounding media. Unlike the previous models, the pressure calculation accounts for slip and the prevailing flow regime, based on noted correlations. Furthermore, heat loss to the surrounding formations is treated rigorously. The overall heat transfer coefficient involved permits the consideration of a variety of well completions. The model was employed for a series of tests to evaluate the effects of the injection pressure, injection rate, time, and well completion on the downhole steam pressure and quality. It was found that the slip concept and the flow regime are essential elements in wellbore steam/water flow calculations. Pressure drop was found to increase with a decrease in the injection pressure, as also with more obvious parameters. An increase in the injection pressure or tubing size and/or a decrease in the injection rate led to a decrease in steam quality at a given depth.

Geologic and Geophysical Study of Cerro Prieto Geothermal Field, Mexico: ABSTRACT

The Cerro Prieto geothermal field is near the southwestern margin of the Colorado River delta, Baja California. The subsurface stratigraphy at Cerro Prieto is characterized by complex vertical and lateral variations in lithofacies, which is typical of deltaic deposits. The geothermal production zone is not a uniform reservoir layer overlain by a laterally continuous top seal of low-permeability strata. The top of the geothermal-related hydrothermal alteration zone has a dome-like configuration which cuts across the sedimentary strata. Shales in the altered zone exhibit high densities and high resistivities on the well logs relative to those outside the zone. The geothermal producing intervals generally straddle or underlie the top of the altered shale zone. Sandstones in the hydrothermal alteration zone commonly have fair to good porosities (15 to 35% or higher), which have resulted from the removal of unstable grains and carbonate cement by solution. Open fractures are unusual in the altered zone, based on core description. While fractures may be an important contributor to local reservoir permeability, secondary matrix porosity and permeability are considered to be more important volumetrically in the Cerro Prieto reservoirs. Detection of geothermal anomalies in the Cerro Prieto region may be difficult from resistivity, magnetic, or gravity data. However, the occurrence of a reflection-poor zone coincident with the hydrothermal alteration zone suggests that the seismic reflection method may be a good approach to detecting these anomalies. Other types of geophysical data are necessary to eliminate alternate causes of reflection-poor zones on seismic profiles. End_of_Article - Last_Page 951------------

Coatings in geothermal energy production

Geothermal energy has a forecasted potential of 25000 MW years of electrical and 16 000-67 000 MW years of thermal energy capacity by the year 2000. Current estimates indicate that lower temperature resources exist in at least 39 states. The development of these resources requires a wide range of cost-effective materials. The purpose of this paper is to review geothermal conditions and the present use of coatings in geothermal production, and to assess the potential for their future applications. The early identification of such materials needs is an essential step for planning the total requirements for well drilling and facilities construction in all sectors of the energy program.

Seismicity of the Coso Range, California

A 16‐station seismographic network, approximately 40 km north‐south by 30 km east‐west, was installed in the Coso Range, California, in September 1975 as part of a geological and geophysical assessment of the geothermal resource potential of the range. During the first 2 years of network operations, 4216 local earthquakes (0.5 ≤ m ≤ 3.9) defined zones of seismicity that strike radially outward from a Pleistocene rhyolite field located near the center of the Coso Range. Most earthquakes were located in zones showing a general northwest trend across the range. Six earthquake swarms occurred within the area that includes the rhyolite field. Fault plane solutions show regional north‐south compression: earthquakes located in northwest striking zones generally had right lateral strike slip focal mechanisms, those in northeast striking zones left lateral strike slip focal mechanisms, and those in north‐south striking zones both normal and strike slip focal mechanisms. Earthquake depths showed little variation across the Coso Range; the depth distribution is similar to that of several carefully studied segments of the central San Andreas fault. The b value calculated for the entire range is 0.99±0.08. The rhyolite field has a significantly higher b value of 1.26±0.16; if only the shallow events (depth <5 km) are used in the calculation, the b value for this area becomes even higher, 1.34±0.24. The higher b values were interpreted as reflecting the existence of short average fault lengths (<5 km) within the rhyolite field. The seismic data and other data suggest that the fault system lying between the rhyolite field and the adjacent Coso Basin is an important tectonic boundary. Present information is insufficient to determine the geothermal production capability of this fault system, but it does suggest that the system is a good target for further exploration.

Elimination of Water Line Blockage by Colloidal Silica during Geothermal Production of Electricity

Elimination of Water Line Blockage by Colloidal Silica during Geothermal Production of Electricity

Measured crustal deformation in Imperial Valley, California

Precise geodetic surveys since 1972 indicate that significant vertical deformation of the land surface continues in Imperial Valley, California. Measured vertical changes as great as 3–5 cm per year indicate that two types of tectonic movement are occurring: (1) a downward regional tilt of the valley surface from the Mexican border northward toward Salton Sea, and (2) a deepening of the structural trough presently occupied by Salton Sea. A comparison of 1972ndash;1977 change contours with 1927 topographic contours shows gross parallelism, suggesting that the recent deformation is a continuation of the tectonism that formed the Salton trough. Ground movement since 1972 has tended to steepen slightly the gradients of streams, canals, and drains on the valley floor and to increase the capacity of Salton Sea. A usable record of eight years of background measurements of tectonic change are available prior to the impact of geothermal production in Imperial Valley.

Regional and local networks of horizontal control, Cerro Prieto geothermal area

The Cerro Prieto geothermal area in the Mexicali Valley 30 km southeast of Mexicali, Baja California, is probably deforming due to (1) the extraction of large volumes of steam and hot water, and (2) active tectonism. Two networks of precise horizontal control were established in Mexicali Valley by the U.S. Geological Survey in 1977 – 1978 to measure both types of movement as they occur. These networks consisted of (1) a regional trilateration net brought into the mountain ranges west of the geothermal area from survey stations on an existing U.S. Geological Survey crustal-strain network north of the international border, and (2) a local net tied to stations in the regional net and encompassing the area of present and planned geothermal production. Survey lines in this net were selected to span areas of probable ground-surface movements in and around the geothermal area. Electronic distance measuring (EDM) instruments, operating with a modulated laser beam, were used to measure the distances between stations in both networks. The regional net was run using a highly precise long-range EDM instrument, helicopters for transportation of men and equipment to inaccessible stations on mountain peaks, and a fixed wing airplane flying along the line of sight. Precision of measurements with this complex long-range system approached 0–2 ppm of line length. The local net was measured with a medium-range EDM instrument requiring minimal ancillary equipment. Precision of measurements with this less complex system approached 3 ppm for the shorter line lengths. The detection and analysis of ground-surface movements resulting from tectonic strains or induced by geothermal fluid withdrawal is dependent on subsequent resurveys of these networks.

Three-Dimensional Geothermal Reservoir Simulation

Abstract This paper presents the development of a three-dimensional, finite-difference model for the simulation of geothermal reservoirs. The model is designed to simulate geothermal reservoirs that contain water in any of its vapor or liquid states and provisions are included for properly treating changes provisions are included for properly treating changes of state during a time step. This logic provides for a stable calculation of state change and eliminates pressure, heat balance, and material-balance errors. pressure, heat balance, and material-balance errors. Mass and energy balances are solved simultaneously using an implicit pressure-explicit saturation (IMPES) formulation. An implicit treatment of production rates, capillary pressure, and transmissibilities is included as an option. Thus, entire field, cross-sectional, or individual well studies can be performed efficiently. Example problems are presented to demonstrate the model's utility and to provide insight into the nature of geothermal production under various conditions. In particular, an example is presented of a reservoir initially containing subcooled liquid where fluid conditions near the production well range from subcooled liquid to saturated steam and then to superheated steam. Introduction Geothermal energy represents an essentially untapped, alternate source of energy world-wide. Exploration for this type of energy has increased, however, and should lead to the discovery and development of new geothermal areas. Notable producing geothermal fields include Wairekei in producing geothermal fields include Wairekei in New Zealand, Cero Prieto in Mexico, Matsukawa in Japan, Larderello in Italy, and The Geysers in California. Recently, industry literature has dealt with zero-(one-cell), one-, and two-dimensional, geothermal reservoir simulation. Most studies treat steam in only one state or mention the difficulty of simulating blocks that change from one state to another. Whiting and Ramey presented a zero-dimensional, geothermal model that included water influx. They discussed reservoir performance during the various states that steam can assume. Their study also included a successful match of the pressure/ production performance of the Wairekei geothermal production performance of the Wairekei geothermal reservoir in New Zealand from 1956 to 1966. Coats developed a three-dimensional, finite-difference, steam-flooding model that simultaneously solved the mass and energy equations. An IMPES formulation was used to solve for pressures implicitly followed by a solution for temperatures, saturations, and so forth. Saturations calculated using explicit rates, capillary pressures, and transmissibilities were recalculated at the end of each time interval, using an implicit formulation for these variables. Brigham and Morrow discussed the P/Z behavior of geothermal steam reservoirs. Their model was similar to Whiting and Ramey's model, but they allowed for the presence of a vapor and liquid zone. Mass and energy balances were written for both zones, and logic for a constant or falling liquid level was included. Martin analyzed internal steam drive in geothermal reservoirs by assuming that temperature, pressure, and fluid saturation gradients as well as capillary pressure and gravity were negligible. Gould described the development of a vertical two-phase, pressure-drop calculation for flow in geothermal wells. He discussed the effect of heat transfer to the surrounding formation and the effect of steam quality on production. Mercer and Faust developed a two-dimensional (areal), two-phase geothermal model using a Galerkin finite-element formulation in space and finite-difference formulation for time. They chose pressure and enthalpy as dependent variables and pressure and enthalpy as dependent variables and solved for these two variables simultaneously. They presented a 10-month simulation of a hypothetical hot-water reservoir with initial conditions similar to those in the Wairekei reservoir. No provisions were included during the course of a run for changing states - for example, from subcooled liquid to saturated steam. SPEJ P. 151

Analysis of Internal Steam Drive in Geothermal Reservoirs

Petroleum reservoir analysis methods are applied to simple closed geothermal reservoirs that produce by internal steam drive. The fundamental assumption is that fluid flow in a geothermal reservoir can be treated as flow through a porous medium, and Darcy's law and relative permeabilities are applicable. Calculated performances are given for various types of reservoirs. Results indicate that hot-water reservoirs can have complicated behaviors. Introduction Testing of geothermal energy prospects has accelerated in recent years. Increased understanding is needed of the fundamental heat and fluid flow involved in geothermal reservoir production. Techniques used by petroleum production researchers are particularly well suited to the study of these fundamentals and to geothermal reservoir engineering research in general. Some geothermal reservoirs are similar to oil and gas reservoirs. These reservoirs are porous media through which the fluids flow according to Darcy's law. Furthermore, some geothermal reservoirs have the equivalent of cap rocks. The analogy of geothermal reservoirs with oil and gas reservoirs is the basis for the fundamental assumption of this paper; fluid flow in a geothermal reservoir can be treated as flow through a porous medium, and Darcy's law and relative permeabilities are applicable. There are many analogies between petroleum and geothermal reservoir engineering. For example, a number of the drives that supply reservoir energy are similar. The edge water drive in a petroleum reservoir is analogous to influx from cooler aquifers in geothermal reservoirs. Solution gas drive in petroleum reservoirs is analogous to two-phase, internal steam drive in geothermal reservoirs. Compaction drive can occur in both types of reservoir. Waterflooding an oil reservoir is analogous to water cycling in a hot-water geothermal reservoir. Methods of analysis similar to those used in petroleum reservoir engineering can be used for geothermal reservoirs, as illustrated by the development of the material and heat balances in Ref. I. The present paper presents an analysis of internal steam drive using methods similar to those used for solution gas drive in Ref. 2. The analysis is based on the following assumptions. The temperature, pressure, and fluid saturation gradients are small; the steam and hot water are produced according to their respective mobilities as determined by relative permeabilities and viscosities; and the effects of capillary pressure and gravity can be neglected. Some gravitational effects, however, are treated qualitatively in the discussion. Throughout the analysis and discussion, the produced steam and hot water are calculated neglecting the pressure and temperature drops near the wells and in the well bores . The effects of these additional changes must be introduced to obtain steam and hot-water production rates at the wellhead. Discussion Temperature-Pressure Behavior As pointed out in Ref. 1, initial temperature and pressure in a geothermal reservoir determine its reservoir type. The solid line in Fig. I presents the boiling curve for pure water. (Curves for actual geothermal brines will be modified by the dissolved salts.3) Points to the right of the curve and below the critical temperature represent hot-water reservoirs. Points to the left of the curve and above the critical temperature represent single-phase or steam reservoirs. Temperature-Pressure Behavior As pointed out in Ref. 1, initial temperature and pressure in a geothermal reservoir determine its reservoir type. The solid line in Fig. I presents the boiling curve for pure water. (Curves for actual geothermal brines will be modified by the dissolved salts.3) Points to the right of the curve and below the critical temperature represent hot-water reservoirs. Points to the left of the curve and above the critical temperature represent single-phase or steam reservoirs.

Energy in the 1980s - Geothermal power

This paper deals mainly with the development of utilization of endogenous fluids in the world and particularly in Italy, together with a forecast of the potential increase in geothermal production. At the end of 1972 the installed capacity of the world’s geothermoelectric plants was approxim ately 1000 M W , of which 390.6 M W are installed in Italy. In the same year the electric energy generated by Italian power stations was 2582.4 GW h. In some countries, geothermoelectric energy costs ranged from 1.4 to 2.5 U.S. mills/M J (5 to 9 mills/kW h) as com pared with 1.66-3.9 U.S. mills/M J (6-14 mills/ kW h) for alternative sources. T he total geothermal capacity in the world is expected to double and perhaps to triple in the 1980s, as new installations are being constructed or planned in several therm al areas. The utilization of geothermal fluids for evaporating low-boiling liquids (freon, isobutane, etc.) or for driving a gravim etric loop, offers attractive possibilities of using therm al waters also for the generation of electricity. In many countries, low enthalpy fluids are used directly for other purposes (domestic and greenhouse heating, refrigeration and air-conditioning, production of fresh water, drying seaweeds and diatomites, etc.). The cost of geothermal heat thus employed is 0.7-1.2 $/GJ as com pared with about 2.6 $/GJ if fossil fuels are used. Due to this attractive cost, in the next few years there should be a rem arkable development in this type of utilization of low enthalpy fluids.

Geothermal production of electrical energy and certain minerals

Energy sources of Uganda actually exploited are traditional and are not sufficient to cover the energetic need of the country for the next few years. The author gives a list of the geothermal manifestations in the country and considers that their exploitation could be of great interest both from an energetical point of view and for certain minerals contained herein.

Present state of drilling and repairing of geothermal production wells in Japan

Since Japan is a prominently volcanic country, it is blessed with many hot springs and abundant geothermal resources. As a result of exploration during the past ten years, many geothermal wells were drilled, and geothermal electric power stations have been constructed in two areas of Matsukawa in the Iwate Prefecture and at Otake in Kyushu. Drilling accomplishments in the areas of Shikate in Hokkaido, Matsukawa and Takinoue in Iwate Prefecture, Hachimantai in Akita Prefecture, Onikobe in Miyagi Prefecture, and Takinoyu and Otake in Kyushu will be described in this report.

Geothermal Energy: ABSTRACT

The search and utilization of geothermal energy commenced in Italy in the early 1900s. Today, Italy produces sufficient power from geothermal energy to operate its entire network of electric railroads. This amounts to approximately 400,000 kw. One hundred areas in 15 different countries are being explored for geothermal energy. Other countries which are currently utilizing geothermal energy are: Iceland, for domestic and industrial heating; Japan, for electrical power and recovery of salt from sea water; and New Zealand, U.S.A., and Mexico for electrical power. The Geysers area of northern California was first investigated for its geothermal potential in 1922. The project was not successful as there was sufficient electrical power being produced from fossil fuel and by hydroelectric plants. The rapid industrialization and population explosion in the western states have led to an increase in demand for energy. From 1945 to 1960, electrical power production increased 239% for the nation and 252% in the western states. The FPC predicts a 275% rise nationally by 1980, based on 1960 power demands, with a forecast of 320% rise for the western states. To meet these demands for electrical power, all forms of energy known to man must be harnessed. The first commercial geothermal power production, in the United States, began at The Geysers in 1960 at the rate of 12,500 kw. In April 1967 the capacity was increased to 56,000 kw. It is estimated that the capacity can be increased to 1,000,000 kw. Recognizing geothermal energy as a source of power, the U.S. Geological Survey is conducting a nation-wide investigation of all geothermal areas which may have this potential. The state Bureaus of Mines of California, Oregon, Nevada, Utah, and New Mexico have conducted their own studies to evaluate their geothermal areas. Locating a geothermal area which may have commercial power potential is difficult. The most obvious areas of hot springs and geysers currently are being investigated. It is conceivable the areas which may hold the greatest potential cannot be detected at the surface. The drilling and development of a geothermal area are extremely hazardous and expensive, but technical problems will be solved, and costs reduced, as future increased power demands escalates the exploration for geothermal power. End_of_Article - Last_Page 1905------------