Geothermal Technologies Office

Geochemical and petrographic studies of the rhyolites and mafic inclusions from Satsuma-Iwojima volcano were carried out in order to investigate evolution of a silicic, bimodal magma system during the post-caldera stage. Abundant mafic inclusions, which are fine-grained with vesicles in their cores, are present in the Showa-Iwojima rhyolitic lava. Inclusions with similar textures are found in Iwodake volcanic bombs but are less common than in the Showa-Iwojima lava. The major and trace element compositions of the inclusions plot along mixing lines connecting the host rhyolites with spatially and temporally associated basaltic to basaltic andesite magmas. Plagioclase phenocrysts in the inclusions have a large variation in core compositions (An42 to An96), and exhibit various zoning profiles and reaction textures, indicating they coexisted with melts ranging from basaltic to rhyolitic composition. Pyroxenes also exhibit a wide range in composition and a variety of zoning patterns consistent with multiple sources. These results suggest that a stratified magma chamber exists beneath the volcano, consisting of a lower basaltic layer, an upper rhyolitic layer and an episodically-present, thin middle layer of andesite. Variations in the chemistry of the Iwodake and Showa-Iwojima mafic inclusions suggest that multiple injections of very similar basaltic magma have occurred since the growth of the Iwodake dome. More extensive textural disequilibrium shows that the Showa-Iwojima rhyolites formed through more extensive interaction with mafic magma. The mafic-felsic interaction is consistent with degassing model of a magma chamber estimated by other researchers, which consists of degassing of upper rhyolitic magma by convection in a conduit and supply of a CO2-rich volatile phase from underlying basaltic magma to the rhyolitic magma.

Realization of EGS development would make geothermal a significant contender in the renewable energy portfolio, on the order of 100+ GWe in the United States alone. While up to 90% of the geothermal power resource in the United States is thought to reside in Enhanced Geothermal Systems (EGS), hurdles to commercial development still remain. The Geothermal Technologies Office, U.S. Department of Energy (DOE), began in 2011 to outline opportunities for advancing EGS technologies on five- to 20-year timescales, with community input on the underlying technology needs that will guide research and ultimately determine commercial success for EGS. This report traces DOE's research investments, past and present, and ties them to these technology needs, forming the basis for an EGS Technology Roadmap to help guide future DOE research. This roadmap is currently open for public comment. Send your comments to geothermal@ee.doe.gov.

Abstract Borehole televiewer, temperature, and flowmeter data recorded in six wells penetrating a geothermal reservoir associated with the Stillwater fault zone in Dixie Valley, Nevada, were used to investigate the relationship between reservoir permeability and the contemporary in situ stress field. Data from wells drilled into productive and nonproductive segments of the Stillwater fault zone indicate that permeability in all wells is dominated by a relatively small number of fractures striking parallel to the local trend of the fault. However, Coulomb failure analysis using our fracture orientations in conjunction with stress orientations and magnitudes determined by Ref. 1 suggests that fault zone permeability is high only when individual fractures as well as the overall Stillwater fault zone are optimally oriented and critically stressed for frictional failure. Fracture geometry may also play a significant role in determining reservoir productivity. The well-developed populations of low-angle fractures present in wells drilled into the producing segment of the fault are not present within the relatively impermeable segment of the Stillwater fault zone. P. 315

Abstract Geothermal energy can provide answers to many of America’s essential energy questions. The United States has tremendous geothermal resources, as illustrated by the results of the DOE GeoVision analysis, but technical and non-technical barriers have historically stood in the way of widespread deployment of geothermal energy. The U.S. Department of Energy’s Geothermal Technologies Office within the Office of Energy Efficiency and Renewable Energy has invested more than $470 million in research and development (R&D) since 2015 to meet its three strategic goals: (1) unlock the potential of enhanced geothermal systems, (2) advance technologies to increase geothermal energy on the U.S. electricity grid, and (3) support R&D to expand geothermal energy opportunities throughout the United States. This paper describes many of those R&D initiatives and outlines future directions in geothermal research.

In 1985, Unocal drilled the first deep test well in the western moat of Long Valley caldera, ∼1 km east of the Inyo Craters. Well IDFU 44‐16 penetrated a thinner section of Bishop Tuff than that found in earlier deep exploration wells on the resurgent dome. Precaldera volcanics were encountered at 1183 m and metamorphic basement at 1615 m. The precaldera volcanics yielded a radiometric age of 1.98±0.1 Ma and are tentatively correlated with Tertiary andesites and dacites on the caldera's western wall. These stratigraphic relations suggest that the caldera's structural margin is at least 4 km east of the current topographic margin. Temperatures reach a maximum of 218°C at 1100 m in IDFU 44‐16; however, temperature reversals occur below this depth. Temperature and permeability measurements indicate a lateral outflow of hot water over cold recharge near the caldera's structural margin. While these discoveries support the existence of hightemperature fluids in the western moat of Long Valley caldera, the ultimate source of the geothermal system remains to be discovered.

Grout is used to seal the annulus between the borehole and heat exchanger loops in vertical geothermal (ground coupled, ground source, GeoExchange) heat pump systems. The grout provides a heat transfer medium between the heat exchanger and surrounding formation, controls groundwater movement and prevents contamination of water supply. Enhanced heat pump coefficient of performance (COP) and reduced up-front loop installation costs can be achieved through optimization of the grout thermal conductivity. The objective of the work reported was to characterize thermal conductivity and other pertinent properties of conventional and filled cementitious grouts. Cost analysis and calculations of the reduction in heat exchanger length that could be achieved with such grouts were performed by the University of Alabama. Two strategies to enhance the thermal conductivity of cementitious grouts were used simultaneously. The first of these was to incorporate high thermal conductivity filler in the grout formulations. Based on previous tests (Allan and Kavanaugh, in preparation), silica sand was selected as a suitable filler. The second strategy was to reduce the water content of the grout mix. By lowering the water/cement ratio, the porosity of the hardened grout is decreased. This results in higher thermal conductivity. Lowering the water/cement ratio also improves such properties as permeability, strength, and durability. The addition of a liquid superplasticizer (high range water reducer) to the grout mixes enabled reduction of water/cement ratio while retaining pumpability. Superplasticizers are commonly used in the concrete and grouting industry to improve rheological properties.

ABSTRACT Well cement carbonation by CO2 containing gas or brine can happen to CO2 flooded oil fields, gas fields and geothermal fields. Due to the Unocal's interests in these applications, especially in the high temperature geothermal wells, a field and laboratory testing program was conducted to examine the effects of CO2 gas on high temperature cement. Wellhead cement samples from geothermal wells in the Brawley and Geysers fields were collected and analyzed for carbonation. The degree of cement carbonation was found to be dependent on factors such as, temperature, CO2 content in the fluid and location. Both the carbonated and the uncarbonated cement have developed extensive fractures and fine fissures in the matrix due to thermal cycles. The carbonated cement has an acceptable level of compressive strength, but its permeability is normally higher than desired. Preliminary results from laboratory cement carbonation tests under simulated downhole high temperature, high pressure conditions are presented. A new analytical technique was used to measure the depth of carbonation. The CO2 diffusion coefficient in the cement solid matrix was estimated with this technique. By comparing field, lab and published data, the carbonation mechanism in high temperature cement is found to be a function of several parameters, i.e., temperature, CO2 content in the fluid and cement additives.

Summary This paper describes the reservoir simulation model developed for East Mesa field properties and summarizes the reservoir engineering evaluation of the reserves and field performance. Geothermal reservoirs should be evaluated in terms of efficient "energy mining" rather than fluid recovery. The results indicate the behavior of the field under various scenarios of development designed to operate a 64-MW electric power plant. Introduction The East Mesa geothermal field is in an area of anomalously high heat flow on the east flank of the Salton Trough at the southeast corner of the Imperial Valley in California. Twenty-four wells have been drilled thus far, including 10 by Republic Geothermal Inc. in the northern portion, five by the U.S. Bureau of Reclamation in the central area, and eight by Magma Power Co. to the south (Fig. 1). Because of the already extensive investigations, a great deal is known about the East Mesa reservoir and its properties. Republic now is proceeding with commercial development at the northern end of the field, starting with a 64-MW power plant project.Geothermal resource development differs most significantly from petroleum resource exploitation in that an additional factor is involvedie., the recovery of thermal energy. The problems of fluid flow in a porous media are, of course, similar to the petroleum industry problems, but the ultimate recovery is measured in terms of energy mining efficiency. The produced fluid acts only as a transport mechanism and may be cycled through the reservoir to extract heat from the rock as many times as is economically feasible.This paper presents the reservoir model developed for Republic's East Mesa properties and summarizes the reservoir simulation study performed to optimize the exploitation of this resource. Reservoir Properties Petrophysical Properties Logs, ditch cuttings, and cores show that the upper 10,000 ft (3048 m) of stratigraphic section at East Mesa is a sequence of deltaic clastic sediments that includes abundant amounts of fine- to medium-grained sandstones, fine- to coarse-grained siltstones, and lesser amounts of mudstones. Mineralogically, the sands are compositionally equivalent to Colorado River delta sands, being mostly quartz (70%), lithic fragments (20%), and feldspars (10%). Post-depositional alterations are principally the addition of authigenic carbonate and quartz as overgrowths and veinlets and the conversion of the detrital phyllosilicates to illite and chlorite.The basic petrophysical properties of sand/shale discrimination, porosity (phi), and permeability (k) employed in the model were obtained from log analyses for eight existing wells in the Republic area (i.e., Producers 16–29, 16–30, 38–30, 58–30, and 78–30/78-30RD and Injectors 18–28 and 52–29). Table 1 summarizes net sand thickness (h), average sand porosity (phi) weighted for the presence of shales, and geometric mean sand permeability (k) for four depth-interval groupings. The data show good sand development in the wells between 2,500 and 7,000 ft (762 and 2134 m). Although the properties vary considerably between wells, they generally improve away from the center of the temperature anomaly, show a gradual decline with increasing depth, and exhibit rapid deterioration below 7,000 ft (2134 m). JPT P. 735^

This report tabulates an extensive geochemical database on waters, gases, scales, rocks, and hot-spring deposits from the Dixie Valley region, Nevada. The samples from which the data were obtained were collected and analyzed during 1996 to 1999. These data provide useful information for ongoing and future investigations on geothermal energy, volcanism, ore deposits, environmental issues, and groundwater quality in this region.

ABSTRACT Republic Geothermal, Inc., and its subcontractors have planned and executed six experimental fracture stimulation treatments under the Department of Energy-funded Geothermal Reservoir Well Stimulation Program (GRWSP). The program, begun in February 1979, is ultimately to include eight full-scale field hydraulic and chemical stimulation experiments in geothermal wells. This paper describes the six treatments completed to date. Two stimulation experiments were performed at Raft River, Idaho, in late 1979. This is a naturally fractured, hard rock reservoir with a relatively low geothermal resource temperature (290°F). A planar hydraulic fracture job was performed in Well RRGP-5 and a dendritic, or reverse flow, technique was utilized in Well RRGP-4. In mid-1980, two stimulation experiments were performed at East Mesa, California. The stimulation of Well 58-30 provided the first geothermal well fracturing experience in a moderate temperature (350°F) reservoir with matrix-type rock properties. The two treatments consisted of a hydraulic fracture of a deep, low-permeability zone and a dendritic fracture treatment of a shallow, high-permeability mud/cement-damaged zone in the same well. In early 1981, an acid etching stimulation treatment was performed in the Ottoboni State 22 well located in The Geysers geothermal area of California. The treatment involved the injection of 476 bbl of 10% HF-5% HCT acid behind a 476 bbl slug of high viscosity crosslinked gel fluid. This technique was intended to take advantage of the fluid mobility differences to etch discrete flow channels, or fingers, in the fracture faces. A 7,600 bbl hydraulic fracture treatment was also performed in early 1981 in the Baca 23 well of the Redondo Creek area of New Mexico. The stimulation interval was in the upper part of the Bandelier Tuff, a 450°F interval in which the well had not encountered productive natural fractures. This treatment utilized a large cooling water prepad and temperature resistant proppants, i.e., sintered bauxite and resin-coated sand. The stimulation experiment results to date were evaluated using short-term production tests, conventional pressure transient analysis, interference pressure data, chemical and radioactive tracers, borehole acoustic televiewer surveys, fracture mapping with geophones, and numerical models. This combination of evaluation techniques yielded an interpretation of fracture geometry and productivity enhancement. A discussion of the pre-stimulation and post-stimulation data and their evaluation are provided for each experiment in this report. Five of the six stimulation experiments were at least technically successful in stimulating the wells. The two fracture treatments in East Mesa 58-30 more than doubled the producing rate of the previously marginal producer. The two fracture treatments in Raft River and the one in Baca were all successful in obtaining significant production from previously unproductive intervals. However, these three treatments failed to establish commercial production due to deficiencies in either fluid temperature or flow rate or both. The acid etching treatment in the well at The Geysers did not have any material effect on producing rate. Evaluations of the field experiments to date have suggested improvements in treatment design and treatment interval selection which offer substantial encouragement for future stimulation work.

Characterizing productive geothermal systems is challenging yet critical to identify and develop an estimated 30 gigawatts electric (GWe) of undiscovered hydrothermal resources in the western U.S. This paper, undertaken by the U.S. Department of Energy’s Geothermal Technologies Office (GTO), summarizes needs and technical pathways that target the key geothermal signatures of temperature, permeability, and fluid content, and develops the time evolution of these pathways, tying in past and current GTO exploration Research and Development (R&D) projects. Beginning on a five-year timescale and projecting out to 2030, the paper assesses technologies that could accelerate the confirmation of 30 GWe. The resulting structure forms the basis for a Geothermal Exploration Technologies Roadmap, a strategic development plan to help guide GTO R&D investments that will lower the risk and cost of geothermal prospect identification. This roadmap is currently open for public comment. Send your comments to geothermal@ee.doe.gov.

Natural gas hydrates may contribute to both future energy supplies and to the increase of atmospheric greenhouse gases. Evaluation of the importance of gas hydrates requires an improved knowledge of the present hydrate distribution. Analysis of thermal and geophysical logs from 369 wells in the Canadian Arctic Islands and the Beaufort Sea-Mackenzie Delta regions indicates that a maximum of 1,900 to 3,900 Gt of methane may be stored as hydrate in this region. Consideration of the recent geological and climatic history of the area demonstrates that the volume of hydrate is variable with time. Decomposition of hydrates is possibly occurring beneath approximately 73,000 km{sup 2} of the Canadian Beaufort Shelf. Approximately 10{sup 5} m{sup 3} hydrate/km{sup 2} may become unstable over a 100 year period due to marine transgression. In contrast, cooling of sediments and hydrate formation is occurring in the Arctic Islands as new land emerges from the ocean in response to isostatic rebound.

Abstract Ratio values of the reflected energy available through different Landsat band-pass filters were formed using laboratory spectra of 284 particulate rock and soil specimens, and the potential for using these data to discriminate among rock types was examined. Based exclusively on the intrinsic spectral information in the multispectral scanner (MSS) bands, thereby excluding textural, geomorphic, and vegetational effects that may occur in the field, it was concluded that the ratios can generally be used to discriminate different lithologic units. Further, only mafic and ultramafic rocks, and alteration involving ferric oxide staining, typically display sufficiently characteristic spectral behavior to allow specific identification. Certain unique features, such as those produced by chrominum in some chloritic quartzites can be used for discrimination of a few rare rock types.

Summary The flow of steam/water mixtures into geothermal wells is analyzed by use of a two-phase model for flashing flow. The model includes the effect of heat transfer from the formation rock to the two-phase mixture. In the reservoir/well system, the two-phase flashing flow is assumed to occur in fractures. The model can be used to forecast the mass flow and enthalpy characteristics of two-phase geothermal wells. Relative permeability functions are derived for flashing steam/water flow in the feed-zone fractures of geothermal wells.

ABSTRACT High temperature make-up and break-out tests were conducted on full size 6–1/4" (15.88 cm) OD × 2–3/4" (6.99 cm) ID NC46 rotary shouldered connections to determine changes in performance between room temperature and 500°F (260°C). The tests measured the slope of the torque vs. rotation curve and the torque required to initiate additional circumferential movement after the tool joint connection had been made up to 20.500 Ibf–ft (27.794 N-m) make-up torque at room temperature (move torque). Results of room temperature tests indicated that the move torque was essentially equal to the make-up torque and the slopes of the torque vs. rotation curves were similar. High temperature tests produced significantly different results. A used connection was torqued to 48,200 Ibf–ft (65.350 N-m) without failure, while a new connection only reached a maximum torque of 25.600 Ibf–ft (34.709 N-m) before failure; a value which is significantly less than the API torque to yield value of 44.871 Ibf–ft (60.837 N-m). It was found that increased thread interference from the rough surface finish typically found oh the thread flanks of "used" connections was responsible for the change in performance. The problem of downhole make-up was successfully overcome in the field by implementation of new break-in procedures and through use of a special high temperature thread compound. This compound was developed to increase the coefficient of friction at high temperatures in new connections to provide additional resistance to downhole make-up during the critical break-in period.

The great majority of earthquakes that occur each year around the world have natural causes. A small number of lesser-magnitude seismic events have been related to human activities and are called “induced seismic events” or “induced earthquakes” (NRC, 2012). Of concern are induced events that are large enough to be noticed by the public, typically events larger than magnitude 3 (note the range earthquake sizes that are felt can widely vary depending on project location and site characteristics). Induced seismic activity has been described since at least the 1920s and attributed to various human activities including the impoundment of water reservoirs, controlled explosions related to mining and construction, underground nuclear tests, and energy technology developments that involve injection or withdrawal of fluids from the subsurface. Historically known induced seismicity has generally been small in both magnitude and intensity of ground shaking.

Abstract The Geysers geothermal field, located in Lake, Sonoma, and Mendocino Counties, California is the largest developed geothermal system in the world. Electric power generation started at The Geysers in 1960 with a 12 MW (gross) plant. The total installed capacity in the field peaked in 1989 at 2,043 MW. As more and more power plants were built during the 1980s and net mass withdrawals increased, reservoir pressures at The Geysers declined, eventually resulting in steam shortfalls and declining generation levels. This net withdraw is due to the fact that geothermal power plants at The Geysers typically lose about 70 to 80% of produced mass to evaporation in cooling towers, with the balance of mass being returned to the reservoir through injection of steam condensate. In response to this decline, field operators made modifications to the pipelines and turbines to be able to operate more efficiently at lower system pressures. Based on studies funded by the California Energy Commission that showed that injection of water from outside sources was the most effective method of managing the long-term decline in the resource, a program of augmented injection, using large volumes of treated sewage effluent, was started in the late 1990s. This program of augmented injection has brought mass injected, more or less, into parity with mass produced, and the rate of reservoir pressure decline has been significantly reduced. Still, optimizing the distribution of augmented injection throughout the field and making corresponding adjustments to plant and pipeline facilities is a complicated process, with many interdependencies. To aid in ongoing optimization of the field, an integrated model has been developed for the Northern California Power Agency (NCPA) that combines reservoir simulation with mathematical modeling of the wellbores, the pipelines, and the power plants. This integrated model, funded in part by the California Energy Commission, has proven very useful for evaluating the most cost-effective improvements to the combination of wells and surface facilities, and to study the benefit of increasing the volume of augmented injection.

At the request of the U.S. Department of Energy, Office of Geothermal Technologies, Sandia National Laboratories convened a group of drilling experts in Berkeley, CA, on April 15-16, 1997, to discuss advanced geothermal drilling systems. The objective of the workshop was to develop one or more conceptual designs for an advanced geothermal drilling system that meets all of the criteria necessary to drill a model geothermal well. The drilling process was divided into ten essential functions. Each function was examined, and discussions were held on the conventional methods used to accomplish each function and the problems commonly encountered. Alternative methods of performing each function were then listed and evaluated by the group. Alternative methods considered feasible or at least worth further investigation were identified, while methods considered impractical or not potentially cost-saving were eliminated from further discussion. This report summarizes the recommendations of the workshop participants. For each of the ten functions, the conventional methods, common problems, and recommended alternative technologies and methods are listed. Each recommended alternative is discussed, and a description is given of the process by which this information will be used by the U.S. DOE to develop an advanced geothermal drilling research program.

Geothermal Well Stimulation Experiments and Evaluation Don A. Campbell; Don A. Campbell Republic Geothermal, Inc. Search for other works by this author on: This Site Google Scholar Charles W. Morris; Charles W. Morris Republic Geothermal, Inc. Search for other works by this author on: This Site Google Scholar Robert V. Verity Robert V. Verity Republic Geothermal, Inc. Search for other works by this author on: This Site Google Scholar Paper presented at the SPE Annual Technical Conference and Exhibition, San Antonio, Texas, October 1981. Paper Number: SPE-10316-MS https://doi.org/10.2118/10316-MS Published: October 04 1981 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Campbell, Don A., Morris, Charles W., and Robert V. Verity. "Geothermal Well Stimulation Experiments and Evaluation." Paper presented at the SPE Annual Technical Conference and Exhibition, San Antonio, Texas, October 1981. doi: https://doi.org/10.2118/10316-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE Annual Technical Conference and Exhibition Search Advanced Search Members SPE-AIMEAbstractRepublic Geothermal, Inc., and its subcontractors have planned and executed six experimental fracture stimulation treatments under the Department of Energy-funded Geothermal Reservoir Well Stimulation Program (GRWSP). The program begun in February 1979, is ultimately to include eight full-scale field hydraulic and chemical stimulation experiments in geothermal wells. This paper describes the six treatments completed to date.Two stimulation experiments were performed at Raft River, Idaho, in late 1979. This is a naturally fractured, hard rock reservoir with relatively low geothermal resource temperature (290 degrees F). A planar hydraulic fracture job was performed in Well RRGP-5 and a dendritic, performed in Well RRGP-5 and a dendritic, reverse flow, technique was utilized in Well RRGP-4.In mid-1980, two stimulation experiments were performed at East Mesa, California. The stimulation of Well 58-30 provided the first geothermal well fracturing experience in a moderate temperature (350 degrees F) reservoir with matrix type rock properties. The two treatments consisted of a hydraulic fracture of a deep, low- permeability zone and a dendritic fracture treatment of a shallow, high-permeability mud/ cement-damaged zone in the same well.In early 1981, an acid etching stimulation treatment was performed in the Ottoboni State 22 well located in The Geysers geothermal area of California. The treatment involved the injection of 476 bbl of 10%. HF-5% HC1, acid behind a 476 bbl slug of high viscosity crosslinked gel fluid. This technique was intended to take advantage of the fluid mobility differences to etch discrete flow channels, or fingers, in the fracture faces.A 7,600 bbl hydraulic fracture treatment was also performed in early 1981 in the Baca 23 well of the Redondo Creek area of New Mexico. The stimulation interval was in the upper part of the Bandelier Tuff, a 450 degrees F interval in which the well had not encountered productive natural fractures. This treatment utilized a large cooling water prepad and temperature resistant proppants, i.e., sintered bauxite and proppants, i.e., sintered bauxite and resincoated sand.The stimulation experiment results to date were evaluated using short-term production tests, conventional pressure transient analysis, interference pressure data, chemical and radioactive tracers, borehole acoustic televiewer surveys, fracture mapping with geophones, and numerical models. This combination of evaluation techniques yielded an interpretation of fracture geometry and productivity enhancement.A discussion of the pre-stimulation and post-stimulation data and their evaluation are post-stimulation data and their evaluation are provided for each experiment in this report. provided for each experiment in this report. Five of the six stimulation experiments were at least technically successful in stimulating the wells. The two fracture treatments in East Mesa 58-30 more than doubled the producing rate of the previously marginal producer. The two fracture treatments in Raft River and the one in Baca were all successful in obtaining significant production from previously unproductive intervals. However, these three treatments failed to establish commercial production due to deficiencies in either fluid temperature or flow rate or both. The acid etching treatment in the well at The Geysers did not have any material effect on producing rate. Evaluations of the field experiments to date have suggested improvements in treatment design and treatment interval selection which offer substantial encouragement for future stimulation work.IntroductionThe stimulation of geothermal wells presents some new and challenging problems. Formation temperatures in the 300-600 degrees F range must be dealt with. Keywords: baca 23, stimulation experiment, drillstem/well testing, stimulation treatment, drillstem testing, hp guar, experiment, fracture treatment, proppant, stimul ati Subjects: Hydraulic Fracturing, Formation Evaluation & Management, Drillstem/well testing This content is only available via PDF. 1981. Society of Petroleum Engineers You can access this article if you purchase or spend a download.

Deposition of CaCO/sub 3/ from natural geothermal fluid was studied by using porous substrates made from several granular materials. These experiments aimed to explore connections between the process of steam flash from superheated CO/sub 2/-charged water and the consequent changes in the carbonate chemical equilibria. The substrates were characterized pre- and post-experiment. Flow rates and compositions of input and output fluids were determined. The resultant CaCO/sub 3/ deposits were examined from several points of view. (MHR)