Liquid-dominated Geothermal Reservoirs Research Articles

Temperature-Transient Analysis for Matrix Linear Flow Toward Infinite-Conductivity Hydraulically Fractured Wells

SummaryThis work presents novel analytical temperature-transient solutions for matrix linear flow toward an infinite-conductivity hydraulically fractured well producing under specified constant rate (CR) or constant bottomhole pressure (CBHP) production. The solutions apply to the single-phase flow of a slightly compressible fluid with constant viscosity (e.g., undersaturated oil reservoirs with irreducible water saturation or liquid-dominated geothermal reservoirs). They include the effects of conduction, convection, the Joule-Thomson (J-T) expansion of fluids and adiabatic expansion of the total rock and fluid system, and fluid loss fracture damage and assume constant rock and fluid physical and thermophysical properties with pressure and temperature. They are obtained by using Laplace (for CR) and Boltzmann (for CBHP) transformations. To validate the analytical solutions, an in-house numerical solution is also developed. It solves the mass and thermal energy balance equations coupled simultaneously and accounts for the variation of rock and fluid properties with pressure and temperature. The in-house simulator was validated by using a commercial reservoir simulator. Results indicate that the fracture surface temperature is decreasing with a square root of time for CR production but is constant for CBHP production. The temperature responses for both modes of production are controlled by the adiabatic expansion of the rock and fluid properties and the thermal diffusivity of the rock. The effect of thermal conductivity plays a significant role in both production modes as the matrix permeability decreases. The fracture damage has different signatures on temperature transients depending on the mode of production. The approximate analytical solutions show the information content of temperature-transient data acquired from an infinitely conductive hydraulically fractured well under matrix linear flow. They are simple and can be used to perform matrix linear-flow analysis jointly with pressure and rate transient data to estimate the physical and thermophysical properties of the rock and fluids. We also propose a simple correction to fluid viscosity variation as input for the analytic solutions to accurately estimate the physical and thermophysical parameters in case drawdowns are significant.

Sensitivity Analysis Using One-Factor-at-a-Time and Response Surface Method in Liquid-Dominated Geothermal Reservoir

In addition to extensive information that has been obtained from pre-feasibility, exploration, and drilling phase, we can improve our knowledge of reservoir behavior related to thermal extraction using sensitivity analysis. Such analysis is commonly applied to address technical uncertainty and risks in economic evaluation. The purpose of this study is to determine the parameters that have the most influence on thermal power generation using two different approaches named one-factor-at-a-time or OFAT and response surface method or RSM. Moreover, RSM analysis allowed us to make a predictive model for thermal power extracted in liquid-dominated geothermal reservoir. Literature study is conducted to understand various properties commonly encountered in a liquid-dominated geothermal reservoir including porosity, conductivity, reservoir temperature, and permeability. This information is then used to construct reservoir model in CMG STARS simulator with a single producer and injector. Two different sampling method, named OFAT and Box-Behnken are used to construct dataset, each contains different combination of levels of reservoir porosity, conductivity, temperature, permeability, and re-injection temperature. A total of 31 models using OFAT method with 7-level for each parameter are simulated to understand individual effect of each parameter. Meanwhile, 47 models are constructed using RSM method with 3-level for each parameter to evaluate the effect of interaction between parameters on thermal generation potential as well as constructing predictive model. Sensitivity analysis using both OFAT and RSM agree that the reservoir temperature is the most significant characteristic of geothermal reservoir to affect its thermal power potential. Meanwhile, re-injection temperature that initially expected to strongly effect the lifetime and sustainability of a liquid-dominated geothermal utilization is insignificant. This finding suggest that optimization re-injection temperature is solely for the purpose of maintaining sustainability of geothermal reservoir or cater the concern of environmental issue on wastewater management, and not for maximizing the thermal extraction.

3D structure of the Campi Flegrei caldera central sector reconstructed through short-period magnetotelluric imaging

The Campi Flegrei caldera experienced an unrest phase dating to 2005, which primary expression is the impressive ground uplift, accompanied by increasing degassing and seismic activities. Such last two phenomena developed mainly in the caldera central sector, including the Solfatara–Pisciarelli complex. However, the inner structure of such an area is still not defined, and this originates a poor understanding of the ongoing unrest. This paper describes the results of a new magnetotelluric survey performed in the Campi Flegrei caldera central sector. Through the inversion of data collected in 47 independent soundings, a 3D model of the electrical resistivity has been retrieved, which evidenced a partition of the investigated structure. The Agnano–Astroni area seems to be associated with a liquid-dominated geothermal reservoir, whereas the Solfatara–Pisciarelli area seems to be characterized by a single mixed liquid and gasses-dominated geothermal reservoir, which supplies the main caldera fumaroles. The proposed reconstruction of the geometrical characteristics of the hydrothermal system and the primary fluid rising pathways gives substantial clues about the significance of the detected structures in the evolution of the caldera unrest.

CO2 –water mixture reinjection into two-phase liquid dominated geothermal reservoirs

Abstract Geothermal energy resources are considered to be one of the main contributors to clean, renewable and low-risk energy production. However geothermal power production may result in some greenhouse gas (GHG) emissions. Injection of GHGs into geothermal reservoirs can be used to reduce these emissions, providing reservoir pressure support and possibly improve reservoir permeability. To understand the migration and behavior of injected gases in the reservoir and to forecast gas breakthrough, simulation studies are required. This work investigates the possible impacts of infield reinjection of CO2 in two-phase liquid-dominated geothermal reservoirs using an earlier 3D numerical model of the Wairakei-Tauhara system as a representative case study. Wairakei-Tauhara is an interesting case study as it has been operated with no reinjection for most of its lifetime. The work investigated the impact of various scenarios of separated geothermal water and CO2 reinjection on reservoir sustainability. The breakthrough of CO2 was also monitored since it can result in higher gas production and lower power generation. The modelling results showed that the injection of CO2-water mixture helps to maintain the reservoir's pressure, but, at the same time, it may suppress natural recharge and boiling, which results in reduction of the enthalpy of the produced fluid.

Decline Curve Analysis for Production Forecast and Optimization of Liquid-Dominated Geothermal Reservoir

Power projects in the geothermal field has a long span of about 30 years. The power supply should be maintained at a certain value across a range of time. A geothermal field, however, has the characteristics of natural production decline with time. In a geothermal field, development of decline curve model of steam production is important for forecasting production decline in the future. This study was developed using decline curve by production data along 3 years liquid-dominated geothermal reservoir in Ulubelu field. Decline curve in geothermal field based on decline curve in petroleum industry. The decline curve was correlated by reservoir management in geothermal. The purposes of this study to get best match model decline curve and forecasting production in the future. Based on decline curve analysis by production data in Ulubelu field, the result model decline curve is exponential model. From the model, we can get the value of decline rate in the field is 9.4 %/year. Then, the formula of forecasting steam flow used exponent decline to forecast in the future. By using separated system cycle in Ulubelu field, the minimal steam flowrate towards turbine was 502018.4 ton/month. Based on formula of forecasting production and minimal steam flowrate, we can get the time make up wells to maintain steam supply for stability in generator power capacity.

Volcano-hosted vapor-dominated geothermal systems in permeability space

Although volcano-hosted vapor-dominated geothermal systems are rare, West Java, Indonesia, has five such systems: Kamojang, Darajat, Patuha, Telagabodas, and Wayang Windu. This paper seeks an explanation for such vapor-dominated geothermal systems through heat and mass transfer numerical modeling based on the characteristics of these five systems. Specifically, the 3D model TOUGH2 is used to explore heat input and permeability conditions that lead to vapor-dominated systems. Our generic model consists of a reservoir, a host rock, and a caprock. The size of the reservoir is 16km2 and 2.8km thick, with 10% porosity and a permeability of 10−13m2. The initial condition of the model is fully liquid saturated at a normal geotherm with hydrostatic pressure. An intrusive heatpulse of 8MW/km2 for 9kyr is applied to the base to the reservoir and the resulting geothermal system characteristics are mapped out in permeability space. A vapor-dominated system is produced when the hostrock permeability is 5×10−17m2 or less accompanied by the caprock permeability varying from 10−17 to 4×10−16m2. The caprock permeability assures that the escaping steam exceeds the incoming liquids; the hostrock permeability prevents flooding until the heat source is turned off. Increasing the basal heat input to 12MW/km2 shifts the maximum host-rock permeability for vapor systems to 10−16m2, but there is minimal change in the maximum caprock permeability. In all models the maximum duration of the vapor reservoirs is 1.5kyr, at which point the reservoir either dries out or floods. The timescale for vapor reservoir stability is an order of magnitude less than that for the formation or cooling of liquid-dominated geothermal reservoirs. The factors contributing to the occurrence of the five vapor-dominated reservoirs in West Java are intense heating due to prolonged active volcanism, an absence of shear faulting, and the restrictive range of low permeability in the host and caprocks surrounding a relatively permeable reservoir.

Organic Rankine Cycle Power Systems: From the Concept to Current Technology, Applications, and an Outlook to the Future

The cumulative global capacity of organic Rankine cycle (ORC) power systems for the conversion of renewable and waste thermal energy is undergoing a rapid growth and is estimated to be approx. 2000 MWe considering only installations that went into operation after 1995. The potential for the conversion of the thermal power coming from liquid-dominated geothermal reservoirs, waste heat from primary engines or industrial processes, biomass combustion, and concentrated solar radiation into electricity is arguably enormous. ORC technology is possibly the most flexible in terms of capacity and temperature level and is currently often the only applicable technology for the conversion of external thermal energy sources. In addition, ORC power systems are suitable for the cogeneration of heating and/or cooling, another advantage in the framework of distributed power generation. Related research and development is therefore very lively. These considerations motivated the effort documented in this article, aimed at providing consistent information about the evolution, state, and future of this power conversion technology. First, basic theoretical elements on the thermodynamic cycle, working fluid, and design aspects are illustrated, together with an evaluation of the advantages and disadvantages in comparison to competing technologies. An overview of the long history of the development of ORC power systems follows, in order to place the more recent evolution into perspective. Then, a compendium of the many aspects of the state of the art is illustrated: the solutions currently adopted in commercial plants and the main-stream applications, including information about exemplary installations. A classification and terminology for ORC power plants are proposed. An outlook on the many research and development activities is provided, whereby information on new high-impact applications, such as automotive heat recovery is included. Possible directions of future developments are highlighted, ranging from efforts targeting volume-produced stationary and mobile mini-ORC systems with a power output of few kWe, up to large MWe base-load ORC plants.

A Simple Model of a Two-Layered High-Temperature Liquid-Dominated Geothermal Reservoir as a Part of a Large-Scale Hydrothermal Convection System

The Kakkonda geothermal reservoir, Japan, is a typical high-temperature liquid-dominated geothermal reservoir, except for its distinctive two-layered temperature structure. It has a shallow permeable reservoir of 230–260°, and a deep less permeable reservoir of 350–360°. Geology and hydrology indicate that the shallow reservoir is one to two orders of magnitude more permeable than the deep reservoir, but that the two reservoirs communicate. It has been widely assumed in engineering and scientific circles that the connection between the two reservoirs is a zero or low permeability barrier to fluid flow. We show that this hypothesis is untenable, based on both physical evidence and numerical simulation. We numerically model the evolution of the geothermal system as it heats after emplacement of an intrusion. The two-layered temperature structure is found to be a consequence of the permeability difference, i.e. the two-layered permeability structure.

Magnetic anomalies associated with high temperature reservoirs in the taupo volcanic zone (New Zealand)

Distinct magnetic total force anomalies are associated with many, but not all, liquid-dominated geothermal reservoirs in the Taupo Volcanic Zone, which stand in thick, young (<0.7 Ma) volcanic host rocks. The anomalies are caused by demagnetised rocks (a result of hydrothermal alteration) in the upper 0.5–1 km section of the reservoirs; the phenomenon has been confirmed by core studies. Four different patterns of magnetic anomalies have been recognised. The most common type can be found over high-temperature systems where demagnetisation is confined to the main reservoir. Different anomaly patterns are associated with prospects characterised by subsurface outflows and reservoirs hosted in both normally and reversely magnetised rocks. A rather subdued and almost featureless pattern occurs over a few prospects where rocks lying outside the reservoir have also lost thei magnetisation by interaction with acidic, steam-heated water.

Fluid inclusion evidence for rapid formation of the vapor-dominated zone at Sulphur Springs, Valles caldera, New Mexico, USA

Microthermometric measurements were obtained for 618 fluid inclusions in hydrothermal quartz, fluorite and calcite and magmatic quartz phenocrysts in intracaldera tuffs from the VC-2A core hole in order to study evolutionary processes of the Sulphur Springs hydrothermal system in the Valles caldera. Relatively high Th values in samples from shallow depths indicate erosion of about 200 m of caldera fill since deposition of hydrothermal minerals at shallow depths in the Sulphur Springs hydrothermal system, accompanied by a descent in the water table of the liquid-dominated reservoir. For samples collected below the current water level of the well, the minimum values of homogenization temperature (Th) fit the present thermal profile, whereas minimum Th values of samples from above the water level are several tens of degrees higher than the present thermal profile and fit a paleo-thermal profile following the boiling point curve for pure water, as adjusted to 92 °C at 20 m below the present land surface. This is attributed to development of an evolving vapor zone that formed subsequent to a sudden drop in the water table of the liquid-dominated reservoir. We suggest that these events were caused by the drainage of an intracaldera lake when the southwestern wall of the caldera was breached about 0.5 Ma. This model indicates that vapor zones above major liquid-dominated geothermal reservoirs can be formed due to dramatic changes in geohydrology and not just from simple boiling.

1991 Reservoir Assessment and Electrical Generation Forecast for California's Liquid-Dominated Geothermal Reservoirs

1991 Reservoir Assessment and Electrical Generation Forecast for California's Liquid-Dominated Geothermal Reservoirs

Water-Influx Modeling of the Svartsengi Geothermal Field, Iceland

Summary In this paper, lumped-parameter models are presented for confined and unconfined liquid-dominated geothermal reservoirs without recharge and compared to production data from the Svartsengi geothermal field in Iceland. They show that recharge or water influx is likely to affect the field's drawdown with time. Three petroleum reservoir water-influx methods.are then presented for steady-state, pseudosteady-state, and unsteady-state aquifers encroaching into the geothermal reservoir. History matching shows that the reservoir/aquifer system is best described as unsteady state and radial, with the aquifer boundary taken at infinite distance.

Evaluation Of Bottomhole Treatment Pressure for Geothermal Well Hydraulic Fracture Stimulation

Summary The geothermal reservoir well stimulation program (GRWSP) group performed a large hydraulic fracture treatment in the well Baca 20, located in the Union Geothermal Co. of New Mexico Redondo Creek project area in north-central New Mexico. This is the highest temperature well in the world to be successfully fractured with proppant to date. The treatment involved use of a large cooling water prepad followed by a high viscosity fracturing fluid carrying sintered bauxite as the proppant. A nonproductive 240-ft [73-m] openhole interval, with a formation temperature of 520F [271C], was selected and isolated for the job. Poststimulation tests and analyses indicate a fracture was successfully created with a large vertical height near the wellbore. A number of fracture evaluation techniques were used to analyze the job, including some that are unique. Among these techniques were fracture mapping by monitoring the microseismic events caused by the fracture job, downhole treating pressure data analysis, temperature profiles, electric log surveys, production tests, and chemical tracer monitoring. The poststimulation fluid productivity of the treated interval was subcommercial, probably because of low formation permeability surrounding the artificially created fracture. Introduction The GRWSP, sponsored by the U.S. DOE, was initiated in Feb. 1979 to pursue industry interest in geothermal well stimulation work and to develop technical expertise in areas related to geothermal well stimulation activities. Republic Geothermal Inc. and its principal subcontractors (Santrol Products Inc., Maurer Engineering Inc., Ten-a Tek Inc., and Vetter Research) have completed seven full-scale field experiments to date. One experiment, performed on Oct. 5, 1981, is the Baca 20 well in New Mexico. The Baca reservoir lies within the Jemez Crater, Valles Caldera, and is defined by more than 20 wells completed to date in the Redondo Creek area by Union. The main reservoir, 4,000 to 6,000 ft [1220 to 1830 m] in thickness, is composed of volcanic tuffs with low permeability and a primary flow system of open fracture channels. In the Redondo Creek area, wells have encountered a high-temperature &amp;gt;500F [260C]) liquid-dominated geothermal reservoir, but several wells have not been of commercial capacity, primarily because they lacked productive natural fractures at the wellbore. Baca 20 is near several of the better production wells in the Redondo Creek area. The original Baca 20 hole drilled toward the southeast was nonproductive. The well was redrilled to the northeast and marginally non-commercial production was obtained. The production interval of 3,322 ft [1013 in] extended from 2,505 to 5,827 ft [764 to 1777 m] in depth. A long-term production test performed in 1980 resulted in a stabilized flow rate of about 56,000 lbm/hr [25 400 kg/h] with a 56% steam fraction and a wellhead pressure of 116 psig [800 kPa]. The calculated permeability-thickness product was approximately 3,000 md-ft [915 md-m]. The primary in-flow zone was located at a depth of about 4,000 ft [1220 m] with deeper zones probably supplying some fluids. Unique pressure data were obtained during the treatment. These bottomhole pressure measurements, along with other techniques, were used to evaluate the fracture treatment and the ability of fracture design models to predict results in this type reservoir. The large hydraulic fracture job, described in the next section, was intended to continue development of the high-temperature stimulation technology needed for geothermal applications and to create the high-conductivity flow channel needed to make Baca 20 a commercial well. Description of Stimulation Treatment Baca 20 was originally completed as shown in Fig. 1A with a 9 5/8-in. [24.5-cm] liner cemented at 2,505 ft [764 m] and a 7-in. [17.8-cm] slotted liner hung at 2,390 ft [729 m] with the shoe at 5,812 ft [1772 m]. The 7-in. [ 17.8-cm] slotted liner was pulled, lost circulation zones cured using cement plugs, and then a 7-in. [17.8-cm] blank liner was cemented in place at 4,880 ft [1488 m] to isolate the desired treatment interval. Since the fracture interval was to be from 4,880 to 5,120 ft [1488 to 1561 m], a sand plug was placed from 5,827 ft total depth to 5,400 ft [1777 to 1646 m] and then capped with cement to 5,120 ft [1561 m]. The recompletion is shown in Fig. 1B. This particular 240-ft [73-m] interval was chosen primarily because the best production in the area has been found in comparable intervals near the bottom of the Bandelier tuff and because of its high reservoir temperature (520F [271C]). JPT P. 829^

An axisymmetric model for the charging of a liquid-dominated geothermal reservoir

Heat and mass transfer processes occurring in a model of an axisymmetric liquid-dominated geothermal reservoir are described. The system is composed of a vertical cylindrical region of fractured rock surrounded by a much larger annular aquifer. Hot liquid water, convected into and up the central cylindrical zone is forced into the neighbouring aquifer. Heat is lost to the cold surface as the liquid flows horizontally (radially) in the aquifer. A combination of boundary layer techniques and numerical methods are used to obtain solutions for velocity, temperature and pressure distributions in the system and for the heat flux emanating from the surface of the cap rock. The deep portion of the axisymmetric aquifer is found to be cooled faster than the equivalent part of a planar model.

Nonstatic Reservoirs: The Natural State of the Geothermal Reservoir

Summary Above-hydrostatic-reservoir-pressure gradients are found in many geothermal fields before exploitation. In higher-temperature fields, steam and water also coexist in the upper levels. These factors indicate natural upflow in these reservoirs-i.e. the dynamic state of the fluid. Analysis of flow and pressure data under these dynamic conditions can lead to relevant large-scale reservoir information. Introduction It has been suggested that the existence of a natural surface discharge from an oil reservoir must imply a nonstatic pressure distribution down through the fluid in that reservoir. To date, however, no such nonstatic pressure distribution has been identified in any oil reservoir. In contrast, most liquid-dominated geothermal reservoirs -- i.e., both hot water and two-phase -- have significant natural throughflow, and hence the nonstatic pressure distribution has been sought with interest. Until recently, the data supporting the enhanced pressure gradient have been sparse because wells commonly have been discharged, and the reservoir disturbed, before a suitable spectrum of data has been obtained. The mere presence of a significant length of open hole, as is commonly the case in geothermal exploitation, also distorts the pressure pattern. Study and reinterpretation of early (1950–56) Wairakei data have led to a much better picture of the natural pressure/depth profile for that field. In this paper we use this new information with other information about the reservoir in its natural state to determine an average (field) vertical permeability and the depth to which boiling may have occurred. Because the horizontal permeability of the flow strata is usually at least an order of magnitude higher than the mean vertical component (which includes the effects of any lower-permeability cross strata), it is horizontal permeability that controls the pressure transients of pump and injection tests. The vertical component is, however, important once water begins to drain down to the well feed level as the field pressure declines, and it has a strong influence over long-term behavior. Although we now can distinguish between liquid/water and steam/water (two-phase) conditions around a well, we are not yet able to pick up the phase-change boundary unless it is close. Even in long-term field tests, the horizontal/vertical permeability contrast may result in the pressure transients sensing the side boundaries before they show any effect of this horizontal one. Since extraction and injection from and into a two-phase section of a reservoir result in different effects from extraction and injection from and into a liquid-charged section, a pre knowledge of the depth of the two-phase zone could result in some savings in both drilling effort and costs. The Geothermal Reservoir It first was suggested at the beginning of the century that hot spring water might be meteoric water that entered the ground some distance away and circulated deeply enough to pick up the required heat. JPT P. 189^

Improved Energy Recovery From Geothermal Reservoirs

Summary Numerical stimulation methods are used to study how the exploitation of different horizons affects the behavior of a liquid-dominated geothermal reservoir. Our reservoir model is a schematic representation of the Olkaria field in Kenya. The model consists of a two-phase vapor-dominated zone overlying the main liquid-dominated reservoir. Four different cases were studied, with fluid produced from:the vapor zone only.the liquid zone only,both zones, andboth zones but with lower values for vertical permeability and porosity assumed. The results indicate that production from the shallow two-phase zone, although resulting in higher enthalpy fluids, may not be advantageous in the long run. Shallow production gives rise to a rather localized depletion of the reservoir, whereas production from deeper horizons may yield a more uniform depletion process if vertical permeability is sufficiently large. The exploitation from deeper zones causes boiling and subsequent upflow of steam that condenses at shallow depths. This tends to make temperatures and pressures more uniform throughout the reservoir, resulting in maximum energy recovery.Brief consideration is given to the possibility of achieving similar improvements in energy recovery from vapor-dominated reservoirs through production from deeper horizons. This appears unlikely but cannot be completely ruled out because of uncertainties about the characteristics of vapor-dominated systems at depth. Introduction In the development of a geothermal resource, an appropriate production strategy must be selected. This ineludes deciding on the optimal well spacing and depths of completion. In many cases, these decisions are based solely on achievable levels of power production and well completion costs. without due consideration being given to ultimate energy recovery. Thus. the production wells often are located very close to each other, and drilling is terminated as soon as sufficiently hot and productive horizons are penetrated. Completing production wells near the top of the reservoir may lead to a more rapid decline and a low recovery ratio for the geothermal resource, Selection of an exploitation strategy should be based on appropriate reservoir engineering calculations that will result in an optimal balance between energy recovery and investment costs. Calculations aiming at an optimization of field development were carried out by Morris and Campbell for the East Mesa geothermal field in the Imperial Valley, CA.The economic value of a geothermal well depends not only on its deliverability, as in he case of an oil well, but also on the enthalpy of the produced fluids. If there are two-phase or vapor zones in the field (e.g., Baca, U.S.; Olkaria, Kenya; Broadlands, New Zealand), there is an incentive to produce from them rather than from deeper liquid reservoirs, because fluids of higher enthalpy can be obtained. The short-term benefits are obvious, but in the long run a lower-energy recovery ratio from the field may result.In this work, the behavior of a liquid-dominated geothermal reservoir in response to production from different horizons is studied by use of numerical simulation methods. We use the Olkaria geothermal field in Kenya as an example of a two-phase vapor-dominated zone overlying the main liquid-dominated reservoir. One of the important questions in the Olkaria field development is which zone it is most beneficial to produce. This paper is the first attempt to answer that question. We also briefly consider the possibility of improving energy recovery from vapor-dominated reservoirs by tapping deeper horizons. JPT P. 1920^

Results of Interference Tests From Two Geothermal Reservoirs

Results are presented from interference tests on two liquid-dominated geothermal reservoirs in the U.S. The collected pressure data show that interference effects can be masked by earth tides and other effects. Well known techniques of petroleum engineering and hydrogeology are used to estimate hydraulic characteristics and to infer the presence of barrier and leaky boundaries. Introduction An important facet in the problem of geothermal energy development is assessing the productivity and size of a geothermal reservoir. Modern techniques of well-test analysis (pressure drawdown, buildup, and interference tests) developed in petroleum engineering and hydrogeology have been applied successfully to two liquiddominated geothermal reservoirs in the U.S.: one in the Raft River Valley of Idaho and the other at East Mesa in the Imperial Valley of California. These tests gave reasonable estimates of the permeability and storage parameters for the two reservoirs. In addition, the tests also parameters for the two reservoirs. In addition, the tests also illustrate the type of instrumentation that can be used in testing geothermal wells as well as the nature of the data that can be collected. A large body of literature is available on well testing in both petroleum engineering and hydrogeology. Ramey recently has summarized the practical aspects of modern well-test analysis. This paper reviews the results of interference tests performed with a very sensitive pressure-measuring performed with a very sensitive pressure-measuring device on two geothermal reservoirs. As used in this paper, the term "interference test" denotes the fluid production from one well and measurement of pressure transients in a nearby observation well. The geologic setting for each reservoir is given and the instrumentation is presented. Some unusual features of the data are discussed, followed by the methods of interpretation that were used. Description of the Geothermal Reservoirs Raft River Valley Field, Idaho The Raft River Valley geothermal field (Fig. 1) is located on a graben filled with Tertiary and Pleistocene sediments and volcanics, with an aggregate thickness of about 5,000 ft. The sediments rest on a basement of quartzites, schists, and quartz monzonites of Precambian age. Precambian age. Wells RRGE 1 and RRGE 2 were drilled in 1975 and successfully produced hot water at approximately 295 deg. F from a geothermal reservoir occurring at the base of the sediments at 3,500 to 5,000 ft below the land surface. Well RRGE 2 is northeast and 4,000 ft from Well RRGE 1. Both wells are artesian with wellhead pressures of about 150 psi when shut in. During construction, both wells indicated free flows of about 400 gal/min. The completion details for the two wells are summarized in Table 1. Subsurface correlations of borehole data suggest that the sediments dip toward Well RRGE 2 with apparent northeasterly dips increasing from about 3 deg. in the upper portion to about 7 deg. toward the bottom. Also, it is known portion to about 7 deg. toward the bottom. Also, it is known that Well RRGE 1 pierced a fault zone between 3,800 and 4,500 ft. Apparently, Well RRGE 2 did not intercept any faults. East Mesa Field, California The East Mesa geothermal field (Fig. 2) is located on the eastern part of the Salton Trough in the Imperial Valley of California. JPT P. 10

Buoyancy induced flows in a saturated porous medium adjacent to impermeable horizontal surfaces

Boundary-layer analysis is performed for the buoyancy-induced flows in a saturated porous medium adjacent to horizontal impermeable surfaces. Similarity solutions are obtained for the convective flow above a heated surface or below a cooled surface, where wall temperature is a power function of distance from the origin. Analytical expressions for boundary-layer thickness, local and overall surface heat flux are obtained. Applications to convective flow in a liquid-dominated geothermal reservoir are discussed.

Heat and mass transfer in liquid-dominated geothermal reservoirs

Heat and mass transfer in liquid-dominated geothermal reservoirs

Heat and mass transfer in liquid-dominated geothermal reservoirs

Heat and mass transfer in liquid-dominated geothermal reservoirs