As in geothermal fields around the world, at Cerro Prieto geothermal field , Baja California, former exploratory and production wells are used to inject residual brine. Since the s, studies and activities have been carried out to find ways to recharge the reservoir and dispose of brine without harming the environment or underground aquifers.
These include infiltration and cold-and-hot injection. Some of the studies are presented here, including analyses of litho-facies; core samples; pressure, temperature and spinner logs; well tests and injection rates-plus some studies on the shallow aquifer. All have been useful in fulfilling requirements made by environmental authorities. Because injection rates constantly decrease due to formation damage, it is proposed an additional technique be used to reduce such damages and prolong the lifetime of cold-and-hot injection wells-while ensuring the environment and shallow aquifers are not affected.
Desde la decada de los 80 se han realizado diversos estudios y acciones en ese campo geotermico para recargar al yacimiento y para disponer del fluido residual, sin ocasionar danos al ambiente ni a los cuerpos hidricos del subsuelo, que van desde la infiltracion hasta la inyeccion en frio y en caliente. Este articulo presenta los diferentes estudios realizados con ese objetivo en el campo, incluyendo el analisis de litofacies, de nucleos de formacion, de registros de presion, temperatura y spinner, las pruebas en pozos y analisis de tasas de aceptacion, asi como los efectuados en el acuifero superficial.
Todos ellos han sido de utilidad para atender los requerimientos de las autoridades ambientales. Finalmente, y en virtud de que las tasas de aceptacion de los pozos. The wells of this zone produce two-phase fluids, with different characteristics as far as their steam fraction content; in the central part and towards the NW the fluids are of dominant liquid type whereas towards the E and the S, the fluid contains a relatively higher steam fraction.
The results of gaseous equilibrium FT- HSH3 showed that the fluids in the deposit are at temperatures between Celsius degrees and Celsius degrees and contain steam fractions between 0. The data found for the natural state are aligned in a tendency defined in the diagram FT- HSH3, that suggest the wells receive different proportions from preexisting steam in the deposit, which are mixed with the liquid phase to produce the observed discharges.
The present data, besides showing the presence of deposit steam, also indicates the entrance of lower temperature fluid in the central part of sector CP IV. Los pozos de esta zona producen fluidos bifasicos, con diferentes caracteristicas en cuanto a su contenido de fraccion de vapor: Los resultados de equilibrio gaseoso FT-HSH3 mostraron que los fluidos en el yacimiento se encuentran a temperaturas de entre grados Celsius y grados Celsius y contienen fracciones de vapor de entre -. Los datos hallados para el estado natural se alinean en una tendencia definida en el diagrama FT-HSH3, que sugiere que los pozos reciben diferentes proporciones de vapor pre-existente en el yacimiento, que se mezclan con fase liquida para producir las descargas que se observan.
Los datos actuales, ademas de mostrar la presencia de vapor de yacimiento, tambien indican la entrada de fluidos de. A full scale, wellhead Biphase turbine was manufactured and installed with the balance of plant at Well of the Cerro Prieto geothermal resource in Baja, California.
The Biphase turbine was first synchronized with the electrical grid of Comision Federal de Electricidad on August 20, The Biphase power plant was operated from that time until May 23, , a period of 2 years and 9 months. A total of 77, kWh were delivered to the grid.
The power plant was subsequently placed in a standby condition pending replacement of the rotor with a newly designed, higher power rotor and replacement of the bearings and seals. The maximum measured power output of the Biphase turbine, kWe at psig wellhead pressure, agreed closely with the predicted output, kWe. The design relations used to predict performance and design the turbine were verified by these tests. The performance and durability of the Biphase turbine support the conclusion of the Economics and Application Report previously published, Appendix A. The newly designed rotor the Dual Pressure Rotor was analyzed for the above power condition.
The Dual Pressure Rotor would increase the power output to kWe by incorporating two pressure letdown stages in the Biphase rotor, eliminating the requirement for a backpressure steam turbine. The power plant availability was low due to deposition of solids from the well on the Biphase rotor and balance of plant problems. A great deal of plant down time resulted from the requirement to develop methods to handle the solids and from testing the apparatus in the Biphase turbine.
Finally an online, washing method using the high pressure two-phase flow was developed which completely eliminated the solids problem. The availability of the Biphase turbine itself was Comments on some of the drilling and completion problems in Cerro Prieto geothermal wells. From to the present, 85 wells with a total drilling length exceeding , m have been constructed at Cerro Prieto , a modest figure compared to an oil field.
Overview of Cerro Prieto studies
This activity took place in five stages, each characterized by changes and modifications required by various drilling and well-completion problems. Initially, the technical procedures followed were similar to those used in the oil industry. However, several problems emerged as a result of the relatively high temperatures found in the geothermal reservoir. The various problems that have been encountered can be considered to be related to drilling fluids, cements and cementing operations, lithology, geothermal fluid characteristics, and casings and their accessories.
As the importance of high temperatures and the characteristics of the geothermal reservoir fluids were better understood, the criteria were modified to optimize well-completion operations, and satisfactory results have been achieved to date. Well MA has been the most productive in the Cerro Prieto field , producing around 40 million tons of fluid. The well went on line in February and was in continuous operation until June Monthly measurements for over 30 years of operating conditions and chemical and isotopic analyses of the fluids allow identification of the most significant processes occurring in the zone where the well is located.
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Three dominant recharge types have been identified, each lasting about 10 years. They are a a recharge of fluids of lower temperature than the production fluids, even though the chemical and isotopic compositions are similar; b a recharge of lower-temperature fluids with diluted chemical and isotopic compositions; and c a progressive recharge of reinjected water with a higher chloride concentration and heavy isotopic composition.
The production and reinjection rates for over 30 years of production history in the MA well zone allow for speculation of a reservoir pressure recovery, which is confirmed with a calculation using production data from well MA. The evolution of the reservoir pressure in the zone contrasts with the rest of the reservoir, where a constant pressure drop is observed, particularly toward the central and eastern parts of the field.
Fue integrado a produccion en febrero de y hasta junio de ha permanecido en produccion en forma continua. Las mediciones mensuales de sus condiciones operativas y los analisis quimicos e isotopicos del agua producida permiten identificar los procesos mas significativos que han ocurrido a lo largo de esos mas de 30 anos en la zona donde se localiza el pozo. Se han identificado tres tipos de recarga dominantes que se presentan durante un periodo cercano a 10 anos cada uno, los cuales son: Analysis of the automation and control of the well production conditions in the Cerro Prieto geothermal field , Mexico; Analisis de la automatizacion y del control de las condiciones de produccion de los pozos del campo geotermico de Cerro Prieto , BC, Mexico.
Through 31 years of development of the Cerro Prieto geothermal field , the number of wells in operation and the distances between them has been increasing. Now there are wells producing a mixture of water and steam at different ratios, depending on the reservoir characteristics pressure, temperature, depth, etc. Therefore, Comision Federal de Electricidad CFE has started a pilot plan to handle the automation and control of the operating conditions of production wells, and to install a data production acquisition system.
The initial results of the system are in this paper. Ahora hay mas de pozos produciendo una cantidad de mezcla de agua y vapor a diferentes rangos, dependiendo de las caracteristicas del yacimiento presion, temperatura, profundidad, etc. Como resultado la Comision Federal de Electricidad CFE ha dado inicio a un plan de pruebas para llevar a cabo la automatizacion y control de las condiciones de operacion de los pozos productores, e instalar un sistema con equipos para recoleccion de datos del campo, cuyos primeros resultados se presentan en este articulo.
The goal is to trace the origin of reservoir fluids and to place paleoclimate and structural-volcanic constraints in the region. Radiogenic in situ 4 He production age modeling at LTV, combined with the presence of radiogenic carbon 1. CP geothermal water is composed of infiltrated Colorado River water with a minor impact by halite dissolution, whereas a vapor-dominated sample is composed of Colorado River water and vapor from deeper levels. Exploration and development of Cerro Prieto. A brief retrospective of the exploration and field model development at Cerro Prieto are presented.
Representative field models are presented for each of the work phases. A model integrating information from these studies was developed. Even though geothermal energy is a renewable energy source that is seen as cost-effective and environmentally friendly, emissions from geothermal plants can impact air, soil, and water in the vicinity of geothermal power plants. The objective of this study was to evaluate whether the emissions generated by the geothermal complex have increased the soil mercury concentration in the surrounding areas.
Additionally, four soil depth profiles were performed in the vicinity of the complex. The mercury concentration ranged from 0. Our results show that the activities of the geothermal complex have led to an accumulation of mercury in the soil of the surrounding area. More studies are needed to determine the risk to human health and the ecosystems in the study area.
Hydrothermal alteration zones and present reservoir conditions: Geological factors are as essential for locating new wells as they are for defining the production zones of these wells. It has been observed that the continuous variation of reservoir thermodynamic conditions temperature, pressure and enthalpy is due mainly to the exploitation of geothermal resources. The presence of new thermodynamic conditions recorded at the reservoir has led to the re-location of production wells originally located during the drilling campaign of to In turn, this is related to the current, superior, thermodynamic reservoir conditions.
Based on this, a new geologic approach is proposed to define possible production zones for new wells, relating the ZAH zones to current thermodynamic reservoir conditions. Por otra parte, tambien se ha constatado que la continua variacion de las condiciones termodinamicas del yacimiento temperatura, presion y entalpia es originada en buena medida por la explotacion del recurso geotermico.
La ocurrencia de nuevas condiciones. Heat losses estimation associated with the physical state of the thermal insulation of pipes vaporductos network in Cerro Prieto geothermal field ; Estimacion de perdidas de calor asociadas al estado fisico del aislamiento termico de las tuberias de la red de vaporductos del campo geotermico Cerro Prieto.
The Cerro Prieto Geothermal Field CPGF steam transportation network is constituted by km of pipes with diameters ranging from 8 to 48 inches, which transport the steam of producing wells to 13 power plants which have a total installed capacity of MWe. Originally, the pipes are thermally insulated with a mineral wool or fiber glass layer and an external aluminum or iron cover. Due to the insulation material has been exposed to weather conditions during the field operation it shows nowadays different grades of wear-out, or even it is lacking in some parts of the network, causing higher heat losses from the pipes to the environment.
In this work, the magnitude of the heat losses related with the present condition of the thermal insulation throughout the pipeline network is assessed. This involved determining the longitude and diameter, as well as the insulation condition of each single pipeline section, and the calculation of the heat transfer coefficients for the different thermal insulation conditions defined for this study.
Originalmente, estas tuberias son aisladas termicamente con una capa de 2 pulgadas de material aislante a base de lana mineral o fibra de vidrio, y una proteccion exterior de aluminio o hierro. Debido principalmente al impacto de las condiciones meteorologicas durante el tiempo de operacion del campo, en algunas porciones de la red el aislante presenta actualmente distintos grados de deterioro, o incluso se encuentra ausente, lo cual se traduce en una mayor perdida de calor desde las tuberias hacia el medio ambiente.
En el presente trabajo se evalua la magnitud de las perdidas de calor asociadas al estado fisico del aislamiento termico de las. After 35 years of exploitation of the CP-I Cerro Prieto I sector of the Cerro Prieto geothermal field , its thermal conditions have been declined substantially; the number of production wells is reduced and exploitation has been abandoned in some zones. However with a binary cycle, it is still possible to generate electricity from the remaining reservoir energy.
To do so, one needs to know a detailed reservoir history of the sector, identifying the best potential strata to be assessed. In this paper, the CP-I reservoir evolution is presented and its exploitation and main reservoir characteristics -which play important roles- are identified. The CP-I zones offering the best conditions for binary cycle exploitation are identified. Exploiting partially abandoned reservoir sections is crucial for the future of the field.
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If such sections can be made to produce, this will help reduce the progressive steam-production decline in the occurring since production began. The production decline had been mitigated by a large area available for drilling replacement production wells, but such an area is limited now, due to the vast number of operating wells. Sin embargo, aun es posible aprovechar la energia que contiene este sector del yacimiento para la generacion de electricidad mediante ciclo binario.
Para ello primeramente se debe conocer en detalle cual ha sido la evolucion del yacimiento en este sector, identificando los estratos de mejor potencial para evaluarlos posteriormente. En este estudio se presenta la evolucion del yacimiento de CP-I como respuesta a su explotacion, identificando las principales caracteristicas del yacimiento que determinan su comportamiento. Determination of heat losses in the Cerro Prieto , Baja California, geothermal field steam transportation network based on the thermal insulation condition of the steam pipelines; Determinacion de perdidas de calor en la red de transporte de vapor del campo geotermico de Cerro Prieto , Baja California, con base en el estado fisico del aislamiento termico de vaporductos.
In Cerro Prieto Geothermal Field CPGF , the steam from producing wells is transported to power plants through a large and complex system of pipes thermally insulated with a 2 inches thick mineral wool or a fiber glass layer and an external aluminum or iron cover. The insulation material has been exposed to weather conditions during the field operation and has suffered density and thickness changes. In some cases the insulation has been lost completely, increasing heat transfer from the pipes to the environment. This paper analyzes the impact of the conditions of thermal insulation on heat losses in the CPGF steam-pipeline network.
The heat losses are calculated by applying an iterative method to determine the surface temperature based on a heat balance calculated from the three basic mechanisms of heat transfer: Finally, using length and diameter data corresponding to the condition of the thermal insulation of each pipeline-and field operation data, the overall heat losses are quantified for steam lines throughout the pipeline network in the field. The results allow us to evaluate the magnitude of the heat losses in comparison with the overall energy losses occurring during steam transport from wells to the power plants.
Debido a la exposicion a las condiciones meteorologicas a traves del tiempo de operacion del campo, el aislamiento ha experimentado cambios en su densidad y espesor y en ocasiones se ha perdido por completo, lo cual repercute en una mayor transferencia de calor de las tuberias hacia el medio ambiente. Evolution of the Cerro Prieto geothermal system as interpreted from vitrinite reflectance under isothermal conditions. Temperature estimates from reflectance data in the Cerro Prieto system correlate with modern temperature logs and temperature estimates from fluid inclusion and oxygen isotope geothermometry indicating that the temperature in the central portion of the Cerro Prieto System is now at its historical maximum.
Isoreflectance lines formed by contouring vitrinite reflectance data for a given isothermal surface define an imaginary surface that indicates an apparent duration of heating in the system. The distribution of hydrothermal minerals, mineral assemblages and fluid inclusion data were taken from drill cuttings from the production zone of wells all over the Cerro Prieto geothermal field. The production zone has been termed the silica-epidote mineralized zone SEMZ , and is located in the deep part of the gray shale where thick layers of sandstone are found.
Common mineral assemblages show three temperature ranges in the SEMZ: Las muestras de recortes y nucleos de perforacion estudiados provienen de la zona de produccion a la que se le ha denominado Zona Mineralizada de Silice-Epidota ZMSE , que se encuentra en la parte profunda de la lutita gris con importantes horizontes de areniscas.
En esta zona las asociaciones parageneticas mas comunes han mostrado tres intervalos de temperatura para la ZMSE: Evaluation of geologic characteristics at Cerro Prieto. Computerized well-log analysis of Cerro Prieto has led to the identification of a relatively large and irregular low-density volume extending from near the surface in the vicinity of Laguna Volcano to greater depths toward the northeast. This low-density volume is located about a plane of symmetry of a self-potential anomaly and a group of northeast trending active faults.
The presence of a volume of relatively high-density rock has been recognized at shallow depths in the initially developed part of the resource. It is believed to be due to minerals deposited by cooled, rising geothermal brine. Storativity calculated from well logs at the south end of the western part of the field shows acceptable comparison with storativity calculated from well tests.
The amount of fluid produced from the field during the period is greater than the amount in situ calculated from the completed interval thicknesses. Because this part of the field is still producing today, fluid must be recharging this part of the field. Production induced boiling and cold water entry in the Cerro Prieto geothermal reservoir indicated by chemical and physical measurements. Chemical and physical data suggest that the relatively shallow western part of the Cerro Prieto reservoir is bounded below by low permeability rocks, and above and at the sides by an interface with cooler water.
There is no continuous permeability barrier around or immediately above the reservoir. Permeability within the reservoir is dominantly intergranular. Mixture with cooler water rather than boiling is the dominant cooling process in the natural state, and production causes displacement of hot water by cooler water, not by vapor. Local boiling occurs near most wells in response to pressure decreases, but no general vapor zone has formed. Progress on the biphase turbine at Cerro Prieto. The status of a Biphase turbine power plant being installed at the Cerro Prieto geothermal field is presented.
The major modules for the power plant are completed except for a back pressure steam turbine. The power plant will be started in April with the Biphase turbine alone followed by the addition of the steam turbine module two months later. The current power plant performance level is kWe due to a decline in the well. An increase in power output to kWe by adding the flow from another well is planned.
The addition of five Biphase power plants with a total power output of Criteria for determining casing depth in Cerro Prieto. On the basis of geological data obtained during drilling and its relation to electric logs, together with the problems that arose when drilling through formations until the production zone was reached, it is possible to establish the most suitable manner to line a well and thus formulate an optimum casings program.
The main criteria to be taken into consideration in preparing such a program and its application in the drilling of wells programmed in Cerro Prieto to optimize and economize such drilling and achieve suitable techniques for well completion are presented. The criteria are based on the characteristics of the Cerro Prieto field and on casing design factors, as well as a experience gained during drilling in such a field.
Microfossils including benthic and planktic foraminifera, ostracodes, calcareous algae, fish skeletal material, and fragments of pelecypods were found in 14 core samples from depths of to m in the Cerro Prieto geothermal field , providing evidence of both the age and depositional history of sediments comprising the m-thick Pliocene and Pleistocene section in this area.
Ostracodes of brackish water and marine origin constitute the most common microfossils present in this sequence occurring in 8 samples; in situ littoral and neritic species of benthic foraminifera occur in 5 samples with planktic species present in 2 samples. Distributional patterns of ostracodes and foraminifera together with previously analyzed lithofacies Lyons and van de Kamp, indicate that the Cerro Prieto section represents an intertonguing complex of alluvial, deltaic, estuarine, and shallow marine environments deposited along the front of the Colorado River delta as it prograded across the Salton Trough during Pliocene and Pleistocene time.
Foraminiferal evidence indicates that a sand and shale unit commonly present at depths between and m represents a significant mid-Pleistocene marine incursion in the Cerro Prieto area. Reworked specimens of Cretaceous foraminifera and fragments of the Cretaceous pelecypod Inoceramus were found in five samples further substantiating the Colorado Plateau provenance of a significant portion of the Colorado River deltaic sediments in the Cerro Prieto area.
Basic aspects of the Cerro Prieto reservoir water recharge; Aspectos basicos de la recarga de agua al reservorio de Cerro Prieto. The Cerro Prieto geothermal field , located 30 km South of Mexicali City, Baja California, has at present an installed capacity of MW in geothermal power plants, that operating with endogenous steam, make use of the underground energy by means of deep wells, from which about 80 million cubic meters per year of high enthalpy water and steam mixture are extracted.
During the exploitation physical an chemical changes in the hydrothermal fluids discharged by the wells have been detected, which shows, among other things, an elevated water recharge, located towards the West area of the field and a low recharge in the part of the east zone area. For this reason the hot brine waste re-injection is recommended, previously treated to eliminate the silica excess to thermally an hydraulically recharge the reservoir in that part of the field.
Durante la explotacion se han percibido cambios fisicos y quimicos en los fluidos hidrotermales descargados por los pozos, lo que indica, entre otras cosas, una recarga elevada de agua localizada hacia el poniente del campo y una recarga baja en una zona de la parte oriental.
Por ello se recomienda la reinyeccion de salmuera geotermica caliente de desecho previamente tratada para eliminar el exceso de silice para recargar termica e hidraulicamente el reservorio en esa parte del campo. Magnetotelluric studies at the Cerro Prieto geothermal field. The simple model shown suggests a lateral discontinuity in the vicinity of Nueva Leon. Agricultural development in the Mexicali Valley and in the high cost of electric power required to operate the irrigation wells in the Valley prompted the Mexican government to investigate the possibility of taking advantage of thermal manifestations in the area located 28 km southeast of the city of Mexicali to generate electric power and thereby partially decrease the flight of foreign exchange.
In , a geologic study of the southern and southeastern zone of Mexicali was conducted to identify the possibilities of tapping geothermal resources. The purpose of this study was to gain knowledge of the geologic conditions in this area and, if possible, to establish the location of exploratory and production wells and, on the basis of the results of the former, examine the geologic history in order to gain knowledge and understanding of the structural control of the steam.
On the basis of this study, it was recommended that 3 exploratory wells should be drilled in order to locate weak zones that would easily allow for steam flow. Subsurface imaging in a sector of Cerro Prieto transform fault near to pull-apart basin, Mexicali Valley, Baja California, Mexico, based on crooked lines 2D seismic reflection.
In the transition zone between San Andres continental transformation system and the coupled transform faults system and rifting of Gulf of California is located the Cerro Prieto pull-apart basin delimitated by Imperial fault northeast and Cerro Prieto fault CPF southwest , this last, is the limit west of Cerro Prieto geothermic field CPGF. By decades, technical and investigation works in Cerro Prieto geothermic field and its vicinity had mapped faults at several depths but do not stablish a clear limit where this faults and CPF interact due the complex hydrothermal effects imaging the subsurface.
The profiles showing the presence of a zone of uplift effect due to CPF. Considering the proximity of the profiles to CPF, it is surprising almost total absence of faults. A strong reflector around 2 km of depth, it is present in all profiles. This seismic reflector is considered a layer of shale, result of the correlation with a well located in the same region. Changes in steam production due to the reservoir conditions in Cerro Prieto , Baja California; Cambios en la produccion de vapor debido a las condiciones del yacimiento en Cerro Prieto , Baja California.
In more than 35 years of exploitation, thermodynamic conditions have changed in the Cerro Prieto geothermal reservoir. The effects are analyzed of the changes to the reservoir and their consequences to steam production in different field zones. For steam production, the most important features of reservoir fluids are enthalpies and pressures. The evolution of these features is presented in an enthalpy-pressure diagram. Here it can be seen that some reservoir zones have almost reached abandonment conditions.
En este trabajo se analiza el efecto de esos cambios del yacimiento y su repercusion en la produccion de vapor para las diferentes zonas en las que se ha dividido el campo. Las propiedades mas importantes del fluido en el yacimiento para la produccion de vapor son su entalpia y su presion, por lo que se presenta la evolucion de esas propiedades en un diagrama de presion-entalpia, en el que se observa que hay zonas del yacimiento que estan proximas a alcanzar condiciones de abandono.
Performance of casings in Cerro Prieto production wells. A careful evaluation of different production casings used at Cerro Prieto from to date has shown that the following casings have yielded particularly impressive results: These casings differ from others of the same diameter but lighter weight which were also used at the field.
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The results are favorable in spite of severe construction problems, especially the loss of circulation during cementing operations, which we encountered in some of the wells where these casings were used. The use of gravity-fed fine sand as packing material and the arrangement of the production and intermediate casings were important in avoiding damage due to tension-compression stresses and, above all, damage due to internal or external corrosion over time.
This situation is clearly evidenced if we compare the damage to the above casings with that experienced by grade N production casings, especially in a corrosive environment. The Cerro Prieto pull-apart basin is located in the southern part of San Andreas Fault system, and is characterized by high seismicity, recent volcanism, tectonic deformation and hydrothermal activity Lomnitz et al, ; Elders et al. Since the Cerro Prieto geothermal field production started, in , significant subsidence increase was observed Glowacka and Nava, , Glowacka et al. Analysis of existing deformation data Glowacka et al.
These faults ruptures cause damages to roads and irrigation canals and water leakage. Since , a network of geotechnical instruments has operated in the Mexicali Valley, for continuous recording of deformation phenomena. Mexicali Valley Crustal Strain Measurement Array includes two crackmeters and eight tiltmeters installed on, or very close to, the main faults; all instruments have sampling intervals in the 1 to 20 minutes range.
Additionally, there are benchmarks for measuring vertical fault displacements for which readings are recorded every 3 months. Since the crackmeter measures vertical displacement on the fault at one place only, the question appears: We used the Wells and Coppersmith relations between. Analysis of the Nuevo Leon magnetic anomaly and its possible relation to the Cerro Prieto magmatic-hydrothermal system.
The broad dipolar magnetic anomaly whose positive peak is centered near Ejido Nuevo Leon, some 5 km east of the Cerro Prieto I Power Plant, has long been suspected to have a genetic relationship to the thermal source of the Cerro Prieto geothermal system. This suspicion was reinforced after several deep geothermal wells, drilled to depths of 3 to 3. A detailed fit of the observed magnetic field to a computer model indicates that the source may be approximated by a tabular block 4 by 6 km in area, 3.
Mafic dike chips from one well, NL-1, were analyzed by means of electron microprobe analyses which showed tham to contain a titanomagnetite that is paramagnetic at in-situ temperature conditions. As the dike mineralogy does not account for the magnetic anomaly, the magnetic source is believed to be a deeper, magnetite-rich assemblage of peridotite-gabbro plutons. The geological model derived from the magnetic study is generally supported by other geophysical data.
In particular, earthquake data suggest dike injection is occurring at depths of 6 to 11 km in an area beneath the magnetic source. Thus, it is possible that heat for the geothermal field is being maintained by continuing crustal extension and magmatic activity. The need to know the exact location in the field of the fault traces in Mexicali has been an important affair due that the topography in this valley is almost flat and fault traces are hidden by plow zone, for this reason, the southern and northern ends of the San Jacinto and Cerro Prieto fault zones, respectively, are not well defined beneath the thick sequence of late Holocene Lake Cahuilla deposits.
The purpose of this study was to verify if Cerro Prieto fault is the continuation to the southeast of the San Jacinto Fault proposed by Hogan in who based his analysis on pre-agriculture geomorphy, relocation and analysis of regional microseismicity, and trench exposures from a paleoseismic site in Laguna Xochimilco, Mexicali. The results of this study allow us to think in the. Two-phase characteristics of the feeding fluid of Cerro Prieto IV wells Mexico obtained by gas equilibrium; Caracteristicas bifasicas del fluido de alimentacion de pozos de Cerro Prieto IV Mexico , obtenidas por equilibrio gaseoso.
The gas composition of fluids produced by CP IV geothermal wells from the Cerro Prieto field was studied in order to identify different types of fluids entering the wells by estimating their temperature and excess steam. The results for the reservoir natural state indicated the presence of fluids with heterogeneous reservoir temperature between and degrees Celsius and excess steam values, which were found from negative boiled liquid that has lost steam when flowing to the well to one steam phase with zero liquid saturation. Also, the results suggested that a steam phase could occur at CP IV which is added to the feeding fluid, depending on the operation conditions of the wells.
The origin of this steam could be the boiling of the deeper liquid due to a pressure drop. Se utilizo un metodo de equilibrio gaseoso basado en la reaccion de Fischer Tropsch y el equilibrio combinado pirita-pirrotita FT-HSH3. Los resultados obtenidos indican que en el estado inicial del yacimiento existen fluidos que muestran heterogeneidad en los valores de temperatura de yacimiento entre y grados Celsius , asi como en el exceso de vapor con valores desde negativos liquido que despues de ebullir ha perdido vapor en su trayecto hacia el pozo hasta uno vapor con cero saturacion de liquido.
El estudio individual de los pozos con fenomenos de ebullicion muestra que a traves del tiempo. These proceedings include both English and Spanish versions of each paper presented at the symposium. Illustrations and tables, which have been placed between the two versions, include captions in both languages. Forty-one papers are included. Five papers were indexed for EDB previously. Separate abstracts were prepared for thirty-three papers and three were listed by title.
Imperial County geothermal development annual meeting: All phases of current geothermal development in Imperial County are discussed and future plans for development are reviewed. Drilling rate for the Cerro Prieto stratigraphic sequence. Drilling practice at the field has been modified in several ways as better information is being obtained. The stratigraphic sequence of the area is made up of three sedimentary rock units of deltaic origin having different densities. These units have been named non-consolidated, semi-consolidated, and consolidated rocks; the thermal reservoirs are located in the latter.
To investigate how the drilling rates are affected by the three rock units, plots of drilling advance versus time were made for a large number of wells. A typical plot is shown and drilling rates are practically constant in three different zones; that is, the drilling rate has only two breaks or changes in slope. Mexican geothermal development and the future. Geothermics in Mexico started in , by drilling the first geothermal well in Pathe, State of Hidalgo, which reached a depth of meters. In electrical generation from geothermal origin began, with an installed capacity of 3.
From to Mexico increased its installed capacity to MW, by developing three geothermal fields: Comision Federal de Electricidad CFE, Federal Commission of Electricity has planned to increase the geothermal -electric installed capacity through construction and installation of several projects. Repowering of operating units and development of new geothermal zones will also allow Mexican geothermal growth.
Symposium in the field of geothermal energy. Mexico and the US are nations with abundant sources of geothermal energy, and both countries have progressed rapidly in developing their more accessible resources. These successes, however, are only a prologue to an exciting future. All forms of energy face technical and economic barriers that must be overcome if the resources are to play a significant role in satisfying national energy needs.
Geothermal energy--except for the very highest grade resources--face a number of barriers, which must be surmounted through research and development. Sharing a common interest in solving the problems that impede the rapid utilization of geothermal energy, Mexico and the US agreed to exchange information and participate in joint research. An excellent example of this close and continuing collaboration is the geothermal research program conducted under the auspices of the 3-year agreement signed on April 7, by the US DOE and the Mexican Comision Federal de Electricidad CFE.
The major objectives of this bilateral agreement are: Status of geothermal resources in Mexico. Except for some isolated instances with tourist or therapeutic objectives and some attempts in the Cerro Prieto geothermal field , there are no projects for direct heat utilization of geothermal resources in Mexico. Therefore, all places that are studied are studied with geothermal -electric objectives. It is convenient to keep in mind that in Mexico, by law, the Comision Federal de Electricidad CFE is the public utility in charge of electrical energy service. This institution is directly responsible for the exploration, development and commercial use of geothermal energy for electrical generation.
Therefore, this paper includes the present and planned exploration and utilization of geothermal resources only for electricity generation for the period to the present. Likewise, starting 5 years ago, the CFE efforts have been directed toward the development of high enthalpy fields.
Update of Geothermics in Mexico. Gutierrez Negrin, Luis C. This means the country is located in third place, worldwide, just behind the USA and Philippines. Thirty-six power plants of several types condensing, back pressure and binary cycle , between 1. These production wells have depths between and 4, meters. During , steam produced in those fields equaled Esto coloca al pais en el tercer lugar mundial, detras de Estados Unidos y Filipinas. En esos campos operan treinta y seis unidades de tipos diversos a condensacion, a contrapresion y de ciclo binario , entre 1. Estos pozos productores tienen profundidades entre y 4, metros.
Durante el vapor producido en los campos sumo Calc-silicate mineralization in active geothermal systems. The detailed study of calc-silicate mineral zones and coexisting phase relations in the Cerro Prieto geothermal system were used as examples for thermodynamic evaluation of phase relations among minerals of variable composition and to calculate the chemical characteristics of hydrothermal solutions compatible with the observed calc-silicate assemblages.
In general there is a close correlation between calculated and observed fluid compositions. The aggressiveness of the geothermal steam controlled; La agresividad del vapor geotermico controlada. The first two units of Cerro Prieto have generated electric energy since ; in completed 15 years of continuous operation, without corrosion problems in the turbines in spite of the utilization of geothermal steam. The experience and the good results obtained during the first years of operation of these two units of La experiencia y los buenos resultados obtenidos durante los primeros anos de operacion de estas dos unidades de Evaluation of a process for the removal of gases contained in geothermal steam through condensation and re-evaporation; Evaluacion de un proceso de remocion de gases contenidos en el vapor geotermico, por medio de la condensacion y de revaporacion.
During the exploitation of a geothermal field , in producing steam with the purpose of generating electricity, brines and waste gases are obtained. The hydrogen sulfide exhaust to the environment implies pollution problems, for this reason processes have been developed for the oxidation of these gases downstream the turbogenerator either in the flow of separated gases in the steam condensation or in the condensate produced. The Instituto de Investigaciones Electricas IIE has collaborated with CFE in the evaluation of the environmental impact of this gas and in the development of the processes for its abatement.
Durante la explotacion de un campo geotermico, al producir vapor con el proposito de generar electricidad, se obtienen salmueras y gases de desecho. La descarga de acido sulfhidrico a la atmosfera implica problemas de contaminacion, por esta razon se han desarrollado procesos para la oxidacion de este gas aguas abajo de la turbina generadora, ya sea en la corriente de gases que se separan en la condensacion del vapor o en el condensado producido.
El Instituto de Investigaciones Electricas IIE ha colaborado con la CFE en la evaluacion del impacto ambiental de este gas y en el desarrollo de sus procesos de abatimiento. Research and technological development on heat pumps in Mexico operating with geothermal energy; Investigacion y desarrollo tecnologico sobre bombas de calor en Mexico operando con energia geotermica. The systems tried on include heat pumps by mechanical compression, thermal absorption and thermal transformers. To date, there are plans to install and test a geothermal heat pump connected to the subsoil , in Cerro Prieto , Mexicali, Baja California, Mexico.
Los sistemas que se probaron incluyen bombas de calor por compresion mecanica, absorcion y transformadores termicos. Research on heat pumps in Mexico operating with geothermal energy and waste heat; Investigacion sobre bombas de calor en Mexico operando con energia geotermica y calor de desecho. Tested systems include mechanical compression, absorption and heat-transformers.
Los sistemas probados incluyen compresion mecanica, absorcion y transformadores termicos. Trace Element Geochemistry of Silica Phases: The study of mineral textures coupled with trace element geochemistry has proven to be a useful tool to understand the evolution of geological environments. Thirteen samples were collected from a m long drill core. Samples were first studied under petrographic microscopy followed by scanning electron microscopy coupled with a cathodoluminescence detector CL-SEM.
Vein type A has only a colloform texture, whereas vein type B, younger and crosscutting the type A, shows zonation, colloform, and jigsaw textures. A comparison between vein type A and B, show that vein type A is Al-Na-K-Li poor , 36, , and ppm average, respectively and As-Sb rich 43 and ppm average, respectively.
Our preliminary results show that the trace element geochemistry is strongly related to the different silica textures, which formed as a response to different thermodynamic conditions and fluid-rock ratios. Geothermal fields of China. There are over known occurrences of geothermal phenomena in China. These lie mainly in four major geothermal zones: Hot water has also been found in boreholes in major Mesozoic-Cenozoic sedimentary basins. This paper presents a summary of present knowledge of these geothermal zones. The geological settings of geothermal occurrences are associated mainly with magmatic activity, fault uplift and depressional basins and these are described by examples of each type.
Increased multipurpose utilisation of geothermal resources is planned and examples are given of current usages. Environmental impact in geothermal fields. Generally, water exploitation and deep steam of geothermal fields may be cause of a pollution potential on the surface, specially by the chemical composition of geothermal water which has a high concentration of minerals, salts and heavy metals. The utilization of stable isotopes as deuterium and oxygen 18 as radioactive tracers and water origin indicators allow to know the trajectories and sources of background waters as well as possible moistures between geothermal waters and meteoric waters.
Some ions such as chlorides and fluorides present solubilities that allow their register as yet long distances of their source. Low enthalpy geothermal energy technologies are being developed around the world as part of policies to replace the use of conventional sources of energy by renewable ones. In Chile, interest in applying this technology is focused on the Magallanes Basin Austral Basin in Argentina in the extreme south of the country, where important hydrocarbon deposits have been exploited for more than six decades with more than 3, wells drilled to depths of over 4,m.
This formation has been drilled mainly at depths of m to m, the estimated geothermal gradient in the zone is 4. To understand in detail the behavior and distribution of the different lithofacies of the Springhill Formation in the Sombrero Oil and Gas Field , sedimentological and geological 3D models have been generated from existing well logs and seismic data. To comprehend the quality of the reservoirs on the other hand, many petrophysical studies of drill core samples representative of the different lithofacies, complemented by electric well log interpretations, were carried out. Results confirm the existence of at least two quartz-rich sandstone lithofacies as potential geothermal reservoirs.
In the principal settlement in this area, Cerro Sombrero township 1, population , the annual average temperature is 6. Geothermal Field Investigations of Turkey. Geothermal energy is a type of energy that are found in the accessible depth of the crust, in the reservoirs by way of the permeable rocks, specially in heated fluid. Geothermal system is made of 3 main components; heat source, reservoir, and fluid bearing heat.
Geothermal system mechanism is comprise of fluid transmission. Convection current heat transmission is caused by heating and causes the fluid in the system to expand. Heated fluid with low density show tendency to rise in system.
Geothermal system occurs with variable geophysics and geochemical properties. Geophysical methods can determine structural properties of shallow and deep reservoirs with temperature, mineralization, gas amount, fluid movement, faulting, and sudden change in lithostratigraphic strata. This study revealed possible reservoir structures and showed examples of geophysics and gas measuring results in Turkey which is wealthy in regard to Geothermal sources.
Cerro del Agua scoria cone m. Dos Cerros is a lava shield which covers an area of The Dos Cerros eruption took place close to 14, yr BP as constrained by radiocarbon dating. Rocks from these three volcanoes are olivine-hypersthene normative basaltic andesites and andesites with porphyritic, aphanitic, and glomeroporphyritic textures. Pelagatos rocks also present quartz xenocrysts.
Due to their high Cr and Ni contents, and high Mg s, Pelagatos rocks are considered to be derived from primitive magmas, hence the importance of this volcano for understanding petrogenetic processes in this region. Major and trace element abundances and petrography of products from these volcanoes indicate a certain degree of crystal fractionation during ascent to the surface.
However, the magmas that formed the volcanoes evolved independently from each other and are not cogenetically related. There is no clear evidence of important crustal contributions in the compositions of Pelagatos and. Klamath Falls geothermal field , Oregon. Klamath Falls, Oregon, is located in a Known Geothermal Resource Area which has been used by residents, principally to obtain geothermal fluids for space heating, at least since the turn of the century.
Over shallow-depth wells ranging from 90 to 2, ft 27 to m in depth are used to heat 35 MWt over structures. This utilization includes the heating of homes, apartments, schools, commercial buildings, hospital, county jail, YMCA, and swimming pools by individual wells and three district heating systems. Larger facilities and district heating systems use lineshaft vertical turbine pumps and plate heat exchangers. Well water chemistry indicates approximately ppM dissolved solids, with sodium sulfate having the highest concentration.
Some scaling and corrosion does occur on the downhole heat exchangers black iron pipe and on heating systems where the geo-fluid is used directly. Isotope study in geothermal fields in Java Island. Study in two geothermal fields , Dieng and Kamojang, in Java island by utilizing isotope technique has been carried out. Isotopic data of wells, springs and other geothermal manifestations providing informations on the recharge area of precipitation contributed to geothermal resources, flow paths and origin of geothermal fluids. The data of oxygen shift has also provided information on the characteristic the fields.
Relation between 1m depth temperature and average geothermal gradient at 75cm depth in geothermal fields. Shallow ground temperatures such as 1m depth temperature have been measured to delineate thermal anomalies of geothermal fields and also to estimate heat discharge rates from geothermal fields. As a result, a close linear relation between 1m depth temperature and average geothermal gradient at 75cm depth has been recognized in many geothermal fields and was used to estimate conductive heat discharge rates.
Overview of Cerro Prieto studies - PDF Free Download
However, such a linear relation may show that the shallow thermal regime in geothermal Structural investigations of Great Basin geothermal fields: Because fractures and faults are commonly the primary pathway for deeply circulating hydrothermal fluids, structural studies are critical to assessing geothermal systems and selecting drilling targets for geothermal wells. Important tools for structural analysis include detailed geologic mapping, kinematic analysis of faults, and estimations of stress orientations. Structural assessments are especially useful for evaluating geothermal fields in the Great Basin of the western USA, where regional extension and transtension combine with high heat flow to generate abundant geothermal activity in regions having little recent volcanic activity.
The prolific geothermal activity is probably due to enhanced dilation on N- to NNE-striking normal faults induced by a transfer of NW-directed dextral shear from the Walker Lane to NW-directed extension. Most fields are associated with steeply dipping faults and, in many cases, with Quaternary faults. The structural settings favoring geothermal activity are characterized by subvertical conduits of highly fractured rock along fault zones oriented approximately perpendicular to the WNW-trending least principal stress.
Features indicative of these settings that may be helpful in guiding exploration for geothermal resources include major steps in normal faults, interbasinal highs, groups of relatively low discontinuous ridges, and lateral jogs or terminations of mountain ranges. CCAT-prime is a six meter aperture off-axis submillimeter telescope that we plan to build at m elevation on Cerro Chajnantor in Chile. The CCAT-prime optics are based on a cross-Dragone design with high throughput and a wide field -of-view optimized to increase the mapping speed of next generation cosmic microwave background CMB observations.
These characteristics make CCAT-prime an excellent platform for a wide range of next generation millimeter and submillimeter science goals, and a potential platform for CMB stage-IV measurements. Here we present the telescope design for CCAT-prime and review the science goals. Taking advantage of the high elevation site, the first generation instrument for CCAT-prime will measure seven different frequency bands from um to 3mm.
A regional aeromagnetic survey of the area was completed in to determine the basement configuration of the Mexicali Valley. The location of a number of strike-slip and normal faults was revealed from this study Evans, Between and detailed resistivity surveys of the area were made Garcia, The results showed that the field was associated with a large resistivity low which later was found to be due to highly conductive and altered sediments near the surface Goldstein and Razo, A number of faults were identified, including a major one striking n o r t h w e s t - s o u t h e a s t , parallel to the railroad tracks.
To replace damaged wells and to find additional steam, to increase power production in the future, 14 new wells were drilled at Cerro Prieto between and One of the wells M was located approx. Its purpose was to explore the eastern region where geophysical data indicated a deep extension of the reservoir. In Mercado presented a revised model showing the movement of geothermal fluids in the field Fig. It was a refinement of his model and was based on new geothermometric M.
Mercado's convective model for the Cerro Prieto field. Mercado's convectwe m o d e l for the C e r r o Prieto field. The fluid circulation patterns and temperature distributions shown, especially in the western part of the field, have, in general, been confirmed by subsequent studies. Passive seismic studies in the area of Cerro Prieto were carried out in to using portable stations.
In five permanent stations were established in the area. The results indicated right-lateral strike-slip faulting parallel to the northwest-southeast striking Cerro P r i e t o - Imperial transform fault system, and dip-slip faulting along some of the faults oblique to that system Albores et al. Because of their success in the limited area southeast of the Cerro Prieto volcano, CFE in began a series of geophysical studies in the Mexicali Valley to define the extent of the Cerro Prieto field and to locate other geothermal anomalies.
Schlumberger resistivity surveys identified in the area of the field a resistivity low which at that time was assumed to be closely associated with the so-called Cerro Prieto basement horst which had been inferred from gravity data Razo et al. Later it was shown that this resistivity low was due to surface effects related to highly conductive near-surface materials Wilt et al.
On the other hand, Lyons and van de Kamp indicated that there does not seem to be any convincing geophysical evidence for a basement horst underlying the field. Gravity, magnetic and reflection seismic surveys carried out in enabled Fonseca and Razo to construct a structural map of the basement. There now exists disagreement about this map since some of the data seem to reflect the alteration of the sediments or the presence of volcanic layers in the valley fill Lyons and van de Kamp, However, these studies identified a number of northeast-southwest faults which, at least partially, were confirmed by well log correlation studies.
The data gathered were very useful for understanding the subsurface geology at Cerro Prieto e. Lyons and van de Kamp, ; Majer and McEvilly, in preparation. For example, the magnetic study showed a high centered approx. After the surveys, CFE carried out additional geophysical studies in the Mexicali Valley, most of them to locate new geothermal areas. Only a heat flow study Diaz, and a few lines of a seismic reflection survey Fonseca et al.
All this time, the monitoring and analysis of the seismic activity continued to study the structure and tectonics of the region Reyes and Razo, ; Reyes et al. Puente and de la Pefia and de la Pefia et al. They showed a complex horst-and-graben basement structure and faulting of the sedimentary fill. This contact was used as a stratigraphic marker horizon. The cuttings from new wells have been carefully studied by CFE, using mainly a binocular microscope to determine the appearance of key minerals which indicate the presence of high subsurface temperatures.
These studies, which are useful to establish well completion depths, have produced lithologic columns and cross-sections showing the distribution of sand M. J L i p p m a n n percentage and mineral zones in the field Cobo, ; Cobo and Bermejo, in preparation. Over the years the interpretation of geophysical well logs has been performed by several Mexican authors with the purpose of developing a geologic model of the system Abril and Noble, ; Prian, a, b, ; Diaz et al. Between that year and more than 75 wells were completed at Cerro Prieto Cobo and Bermejo, in preparation.
Thirteen of these were planned to be deep step-out wells to help define the field boundaries, i. This reservoir B or 13 is at approx. After well E-I was completed, a number of deeper wells E-series, Fig. Only two of these 13 exploration wells penetrated basement, well S at m and well M at m, even though one well, H-2, was drilled to m. The cuttings of wells H-2, M and NL-I indicated that they had drilled through a series of mafic and silicic dikes at depths between and m.
These were also found in production well T, Elders et al. Data on the production characteristics of the Cerro Prieto wells and the chemistry of the fluids produced have been collected and analyzed since the mids. Details on the chemical and physical characteristics of the fluids produced by the different wells, the reservoir temperatures computed on the basis of geothermometers, the composition of the reservoir fluids, and their spatial and temporal variations have been discussed by several Mexican authors Mercado and Samaniego, ; Mafi6n et al.
A general decrease of reservoir temperatures with time, localized boiling near the wells and the recharge of colder waters from the west and hot waters from the northeast have been indicated by these studies. Between and three first-order leveling surveys were carried out in the area of Cerro Prieto. The network used in these studies was tied to stations north of the border. In the production area of the field increased ground subsidence was observed.
However, it was not clear how much of it was due to fluid extraction and how much to ground shaking related to the strong 6. A few papers describing the data and results have been published e. Rivera and Ramey, ; Abril and Molinar, ; Rivera et al. The results of C F E ' s downhole pressure measurements and the pressure drawdowns observed in the field have been discussed by Bermejo et al. The distribution of temperatures in the field have been given by several authors.
The latest and most complete set of data is by Navarro et al. Over the years CFE has used commercial laboratories to measure hydraulic properties of cores. Permeability and Overview o f Cerro Prieto Studies porosity data on Cerro Prieto cores have recently been reported by l i e Contreras et al. A number of modeling studies and analysis of production data have been made by CFE and its contractors; part of the results have been reported.
Rivera indicated that the behavior of the Cerro Prieto reservoir and wells could be described using decline curve analysis. In Rivera described how a graphic procedure could be used for forecasting production. Liguori simulated the evolution of Cerro Prieto using a mathematical model.
He found that a very low heat transfer coefficient between rocks and fluids was adequate to match observed values which he attributed to flow through microfractures as well as pores. His results showed a good match in the steam production rate, but the computed rate of water production was low and the enthalpy too high.
Liguori indicated that this was caused by the vertical leakage of colder waters into the reservoir which was not considered by his model. Saltuklaroglu analyzed the interference effects between wells. From observation well data he established an average rate of water level drop of 0. Later this value was used by Grant et al. Based on a simplifed reservoir model Molinar et al, calculated a year production life for Cerro Prieto at an electric power production capacity of MW e.
Using standard groundwater analysis techniques, Shnchez and de la Pefia showed that the a reservoir is very permeable and is recharged from all sides. A permeability- thickness value of 3. The hydrological model of Halfman et al. The injection operation has been described in detail by Cortez et al. It is worthwhile to indicate that a sudden increase in reinjection rate was observed after the June earthquake; it jumped from approx. Previously, several treatment methods for colder approx.
Geochemical studies on Cerro Prieto also began before the formal agreement was signed. In close cooperation with CFE the geochemical data gathered on Cerro Prieto since were summarized and interpreted by Mafi6n et al. On the basis of early CFE and U. In a preliminary model of the structure of the field was developed by Noble et al.
A self-potential survey conducted in late detected a large-amplitude, long-wavelength anomaly over the field. In a more detailed study defined a dipolar self-potential anomaly M. L i p p m a n n running through the center of the production field Fig. The source of it appeared to correspond to a north-trending fault and be caused, possibly, by an electrokinetic streamingpotential mechanism Corwin et al. Self-potential anomaly over the Cerro Prieto field from Corwin et al.
The dashed line indicates the position of the charged plane. Other geophysical studies were restricted to the interpretation of CFE Schlumberger resistivity and gravity data using numerical modeling techniques. The gravity interpretation gave clear evidence of a n o r t h - northwest trending fault and several trending northeast. The data showed a 'basement' high in the production area which was interpreted to be the result of a shallow zone of densified sediments Goldstein, In , Elders and his group at the University of California at Riverside UCR began thorough petrological and light isotope studies of well cuttings and cores.
A number of regularly distributed metamorphic mineral zones were recognized in the field. The progressive changes in mineralogy indicated a systematic relationship with reservoir temperatures Elders et al. The isotope studies indicated that the 8'80 for calcite in sandstones could be used to estimate stable reservoir temperatures and that the same parameter in shales could indicate the extent and distribution of subsurface flow Olson, Other results of this work indicated that the Cerro Prieto hydrothermal system is relatively open to fluid flow.
The analysis of cuttings and cores continued at UCR over the entire 5-year cooperative program, adding vitrinite, fission-track annealing and geophysical well log studies to the petrologic and light isotope work begun earlier Elders et al. Mainly on the basis of the results of these studies, Elders et al, in press developed a model for the natural preproduction flow regime at Cerro Prieto Fig. A heat source for the hydrothermal system was suggested to lie to the northeast in an area where wells drilled through mafic and silicic dikes.
From that source an inclined plume of hot water ascends toward the southwest, boiling in places and precipitating minerals which tend to seal the rock pores. The plume discharges upward and horizontally to the southwest creating surface manifestations and shallow zones of temperature reversals. The model also shows cold water recharge from the northeast which may also seal the reservoir pores as these waters are heated.
Southwest - northeast section across the Cerro Prieto field showing the flow regime proposed by Elders et al. In a study of the paleomagnetism of the rhyodacitic rocks of the Cerro Prieto volcano was made. Magnetic polarity and paleopole position data suggested that the volcanism was initiated about , years ago.
The youngest volcanics reaching the surface cooled about 10, years ago de Boer, The analysis of geophysical well logs was conducted during the entire length of the program as new wells were completed. Noble and Abril described the problems found in interpreting logs obtained from Cerro Prieto wells.
Later, and along the same line Ershaghi et al. Using mainly wireline well logs and surface geophysical data Lyons and van de Kamp developed a geologic model of the area that was significantly more detailed than any of the earlier models. They proposed three groups of faults of different ages and presented a depositional model for the reservoir that showed a transition from a deltaic environment in the east, to a marine environment in the west.
These authors gave well log evidence that disputed the basement-horst structural model; they showed that the gravity high over the reservoir is due to the high densities of the indurated shales of Unit B. They also showed that the reservoir is not overlain by a laterally continuous low-permeability layer, that the reservoir sandstones present secondary porosity and that the production intervals in the wells generally straddle or underlie the top of the high-density and high-resistivity shales.
Lyons and van de Kamp seem to have been the first to suggest that the positive magnetic anomaly, approx. The degree and distribution of hydrothermal alteration, and M. L i p p m a n n the origin and distribution of dissolution secondary porosity in the field were discussed by Vonder H a a r , Teihnan and Cordon briefly described how the geologic model of Cerro Prieto evolved as new exploration data became available.
It showed two types of faults: On the basis of new data, this map was somewhat modified during a second workshop Zelwer, Overview o f Cerro Prieto Studies Recently a micropaleontological analysis of 30 core samples was completed Ingle, The distributed patterns of ostracodes and foraminifera, together with the lithofacies studies of Lyons and van de Kamp , indicated that the sediments at Cerro Prieto represent a complex of alluvial, deltaic, estuarine and shallow marine environments.
These sediments were deposited along the front of the Colorado River delta as it prograded across the Salton Trough during the Pliocene and Pleistocene. The existence of reworked Cretaceous specimens confirmed that a significant part of the deltaic sediments in the area derived from the Colorado Plateau. After an extensive analysis of geophysical and lithological well logs, Halfman et al.
By superimposing on the model downhole temperature and well completion data it was possible to establish the movement of the geothermal fluid in the field, prior to its exploitation Fig. The hot fluid appears to enter the system from the southeast, from the area where igneous dikes are believed to have intruded into the valley fill Lyons and van de Kamp, ; Elders et al. Then, the fluid moving westward through permeable layers ascends gradually to shallower depths by flowing upward through faults and sandy gaps in shaly layers acting as local cap rocks.
Eventually, in the western part of the field, part of the geothermal fluid leaks to the surface and the rest mixes with colder groundwaters. Halfman's model seems to indicate that the Michoachn fault Fig. This study has identified three faults called H, L, and S on Fig. Reflection seismic data Majer and McEvilly, in preparation , the location of boiling zones in the reservoir Nehring and D'Amore, in press and the result of numerical modeling studies Lippmann and Bodvarsson, have substantiated the existence of these faults.
The model has also shown, confirming the conclusions of others, that there is no laterally continuous cap rock at Cerro Prieto which prevents the leakage of geothermal fluids from the reservoir. In the first LBL detailed seismological study was conducted at Cerro Prieto; two others were made in and Majer and McEvilly, , , in preparation. In addition, in late a downhole geophone was installed in a m-deep well near well M The purpose of this work was to determine the relation of wave propagation characteristics and microearthquake activity to the production zone, recharge areas, heat source and general lithology and structure of the field.
The events registered in indicated strike-slip movement along n o r t h w e s t - s o u t h e a s t trending faults. The results of later surveys did not permit establishing the type of faulting associated to the monitored events. The seismic events were clustered near the center of the production area, at depths from 2 to 5 km, on a fairly well defined north - south plane extending from well M to the power plant. On the other hand, the events were distributed in a rather diffuse pattern concentrated on the western edge of the field. The diffuse pattern of the events and the A ': Location of the main faults controlling the subsurface flow of geothermal fluids in the Cerro Prieto field from Halfman et al.
Also shown is the position of cross-section A - A ' given in Fig. During the to period four precision gravity surveys were conducted at Cerro Prieto to study the possibility of geothermally induced subsidence Grannell et al. Comparison of results from year to year showed subsidence clearly associated with the June earthquake. Also, significant changes were observed at several stations in the western older part of the field. The pattern of these latter changes is elliptical in a northwest-southeast direction parallel to the structural grain and faulting in the region.
L i p p m a n n correlating precision gravity and leveling data, Zelwer and Grannell in preparation concluded that changes in gravity and surface elevation correlate well, and were primarily produced by compaction that occurred in response to the June earthquake. However, Grannell et al. Zelwer and Grannell in preparation also indicated that a density increase is taking place in the reservoir zone because of mineral precipitation or the entrance of cooler, denser, waters.
Further analysis of the data will be required to clarify the importance of fluid extraction on the subsidence observed at Cerro Prieto. A twodimensional vertical resistivity model along a n o r t h e a s t - s o u t h w e s t line across the field line E - E ' was developed Wilt et al. It showed that the production region is characterized by high resistivity 4 ohm-m relative to the surrounding region 1 to 2 ohm-m. The higher resistivity is assumed to be related to the densification of the shales in Unit B. Top of A B horizon Two-dimensional resistivity model for a southwest northeast line crossing the Cerro Prieto field Line E E ' ; Wilt and Goldstein, The studies improved the resistivity model for the eastern part of the field Wilt and Goldstein, It revealed that the 4 o h m - m body associated with the producing zone dips eastward at 30 to 50 degrees to a depth greater than 2 km Fig.
A narrow, steeply dipping 1. Repetitive high-precision d i p o l e - d i p o l e resistivity measurements taken during the period to over line E - E ' showed a consistent pattern of apparent resistivity changes. A zone of increasing resistivity is related to the production region; above and flanking this region are zones of decreasing resistivities. There is also an unresolved component that might relate to ascending hot fluids at the eastern edge of the producing zone Wilt and Goldstein, in press. Overview o f Cerro Prieto Studies The changes in apparent resistivities detected at Cerro Prieto from the d i p o l e - d i p o l e monitoring surveys were studied by Pruess et al.
Based on schematic one- and two-dimensional reservoir simulations, assuming the existence of waters of different salinity and temperature, changes in formation resistivity were computed which were then transformed into changes in apparent resistivity that would be observed at the surface. Over a period of three years starting in , three magnetotelluric MT studies were made in the area of the field.
The initial purpose of the MT soundings was to provide additional and deeper subsurface resistivity data to supplement the d i p o l e - dipole and Schlumberger surveys c o n d u c t e d in the region. S u b s u r f a c e resistivity models developed jointly f r o m the d i p o l e - d i p o l e resistivity and MT data sets helped define the deep resistivity structure of the field.
The models also showed: Later MT studies were conducted to help delineate a possible boundary on the south side of the thermal area. Recently Goldstein et al. Their modeling studies, coupled with the analysis of cuttings of mafic dikes recovered from well NL-I, and viewed in conjunction with other geological and geophysical data, gave further support to the hypothesis that Cerro Prieto is located in a pullapart basin like others in the Salton Trough and the Gulf of California Lomnitz et al.
These authors estimate that the top of the main magnetic source body is approx. On the basis of preliminary thermal modeling results, Elders et al. The model age for such an event is 40, to 50, years, which is in the range of the age for the volcanic activity at Cerro Prieto de Boer,