Underground Power

comisicin federal de ziectrk,idad

CURD PRIETO

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency Thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.

"The geothermal energy is a privilege and a great promise for the generation of electric power. It is satisfactory "indeed to observe that ambitious project of Comisi6n Federal de Electrici-dad is on its way".

LUIS ECHEVERRIA , PRESIDENT OF MEXICO

ORGANIZATION

The Cerro Prieto Geothernzoelectrical projectis the result of the team work of the General Mana-gements of Planning and Program, Construction, andOperation of the Comision Federal de Electricidad.

The General Management of Planning and Pro-gram, through its Department of Geothermal Re-sources, is in charge of the research, developmentand Maintenance of the wells and of the geothermalfields as a whole.

The General Management of Construction isin charge of the project and of the direction andsupervision of the civil engineering works and ofthe assembly of the geothermoelectric plant.

The General Management of Operation is incharge of the control of the generating- plant op-eration and of the distribution of electricity to helpmeet the demand in the State of Baja California.

In the realization of the project as well as inthe supply of equipment and materials Mexican aswell as American, British, Japanese, Belgian, Swiss,Italian and French companies entered.

"The fountains that spring forth in levelcountry they call `arneyalli', which means water

that gushes, some of these springs are salty andhave bad taste and bad odor ...

To the springs that flow from their deepinsides raising up the sand, so that it seems thatthe sand itself is flowing, they call `xalatl', whichmeans sand water ...

Fray Bernardino de Sahagnn. General His-tory of the Things of New Spain".

GEOTHERMAL ENERGY

One of the forms of energy, oldest if its originis considered but newest as concerns its scientificexploitation by man, is the goethermal energy.

Geothermal energy, as its name implies, is heatenergy, proper of the earth's core, which moves up inmagma flows and through the fissures existing inthe solid and solid-liquids media of the interior ofthe earth's crust, towards levels closer to the earth'ssurface where, if favorable geological characteristicsare encountered for its accumulation it persists andtransmits itself to underground waters.

By means of wells specifically drilled, these sub-terranean waters, which have a large amount ofthermal energy stored, come up to the surface,turning into the steam that man uses for the ob-tention of electrical power.

THE COMISION FEDERALDE ELECTRICIDAD

It is a descentralized government official agency,in charge of power generation in Mexico; which hascommenced, starting in 1950, the studies towardsthe exploitation of this resource in the thermal zonesof the country; which studies crystalize today in thefirst commercial geothermal power plan in Latin-america: the geothermoelectric project of Cerro Prie-to, Baja California, which reinforces the supply ofpower for the State of Baja California.

Initial discharge from a well where the steamcarries an enormous amount of sand.

CERRO PRIETO GEOTHERMAL PROJECT

LOCATION

The geothermal project of Cerro Prieto, B. C.,is located at approximately 30 kilometers south ofMexicali, capital of the State of Baja California,between 114 50' and 115 48' of west longitude andbetween 31 55' and 32 44' of north latitude.

\ The region in the middle of the desert, is a plainon the Colorado river delta, with the Cerro Prietoprominence standing out.

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GEOGRAPHICAL LOCATION OF CERRO PRIETO FIELD

View of the geothermal field from Cerro Prieto.

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The plain is flat slightly rounding off and slop-,

ping towards the sea; it is limited by the Cucapa:2Sierra which trends northwest and ends at the Cen-tinela hill, and by the El Mayor dnd Los PinitosSierras to the south.

The area is connected with the city of Mexicaliby both the Sonora Baja California Railroad and thePascualitos Pescaderos State road which interconnectswith the Mexicali-San Luis Rio Colorado Highway.

Pond of boiling mud in the Vulcano Lagoon.

PRELIMINARY EXPLORATION

The initial stage of investigation and detectionof a ;geothermal zone consists of looking for surfacemanifestations such as thermal springs, geysers,fumaroles, ponds of boiling mud, etc., which, in thecase of Cerro Prieto site, were found in the plutonicLandscape of the Vulcano Lagoon where a spectacleworthy of the primitive stages of our planet as-tonishes the visitor.

Mexican technicians thought that, accordingwith the magnitude of these manifestations, the zonepresented great possibilities for exploitation, whichled to an intensive stage of geological, geophysicaland geochemical works which started and continuesto !develop at present.

View of the Vulcan() Lagoon where the high- degree of hydrothermal alteration and the

effect of the , environment on vegetation isvisible.

-30r0.4-Cone of mud volcano formed by successive -

eruptions of clays.

Geological works include from surface geologyto aerogeology to obtain morphological, geotectonic,etc., maps, which serve as a basis to detect fissuredzones or those showing important alterations ohydrothermal origin.

Magnetometry measures the variations of theearth"s magnetic field, relation them to the

subsoil structure.

Geophysical studies cover gravimetric, magne-tometric, thermometric, seismic and resistivity data,whose purpose is to determine the structure of thezone and the possible locations with the thermalanomalies and confinement of underground water.

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Studies om the thermal flow furnish data toobtain profiles of the geothermal gradient.

Seismic studies are useful to determine thesubsoil structure by means of either the reflec-tion or the transmission of mechanical waves.

Gravimetry is used to detect variations in themean density of the subsoil.

Resistivity measurements of the thermal fieldaid in detecting different layers of materials aswell as the possible identification of their

nature.

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Method used for sampling gases from surface.manifestations.

Chemical analyses are carried out by Meansof the most modem techniques.

Geochemical studies cover the sampling of waterand gases of the surface manifestations and theirposterior analysis to correlate the chemical com-position of the samples with the possibility of geo-thermal exploitation of the zone.

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SKETCH OF SUPPOSED GEOLOGICAL CROSS SECTION

CERRO PRIETO VOLCANOGEOTHERMAL WELL

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ALTERNATE BEDS OF WIWISHALE AND SANDSTONE MaiSATURATED WITH HOT WATER. OBIREINHII

FRACTURES IN BASEMENT THROUGH WHICH ,t6Ali MAGMATIC GASES FLOW IS ESTABLISHED.

GEOLOGY

As a result of both studies of geological inves-tigations and the inspection of the cores obtainedduring the drilling of deep wells, the geologicalstructure of the field is established.

In the case of the Cerro Prieto thermal field,at a depth of approximately. 2500 meters, the granitebase was encountered which, maybe, is highly fis-sured since, tectonically, the zone is related to theSan Andres systems of faults, which extends intothe United States four main faults being visible,crisscrossed by several secondary faults and coveredby the delta alluvial deposits from the Coloradoriver.

Underlained by the base granite, and down to adepth of approximately 70 meters, alternate layersof lutites and sandstones are encountered, the sand-stones being saturated by overheated water due tothe transmission of heat by the flow of gases andvapors at a high temperature through the fissuredbasalt rock.

Lastly, acting as a seal to the deposit, there isa layer 700 m. thick of impervious plastic clayswhich keep the hot water trapped, preventing theflight of heat to the surface.

CUCAPAH RANGE

DRILL-ING

The drilling techniques used in the geOtherMaldo not appreciably differ' from those used in,

the drilling of oil well:3.- Onee the drilling, site is chosen, the ground

around it is compacted to insure its Stability and

View of drilling pipes on the monkey boardand stowed in banks.

Rotary rig. The mast with the drilling pipingas well as the traveling pulley and the mud

cooling tower may be seen.

trench for,.a , ',drilling ,cellar is excavated, 'generallyto -a depth of 2 to 3 meters,- Proceeding afterwardsto install; the rOtarydrilling equipment.

main mud tank

mud pumpvibrating screen

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Drillholes are bored in various diameters whichdecrease as depth increases. At the Cerro Prietosite, in most of the wells drilling starts with a 22"

,'diameter, which is substituted by a 15" diarneter tobe again substituted by another diameter of 10-5/8"at the depth of 1000 meters; which diameter isretained down to the total depth of the well which,generally, is 1400 m.

Utilization of power wrenches for the screwingup of the drill string.

crown blockcooling tower

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concrete cellar-_-..:

traveling block

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Sketch of drilling equipment.

lowout preventar

gate valve

chemical additives pump

drill pipebi t

As in the case of oil drilling, drilling fluids areused to lubricate and cool the bore as well as to bringup to the surface the formation core samples. Thesefluids consist of bentonitic type slurries havingseveral aditives since, due to the obnormal ge-othermal gradient, all drilling muds tend to plastisizeat the bottom of the well; for the same reason, acooling tower is installed in order to cool the circula-tion slurry.

draw works

Motor

0 16"A NCHORING CASING

Three-cone drilling bits. Samples cores of the litological column ex-tracted during drilling.

Miring actual drilling there are frequently lossesof fluids through fissures or fractures of the layerscrossed. If such fissures are considered sterile, theyare sealed with vegetable fibers, mica flakes, celophanechips, or, in some cases cement. If the fissures liein zones which very possibly will be productive,drilling of the well is considered as completed upon

-reaching them.As drilling progresses, it is necessary to harness

well with seamless steel piping. Pipes generally usedcit Cerro Prieto, are 16" diameter for anchoring;11-3/4" for lining, and 7-5/8" for production. Allthese pipes are casehardened by using Portlandcement with set delaying aditives as the setting timediminishes with the high temperatures.

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Schematic section, of a geothermal well.

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PRODUCTION CASING

Explosive load to perforate the productionpipe and slotted production pipes.

',1400 m.

The productive zones of the wells, which aredetected by means of electrical, sonic and thermallogs recorded in each of them, are made to flow,in some cases, by perforating pipes by means oshots and in others, through a previously slottedfinal section rof pipe.

To keep the well under control at all times duringthe drilling, safety equipment is installed on theanchor pipe which consists of a blowout prevent or,which seals the well automatically when pressuresbecome dangerous.

When drilling of the well is terminated, thissafety equipment . is disassembled and in the pipe'head a valve .tree is installed from which all ductsof the geothermal . fluids branch oitt.View of a valve tree.

PRODUCTION

The output of Cerro Prieto geothermal wells'consists of a mixture of water and steam which, tobe exploited, needs to be separated so as to sendthe dry steam to the turbines of the geothermoelectricpower plant.

The separation of the mixture water-steam, isachieved by letting the flow of the well pass throughcentrifugal separators where the action of the cen-trifugal force makes the water adhere to the separa-tor walls and then descend to it's bootom from whereit goes to the silencers while the steam, due to islower densiy, rises in the separator and is extractedthrough a central pipe towards the collecting net.

The separated water is discharged into thesilencers and, later, to the drainage channels.

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Diagram of the flow in the well; the over-heated water of the deposit flows through thegrooves of the pipe, partly evaporating andon the surface the mixture water-steam is

separated in a centrifugal separator.

The purpose of the silencers is to reduce thenoise produced by the steam discharge or the waterdischarge at high pressure into the atmosphere. AtCerro Prieto, two different types of silencers areused: horizontal silencer and twin-barrel verticalsilencers.

The first type of silencer is formed by a seriesof pipes of increasing diameter, whose effect is togradually reduce the flow, speed thus diminishingthe noise produced by discharging into the at-mosphere.

The second type consists of twin vertical pipes,made of wood, resting on a concrete structure. Thedischarge:pipe,4 ti2e, _separator connects directlywith the cohcrete struoture where the flow of theseparated- water or of Mixture is divided intotwo currents .tb the vertical tubes wherein, becauseof the centrifugal effect similar to that of theseparators, the water is separated from the steamthat has resulted from the reduction of pressure,the steam flowing out through the upper part intothe atmosphere and the remaining water throughthe lower part to the drainage channel. Since the-tubes are of large-diameter, the outlet speed of thesteam is low and the noise produced by its dis-charge is reduced.

Diagram showing the performance of a cy-clone separator and the double-barrel vertical

silencers.

View of flow measurement.

cyclone

WEL.I. -HEAD EQUIPMENT

Drawing showing the location of wells andsteam transportation pipes.

STEAM TRANSPORTATION

The separated steam flowing out of the separatoris conducted through hundreds of meters of pipingto the geo thermoelectric power plant.

This steam carries with it a small amount ofwater which, along with the one formed by con-densation of a small part of the flow, is separated,by means of steam traps, on the way to the plant,since the steam must be perfectly dry upon enteringthe turbines.

For added safety, at the entrance of the plant,the total steam flow goes through moisture separa-tors, where any vestige of dampness is eliminated.

Transportation pipes are arranged in fourbranches which connect with all production wells.

In every branch, large expansion curves areinstalled to absorb the mechanical stresses broughtabout by the thermal expansion of the pipes.

At the power plant, these branches are connectedto two steam collectors, from which the pipes forthe turbogenerators branch out.

The total length of pipe with diameters 16" to34", is more than 6 kilometers, while additionally,there are several kilometers of secondary pipe linesof lesser diameters.

non condensable gases

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steam-jetair ejector

steam-jetair ejector

steamline no._

steamline no 4

steam UNIT No

hot watercold water

GENER ATORsteamline no I

75 psigsteamline no 2

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cooling to w e r

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General view of the model for the powerhouse and annexes.

Steam collector and moisture separatorstanding in front of the -engine house under

construction.

Mixture condensers installed outside thepower house.

THE GEO THERMOELECTRIC POWER PLANT

The power house for this first stage, was designedalong the general lines of the conventional thermalpower plants. The structure, of galvanized steel, cou-ers an area of 60 x 14.5 m. with a height of 30 m.Inside it; the turbogenerators with their auxiliaryequipment, are found with the exception of the con-densers Which, because of their size, were installedon the outside of the engine house.

All turbogenerators, were built with specialmetal alloys to reduce the amount of both

corrosion and erosion.

The engine house is built on two levels where-in turbogenerators, oil and hydrogen systems, in-struments laboratory, control room, several admi-nistrative and operation offices are distributed.

The exhaust steam, after being used in the tur-bogenerators, is condensed by means of mixturecondensers in which cold water is injected which,when mixing with the low pressure steam, condensesit, and then flows jointly to the system of watercirculation.

The non-condensable gases are eliminated fromthe condensers by means of steam operated ejectors. Structure of the power house where its two

levels can be seen.

Taking into account the fact that the geothermalzone is in the desert, and that the available waterdoes not fulfill the necessary requirements for useas a liquid ,medium for cooling, it is necessary touse the same condensed steam to recover the waterflow for cooling the system, for which purpose it isrecirculated through a tower built for that purpose.

View of the cooling tower and the circulationpumps.

View of the cooling tower under construction.

This cooling tower is the outstanding pieceof equipment in the zone due to its dimensions(146 x 25 x 18 m). It is capable of cooling 27,000ms/hr. of water 16C. The forced induced draft,crossed flow tower, is made of treated wood.

The hot water is sent to the cooling tower bymeans of two centrifugal pumps of mixed flow witha capacity each of, 6,950 m3/hour, equipped with386 HP motors; the cold water is sent to the con-denser and the cooling equipment by means of similarpumps, but of only 6,750 m 3/hr. capacity and with560 HP motors each.

-

View of 'substation and transfoi-Mers (model),

Adjoining the engine house is the substationwith a double bar arrangement of disconnectingswitches for an adequate radial connection of theplant to the Tijuana-Mexicali Electrical System;with two reserve outlets left for future lines. Thepower supply'' Will be carried out through two 161KV , transmission lines.

The main transformers are located near 1bY theengine house in a conventional patern, so as to con-nect with an isolated phase bar to the generators:

Insulator and conductors used in the sub-station were subjected to weathering tests.

BENEFITS AND FUTURE POSSIBILITIES

The plutonic field of Cerro Prieto is not theonly one in Mexico; 120 additional thermal sites areknown, extending all the way from Tijuana to theTacand volcano at the southern end of the country;the ,Comision Federal de Electricidad is carrying outconstant studies at Pathe, municipality of Tecozau-tla, State of Hidalgo, where in 1956 the first steamjet was obtained. Two others are located at LosNegritos, municipality of Villamar and Ixtlan delos Hervores, municipality of Ixticin de los Hervores,both municipalities in the State of Michoacan.

The benefits to be derived from the installationof the geothermoelectric power Plant of Cerro Prie-to in Mexicali, Baja California, are inc. reased due tothe favorable geographical location of the area.

These location factors are:

1.When the geothermoelectric power plant goesinto operation it will be connected with the Tijuana-Mexicali System, thus reducing the problems whichthe considerable length of this transmission line causessuch as: blackouts for failures, regulation, etc.

2.Saving of fuels in a zone of difficult supply.Since oil is largely extracted along the coast of theGulf of Mexico, to supply the plants along thePacific coast, it is necessary to transport fuels throughthe Isthmus of Tehuantepec, which operation cannot currently be carried out in sufficient volume tomeet the demand, thus leaving only the alternativeof either transportation by tanker through thePanama Canal, or of importing it.

The electric system of the State of Baja Ca-lifornia depends at present on one single plant, thatof Tijuana. Any unforeseen failure can originateblackouts, which have already happened and whichare very damaging to the local economy.

Another factor to be considered is the fact, thatwith the installation and operation of the plant,with the exploitation of this energy resource, fluc-tuations in the price of fuels have no effect.

Activities concerning drilling of wells, are con-stantly scheduled and the news wells not only rein-force the supply of steam for the geothermoelectricalpower plant but, additionally, increase the productionof the field to plan extensions which will permit notonly meeting the increase in the demand of elec-tricity but also to partially substitute the powergeneration from the Tijuana plant, with the purposeof saving on fuels and of increasing the systemreserve capacity.

At present, the pilot plant built for the pro-duction of potable water to meet the needs of con-struction of the geo thermoelectric power plant,continues in full operation and the experience beingderived from it will be very useful to plan the largescale production of water.

The Comision Federal de Electricidad keeps incontatc with the Comision para el Aprovechamientode Aguas Salinas, with the pupose of carrying outstudies concerning the production of potable water,utilizing the geothermal steam already used in theturbines and which may be used for the supply, asmentioned earlier, of good quality potable water forMexicali.

Also, research has been started to recover chem-ical products which are either dissolved or in sus-pension in the water separated from the steam andwhose exploitation makes us visualize in the futurean increment in the industrialization and devel-opment of the State of Baja California.

The initiation of the commercial operation ofthe plant's first unit has been programmed for thesecond semester of 1972, the second unit to enterinto operation two or three months later.

COSTS,The investment in the construction of the Cerro

Prieto geothermoelectric power plant, has risen to14,400,000 dollars.

From this total, 7,200,000 were invested in theplant's equipment; 2,080,000 were charged to thedrilling of the wells and the remainder was spentin labor and overhead costs.

According to the economical studies carried outby the Comision Federal de Electricidad, the yearlyexpenses of the power plant will come up to 1,440,000dollars.

If the fact is taken into account that the zoneof Baja California does not have energy resources ofanother kind, it can be said that the operation ofgeothermoelectric power plant will represent a yearlysaving of 170,000 dollarS, Which savings will increaseconstantly since the cost of the fuels used in con-ventional thermoelectric power plant Will keep onrising.

Well No. 2 in the geothermal field of Pathe.

View of the engine house and substation inthe geothermal field of Pathe, municipality

of Tecozautla,. State of Hidalgo.

Rotary drilling equipment used in thegeothermal field of Los Negritos, municipality

of Villamar, State of Michoacan.Well No. 2 in the geothermal field of halal.'

de los Hervores.

INSTALLED CAPACITYYEAR 1971

HYDRO

KWTHERMAL

KWTOTAL

KWHYDRO

KWTHERMAL

KWTOTAL

KW

Baja California 328,563 328,563 xtapantongo 1'049,100 473,000 1'522,100Noroeste 192,200 192,855 385,055 Centro Sur 38,228 46,310 84,538

Norte 38,250 399,626 437,876 Centro Oriente 21,820 40,500 62,320

Golfo Norte 31,500 523,571 555,071 Oriente 450,280 143,950 594,230

Huasteca 20,160 41,970 62,130 Sureste 753,523 47,878 801,401

Occidente 63,140 57,852 120,992 Peninsular 86,000 86,000

Centro Norte 1,248 1,248 TOTAL C. F. E. 2'920,401 2'833.830 5'754,231

Centro 2,800 367,425 370,225 CLFC 313,195 354,200 667,395

Jalisco 98,575 74,750 173,325GRAND TOTAL: 3'233.596 3'188.030 6'421.625

Centro Occidente 159,577 9,580 169,157

NATIONAL ELECTRIC INDUSTRYOPERATING CAPACITY

KW

YEARS HYDRO THERMAL TOTAL

1968 2'508,831 2'287,492 4'796,323

1969 3'228,716 2'429,221 5'657,937

1970 3'228,206 2'839,414 6'067,620

1971 3'233,596 3'188,030 6'421,626

441

;:comIstorf.- 5EDERAL DE ELECTrilCIDADDirecto r General: LIC. GUILLERMO VILLARREAL CARAVAN -1'ES-

_,

b-Directi)r General: I NG. ADQL,F0- FRANC PEDROZALIC. JOilCiEzliEREDIA FERRAE7'

Corilkion Editorial: JOAOtirti_ VI LLASANA V ALONSOJOSE ANGEL AGUI [AR

1971R5dano 14,

jVJxico 5,'D. F.

ORGANIZATIONGEOTHERMAL ENERGYLOCATIONPRELIMINARY EXPLORATIONGEOLOGYDRILLINGPRODUCTIONSTEAM TRANSPORTATIONTHE GEOTHERMOELECTRIC POWER PLANTBENEFITS AND FUTURE POSSIBILITIESCOSTS