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394

ENTRADA DELFLUIDO

964-Z

PLACA DE DISTRIBUCION

1* 4

TUBO 4" 0ARENA

1I .... .1.,

MALLA RETEN DE ARENA

TORNILLOS DE FIJACION

-1 .2 « PLACA CON ORIFICIOS

Figura 6. Detalle de lecho de prueba tipo media caRa para observaci6n longitudinal.

4.- Jones, F.0.: "Influence of Chemi--

cal Composition of Water on Clay -

Blocking of Permeability", Jour. -

Pet. Tech. (April 1964 ) 441.

INTRODUCTION

5.- Hewitt, C .H.: "Analytical Technique

for Recognizing Water Sensitive --

Reservoir Rocks", Jour. Pet. Tech.

( August 1963 ) . 813.

PRELIMINARY STUDIES OF BRINE REINJECTION

AT THE CERRO PRIETO GEOTHERMAL FIELD

At the present time, Units 1 and 2 of theCerro Prieto power plant generate 75 MW of power.

For this purpose about 2200 tons/hr of fluids areproduced. Of this, 700 tons/hr of steam are sentto the plant and 1500 tons/hr of spent brine arediscarded into an evaporation pond.

The thermal energy extracted is estimated tobe on the order of 723 x 109 cal/hr, of which

about 260 x 109 cal/hr is lost with the discardedwater to the atmosphere. If, instead of disposingthis water, it were possible to recirculate it bysending it back into the reservoir, most of theenergy presently dissipated into the atmospherecould be returned underground. Reinjection wouldalso lengthen the productive life of the reservoirbecause it would constitute an additional sourceof fluid recharge. Furthermore. reinjection ofseparated brines would solve the problem ofsurface disposal. About 1500 tons/hr of brinesare presently sent to the evaporation pond, andthe problems will become more acute when Units3 and 4, each with 37.5-MW capacity, go on linein mid-1979. At present, a number of studies are,being conducted to evaluate alternative methodsof injection. The methods being considered are:cold or hot injection with open, closed, or mixedsystems.

For each of these system, laboratory testswill be carried out using columns packed with

different grain-sized sands. The sands usedare from alluvial fans of the Cucapa range.

The purpose of these tests is to establish thescale-forming tendencies of the water wheninjected under different conditions ( Figures1, 2 and 3 ). Later, similar tests will be madeon models built with natural sandstones.

Because of its favorable characteristics,well M-6 ( see Figure 1 ) might be used in a pilotinjection field test. The feasibility of rein-

jecting into two different levels, at 300 m andbetween 527 and 741 m depth, is being evaluated.Other possible wells for reinjection could beM-3 and M7.

PROGRAM DESCRIPTION

The injection of brine into a geothermalfield presents several problems that must bethoroughly evaluated before proceeding with apilot test. This is necessary to avoid eitherlowering the production temperature of the

reservoir, or plugging certain parts of itdue to the chemical precipitation in the rockmatrix from reactions between the injectedand the reservoir water. Figures 4, 5, and 6

show tentative sketches of the proposed apparatusfor the first tests.

The process of injecting water into areservoir is not new. For several decades

the oil industry has used water injection inthe secondary recovery of hydrocarbons.1 Itis therefore possible to identify some commonproblems of water injection in both oil fields

SOPORTE DE MALLA

i

< 3 n-, :

and geothermal systems. It is also important

to recognize some basic differences betweenthe two processes. Among the differences are:(a) the development of separate thermal andchemical fronts in the geothermal reservoirwhen brine is injected; and (b) the differences

in the concentration and temperature of brinesfrom oil fields and those produced in geothermal

fields. For a system such as Cerro Prieto,which has both intragranular and fracturedpermeability and porosity, the basic problems

are the following:

1. Corrosion of the surface installations

and in the we112

2. Harmful effects of sulfur, iron, ands'ludge-forming bacteria, if theinjection is an open one3

3. Chemical precipitation in the surfacepipes, when the effluents of severalwells producing from different horizons

are mixed

4. Chemical precipitation in the porousstructure of the reservoir due toincompatibility between the injected

and the reservoir water

5. Possible reduction in the permeabilityof the rock in the reservoir due to

the swelling and/or dispersion ofclays present4,5

More detailed studies are being carriedout in order to be able to determine as manyvariables as possible before undertaking a

pilot field test.

FIGURE CAPTIONS

Figure 1. Flow diagram of scaling tests in"artificial sand layers" in well M-21A, using

hot water.

Figure 2. Flow diagram of scaling tests in sandbeds using cold separated water from which silica

has been removed by settling.

Figure 3. General arrangement of scaling testsin sand layers in sand beds using water fromwhich silica has been removed by settling.

Figure 4. Sand bed ( spool type ) for scaling tests

and transversal examination.

Figure 5. Test bed for continuous observation.

Figure 6. Half-round type test bed for longitudinal

observations.

395

ESTUDIOS PRELIMINARES DE LA REINYECCION DE LASAIMUERA PRODUCIDA EN EL CAMPO GEOTERMICO

INTRODUCCION

DE CERRO PRIETOJ. Rivera R,

Comisi6n Federal de Electricidad, Mdxico, D.F., MdxicoS. Mercado G.

Instituto de Investigaciones Eldctricas, Cuernavaca, Morelos, MaxicoC. F. Tsang

Lawrence Berkeley Laboratory, University of CaliforniaBerkeley, California, USA

En la actualidad la planta geotermoel&c--trica de Cerro Prieto genera 75 MW en lasunidades 1 y 2, con una extracci6n mediade aproximadamente 2200 ton/hr de fluidosde los cuales 700 ton/hr corresponden a -vapor y 1500 ton/hr estdn constituidas --por salmuera que se desecha a una lagunade evaporaci6n.

Se estima que la energia calorifica ex---traida es del orden de 723 x 109 cal/hr,desechdndose a la atm6sfera en el agua --separada. una cantidad del orden de 260 x109 cal/hr. Se considera que si en vez --

SEPARADOR PRIMARIO

V. S.A. R

M 2IA

ORIFICIOS

1 il'•1A. S. 1 1•

loopsig.

--1

de desechar esta agua fuera posible re---circularla, envidndola de nuevo al yaci--miento, se devolveria al subsuelo gran --parte de esta energia que actualmente sedisipa, 10 cual alargaria por necesidad -la vida productiva del campo, ya que se -le suministraria tambi&n una fuente adi--cional de recarga hidrdulica.

Por otra parte, la reinyecci6n del fluidode desecho resolveria el problema de la -eliminaci6n superficial del mismo, ya quesi actualmente se envian a la laguna de -evaporaci6n aproximadamente 1500 ton/hr -de salmuera, el problema se agudizard alentrar en operaci6n las unidades 3y4--

FLASHEADOR PILOTO

V. S.8. R

III 1

23

AGUA SEPARADA 20. FLASHEO

Ar CON PRESION DEL SEPA-RADOR PRIMARIO.

8.-CON BOMBEO PARA INCRE-| I MENTAR LA| 2•ESION

TDESCARGAS A CANALETADE DRENAJE DEL POZO.

Figura 1. Diagrana de flujo de pruebas de incrustaciones con agua caliente en"estratos arenosos artificiales" en pozo M-21A.

XBL 793-8800

.i

1::4:

391

392

VS. AR

SEPARADOR PRIMARIO

VS, VR

SEPARADORPILOTO

T fAGUA SEPARADA 20. FLASHEO

PILETAS DE ASENTAMIENTODE SILICE ( BORDOS DE TIE-RRA CON pvc.)

1 +BOMBAC ELECTRICA )

LECHO ( S) DE PRUEBA

\-j

>1CANALETA DE

DRENAJE DEL POZO

E'igura 2. 9iagrama flujo de prueba de incrustaci6n en lechos arenosos con aguaseparada fria (stlice asentada) .

con capacidad de generacion. de 37.5 MW cada| una a mediados del ano de 1979.

RESUMEN

Actualmente se estgn 1levando a cabo unase•ie de estudios con obj eto de evaluar -diversas alternativas de sistemas de in--yecci6n, dentro de las que se contemplanlas siguientes: inyecci6n en caliente 0 -en| frfo, contando con sistemas abiertos,cerrados o mixtos.

Para cada uno de estos sistemas se reali-zardn pruebas de laboratorio en columnaserr©acadas con arena proveniente de los --a•anicos aluviales de las montafias Cucapdcon diversos arreglos granulom6tricos. E.2tas pruebas tienen como objeto investigarla tendencia incrustante del agua que se-r• inyectada baj o diferentes condiciones( Figs. 1, 2 y 3 ). Posteriormente se tie-ne programado realizar este tipo de prugbas en patrones construidos con arenis--cas naturales.

Dadas las caracteristicas favorables quepresenta el pozo M-6 ( ver Fig. 1 ), se hapensado en la posibilidad de utilizarlocomo pozo piloto para 11evar a cabo unaprueba de campo. Se estd evaluando la --

factibilidad de reinyecci6n a dos nive--les diferentes, 300 m y en el intervalocomprendido entre los 527 y 741 m de pr.gfundidad. Otros posibles candidatos sonlos pozos M-3 y M-7.

GENERALIDADES

M2IA0

0

La inyecci6n de la salmuera. producida enun campo geotdrmico presenta varios pro-

DESCARGA A CANALETA DEDRENAJEl• -LECHO (S) DE PRUEBA

81

T k.AGUA SEPARADADEL 20. FLASHEOLillI

PILETAS DE ASENTAMIENTO DE SILICE DE APROX.5 x 5 m CON BORDOS DE Im DE ALTURA. ..Figura 3. Arreglo general de pruebas de incrustacionen lechos arenosos con agua separada fria (siliceasentada).

M 21-A

ASl

'4

1

2

T

0

BOMBA (ELECTRICA)

393

blemas que es necesario evaluar exhaustlvamente antes de proceder a efectuar unaprueba piloto en el campo mismo, ya quede no hacerlo asi, se corre el grave ---riesgo de contaminar tdrmicamente el ya-cimiento, o bien, originar el taponamiento de ciertas porciones del mismo, debi-do a la precipitacidn de compuestos insqlubles en la matriz rocosa, originado --por reacciones quimicas entre el agua inyectada y la que se encuentra en el yaclmiento. Las Figs. 4, 5y6 muestran es--quemas tentativos de los arreglos pro---puestos para efectuar las primeras prue-bas.

El proceso de inyecci6n de agua a un ya-cimiento no es en si una tdcnica novedo-sa, ya que se ha venido 11evando a caboen la tecnologia de la explotaci6n petrqlera durante varias ddcadas en el proce-so conocido como recuperaci6n secundariade hidrocarburos mediante inyecci6n del

1agua .

Resulta entonces posible identificar al-gunos problemas comunes tanto a la inyeaci6n de agua a yacimientos petroleros cgmo a sistemas geotdrmicos; siendo impor-tante tambidn reconocer algunas diferen-cias bdsicas entre ambos casos. Dentro -de las diferencias podemos mencionar eldesarrollo de los frentes tdrmico y qui-mico que se tienen en el yacimiento geo--tdrmico al inyectar la salmuera, asi comotambidn el hecho de que no es frecuente -manejar en los campos petroleros salmue--ras con la concentraci6n y temperatura delas producidas en los geotdrmicos.

Para un sistema como el de Cerro Prieto -que cuenta con porosidad y permeabilidadtanto intergranular como por fractura, --los problemas bdsicos a resolver son lossiguientes:

1.- Corrosi6n tanto en las instala--ciones superficiales como en elpozo.2

MAMB•RA DE DISTRIBUCION341·- if

MALLA PARA RETENCION DEARENA / ARENA

t' ., 1 lit......-. ...

Figura 4. Detalle de arreglo de lecho arenoso parapruebas de incrustaci6n, tipo carrete para examentransversal.

_3-IIL

•UNION ESPECIAL2 0 ARENA /

I TUBO OE ACERO- 1 i TUBO OE VIORIC) 2" 0• 11.. ,«

-+ 2m , 0.5 I +

Figura 5. Detalle de lecho de prueba para observaci6ncontinua.

2.- Si el sistema de inyecci6n es --abierto, se tiene la posible ac-ci6n nociva de bacterias tales -como las sulfato reductoras, lasdel fierro y las formadoras de -cien03.

3.- Precipitaci6n de substancias in-solubles en lineas conductoras -superficiales al mezclarse el --efluente de varios pozos que prQducen de diferentes horizontes.

4.- Precipitaci6n de compuestos ins.Qlubles en la estructura porosa -del yacimiento debida a problemasde incompatibilidad entre el ---agua inyectada y la presente enel yacimiento.

5.- Posible disminuci6n de permeabi-lidad de la roca del yacimientodebida al hinchamiento y/0 dis--persi6n de las arcillas presen--tes.4,5

Trabajos mds detallados estan siendo ---efectuados con objeto de poder determi--nar tantas variables como sea posible antes de 1levar a cabo una prueba a escalade campo.

REFERENCIAS

1.- Rivera, R.J.: Notas del Curso Re-cuperaci6n Secundaria de Hidrocarburos Mediante la Inyecci6n de --Aqua, Division de Estudios Supe--riores, Facultad de Ingenieria, -Universidad Naciona.1 Aut6noma deMaxico. ( 1977).

2.- Uhlig, H.H.: Corrosi6n Handbook,John Wiley & Sons. Inc. New York( 1948).

3.- Amstutz, R.W. & Reynolds, L.C.: --"Engineering Aspects of WaterfloodBactereology", Jour. Pet. Tech. --( Oct. 1963 ) 1073.

TUBO DE VIDRIO]

-0.5�442-

t 14-1 m -X 2. --X--1 m-

394

SOPORTE DE MALLA

ENTRADA DELFLUIDO

-,f) -3 -7ST°«c-

PL.ACA DE DISTRIBUCION

1P 4

TUBO 4" ID

7'»1.'. ,1. :

MALLA RETEN DE ARENA

TORNILLOS DE Fl JACION:.'.*4;::1 '2 0 PLACA CON ORIFICIOS

Figura 6. Detalle de lecho de prueba tipo media cana para observaci6n longitudinal.

4.- Jones, F.0.: "Influence of Chemi--cal Composition of Water on Clay -Blocking of Permeability", Jour. -Pet. Tech. (April 1964 ) 441.

INTRODUCTION

5.- Hewitt, C.H.: "Analytical Techniquefor Recognizing Water Sensitive --Reservoir Rocks", Jour. Pet. Tech.( August 1963 ) . 813.

PRELIMINARY STUDIES OF BRINE .REINJECTIONAT THE CERRO PRIETO GEOTHERMAL FIELD

' At the present time, Units 1 and 2 of theCerro Prieto power plant generate 75 MW of power.For this purpose about 2200 tons/hr of fluids areprbduced. Of this, 700 tons/hr of steam are sentto| the plant and 1500 tons/hr of spent brine arediscarded into an evaporation pond.

1 The thermal energy extracted is estimated tobe on the order of 723 x 109 cal/hr, of whichabout 260 x 109 cal/hr is lost with the discardedwater to the atmosphere. If, instead of disposingthis water, it were possible to recirculate it bysending it back into the reservoir, most of theenergy presently dissipated into the atmospherecould be returned underground. Reinjection wouldalso lengthen the productive life of the reservoirbecause it would constitute an additional sourceof fluid recharge. Furthermore, reinjection ofseparated brines would solve the problem ofsurface disposal. About 1500 tons/hr of brinesar6 presently sent to the evaporation pond, andth4 problems will become more acute when Units3 and 4, each 'with 37.5-MW capacity, go on linein mid-1979. .A.t present, a number of studies arebeing conducted to evaluate alternative methodsof injection. The methods being considered are:cold or hot injection with open, closed, or mixedsystems.

For each of these system, laboratory testswill be carried out using columns packed withdifferent grain-sized sands. The sands usedare from alluv.Lal fans of the Cucapa range.

The purpose of these .tests lS to establish thescale-forming tendencies of the water wheninjected under different conditions ( Figures1, 2 and 3 ). Later, similar tests will be madeon models built with natural sandstones.

Because of its favorable characteristics,well M-6 ( see Figure 1 ) might be used in a pilotinjection field test. The feasibility of rein-jecting into two different levels, at 300 m andbetween 527 and 741 m depth, is being evaluated.Other possible wells for reinjection could beM-3 and M7.

PROGRAM DESCRIPTIONThe injection of brine into a geothermal

field presents several problems that must bethoroughly evaluated before proceeding 'with apilot test. This is necessary to avoid eitherlowering the production temperature Of thereservoir, or plugging certain parts of itdue to the chemical precipitation in the rockmatrix from reactions between the injectedand the reservoir water. Figures 4, 5, and 6show tentative sketches of the proposed apparatusfor the first tests.

The process of injecting water into areservoir is not new. For several decadesthe oil industry has used water injection inthe secondary recovery of hydrocarbons.1 Itis therefore possible to identify some commonproblems of water injection in both oil fields

1 --1.'-0* -1.,1

< 3m )