- Email: [email protected]
The Cerro Prieto geothermal field: Present and future
Geothermtcs, Vol 8, pp 151- 153
Pergamon Press Ltd 1979 Printed in Great Britain © CNR
THE CERRO PRIETO GEOTHERMAL FIELD: PRESENT AND FUTURE H ALONSO E Cormsl6n Federal de Electrtctdad, Coordmadora Ejecuttva de Cerro Prteto, Mextcah, B C , Mextco
From 1949 to 1950, the Comlst6n Federal de Electrlcldad (CFE) sent a group of engineers and techmclans to visit the geothermal field m Larderello, Italy At that time, Mexico was interested in the posslbd~ty of using geothermal energy from the numerous geothermal manifestations throughout the country As a result of that mission, an inventory of geothermal manifestations was begun Special emphasis was placed on the Path6 area, in the state of Hidalgo, 120 km north of Mexico City, because of its geographic location Surflclal geological studies were carried out in this area, gradient wells were drilled, and chemical analyses of thermal manifestations were performed Based on th~s reformation, the first exploratory well was drilled between 1955 and 1956 The success of this first exploration well marked the beginning of the development of geothermal technology in Mexico In 1959, the first 3500 kWe experimental unit was installed This umt was dismantled after 14 yrs, when It was operating at a c a p a o t y of less than 500 kWe Based on the results obtained in Path6, the exploration of the Ixtl~n de los Hervores geothermal field, in the state of Mlchoac~in, was started in 1956 Two wells were drilled, one of which has been producing hot water and steam for the past 21 yr Geothermal explorations were then undertaken in Los Negrltos, where some wells were also drilled with positive results At the beglnnmg of 1969, exploration work started in the Cerro Prleto geothermal area, with surflclal geological surveys and some chemical analyses of thermal manifestations This enabled us to pinpoint the first well, from which we obtained a w a t e r - s t e a m mixture Two more wells were drilled at a later date, one at 700 m and another at 450 m depth, and very promising temperatures were observed As a result of this, we decided to undertake detailed geological, geochemical and geophysical studies, starting with a seismological refraction survey in 1962 The results of the survey made the present development of the Cerro Prleto field possible Based on this study, we located the first deep well (M-3), reaching down to a depth of 2550 m and penetrating the granitic basement Production was achieved at a depth between 700 and 900 m, and we observed a lower temperature when we went below this depth Well M-4, about 25 km north-east of well M-3, was drdled later, in an attempt to cross the well through an important fault detected by the seismological study Well M-4 reached a depth of 2000 m, with a bottom-hole temperature of 36°C Well M-5, which is 2 5 km south of M-3, marked the discovery of the field and established the bas~s for future development at Cerro Pneto due to ~ts excellent production characteristics In 1967, it was decided to drdl 14 wells in order to build the first 75,000 kW power plant Simultaneously, detailed geological and geochemical studies were carried out, the most outstanding of which was the one performed by Washington State University using stable~sotope analysis to define the origin and age of water supplying the Cerro Prleto field A decision was reached to install the first two units with a total capacity of 75,000 kW, after drllhng the 14 aforementioned wells ( 1 9 6 7 - 1969), and after carrying out production tests m different wells These umts were put into commercml operation in 1973, and have continued 151
152
H Alonso E
w o r k i n g satisfactorily since then, wzth a plant efficiency that has g r a d u a l l y reached 90% The o p e r a t i o n o f this plant saves the C F E 1 million barrels o f o l l / y r S i m u l t a n e o u s l y with c o n s t r u c t i o n and o p e r a t i o n o f the first p o w e r station, detailed geophysical studies c o n t i n u e d to be carried out to the south a n d east o f the present field It was c o n c l u d e d that the geological structure closest to the field IS m a d e up o f a series o f parallel faults, s o m e o f which are visible in the Sierra C u c u p a h , and a horst that coincides with the presently e x p l o i t e d area and with m a i n d o w n t h r o w n structures t o w a r d the east o f C e r r o P n e t o Based on this, we decided to drill a well (M-53) outside the present e x p l o i t a t i o n area This well, at a d e p t h o f 2000 m, p r o v e d to have a p r o d u c t i o n o f a b o u t 100 t / h o f steam and a b o t t o m - h o l e t e m p e r a t u r e o f 340°C This, a n d well M-51, situated to the south o f the present field, o p e n e d up a new era In the e x p a n s i o n possibilities o f C e r r o P r l e t o The result was the c o n s t r u c t i o n o f a new 75,000 k W station (units 3 and 4), fed by 14 wells, lying east a n d south o f the present tleld These wells have better characteristics than those s u p p l y i n g units l a n d 2, since the m a j o r i t y o f them ha'~e a b o t t o m - h o l e t e m p e r a t u r e o f between 300 and 350°C and p r o d u c e between 80 and 140 t / h o1 steam (This is the case for well M-51) T h e 14 a f o r e m e n t i o n e d wells are c o m p l e t e d a n d the steam lines are being Installed a n d readied for c o n n e c t i o n with the second 75,000 k W station, which will go on-line c o m m e r c i a l l y at the b e g i n n i n g o f next year (1979) Based on experiences a c q u i r e d in 1977, it was decided that in 1978 we w o u l d drill 26 wells in the eastern part o f the present field, to s u p p l y a third p o w e r station, which will be called C e r r o P r l e t o lI As an interesting f o o t n o t e , we would like to point out that most o f the wells a l r e a d y drilled ha'~e a 7 5/8-1n - d i a m e t e r p r o d u c t i o n casing (I-55 and K-55) Due to the p r o b l e m s o c c u r r i n g in these well casings, we u n d e r t o o k a s t u d y a n d decided to change the c o n s t r u c t i o n characteristics o f wells for the C e r r o P r l e t o II station We decided to use 9 5/8-1n - d i a m e t e r (N-80) instead of 7 5/8-1n - d i a m e t e r p r o d u c t i o n casings (J-55 a n d K-55) W i t h this new d i a m e t e r , we h o p e to o b t a i n p r o d u c t i o n that will fluctuate between 170 a n d 180 t / h o f s e p a r a t e d steam, this as feasible, since we have o b s e r v e d p r o d u c t i o n o f 140 t / h with a 7 5/8-1n - d i a m e t e r p r o d u c t i o n casing in well M-51 This will represent an i m p o r t a n t saving for the future C e r r o P r l e t o II plant If it is possible to o b t a i n an average well capaclt~ o f 15 M W e , we will need to drill fewer wells, even t h o u g h they might ha,~e to be deeper On the eastern part o f the field, the depth o f the p r o d u c i n g areas varies between 2000 a n d 2500 m C o n s t r u c t i o n o f the C e r r o P r l e t o lI p l a n t is scheduled to begin in 1980 W e h o p e to start the first stage o f the c o m m e r c i a l o p e r a t i o n in 1983 a n d the second stage in 1985 The total capaclt} ot this plant will be 220,000 k W In general terms, this is the most relevant d a t a r e g a r d i n g the present field o f C e r r o Prleto As for o t h e r areas o f g e o t h e r m a l interest, we have begun geologic, g r a v l m e t r i c , magnetic, and electrical-resistivity studies, as well as t h e r m a l gradient studies south a n d north o f the present field In the s o u t h e r n p o r t i o n , a b o u t 17 km f r o m the present h e l d , we have f o u n d an extremely interesting resistivity a n o m a l y , which also coincides with an a r e a o f e a r t h q u a k e swarms We are awaiting results o f seismological studies begun in S e p t e m b e r 1978 These studies co~,er the present field and its southern extension (where the a f o r e m e n t i o n e d a n o m a l y is situated) and seek to define the structure and locate a deep e x p l o r a t i o n well If it proves to be p r o d u c t i v e , this w o u l d definitely b r o a d e n the possibilities o f the C e r r o P r l e t o h e l d T h e r m a l g r a d i e n t wells were also drilled In the n o r t h e r n part o f the field, m an area called Tule C h e c k , to c o m p l e m e n t the geophysical studies a l r e a d y carried out These included resistivity, g r a v l m e t r l c , m a g n e t i c a n d geochemical studies o f surface m a n i f e s t a t i o n s In a d d i t i o n , we have p l a n n e d seismic studies, which will enable us to locate an e x p l o r a t o r y well in this a r e a in 1979 On the o t h e r h a n d , in o r d e r to p i n p o i n t a d d l n o n a l g e o t h e r m a l areas, studies will be u n d e r t a k e n in a region called Mesa de A n d r a d e , where surhc~al geological surveys ,ire
The Cerro Prteto Geothermal Field Present and Future
153
already under way This area is situated approx 40 or 50 km s o u t h - e a s t of the Cerro Prleto geothermal field, available Information, which is still very scarce, shows that ~rrlgatlon wells drilled m th~s region have abnormal temperatures of around 50°C at depths of 100 - 150 m We have scheduled geophysical studies for this area (resistivity, gravlmemc, magnetic, thermalgradient and seismic studies) in order to determine the location of an exploratory well, which will probably be drilled next year, depending on the result of these studies In Baja California, all construction programs for geothermal plants have been contingent on the Increase in demand for energy The electrical system In the state is an isolated one, and operates with two power stations one located in the city of R o s a m o , south of TIjuana (thermoelectric), and the other operating in Cerro Prleto (geothermal) In order to build power stations whose capacities will go beyond the needs of the northern zone, we are contemplating connecting the existing system to the national distribution network, which is approx 700 km away at its closest point If the government approves this connection, the building programs for geothermal plants would change, and instead of planning for a 400,000 kW capacity for 1984-1985, we could consider installing 700,000 kW We must point out that the proven capacity in the area surrounding the Cerro Prleto field is about 750,000 kW In very broad terms, these are our future programs, they are especially important to Cerro Prleto and Baja California, since this is practically the only easy-to-operate and clean natural energy resource available in the region Pollution problems are minor compared with other types of power plants The problem of waste water has several solutions, among them recovery of chemical products, drainage into the Laguna Salada or another area close to it, or relnjectlon The outlook for the central part of the country ~s also very positive Once we develop the geothermal fields under study at this time, we hope to have a minimum installed capacity of 4000 MWe throughout our country by the year 2000
Pergamon Press Ltd 1979 Printed in Great Britain © CNR
THE CERRO PRIETO GEOTHERMAL FIELD: PRESENT AND FUTURE H ALONSO E Cormsl6n Federal de Electrtctdad, Coordmadora Ejecuttva de Cerro Prteto, Mextcah, B C , Mextco
From 1949 to 1950, the Comlst6n Federal de Electrlcldad (CFE) sent a group of engineers and techmclans to visit the geothermal field m Larderello, Italy At that time, Mexico was interested in the posslbd~ty of using geothermal energy from the numerous geothermal manifestations throughout the country As a result of that mission, an inventory of geothermal manifestations was begun Special emphasis was placed on the Path6 area, in the state of Hidalgo, 120 km north of Mexico City, because of its geographic location Surflclal geological studies were carried out in this area, gradient wells were drilled, and chemical analyses of thermal manifestations were performed Based on th~s reformation, the first exploratory well was drilled between 1955 and 1956 The success of this first exploration well marked the beginning of the development of geothermal technology in Mexico In 1959, the first 3500 kWe experimental unit was installed This umt was dismantled after 14 yrs, when It was operating at a c a p a o t y of less than 500 kWe Based on the results obtained in Path6, the exploration of the Ixtl~n de los Hervores geothermal field, in the state of Mlchoac~in, was started in 1956 Two wells were drilled, one of which has been producing hot water and steam for the past 21 yr Geothermal explorations were then undertaken in Los Negrltos, where some wells were also drilled with positive results At the beglnnmg of 1969, exploration work started in the Cerro Prleto geothermal area, with surflclal geological surveys and some chemical analyses of thermal manifestations This enabled us to pinpoint the first well, from which we obtained a w a t e r - s t e a m mixture Two more wells were drilled at a later date, one at 700 m and another at 450 m depth, and very promising temperatures were observed As a result of this, we decided to undertake detailed geological, geochemical and geophysical studies, starting with a seismological refraction survey in 1962 The results of the survey made the present development of the Cerro Prleto field possible Based on this study, we located the first deep well (M-3), reaching down to a depth of 2550 m and penetrating the granitic basement Production was achieved at a depth between 700 and 900 m, and we observed a lower temperature when we went below this depth Well M-4, about 25 km north-east of well M-3, was drdled later, in an attempt to cross the well through an important fault detected by the seismological study Well M-4 reached a depth of 2000 m, with a bottom-hole temperature of 36°C Well M-5, which is 2 5 km south of M-3, marked the discovery of the field and established the bas~s for future development at Cerro Pneto due to ~ts excellent production characteristics In 1967, it was decided to drdl 14 wells in order to build the first 75,000 kW power plant Simultaneously, detailed geological and geochemical studies were carried out, the most outstanding of which was the one performed by Washington State University using stable~sotope analysis to define the origin and age of water supplying the Cerro Prleto field A decision was reached to install the first two units with a total capacity of 75,000 kW, after drllhng the 14 aforementioned wells ( 1 9 6 7 - 1969), and after carrying out production tests m different wells These umts were put into commercml operation in 1973, and have continued 151
152
H Alonso E
w o r k i n g satisfactorily since then, wzth a plant efficiency that has g r a d u a l l y reached 90% The o p e r a t i o n o f this plant saves the C F E 1 million barrels o f o l l / y r S i m u l t a n e o u s l y with c o n s t r u c t i o n and o p e r a t i o n o f the first p o w e r station, detailed geophysical studies c o n t i n u e d to be carried out to the south a n d east o f the present field It was c o n c l u d e d that the geological structure closest to the field IS m a d e up o f a series o f parallel faults, s o m e o f which are visible in the Sierra C u c u p a h , and a horst that coincides with the presently e x p l o i t e d area and with m a i n d o w n t h r o w n structures t o w a r d the east o f C e r r o P n e t o Based on this, we decided to drill a well (M-53) outside the present e x p l o i t a t i o n area This well, at a d e p t h o f 2000 m, p r o v e d to have a p r o d u c t i o n o f a b o u t 100 t / h o f steam and a b o t t o m - h o l e t e m p e r a t u r e o f 340°C This, a n d well M-51, situated to the south o f the present field, o p e n e d up a new era In the e x p a n s i o n possibilities o f C e r r o P r l e t o The result was the c o n s t r u c t i o n o f a new 75,000 k W station (units 3 and 4), fed by 14 wells, lying east a n d south o f the present tleld These wells have better characteristics than those s u p p l y i n g units l a n d 2, since the m a j o r i t y o f them ha'~e a b o t t o m - h o l e t e m p e r a t u r e o f between 300 and 350°C and p r o d u c e between 80 and 140 t / h o1 steam (This is the case for well M-51) T h e 14 a f o r e m e n t i o n e d wells are c o m p l e t e d a n d the steam lines are being Installed a n d readied for c o n n e c t i o n with the second 75,000 k W station, which will go on-line c o m m e r c i a l l y at the b e g i n n i n g o f next year (1979) Based on experiences a c q u i r e d in 1977, it was decided that in 1978 we w o u l d drill 26 wells in the eastern part o f the present field, to s u p p l y a third p o w e r station, which will be called C e r r o P r l e t o lI As an interesting f o o t n o t e , we would like to point out that most o f the wells a l r e a d y drilled ha'~e a 7 5/8-1n - d i a m e t e r p r o d u c t i o n casing (I-55 and K-55) Due to the p r o b l e m s o c c u r r i n g in these well casings, we u n d e r t o o k a s t u d y a n d decided to change the c o n s t r u c t i o n characteristics o f wells for the C e r r o P r l e t o II station We decided to use 9 5/8-1n - d i a m e t e r (N-80) instead of 7 5/8-1n - d i a m e t e r p r o d u c t i o n casings (J-55 a n d K-55) W i t h this new d i a m e t e r , we h o p e to o b t a i n p r o d u c t i o n that will fluctuate between 170 a n d 180 t / h o f s e p a r a t e d steam, this as feasible, since we have o b s e r v e d p r o d u c t i o n o f 140 t / h with a 7 5/8-1n - d i a m e t e r p r o d u c t i o n casing in well M-51 This will represent an i m p o r t a n t saving for the future C e r r o P r l e t o II plant If it is possible to o b t a i n an average well capaclt~ o f 15 M W e , we will need to drill fewer wells, even t h o u g h they might ha,~e to be deeper On the eastern part o f the field, the depth o f the p r o d u c i n g areas varies between 2000 a n d 2500 m C o n s t r u c t i o n o f the C e r r o P r l e t o lI p l a n t is scheduled to begin in 1980 W e h o p e to start the first stage o f the c o m m e r c i a l o p e r a t i o n in 1983 a n d the second stage in 1985 The total capaclt} ot this plant will be 220,000 k W In general terms, this is the most relevant d a t a r e g a r d i n g the present field o f C e r r o Prleto As for o t h e r areas o f g e o t h e r m a l interest, we have begun geologic, g r a v l m e t r i c , magnetic, and electrical-resistivity studies, as well as t h e r m a l gradient studies south a n d north o f the present field In the s o u t h e r n p o r t i o n , a b o u t 17 km f r o m the present h e l d , we have f o u n d an extremely interesting resistivity a n o m a l y , which also coincides with an a r e a o f e a r t h q u a k e swarms We are awaiting results o f seismological studies begun in S e p t e m b e r 1978 These studies co~,er the present field and its southern extension (where the a f o r e m e n t i o n e d a n o m a l y is situated) and seek to define the structure and locate a deep e x p l o r a t i o n well If it proves to be p r o d u c t i v e , this w o u l d definitely b r o a d e n the possibilities o f the C e r r o P r l e t o h e l d T h e r m a l g r a d i e n t wells were also drilled In the n o r t h e r n part o f the field, m an area called Tule C h e c k , to c o m p l e m e n t the geophysical studies a l r e a d y carried out These included resistivity, g r a v l m e t r l c , m a g n e t i c a n d geochemical studies o f surface m a n i f e s t a t i o n s In a d d i t i o n , we have p l a n n e d seismic studies, which will enable us to locate an e x p l o r a t o r y well in this a r e a in 1979 On the o t h e r h a n d , in o r d e r to p i n p o i n t a d d l n o n a l g e o t h e r m a l areas, studies will be u n d e r t a k e n in a region called Mesa de A n d r a d e , where surhc~al geological surveys ,ire
The Cerro Prteto Geothermal Field Present and Future
153
already under way This area is situated approx 40 or 50 km s o u t h - e a s t of the Cerro Prleto geothermal field, available Information, which is still very scarce, shows that ~rrlgatlon wells drilled m th~s region have abnormal temperatures of around 50°C at depths of 100 - 150 m We have scheduled geophysical studies for this area (resistivity, gravlmemc, magnetic, thermalgradient and seismic studies) in order to determine the location of an exploratory well, which will probably be drilled next year, depending on the result of these studies In Baja California, all construction programs for geothermal plants have been contingent on the Increase in demand for energy The electrical system In the state is an isolated one, and operates with two power stations one located in the city of R o s a m o , south of TIjuana (thermoelectric), and the other operating in Cerro Prleto (geothermal) In order to build power stations whose capacities will go beyond the needs of the northern zone, we are contemplating connecting the existing system to the national distribution network, which is approx 700 km away at its closest point If the government approves this connection, the building programs for geothermal plants would change, and instead of planning for a 400,000 kW capacity for 1984-1985, we could consider installing 700,000 kW We must point out that the proven capacity in the area surrounding the Cerro Prleto field is about 750,000 kW In very broad terms, these are our future programs, they are especially important to Cerro Prleto and Baja California, since this is practically the only easy-to-operate and clean natural energy resource available in the region Pollution problems are minor compared with other types of power plants The problem of waste water has several solutions, among them recovery of chemical products, drainage into the Laguna Salada or another area close to it, or relnjectlon The outlook for the central part of the country ~s also very positive Once we develop the geothermal fields under study at this time, we hope to have a minimum installed capacity of 4000 MWe throughout our country by the year 2000