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Steady State Numerical Modelling of Los Humeros Goethermal Field
Ahara Scherezade Díaz Martos
Thesis of 30 ECTS credits
Master of Science (M.Sc.) in Renewable Energy
April 2018
ii
Steady State Numerical Modelling of Los Humeros Goethermal Field
Thesis of 30 ECTS credits submitted to the School of Science and
Engineering at Reykjavík University in partial fulfillment of the requirements for the degree of
Master of Science (M.Sc.) in Renewable Energy
April 2018
Supervisors:
Professor Juliet Ann Newson, Director at Iceland School of Energy Reykjavík University,
Iceland
Examiner:
Professor Michael John O’Sullivan
University of Auckland, New Zealand
iv
Copyright
Ahara Scherezade D. Martos
April 2018
vi
Steady State Numerical Modelling of Los
Humeros Geothermal Field Ahara Scherezade D.Martos April 2018
Abstract
Los Humeros Geothermal field located inside a Pleistocene caldera collapse,
near the east limit of the Volcanic Transmexican Belt, in Puebla, 180 Km
east from Mexico City. The field was first commissioned by CFE in 1990.
and is the third largest in Mexico with 95 MW capacity installed. The
reservoir is estimated to cover an area of more than 400Km2, around 350°C
temperature liquid dominated reservoir with low permeability matrix, which
seems to be associated with fractures. A 3D model was created for this thesis
project that tests the possibility that La Antigua, a NW-SE fault, is the main
source of heat and flow in the system. Based on this conceptualization, a
TOUGH2 numerical model was calibrated with field data, namely the
temperature for depth profiles from the existing wells. The results shows
that La Antigua fault could be the main conduit for heat and flow, which
matched measured well temperatures with 110 Kg/s of total mass flow, with
an specific enthalpy of 1670 KJ/Kg. The model also shows the important
role that plays the low permeability reservoir and the clay cap above the
field.
viii
Steady State Numerical Modeling á Los
Humeros jarðhitasvæðinu
Ahara Scherezade D.Martos April 2018
Útdráttur
Los Humeros jarðhitasvæðin, sem staðsett er innan Pleistocene öskjuhrunsins,
nálægt austurhæðinni á Transcanic Belt í Volcanic, í Puebla, 180 km austur frá
Mexíkóborg. Svæðið var fyrst ráðið af CFE árið 1990 og er þriðja stærsti í
Mexíkó með 95 MW afkastagetu. Lónið er áætlað að ná yfir svæði sem er
meira en 400Km2, um 350 ° C hitastig vökvastýrða vatnsgeymis með lágt
gegndræpi, sem virðist tengjast sprungum. A 3D líkan var búin til fyrir þetta
ritgerð verkefni sem prófar möguleika á að La Antigua, NW-SE villa, er helsta
uppspretta hita og flæði í kerfinu. Byggt á þessari hugmyndafræði var
TOUGH2 töluleg líkan kvarðaður með gögnum um gögnum, þ.e. hitastig
dýptar sniða frá núverandi brunna. Niðurstöðurnar sýna að La Antigua bilun
gæti verið aðalleiðslan fyrir hita og flæði sem samsvarar mældum hitastigi við
110 kg / s af heildarmassaflæði með sérstökum æðalíf 1670 KJ / kg. Líkanið
sýnir einnig mikilvægu hlutverki sem gegnir lágt gegndræpi og leirhettunni
fyrir ofan reitinn.
xx
Steady State Numerical Modelling of Los Humeros
Geothermal Field
Ahara Scherezade Díaz Martos
Thesis of 60 ECTS credits submitted to the School of Science and
Engineering at Reykjavík University in partial fulfillment of the requirements for the degree of
Master of Science (M.Sc.) in Renewable Energy
Student:
Ahara Scherezade Díaz Martos
Supervisors:
Juliet Ann Newson
Examiner:
Michael John O’Sullivan
xii
The undersigned hereby grants permission to the Reykjavík University Library to reproduce
single copies of this Thesis entitled Steady State Numerical Modelling of Los Humeros
Geothermal Field and to lend or sell such copies for private, scholarly or scientific research
purposes only.
The author reserves all other publication and other rights in association with the copyright
in the Thesis, and except as herein before provided, neither the Thesis nor any substantial
portion thereof may be printed or otherwise reproduced in any material form whatsoever
without the author’s prior written permission.
04-May-2018
date
Ahara Scherezade Díaz Martos
Firstname Last name Master of Science
xiv
To all street dogs.A todos los perros callejeros
xvi
Acknowledgements
I would like to thank all member of Gerencia de Proyectos Geotermoelécticos of
CFE, with special mention to Miguel Ramirez, for his help and his effort to grow
this industry in Mexico.
I am also grateful to my tutor, Juliet Newson, for her patient and good advices
since the very beginning. A pleasure work with you.
Thanks to my family, Carmen, Damaris, Isaac, Victor, and also those who are in
the second level, Angelita y Manolo, all they are my real team.
Thanks to all the pets in my life: Delta, Mapacha, Mia, Suri for the unconditional
love.
Thanks Farooq, Mathias, Juliet, Niels for the laughs in Iceland. Thanks geonenas
power, friendship never ends. Thanks DramaQueen and ExperienceHunter for
your visit. Thanks all master´s students that welcomed so well.
Preface
This dissertation is original work by the author, Ahara Scherezade Díaz Martos.
xviii
xx
Contents
Acknowledgements ..................................................................................................................1
Preface .......................................................................................................................................3
Contents ....................................................................................................................................6
List of Figures ..........................................................................................................................9
List of Tables ..........................................................................................................................10
List of Abbreviations .............................................................................................................11
List of Symbols ......................................................................................................................12
Chapter 1 Introduction ...........................................................................................................1
Chapter2: Background............................................................................................................2
2.1 Geological Settings ........................................................................................................2
2.2 Stratigraphy ....................................................................................................................4
2.3 Tectonics .....................................................................................................................7
2.3.1 Local Structure ...............................................................................................8
2.4 Geophysics ................................................................................................................10
2.4.1 Magnetotellurics ...........................................................................................10
2.4.2 Seismicity .....................................................................................................11
2.5 Hydrogeology ...........................................................................................................14
2.6 Natural Recharge ......................................................................................................14
2.7 Geochemistry ............................................................................................................15
2.7.1 Surface manifestations .................................................................................17
Chapter 3: Conceptual Model ..............................................................................................18
3.1 3D Model .....................................................................................................................18
3.2 Geological 3D Model................................................................................................18
3.3 Permeability 3D Model .............................................................................................20
3.4 Temperature 3D Model .............................................................................................22
3.5 Combined 3D Model ................................................................................................23
Chapter 4: Numerical Model ................................................................................................26
4.1 Introduction ..................................................................................................................26
4.2 Grid Design ..................................................................................................................26
4.3 Permeability ..............................................................................................................29
4.4 Boundary conditions .................................................................................................29
4.5 The modelling process ..............................................................................................29
4.6 Heat and mass flows .................................................................................................29
4.7 Natural state well temperatures.................................................................................31
Chapter 5:Results ..................................................................................................................35
5.1 North zone.................................................................................................................36
5.2 Centre zone ..................................................................................................................42
5.3 South zone ...................................................................................................................45
5.3 Permeability distribution .............................................................................................49
5.4 Shallow boiling zone ...................................................................................................50
Chapter 6: Conclusion and future work..............................................................................52
Bibliography ...........................................................................................................................54
xxiii
List of Figures Figure 1: Location of Los Humeros Geothermal Field, Puebla state, Mexico[1] ............................................. 2 Figure 2:a) Location of Los Humeros and all quaternary volcanoes over the Mexican Volcanic Belt[2].b)
Contour map of the Oriental-Serdán basin area, with Los Humeros Caldera (LHC) at the north, La Malinche (MA) at the west, Pico de Orizaba-Citlaltépetl (OP) and Cofre de Perote (CP) range at the east.[3] .................................................................................................................................................. 3
Figure 3: Location of Los Humeros , highlights the two caldera collapsed, Los Humeros and Los Potreros[4] 4 Figure 4: Detail of the Geological Map, showing the emplacement of Los Humeros Caldera between the
Teziutlán mountain range and the SMO. At the bottom Oaxaca block[6] ............................................. 5 Figure 5: geological map by CFE based on Carrasco, 2008, Camilo Yáñez, INEGI, Servicio Geológico
Mexicano,fotointerpretación[6, p. 67] .................................................................................................. 7 Figure 6: Map of the Centre of the Mexican Republic by Federico Moser, where locate and describe several
masses that now are denominated like blocks Modified from Santoyo et.al [6, p. 39] .......................... 8 Figure 7: a)Lineament map in the project field, where the preferential directions trends NW-SE[6],
b)Lineaments inside Los Potreros caldera, with the main lineaments NW-SE, N-S and E-W, modified from CFE. 9
Figure 8:Resistivity plant map at 1,000 m.b.g.l From the gradient changes we see the N-S (dotted black lines), NW-SE(dotted white lines) and W-E (dotted purple lines), SW-NE (dotted purple lines[4]). ..... 11
Figure 9:Seismic hypocenters in Los Humeros Geothermal Field. Views from Leapfrog model by CFE. ....... 13 Figure 10: Piezometric Map of Tepeyahualco, Perote y Los Humeros micro basins. The confluence of the
three micro basins and the theoretical area recharge from LHGF is pointed with an yellow circle.[6]. 14 Figure 11: Rrelative content of Cl-SO4-HCO3 of the well discharge from C.G.Los Humeros, Puebla,
Mexico[4] ............................................................................................................................................ 16 Figure 12: Relative content of K-Mg-Na of the well discharge from C.G.Los Humeros, Puebla, Mexico,
indicating the degree of water-rock equilibrium for the well discharge. ............................................. 16 Figure 13: Chemistry of this thermal manifestations (red dots) in Los Humeros Geothermal Area (wells
blue dots). ........................................................................................................................................... 17 Figure 14: Leapfrog plan view of the different Leapfrog models, CFE models centre and south, and New
Geological Model resulted in this project. ........................................................................................... 19 Figure 15: Comparation of S-N geological profile:a)profile provided by CFE, b)profile drawn in this project
with Leapfrog ...................................................................................................................................... 20 Figure 16: SW-NE profile of the geological model of Los Humeros, Puebla ................................................. 20 Figure 17: Permeability profile 3D model of LHGF. ..................................................................................... 22 Figure 18: a)Plant view of Los Humeros isothermal temperatures at 500 m.a.s.l.b) NE-SW profile showing
the increasing temperature below “La Antigua” fault ......................................................................... 23 Figure 19: 3D Fault Model ........................................................................................................................... 23 Figure 20: Profile of the combined 3D Model.............................................................................................. 24 Figure 21: View of La Antigua Fault zone in the combined 3D model .......................................................... 24 Figure 22: Plan section of La Antigua Fault zone in the high permeability reservoir .................................... 25 Figure 23: a)Grid structure plan view of Los Humeros model, with SW-NE profile trace. b detailed view of
plan map c) SW-NE profile d) detailed of SW-NE profile with some wells ........................................... 28 Figure 24: Heat Flow distribution in layer 3, where reddish blocks are 100mW /m2 ................................... 30 Figure 25: Mass flow inputs in layer 31 ....................................................................................................... 31 Figure 26: a)View of wells and La Antigua fault zone- b)Static temperatures of wells drilled out of the La
Antigual fault zone c) Static temperatures of wells drilled in the La Antigual fault sone .................... 33 Figure 27: Examples of static wells temperatures that falls in the same columns of the grid design ........... 34 Figure 28: a)250, 300 and 350°C Iisotherms vs calculated temperatures (>250°C), b)150, 200,250 and 300°C
Isotherms from well data vs calculated temperatures (>150°C) .......................................................... 47 Figure 29: profile with wells H-3 and H-9 and its modelled temperatures. Run 41. The improvement in the
profiles is mostly done by the clay cap introduced .............................................................................. 48 Figure 30: Permeability distribution of the model. a)rock type distribution across the profile)k1 and k2
distribution c)k3 distribution .............................................................................................................. 50 Figure 31: Vapour saturation in layer 2 (2740 m.a.s.l) ................................................................................. 50 Figure 32: Heat Flow (MW) in layer 1 .......................................................................................................... 51
xxiv
List of Tables Table 1: Hydrometeorological balance[6]...................................................................................................... 15 Table 2: Lithology and conceptual model correlation .................................................................................... 21 Table 3: summary table of the 3D conceptual models developed for LHGF ................................................... 25
List of Abbreviations
MSc Masters of Science
CFE Federal Electricity Commission of Mexico
LHGF Los Humeros Geothermal Field
TMVB Trans Mexican Volcanic Belt
SMO Sierra Madre Oriental Mountain Range
m.a Million Years Ago
CONAGUA National Water Commission of Mexico
TEM Transient Electric Method
m.b.g.l meters below ground level
m.a.s.l meters above sea level
m.b.s.l meters below sea level
MT Magnetoteluric
TOUGH2 "Transport Of Unsaturated Groundwater and Heat”
xxvi
List of Symbols
Symbol Description Value/Units
k
Permeability Darcy MW Power Megawatt
Mm3/year Water Flow Millions cubic
meters a year
mW/m2 Heat Flow Milliwats per square meter
Ωm Resistivity Ohm* meter
1
Chapter 1 Introduction Los Humeros Geothermal Field (LHGF) is the tirth oldest geothermal power plant in Mexico.
Built and operated by Electric Federal Commission (CFE), with exploration started in 1968,
the first well drilled in 1981, and commercial operation beginning in April 1990[1].
Today LHGF has an installed total capacity of 95.7 MW, with a total of 58 drilled wells, 27
in production and 4 for injection.
The aim of this project is to define the natural state model of the field, using a new conceptual
permeability model that could explain the system simply while, taking into account all data
available at the moment. The model is calibrated by matching natural state temperatures in
the wells.
Models are important as they help in the technical and economical point of view of the project,
answering questions related with the field management; e.g how long a system can be
economically utilized, the production and reinjection strategy, and make-up well siting.
Modelling needs to be understood as an iterative process, as the model answers questions
regarding the field, any information of the field should be integrated in the model, in order to
maintain it in an updated state.
This project starts with the review of all the information provided by CFE, which is exposed
in Chapter2. The documentation provided was enough to give an general overview of the
stratigraphy, structural geology, hydrogeology, and geochemistry of the field, Most of the
information is focus on unpublished company documents, and the author thanks CFE for
access.
Chapter 3 is focussed on the process of the 3D model designed, the conceptual model
generated based on it, development of the conceptual permeability model of the system, and
the design of the numerical model.
Chapter 4 explains the basics of numerical modelling and how this study reached the results
and the modifications required for the conceptual model in order to match the static
temperatures at the time the wells were drilled.
Plots results of modelled versus the provided natural state temperatures are shown in chapter
6.
2
Chapter2: Background
2.1 Geological Settings Los Humeros Geological Complex is located in the Oriental Part of Puebla State, near the
border with Veracruz State, 19 Km NW from Perote City. Its average height is 2800 m.a.s.l
(fig.1).
Figure 1: Location of Los Humeros Geothermal Field, Puebla state, Mexico[1]
The Trans Mexican Volcanic Belt (TMVB), extends E-W for over 1000 Km in central
Mexico (fig 2a). At the east edge of it, the oriental Serdán Basin (elevation of 2400m) is
located, where bimodal volcanism with rhyolitic domes and cinerite cones of basaltic
composition coexist. Los Humeros caldera complex is flanked by the basin on its north side
(fig 2b).
Los Humeros is one of the four Pleistoncene silicic centres that have been identified within
this belt of andesitic stratovolcanoes and cinder cones
3
a)
b)
Figure 2:a) Location of Los Humeros and all quaternary volcanoes over the Mexican Volcanic Belt[2].b) Contour map of the
Oriental-Serdán basin area, with Los Humeros Caldera (LHC) at the north, La Malinche (MA) at the west, Pico de Orizaba-
Citlaltépetl (OP) and Cofre de Perote (CP) range at the east.[3]
4
The field is dominated by two caldera collapse events. The first known as Los Humeros,
originated 500,000 years ago, with an explosion of 180 Km3 of Xaltipan ignimbrite. Later on
this episode, rhyolites and dacite domes were created, accompanied with further pyroclastic
events (Zaragoza Ignimbrite), and a second caldera collapsed (Los Potreros), where the
geothermal field is located (fig3).
Figure 3: Location of Los Humeros , highlights the two caldera collapsed, Los Humeros and Los Potreros[4]
The volcanic activity ended 20,000 years ago with the effusion of fluid basalts on the edge of
the caldera. This is the most recent evidence of a magma chamber in the subsurface, which is
the heat source of the geothermal field.
2.2 Stratigraphy The geology can be divided into regional basement, tertiary intrusives, precaldera volcanism
( mainly andesitic), caldera volcanism (formation of Los Humeros and Los Potreros calderas)
and post-caldera volcanism[5].
2.2.1 Basement The Los Humeros caldera complex is located between two important geological structures:
The Macizo de Teziutlán, a Jurassic granitic massif and the Sierra Madre Oriental, a folded
Mesozoic limestone mountain range (fig 4). Both plays an important role in the geothermal
complex, since they are the basement of the geothermal field, and the deformation creates
NW-SE faulting observed in the Los Humeros area.
The basement outcrops at the north of the Los Humeros caldera (fig 5).
5
Figure 4: Detail of the Geological Map, showing the emplacement of Los Humeros Caldera between the Teziutlán
mountain range and the SMO. At the bottom Oaxaca block[6]
1.1.1. Tertiary Intrusives Multiple intrusion phases have been documented during the tertiary era, in the surroundings
of Los Humeros caldera, mainly affecting the Mesozoic sedimentary rocks. The intrusives
are predominantly diorites, biotite tonalites and diabases.
1.1.2. Pre-caldera volcanism Pre-caldera volcanism of the region can be integrated in two consecutive sequences:
• Miocene Volcanism: located in the occidental sector of Los Humeros Caldera, forming
prominent sequences of andesites, around 400 meters thick, related to the Cerro Grande
volcano [7].
The volcanism occurred in a relatively short time of period, from 8.9 to 11 m.a, giving
an average of 10m of andesite every 200,000 years. A common feature of these rocks
is that they are very well-defined volcanic conduits.
• Plio-Pleistocen Volcanism: This outcrops mainly in the north part of the area.
Correlation cuttings recovered at 1300 and 1500 m, indicates that the andesites are up
to 1.5 Km thick.
1.1.3. Caldera Volcanism The evolution of Los Humeros Caldera can be divided in four phases of explosive volcanism.
We will highlight the two that originated the calderas:
• Xáltipan Ignimbrite: Occurred around 0.46 m.a. Represents the most explosive phase
and formed Los Humeros caldera. It has an irregular shape with dimensions
approximately 21*15 Km, elongated in the E-W trend. For this explosive event it is
calculated an eruption of more than 115 Km3 of magma (Ferriz and Mahhod 1984).
6
The ignimbrites are usually unwelded deposits, but welded outcrops can be seen in in
the Canyon of Apulco River. The material is mainly rhyolite pumice (77% silicate) and
rhyo-dacite pumice. There are also abundant small clasts of obsidian, and some
andesite and basalt.
• Zaragoza Ignimbrite: The most recent explosive, around 0.1 m.a. event created Los
Potreros volcanic caldera, with 9 -10 Km diameter. The resulting Zaragoza ignimbrite
has an estimated volume of 15 Km3, and is emplaced in a radial manner around the
centre of the caldera[4], reaching distances up to 18 Km from the caldera border. The
ignimbrite is accompanied with two layers of pyroclasts below and above the
ignimbrite, with thickness up to 2.5 m for the lower and only 1 m for the upper one, the
ignimbrite alone can reach nearly 20 m at the south of the caldera.
1.1.4. Post-caldera volcanism Relatively large pyroclastic events, synchronously with andesites and basaltic andesites were
erupted around 0.04 m.a, in the south and east of the caldera.
Later, explosive activity of pumice is intercalated with pyroclastic, followed with rhyodacite
and andesite lavas (Arenas and San Antonio) located in the centre and in the north of what is
suggested to be the Potreros extension,0.02-0.03 m.a.
The last volcanic event related to the Los Humeros caldera genesis happened 0.02 m.a and is
represented by the eruption of basaltic ash, in the centre and margins of the caldera (Carrasco
N.G, 2008).
7
Figure 5: geological map by CFE based on Carrasco, 2008, Camilo Yáñez, INEGI, Servicio Geológico
Mexicano,fotointerpretación[6, p. 67]
2.3 Tectonics The regional structure is complicated since many different structural episodes occurred
during the genesis of the magmatic emplacement and volcanic eruptions.
The main structures are shown in figure 6. The Oaxaca Bloc (block IV) is a Palaeozoic mass
that was pushed through the north due to the subduction forces, reacting this volcanic
curvature shape: Popocatéplt (Popo) at the west, Malinche- Matlacueyatl (M) at the centre,
Citlaltépetl-Pico de Orizaba (PO)at the east. With an alignment NNE-SSW a a large volcanic
system, Cofre de Perote- Nauhcampatépetl (CP), and just over the Teziutlán solid, shows up
Los Humeros caldera (LH)
8
Figure 6: Map of the Centre of the Mexican Republic by Federico Moser, where locate and describe several masses that
now are denominated like blocks Modified from Santoyo et.al [6, p. 39]
2.3.1 Local Structure The structure that dominates the geothermal field is the circular Los Humeros Caldera, limited
by faults and fractures that follows the same NW-SE lineament that the SMO and also N-S
and the E-W lineaments[6]:
a) The NW-SE (and its perpendicular NE-SW) are though to transport the hot fluids. In
the geothermal field these are represented by Mal País, Antigua, Los Humeros and
Maxtaloya faults
b) N-S, this last can be also divided in to North or South, due to the Teziutlán Structure,
with an alignment suggested to be E-W.
c) E-W faults, represented by Las Papas and Las Cruces faults.
M
LH
PO Popo
CP
9
a)
b)
Figure 7: a)Lineament map in the project field, where the preferential directions trends NW-SE[6],
b)Lineaments inside Los Potreros caldera, with the main lineaments NW-SE, N-S and E-W, modified from CFE.
Los Potreros
Caldera
Los Humeros
Caldera
Las Papas
Lo
ma
Bla
nca
Lo
s P
otr
ero
s
Ca
lder
a
Co
lla
pse
Lo
s C
on
ejo
s
10
These faults are really important in the conceptual model of the field, as they are expected to
act as the “conduit” of the heat flow that makes the area exploitable. The permeability of the
area is suggested to be due to fractures, and they are related (or at least increased by) the
lifting of the basement rocks though the west margin of the field.
2.4 Geophysics This section describes the magneto-telluric and passive seismic methods which yield the most
information about the geothermal system.
2.4.1 Magnetotellurics Magnetotelliric method (MT) has been proved as one of the most successful techniques for
modelling geothermal systems, specially when trying to locate the low resistivity and
permeability hydrothermal smectite clay cap that acts as the trap over high temperature
geothermal fields (Ussher et. Al, 2000).
CFE has constructed a 3D model with all data collected from different geophysical
exploration campaigns undertaken from 2005 to 2011. Figure 8 shows the resistivity map of
the field at 1000 m depth, where predominant values range from 3 to 1505 Ω*m. It is possible
to see different resistivity contrasts that indicates lineaments that seems to be related with the
structural data[4].
This data has helped to define structures like “La Cuesta” and “La Antigua” at its maximum
depths, being captured in Leapfrog model. Both caldera collapse are also drawn in the
resistivity map.
Two main important conclusions of this study are:
• The field roof is around 1,000 m.b.g.l [3] . This correlates with the ignimbrite deposits
described in wells approximately between 700 to 1000 m.b.g.l.
• The resistivity profiles, corroborate the NW-SE trends (dotted white lines), NS (dotted
black lines) and E-W (purple lines). Fig 8.
11
Figure 8:Resistivity plant map at 1,000 m.b.g.l From the gradient changes we see the N-S (dotted black lines), NW-
SE(dotted white lines) and W-E (dotted purple lines), SW-NE (dotted purple lines[4]).
2.4.2 Seismicity A six sensor telemetric seismic network was installed in the vicinity of Los Humeros
Geothermal system in 1997[4].
Spatial analysis shows that the most active seismic zones seems to be located inside the
geothermal field, and that this activity could be associated with the structural systems
described in the geology.
Figure 9 shows that most of the hypocentres located are aligned with the NW-SE fault, and
its depths varies from +1000 to -1000 m.b.g.l, which could indicate a relationship with
injection activity from the geothermal development.
12
a)
13
b)
Figure 9:Seismic hypocenters in Los Humeros Geothermal Field. Views from Leapfrog model by CFE.
2.4.3 Possible Heat source
Several models have been proposed as the possible heat source of the caldera geothermal
system. Robin (1982) proposed a shallow magmatic chamber in terms of petrologic evolution.
Verma (1985) proposed a stratified magma chamber with two conduits around 5 km depth,
estimated from geochemistry balance. Campos-Enriquez and Garduño-Monroy (1987)
proposed two separated heat sources associated with the two geothermal systems (Los
Potreros and Los Humeros) between 10 to 20 Km depth which was, deduced from basic 1D
modelling at MT data. Jorge Azate and Fernando Corbo-Camargo (2018) proposed a
fractured propylic intrusive body of average crustal and relatively high resistivity, presumed
having high calorific capacity and being heated from below[8].
Esteban Jimenez, Saul Pulido, Jorge Soto and Mayra Estrada highlight the absence of seismic
hypocentres in two zones between 300 and 1000 m.b.s.l (3100 and 3800 m.b.g.l) that could
be related with magmatic bodies[4, p. 42].
14
2.5 Hydrogeology
Los Humeros is a liquid dominated field in which permeability is mainly due to faults, highly
related to the structural deformation that has occurred in the area.
One of the main inputs for the model is the recharge, which is discussed in the following
section.
2.6 Natural Recharge
There are three hydrogeological basins in Los Humeros area: RH-18: Region hydrological
Balsas, RH-27: Region hydrological Norte de Veracruz Tuxpan-Nautla and RH-28: Region
hydrological Papaloapan (data from CONAGUA)[6].
These that can further be subdivided into 15 micro basins. The three ones in the area of
interest are showed in the following map (fig 10).
Figure 10: Piezometric Map of Tepeyahualco, Perote y Los Humeros micro basins. The confluence of the three micro basins
and the theoretical area recharge from LHGF is pointed with an yellow circle.[6].
Los Humeros
15
There are three catchments that are thought to contribute to recharge Los Humeros
geothermal system: Los Humeros, Tepeyahualco and Perote basins.
The Los Humeros catchment has the biggest area in the caldera. Besides the shallow water
storage in the caldera, there is though to be significant infiltration into to the subsurface and
faults. The piezometric map shows how both Tepeyahulco and Perote micro basins flows
predominantly E-W, reaching the basaltic lava flows. Their confluence with Los Humeros,
where the three catchments come together, is considered to be the recharge zone.
Historical piezometric data from CONAGUA, shows that the piezometric change in Humeros
aquifer is around 1-2 meters since the field began production. This suggest that the aquifer
has reached the equilibrium and the extracted water from the wells do not exceed the natural
recharge of the aquifer. Humeros presents a static piezometric level of 2300m.a.s.l[6].
A hydrometeorological balance study was done by CFE taking into account all the parameters
mass inputs and mass outputs. Using the Thornthwaite methodology[9], this study was
centralized in Los Humeros, Perote and Tepeyahualco basins, as they are the ones that
influence Los Humeros area.
Considering Entrances (E) =infiltration volume and Outputs (S)=extracted volume due to
water wells, and E=S for equilibrium conditions, we have the aquifer recharge:
Table 1: Hydrometeorological balance[6]
For all explained above, the intersection between Tepeyahualco and Perote basins is the most
important recharge zone of Los Humeros geothermal field, is suggested to have a vertical
meteorological recharge and a large (338 Mm3/year) deep recharge, and a total recharge of
390 Mm3/year.
This data provided seems too high for the low permeability geothermal field and appears to
be based on an analysis of very shallow aquifers. This does not consider the infiltration to the
deep geothermal system.
2.7 Geochemistry Figure 11 shows that the centre of the system is dominated by bicarbonate water, which is
relatively cool marginal water with dissolved CO2.
The North is characterized by water with condensed steam and with a significant amount of
sulphate.
Finally the southern part of the system and the deepest wells produce from neutral pH-Cl
dominated reservoir[4].
16
Figure 11: Rrelative content of Cl-SO4-HCO3 of the well discharge from C.G.Los Humeros, Puebla, Mexico[4]
Most of the wells are in partial equilibrium with the rock, with reservoir temperatures between
220-300 °C, with some exceptions: H-3, H-12, H-15, H-17, H-19, H-30, H-31, H-33 and H-
15 are located in the region of unmatured waters, due to the low salinity of their brines, and
possibly because the water is a mixture of brine and condensate, Fig 10.Most of the wells are
high enthalpy with a relatively small amount of brine, so the accuracy of the liquid
geothermometers may not be good.
Figure 12: Relative content of K-Mg-Na of the well discharge from C.G.Los Humeros, Puebla, Mexico, indicating the
degree of water-rock equilibrium for the well discharge.
Deepest zones (equilibrium)
Shallowest zones (periferic Waters) Condensate zones
(steam heated)
CENTER NORTH
SOUTH
17
Wells with higher gase content are located in the surroundings of “La Antigua”, a conductor
structure of geothermal fluids. This area is characterized as a condensation zone, where gases
are concentrated and where there gases have direct contact with the deep geothermal fluids.
2.7.1 Surface manifestations This geothermal field is characterized by a lack of geothermal superface features. There is no
known lateral subsurface outflow [1]. Only warm soils of around 25°C are mapped around
“La Antigua” fault area. The lack of significant surface features could be explained due to
the low permeability of the reservoir, but also because of the thick low permeability layer that
hides the lower heat resource below it.
Figure 13: Chemistry of this thermal manifestations (red dots) in Los Humeros Geothermal Area (wells blue dots).
18
Chapter 3: Conceptual Model The conceptual model is the first step in the development of the numerical model.
A conceptual model integrates all the available information into a consistent three-
dimensional explanation of the geothermal system. This is explained in terms of the important
characteristics of the geothermal system, namely: the geologic, hydraulic and thermal
structure, the mass and heat flows, and the thermodynamic and chemical state of the reservoir
fluid[10].
A high temperature geothermal system is by definition part of a much large earth system.
Thus our conceptual model must include an indication of the boundary conditions of the
system. Generally the side boundaries will be the groundwater conditions on the margins of
the system. The bottom conditions will be the heat flow (and possibly the mass flow) from
great depth.
3.1 3D Model Leapfrog Geothermal is an 3-D modelling visualisation software and resource management
tool, developed by ARANZ Geo (Applied Research Associates Ltd), with geoscientific input
from GNS Science which was developed to meet the 3-D computing needs of the geothermal
industry. Leapfrog Geothermal is based on implicit modelling methods that represent
geology, structure, geophysical and reservoir data with fitted mathematical functions.
Complex geological models consistent with all 3D data are built by combining measured field
data, specialist interpretation and user editing[11].
A Leapfrog Model was originally provided to the author by CFE. This model contains 47
wells, 15 faults, 1 anticlinal and 2 caldera collapses (Humeros and Potreros) in GIS layers,
and two different Geological Models (North and Centre, fig 14). This model is inadequate as
a complete conceptual model of the system or for numerical modelling, because it does not
comprise the entire geothermal area as understood to be a whole system. Hence a new 3D
geological model was created for our study.
3.2 Geological 3D Model From the original geological model, a new Geological Model is created in this project. The
new model is wider than the old one to ensure a reasonable representation of the geological
framework. As the geothermal field is located within Los Potreros Caldera, the model is
extended to Los Humeros Caldera collapse, ended with an extension of 552 Km2
approximately (23Km*24Km, fig.14).
19
Figure 14: Leapfrog plan view of the different Leapfrog models, CFE models centre and south, and New Geological Model
resulted in this project.
The stratigraphy is drawn following the lithology of 47 wells provided in the CFE Leapfrog
model, and supported by the sequence explained in the geological reports provided by CFE
and described in section 2.2.
The 3D program itself correlates the stratigraphy of the wells and the results match with the
profiles provided by CFE (fig 15)
a)
20
b)
Figure 15: Comparation of S-N geological profile:a)profile provided by CFE, b)profile drawn in this project with Leapfrog
As the model is much longer than the drilled area, the program interpolates the end of each
layer without any guide. In this cases, it is possible to re-draw the surfaces, guided with the
profiles provided, in order to get most accurate results.
Figure 16 shows the final SW-NE profile that shows the 10 different geological layers.
Figure 16: SW-NE profile of the geological model of Los Humeros, Puebla
3.3 Permeability 3D Model The Geological Model was simplified to create a model that better represents the permeability
characteristics of the field. For that purpose, every lithology was re-defined as a layer in the
conceptual model, ended with five final conceptual layers, as shown in table 2:
21
Table 2: Lithology and conceptual model correlation
Lithology Permeability Conceptual
Model
Basalts
Cover Lytic Tuff
Ignimbrite Clay Cap
Microlitoc Andesite
(Augita)
Reservoir
Vitreous Tuff
Andesite Pilolaxitica
Basalt Andesite
Basement Limestone
o Cover: the cover comprises all the different products erupted after the caldera
collapse (section 2.1). A very important characteristics of this layer is that comprises
the water table at 2,300 m.a.s.l, as mentioned above.
o Clay Cap: the usual way to define the top of a geothermal reservoir is using
geophysics, as low resistivity is closely correlated with the low permeability smectite
clay cap [12]. We had no access to this data for this study, but being a field well
defined by its wells, it was assumed that the ignimbrites deposits (Caldera vulcanism,
section 1.1.4) as the impermeable layer acts as the top of the reservoir. This match
with the geophysics conclusions that ensures that the roof of the reservoir is at 1000
m.b.s.l (section 2.4).
o Reservoir: the reservoir is suggested to be located in the pre-caldera andesite
deposits, and is a liquid dominant reservoir, near saturation state. It is considered to
be only one reservoir, around 1000 m height, but with two very differentiated zones:
o Higher permeability & less temperature (260°C)
o Lower permeability & more temperature (300°C).
This division is made taking into account the observations including the limited loss
circulation during drilling, low productivity index and though simulations of the
production zones in some of the wells[1].This is represented in the 3D model as a
straight at 1000 m.a.s.l in all the field:1400-1800 m.b.n.t (high k) and below it in the
lower k reservoir.
Due to the low permeability of the deepest reservoir zone, it is suggested to create
conditions for boiling when a well is discharged, creating a fluid with ex exceeds
temperature (higher production enthalpies in most of the wells [13]. López
Hernández y Cedillo Rodríguez (1996) ensures that the system permeability occurs
in separated “lent’s bodies”, among which the permeability communication is poor.
o Basement: the basement comprised both the crystalline metamorphic rocks and
sedimentary deposits (section 2.2.1). The Basement outcrops in the north of Los
Humeros Caldera and has a clear negative slope W-E (fig 17)
22
Figure 17: Permeability profile 3D model of LHGF.
3.4 Temperature 3D Model CFE also provided natural state temperature versus depth for 38 of the wells. Most are
interpreted from well completion test measurements, and from stable wellbore non-flowing
temperatures. However, as most of the wells were drilled before the exploitation of the field,
it is assumed all temperatures are natural state.
With this data, a temperature model was created in Leapfrog. The Radial Basin Function
(RBF) interpolant is the common model for viewing the distribution of numerical data, as
temperature. The model interpolates the temperature data and creates isotherms, that were
plotted in fig.18 below.
a)
23
b)
Figure 18: a)Plant view of Los Humeros isothermal temperatures at 500 m.a.s.l.b) NE-SW profile showing the increasing
temperature below “La Antigua” fault
By viewing temperature field data with the faults, we can clearly see a tendency of the highest
temperatures related with the NW-SE faults, The “La Antigua” fault, is suggested to be the
main transmitter of heat in the system (fig 18)
This also matches with the fact that almost all the thermal manifestations in the area are
related with these NW-SE faults (fig 13).
3.5 Combined 3D Model As explained above, “La Antigua” fault will be the main source of flow and heat in the
geothermal field. The surroundings of this area act as a lower permeability zone where the
hot fluid reach the surface. For that purpose, a fault model was defined in Leapfrog, where
an area of 500 meters around the fault is defined as faulted zone, and the rest is non-faulted
area
Figure 19: 3D Fault Model
As the fault intersects any of the lithologies of the permeability model, the result combined
model has ten layers with every lithology from the Permeability Model and the same layer
“faulted” (fig 20).
24
Figure 20: Profile of the combined 3D Model
Figure 21: View of La Antigua Fault zone in the combined 3D model
25
Figure 22: Plan section of La Antigua Fault zone in the high permeability reservoir
Table 3: summary table of the 3D conceptual models developed for LHGF
Geological
Model
Permeability
Model
Fault
Model
Combined
Model
Basalts
Shallow Aquifer
(Cover)
Fault
Zone
Lithology
Cover-Faulted
Lytic Tuff
Cover
Ignimbrite
Clay Cap
Clay Cap-Faulted
Clay Cap
Microlotic
Andesite
Reservoir high k
Reservoir Low k
Reservoir high k-
Faulted
Reservoir high k
Vitreous Tuff
Reservoir Low k-
Faulted
Pilolitic
Andesite
Reservoir Low k
Basaltic
Andesite
Basement
Basement Faulted
Limestone Basement
26
Chapter 4: Numerical Model
4.1 Introduction Modelling a geothermal system is the process of numerically describing and solving the
equations of flow of mass and heat though a porous and/o fractured media [14].
TOUGH2 (Pruess 2004) is a numerical simulator for no isothermal flows of multi-
component, multi-phase fluids in porous and fractured media. Its finite volume formulation
gives it the flexibility to model in one, two or three-dimensional problems with rectangular
or irregular computational grids. The original version of TOUGH2 was developed at the
Lawrence Berkeley Laboratories (University of California Berkeley).
The computer program used for this study is called AUTOUGH2, a version of the TOUGH2
code, developed at the University of Auckland, which contains enhanced features for
modelling geothermal reservoirs.
Since TOUGH2 is the code used for the numerical simulation, PyTOUGH was used to
describe the grid, and TIM is the graphical tool for visualization also built on top of
PyTOUGH[15].
Modelling of the natural state of a field is used to verify if the permeability distribution is an
appropiate method if the assumptions done related to the magnitude and location of the flows
are correctly located and quantifier. Additionally is necessary stablish the previous conditions
that represents the field state before being exploited, which will be used to adjust the available
data of production, injection and consider future scenarios [13].
4.2 Grid Design Taking into account the orientation of the main principal family fractures, and seeing the
evidences that the heat comes from the surroundings of La Antigua fault, the grid is design
in the fracture direction, NW-SE.
The program language PyTOUGH is used to build the model grid. For the design, it is chosen
a rectangular net with 22,000*21,000*4,600 meters in the x. y, and z direction, distributed in
36, 38 and 31blocks respectively. Most of the blocks are 500 meters in size in both horizontal
direction (x & y), and 100 meters vertically (z) to ensure the quality of the data processing.
Far from the heat source, the blocks are bigger (1000 meters) to decrease computational time
(fig 21d). There are 1368 blocks per layer, and 31 layers (42,408 blocks in total), extending
to a depth of 1800 m.b.s.l. The land surface at Los Humeros is approximately 2800 m.a.s.l.
The net is rotated 25 degrees to the west so the net matches with the main fault direction (fig
21a). The grid is 4,600 meters depth, more than double that the average depth of the drills
(2,000-2500 meters depth), to ensure the grid covers all the heat source.
Every grid block has the numerical values for rock properties such as grain density, porosity,
permeability (x,y and z directions), thermal conductivity, and specific heat.
Hence the reservoir is represented by a system of multiple interconnected elements
(discretized).
27
a)
b)
28
c)
d)
Figure 23: a)Grid structure plan view of Los Humeros model, with SW-NE profile trace. b detailed view of plan map c) SW-
NE profile d) detailed of SW-NE profile with some wells
29
4.3 Permeability Leapfrog has the capability to assign the structure of the geological model into a grid to
provide an initial permeability structure for the numerical model.
4.4 Boundary conditions Boundaries are one of the most important part of the model generation, as it needs to be a
realistic representation of how the model interacts with the larger system within belongs.
• Side boundaries: side boundaries are extended outside the geothermal area to reduce
the boundary condition effect in the simulation. As explained in section 3.2, even if the
geothermal field is located inside Los Potreros caldera collapse, the model is extended
up to Los Humeros caldera collapse (fig.14).
• Top boundary: the top of the model represents the water table, which is open to the
atmosphere. Water table is represented as a flat surface at 2300 m.a.s.l. The saturated
atmosphere has a pressure of 1 bar and a temperature of 13°C representing the annual
average temperature.
• Bottom boundary: defining this bottom boundary condition is a challenge because we
have very little information from depths beyond the well depth. The model is around
4,400 meters deep, aproximately the double of the average wells depth. At the base of
the model, heat and mass inputs: steady state flow and the anomalous geothermal heat
flow (see section 4.6).
4.5 The modelling process The objective of this thesis is to simulate the natural state heat and mass flow in the
geothermal system prior to the fluid extraction.
To start the TOUGH2 run, an input data file is needed which contains all the thermodynamic
characteristics of the all grid blocks, and the heat flows inputs and outputs.
Default conditions are assigned to every block in the first run. The results obtained are
represented in a plot in TIM viewer, where verified natural temperature data can be compared
with the modeled data. The relevant modifications are made and the model is run back again
and new results will be obtained and plot. This iteration process was continued until the
results had the desired matching parameters.
It was noted during the study that the location and magnitude of deep inflows needs to be
adjusted. This process can create inconsistences in the conceptual model and should be
reviewed for further study.
4.6 Heat and mass flows As explained in section 3.2.1, the bottom boundary (layer 31, -1800 m.b.g.l) is one of the
most difficult to define, as all data below the wells (>2200 m.b.g.l) is indirect information.
Considering that the average heat flow in the earth’s surface is approximately 60mW/m2, the
occurrence of an anomalous gradient is connected to the relevation of strongest heat flow
values, where volcanic activity and presence of fluids and activity transports, and the heat
flow values overcome the value of 100 mW/m2 [16].
Taking into account all this data, heat flow values of all blocks in layer 31 (-1800 m.b.g.l.)
are 60 mW/m2, except in the surroundings of La Antigua fault, where there is a heat flow of
100mW /m2 (fig 22).
30
Figure 24: Heat Flow distribution in layer 3, where reddish blocks are 100mW /m2
Regarding mass flow, the hydrogeological study (section 2.5) suggest an inflow of 390
Mm3/year.However, this is based on very shallow data and is not considered reasonable for
this system which has only a small mass surface discharge.
During the modelling process, the initial mass inflow was minimum and was slowly increased
until a final figure of 110 Kg/s was eached and the temperatures where matched. An important
feature is the distribution, where all mass flow was in the blocks of La Antigua fault zone.
100 mW/m2 area
31
Figure 25: Mass flow inputs in layer 31
4.7 Natural state well temperatures Natural state temperatures from 38 wells are provided by CFE in order to calibrate the model.
Most of the wells were drilled before the exploitation of the field. However, there are wells
that were drilled after the start of production. In this case these wells are assumed to have not
been thermally impacted by the reservoir exploitation.
The extension of Los Humeros geothermal field has not been completely defined though
drilling, but looks like some limits can defined approximately by some relatively cool
wells[13].
Figure 24 shows the spatial distribution of the drilled wells and the La Antigua fault zone.
When static temperatures are plotted, a tendency of higher values at the bottom of the wells
(many over 300°C) can be seen in the surroundings of La Antigua (24b).
32
a)
b)
33
c)
Figure 26: a)View of wells and La Antigua fault zone- b)Static temperatures of wells drilled out of the La Antigual fault
zone c) Static temperatures of wells drilled in the La Antigual fault sone
On the other hand, when the grid was designed, some of the wells used for calibrating the
model were falling into the same block column in the grid.
As explained above, TOUGH2 will solve the flow equations and give a result for each block,
so every well that occurs in the same block will have the same final model result. In order to
check that all the temperature in the same block are similar, the temperatures of the coincident
wells are plotted together. Figure 25 shows that most of the wells that falls into the same
block columns have similar temperature profiles.
34
Figure 27: Examples of static wells temperatures that falls in the same columns of the grid design
35
Chapter 5: Results The results are shown in the plots below. Per well, they show the temperatures modeled
(blue color) and the natural state provided temperatures (red color) in depth.
The plots are presented following the division given by CFE, dividing the area in north,
center and south.
The north area exhibited very good matching general trend. Higher temperatures that
expected in the upper part of the reservoir (20-50°C, H-9and H-3) and some inversions
below the maximum well depths (H-22, H-29 and H-37). The best matches seem to be in the
surrounding of La Antigua fault (fig.27).
The center presents also very good match in general, with some exceptions as H-5 and H-
23. Seems to be lower gap temperature in the upper part. Same presence of temperature
inversion at the bottom.
The south area was not matching until an extension of La Antigua fault was created, putting
some heat and flow coming from this area (Maztaloya fault). H-14 is a well drilled out of
the field and it is curious to see that until 2,000 meters elevation it perfectly matches but
below that depth, modelled temperatures are much lower than that the provided. This well
profile data may not truly represent field conditions.
36
5.1 North zone
37
38
39
40
41
42
5.2 Centre zone
43
44
45
5.3 South zone
46
47
Another way to visualize the results is plotting the modelled temperatures vs the static
isotherms in Leapfrog (fig 32). Temperatures around “La Antigua” are well represented in
the reservoir (fig 32a), but becoming too hot as they approach the lower aquifer (fig 27).
a)
b)
Figure 28: a)250, 300 and 350°C Iisotherms vs calculated temperatures (>250°C), b)150, 200,250 and 300°C Isotherms
from well data vs calculated temperatures (>150°C)
48
The best matches seems to be in the surrounding of La Antigua fault, in the north area (fig.28) The
upper temperatures were matched when the permeability of the cap was decreased.
Figure 29: profile with wells H-3 and H-9 and its modelled temperatures. Run 41. The improvement in the profiles is mostly
done by the clay cap introduced
49
5.3 Permeability distribution The final permeability distribution is shown in figure 26. The first profile (26a) shows the
rocks type perpendicular to the fault zone. 26b shows the permeability distribution in the x
and y direction (both direction have exactly the same distribution). Here we can see only
three different permeabilities; the cap with the lowest permeability (and probably
representing a clay alteration zone) followed by the basement, and then the reservoir is the
most permeable.
Permeability distribution in z direction is more diverse and much more correlated with the
lithology. From lower to high permeability we have: the cap, the low permeability reservoir,
the cover and no faulted basement, high permeability reservoir and faulted basement (figure
26c).
a)
b)
50
c)
Figure 30: Permeability distribution of the model. a)rock type distribution across the profile)k1 and k2 distribution c)k3
distribution
5.4 Shallow boiling zone The model shows boiling in the upper layers. This boiling starts in layer number 10 (1,940
m.a.s.l) and reaches maximun in layer 2 (fig 30). The steam appears around La Antigua fault
and reaches the surface, this matches anecdotal evidence that before exploitation, steam
manifestations existed in the area.
Figure 31: Vapour saturation in layer 2 (2740 m.a.s.l)
This fact is very important and should be corroborated with exploration field data, because
with this data we could match the surface manifestations.
51
Total heat flow in the system is 183 MW, which indicates the possibilities of
expansion of the field.
Figure 32: Heat Flow (MW) in layer 1
52
11
Chapter 6: Conclusion and future
work
This study presents a natural state TOUGH2 model of Los Humeros Geothermal Field,
the tirth biggest geothermal field in Mexico, with more than 50 drilled wells and 98 MW
of installed capacity, which has been in production since 1990.
Geological and geophysical information is used as the basis for a new conceptual
permeability model built using Leapfrog geological modelling software. The geological
model was simplified to create a model that better represents the permeability
characteristics of the field. The final is represented by ten layers, which is the result of
double the five geological layers because of the fault zone. From top to bottom: cover,
clay cap. reservoir high k, reservoir low k and basement. A NW-SE structure through the
system, known as La Antigua fault, is interpreted to be the location of the up flow zone
for geothermal fluid. The surrounding sub-horizontal volcanic and volcaniclastic layers
host the geothermal reservoir below a clay cap, which is indicated by geophysics.
A new 3D model was built for this project. Based on the wells lithology, the geological
model is expanded on its edges until Los Humeros caldera collapse (22Km*21Km). The
bottom boundary is 4,4000 meters depth, and the top boundary is the surficial aquifer
water table, a flat surface at 2300 m.a.s.l, open to saturated atmosphere with 1bar pressure
and 13°C.
The grid designed for this numerical model has 42,408 blocks and is 22 km x 21 km in
areal extent, with a vertical depth of 4.6 km. The grid is oriented NW-SE to the main fault
structure of La Antigua. The side boundaries of the model are closed, the upper boundary
is open to the atmosphere and the bottom has a heat and mass input which is interpreted
to be the recharge for the geothermal system. The model is calibrated by matching the
natural state temperatures from the wells.
In general terms, the model matches the static temperatures provides, meaning that even
if is not the unique, it can be a possible solution of the temperature distribution of the
field.
The model was conceptually built as the same time as plotting the layers and temperature,
being a progressive and active process. The plot of well static temperatures shows a high
temperature convergence around the NW-SE La Antigua fault. The final permeability
conceptual model is a fault dominated system, with La Antigua NW-SE 500m buffered
fault zone as the main heat and mass input, heating up the rest of the system by conduction
and convection.
The model presented high sensibility to permeability changes, due to its low permeability
conditions. Two layers seems to play an important role in the temperature model: the
deeper reservoir and the clay cap. Its low permeability seems to flash the fluid in the first
case, creating boiling in the system, and the clay cap acts as a seal that keeps the heat
below.
In general trend, modelled temperatures match the steady state temperatures. The
temperaturematch in the shallow zone could be improved modelling the shallow aquifers
in more detail. For this initial study, production data was not used to calibrate the model.
For this reason, the absolute permeabilities in the model will depend on the steady mass
flows through the model. In turn, this implies that the total hot inflow to the base of the
model is roughly proportional to the permeability. The final calibrated model has a hot
fluid recharge of 110 kg/s with a specific enthalpy of 1670 KJ/Kg, and a total heat flow
53
of 183 MW
The model suggests a permeability structure and the location of the deep recharge to the
system. Further work will include processing the production data for model input (mass
flows from the wells) and calibration (production enthalpy and reservoir pressure over
time). This will provide a better control on the absolute values of permeability, porosity
and deep recharge to the geothermal reservoir.
54
Bibliography [1] M. Ramirez Montes and M. Flores Armenta, “Análisls de los pozos productores de
la zona centro y sur del campo geotérmico Los Humeros, Puebla,” CFE, Unpublished
report, 2006.
[2] G. Carrasco-Núñez and A. Rossotti, Stratigraphy of the 8.5 - 9.0 ka B.P. Citlaltépetl
pumice fallout sequence, vol. 21. 2004.
[3] R. Alvarez and V. V. Yutsis, “Potential fields modeling of the Serdán Oriental
basin, Eastern Mexico,” J. South Am. Earth Sci., vol. 80, pp. 375–388, 2017.
[4] E. Jimenez Salgado, S. Pulido Arreola, J. Soto Peredo, and M. C. Estrada Rios,
“Modelo geológico conceptual de Los Humeros, Puebla,” CFE, Unpublished report,
2014.
[5] G. Ramirez Silva, “Estratigrafía Volcánica de la secuencia andesítica del campo
geotérmico de Los Humeros,” CFE, Unpublished report.
[6] E. Jimenez Salgado, “Estudio hidrogeológico en el campo geotérmico de Los
Humeros, Pue.,” CFE, Unpublished report, 2014.
[7] M. C. Estrada Rios, “Evolución química e isotópica de pozos productores e
inyectores en el C.G.Los Humeros, Pue, periodo 2015,” CFE, Unpublished report, 2015.
[8] J. Arzate, F. Corbo-Camargo, G. Carrasco-Núñez, J. Hernández, and V. Yutsis,
“The Los Humeros (Mexico) geothermal field model deduced from new geophysical and
geological data,” Geothermics, vol. 71, pp. 200–211, Jan. 2018.
[9] E. Custodio, M. R. Llamas, and U. politécnica de Barcelona, Hidrología
subterránea. Ed. Omega, 1996.
[10] M. A. Grant and P. F. Bixley, “Chapter 1 - Geothermal Reservoirs,” in Geothermal
Reservoir Engineering, 2nd ed., M. A. Grant and P. F. Bixley, Eds. Boston: Academic
Press, 2011, pp. 1–8.
[11] S. Alcaraz, R. Lane, K. Spragg, S. Milicich, and G. Bignall, “3D Geological
Modelling Using New Leapfrog Geothermal Software,” p. 6.
[12] W. Cumming, Geothermal Resource Conceptual Models Using Surface
Exploration Data. .
[13] “Actualización del modelo conceptual y numérico del campo geotérmico de los
Humeros, Puebla, México.,” Geothermex, Unpublished report, 2008.
[14] E. Karmon, “Natural State Modeling of the Ngawha Geothermal Field, Northland,
New Zealand,” University of Auckland, 1999.
[15] “Pythough.” .
[16] A. Franco and F. Donatini, “Methods for the estimation of the energy stored in
geothermal reservoirs,” J. Phys. Conf. Ser., vol. 796, p. 012025, Jan. 2017.
55
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