Tracking an Energy Elephant Draft Report by Fvx296q

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									                          NSF-SEES WORKSHOP DRAFT REPORT:

         TRACKING AN ENERGY ELEPHANT: SCIENCE AND ENGINEERING
        CHALLENGES FOR UNLOCKING THE GEOTHERMAL POTENTIAL OF
                          SEDIMENTARY BASINS


1.0 INTRODUCTION

Presently, less than 1% of the energy grid in the United States derives from geothermal systems
(DOE/EIA, 2010). The total amount of heat energy present within the Earth, however, is
enormous (>14x106 EJ within U.S. at drillable depths), and represents a sustainable energy
source well beyond current or projected domestic electrical needs (100EJ in 2005) (Tester, et al.,
2006; DOE, 2008). As such geothermal energy is one of the few achievable energy sources that
genuinely have the magnitude and availability to serve as an alternative energy source on the
gigawatt scales of coal and nuclear generators. Likewise, geothermal energy is base load unlike
most renewables that have variable load configurations that do not provide for steady power
flow.


Convective geothermal systems currently account for all of the 3000 MWe produced in the US
and the 10,000 MWe produced worldwide. These are the “conventional” hydrothermal sources
characterized by fractures that allow hot water to locally and quickly reach shallow depths. The
largest of these systems (e.g. The Geysers, CA, Cerro Prieto, Mexico; Larderello, Italy) currently
generate approximately 700-850 MWe each. The USGS (2008) estimates the mean power
potential of identified convective systems distributed over the western 13 states, including
Alaska and Hawaii, at 9057 MWe. They further estimated the mean power potential of
undiscovered resources to be an additional 30,033 MWe.


Although the potential of conventional convective resources is large, the power potential of
“unconventional” resources, which include deep sedimentary basins, is significantly greater.
Heat in deep sedimentary basins is transferred primarily by conduction. In contrast to the
relatively small areal extent and size of even the largest convective geothermal systems,
sedimentary basins have areal extents of hundreds of kilometers, potentially little interaction

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with the near surface environment, and the necessary natural matrix porosities for large scale
power generation (Nalla and Shook, 2004). Sedimentary basins thus have the potential to move
geothermal toward a meaningful portion of our energy needs, and do so with minimal
environmental impact and without concerns of long-term depletion.


Temperatures adequate for geothermal development (>~150oC) are accessible throughout the US
at drillable depths. However, permeabilities may not be sufficient everywhere to produce the
commercial flow rates necessary for large scale geothermal power. Deep sedimentary basins
have the attribute of having natural matrix permiabilty and the potential to address this issue. As
well, this permeability can be augmented by hydraulic fracturing or the application of other
techniques to create Enhanced Geothermal System (EGS) production (Elsworth, 1989; Tester, et
al., 2006; DOE, 2008). Further, efforts by the oil and gas industry to improve productivities of
deeply buried sedimentary rocks provide a solid head start for emerging sedimentary-basin
geothermal technologies.

Geothermal development and research reflects the true spirit of the sustainability concept, and
dovetails directly with the NSF SEES priorities. Tapping the full potential of this energy source
and growing it beyond the current low usage rates, however, requires that we gain a much better
understanding of natural and engineered geothermal systems within sedimentary basins than we
presently possess

On November 6-9, 2011 in Salt Lake City we gathered a diverse group of scholars and
practitioners tied to geothermal interests to address this potential directly. Particularly, we
assembled a cross disciplinary group of geoscientists, engineers, and educators to assess the
basic science and engineering questions that must be addressed in order to tap this energy
resource. We also considered the potential of geothermal energy from sedimentary basins and the
needs required by the geothermal community to advance these fronts. The following report
details the finding of this workshop group.

1.1 Overview of Workshop Participants and Findings



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The NSF SEES workshop “Tracking an Energy Elephant…,” was proposed in the spring of
2011 and convened November 6-9, 2011 in Salt Lake City to address one central question.


“What are the basic science and engineering questions that need to be addressed in order to
make geothermal energy production from sedimentary basins practical?”


The PI’s (John Holbrook, Walt Snyder, and Joseph Moore) of the workshop proposal assembled
an expanded steering committee of engineers, geoscientists, educators, and informatics scholars
to advise the project and assemble the diversified core of scholars and practitioners needed to
address this question. This Steering Committee assembled a core of 30 invited participants; then
advertised for applications for an additional 30 participants. Response was overwhelming. Over
120 applications were received, reflecting an overt need for a forum to discuss ideas related to
the topic of sedimentary-basin geothermal. Total attendance was 71, including conveners and
NSF visitors (APPENIX A: Table 1).


Workshop participants ranged widely over the fields of geoscience, engineering, informatics,
education, and policy/economics, and were diversely represented nationally and internationally
by members of academia, the geothermal and petroleum industry, and government (APPENDIX
A: Table 1). Participants also represent the emerging and standing leadership in geothermal
research and within their respective fields. These participants have remained as an interactive
group since the workshop and provided feedback throughout the preparation of an RCN proposal
on this same topic, which was delivered to NSF for consideration shortly after the workshop.
The workshop represents the first time this community of interdisciplinary scholars assembled
for the purpose of sedimentary-basin geothermal research.


The workshop participants were enthusiastic about the potential of sedimentary-basin rooted
geothermal systems as a practical energy source. The consensus that grew from the group was
that sufficient harvestable geothermal energy was available to provide a large and sustainable
contributor to the U.S. energy portfolio, particularly the electric base load, if we began to tap the
larger and more regional heat reservoir available from sedimentary basins. There was general
agreement that this could be done realistically, and was indeed already beginning on small
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scales. The fundamental barrier to the use of geothermal energy for electric generation on the
scale of nuclear, coal, and gas was not availability or attainability of the resource, but was related
to high up-front costs and failure risks related to large power-plant development. The source of
hesitation thus does not appear to be the lack of practical and current potential of the resource.
Private and public producers of geothermal power instead require better understanding of
geothermal systems within sedimentary basins so that they may better predict locations where
sufficient fluid and heat can be extracted to recoup the high up-front costs of plant development
(e.g., Sener, 2009). These locations exist, are commonly discovered, and industry, both
nationally and internationally, are recently starting the careful steps forward as they begin to take
advantage of this emerging sedimentary approach to geothermal harvesting (e.g., Brown, 2011).
The workshop participants identified several areas of fundamental and basic research required to
lower the upfront risks and provide the science and engineering breakthroughs that could
accelerate geothermal development. The consensus was that the geothermal industry is on the
verge of expansion, but in need of some basic science and engineering advances to reach a
nearby tipping point.


The intention of the workshop was to provide a road map for how the NSF's community, through
fundamental research, facilities development, and education, can help make the vast geothermal
potential of sedimentary basins a significant part of the nation's renewable energy portfolio. This
is built upon the presumption that the ability to translate that potential into productive use lies in
the application of basic science and engineering to overcome technical challenges that currently
restrain the application of these complex systems for electrical base load. To this end, the group
identified several fundamental issues and questions that could be addressed through support to
individuals and groups by NSF. This report expands further upon the specific findings of the
group in the following chapters. Each chapter is prepared by members of the Steering
Committee in accordance to their area of expertise.




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2.0 THE PROMISE OF GEOTHERMAL ENERGY
By John Holbrook and Walter Snyder


The nation's potential for geothermal energy is vast. The total energy locked in geothermal
sources exceeds all other ambient energy supplies, and simmers in abundance beneath the feet of
all Americans everywhere. For perspective, the total solar heat reaching the Earth’s surface is
sufficient to raise the temperature of the Earth to approximately 14.50C (IPCC, 2007). This
constitutes a substantial amount of heat energy, and proves sufficient to drive the biological
cycle and still leave some meaningful surplus for ongoing development of industrial solar
energy. Little of this large energy source is stored and retained however. Comparatively,
geothermal energy banks a steady heat that raises the globe to this same surface temperature at
an average depth of only 580 m, drilling depths considered very shallow throughout the
geothermal and petroleum industries. The temperature only increases with depth from there,
rising to over 500-10000C at the base of the Earth’s crust. This internal heat runs the tectonic
systems that give us mountains, basins, earthquakes, and volcanos as it drives the motion of the
lithospheric plates (Figure 2).


What is even more significant is that large portions of this buried geothermal energy may be
harvestable. The currently maintained global radiation of heat energy from the interior of the
globe is approximately 44 terawatts (Davies and Davies, 2010; The KamLand Collaboration,
2011). This energy is available without endeavoring to mine the heat accumulated over geologic
time, and merely involves interception and capture of the heat radiated to space (Figure 2).
Estimates of 1+ megawatt per square kilometer of basin area are considered conservative and
sustainable for net power generation based on current heat flow measurements (Tester, et al.,
2006; Williams, 2007; DOE, 2008). Successful production at this rate over 1000 km2 would
generate at least one gigawatt, roughly equal to the production of a typical nuclear power plant.
For perspective, the installed electric capacity of the U.S. is roughly one terawatt (1000
gigawatts) with substantially less in actual use at any time (DOE/EIA, 2010). Deep geothermal
heat extraction becomes practical at temperatures beginning between 100 and 150 Celsius,
occurring typically at depths of 2-6 km (Tester, et al., 2006; Blackwell, et al., 2007; William,
2007; Esposito and Augustine, 2011). The area of sedimentary-basin with fill exceeding 4 km
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deep is over 500,000 km2, and occurs dispersed across the U.S., commonly near the population
centers where maximum usage is possible at minimum cost for transmission (Figure 1). Many of
these basins approach the needed temperatures by these depths (Figure 2). The Tester, et al.
(2006) study offered a conservative estimate of 100,000 EJ of geothermal heat energy available
as a resource base below 4 km in conterminous U.S. sedimentary basins. The potential for
sedimentary-basin geothermal to replace a sizeable proportion of the current carbon-rich
(100EJ/year at approximately 50% coal; DOE/EIA, 2010) energy production, and to absorb
future growth in energy needs, is thus very realistic.


Extraction of geothermal heat resources requires three conditions: 1) heat; 2) water; and 3)
permeability. Permeability is also a proxy for natural or enhanced conduits for fluid flow. There
are several "types" of geothermal development systems in practice or in theory. Most of the
current plants take advantage of localized sources of anomalously high heat flow due to
hydrothermal convection related to thermal and permeability anomalies. Sedimentary basins
alternatively have much larger rock volumes with cumulatively greater, but typically more
dispersed, total heat. Sedimentary basin geothermal resources can be currently broken down
into: 1) co-produced fluids from oil and gas fields; 2) geopressured regimes; and 3) deep
sedimentary extraction with natural and enhanced permeability. Though the classification of
geothermal systems is still actively evolving, there are generally three other types extant within
the U.S. These other types depend upon localized high-heat flow and include 4) hydrothermal
(in particular "Basin and Range" type); 5) magmatic; and 6) Enhanced Geothermal System
(EGS) that depend on induced fracture of otherwise non-permeable hot and dry rock.
Hydrothermal/magmatic systems provide most of the 3 gigawatts of electric capacity currently
available in the U.S. and hot-dry rock studies have been the focus of added attention in recent
years (Tester, et al., 2006; DOE, 2006; DOE, 2008). Aggressive goals like a 10% increase by
2014, doubling the geothermal capacity by 2020, and 100,000MW in 50 years (DOE, 2008;
reaffirmed in DOE-GTP Mission and Goals: April 11, 2011) require developing new
technologies and other types of resources, including power production from sedimentary basins,
engineered geothermal systems (EGS) and other novel resources (Shook, 2009).


Einstein famously approached Roosevelt to inform him of the vast energy that may be stored
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within the atom that we then lacked the technology to tap. Similarly, we have long known of the
vast bank of geothermal energy stored within the Earth’s interior that remains beyond practical
reach. Unlike nuclear power, however, geothermal energy does not rely on potentially risky
generation or waste-storage processes. It is already there in its full quantity. Likewise, water
extracted from deep basin aquifers for heat will be recycled directly back into the aquifer to
provide pressure support, meaning geothermal systems can be regarded as matter-closed systems
and thus gas, liquid, and solid waste effluent is negligible at the surface. With proper
management, the heat can be extracted from geothermal fluids with negligible material pollution
of the surface or atmosphere (Duffied and Sass, 2003; Blodgett and Slack, 2009; Tester, et al.,
2006). Our technical and economic barriers are in gaining the capacity to harvest this abundant
energy that we already have. A meaningful technological push released the energy of the atom.
A push of basic research could prove to be the step which one day plugs into the vast and
untapped energy potential of the Earth interior.




Figure 1: Distribution of sediment thickness in the conterminous U.S. 4 km isopach in black.
Numerous basin-and-range basins over 4km excluded for small resolution (Tester, et al., 2006)




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Figure 2: Average temperature at 4.5 km, conterminous United States. (Tester, et al., 2006, after
Blackwell and Richards, 2004)




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3.0 UNDERSTANDING THE NATIVE BASIN
By John Holbrook and David Blackwell


3.1 Introduction


To develop geothermal energy on the 100MWe scales desired for integration of this resource into
the public electric grid requires a deep understanding of the natural geothermal resources
available from the targeted sedimentary basins and what natural conditions will determine
effective heat recovery either from natural or artificially produced fractures. The two conditions
the native sedimentary basin provides are a reservoir of heat and an infrastructure of natural or
constructed plumbing that will permit flow and extraction of geothermal fluids, mostly water.


The scales of heat and flow needed for economic geothermal production, however, are high. For
instance, a well yielding 10MWe pumping 100kg/s at 10c/kWh would gross $24k/day. A well
drilled to the 3-6 km depth needed to attain >150 Celsius in most sedimentary basins would cost
roughly $7-10 million to drill, then as much as $5 million in additional development costs (e.g.,
fracing, logging, etc.). A successful well such as this would take about two years to pay for
itself, this before costs of the plant are factored. For perspective, a 5,000 bbl/day oil well would
gross $400k/day at $80/bbl and pay for itself at 17x this rate (Based on Calculations by Rick
Allis in workshop keynote address). Wells producing high fluid volumes at great depth are
needed to make geothermal power economical (Tester et al., 2006, 2007). Wells of this quality
are known from sedimentary basins (e.g., the Texas Gulf Coast, AAPG Explorer, Nov. 2011),
but are not routine. In fact, the national average for water production is .021kg/sec per
petroleum well (after Veil et al, 2004). Production data, however, may not be the best way to
evaluate fluid production potential as water production is the enemy of hydrocarbon production,
and actively avoided. Injection or disposal wells on the other hand give a better idea of fluid
production capacity and injection volumes are closely correlated to the capacity of a formation to
produce fluid. Figure 3 shows the injection capacity of water disposal wells used for the Barnett
Shale Gas Field in north Texas. These data show that over county wide areas there are
sedimentary formations capable of taking 20,000+ bbl/day of fluid that are currently not being
tapped for geothermal extraction.
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A successful geothermal energy plant will likely involve multiple wells in close proximity. It is
thus not unreasonable to expect that a 100MWe plant would be fed by as many as 20 wells with
$200 million invested in drilling, plus additional injection and makeup wells. The high upfront
costs entailed in geothermal energy means that entrepreneurs willing to invest in this energy
source will require assurance that they have identified the best possible locations within the best
possible basin conditions in order to raise the probability of prompt financial return on
investments. This means better characterization of basin conditions to assure sufficient lowing
of risks to potential investors when selecting possible well sites. Such predictions require a
better fundamental understanding of the basic science behind the processes and structure of the
native conditions of sedimentary basins. This report summarizes discussions aimed at these
issues at the November 2011 “Tracking an Energy Elephant” workshop on geothermal energy
from sedimentary basins.




Figure 3: Distribution and injection rates for waste-water wells from shale-gas production of the
Barnett Shale in North Texas.
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3.2 The Heat Resource


Heat is the commodity that geothermal systems acquire, and any discussion of geothermal
systems must begin with a discussion of the heat available for extraction. The heat of the Earth
at depth is currently mapped at a first solid pass (Figure 2). This critical information provides a
tally of the available resource and a foundation for moving forward toward a deeper
understanding of geothermal systems. Conservative estimates of 100,000 EJ of geothermal heat
energy are available as a resource base below 4 km in conterminous U.S. sedimentary basins
(Tester et al., 2006). This compares to a yearly usage of about 100EJ in US electrical power
consumption. This heat is generated mostly from radioactive decay, and represents both new
heat emanating from depth and heat retained from prior emission by the blanketing effect of low-
conductivity rock. The heat is not evenly dispersed, and temperatures are higher at shallower
depths in regions of higher heat flow and greater thermal retention. Necessary temperatures for
geothermal extraction, however, occur at some depth at all locations. Geothermal energy thus
has potential as a heat resource at any site.


The larger unknowns of geothermal heat are the nature of thermal movement and the potential
reactions of the basin heat system once heat extraction begins. How heat moves and is recharged
naturally in sedimentary basins is a fundamental science question that pertains to basic Earth-
system processes. It dictates subsurface chemical systems, affects rock mechanical process and
deformation, and imprints on fluid density and flow cells. These fundamental questions become
even more critical the moment heat extraction begins and the system is forcibly changed. Better
understanding of the workings of induced and natural temperature distributions is thus critical to
predictions of heat behavior under geothermal production. Many issues pertaining to heat
processes were broached at the workshop. Most of these can be grouped into two larger
questions.


Question 1: How does heat move within sedimentary basins at large scales and how does this
impact the renewability of the resource?


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Most of our understanding of heat movement in sedimentary basins is based upon coarse data
sets and depends upon several assumptions. In general we assume that heat moves mostly by
low-rate conduction in older sedimentary basins where porosities are lower. In some older
basins, however, aquifers are found to transfer much more significant quantities of heat, such as
in the case of the Madison aquifer in the Great Plains (Gosnold, 19xx). In young sedimentary
basins, such as the Gulf Coast, the mechanisms of heat transfer are much more complicated and
not well understood. Compaction release of water, surficial sedimentation, salt dome movement
and distribution, geopressure effects, and oil and gas migration may all play a part in the
evolution of the thermal regime (Sharp, etc,) . In addition, heterogeneities in the thermal
conductivity of rocks may affect the anisotropy of heat transfer, or may influence the mechanical
properties of rock fracture when generating enhanced porosity. Likewise, the role of convection
vs. conduction as a means of heat movement and the thresholds that define these alternative and
complimentary processes are unresolved.


Our understanding of these processes at the levels of detail needed to understand geothermal
processes is cursory at this time as knowledge of these processes at a deep level has not been
held as critical to prior science drivers. The need to understand geothermal systems changes this
priority structure and increases the need to better grasp the flow of heat. As heat is extracted,
how is it restored? Can it be restored on time scales practical for human use? In short, as in-
place heat is extracted we must know how much of this geothermal energy is from mining a
known heat resource vs. harvesting from a continuously renewing resource? To know this, we
must know how heat moves in these complex systems, and we must be able to predict how the
heat system will respond when heat is removed at non-native rates.


At present, we have some general basis for predictions that seem encouraging. For instance, the
time for thermal recovery of about 90% of the lost temperature is assumed to be 3 to 4 times the
period of production (Prichartt, 1998; Rybach, 2010). A possible scenario suggested then would
be an approximately 5X5 km developed area producing 25 MW of electrical energy could feed a
plant located at one corner of the square. Assuming a 25 year production period another square
would be developed with the plant still at the corner over the following 25 years. This sequence
would be repeated two more times and after a 75 year recovery period the first 5 km square
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would be exploited again. The temperatures in the original square would have returned to about
90 % of the original value. This sequence could be repeated resulting in a very long lived
resource. Of course the plant itself would likely have to be rebuilt on some 25 to 30 year cycle
as well. Such scenarios are speculative at this time and depend on a currently limited
understanding of basin heat systems that are in need of exploration and testing.




Question 2: How is heat stored and released on the local and micro scales and how does this
impact efficiency of heat sweep?


Heat is generally extracted from the rock by injection and extraction of water causing a flow
through the heated rock. For this process to serve as a proper means to extract heat, the heat in
the rock must be transferred to the liquid. At any temperature, 5% porosity means 80% of the
heat is in the rock, and multiple sweeps of water are needed to recover the heat (i.e. the heat
capacity of water is about 4 times that of rock). In an analysis of the potential for producing
enhanced geothermal energy (EGS) from sedimentary rocks, Nalla and Shook (2008) found that
even a small amount of porosity was a significant factor in the movement of heat and for
increasing the efficiency of extracting energy from fractures induced into reservoirs. While the
physics of how water is heated by contact with hot rock is established, many processes inherent
to the complications of water flow and heat transfer in deep basins are not. For instance, what
are the optimal surface-area and overall pore structure conditions for heat transfer, and how do
natural variations in these characteristics affect optimal spacing between injection and
production wells? How does the geochemical evolution of the brines, rock, and porosity relate to
heating and cooling of fluids inherent to this process over multiple sweep cycles? How does the
micro-heat network evolve during heat extraction to provide positive or negative feed-back in
heating rates and distances? What are sustainable rates of heat extraction? Will continued local
disruption of the heat matrix induce vertical or other non-predicted flow cells? Each of these
questions and more has immediate pertinence as pumping is planned and commenced. Any
predictive planning for these contingencies requires a clear and basic understanding of local-
scale and micro-scale heat flow and exchange that we presently do not have.


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3.3 The Basin Pluming System


The heat resources needed to sustain geothermal production are common to most basins at some
reasonably drillable depth. The high flow rates of geothermal fluids that are required to extract
heat economically from these depths, however, are an important factor. These flow rates hinge
on the permeability of the basin sediments. The permeability of rocks can be enhanced by
intentional engineered fracturing, which is the cornerstone of Enhanced Geothermal System
(EGS) reservoir creation. EGS systems are understood to be a method for extracting heat from
low permeability basement rock through generation of artificial fractures. An area of challenge
for EGS development is the generation of sufficient fracture volumes and connectivity to permit
permeable flow over sufficient distances, times, and rock volumes to collect sustainable and
economic quantities of heat. Sedimentary rock, however, has the matrix advantage over
traditional EGS. Sedimentary rocks have natural matrix permeability that is known to permit
large volumes of fluid to travel over long distances within rocks that are not artificial fractured.
Geothermal production from sedimentary basins holds the promise of a solution to the issues
facing existing EGS development by permitting matrix flow that can connect both discrete
engineered fractures and can permit flow between artificially fractured volumes through
unenhanced porosity within the native sedimentary rocks.


Predicting sites where native permeability will be sufficient to permit adequate fluid flow
between enhanced fractures needed to support geothermal extraction requires a much better
understanding of the basic construction of sedimentary basins than we currently enjoy. Much
advancement has been made regarding basin flow thanks to the needs of the petroleum industry.
The fluid volume requirements, connectivity, flow distances, and flow sustainability needed of
geothermal systems surpass the needs of petroleum extraction, however, and present a new order
of challenges that must be met with basic research into sedimentary basin processes.
Particularly, we need to understand fluid flow paths at a detailed level, and the factors that
control reservoir quality. In turn, we need to understand the interaction of these flowing fluids
and the basin heat in order to predict the evolution of heat systems and heat-sweep efficiency.
Geothermal systems in sedimentary basins are complex, with many pertinent systems that must
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be understood both individually and interactively. The critical questions for constraining the
permeability systems that allow transport of fluid between induced and natural fractures pertain
to the inherited primary matrix permeability of the basin sediments, the natural secondary
permeability from fractures and diagenesis, and the interaction of the two. Knowledge of these
factors is critical for understanding what controls high permeability at geothermal depths.


Question 1: What are the fundamental sedimentary processes that control the filling of
sedimentary basins across all scales, and how do they impact permeability, connectivity, and
heterogeneity of deep-basin flow paths?


Abundant sedimentary deposits are found below the depths of 3km where adequate temperatures
can be expected in basins throughout the U.S. (Figure 1). Much of this shows good porosity, as
evidenced from oil production records in both clastic and limestone strata. The key to turning
this association of permeability and depth into geothermal energy lies in understanding the
factors that control this porosity and in determining the connectivity of those porous units that
result in permeability. This requires an understanding of the sedimentary architecture that
dictates the various flow units at different scales and their vertical and lateral connections.
Understanding if flow is diffuse though a large flow unit, or segregated though multiple smaller
units will affect the efficiency of the heat sweep, as well as predicting the best locations of
injection and extraction wells at the respective ends of the flow. Stratal flow units are also well
known to be heterogeneous, dictating that flow contort around depositional obstructions that may
occur at fine (e.g. mud drape of a single ripple, etc.) to large (e.g., coarse linear shoal deposits
within a marine mud matrix, etc.) scales. Effective flushing of fluids through the geothermal
system requires a deep understanding of this plumbing. Understanding these flow units is a
predicate for successfully predicting locations where adequate flow can be attained to support
large-scale geothermal systems and is where all assessments of flow in sedimentary basins must
begin. Limiting the risk in assessing locations for adequate flow is a predicate for economic
initiation of sedimentary basins as a source of geothermal energy. This all derives from gaining a
basic and fundamental understanding of how surficial processes, tectonic systems, and climatic
drivers conspire to fill a sedimentary basin at the finest to largest scales.


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Question 2: What are the digenetic processes that operate in deep sedimentary basins and how
do they augment or deduct permeability as they evolve?


Once sediment is buried, chemical and physical processes within the basin system begin to alter
the sediment form. These “diagenetic” processes have potential to alter the primary permeability
of the initial sediment. These processes can both diminish (e.g., cementation, compaction, etc.)
or enhance (e.g., dolomitization, dissolution, etc.) permeability, and most certainly will modify
permeability. The longer and deeper the sediments are buried, the more diagenesis of sediment
can effect primary porosity. Great depth and great time of burial are both hallmarks of the
sediments from which geothermal waters would be extracted. Improved understanding of
enduring diagenetic modification of basin sedimentary rocks is critical to prediction of flow
paths and where and how these are enhanced vs. diminished by diagenesis. As well, the
diagenetic system is changed by the large volumes of repeated flush that geothermal systems
require. The need for geothermal systems to endure for decades means a system that once was
closed is now open and subject to accelerated exchange of pore fluids over extended periods. The
permeability needs to remain open throughout the duration of this flooding without generating
paths of fluid bypass or clogging with diagenetic precipitates. Prediction of all this requires a
better understanding of the chemistry of basin brines and the physiochemical processes that do
and can evolve within a deep sedimentary basin.


Question 3: What controls the natural processes whereby fractures form and evolve within basin
sediments, and what is the impact of these fractures on the transmission of fluid flow?


The natural stresses that cause rocks to break generate fractures through which fluids may flow.
Indeed, it is truly rare to find an unfractured rock from a deep sedimentary basin. These
fractures may occur as displaced faults, but more commonly as non-displaced joints. The
capacity of these fractures to divert flow to and from conduits that are not predicted by matrix
porosity has emerged as an increasing concern over the past decade for the petroleum industry.
Because of the higher flow rates required of geothermal production, these concerns are
compounded. The detail to which these fractures need to be understood is thus escalated.
Numerous issues emerge when fractures are factored into flow predictions. How will natural
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fractures interact with matrix porosity and engineered fractures? What is the impact of gouge in
making fractures barriers instead on conduits? Can overpressuring be used to open fractures
normally closed by confining pressure, and, if so, is this always beneficial? Are fractures joined
to form continuous conduits or rather “chutes and ladders” for flow between matrix permeability
units? How will the pressure changes inherent to long-term high-volume flushing modify the
fracture environment? Effective predictions of these issues all revolve around gaining a better
basic understanding of the processes by which natural fractures form and evolve.


3.4 Summary


Geothermal energy production from sedimentary basins appears feasible with respect to natural
heat, water, and permeability resources. The barrier that must be overcome is limiting the risk
of the high-cost of geothermal plant installation by better being able to predict the permeability
and heat distributions. The viability of the oil and gas industry hinges upon learning more about
basin processes in order to better select drill sites and lower the risk of failure. Geothermal
shares this same concern, but differs greatly in that the flow rates needed are considerably
higher, flows must be maintained much longer, the pore volumes will likely be exchanged more
than once, and all the heat sweep and regeneration must be sufficient to provide the requisite
power. This requires a new level of understanding for the basic science that determines the
processes by which heat moves and a sedimentary basin is filled and modified in order to predict
where these optimal conditions will occur. This need exceeds our current understanding of the
basic sciences behind sedimentary basin filling, thermal evolution, and permeability structure.
As all basins are not the same, portability of sedimentary basin hosted geothermal systems
requires that the inter-basin variations in basic basin processes are understood as well.




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4.0 ENGINEERING ISSUES IN SEDIMENTARY BASIN GEOTHERMAL ENERGY
by Herbert H. Einstein and Charles Fairhurst


4.1 Introduction


The Engineering discussions at the Workshop examined issues of developing EGS reservoirs in
sedimentary basins from a variety of viewpoints –but no clear direction emerged as to paths to be
followed. It was evident from the outset that, although there was considerable enthusiasm for the
concept of EGS in sedimentary formations in the US, the Workshop appeared to be the first time
in the US that an interdisciplinary group had been convened to examine the engineering
feasibility of EGS in sedimentary formations. Workshop participants included colleagues from
Europe, Australia and New Zealand. Although consideration of engineering issues related to
sedimentary EGS may have been given some greater attention in these countries, it appears that
EGS technology is still in the early stages of development in these countries also.


The topic, "Engineering Challenges” was addressed with a keynote on Numerical Modeling by
Dr. W. Pettitt and breakout/and plenary discussions on the topic. The slides used by Dr. Pettitt
are available at the SedHeat website http://www.SedHeat.org. The report will, therefore,
concentrate on the discussions. It will be based on the suggested questions/problems that were
distributed prior to the session on this topic (Appendix B). One of the three breakout groups
followed these suggestions in detail, one of the other ones also did so roughly. Where additional
topics were brought up, be that within breakouts or in the following plenary discussion, they are
summarized under “other topics”.


The topic of understanding the processes involved in EGS reservoir development in Sedimentary
Basins and numerical models of the in-situ rock mass selected for stimulation was given some
emphasis at the Workshop. Rather than overemphasize this topic in the main text of the report,
Professor Fairhurst has prepared a discussion of it as Appendix C to the report. Other important
engineering challenges associated with Sedimentary EGS that were raised during the meeting are
noted below.


                                                                                                 18
4.2. Detailed Engineering Issues


4.2.1 Well Hole Drilling.
Although drilling technologies in sedimentary rocks are well established through their use in
hydrocarbon extraction, there are several specific geothermal issues that require further work.
Clearly, wells in geothermal energy production from sedimentary rock will experience higher
temperature. Of particular concern are proppants, packers and cementing where present
technology may not work under high temperatures. Although hydrocarbons are being produced
from ever increasing depths, issues of high temperatures are becoming severe.
Research is definitely needed in all these areas. Operational tools, such as pumps and logging
instruments (e.g. for our geophysics) may not work at temperatures at and above 200°. These
problems may also affect the ability to produce horizontal/smart wells.


A question that was not brought up is the economics of all this additional development. While
the hydrocarbon market is very large, (oil and gas represents approximately 60% of the world
supply of energy) such that there is commercial interest in developing specialized equipment,
this may not be the case currently in geothermal applications. It appears, however, that one can
benefit from technology in underground coal gasification, which also involves high
temperatures.


Another well drilling related issue is the generally larger (than for hydrocarbon extraction) well-
hole diameter. This is associated with two problems: 1. Adequate drill penetration rate; and 2.
Well-hole stability. The latter problem is made worse by the greater depth (higher in-situ
stresses and water pressures).


4.2.2 Fractures and Fracture Systems
Fractures are a central concern in all aspects of ‘subsurface engineering’, including EGS.
Although several of the details covered below were not discussed in detail during the Workshop,
it was clear that understanding fracture systems and their influence on the success or failure of an
EGS was an underlying concern in many of the discussions.


                                                                                                  19
Information on fracture systems at a potential EGS site is obtained from boreholes and
geophysical surveys. The desired goal is to establish a Discrete Fracture Network (DFN), but
when these are based on information obtained from one or, at most very few, boreholes, DFN’s
have an associated high uncertainty. Much work is still necessary to develop mapping/survey
approaches that provide adequate input for the fracture models.


Developing a better knowledge of the characteristics of an individual fracture (aperture and
aperture variation) is a separate, very difficult challenge. The creation/stimulation of new
fractures clearly is a major engineering issue. It depends on the particular types of rock and
existing fractures. Although the hydrocarbon industry has decades of experience in this domain,
many open questions still exist. In particular, the interrelation between stress and temperature
regimes on the one hand and the development of fractures on the other hand is unresolved. An
important related issue is how to obtain a desirable fracture pattern, (e.g. many small fractures, a
few large fractures; possibility to “steer” newly developed fractures). While many of these
problems are similar to those in igneous rock, the fact that sedimentary rocks are often strongly
anisotropic has to be considered. Related to fracturing is induced seismicity, which will be
discussed in Section 4.2.4.


Given what is said above, it is not surprising that specific modeling problems were brought up,
mostly related to fracture modeling (fracture pattern, individual fractures and fracture
genesis/propagation) as well as stress-temperature interaction. (The topic of modeling for EGS
development has been discussed in some detail by C. Fairhurst in Appendix C to this report)


Somewhat related to modeling is the necessity of laboratory testing. This may be the only way
to vary influencing parameters under strictly controlled conditions. However, so far, no testing
procedure and equipment seems to exist that allows one to simultaneously vary all the
parameters. In addition, there is the issue of scaling. Given this complexity, it is tempting to
exclusively rely on “simulation models” rather than conduct experiments, which may not be the
best way to proceed.



                                                                                                   20
4.2.3 Operation
This issue is closely related to the two preceding ones. Of particular concern is the behavior of
the fractured rock mass subjected to changed temperature and stress conditions. Thermal
breakthroughs may occur or fractures may “scale”, for instance.


Related to operation is monitoring. The interpretation of flow measurements and of remote
(geophysical) signals should, in principle, allow one to keep track of what is going on in the
subsurface. However, the relation between fracturing and microseismic events, for instance, is
not yet established at a satisfactory level. Also, more practically speaking, the operating
equipment may not work satisfactorily (pumps and monitoring equipment exposed to high
temperatures). Even more basic is the lack of knowledge and experience as to what to do
when/if the performance of the reservoir is not as expected.


4.2.4 Induced Seismicity
As mentioned in the discussion of fracturing, induced seismicity is a predicted problem. It
already has led to the end of one EGS project, in Basel, Switzerland, which was stopped in 2004
after earthquakes with magnitudes up to 3.4 occured(albeit in igneous rock). Public concern over
the potential of induced seismicity (‘Earthquakes’ to the public) has also stimulated public
concern with respect to EGS development in the US. Understanding the causes of induced
seismicity is related closely to understanding of how EGS stimulation of fractures and fracture
networks affect the local stress regime at the EGS site. This requires a much better interpretation
of the fracture initiation-, propagation- and coalescence processes.


4.2.5 Risk and Decision Making
Eventually, and hopefully in the near future, economically effective implementation of EGS
development in sedimentary rocks will occur. Decision makers need to have a clear picture of
the costs and benefits i.e. the risks of an EGS operation. What is done at this NSF workshop
should provide the basis for developing economically viable EGS operations and allow all
interested parties to assess this viability. From a research point of view, this requires the
development of procedures, which can represent the relevant uncertainties in all influencing


                                                                                                  21
factors and eventually express them in terms of risk. Also, current numerical models can and
should be used be used to establish uncertainty in predictions due to model uncertainties.


It is essential that Risk Analyses be performed not just in terms of cost alone but also with
respect to effects on resources (particularly water and air) and also on the public. Concerning the
latter, the problems associated with the development of tight shale gas illustrate the wide range
of issues that need to be addressed.


4.2.6 Other Topics
Although not related to engineering alone, two additional issues were brought up in the plenary
discussion of engineering. While these may not represent major obstacles, they certainly show
that additional work needs to be done.
1.       It was stated that except for the Gulf of Mexico sedimentary basins, there are not many
         others that have high enough temperatures at reasonable depths to warrant geothermal heat
         extraction. This statement was debated by others and needs to be clarified.
2.       The only commercially working EGS plant (albeit in igneous rock) is the one in Soultz
         (France), which has an installed power of 1.5 MWel. A single large wind turbine has that
         capacity!!
The lack of growth in EGS development compared to Solar and Wind energy has led to a
growing belief that EGS may not be a viable option. It should be recognized, however, that the
US R&D community in rock mechanics/engineering has had little opportunity to contribute to
R&D on Geothermal Energy. The situation is well summarized by the following comment, part
of a Request for Proposals issued by the US Dept of Energy in 2009.
“Chronic underinvestment in federal R&D in these subsurface [engineering and geosciences]
disciplines has eroded the nation’s capacity to educate and train the next generation workforce
necessary for industry, academia, and government. As a result, the U.S. faces the prospect of
ceding its historic leadership role in these disciplines, and thereby undermining its resource
security”. (U.S. Department of Energy, 2009) 1


1
    Energy Research and Development (Document END09278) Strengthening Education and Training in the Subsurface
Geosciences and Engineering for Energy Development; Section 33, Subtitle C p.3

                                                                                                                 22
4.3 Conclusions


The foregoing discussion illustrates that there is a long way to go and the challenges are great.
There is much that needs to be done, starting with a vigorous R&D program. As a first priority,
additional meetings should be convened to stimulate closer interaction between geologists
familiar with sedimentary EGS opportunities, numerical modelers capable of developing models
on various scales to simulate EGS sedimentary sites, and engineers familiar with well drilling
and other aspects of deep subsurface technology.




                                                                                                    23
5.0 MONITORING AND QUANTIFYING ROCK PROPERTIES WITH GEOPHYSICAL
METHODS
By Ludmila Adam, Kasper van Wijk, and Jonathan Glen


5.1 Introduction


Advances in geophysical tools will be a key component on characterizing deep sedimentary
basins as the next frontier in geothermal exploration. Many field and lab attempts at research and
practical applications for geophysics have focused on individual tools that are specific to each
scale. Geothermal sedimentary reservoirs have hot fluids that over time will change the reservoir
properties and geophysical signatures. These changes come from geochemical alteration,
fracturing, and the temperature and chemical evolution of the fluid phases. To be able to fully
characterize the subsurface processes in a geothermal setting, geophysics will help find and
monitor a dynamic reservoir and bridge geological, geochemical and reservoir engineering
disciplines to answer scientific questions in the context of sustainability. Some of the problems
and ideas in this science path to be targeted by an interdisciplinary team are listed here, but not
limited to the list.


5.2 Geophysical Problems and Needs in the Quest for Sedimentary Geothermal Energy


5.2.1 Integrate geology, geochemistry, reservoir engineering and geophysics
Extracting the most geological and reservoir information from geophysical tools requires
integrating geophysical tools and scales by creating a feed backing loop between disciplines.
Integrating information between potential (magnetics, gravity, electrical, electro-magnetics) and
seismic methods (active and passive source) will help characterize the geology and reservoir
modeling. The integration of these geophysical tools is highly important for geothermal
reservoirs and has not been largely explored in other areas of exploration in the Earth. Significant
research is required to understand the connection between different geophysical, petrophysical
and reservoir parameters in the rocks. Merging different tools to develop the science for
sustainability for geothermal production in sedimentary basins requires research from the
laboratory (geophysics on core and mineral samples) to field (surface and borehole geophysics)
                                                                                             24
and satellite (satellite magnetics, aero-magnetics and aero-EM) based data to ultimately help
delineate the geology and fluid flow paths.


5.2.2 Changes of petrophysical parameters and fluids in the subsurface over time
Temporal changes in the subsurface are expected during geothermal energy production, from
hydrofracturing to increase permeability to rock-fluid interactions in the reservoir and
suprajacent layers. Geophysical data can be acquired over time to monitor the reservoir.
Geophysics is based on contrasts between acoustic, electrical, magnetic and density in the Earth,
and integrating that data to geochemistry (fluid and rock chemistry and alterations) and reservoir
engineering (hydrofracturing, thermal and pressure changes) can be used to spatially map
changes in the reservoir over time. Scientific questions to be addressed would include how
reservoir changes control geophysical properties and the scaling from the laboratory to the field
of such data. Here we present two examples of monitoring reservoir changes and their relation to
geophysics. 1) Alteration in the rock due to fluids and fluid mixtures will precipitate/dissolve
minerals in sedimentary basins. Geophysical methods can monitor the progress of a field if an
understanding of the reservoir (porosity, permeability, composing minerals) and geological
parameters can be effectively correlated to geophysical data. For example, frequency dependence
and attenuation of seismic waves hint to have a correlation to reservoir properties such as
permeability. 2) Alteration mapping which draws on the observation that magnetic anomaly
lows, for example, are often associated with hydrothermal zones. This is due to the fact that
magnetic minerals are often transformed or destroyed during alteration leading to dramatic
changes in the rock’s magnetic properties. These are promising results suggesting that the extent
of alteration in the subsurface may be quantified from magnetic field data. It is likely that this
can also supply information on the duration over which a given system has been active since the
extent of alteration will scale with longevity of the system. Monitoring such changes would
benefit from integrating seismic and potential field methods at all scales.


5.2.3 Sensitivity to temperature is related to minerals properties and fluid phases
New methods for temperature mapping with geophysical methods would include advances in the
acquisition and processing of magnetoteluric data, magnetics and seismic methods. The effect of


                                                                                                     25
temperature on different parts of the reservoir and its relationship to mineral alteration, porosity,
and fluid properties can be correlated to geophysical properties, but how is not well understood.


5.2.4 Geophysical methods and data enhancement
Improved methods for data acquisition, integration for time-lapse data, and innovative
processing techniques will be needed to extract the most information from the data.


5.2.5 Effective media in geophysical parameters for reservoir scale modeling
Significant effort has to be steered towards understanding thermal conductivity, resistivity,
elastic and magnetic effective media theories and upscaling. The interrelation between these
parameters and their relation to the dynamic sedimentary geothermal reservoirs is critical to
integrate geophysics to geology and reservoir flow.


5.2.6 Upscaling of laboratory and borehole data to field
Methods and theories to upscale laboratory data to field systems is the key to the integration of
science for a deep sedimentary basin reservoir and other fluid reservoirs.


5.2.7 Field laboratory
Advancing the proposed ideas might benefit from selecting a natural field laboratory where
geothermal systems in deep sedimentary basins can be studied in detail. That could facilitate the
integration of disciplines that are relevant for performing the science in such reservoirs.


5.2.8 Education and outreach
The research should have a strong component on educating students by involving them in
innovative sustainable research projects from the field, to the lab, to computational geophysics
with an emphasis on cross-disciplinary sciences. By investing in the above research topics, the
next generation workforce will be trained in key areas for the development of science and
sustainable energy.




                                                                                                   26
6.0 MEETING THE CHALLENGES OF EDUCATION AND OUTREACH
By Karin Block


6.1 Introduction


From its inception the workshop (Organized under the domain name “SedHeat”) was devised
with education goals included synergistically with scientific goals. In straddling the engineering
and science worlds, SedHeat has the advantage of capturing the interest of students drawn to
sustainability and providing fundamental training needed to fill the significant workforce
shortages facing nearly every branch of the geosciences in the next 10 years. We are encouraged
by workshop participants’ reports of increased field camp enrollment over the last five years,
particularly at the Colorado School of Mines. This agrees with American Geosciences Institute
(AGI) reports (Gonzales, 2011) on field camps in general. Nonetheless, gender balance in
graduate academic programs and in the oil and gas industry continues to be problematic as many
women drop out of the discipline within 10 years after graduation. In addition, participants agree
with AGI reports (Gonzales, 2011; Gonzales and Keane, 2011) of vast underrepresentation of
minorities in geoscience programs, at state geological surveys, and in industry.


Workshop participants were charged with addressing this pressing need in geoscience and
geoengineering in the context of SedHeat in order to develop strategies to increase the diversity
of the geoscience workforce, attract more students to our disciplines, recruit talent, and
effectively train students while exploring transformative science and invention.


6.2 Short-term Solution for Workforce Shortage


The current high unemployment rate suggests there is no shortage of potential workers and
therefore workforce needs will be market-driven. Several participants encouraged tapping the
pool of early-retiring petroleum geologists to fill senior-level academic positions and provide the
expertise that will lead to SedHeat innovation. However, academic hiring in general hinges on
the availability of funding opportunities. Therefore, the decision makers (proposal peer-


                                                                                                 27
reviewers, geoscience departments, university administrations) need to be convinced of the long-
term potential of SedHeat as a research avenue.


6.3 What can be done through a Research Coordination Networks (RCN) Proposal


6.3.1 Public policy and informal education
Concern was expressed over the disparate public attention solar and wind energy has received
over the last 30 years in comparison to geothermal. Much of the challenge of attaining the
funding required for experimental drilling and exploration is tied to public perceptions and
awareness across society and government. A concerted push to enhance the visibility of
geothermal will influence the creation of a market for the geothermal workforce and reinvigorate
the discipline’s support for field research as frontier basic research rather than as mission
oriented research. Both of these are linked to funding success. For geothermal, significant
emphasis was placed on the putting effort into The Big Invention, rather than nibbling at
improving oil and gas techniques. Instead progress likely comes from working with agencies to
push large-scale innovation, not unlike the DARPA (ARPA)’s involvement in pioneering the
internet.


A concerted effort to promote geosciences and geothermal energy at the informal level can
potentially impact students in elementary school and their parents. Workshop participants
repeatedly mentioned the lack of an Earth science requirement in many states’ elementary and
middle school curricula and how this affects students’ career paths down the line. While
geoscience majors are far more employable than most other scientific disciplines, the perception
among students and their parents is the opposite, except in states where geoscience is part of
everyday life. In Texas, geoscience undergraduate and graduate programs are flourishing
because the general public is aware of the role of geoscience in the local economy and the
resulting employment opportunities.


6.3.2 Removing the stigma of O&G
Environmentally minded students who are attracted to the geosciences to work in the geothermal
energy field may become disappointed if their skill set eventually translates to primary
                                                                                                 28
employment opportunities in oil and gas. The oil and gas industry’s vast R&D resources avails
young geoscientists of opportunities to practice many of the techniques required for geothermal
exploration. An effort to foster inclusion and dialogue among students, rather than an adversarial
tone will benefit the discipline and increase the diversity of students that join the industry. This
strategy will minimize employment risk in the geothermal enterprise. An example of a
successful program that bridges environmental altruism with employment reality is Cornell’s
Geothermal IGERT curriculum focusing on what geothermal, carbon sequestration, and oil and
gas have in common so students are prepared for the jobs that already exist.


6.3.3 Dissemination of Resources
Encouraging academic departments to create geothermal courses, minors, and field experiences
has a low threshold for implementation and therefore requires sharing of resources. A strong
cyberinfrastructure behind geothermal research and education will promote interest in
geothermal issues among academic staff and will provide datasets and materials so that courses
can be taught. Making course materials widely available will promote diversity in how we teach
while incurring a relatively low expense.


6.3.4 Support and Participation from Industry
Coordination with industry needs to be instituted by the geothermal leadership. Sedimentary
geology professorships are dwindling and despite agreements between AAPG and NSF to fund
basic research, the matching funds required from industry to move this initiative forward are
lacking. A formal relationship between the geothermal effort and the AAPG to showcase
research could help the funding effort.


Encouraging industry to become involved with programs to assist students who are
underprepared for college work, such as the Texas Success Initiative Program (TSIP) can
provide training and teaching opportunities. Industry can also be encouraged to help sponsor or
establish a Young Professional Network to help develop a socialization network among budding
geoscientists interested in the energy sector.



                                                                                                  29
An initial influx of NSF-based funding can provide the momentum needed to establish a
community base. Once developed, the network can sustain its efforts by maintaining the
dialogue with industry.


6.3.5 Areas that could use more students/new expertise
The development of new areas of expertise was a recurring theme throughout the workshop.
Specifically, the science of SedHeat needs students who can bridge the gulf between geology and
engineering. A principal theme in the science discussion was the notion that good information
comes from drilling and therefore many graduate-level projects that will advance the science will
stem from experiments in this area. Cross-disciplinary training is considered to be the key to
new discoveries.


Because there currently is a dearth of geothermal-related research in academia, much of the
knowledge gap related to heat flow is largely ignored by the geophysics community except as
related to climate change. This is an avenue of research that excites students and has tremendous
scientific potential in informing how sedimentary geothermal basins are explored.


6.4 What Needs to be Pursued by its Own Funding?


A large portion of the discussion on education and diversity focused on how to increase the
number of undergraduates interested in the geosciences and engineering and how to introduce
geothermal resources into curriculum. The importance of experiential learning and its efficacy in
exciting students at every instructional level was a key point of the discussion. Additionally, the
breakout participants suggested specific ways in which researchers can incorporate education
and goals into traditional NSF-GEO, NSF-ENG and SEES proposals, as well as initiatives that
can be pursued through EHR programs.


6.4.1 Education: K-16 and beyond
      Elementary and Middle School Level:
           o Youth geology field camps are popular and effective at recruiting high school and
               middle school students. Funding these programs remains a challenge, but may
                                                                                                 30
          yield the greatest return on investment to increase the number of minority students
          who engage in geoscience-related activities.
       o Professional development of teachers provides the foundation for transmitting
          knowledge and excitement to students. The inclusion of teacher training
          components as broader impact activities in proposals can serve to increase the
          exposure of students to geothermal themes.
       o Creation of activities that focus on the math, physics, and chemistry of geothermal
          systems broaden the reach of geoscience to state curricula that would otherwise
          exclude Earth science.
   Undergraduate Level:
       o Establishment of a minor in geothermal energy entailing 6-9 credits of specialized
          coursework in addition to field camp.
       o Peer learning and peer recruitment: teaming up inside and outside the classroom
          to develop science and engineering synergistic learning and undergraduate
          outreach to K-12 students.
       o Educational seminars, presentations to underrepresented groups in high school
          and community college as well as their parents to increase diversity.
       o Follow the model of successful long-term programs such as the partnership
          between the tribal community colleges and the National Center for Earth Surface
          Dynamics. Requires support of teachers who champion these types of programs
          and mentor students all the way through graduate school.
   Graduate Level
       o The academic contingent requires the ability to have fundable (small) projects for
          graduate students, both M.S.- and Ph.D.-level, to work on what will advance the
          overall effort.
       o Geothermal avails the geosciences with the opportunity to maintain cross-
          disciplinary networks that will catch and sustain the stream of students. Cross-
          training students will give them the best chance at being employed. Programs
          such as IGERT and SEES are well suited for this type of collaboration but more
          opportunities may be needed.

                                                                                             31
           o Establishment of a professional science masters degree may provide the expertise
               needed to produce a workforce competent in the appropriate geology and
               engineering specialties. Such programs take 1-2 years and partner with industry
               to fulfill an internship in lieu of a research program, similar to MBA.


6.4.2 Plugging the leaky pipeline
Participants in the workshop discussed at length the persistent problem of attrition among
women in sedimentary geology and petroleum engineering careers. Retaining women with
graduate degrees in geoscience and academia may close a significant portion of the workforce
gap we will be facing in the near future. Preventing the loss of talented scientists with graduate
degrees will require developing new strategies for enacting culture change in industry and
academia. The ADVANCE program, in addition to new family-friendly policies recently
implemented by NSF across the directorates, provide opportunities to address the gender
imbalance prevalent among mid-career geoscientists, however the breakout discussion pointed to
a specific need for more institutionalized incentives to minimize the negative impact of gender
and family roles on the career goals of women.




                                                                                                  32
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.




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35
                                             APPENDIX A

Table 1: NSF SEES Workshop Participants "Tracking and Energy Elephant and RCN Core Members

NSF Visitors
Richard    Fragaszy      NSF                        P.D. Engineering (Geomech., Geotech.)
Tim         Killeen      NSF via Web                Assistant Director GEO
Rich        Lane         NSF                        P.D. Sedimentary Geology, Paleobiology
Robert      Detrick      NSF via Web                Division Director EAR


Organizers and Steering Committee
Charlla    Adams         Boise State                Logistics
Karin       Block        CUNY                       St. Committee/Geoinformatics and Education
Herbert     Einstein     MIT                        St. Committee/Underground Construction
Charles     Fairhurst    U. Minnesota               Steering Committee/Rock Mechanics
John        Holbrook     UT Arlington               Organizer/Sedimentary Basin Architecture
Joe         Moore        EGI / U Utah               Organizer/Geothermal Energy Development
Ioana       Paltyon      EGI / U Utah               Logistics
Devri       Roubidoux    Boise State                Logistics
Walt        Snyder       Boise State                Organizer/Stratigraphy and Informatics


Attendees
Mila        Adam         Boise State                Geophysics
Rick        Allis        Utah State Geologist       Geologist, gravity, heat flow
Tom         Anderson     EGI / U Utah               Enhanced Geothermal Systems
Brian       Anderson     Student                    Uni. W.VA.
Kate        Baker        Retired Exxon              Geophysics
Leandro     Balzano      Shell                      Shell new ventures director; will send a rep
Dave        Blackwell    Southern Methodist U       Heat Flow and SMU Geothermal Program
Antonio     Bobet        Purdue University          Rock Mechanics/underground construction
Tom         Buscheck     Lawarnce L. Nat. lab       CO2 sequestration and Geothermal
David       Chapman      EGI / U Utah               Heat flow
Christine   Detournay    Itasca Consulting          Civil Engineer/Modeling
Russ        Detwiler     U.C. Irvine                Geothermal, heat in sediments
Jim         Driscoll     Hot Dry Rocks Pty Ltd      Geothermal Industry
Mason       Edwards      Student                    University of Utah
Derek       Elsworth     DUSEL                      Petroleum Engineering, Fractures
Jerry       Fairley      U of Idaho                 Geochemistry
Jim         Faulds       U Nevada Reno              Structural Geology and Geothermal
Rene        Finicial     Texas Christian U          Student
Johnathan   Glen         USGS                       Geothermal Program Leader

                                                                                                   36
Marte       Gutierrez    Colorado School of Mines     Flow Modeling
Christian   Hardwick     U Utah                       Student
Rob         Harris       Oregon State University      Coll. of Oceanic and Atmospheric Sciences
Denise      Hills        Geologic Survey of Alabama   Sedimentary Geothermal Research
Doug        Hollett      DOE                          P.D. Geothermal Energy
Jack        Hess         GSA                          Executive Director
Cari        Johnson      University of Utah           Geothermal Research
Susan       Johnson      Texas A & M                  Student
Terry       Jordan       Cornell                      Sedimentary geology
Paul        Kasameyer    retired LLNL                 Imperial Valley systems
Shari       Kelly        New Mexico Bureau            Geologist
Peter       Leary        University of Auckland       Institute of Earth Science & Engineering
Ray         Levey        EGI / U Utah                 Director
Mark        McClure      Student                      Stanford
Lisa        McLaughlin   Student                      Texas A&M
John        McLennan     EGI / U Utah                 Geothermal Research
B.J.        McPherson    EGI / U Utah                 Geothermal Research
Paul        Morgan       Colorado Geological Sur.     Geothermal from Petroleum wells
Kerry       Newell       Kansas Geological Survey     Basin Sedimentology and energy
John        Oldow        UTexas at Dallas             Geosciences - Professor and Head
Thomas      Oommen       Mich.Tech. University        Geo-hydrology
Fen         Pan          U Utah                       Student
Varun       Paul         Student                      MO Un. of Sci. and Tec.
Will        Petit        Itasca Consulting            Geothermal Industry
Rob         Podgorney    Idaho National Lab           Modeling
Colleen     Porro        NREL                         Geothermal, Government
David       Pyles        Colorado School of Mines     Dep.t of Geology and Geological Engineering
Jimmy       Randolf      University of Minnesota      Department of Earth Sciences
Tim         Rawling      University of Melbourne      Director of Infrastructure Development,
Joel        Renner       Retired Idaho National Lab   Geol. Engineer - geothermal emphasis
Ladislaus   Rybach       ETH Zurich                   Director, International Geothermal Assoc.
Paul        Schwering    Student                      U. Nevada Reno
Shikha      Sharma       West Virginia University     Geothermal Research
Stuart      Simmons      Colorado School of Mines     Geothermal Resources
Peter       Smeallie     Am. Rock Mechanics As.       Executive Director
Alice       Stagner      ConocoPhillips               Geologist
Azra        Tutuncu      Colorado School of Mines     Energy Engineering
Shams       Ul-Hadi      Student                      University of Houston
Nuri        Uzunlar      SD Sch. of Mines and Tech.   Sediments and Stratigraphy
Kasper      van Wijk     Boise State                  Geophysics, education
Colin       Williams     USGS                         Geothermal Resources
David       Zur          DOSECC                       Education and Public Outreach

                                                                                                    37
38
                                            APPENDIX B



Suggested Topics/Questions Related to Engineering as Distributed at the Workshop Engineering
Issues – Topics to be Discussed
•       Well Hole Drilling
•       Fracture Issues
•       Operation
•       Modelling
•       Risk and Decision Making
•       Other Topics
In all of this, what are the differences between geothermal well drilling and hydrocarbon well drilling in
sedimentary rocks? Possibly: what are the differences between geothermal well drilling in sedimentary
rocks and igneous (metamorphic) rocks?


•     Well Hole Drilling
      - Increase drill penetration rate with conventional drills
      - “New” drill head technology
      - Well hole stability
      - Casing – Cementing
      - Horizontal/Smart drilling
•     Fracture Issues
      - Fracture pattern exploration
      - Fracture creation – fracking
      - Fracture stimulation
      - Induced seismicity
      - Propping
      - Scaling
•     Operation
      - Wellhole (injector, producer) arrangements
      - Circulating fluid
      - Long term performance
      - Restimulation;
      - Powerplant, etc.

•     Modelling
      - Well drill models
      - Fracture pattern models
      - Fluid flow models
      - Stimulation-fracking-propagation models
      - “Operational” models


                                                                                                        39
•   Risk and Decision Making
    - Cost,- Time,- Resource Models
    - Uncertainty assessment and analysis
    - Exploration analysis
    - Decision analysis with updating
    - Risk Analysis

•   Other Topics
    - Other technologies, e.g. deep shafts
    - Environmental problems related to groundwater
    - Environmental problems related to atmosphere
    - …




                                                      40
41
                                                   APPENDIX C

            Rock Fracture Engineering Issues Facing EGS in Sedimentary Formations

                                                  Charles Fairhurst

The following discussion attempts to explain the complexity of the challenge of developing a
successful EGS, whether in sedimentary formations or crystalline rock.


    Lack of understanding of the deformability, strength and general constitutive behavior of a rock
mass and the urgent need to address this problem was identified by Professor Leopold Müller as
the principal reason why he founded the International Society for Rock Mechanics (ISRM) in
19622 Collapse of the Malpasset Dam in December 1959–due to failure of the dam foundation,
and the massive collapse of the mine roof in an underground coal mine in Coalbrook, South
Africa in January 1960 –with approximately 450 lives lost in each disaster, provided the
immediate stimulus for establishing ISRM.


Extensive efforts have been made to tackle the problem of defining rock mass strength in the
subsequent 50 years, but the principal result has been the development of a number of empirical
rules to serve as guides to engineering design, principally in Civil Engineering and Mining
Engineering. These professions had a distinct advantage compared to other ‘subsurface
engineering’ disciplines (e.g. Petroleum Engineering, Geothermal Energy) in that Civil and
Mining engineers have 3D access to the subsurface and are able to observe rock mass response
directly, whereas colleagues in Petroleum and Geothermal Engineering are restricted essentially
to 1D borehole observations, supplemented by geophysical techniques that are able to identify
larger scale geological features - faults and large offsets –but not in the detail required for EGS
design..




2
 When asked, in a radio interview, in 1962, why the ISRM was needed, Professor Müller replied, in essence, “Because we do
not understand the (mechanical ) behavior of a rock mass.” [Fairhurst C. (2009) What is the Strength of a Rock Mass? Vienna-
Leopold Müller Lecture, Proc.5th Colloq. "Rock Mechanics – Theory and Practice" Vienna, Austria, Nov.2009. Mitteilungen für
Ingenieurgeologie und Geomechanik, Vienna Technical University.
                                                                                                                          42
The first attempt to develop EGS in the United States was undertaken by the Los Alamos
Scientific Laboratory with the Fenton Hills (New Mexico) project, started in 1970. After several
years of field testing the project was abandoned. In describing the evolution of the field program,
Duchane and Brown (2002) make the following comment (p.15),


The idea that hydraulic pressure causes competent rock to rupture and create a disc-shaped
fracture was refuted by the seismic evidence. Instead, it came to be understood that hydraulic
stimulation leads to the opening of existing natural joints that have been sealed by secondary
mineralization. Over the years additional evidence has been generated to show that the joints
oriented roughly orthogonal to the direction of the least principal stress open first, but that as
the hydraulic pressure is increased, additional joints open.3


The initial concept at Fenton Hills was to create a massive hydraulic fracture in what was
considered to be a homogeneous, isotropic, granitic rock mass. The hydraulic fracture was
assumed to propagate symmetrically as a planar (penny-shaped) crack from the pressurized
interval in the borehole. (This theoretical notion is still widely assumed, although models of
fracture initiation from a borehole suggest that the hydraulic fracture is likely to start first on one
side of the borehole. Once this happens the initial symmetry of loading is lost and fracture
propagation proceeds in a different manner than assumed in classical theoretical analysis. As
noted by Duchane and Brown, the observed crack propagation was influenced markedly by pre-
existing fracture. It is now acknowledged in EGS that pre-existing fracture systems exert a
major influence on the pattern of development of a stimulated region in EGS. Generally, little
information is available on the network of pre-existing fractures and their mechanical properties.
This introduces considerable uncertainty into the stimulation process.




3
  Duchane, Dave and Don Brown, (2002); Hot Dry Rock (HDR) Geothermal Energy Research and Development at Fenton
Hill GHC Bulletin, December 2002 pp.13-19.

                                                                                                                 43
Figure 1. Distribution of lateral stresses observed at the Bure Underground Research
Laboratory, France. (Wileveau et al, 20074)

With respect to its overall mechanical behavior, rock in-situ is probably the most complex
material encountered in any branch of engineering. Thus,


        rock in situ has been subject to tectonic and gravitational forces for many, many millions
         of years, and has been deformed and fractured in very complex ways .


       The term ‘rock’ covers a wide variety of materials, (granites and other crystallines,
        sandstones, limestones, shales and other sediments, each with a different response to
        applied loads ,both with respect to long term (geological) and short term (engineering)
        loading.


        This is illustrated in Figure 1, which shows stresses determined in sediments of the Paris
        Basin. An argillite–the Callovo-Oxfordien formation, is overlain and underlain by two
        limestones (the Oxfordien and the Dogger formations). It is seen that the horizontal and
        vertical stresses in the argillite are almost equal to each other while there is a substantial

4
 Wileveau, Y., Cornet, F.H., Desroches, J., Blumling, P. (2007) – Complete in situ stress determination in an
argillite sedimentary formation Physics and Chemistry of the Earth Journal Parts A/B/C Volume 32, Issues 8–14,
2007, Pages 866–878

                                                                                                            44
       deviation between them in the limestones. This is because, over geological time, the
       argillite will flow in a viscous fashion until there is essentially no difference between the
       stresses. Also, since the vertical stress is equal to the weight of the overburden, which is a
       constant, the three stresses are all equal to the vertical stress. This is a simple illustration
       of how ‘heterogeneity’ of the rock leads to non-uniform stress distributions. These
       distributions cannot be calculated, since the long term (over geological time) mechanical
       constitutive properties are unknown.


      Fractures represent another type of heterogeneity –the cohesion and coefficient of sliding
       friction on a fault plane limit the forces (especially shear forces) that can be transmitted
       across the fault plane. Water under pressure at depth tends to flow along fractures. The
       temperature of the rock tends to increase with depth. These influences result in complex
       thermo-hydro chemical (THC) coupled effects that can cause the fracture shear strength
       to decrease over time - leading to slip, which may be violent. Fractures may occur in
       sets, formed at different time geologically, when tectonic forces had different
       orientations.


      Injection of fluids under pressure into such regimes will disturb the force equilibrium in
       complex ways.


      In contrast to Civil Engineering and Mining Engineering, there is relatively little practical
       experience of successful EGS systems from which to develop empirical rules of ‘good
       practice’. This implies a greater reliance on principles of mechanics in developing
       engineering designs for EGS.


The remarkable advances in computer power over the past two decades or so offer the possibility
of an alternative ‘route’ to development of practical EGS systems.


Numerical Modeling of EGS Systems



                                                                                                     45
Powerful numerical models are now available that can accommodate geological complexity,
fractures, fluid flow in permeable rock, temperature increase and heat flow, and chemical
(dissolution, precipitation, etc). Problems can be modeled in three dimensions, and followed over
time. The effects of fluid injection on the mechanical response of the ‘simulated rock mass’ can
be modeled.


Simplifications are required to make the models more tractable, but the essential point is that
ability to model the geology in sufficient detail to ascertain the response of the modeled system
is not the primary obstacle to development of a good understanding of how to design an
effective Engineered Geothermal System.


The primary obstacle lies in the difficulty of determining the nature of the pre-existing
fracture systems, and their relevant mechanical properties. This information is essential to the
foundation of a realistic numerical model. A similar problem exists in petroleum engineering.
Considerably more R&D effort has been carried out on petroleum problems, but significant
problems remain in this field also. Figure 2 illustrates the main Thermo-Hydro-Mechanical-
Chemical (THMC) coupled interactions that arise when fluids flow through rock. For many
engineering applications, several of these processes are of secondary importance. Temperature
and chemical effects, for example, are usually not of concern in near surface problems e.g.
design of dam foundations or rock slopes. In the case of EGS, all of the processes illustrated in
Figure 2 are important. Indeed, other factors, not shown in the Figure, assume major significance
e.g. the coupling between flow in fracture systems and flow in the permeable matrix.




                                                                                                  46
             Figure 2. Effects of Coupled in-situ Processes in Rock Mass Behavior. 5

Modeling of EGS systems in sedimentary basins introduces still additional considerations – flow
of fluids may be restricted to formations bounded by impermeable boundary layers, for example.
This requires modeling on a substantially larger scale than that associated, for example, with
extension of the fracture network (sometimes referred to as the process zone) around the tip of a
propagating hydraulic fracture; with possible convection cells generated by fluid flow in a region
of temperature gradients etc. Thus, Scale Effects are important –with much to be done to
introduce these to the Sedimentary EGS problem.

The foregoing discussion illustrates several points.


       Current understanding of the Sedimentary EGS problem is rudimentary.
       Development of engineered systems for Sedimentary EGS will require considerable
        development of numerical models on a variety of scales.
       Development of these models will require a very close interaction between geologists
        who have a good understanding of sedimentary systems and those experienced in
        development of numerical models.
       Geologists have a vast amount of valuable qualitative understanding and insights based
        on direct observations in the field.

5
  Yow, J.L., and J.R. Hunt (2002) "Coupled Processes in rock mass performance with emphasis on nuclear waste
isolation," Int’l J. Rock Mechanics & Mining Sciences, 39 (1) pp. 1-7. A copy of this paper can be seen at
http://ccrm.berkeley.edu/pdfs_papers/2.09/yow_hunt_int_j.pdf

                                                                                                               47
       In many instances, observations by geologists are based on surface expressions of processes
       that are/ or were three-dimensional. Models (both physical and numerical) of these processes
       can be developed in three dimensions, from which two-dimensional models can be
       ‘extracted’. This allows a more productive interaction and dialog between the two groups.


A significant impediment between ‘field -experienced professionals’ and numerical modelers is
recognition that models are, by definition – a simplified representation of the real situation.
All models contain simplifying assumptions. Although these assumptions will be known to the
modeler, their existence, and their influence on the model predictions, may not be fully
appreciated or recognized either by the modeler or the person examining the model predictions.
The cautionary maxim Make everything as simple as possible, but no simpler6 is very
appropriate for development of numerical models.


Various methods are employed to attempt to ensure the validity of numerical predictions.
Comparison with classical analytical solutions can be very valuable –where such solutions exist.
In many cases, however, the critical features included in a model are not easily ‘checked’ in this
way.


A more valuable procedure for evaluating models is to always require that there be more than
one model developed of a particular problem. This allows the predictions of each model to be
compared – and the basis for any differences between the predictions to be discussed and
explained. The model predictions should be examined critically by colleagues experienced in
field observations.




6   Often attributed to Albert Einstein –although the same sentiment appears in earlier writings.
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