NSF-SEES WorkShop rEport

NSF-SEES WorkShop rEport

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SedHeat is a diverse working group of top scholars, practitioners and leaders dedicated to finding solutions to extracting geothermal power from the earth.

Tracking an EnErgy ElEphanT: Science and engineering challenges for unlocking the geothermal potential of sedimentary basins: An NSF-SEES Workshop report

a WOrD aBOUT SEDhEaT - 4

ExEcUTivE SUmmary - 5A Summary of Critical Questions in the Realization of Sedimentary Basin Geothermal Energy

SUmmary Of criTical QUESTiOnS in ThE rEalizaTiOn Of SEDimEnTary BaSin gEOThErmal EnErgy - 6

inTrODUcTiOn - 8

ThE prOmiSE Of gEOThErmal EnErgy - 10

UnDErSTanDing ThE naTivE BaSin - 12• Introduction• Theheatresource• Thebasinplumbingsystem• Summary

mOniTOring anD QUanTifying rOck prOpErTiES WiTh gEOphySical mEThODS - 18• Introduction• GeophysicalproblemsandneedsinthequestforsedimentaryGeothermalEnergy

EnginEEring iSSUES in SEDimEnTary BaSin gEOThErmal EnErgy - 20• Introduction• Detailedengineeringissues• Conclusions

mEETing ThE challEngES Of EDUcaTiOn anD OUTrEach - 24 • Introduction• Issues,strategies,optionsandsolutionsforaddressinggeothermalworkforceand

educational issues

EffOrTS TO DEvElOp a cyBErinfraSTrUcTUrE fOr ThE SEDhEaT cOmmUniTy - 28• Introduction• Initialefforts• Taskforces

rEfErEncES - 30

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ThefollowingreportrecordsthefindingsoftheNSFSEESworkshop“TrackinganEnergyElephant”whichwas proposed in the spring of 2011 and convened November 6-9, 2011 in Salt Lake City to address one centralquestion:“Whatarethebasicscienceandengineeringquestionsthatneedtobeaddressedinorder to make geothermal energy production from sedimentarybasinspractical?”Theworkshopgatheredover 70 participants, ranging 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.

Participants also represent the emerging and standing leadership in geothermal research within their respective fields.Thisreportrepresentsaconsensusoftheoptimism and the challenges expressed by the group.

Theseparticipantshaveremainedasaninteractivegroup since this workshop and form the core of the SedHeat NSF Research Coordination

Network.Thisongoingeffortisdesignedtoprovide a vehicle to further build a community of researchers dedicated to advancements in the area of geothermal energy from sedimentary basins. For more information, or

to join in on the effort, please visit us at www.SedHeat.org.

“ These participants have remained as an

interactive group since this workshop and

form the core of the SedHeat NSF Research

Coordination Network.”

a WOrD aBOUT SEDhEaT

5

On November 6-9, 2011, a group of 71 scientists, engineers, educators, practitioners and planners gathered in Salt Lake City, Utah, for an NSF-SEES Workshop to addressonecentralquestion:

“Whatarethebasicscienceandengineeringquestionsthat need to be addressed in order to make geothermal energyproductionfromsedimentarybasinspractical?”

Theconsensuswasthatlargestoresofheatenergyareavailable from sedimentary basins, but advances in basic science and engineering are needed to economically extract this heat for large-scale electrical generation.

For geothermal resources to be viable, water of sufficient volumeandtemperatureisrequired,alongwithreservoirrocks with sufficient porosity and permeability to store and allow the movement of water through them to the wellbore.ThewesternU.S.isdominatedbyhydrothermalsystems that reflect the structure and high heat flow of this tectonically active area. But these western, largely hydrothermal, resources tend to be small, generating from 10-30 MW per site, are generally localized, and lack the collective resource capacity to have a significantly large impact on U.S. electrical supply.

Enhanced Geothermal Systems (EGS) are those that attempt to extract heat by fluid circulation through induced fractures in otherwise non-porous and impermeable basement rock. But generating sufficient reservoir capacity to accept injected water of sufficient volume, and flow connectivity between injection and production wells,hasprovenhighlychallengingtodate.Incontrast,the strata in deeper portions of sedimentary basins have the native porosity and permeability, can hold large volumes of water, and can be enhanced to hydrologically connect fractures induced by EGS. High subsurface temperatures coupled with effective flow and heat sweep between injection and extraction wells offer the potential for geothermal resources from sedimentary basins that can yield 100’s of MW per site. Heat at drillable depths of 3-6 km in sedimentary basins could generate 1+ MW ofsustainedpowerpersquarekilometerwithnegligibleimpact to surficial systems.

Large areas of deep sedimentary basins in the conterminous U.S. house an estimated 100,000 EJ of powerresource(Tester,etal.,2006).Thepotentialforsedimentary-basin geothermal to replace a sizeable proportionofthecurrentcarbon-rich(100EJ/year;DOE/EIA,2010)energyconsumptionisthushigh.Inaddition,being able to tap geothermal resources of sedimentary basins opens up areas of the US, and indeed the world, that have no other viable source of geothermal energy.

Tappingthelargeenergyresourcesofsedimentarybasinswillrequireameaningfuleffortinbasicresearchgeareddirectly to overcoming current applied challenges. Better understanding of the native sedimentary basin and better engineering and geophysical technologies are needed to provide the breakthroughs that will advance geothermal energy to its potential role as a primary contributor to the U.S.energyportfolio.Thehighup-frontcostsassociatedwith large-scale geothermal energy systems make this industry particularly vulnerable to uncertainty in the proper

placement and development of power plants and the related acceptance of financial risk. Lowering of financial risk to acceptable levels and organic expansion of this industry must start with a concerted effort to address the basicscienceandengineeringquestionsthatunderpintherisksofapplied-researchunknowns.Thiswillnecessarilyrequireadvancementsinworkforcedevelopmentandeducational infrastructure as well.

Thediversityofscienceandengineeringandsocialsciences needed to address these problems also requireadvancedvehiclesforinformationalexchangeand interdisciplinary cooperation addressed by cyberinfrastructureandotherscholarlyexchange.Theprimarybasicquestionsidentifiedbytheworkshopgroupthat need to be surmounted are summarized below.

“ ...advances in basic science and engineering are

needed to economically extract this heat for

large-scale electrical generation.”

ExEcUTivE SUmmary

• Thepotentialfor

sedimentary-basin

geothermal to replace a

sizeable proportion of the

current carbon-rich energy

consumption is high.

• Advancesinbasicscience

are needed to economically

extract this heat for large-

scale electrical generation.

• Itwillrequireadvancements

in workforce development

and educational

infrastructure as well.

kEy finDingS

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SUmmary Of criTical QUESTiOnS

in ThE rEalizaTiOn Of SEDimEnTary BaSin gEOThErmal EnErgy

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EnginEEring of gEothErmal SyStEmS What new or improved well technologies can make drilling and developing large boreholes possible and practical at very high temperatures?

What new techniques can be defined that permit us to predict, control, and monitor stimulated fracture systems in deep, hot, and heterogeneous media?

How can we effectively monitor the evolution of fractures, heat regime, and stress conditions induced by geothermal extraction?

What are the relationships and thresholds between modified fluid pressures and induced seismicity?

Can numerical decision models be generated that effectively predict geothermal operational risk?

Education and cybErinfraStructurEWhat short-term and long-term efforts will prove most effective toward tempering workforce shortages expected of an emerging geothermal industry?

What efforts would prove most effective at raising the current low profile of geothermal energy in the mind of the public and policy makers?

What are the positive and negative feedbacks tied to relationships between the geothermal and oil and gas industries as it relates to perceptions, workforce development, and educational infrastructure?

What are the most effective forms of cyberinfrastructure that may be used to promote sharing of data and education materials to best aid the development of geothermal curricula?

What are the best vehicles for fostering cross-disciplinary education and scholarship between engineering and science disciplines?

What are the best processes for building an educational and workforce pipeline from K-12, through undergraduate, to graduate, to professional in the geothermal sciences, and how can we best assure that women and minorities are not leaked from this system?

What can be done to retain underrepresented groups in the educational and career pipeline toward potential geothermal positions?

What are the cyberinfrastructure platforms that will best facilitate effective exchange of ideas and data and foster greatest participation for the SedHeat community, and what is the best approach for constructing this platform?

thE nativE SEdimEntary baSinHow does heat move within sedimentary basins at large scales and how does this impact the renewability of the resource?

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

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?

What are the diagenetic processes that operate in deep sedimentary basins and how do they increase or reduce permeability as they evolve? 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?

gEophySicSHow can discrete geophysical methods be integrated to identify basin properties critical to geothermal development (e.g. permeability pipes, thermal distribution, etc.)?

What are the critical advances needed to better predict and measure changes in thermal properties of fluids and solids in deep-Earth settings during development and production?

How can geophysical aspects of deep-Earth settings be effectively simulated within the lab?

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Presently, less than 1% of the energy grid in the United Statesderivesfromgeothermalsystems(DOE/EIA,2010).Thetotalamountofheatenergypresentwithinthe Earth, however, is enormous (>14x106 EJ within the U.S. at drillable depths), and represents a sustainable energy source well beyond current or projected domestic electricalneeds(100EJin2005)(Tester,etal.,2006;DOE,2008).Assuch,geothermalenergyisoneofthefew 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 most of the 3000 MWe produced in the US and the10,000MWeproducedworldwide.Thesearethe“conventional”hydrothermalsourcescharacterizedbyfaults, fractures, and regional or local high heat flows that allowwatertolocallyandquicklyreachtemperaturessufficient for electricity generation at relatively shallow depths.Thelargestofthesesystems(e.g.TheGeysers,CA,CerroPrieto,Mexico;Larderello,Italy)currentlygenerateapproximately700-850MWeeach.Williams,etal.,(2008)estimatedthemeanpowerpotentialofidentified hydrothermal systems distributed over the western 13 states, including Alaska and Hawaii, at 9057 MWe, and estimated the mean power potential of undiscovered hydrothermal resources to be an additional 30,033 MWe.

Thepowerpotentialof“unconventional”resources,which includes deep sedimentary basins, is significantly greater than conventional convective systems and would significantly enhance the geothermal resource base if tapped. Heat in deep sedimentary basins is transferred primarilybyconduction.Incontrasttotherelativelysmallareal extent and size of even the largest convective geothermal systems, sedimentary basins have areal extents of hundreds of kilometers, potentially little

interaction with the near surface geologic 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, negligible impact on global climate change, and without concerns of long-term depletion.

Temperaturesadequateforgeothermaldevelopment(>~150° C) are accessible throughout the US at drillable depths. However, permeabilities may not be sufficient everywhere to produce the commercial flow rates necessaryforlargescalegeothermalpower.Deepsedimentary basins have the attribute of having natural matrix permeability that, in conjunction with natural fracture systems, can be exploited to solve this flow-rate issue. As well, this permeability can be augmented by hydraulicfracturingortheapplicationofothertechniquesto create Enhanced Geothermal System (EGS) production (Elsworth,1989;Tester,etal.,2006;DOE,2008).Further,efforts to improve oil and gas productivities of deeply buried sedimentary rocks provide a solid head start for emerging sedimentary-basin geothermal technologies.

Geothermal development and research reflects the truespiritofthesustainabilityconcept.Tappingthefullpotential of this energy source and growing it beyond thecurrentrelativelylowusagerates,however,requiresthat we gain a much better understanding of natural and engineered geothermal systems within sedimentary basins. Without this gain in knowledge, we cannot hope to tap the geothermal energy potential of deep sedimentarybasins.Thisisauniqueopportunityforthescience, engineering and cyberinfrastructure communities to work together to meet our national renewable energy goals.

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 thebasicscienceandengineeringquestionsthatmustbeaddressedinordertotapthisenergyresource.Thefollowing report details the finding of this workshop group.

“ Presently, less than 1% of the energy grid in the

United States derives from geothermal systems

(DOE/EIA,2010).”

inTrODUcTiOn

9

FROM IEA GEOTHERMAL ROAD MAP (2011)

AMBITIOUS

GOAL:

REGIONAL DEVELOPMENTGEOTHERMAL POWER CAPACITY

200 GWe in 2050 (TODAY ~ 12 GWe)

kEy finDingS:

• ThetotalamountofheatenergypresentwithintheEarthisenormousandrepresentsasustainable

energy source well beyond current or projected domestic electrical needs.

• Sedimentarybasinshavethepotentialtomovegeothermaltowardameaningfulportionofourenergy

needs, and do so with minimal environmental impact, negligible impact on global climate change, and

without concerns of long-term depletion.

• Tappingthefullpotentialofthisenergysourceandgrowingitbeyondthecurrentrelativelylowusage

ratesrequiresamuchbetterunderstandingofnaturalandengineeredgeothermalsystemswithin

sedimentary basins.

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Thenation’spotentialforgeothermalenergyisvast,andsimmers 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 14.5° C(IPCC,2007).Thisconstitutes 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 atanaveragedepthofonly580m,drillingdepthsconsidered very shallow throughout the geothermal and petroleumindustries.Thetemperatureonlyincreaseswith depth from there, rising to over 500-1000° C at thebaseoftheEarth’scrust.Thisinternalheatrunsthe tectonic systems that give us mountains, basins, earthquakes,andvolcanoesasitdrivesthemotionofthelithosphericplates.Theextantquestionis:howdowetapthis resource to help serve the energy needs of humanity?

Significantly, large portions of this buried geothermal energymaybeharvestable.Thecurrentlymaintainedglobal radiation of heat energy from the interior of the globeisapproximately44terawatts(TheKamLandCollaboration,2011).Thisenergyisavailablewithoutendeavoring to mine the heat accumulated over geologic time, and merely involves interception and capture of the heat radiated to space. Estimates of 1+ megawatt recoveredpersquarekilometerofbasinareaareconsidered conservative and sustainable for net power generation based on current heat flow measurements (Tester,etal.,2006;Williams,2007;DOE,2008).Successful production at this rate over 1000 km2 would

provide at least one gigawatt. For perspective, the installed electric capacity of the U.S. is roughly one terawatt (1000 gigawatts) with substantially less in actual useatanytime(DOE/EIA,2010).

Deepgeothermalheatextractionbecomespracticalat temperatures beginning between 100 and 150° C, occurringtypicallyatdepthsof2-6km(Tester,etal.,2006; Blackwell, et al., 2007; William, 2007; Esposito andAugustine,2011).Theareaofsedimentary-basinwith fill exceeding 4 km 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(e.g.,Figure2for4.5km).TheTester,etal.(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. Sedimentary-basin geothermal thus has the potential to replace a sizeable portion of the current carbon-rich (100EJ/yearatapproximately50%coal;DOE/EIA,2010)energy production, and to absorb future growth in energy needs. Use of sedimentary-basin geothermal power, with its negligible output of CO2, would thus help to mitigate climate change issues related to current energy sources.

Extractionofgeothermalheatresourcesrequiresthree conditions: 1) heat; 2) water; and 3) permeability. Permeability is also a proxy for natural or enhanced conduitsforfluidflow.Thereareseveral“types”ofgeothermal 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 in contrast

ThE prOmiSE Of gEOThErmal EnErgy

By John Holbrook, Joseph Moore, and Walter Snyder

11

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.

Thoughtheclassificationofgeothermalsystemsisstillactively evolving, there are generally three other types extantwithintheU.S.Theseothertypesdependuponlocalized high heat flow and include; 4) hydrothermal (in particular“BasinandRange”type);5)magmatic;and6)Enhanced Geothermal Systems (EGS) that depend on induced fracture of otherwise nonpermeable 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 addedattentioninrecentyears(Testeretal.,2006;DOE,2006;DOE,2008).Aggressivegoalslikea10%increaseby 2014, doubling the geothermal capacity by 2020, and

100,000MWin50years(DOE,2008;reaffirmedinDOE-GTPMissionandGoals:April11,2011)requiredevelopingnew technologies and other types of resources, including power production from sedimentary basins, engineered geothermal systems (EGS) and other novel resources (Shook, 2009).

Albert Einstein famously approached President Roosevelt to inform him of the vast energy that may be stored 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 riskygenerationorwaste-storageprocesses.Itisalreadythereinitsfullquantity.Likewise,waterextractedfromdeepbasinaquifersforheatcanberecycleddirectlybackintotheaquifertoprovidepressuresupport,meaninggeothermal systems have the potential to be matter-closedsystemsandthusgas,liquid,andsolidwasteeffluent would be negligible at the surface. With proper management, the heat can be extracted from geothermal fluids with negligible material pollution of the surface or atmosphere(DuffiedandSass,2003;BlodgettandSlack,2009;Tester,etal.,2006)andnosubstantiveimpactonclimate trends. Our technical and economic barriers are in gaining the capacity to harvest this abundant energy that we already have with sufficient predictability and efficiency. 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 of the Earth interior.

• The nation’s potential for geothermal energy is

vast, and simmers in abundance beneath the feet

ofallAmericanseverywhere.

• Sedimentary-basin geothermal heat thus has the

potential to replace a sizeable proportion of the

current carbon-rich energy production, and to

absorb future growth in energy needs.

• With proper management, the heat can be

extractedfromgeothermalfluidswithnegligible

material pollution of the surface or atmosphere

(DuffiedandSass,2003;BlodgettandSlack,

2009;Tester,etal.,2006)andnosubstantive

impact on climate trends.

Figure1:DistributionofsedimentthicknessintheconterminousU.S. 4 km isopach in black. Numerous Basin and Range basins over4kmexcludedforsmallresolution(Tester,etal.,2006)

Figure 2: Average temperature at 4.5 km, conterminous United States.(Tester,etal.,2006,afterBlackwellandRichards,2004)

0m

1000m

2000m

3000m

4000m

6000m

8000m

4.5 km

High-grade EGS Areas

50°C

100°C

150°C

200°C

250°C

300°C

kEy finDingS

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13

UnDErSTanDing ThE

naTivE BaSinBy John Holbrook and David Blackwell

introductionTodevelopgeothermalenergyatthe100MWescalesdesired for integration of this resource into the public electricgridrequiresadeepunderstandingofthenaturalgeothermal resources available from the targeted sedimentary basins and what natural conditions will determine effective heat recovery either from natural orartificiallyproducedfractures.Thetwoconditionsthe native sedimentary basin provides are a reservoir of heat and an infrastructure of natural or constructed permeability that will permit flow and extraction of geothermal fluids, mostly water.

Thescalesofheatandflowneededforeconomicgeothermal production, however, are high. For instance, a well yielding 10 MWe pumping 100 kg/s at 10 cents/kWh would gross $24 k/day. A well drilled to the 3-6 km depth needed to attain >150° C in most sedimentary basins would cost roughly $7-10 million to drill, then as much as $5 million in additional development costs (e.g., stimulation, 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/dayoilwellwouldgross$400k/dayat$80/bblandpay 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 geothermalpowereconomical(Testeretal.,2006,2007).Wellsofthisqualityareknownfromsedimentarybasins(e.g.,theTexasGulfCoast,AAPGExplorer,Nov.2011),butarenotroutine.Infact,thenationalaverageforwaterproduction is 0.021 kg/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 activelyavoided.Injectionordisposalwellsontheotherhand 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 BarnettShaleGasFieldinnorthTexas.InjectionwellsfortheBarnettShaleGasFieldinNorthTexasarecapableoftaking20,000-60,000bbl/day.Thisapproximatesthevolume(~45,000bbl/day;Testeretal.,2006)ofextraction needed for practical geothermal power production.

A successful geothermal energy plant will likely involvemultiplewellsincloseproximity.Itisthusnotunreasonable to expect that a 100 MWe plant would be fed by as many as 20 wells with $200 million invested in drilling, plus additional injection and makeup wells. Thehighupfrontcostsentailedingeothermalenergymeans that entrepreneurs willing to invest in this energy sourcewillrequireassurancethattheyhaveidentifiedthe best possible locations within the best possible basin conditions in order to raise the probability of prompt financialreturnoninvestments.Thismeansbettercharacterization of basin conditions to assure sufficient lowering of risks to potential investors when selecting possiblewellsites.Suchpredictionsrequireabetterfundamental understanding of the basic science behind the processes and structure of the native conditions of sedimentary basins.

thE hEat rESourcEHeatisthecommoditythatgeothermalsystemsacquireorrequire,andanydiscussionofgeothermalsystemsmust begin with a discussion of the heat available for extraction.TheheatoftheEarthatdepthiscurrentlymappedatafirstsolidpass(Figure2).Thiscriticalinformation 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, a pool from which energy can be extracted for potential generation of electricity spaceheating(Testeretal.,2006).Thiscomparestoa yearly usage of about 100 EJ in US electrical power consumption. Heat retained at depth is generated mostly from radioactive decay in the earth’s crust, and represents both new heat emanating from depth and heat retained from prior emission by the blanketing effectoflow-conductivityrock.Theheatisnotevenlydispersed, 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 virtually any site.

Thelargerunknownsofgeothermalheatarethenatureof thermal movement and the potential reactions of the basin heat system once heat extraction begins. Unlike typical mining operations that remove material permanently from the ground, heat energy moves and is replenished after initial extraction, making it a sustainable resource. How heat moves and is recharged naturally in sedimentary basins is a fundamental science questionthatpertainstobasicEarth-systemprocesses.Itdictatessubsurfacechemicalsystems,affectsrock

14

mechanical processes and deformation, and imprints on fluiddensityandflowcells.Thesefundamentalquestionsbecome 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 largerquestions.

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

Most of our understanding of heat movement in sedimentary basins is based upon coarse data sets anddependsuponseveralassumptions.Ingeneralweassume that heat moves mostly by low rate conduction in older sedimentary basins where porosities are lower. Insomeolderbasins,however,aquifersarefoundtotransfermuchmoresignificantquantitiesofheat,suchasinthecaseoftheMadisonaquiferintheGreatPlains(Gosnold,1991).Inyoungsedimentarybasins,suchas 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 (Bodner and Sharp,1988).Inaddition,heterogeneitiesinthethermalconductivity 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. Fluid flow (with heat redistribution) will not always follow permeable formations. So-called “cross-formationflow,”drivenbygravityforces,arecommoninsedimentarybasins(c.f.,Toth,2009).

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 previously viewed as a critical sciencedriver.Theneedtounderstandgeothermalsystems changes this priority structure and increases the need to better grasp the flow of heat in the Earth’s crust and sedimentary basins. As heat is extracted, how is it restored? Can it be restored on time scales practical forhumanuse?Inshort,asin-placeheatisextractedwe must know how much of this geothermal energy is from mining a known heat resource vs. harvesting from acontinuouslyrenewingresource?Toknowthis,wemust 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 a 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 (Pritchett,1998;Rybach,2010).Anapproximately25km2 developed area producing 25 MW of electrical energy couldfeedaplantlocatedatonecornerofthesquare.Assuminga25yearproductionperiodanothersquarewould be developed with the plant still at the corner over thefollowing25years.Thissequencewouldberepeatedtwo more times and after a 75 year recovery period the first 25 km2squarewouldbeexploitedagain.Thetemperaturesintheoriginalsquarewouldhavereturnedtoabout90%oftheoriginalvalue.Thissequencecouldlikely 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 the heat sweep?

Heat is extracted from the rock by production of hot waterandsubsequentinjectionofthecooledfluid.Thispromotes fluid flow through the heated rock. For this process to serve as a proper means to extract heat, theheatintherockmustbetransferredtotheliquid.At any temperature,5%porositymeans80%oftheheat is in the rock, and multiple sweeps of water are needed to recover the heat (i.e., the heat capacity of waterisabout4timesthatofrock).Inananalysisofthe potential for enhanced geothermal energy (EGS) development in sedimentary rocks, Nalla and Shook (2008)foundthatevenasmallamountofporositywas a significant factor in the movement of heat and for increasing the efficiency of extracting energy from induced fractures. 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 the 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

15

heat matrix induce vertical or other non-predicted flow cells?Eachofthesequestionsandmorehasimmediatepertinence as pumping is planned and commenced. Any predictiveplanningforthesecontingenciesrequiresaclear and basic understanding of local-scale and micro-scale heat flow and exchange that we presently do not have.

thE baSin plumbing SyStEmTheheatresourcesneededtosustaingeothermalproduction commonly occur in most basins at some reasonablydrillabledepth.Thehighflowratesofgeothermalfluidsthatarerequiredtoextractheateconomically from these depths, however, are an importantfactor.Theseflowrateshingeonthematrixandfracturepermeabilityofthebasinsediments.Thepermeability of rocks can be enhanced by intentional engineered fracturing, which is the cornerstone of EGS reservoir creation. EGS systems are understood to be a method for extracting heat from low permeability basement rock through the generation of artificial fractures. An area of challenge for EGS development is the generation of sufficient fracture volumes, large heat extraction surfaces, and connectivity to permit permeable flow over sufficient distances, times, and rock volumestocollectsustainableandeconomicquantitiesof 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 artificially 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 sufficienttopermitadequatefluidflowbetweenenhanced fractures needed to support geothermal extractionrequiresamuchbetterunderstandingofthe basic construction of sedimentary basins than we currently enjoy. Much advancement has been made regarding basin flow thanks to the needs of the petroleumindustry.Thefluidvolumerequirements,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 factorsthatcontrolreservoirquality.Inturn,weneedtounderstand 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 be understood both individually andinteractively.Thecriticalquestionsforconstrainingthe 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. Knowledgeofthesefactorsiscriticalforunderstandingwhat 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 depthsof3kmwhereadequatetemperaturesforpractical geothermal energy commonly begin and occur in basins throughout the U.S. (Figure 1). Much of these strata show good porosity, as evidenced from oil production records in both clastic and limestone formations.Thekeytoturningthisassociationofpermeability and depth into geothermal energy lies in understanding the factors that control this porosity and in determining the connectivity of those porous unitsthatresultinpermeability.Thisrequiresabetterunderstanding of the sedimentary architecture that

16

dictates the occurrence of flow units at different scalesandtheirverticalandlateralconnections.Thisarchitecture is a manifestation of the sedimentary process that filled the basin and the tectonic, climatic, and other forcing factors that determined how these processes worked over space and time. Better process understanding of the cause and effect links between basin architecture and the basin-filling drivers

will facilitate better prediction of basin permeability structure, a fundamental key for assessing optimal sites for injection and extraction wells. Stratal flow units are also well known to be heterogeneous, dictating the fluid flow contort around depositional obstructions that may occur at fine (e.g. mud drape of a single ripple) to large (e.g., coarse linear shoal deposits within a marine mud matrix) scales. Effective flushing of fluids through thegeothermalsystemrequiresadeepunderstandingof this heterogeneity in the plumbing. A significant barrier to tapping sedimentary basins for geothermal

energy is our ability to identify high-flow-rate locations prior to drilling and stimulating potential development wells. Understanding the sedimentary architecture is fundamental for making these predictions, and is where assessments of flow units within sedimentary basins must begin. Predicting sedimentary architecture 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.

Question 2: What are the diage-netic processes that operate in deep sedimentary basins and

how do they increase or reduce permeability as they evolve?

Once sediment is buried, chemical and physical processes within the basin system begin to alterthesedimentform.These“diagenetic”processeshave potential to alter the primary permeability of the initialsediment.Theseprocessescanbothdiminish(e.g., cementation and compaction) or enhance (e.g., dolomitization and dissolution) porosity, and most certainlywillmodifypermeability.Thelongeranddeeper the sediments are buried, the more diagenesis of the sediment can affect the primary porosity. Great depth and great time of burial are both hallmarks of the

“Effectiveflushingoffluidsthroughthegeothermalsystem

requiresadeepunderstandingofthisheterogeneityinthe

plumbing.Asignificantbarriertotappingsedimentarybasins

forgeothermalenergyisourabilitytoidentifyhighflowrate

locations prior to drilling...”

HOT ROCKSHYDROTHERMAL

HOT FRACTURED GRANITE

POWER

INSULATING SEDIMENTS

HOT DRY ROCKS

+ + + +

+ + +

+ + + +

+ + +

+ + +

+ + + +

Closed System


POWER


HOT WET ROCKS

+ + + +

+ + +

+ + + +

+ + +

+ + +

Underground Water Reservoir


POWER


VOLCANIC

V V V V

V V V

V V V V

V V V

V V V V

V V V

V V V V

V V V



SANDSTONES OR CARBONATES

POWER


SEDIMENTARY

+ + + +

+ + +

+ + + +

+ + +

+ + +


17

sediments from which geothermal waters would be extracted, and both of these factors work in favor of most of the chemical reactions that typify diagenetic porositymodification.Improvedunderstandingofenduring diagenetic modification of basin sedimentary rocks is critical to prediction of flow paths and where and how these are enhanced vs. diminished by diagenetic processes. Critically, diagenetic processes can be driven by the large volumes of fluid that repeatedly flush through the system during geothermal production.Theneedforgeothermalsystemstoendurefor decades means a system must remain open and subject to the accelerated exchange of pore fluids over extendedperiods.Thepermeabilityneedstoremainopen throughout the duration of this flooding without generating paths of fluid bypass or clogging with diageneticprecipitates.Predictionofallthisrequiresabetter 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 frac-tures on the transmission of fluid flow?

Thenaturalstressesthatcauserockstobreakgeneratefracturesthroughwhichfluidsmayflow.Indeed,itis truly rare to find an unfractured rock from a deep sedimentarybasin.Thesefracturesmayoccurasdisplaced faults, but more commonly as non-displaced joints.Thecapacityofthesefracturestodivertflowto 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 ofthehigherflowratesrequiredforgeothermalproduction,theseconcernsarecompounded.Thedetailto which the spatial behavior of these fractures needs tobeunderstoodhasescalated.Thepredictivebasisfor understanding fracture properties derives from understanding the interplay between fracture causal mechanisms and the evolving mechanical properties of the rock. Numerous issues emerge when fractures are factored into flow predictions. How will natural fractures interact with matrix porosity and engineered fractures? What is the impact of gouge in making fractures barriers instead of 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 continuousconduitsorrather“chutesandladders”forflow between matrix permeability units? How will the pressure changes inherent to long-term high-volume flushing modify the fracture environment?

Effective prediction of subsurface fluid flow paths and transmissibility all revolves around gaining a better

basic understanding of the processes by which natural fractures form and evolve as both single fractures and extended fracture zones. Hereby, the kind and degree of natural fracturing (orientation, density, extension, apertures, filling, mechanical properties) can become decisive in planning a geothermal field.

SummaryGeothermal energy production from sedimentary basins appears feasible with respect to natural heat, water, andpermeabilityresources.Thebarrierthatmustbeovercome is risk; we must develop the knowledge framework that helps to limit the risk of the high-cost of geothermal plant installation by being able to better predict the permeability and heat distributions, and if and where both are present within the basin.

Theviabilityofmostoftheoilandgasindustryhingesupon 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 must be exchanged more than once, and the heat sweep and regeneration must be sufficient to providetherequisitepower.Allthismustoccuratdepthstypicallybelowoilandgasproduction.Thisrequiresanew 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 predictwheretheseoptimalconditionswilloccur.Thisneed exceeds our current understanding of the basic sciences behind sedimentary basin filling, thermal evolution, and permeability structure. Finally, as all basins are not the same, portability of our understanding of sedimentary-basin-hostedgeothermalsystemsrequiresthat the inter-basin variations in basic basin processes are understood as well.

• Large-scalegeothermalenergyproductionfrom

sedimentary basins appears feasible.

• Thebarrierthatmustbeovercomeisrisk

of the high-cost of geothermal

plant installation.

•Weneedanewlevelofunderstandingforthe

basic science that determines the processes by

which heat moves and a sedimentary basin is

filledandmodified.

kEy finDingS

18

introductionAdvances in geophysical tools will be a key component for developing the ability to characterize deep sedimentary basins and their potential for geothermal energy. Field and laboratory research have tended to focus on individual tools that are specific to each scale of the experiment. Geothermal sedimentary reservoirs have hot fluids that over time will change the reservoir properties and therefore, their geophysical signatures. Thesechangescomefromgeochemicalalterationof

the rocks, fracturing, and the temperature and chemical evolution of the fluid phases. Geophysics can provide the tools to characterize and monitor dynamic changes in the reservoir, and provide a bridge among the more specific geological, geochemical and reservoir engineering studies. Here we provide some of the interdisciplinary problems and ideas, however, this is not necessarily a comprehensive list.

gEophySical problEmS and nEEdS in thE QuESt for SEdimEntary gEothErmal EnErgyGeophysical tools can be used to image conditions and changes within the deep-basin environment. Commonly, these are the only tools for visualizing critical characteristics for geothermal development like heat distribution, potential flow units, natural and induced fracture systems, and reservoir response to production-inducedconditions.Thebasic-scienceunderstandingof the basin heat and permeability structure used to evaluate basin architecture is usually calibrated against geophysical data in order to come to the final predictive basinmodel(s)usedindecisionmaking.Thebettertheresolution these geophysical data produce, the better the calibration of the process-based decision model.

Geophysicaltechniquesarenotcurrentlyfocusedonthe problems of the geothermal community, and the desired resolution is thus not currently available. Forward strides in geophysics aimed at geothermal goals will be necessary and must come from differing avenues of research defined below.

Question 1: how can discrete geophysical methods be integrated to identify basin properties critical to geothermal development (e.g. permeability pipes, thermal distribution)?

Monitoring and Quantifying Rock Properties with

gEOphySical mEThODSBy Ludmila Adam, Kasper van Wijk, Jonathan Glen and Walter Snyder

“ Geophysics can provide the tools to characterize

and monitor dynamic changes in the reservoir, and

provideabridgeamongthemorespecificgeological,

geochemical and reservoir engineering studies.”

ThermalThinkers:ClintonR.Colwell1,JoelH.Edwards2,CarlHoiland3,andHankHetrick1

19

Extracting the most geological and reservoir information fromgeophysicaltoolsrequiresintegratinggeophysicaltools with data from other disciplines at appropriate scales.Integratinggeophysicalinformationbetweenpotential field (magnetics, gravity) electro-magnetic and seismic (active and passive source) methods will help characterizethegeologyandreservoirmodeling.Theintegration of these geophysical tools is highly important for characterizing geothermal reservoirs, but research isrequiredtounderstandtheconnectionamongthesedifferent geophysical tools and with the petrophysical andreservoirparametersofthereservoirrocks.Thismergingofdifferenttoolsisrequiredtodevelopthescience and engineering necessary for sustainability of geothermal production in sedimentary basins, but requiresresearchfromthelaboratory(geophysicsoncore and mineral samples), field (surface and borehole geophysics), and satellite and airborne remote sensing (satellite magnetics, aero-magnetics and aero-EM).

Question 2: What are the critical advances needed to better predict and measure changes in thermal properties of fluids and solids in deep-Earth settings during development and production?

Geophysical data are critical to first characterize the nature of the petrophysical and geochemical nature of the reservoir and surrounding strata prior to stimulation and production, and then to monitor changes in these units as stimulation and production occurs. Geophysics is based on contrasts between acoustic, electrical, magnetic and density of Earth materials, and integrating those data with geochemistry (e.g., fluid and rock petrography (alteration) and reservoir engineering data (e.g., fracturing, thermal and pressure changes), and both of these can be used to spatially map changes in the reservoir over time. But field and laboratory research is needed to refine our ability to use geophysics to track these types of physical and chemical changes at the spatial and temporal scales necessary for monitoring geothermal stimulation and production activities.

Here are some examples of potential use of geophysics for monitoring the geothermal reservoirs. Permeability changes can in theory be mapped by tracking changes in seismicfrequencyattenuationthatreflecttheincreaseor decrease in permeability from the initial state of the reservoir (before stimulation or production). First, we need to conduct the experiments that allow us to adjust geophysical tools for this purpose, in particular at the temperatures and pressures of deep sedimentary geothermal reservoirs. Alteration of rock (e.g., clay formation) may be amenable to mapping using magnetic methods, if magnetic minerals are altered or destroyed duringthischemicalprocess.Again,thiswouldrequire

laboratory and field experiments to refine our geophysical approach. New methods for temperature mapping with geophysical methods could include advances in theacquisitionandprocessingofmagnetoteluricdata,refined magnetic approaches, and advances in seismic methods.Thethreewaycorrelationoftheeffectoftemperature on different parts of the reservoir and its relationship to mineral alteration, porosity, and fluid properties to geophysical properties is clear, but how toreliablyquantifytheserelationshipsislesswellunderstood.Improvedmethodsfordataacquisition,integration for time-lapse data, and innovative processing techniqueswillbeneededtoextractthemostinformation from the data.

Question 3: how can geophysical aspects of deep-Earth settings be effectively simulated within the lab?

Significant effort has to be steered towards understanding thermal conductivity, resistivity, elastic and magnetic effective media theories and upscaling thisfromthelaboratorytothefield.Theinterrelationbetween these parameters and their relation to the dynamic sedimentary geothermal reservoirs is critical to integrate geophysics to geology and reservoir flow.

Advancing the proposed ideas might benefit from selecting a natural field laboratory where geothermal systems in deep sedimentary basins can be studied in detail.Thatcouldfacilitatetheintegrationofdisciplinesthatare relevant for performing the science in such reservoirs.

• Themergingofdifferenttoolsisrequiredto

develop the science and engineering necessary

for sustainability of geothermal production in

sedimentary basins.

• Fieldandlaboratoryresearchisneededtorefine

our ability to use geophysics to track these types

of physical and chemical changes.

• Significanteffortmustbesteeredtowards

understanding thermal conductivity, resistivity,

elasticandmagneticeffectivemediatheoriesand

upscalingthisfromthelaboratorytothefield.

kEy finDingS

20

EnginEEring iSSUES in SEDimEnTary BaSin

gEOThErmal EnErgyBy Herbert H. Einstein and Charles Fairhurst

21

dEtailEd EnginEEring iSSuESMany of the challenges of geothermal development in sedimentary basins derive directly from engineering the drilling, reservoir conditions, and operation of the producing system. Likewise, controlling critical hazards like induced seismicity and other elements of the risk-decision matrix are pivotal to understand. Some of the most critical challenges are detailed here.

Question 1: What new or improved well technologies can make drilling and developing large boreholes possible and practical at very high temperatures?

Although drilling technologies in sedimentary rocks are well established through their use in hydrocarbon extraction, there are several specific geothermal issues thatrequirefurtherwork.Clearly,wellsingeothermalenergy 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 temperaturesatandabove200°C.Theseproblemsmayalso affect the ability to produce horizontal/smart wells. Otherorganizations(e.g.,theInternationalPartnershipinGeothermalTechnology(IPGT))havealsoalertedto this need.

Another well drilling related issue is the generally larger (than for hydrocarbon extraction) well diameter.Thisisassociatedwithtwoproblems:1.Adequatedrillpenetrationrate;and2.Well-borestability.Thelatterproblemismadeworsebythegreater depth (higher in-situ stresses and pore pressures).

Aquestionistheeconomicsofallthisadditionaldevelopment. While the hydrocarbon market is very large, (oil and gas represents approximately 60% of the world supply of energy) such that there is and can support a commercial interest in

developingspecializedequipment,thismaynotbethecasecurrentlyingeothermalapplications.Itappears,however, that one can benefit from technology in underground coal gasification, which also involves high temperatures.

Question 2: What new techniques can be defined that permit us to predict, control, and monitor stimulated fracture systems in deep, hot, and heterogeneous media? Fractures are a central concern in all aspects of ‘subsurfaceengineering’,includingEGS.Informationon fracture systems at a potential EGS site is obtained fromboreholesandgeophysicalsurveys.ThedesiredgoalistoestablishaDiscreteFractureNetwork(DFN),but when these are based on information obtained from oneor,atmostveryfew,boreholes,DFN’shaveanassociated high uncertainty. Much work is still necessary to develop mapping/survey approaches that provide adequateinputforthefracturemodels.Theinterplayof induced and natural fracture zones will also govern natural heat/fluid movement as well as production patterns.

Developingabetterknowledgeofthecharacteristicsof an individual fracture (aperture and aperture variation)isaseparate,verydifficultchallenge.Thecreation/stimulation of new fractures clearly is a major engineeringissue.Itdependsontheparticulartypesofrock and existing fractures. Although the hydrocarbon industry has decades of experience in this domain, many openquestionsstillexist.Inparticular,theinterrelationbetween 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,afewlargefractures;possibilityto“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.

Somewhat related to modeling is the necessity of laboratory testing.

Thismaybetheonlywaytovaryinfluencing parameters under strictly

controlled conditions. However, so far, no testingprocedureandequipmentseems

to exist that allows one to simultaneously vary all the parameters.Inaddition,thereistheissueofscaling.Given this complexity, it is tempting to exclusively rely on “simulationmodels”ratherthanconductexperiments,which may not be the best way to proceed.

“ Eventually and hopefully in the near future,

economicallyeffectiveimplementationofEGS

development in sedimentary rocks will occur.”

21

22

Question 3: how can we effectively monitor the evolution of fractures caused by changes in heat regime and stress conditions induced by geothermal extraction?

Subsurface operational issues are closely related to the two preceding ones. Of particular concern is the behavior of the fractured rock mass subjected to changedtemperatureandstressconditions.Thermalbreakthroughs may occur or fractures may become cloggedwithchemicalprecipitates(“scale”),forinstance.

Relatedtooperationismonitoring.Theinterpretationof 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,morepracticallyspeaking,theoperatingequipmentmay not work satisfactorily (pumps and monitoring equipmentexposedtohightemperatures).Evenmorebasic is the lack of knowledge and experience as to what to do when/if the performance of the reservoir is not as expected.

Question 4: What are the relationships and thresholds between modified fluid pressures and induced seismicity?

As mentioned in the discussion of fracturing, induced seismicityisapredictedproblem.Italreadyhasledtotheend of one EGS project, in Basel, Switzerland, which was stoppedin2004afterearthquakeswithmagnitudesupto3.4 occurred (albeit in igneous rock). Public concern over thepotentialofinducedseismicity(‘Earthquakes’tothepublic) has also stimulated public concern with respect to EGS development in the US. Understanding the causes of induced seismicity is related closely to understanding how EGS stimulation of fractures and fracture networks affectthelocalstressregimeattheEGSsite.Thisrequiresamuchbetterinterpretationofthefractureinitiation, propagation and coalescence processes.

Question 5: can numerical decision models be generated that effectively predict geothermal operational risk?

Eventually and hopefully in the near future, economically effective implementation of EGS development in

“ Fractures are a central concern in all aspects

of ‘subsurface engineering’, including EGS..”

23

sedimentaryrockswilloccur.Decisionmakersneedtohave a clear picture of the costs and benefits, that is, the risks of an EGS operation. Allowing all interested parties toassesstheserequiresthedevelopmentofproceduresthat can represent the relevant uncertainties in all influencing factors and eventually express them in terms of risk. Also, current numerical models can and should be used to establish uncertainty in predictions due to model uncertainties.

ItisessentialthatRiskAnalysesincludenotjustconventional economic risk, but environmental and political risks, the later including public perceptions, both favorable and unfavorable. Concerning the latter, the problems associated with the development of tight shale gas illustrate the wide range of issues that need to be addressed.

concluSionSTheforegoingdiscussionillustratesthatthereisalongwaytogoandthechallengesaregreat.Thereismuchthatneedstobedone,startingwithavigorousR&Dprogram. As a first priority, opportunities to collaborate must be fostered 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.

• Thereareseveralspecificgeothermalissues

related to drilling technologies in sedimentary

rocksthatrequirefurtherwork.

•Weneedanunderstandingofpreexisting

naturalfracturesystemsandtheirinfluenceon

the success or failure of an EGS.

•Ofparticularconcernisthebehaviorofthe

fractured rock mass subjected to changed

temperature and stress conditions.

• Fracturingandinducedseismicityisa

predictedproblemthatrequiresamuchbetter

interpretation of the fracture initiation,

propagation and coalescence processes.

• Decisionmakersneedaclearpictureofthe

costsandbenefits,orrisks,ofanEGSoperation.

kEy finDingS

24

introductionInstraddlingtheengineeringandscienceworlds,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. 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.Inaddition,participantsagreewithAGIreports(Gonzales,2011;GonzalesandKeane,2011)ofvast underrepresentation of minorities in geoscience programs, at state geological surveys, and in industry.

We are all 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.

iSSuES, StratEgiES, optionS, and SolutionS for addrESSing gEothErmal WorkforcE and Educational iSSuES

Question 1: What short-term and long-term efforts will prove most effective in tempering workforce shortages expected of an emerging geothermal industry?

Thecurrenthighunemploymentratesuggeststhereis no shortage of potential workers and therefore workforce needs will be market-driven. Another possibility is 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,thedecisionmakers(proposalpeer-

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

Question 2: What efforts would prove most effective at raising the current low profile of

geothermal energy in the mind of the public and policy makers?

Solar and wind energy have experienced a disparate level of public attention over the last 30 years compared to geothermal. Much of the challenge of attaining the fundingrequiredforexperimentaldrillingandexplorationis tied to public perceptions and awareness across society and government. We assert that a concerted

“ Solar and wind energy have experienced a

disparate level of public attention over the

last30yearscomparedtogeothermal.”

mEETing ThE challEngES Of EDUcaTiOn & OUTrEach By Karin Block

25

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. All of this is linked to funding success. For geothermal, progress likely comes from working with agencies to push large-scale innovation, not unlike the DARPA(ARPA’s)involvementinpioneeringtheinternet.

A concerted effort to promote geosciences and geothermal energy at the informal level can potentially impact students in elementary school and their parents. AnissueisthelackofEarthSciencerequirementinmany states’ elementary and middle school curricula and how this affects students’ career paths down the line. While geoscience majors rank as one of the most employable of all scientific disciplines, the perception among students and their parents is the opposite, except in states where geoscience is part of everyday life (e.g. Holbrook,1997,GonzalesandKeane,2011).InTexas,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.

Question 3: What are the positive and negative feedbacks tied to relationships between the geothermal and oil and gas industries as it relates to perceptions, workforce development, & educational infrastructure?

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 employment opportunities in oil and gas.Theoilandgasindustry’svastR&Dresourcesavailsyoung geoscientists of opportunities to practice many ofthetechniquesrequiredforgeothermalexploration.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 theindustry.Thisstrategywillminimizeemploymentrisk in the geothermal enterprise. An example of a successful program that bridges environmental altruism withemploymentrealityisCornell’sGeothermalIGERTcurriculum focusing on what geothermal, carbon sequestration,andoilandgashaveincommonsostudents are prepared for the jobs that already exist.

Industryhasthepotentialtodirectlyaidinworkforcedevelopment. Coordination with industry needs to be instituted by leaders in geothermal research and development to accomplish this goal. For instance, professorships in fields critical to the geothermal industry like sedimentary geology are dwindling and this is a

widely recognized issue discussed within professional societies(e.g.,AAPG,SEPM,GSA,andGRC).Industryinvolvement here could help stem this tide. Encouraging industry to become involved with programs to assist students who are underprepared for college work, such astheTexasSuccessInitiativeProgram(TSIP)canprovidetrainingandteachingopportunities.Industrycanalso be encouraged to help sponsor or establish “young professionalnetworks”tohelpdevelopasocializationnetwork among budding geoscientists interested in the energy sector.

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.

Question 4: What are the most effective forms of cyberinfrastructure that may be used to promote sharing of data and education materials to best aid the development of geothermal curricula?

Encouraging academic departments to create geothermal courses, minors, and field experiences has a high threshold for implementation but can be promoted by 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.

26

Question 5: What are the best vehicles for fostering cross-disciplinary education and scholarship between engineering and science disciplines?

Thedevelopmentofnewareasofexpertiseisarecurringtheme. Specifically, the science and engineering of SedHeat needs students who can bridge the gulf between geology and engineering. 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 a better understanding of geothermal heat is largely ignored by much of the academic community. Thisisanavenueofresearchthatexcitesstudentsandhas tremendous scientific potential in informing how sedimentary geothermal basins are explored.

Question 6: What are the best processes for building an educational and workforce pipeline from k-12, through undergraduate, to graduate, to professional in the geothermal sciences, and how can we best assure that women and minorities are not leaked from this system? A large portion of the discussion on education and diversity focuses on how to increase the number of undergraduates interested in the geosciences and engineering and how to introduce geothermal resources intothecurriculum.Theimportanceofexperientiallearning and its efficacy in exciting students at every instructional level is key. Below are expressed some challenges and possibilities. Elementary and Middle School Level:

• Youthgeologyfieldcampsarepopularandeffectiveat recruiting high school and middle school students. Funding these programs remains a challenge, but may yield the greatest return on investment to increase the number of minority students who

engage in geoscience-related activities.• Professionaldevelopmentofteachersprovides

the foundation for transmitting knowledge and excitementtostudents.Theinclusionofteachertraining components as broader impact activities in proposals can serve to increase the exposure of students to geothermal themes.

• Creationofactivitiesthatfocusonthemath,physics,and chemistry of geothermal systems broadens the reach of geoscience to state curricula that would otherwise exclude Earth Science.

Undergraduate Level: •Establishmentofaminoringeothermalenergy

entailing 6-9 credits of specialized coursework in addition to field camp would foster preparation for future geothermal study and careers.

•Peerlearningandpeerrecruitment:Benefitswouldbe gained from teaming up inside and outside the classroom to develop science and engineering synergistic learning and undergraduate outreach to K-12students.

•Educationalseminars,presentationstounderrepresented groups in high school and community college as well as their parents would increase diversity.

•Followingthemodelofsuccessfullong-termprograms such as the partnership between the tribal community colleges and the National Center for EarthSurfaceDynamicswouldrequirethesupportofteachers who champion these types of programs but would mentor students all the way through graduate school.

Graduate Level:•Theacademiccontingentrequirestheabilitytohave

fundable (small) projects for graduate students, both M.S.-andPh.D.-level,toworkonwhatwilladvancethe overall effort.

•Geothermalavailsthegeoscienceswiththeopportunity to maintain cross-disciplinary networks that will catch and sustain the stream of students. Cross-training students will give them the best chanceatbeingemployed.ProgramssuchasIGERTand SEES are well suited for this type of collaboration but more opportunities may be needed.

•Establishmentofprofessionalsciencemastersdegrees 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 an MBA.

“ Preventing the loss of talented scientists

withgraduatedegreeswillrequire

developing new strategies for enacting

culture change in industry and academia.”

27

Question 7: What can be done to retain under-represented groups in the educational and career pipeline toward potential geothermal positions?

Thereremainsapersistentproblemofattritionamongwomen 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

scientistswithgraduatedegreeswillrequiredevelopingnew strategies for enacting culture change in industry andacademia.TheADVANCEprogram,inadditionto new family-friendly policies, like those recently implemented by NSF across the directorates, provide opportunities to address the gender imbalance prevalent among mid-career geoscientists. However, there is a need for more institutionalized incentives to minimize the negative impact of gender and family roles on the career goals of women.

• Decisionmakers(proposalpeer-reviewers,

geoscience departments, university

administrations)needtobeconvincedofthelong-

term potential of SedHeat as a research avenue.

• Whilegeosciencemajorsrankasoneofthe

mostemployableofallscientificdisciplines,the

perception among students and their parents is the

opposite, except in states where geoscience is part

of everyday life.

• AninitialinfluxofNSF-basedfundingcanprovide

the momentum needed to establish a community

base of support.

• Astrongcyberinfrastructurebehindgeothermal

research and education will promote interest in

geothermalissuesamongacademicstaffandwill

provide datasets and materials so that courses can

be taught.

• SedHeatneedsstudentswhocanbridgethegulf

between geology and engineering.

• Thereisaneedformoreinstitutionalized

incentives to minimize the negative impact of

gender and family roles on the career goals

of women.

kEy finDingS

28

introductionCyberinfrastructure(CI)canprovideapowerfulplatformfor collaboration, in particular for interdisciplinary communities such as that of SedHeat, as well as provide a bridge to the education community and the public. We need, as an expanded community, to be able to capture and share data and also software code formodelinganddatareduction.Thecentralquestionfor a cyberinfrastructure effort serving the SedHeat community is rather direct.

What are the cyberinfrastructure platforms that will best facilitate effective exchange of ideas and data and foster greatest participation for the Sedheat community, and what is the best approach for constructing this platform?

AlthoughacomprehensiveCIsystemthatcansupportall aspects of the SedHeat community does not exist, the SedHeat organization can play a central role in coordinating the various activities necessary to develop and/or bring together existing efforts that can comprise acomprehensiveCIplatformfortheSedHeatinitiative.Thiswillnotbeeasysincemanycomponentpartsdon’texist and some existing data sites have not considered the possibility of expanding their scope to accommodate SedHeat community needs.

“ Cyberinfrastructure (cI) can provide a

powerful platform for collaboration, in

particular for interdisciplinary communities

such as that of SedHeat.”

EffOrTS TO DEvElOp a cyBErinfraSTrUcTUrE fOr ThE SEDhEaT cOmmUniTyBy Walter Snyder

WOrkflOWS gEoStrat / gdEx community WorkfloW - ExpandEd

NSF workshop on Science & Engineering Challenges for Unlocking the Geothermal Potential of Sedimentary Basins - Nov. 7-9, 2011

29

initial EffortSTheSedHeatinitiativewilldevelopacommunityportal that will provide access to whatever data systems support the broad SedHeat community.ThisportalmaybepartoftheSedHeat web site (www.sedheat.org) or astandalonesite.Theportalcanprovideadedicated, secure space for students to interact, exchangeideasandcollaborate.Itwillprovideaplace for students to place resumes as they near theendoftheirstudentcareers.Itwillkeepup-to-datelists of activities, funding possibilities, and upcoming webinars, workshops, and sessions at professional meetings.Itshouldincludewiki’sandblogsonvarioustopics, some open to the public, some only for internal use, some for targeted issues - all depending on what thecommunitywants.Thedatasystem(s)willalsocollaborate with other existing data systems that may not want to be part of the immediate family of SedHeat systems.Therewasacommonawarenessoftheneedto share data, standards, protocols, and best practices among our global cyberinfrastructure community. Participation in the EarthCube initiative is also considered animportantpartofthiseffort.ExpandingtheCIfocus to be an international effort is also considered an immediate goal.

taSk forcES task force conceptsWe need community input and acceptance on the most effective ways to manage the data generated by our work and on what is needed to allow us to work with and publish these data. We envision a distributed, federated system that will facilitate the publication of discrete datasets for which the authors receive a citation and a digital object identifier that is associated with each dataset.Thesystemshouldsupportthedevelopmentofvirtual ‘collaboratories’ where multi-investigator projects can manage data in a common space over the internet. Insummary,thegoalistoprovideadatasystemthatgives users a bridge to their immediate colleagues, those of other disciplines and to publications.

“ We envision a distributed, federated system that

will facilitate the publication of discrete datasets

for which the authors receive a citation and a

digitalobjectidentifierthatisassociatedwith

each dataset.”

30

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