Geothermics 50 (2014) 167179

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Geothermics

journa l homepage: www.e lsev ier .com/ l

3D seis s focharact ma

Ewald L MicRdigera Leibniz Institub Geothermie Nc Bavarian Env

a r t i c l

Article history:Received 5 NoAccepted 18 SAvailable onlin

Keywords:3D SeismicsGeothermal exHydrothermalUpper JurassicSeismic attributesSubseismic scaleUnterhaching

as pe geoe. A skm2

ese tizedl orie

1. Introdu

Geotherrenewabletion becausload electricMolasse Batized carbonis present iMolasse Banorth (Rive600650mnorth of ththe Alpine f100150 Cwell as elecand coral rebeds were don the Variarea (Lemconset of Ter

CorresponE-mail add

0375-6505/$ http://dx.doi.oction

mal energy within the framework of a sustainable andenergy supply is increasingly attracting public atten-e of its potential to provide district heating and basepower. The hydrogeothermal reservoir in the Bavarian

sin (Fig. 1) consists of fractured, karstied and dolomi-ates of theMalmFormation (Upper Jurassic). TheMalm

n most parts of the Southern German/Upper Austriansin, and is a highly productive aquifer that dips fromr Danube) to south (Alps). The Upper Jurassic, up tothick, crops out in the north (Swabian-Franconian Alb,e River Danube) and dips gently to 5000m depth atront (Fig. 2). Due to increasing depth, temperatures ofoccur south of Munich enough to generate heat astricity. The uppermost 350400m consists of spongeef systems with intercalated lagoonal deposits. Theseeposited in a shallow and warm marine environmentscan European continental shelf in the Munich studyke, 1988). At the end of the Cretaceous, and with thetiary sedimentation, the area turned into a foredeep of

ding author. Tel.: +49 511 6432320; fax: +49 511 6433665.ress: Ewald.Lueschen@liag-hannover.de (E. Lschen).

the Alpine orogen. Diagenesis has led to the formation of dolomitesthat are nowzoneswith high secondary porosity and karstication,andhas led to the formationof heterogeneouswater pathways. Dueto down-exing of the European crust during the collision withthe African-Adriatic microplate, exure-related synthetic and anti-thetic normal faults developed with Alpine strike directions, whichin the Tertiary Molasse were targets for oil and gas exploration inthe past (e.g. Bachmann et al., 1987; Lemcke, 1988).

The application of 3D seismic measurements for geothermalexploration has a quite short history, in sharp contrast to oil andgas exploration, where this technique is adopted. The rst exten-sive 3D surveys have been performed in the Larderello-Travale areain Tuscany (Italy) in a high-enthalpy, superheated steam environ-ment since 2003 (Casini et al., 2010). High reection amplitudescould be correlated with fractured contact-metamorphic rocks atapproximately20003000mdepthwhere adensenetworkofwellsshowedhighproductivity.Other seismicmeasurements (2D, small-scale 3D) are known from New Zealand (Lamarche, 1992), Japan(Matsushima et al., 2003) and the USA (summarized by Majer,2003), all aimed at exploring fractured reservoirs.

An increasing number of low-enthalpy geothermal plantsare already implemented or being developed in the Municharea with wells drilled into the Malm. Starting with geother-mal doublets (production and reinjection wells) at Straubing,Simbach-Braunau, Unterschleiheim and at Munich-Riem before

see front matter 2013 Elsevier Ltd. All rights reserved.rg/10.1016/j.geothermics.2013.09.007mic survey explores geothermal targeterization at Unterhaching, Munich, Ger

schena,, Markus Wolfgrammb, Thomas Fritzerc,Thomasa, Rdiger Schulza

te for Applied Geophysics (LIAG), Hannover, Germanyeubrandenburg GmbH (GTN), Neubrandenburg, Germanyironment Agency (LfU), Augsburg, Germany

e i n f o

vember 2012eptember 2013e 2 November 2013

plorationreservoir

a b s t r a c t

A 3D seismic survey was undertaken(Malm) hydrothermal reservoir at thlate its potential for sustainable usagthis relatively small survey size of 27tially inuence each other. Among thelements, circular structures, dolomitbrittle disaggregation, and preferentiaocate /geothermics

r reservoirny

hael Dussela,

art of a research project to characterize the Upper Jurassicthermal power plant at Unterhaching, Munich, and to simu-uite of promising geothermal targets could be identied on, where several geothermal projects are expected to poten-argets are fault patterns of high complexity with en-echelonreefs and mounds, reduced seismic velocities which indicatentations of joints and ssures.

2013 Elsevier Ltd. All rights reserved.

168 E. Lschen et al. / Geothermics 50 (2014) 167179

Fig. 1. OverviLeibniz Instituabove 100 C cthe referencesof the article.)

2003, theheat and ea real boorates of up

(http://www.geothermie-unterhaching.de) has been producingapprox. 40MW heat (upgradable to approx. 70MW) since 2007,and up to 3.4MW electrical power since 2009 using the Kalinatechnique. The Gt 1 production well and the Gt 2 reinjection wellpenetrate the top Malm at approx. 3000m depth and reach tem-peratures of up to 133 C (Wolfgramm et al., 2007). Additionally,thirteen other plants are set up in the Munich area or are in theplanning phase.

Theprospect evaluationof theUnterhachinggeothermal projectwas based mainly on temperatures (Schulz et al., 2004), whereaswell locations and the drill paths of Unterhaching Gt 1 and Gt 2were originally dened by reprocessing older 2D seismic prolesobtained from hydrocarbon exploration (Thomas et al., 2010). Anormal fault with a throw of about 250m has been deduced fromtwo reprocessed parallel 2D seismic lines which were up to 4kmapart. TheGt 2well is located just over 1kmaway fromone of theselines at the interpolated position of the normal fault between thetwo seismic lines. Such interpolation is an inherent drawback of 2Dseismic data, and it was questionable whether the borehole reallyintersected the fault zone. The problem of mutual interferencebetween doublets is gaining signicance because more geothermalprojects in the immediate vicinity are in the development phase.

The 3D seismic survey is part of the research project: Geother-mal characterization of karstic-fractured aquifers in GreaterMunich, undertaken by LIAG and LfU (Bavarian EnvironmentAgency, Augsburg). Its aim is to investigate the potential hydraulicand thermal interaction of several adjacent doublets. The main

tiont ande thehe fo

Fig. 2. North(http://www.gCretaceous sedexaggeration imotivafor heaexplorarea, tew of areas for possible hydrothermal use (http://www.geotis.de,te forAppliedGeophysics). Redcolormarks areaswhere temperaturesan be expected. The frame corresponds to Fig. 3. (For interpretation ofto color in this gure legend, the reader is referred to the web version

commissioning of a geothermal power plant forlectrical power at Unterhaching in 2009 generatedm (Fig. 3) (Schellschmidt et al., 2010). Productionto 150 l/s can be achieved. The Unterhaching plant

grated prog

(1) A smallfacies ainjectio

(2) regionational e

(3) hydroge(4) numeri

and cor

-South section (left to right) of the Bavarian Molasse basin extracted from theeotis.de). Blue line marks top of the 600650m thick Upper Jurassic (Malm) above the cryiments below the Tertiary foredeep sediments. The location of the section is shown ins 5:1. (For interpretation of the references to color in this gure legend, the reader is refeis the stipulation that the operation of power plantselectricity production must be sustainable. In order tototal geothermal capacity of the Malm in the Munichllowing subprojects were scheduled within the inte-ram (Schulz and Thomas, 2012):

4 km5km 3D seismic reection survey to explorend geological structures around the Unterhaching Gt 2n well,l geological 3D modeling of structures aided by addi-xisting 2D seismic proles,ological modeling, and

cal simulation of groundwater ow and heat transferresponding forecasting.

web-based interactive geothermal information system GeotISstalline basement. The Malm is capped and sealed by 50150m thickthe upper map together with the geothermal well locations. Verticalrred to the web version of the article.)

E. Lschen et al. / Geothermics 50 (2014) 167179 169

Table 1Acquisition parameters.

Source 3 crab vibrators of 13.3 kN maximum force eachLinear upsweep 1296HzLength 10 sStacking 8-fold

Recording Fixed spread of 2798 channelsDiversity stack for noise attenuation (total length 14 s)Recording length 4 s after stacking and correlationSampling rate 2ms

Layout Non-orthogonal (nominal, pre-planned)Source line interval 300m (nominal)Source point interval 30m2829 vibrator pointsReceiver line interval 300m (nominal)Receiver point interval 30m2798 receiver stations with groups of 12 10-Hz geophones

Field statics 3 short refraction surveys per km2

250m length with 3 shot points (hammer impulse source)25m receiver spacing

In this paper we focus on the interpretation of the 3D seismicsurvey (subproject 1) and its potential for geothermal exploration.Details on acquisition, data processing and the rst results havealso been described by Lschen et al. (2011). Subsequent thermaland hydrological modeling according to the project structure isscheduled for a forthcoming paper.

2. 3D seismic survey

The data acquisition of the 3D seismic survey was done usingthe Vibroseis technique (Table 1) in JuneJuly 2009 by DMT GmbH& Co. KG, Essen, and commissioned by LIAG. The distribution ofurban residential and industrial districts, agricultural elds, forests,a large number of main roads and crossings (Fig. 4) as well as poorweather conditions, with corresponding difcult noise conditions,were highlyout to be qseis correla

(diversity stacking) which were applied before data storing. There-fore, seismic surveys, particularly using Vibroseis, can be regardedas highly suitable for geothermal exploration even in urban areas.Area size and target depth denition (maximum 4km) and thecorresponding maximum source-receiver offsets were reasons toregister all 2829 vibrator points with all 2798 receiver chan-nels, instead of using a roll-along technique. This resulted ina maximum common midpoint (CMP) coverage of 300 in thecenter, decreasing toward the edges (Fig. 5). The xed record-ing spread led to a wide source-receiver offset range (07600m)and to an evenly covered azimuth range (Fig. 6). The devia-tions from the pre-planned uniform layout (non-orthogonal dueto access conditions) resulted in randomly, evenly distributedsource-receiver midpoints, which allowed a CMP binning not onlyinto nominal 15m15m squares, but also into arbitrarily cho-sen 7.5m7.5m squares for better horizontal resolution (Lschenet al., 2011).

Theoriginal survey area of 20km2 surrounding theGt 2wellwasextended in the southeast and in the southwest (Fig. 4) to about27km2 during eld operations, owing to expressions of interestby owners of overlapping commercial license areas. The additionalfractions of the 3D seismic data volume were immediately ana-lyzed by third parties in order to determine new drill paths. Inthisway, scientic research interests could benet fromshort-termcommercial interests and vice versa.

The data processing was carried out by LIAG and consistedmainly in increasing the signal/noise ratio by stacking and in accu-rate structural imaging by depth migration (Table 2). Field andelevation statics were of marginal importance only. In contrast,the automatic residual statics were highly successful. The vibrator-generated frequency range could be fully preserved. Conventionalcommon midpoint (CMP) stacking turned out to be quite robustsince structure and stratication of the overburden of theMalm are

ely uniform. Only very slight improvements were obtainedubseqere

Fig. 3. Distribarea. 3D seismto the web verchallenging. However, the Vibroseis technique turneduite robust, mainly due to the effective role of Vibro-tion, vertical stacking and noise rejection algorithms

relativwith sities wution of geothermal wells in the Molasse basin (in red), mostly used for power generationic survey is centered at Unterhaching south of Munich (compare Fig. 4). (For interpretatiosion of the article.)uent dip move out (DMO) processing. Stacking veloc-analyzed at 150m intervals in all directions. Interval

(from Wolfgramm et al., 2012). Frame marks Greater Munich studyn of the references to color in this gure legend, the reader is referred

170 E. Lschen et al. / Geothermics 50 (2014) 167179

Table 2Main processing sequence.

SEG-D eld data inputGeometry assignmentAir blast attenuationAutomatic spike and noise burst editElevation staticsField staticsResidual staticsSpherical divergence amplitude recoveryBandpass lter (1296Hz)Surface-consistent amplitude compensationMinimum-phase transformationSurface-consistent predictive deconvolutionMuting of refracted arrivalsNormal move out (NMO) correction, dip move out correction (DMO) after

interactive semblance-based stacking velocity analysis, severaliterations with subsequent residual statics analysis

3D CMP stack and 3D DMO stackBandpass lterZero-phase transformation3D nite-difference (FD) depth migration (alternatively time migration)

velocities for time and depth migration (all gures show depthmigrations) were then calculated from these stacking velocities.The velocity model for depth migration turned out to be highlyprecise, since the main lithological markers (e.g. Lithothamnionlimestone) matched to an accuracy of better than 20m (compare

Fig. 8). The relatively small size of the survey area and consid-erations of the corresponding limited aperture of the migrationoperator give rise to migration noise at the edges of the area (com-pare Fig. 12).

For interpretation, the observer or interpretermay examinerstthe three-dimensional data cube presented by vertical sections,inlines and crosslines (at intervals of 15m each), as well as hori-zontal slices of the recording timeordepth (Fig. 7). One seismogramtrace is generated foreach15m15mbin, according to the surveylayout.

The Lithothamnion limestone (Top Eocene, age approx. 34My)forms the most prominent reector due to the strong contrast inrock density and seismic velocity. It is situated underneath theTertiary sandstones and mudstones/marlstones of the BavarianMolasse. These beds of the Molasse were the targets of oil andgas exploration in recent decades. Beneath this dominant reec-tor, which is often used as a reference marker, there are 50150mthick sandstones and marlstones of the Tertiary Eocene und theCretaceous (age up to approx. 144My), decreasing in thickness tothe northwest. The hot water reservoir of the Malm (limestone anddolomite) is sealed against these upper beds. Therefore, the seis-mic target for geothermal exploration and corresponding drillingis more than one kilometer deeper than that of the previous hydro-carbon exploration. This is another reasonwhyolder seismic data isoften used for reprocessing with focus on these new target depths.

Fig. 4. Locatiosurface locatioof the referencnmap of the 3D seismic surveywith vibrator points in red and receiver points in blue colorns are shown in red, and well targets in blue color. Also shown are well heads at Kirchstes to color in this gure legend, the reader is referred to the web version of the article.). The area is centered on the re-injectionwell Unterhaching Gt 2.Wellockach (lower right) and Taufkirchen (lower left). (For interpretation

E. Lschen et al. / Geothermics 50 (2014) 167179 171

3. Interpre

Several emal exploraFig. 8 shownion limesdiscernible,of four 2Dhorizon ofdiscernibletonic deformCretaceousmust have oThe relativezon is indicTertiary.

3.1. Tectoni

Three mdirections omerge in tfault withGt 2 reinjeslip/extensiFig. 5. Location map of the 3D seismic survey (same as in Fig. 4) with bin fold (maxim

tation

xamplesof thedata analysiswith regard to thegeother-tion of the Malm layer are presented in the following.s the interactively picked horizon of the Lithotham-tone. A fault pattern of much higher complexity iscompared to the previously available interpretationseismic lines. Similarly, the immediately underlyingthe Top Malm, as well as of the Base Malm, are also(Fig. 9). Therefore, it is reasonable to conclude that tec-ation associatedwith the fault patternwas active from

times until the Early Tertiary. Furthermore, the faultsriginatedwithin the deeper lying crystalline basement.ly undisturbed bedding above the Lithothamnion hori-ative of a deformation age of not younger than Early

cs

ain fault patterns are discernible with general strikef 25, 45 and 70, respectively (Figs. 8 and 9). They

he southwest. The 45 lineament is a steep normala vertical throw of 200250m, penetrated by thection well. The 70 lineament is a combined strikeon fault system consisting of en-echelon elements

with interbPeacock anularly interaligned joinlineamenthorizon, inthe northwfault patterout withintures are reof the crusEarly Tertiafaults (Bacheral) movemstructures a(Bachmanntoo small tmechanismtem tend toattributablevertical dipAssuming tsouth in th(Reineckersonable.um 301) und processing lines (inlines, crosslines).

edded transfer zones (relay ramps; Eisbacher, 1996;d Sanderson, 1994). These transfer zones are partic-esting, since strong local tension with correspondingts and ssures can create water pathways. The 25

is well pronounced at the Lithothamnion limestonecluding an en-echelon pattern with down-throws ofestern block. Between the 25 and the 45 strikingns, there is a slight updoming discernible which diesthe Oligocene. Generally, the aforementioned struc-lated to extensional stress induced by exural bendingt during the Alpine orogeny in the Cretaceous andry, which produced synthetic and antithetic normalmann et al., 1987). Compression and transverse (lat-ents must also be included, as known from inversion

t the Landshut-Neuoetting basement high further eastet al., 1987). However, the present 3D study area is

o interpret the deformation sense uniquely. The focals of microseismicity aligned at the 45 main fault sys-indicate left-lateral strike slip motion with fault planesto the 25 or 45 striking fault systems with sub-

s (Megies and Wassermann, submitted for publication).he stress regime was predominantly oriented north-e Cretaceous and Early Tertiary as well, as it is todayet al., 2010), left-lateral movements would also be rea-

172 E. Lschen et al. / Geothermics 50 (2014) 167179

Fig. 6. Azimuth pies from the center of the area. Each 15m15m bin shows the source-receiver azimuth fold (color-coded) and the corresponding source-receiver offsets asvector endpoints (normalized at maximum offset of 7600m) for 30 intervals. The background color is the total bin coverage (CMP fold). (For interpretation of the referencesto color in this gure legend, the reader is referred to the web version of the article.)

Fig. 7. Panoramic view of the 3D data cube (3D-FD depth migration) with inlines, crosslines and depth slice, and showing the drill path of Unterhaching Gt 2. Mainlithological markers from the well are shown on the right. The 45 fault, intersected by the Gt 2 well, is marked by a dashed line on the depth slice.

E. Lschen et al. / Geothermics 50 (2014) 167179 173

Fig. 8. Horizon of the Lithothamnion limestone at around the 3000m depth line. Difference in depth approx. 500m from red to dark blue. View is from the south. En-echelonelements with relay ramps of the 70 fault system are marked by red dashed lines. Unterhaching Gt 2 well with Lithothamnion marker is marked close to the 45 fault. (Forinterpretation of the references to color in this gure legend, the reader is referred to the web version of the article.)

Fig. 9. Four horizons with isopachs at 20m intervals. View is from the south. Same color code for depth variation is applied for all horizons (red: high, dark blue: low),maximum variation in color code is 500m. (For interpretation of the references to color in this gure legend, the reader is referred to the web version of the article.)

174 E. Lschen et al. / Geothermics 50 (2014) 167179

Fig. 10. Collaptop in depth sl

3.2. Circula

There ar(Fig. 10) whdepth slicelog studiesof the MalmThese sinkhlution of thwere then pnion limestexplorationAlternativestructure.

3.3. Seismic attributes

A large number of geometrical and dynamic attributes canived from the seismograms. In Fig. 11, an example of thence int sefaultes aer,wcha

carboted mchem

ystemsouthte toutomthisbe dercohereadjaceThesedistancHowevchaoticMalmorientation orfault sin theattribusemi-aable inse sinkhole (doline) at the topMalmor impact structure, circular at itsice (top) and shown as a small syncline in a vertical section (bottom).

r structures

e some circular structures in the vicinity of the faultsich can only be identied as such by 3D seismic data ons together with associated vertical sections. Own ana-in quarries in the Franconian Alb, which is the outcrop, indicate that these structures are sinkholes (dolines).oles collapsed due to karstication and chemical disso-e Upper Jurassic limestone during the Cretaceous, andartly lled with detritus and sealed by the Lithotham-one. Therefore, they might be relevant for geothermal, since they are often aligned with the main faults.ly, this structure might be interpreted as an impact

the horizonnot charactmechanicalTherefore, afault system

A combiis particulashows seismand the diway, largertrayed. Thehowever, binterpretatiupdoming athe structuat the edgeposition, wsignal frequa tuning efattract ourthe massivedue to dolomay incorpfacies in beous reecticarbonatesshown by d

3.4. Seismic

Analysisfor convertor depth mindication oa verticalsurroundin(approx. 4545 fault iscan be explhigher fracshows the hproductivitopposed toof Fig. 13, useismic velage (approxdistance ranof the sours shown, which is a measure of the similarity betweenismogram traces. This allows faults to be displayed.s are predominant and are formed linearly over longert the top of the target layer as shown in Figs. 8 and 9.ithin theMalm layer, they tend tobe circular andof veryracter. This might be due to the brittle character of thenates creating widespread penetrative and chaoticallyechanical disaggregation, enabling internal karstica-ical dissolution. Again, as mentioned above, the mains generally strike 25, 45 and 70, and seem to mergewest. The similarity attribute is the most appropriatedelineate the faults and fractures. On the contrary, theatically picked horizons (Figs. 8 and 9) are less suit-

respect, because they tend to smear out and interpolates close to the faults. Obviously, the fault systems areerized by simple fault planes, but by complex brittledisaggregation in zones several hundred meters wide.dominant role for water pathways is ascribed to theses.

nation and superposition of several different attributesrly benecial (e.g. Chopra and Marfurt, 2007). Fig. 12ogram traces superposed by the coherence attribute

p directions (dip) of the reecting elements. In this(reef) and smaller sponge-algal mounds can be por-

se attributesmaynot be regarded as entirely conclusive,ecause several characteristics are required to favor anon as reefs and mounds. Among them are a slightt the top of the structure, relative transparency within

re, and an abrupt termination or downlap of reectionsof the structure. Another method is spectral decom-hich shows that the reefs are characterized by higherencies at their top (Fig. 12, lower left). This is due to

fect of the thinning of the strata above the reef. Reefsattention for geothermal exploration since they altercarbonates by increasing the porosity to approx. 10%

mitisation (magnesium addition). Therefore, the poresorate a corresponding amount of water. The lagoonaltween is often characterized by stronger and continu-vity, probably due to intercalations of marls within the. Their compact bedding seems to be less prospective, asrilling.

interval velocities

of the seismic propagation speed, which is neededing the travel time (two-way travel time) to depthigration during data processing, provides further

f higher fracture porosity. Fig. 13 (upper part) showssection with seismic interval velocities in the areag the Unterhaching Gt 2 well. Decreased velocities005000m/s) are discernible along the main faultsthedrilled through by the Gt 2 well. The lower velocitiesained by generally increased brittle disaggregation andture porosity. On the other hand, the lagoonal faciesigh velocities typical of massive carbonates. The highery of the Gt 2 well may be attributed to this effect asthe less prospective well in the southeast (right sidepper part, Kirchstockach well). The evaluation of the

ocity benets from the high common midpoint cover-. 300 fold in the center), from the high source-receiverge (offset, 07600m) and the complete azimuth rangece-receiver conguration. Since the structure of the

E. Lschen et al. / Geothermics 50 (2014) 167179 175

Fig. 11. Coherence of seismogram traces shows pattern of geological faults. Coherence cube with depth slice close to Top Malm (top), coherence depth slice at Top Malmwith colored amplitudes (lower left) and depth slice within the Malm (lower right). (For interpretation of the references to color in this gure legend, the reader is referredto the web version of the article.)

Fig. 12. Small and large sponge reefs between lagoons. Seismic amplitudes superposed by the coherence attribute and by the dip attribute (red: dipping toward the NW,blue toward the SE). Note that the edges of the section show a bias to false dips because of the limited size of the survey area and the corresponding limited aperture of thedepth migration (blue in the NW and red in the SE). Lower left: time slice at the Top Malm with amplitudes at 75Hz. Dark color corresponds to higher amplitudes. Possiblereef is highlighted in green color (high amplitudes) according to a crossplot analysis of spectral decompositions (75Hz amplitudes versus full spectral range amplitudes) andcorresponds to the big oval in the top gure. (For interpretation of the references to color in this gure legend, the reader is referred to the web version of the article.)

176 E. Lschen et al. / Geothermics 50 (2014) 167179

Fig. 13. The loand dark colorsection 240 ththe base of thwith coherencsouthwest whthe reader is r

overburdensemblance-transformafor geologicapproach, t150m (Fig.tions. Afterapplied. In Faligned agawhere thesdiscernible.the Malm wvelocities inof microseiclusteringbelow the Gfor publicaobviously rresearch.

Since thto interval vlute valuesw seismic interval velocities (yellow, brown and blue) of the Malm layer close to the faus) point to increased fracture porosity with water pathways. Velocity scale from lower trough drill path of Unterhaching Gt 2 from NW (left) to SE (right) with 150m analyzinge Malm (yellow at the base without meaning). Lower gure: Velocity cube after analyzie depth slice at Top Malm. Red point marks piercing point in Top Malm. Note that low velere the fault zones merge. Blue and green lines mark top and base of the Malm, respectiveferred to the web version of the article.)

of the Malm is relatively simple and uniform, standardbased analysis of the stacking velocity and subsequenttion to interval velocities can be advantageously usedal interpretation. In order to test the reliability of thishe analyzing interval was decreased from originally13, upper part) to 75m (Fig. 13, lower part) in all direc-conversion to interval velocities, a slight smoothingwasig. 13 (lower part) the pattern of decreased velocities isin to the main fault zones. Particularly in the southweste fault zones merge, a larger cluster of low velocities isDecreased velocities are also found below the base ofithin the crystalline Variscan basement. These lowerdicate rock fracturing deeper in the crust. Monitoringsmicity during 20102011 showed a NE-SW orientedof focal depths at 11.5 km in crystalline basementt 2 well target (Megies and Wassermann, submitted

tion). Rupture and friction processes at that depth,elated to the reinjection activity, are presently under

e inherent uncertainty in converting stacking velocitieselocities increases with travel time or depth, the abso-should not be accepted as entirely accurate. Instead,

the resultinsonic velocval velocitiabove, themarkers frothe velocitas extracteerally loweto the scalmic intervatake muchties are parzone. Howvelocities aing fractureappropriatenounced anincluded. Suapproach, ifault zone.at 3100, 33log.lt pattern as opposed to the bedded zones of the lagoonal facies (redhan/equal 4500m/s (yellow) to 6000m/s (dark). Upper gure: Inlineinterval. Kirchstockach well in the SE. Velocity model terminates at

ng the 75m interval, and attening the Top Malm horizon, togetherocities are mainly concentrated along the main fault zones and in theely. (For interpretation of the references to color in this gure legend,

g patterns should be taken as qualitative. However,ities measured within the Malm corroborate the inter-es at least qualitatively, and furthermore, as outlineddepth-migrated seismic volume matches lithologicalm the Gt 2 well. Therefore, we are condent in using

ies for interpretation. The seismic interval velocities,d along the drill path of Unterhaching Gt 2, are gen-r than the sonic velocities (Fig. 14). We attribute thising effect of high-resolution sonic logs versus seis-l velocities derived from surface measurements whichlarger rock volumes into account. The seismic veloci-ticularly inuenced by the larger volume of the faultever, both logs show the same tendency of reducedt 3300m depth where a pronounced water produc-zone is discernible. The log section in Fig. 14 is notfor a precise seismic-to-well tie, since the most pro-d at reection of the Lithothamnion limestone is notch calibration,which is necessarily anone-dimensional

s also hindered by the drill path through a sub-verticalFurthermore, frequent fractures in this fault zone (e.g.00 and 3500m) show unrealistic anomalies in the sonic

E. Lschen et al. / Geothermics 50 (2014) 167179 177

Fig. 14. Litholred) and dip azones and to dis true vertical

3.5. Subseis

Azimuthinformationjoints and lying modea horizontareection c(1998). Lynfor identicativity. ThisAmplitudesogy of the Cretaceous and Upper Jurassic with gamma-ray log (left), velocities from sonicnd azimuth of fractures (right). Red lines within the Litholog mark pronounced water polomitized zones. Dip (black) and azimuth (green) of fractures are derived from a Schlumdepth. (For interpretation of the references to color in this gure legend, the reader is re

mic scale

-selective processing was chosen to obtain possibleof preferential orientations of (vertical) fractures,

ssures on the subseismic resolution scale. The under-l corresponds to transversely isotropic media withl axis of symmetry (HTI). Their approximate P-waveoefcient has been described theoretically by Rgern et al. (1996) used selected source-receiver azimuthsl processing to demonstrate azimuth-dependent reec-

requires preservation of the relative amplitudes.according to this model are maximum when the

source-recetion of fracby scanninThe procedthe observaspread recoously, this ithe CMP-coas a test ontude variatand azimutare alwaysvelocity log (middle, green) with seismic interval velocities (middle,roducing fracture zones. Major water inow is attributed to fractureberger FMI log (Angers & Soehne, 2006). MD is measured depth, TVDferred to the web version of the article.)

iver azimuth is parallel to the preferential orienta-tures (Fig. 15). Here we try to follow this approachg the data volume for all azimuths in 30 intervals.ure benets from the high CMP-coverage and fromtion of the full azimuth range by the xed receiverrded from all vibrator points (compare Fig. 6). Obvi-s valid for the center region of the survey only, whereverage is above 200. This approach may be regardedly. A more complete study should involve the ampli-ion with offset (AVO) and the variation with offseth (AVOA) in CMP gathers (e.g. Rger, 1998). Modelssimplied and we cannot fully exclude that factors

178 E. Lschen et al. / Geothermics 50 (2014) 167179

Fig. 15. Principle of the amplitude-versus-azimuth analysis.

other than vertical fractures and joints contribute to the observa-tions.

In the example shown in Fig. 16 (lower right), the amplitudes inthe center of the vertical section, close to Unterhaching Gt 2 appear

to be maximum within the Malm when an ENE azimuth is chosen.This implies that fractures are preferably orientated in the samedirection and that permeability is maximum in this direction. Dipand azimuth of fractures, derived from FMI-logs, seem to conrmthis in the lower part of the section (3300m, Fig. 14). Other exam-ples in Fig. 16 (upper left) show different amplitudes between the45 und the 70 faults when an azimuth of WNW is chosen. Wespeculate that this might be due to the complex interaction of the45 and the 70 faults and of the relay ramps at the 70 fault.

4. Conclusions and outlook

A suite of preferential geothermal targets could be identied ona relatively small survey size of 27km2, where several geothermalprojects are expected to potentially inuence each other. The bene-t of 3D seismic reection surveyshas thusbeendemonstrated. Theapplication of 3D seismic measurements started to be common forexploration of geothermal reservoirs in the Bavarian Molasse (andin the Upper Rhine Graben) since that time. 3D seismic surveys areundertaken with the objective, as shown in our study, to nd pre-sumably permeable structures, such as fracture zones (associated

Fig. 16. VerticUnterhachingmark positiondifferences inof the article.)al sections (NW-left, SE-right) close to the drill path of Unterhaching Gt 2. Source-receiverGt 2 well trajectory is shown by red line. The four sections correspond to the azimuths sof the main fault zones (45 , 70). Inline 225 is closest to the drill path of Gt 2, inline 275their amplitudes depending on the selected azimuth. (For interpretation of the referencesazimuths of the original dataset were scanned for 30 wide corridors.hown below. Amplitudes are plotted at the same scale. Dashed linesis 750m further to the NE. White ovals mark reections which showto color in this gure legend, the reader is referred to the web version

E. Lschen et al. / Geothermics 50 (2014) 167179 179

with fault zones), karstic sinkholes, sponge or coral reefs (oftendolomitized) and, possibly, alignments of fractures and joints thatare controlling water ow in naturally fractured reservoirs.

The survey layout of small bins, high bin coverage, large source-receiver offset ranges and full source-receiver azimuth coverage,enabled new and unconventional processing and interpretation.The presence of a major sub-vertical normal fault zone, penetratedby the Unterhaching Gt 2 well could be veried. A complex patternof horizons and fault/fracture patterns in theUpper Jurassic (Malm)is discernible which was not known at this detail from 2D seismicsurveying alone. Examples of such 3-dimensional structures aresinkholes which are often aligned with major fault zones. A suite ofdynamic and geometrical seismic attributes, derived from the seis-mic traces, and combinations of them, are helpful to discriminatereef facies and lagoonal facies within the carbonate layer. Seismicinterval velocities as an independent seismic property obtainedduring processing can be interpreted in terms of porosity. The sub-seismic resolution scale is feasible by scanning the source-receiverazimuths during processing, andmaybeused formapping the pref-erential orientation of fractures and joints.

The geometry of faults, horizons and reef and lagoonal facies,derived frogeological mstructed froinformationow logs atof the Malmbrated by tthe projecttions for thfuture.

Acknowled

The GeoinGreaterMistry for the(BMU) undwasnancethorough anWe thankdinterpretatiLandmarks

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3D seismic survey explores geothermal targets for reservoir characterization at Unterhaching, Munich, Germany1 Introduction2 3D seismic survey3 Interpretation3.1 Tectonics3.2 Circular structures3.3 Seismic attributes3.4 Seismic interval velocities3.5 Subseismic scale

4 Conclusions and outlookAcknowledgementsReferences