5 | Regional reservoir assessment
5.3 Results on reservoir facies and properties
5.3.4 Lower Cretaceous: karstic reservoir
At the top of the Mesozoic sequence, karst cavities and enlarged fractures associated with the major Tertiary erosional discordance are observed. These karsts affect principally the massive Calcaires urgoniens Formation but extend at least down to the Pierre-Châtel Formation.
The scattered Phi / K values are usually related to the karst infill, which is composed of continental sandstones and clays (Siderolithic). The position and extension of these karsts are still uncertain in the subsurface. Further geophysical studies are currently carried out to constrain better their spatial distribution and impact on upper Mesozoic units, and to detail lithological characteristics of the sedimentary infill.
Several wells in the region attest that the Lower Cretaceous can be an artesian aquifer. Two wells located at the foothills of the Jura Haute-Chaîne have been recently drilled in the spring of 2016 for drinking water exploration. They showed flow rates of respectively 30 m3/h and 50 m3/h in the karstified Cretaceous unit (SEMM logging report, 2016; CCPG and Hydroforage report, 2016). In Divonne-les-Bains, two shallow wells (∼ 100 m) have supplied thermal bath water for many years, producing 90 m3/h of water at a temperature of 14.4◦ C from the same unit (PGG, 2011). This confirms this karstified reservoir as a promising target for low enthalpy geothermal applications. Indeed, flow rates are high, but water temperature remains low (∼ 15◦ C) due to their shallow depth production.
5.4. Conclusion 119
5.4 Conclusion
The sedimentology and petrophysical attributes of the GGB subsurface sequence indicate the Kimmeridgian Complexe récifal and Calcaires de Tabalcon units to be the most promising reservoir in the area. However, heterogeneities linked to depositional trends and diagenetic imprints complicate the prediction of reservoir property through the subsurface: microporous patch reef bodies overlay a more continuous layer in which strong dolomitization increases the reservoir quality. High-K fracture zones may improve also fluid circulation, but a diagenetic cementation trend seems to seal such structures to the southeast of the study area. Further analyses are required to assess this reservoir unit into more details.
B u n t s a n d s t e i n
Molasse Karstified Lower Cretaceous Tithonian-Kimmeridgian Kimmeridgian Dogger Muschelkalk Buntsandstein other units 0
0.01
1100 10-17 10 Porosity [%]
Per meability [mD
]
Permeability [m2]
2030
10-15
10-13
10 11 12 13 14 15 34 36 7 8 9
Sample
ESS-101, ER-7HU-2, ER-34 1 cm
!"#$%&'()*+,#-".#,/('0#12 345678&9:10'
;#<*,2=,0(>>0$
?1@->0(1A510>0(1BC01D*EF*,)BG-1'>(1@>'*01HI
?1'*,J(E 5)*K(/* =%0$D1*>>2 L/M QuartzFine to coarse quartz- sandstoneSub-rounded to sub- angular quartz grainsargilaceous to evaporitic cementsub-angular/rounded quartz grainsContinental/fluvial to proximal deltaic Strata?
Geology MineralogyMacrofaciesMicrofaciesMain diagenetic featuresMain componantsPlatform morphology / depositional environmentGeometryFracturation/karstification Porosity [%]Permeability [mD]Density [g/cm3]Vp [m/s] av = 12.03 med = 14.07av = 66.10 med = 0.418av = 2.67 med = 2.654756InterparticleMatrix
Average for the "Triassic interval" (adapted from CREGE, 2012) 2.9no datano datano dataBrine, gas, oil 111-310 Heat productivity [µW/kg3]Fluid typeSalinity [g/l]
PetrophysicsThermal parameters (from PGN, 2013)Fluid parameters Measurements on plug (average and median) Pore typeReservoir typeInterval name in PGN, 2013 Thermal conductivity dry Thermal conductivity wet
Thermal capacity [J/(kg*°K)] 0255075100mineral %
M u s c h e l k a l k
Molasse Karstified Lower Cretaceous Tithonian-Kimmeridgian Kimmeridgian Dogger Muschelkalk Buntsandstein other units 0
0.011
100 10-17 10 Porosity [%]
Per meability [mD ]
Permeability [m2]
2030
10-15
10-13
!"#$%&'()*+,#-".#,/('0#12 345678&9:10' 70;;<*2=,0(>>0$
510>0(1?@(;010(1AB(<>*,(-)>'2A7->$%*<C(<CDEF
5)*G1'*,H(< I(/* =%0$C1*>> dolomite, calcite, anhydrite (gypsum) Alternating dolomite and whitish anhydrite with few calcitic bioclastic layers Microcrystalline to xenotopic dolomite with anhydrite nodules, oolithic mimetic-dolomite grainstone, crystalline anhydrite with dolomite hypidiotopic crystals and thin, argilaceous laminations
Early dolomitisation (additionally to primary) Ooids, evaporitic cement and nodules Flat fore shore/supra-inter- tidal environmentStratapotentially brittle behaviour
Geology MineralogyMacrofaciesMicrofaciesMain diagenetic featuresMain componantsPlatform morphology / depositional GeometryFracturation/karstification Porosity [%]Permeability [mD]Density [g/cm3]Vp [m/s] av = 1.96 med = 1.1av = 5.42 med = 0.003av = 2.80 med = 2.836125tightfracturedAverage for the "Triassic interval" (adapted from CREGE, 2012)2.9no datano datano dataBrine, gas and acid gas (H)1.1-250 Heat productivity [µW/kg3]Fluid typeSalinity [g/l]
PetrophysicsThermal parameters (from PGN, 2013)Fluid parameters Measurements on plug (average and median) Pore typeReservoir typeInterval name in PGN, 2013 Thermal conductivity dry Thermal conductivity wet
Thermal capacity [J/(kg*°K)] 0255075100mineral %
16 17 38 39 40 41 43 44 45 48 49
HU-2, ER-48HU-2, ER-54 1 cm
D o g g e r
Molasse Karstified Lower Cretaceous Tithonian-Kimmeridgian Kimmeridgian Dogger Muschelkalk Buntsandstein other units 0
0.01
1100 10-17 10 Porosity [%]
Per meability [mD ]
Permeability [m2]
2030
10-15
10-13
!"#$%&'()*+,#-".#,/('0#12 345678&9:10' ;('%#10(1<=01)1(->?(=$(0,*@2'*,,*-A>BC2D2EFC ;(G#$0(12H(@@I(1)>?(=$(0,*@2J2*1',#K-*@FC
5)*L(/*M1'*,N(=
70OO=*2P-,(@@0$23Q#))*,9 R%0$S1*@@ calcite, quartzGreyish, fine-grain bioclastic limestone
Fine grain, well sorted bio-pelsparite rich in echinids Synthaxial and equigranular cement mainly Abundant endofauna (bivalves, urchins (Cholyrites), small forams
Ramp/external ramp, subtidal environmentStratapotentially brittle behaviour calcite, quartz
Yellowish bioclastic limestone, chert nodules, foresets and pinch-outs, stylolites Crinoid-rich packstone, with small, sub-angular detritic quartz grains Synthaxial and equigranular cement mainly, silicification, strong compaction (dissolution-imbrication) Crinoids, small forams, quartz grains Ramp/internal ramp, subtidal in wave-active zone (hydraulic dunes)Stratapotentially brittle behaviour
MineralogyMacrofaciesMicrofaciesMain diagenetic featuresMain componantsPlatform morphology / depositional environmentGeometryFracturation/karstification
Geology Porosity [%]Permeability [mD]Density [g/cm3]Vp [m/s] av = 1.91 med = 1.65av = 0.36 med = 0av = 2.65 med = 2.654860tightfracturedno equivalentno equivalentno equivalentno equivalentno equivalent av = 2.15 med = 2.05av = 0.024 med = 0av = 2.66 med = 2.664835tightfracturedCalcaires à entroque (2 measures)
av = 2.6545 med = 2.6545av = 2.803 med = 2.803 av = 840.7 med =840.7av = 0.43268446 med = 0.43268446 Fluid parameters Measurements on plug (average and median) Pore typeReservoir typeInterval name in PGN, 2013
Thermal conductivity dry [W/(m*°K)]
Thermal conductivity wet [W/(m*°K)]Fluid typeSalinity [g/l] Salt water and oil indications0.58-40 Thermal capacity [J/(kg*°K)]
Heat productivity [µW/kg3]
PetrophysicsThermal parameters (from PGN, 2013) 1 cm
SAV-106, ER-72: BathonianHU-2, ER-59: Bajocian
0255075100mineral %
104 58 59 61 69 70 74 75 76 77 78 79 80 81 82 BAJ
M a l m
Molasse Karstified Lower Cretaceous Tithonian-Kimmeridgian Kimmeridgian Dogger Muschelkalk Buntsandstein other units 0
0.01
1100 10-17 10 Porosity [%]
Per
!"#$%&'()*+,#-".#,/('0#12 345678&9:10' ;(<$(0,*=2>*2?(1>(0@*A2B2CA ;(<$(0,*=2,D$0E(-FGA2B2HHA ;(<$(0,*=2>*2I(J(<$#1GA2B2CA
:""*,2K-,(==0$237(</9
L0//*,0>)0(1BI0'%#10(1 6**E2;#/"<*F
!'0#<<*'=
M1'*,N(< 5)*O(/* I%0$P1*==2 Q/R calcite
White, oo-bioclastic, gastropod-rich limestone, small-scale shallowing upward sequences Oolithic grainstone, gastropod rudstone Early and burial cements (isopachous, synthaxial, blocky); mouldic/vuggy dissolution
Ooids, numerous large gastropods (Nerineacean) Flat-topped, prograding sediments on underlying reefs/shallow marine, back-reef, oolithic shoal
Strata
Meter-spaced fractures (recognized in Roche Blanche, Jura Mountains), possible karstification, to be verified calcite, dolomite
White, crayish bioclastic to bioconstructed limestone bioclastic grain/packstone, corallian and microbial boundstone Early and burial cements (isopachous, synthaxial, drusic and blocky, large micritic coating, patchy dolomitization Corals, microbial crust and coating, encrusting forams and microproblematica, large complex forams, dasycladacean algae, Rampe-type to flat- top, uneven topography/shallow marine, reef-related environments
Patches/strata at the base of patch reefs (Calcaires de Tabalcon)
Early fracturation (differential compaction according to facies characteristics), brittle mechanical behaviour, can be heavily fractured (Le Reculet, Jura Mountains; indicated in wells), possible karstification, to be verified calcite, dolomite
Brownish, micritic, limestone ("purée de pomme")/sucrosic dolomite Thrombolitic pack/grainstone, rich in micro-encrusters Similar early and burial cements than reef facies, and microcrystalline/ Stratabound dolomitization
Tubiphytes morroniensis, reddish serpulids "en pelote"
Flat-topped, uneven topography/ subtidal, reef frontStrata Brittle bahaviour, fractured in fault damage zones (recognized in Le Coin), possible karstification, to be verified
GeometryFracturation/karstification
Geology MineralogyMacrofaciesMicrofaciesMain diagenetic featuresMain componantsPlatform morphology / depositional environment Porosity [%]Permeability [mD]Density [g/cm3]Vp [m/s] ---no data
micro pores in automicrite below SB, residual intecrystalline in cement and mouldic pores, vugs Matrix, fractured (and karstified?)
"Banc à nérinées", Kimmeridgian (1 measurement)no data2.74no data0.7375 av = 8.73 med = 10.07av = 4.58 med = 1.31av = 2.69 med = 2.694645
micropores in automicrite (reef- related facies) below SB, residual intecrystalline in cement and mouldic pores, vugs
Matrix, fractured (and karstified?) av = 7.97 med = 9.27av = 6.37 med = 3.17av = 2.74 med = 2.75no data
intercrystalline in sucrosic dolomite, microporosity in automicrite below SB Matrix, fractured (and karstified?)
PetrophysicsThermal parameters (from PGN, 2013)Fluid parameters Measurements on plug (average and median) Pore typeReservoir typeInterval name in PGN, 2013 Thermal conductivity dry [W/(m*°K)]
Thermal conductivity wet [W/(m*°K)]
Thermal capacity [J/(kg*°K)]
Heat productivity [µW/kg3]Fluid typeSalinity [g/l] Fresh and salt water, gas indications
0.3-40 "Calcaire micritique massif", Kimmeridgian (6 measurements)
av = 2.9322 med = 2.876av = 2.8325 med = 2.8325 av = 836.04 med = 854.1av = 0.62101889 med = 0.62101889
L o w e r C r e t a c e o u s
Molasse Karstified Lower Cretaceous Tithonian-Kimmeridgian Kimmeridgian Dogger Muschelkalk Buntsandstein other units 0
0.01
1100 10-17 10 Porosity [%]
Per meability [mD ]
Permeability [m2]
2030
10-15
10-13
!"#$%&'()*+,#-".#,/('0#12 345678&9:10'
;#<*,2=,*'($*#->
34(-'*,0?0(1@A9B(,,*/0(1=(C$(0,*>2-,)#10*1>D(CC#,E*:,)#10*12EC(1$FG2A2HIG
J(/*K1'*,?(C 5)* L%0$M1*>> Calcite, few dolomite layers White, oo-bioclastic, rudist-rich limestone, stylolites Bioclastic pack/grainstone to wackestone, abundant photozoan fauna, rudist rudstone
Large early and burial cements (mainly synthaxial, blocky) Ooids, small benthic and large complex forams (including orbitolinids), rudists, dasycladacean algae
Ramp, uneven topography/shallow marine, internal platform environment StrataIntense karstification linked to top Mesozoic unconformity, fracturation
Geology MineralogyMacrofaciesMicrofaciesMain diagenetic featuresMain componantsPlatform morphology / depositional environmentGeometryFracturation/karstification Porosity [%]Permeability [mD]Density [g/cm3]Vp [m/s] av = 2.45 med = 1.72av = 11.02 med = 0.006av = 2.67 med = 2.67no dataTight, mouldic in thin beds (dm- scale)
fractured and karstified Average for the "Lower Cretaceous interval" (adapted from CREGE, 2012)
3no datano datano dataFresh water mainly, few oil indications0.3-2.71 Heat productivity [µW/kg3]Fluid typeSalinity [g/l]
PetrophysicsThermal parameters (from PGN, 2013)Fluid parameters Measurements on plug (average and median) Pore typeReservoir typeInterval name in PGN, 2013 Thermal conductivity dry [W/(m*°K)]
Thermal conductivity wet Thermal capacity [J/(kg*°K)]
112 171 173 174 175 184 185 186 187 188 191 198 199 200 201 203 204 213 214 215 219 220 226 228 229 231
0255075100mineral % 1 cm
SAV-109. ER-191Gex-6, ER-204
125