Fluid saturation and Permeability of Crystalline Basement ... · 10 11/9/18 Ingrid Stober Institute of Applied Geosciences, Geothermics Division In 1970s the deep crystalline basement

KIT – University of the Baden-Württemberg State and National Research Center in the Helmholtz Association

Institute of Applied Geosciences

www.kit.edu

Fluid saturation and Permeability of Crystalline Basement of the

Continental Crust

Ingrid Stober

[email protected] FORCE 2018 Stavanger, Norway

Institute of Applied Geosciences, Geothermics Division 2 11/9/18 Ingrid Stober

Former considerations: Upper Continental Crust

  Fluid absent, impermeable   In numerical models of hydrogeologists: fluid tight basement  Deep geothermal exploration: concept of Hot-Dry-Rock (HDR), thermal

energy is stored exclusively in the rock. Thus, to harvest the energy, fractures had to be created artificially → fracturing: Los Alamos, Urach3, Cornwall etc.

 Nagra, CH: disposal of high-level radioactive waste: crystalline basement rocks as geological barrier


Outline

"   Groundwater in the Upper Continental Crust - Observations "   Hydrogeologist‘s experience – wet continental crust "   Permeability of crystalline basement

"   Example: KTB pumping test "   Flow – Thermal springs


“Groundwater” in the continental crust

600

800

aquitard

aquiclude greenschist

0

200

400

TEMPERATURE(ûC)

DEPTH(km)

0

10

20

30

40

MOHO

ultramafic

transition zone

sub-greenschist

mantle

continental crust

interconnectedfracture pore space

isolated porespace

base of aquifer

brittle upper crust

ductile lower crustamphibolite

aquifer

Upper Continental Crust: Descriptions of drilling foremen, geophysical logs of boreholes together with geological profiles, and findings in mines show that water-bearing features are related to: •  Fault and fracture zones, rock bodies extremely

damaged by brittle deformation zones of sheared, broken, shattered, and crushed rock (breccia).

•  Contact zones between granitic rocks (granites, granite dykes and granite porphyries) and paragneisses (also intensively fractured granite dykes within paragneisses).

•  Old circulation-path like: hydrothermally altered or deformed zones, mineral veins or open fractures filled with minerals.

The majority of the common biotite-rich gneisses on the other hand could be extremely low permeable.


Groundwater in the Upper Continental Crust - Observations .

12

10

8

6

4

2

0mines KTB Kola

dept

h (k

m)

depth in continental crust,where water had been found

geo-thermal

wells

KTB - German continental deep drilling program, to 9.1 km

Kola - Russian super deep well on the Kola peninsula, to 12.5 km

The Upper continental crust is not dry, it is water conducting! Interconnected water-conducting pore-space (e.g. fractures, fault zones)

Institute of Applied Geosciences, Geothermics Division 6 11/9/18

Observations: Gotthard Rail Base Tunnel

European Rail Systems

above the tunnel up to 2700 m oberburden


In the Gotthard Rail Base Tunnel

water inflow


Cross section and locations of water sampling in the GRBT

Length: 10 km

granites and gneisses units are steeply dipping meteoric water flows along fractures (parallel to gneissosity) 150 water samples along Amsteg section along flow path: reaction of the fluid with the rock matrix


Observations in rocks: Geochemical indications of young and older (former) water conducting features


In 1970s the deep crystalline basement was thought to be dry and without open fractures (Hot-Dry-Rock). Therefore distinct hydraulic stimulation techniques from the oil industry were used with the intention to create artificial open fractures to extract the Earth‘s heat from the rocks. Investigated depth: 2-5 km. These tests showed that the creation of new hydraulic fractures was not the dominant process. It was the opening, widening and sometimes the shearing of natural joints, depending on the induced pressure. The fracture pore space of the upper part of the continental basement rocks is filled with an aqueous fluid. The crustal basement is a confined, fractured hard-rock aquifer of low permeability with water present in an interconnected fracture system.

creation of a new fracture

opening, widening of natural fractures

time

pres

sure

pr

essu

re

Hydrogeologist‘s experience: Wet continental crust


Water conducting fractures are interconnected over large volumes

Rise and fall of the Earth surface 2 times per day (earth-tides), causes fluctuations of water table in deep boreholes due to compressibility of up to 18 cm. Porosity of crystalline basement is very low (~ 0.5%). Thus, a huge volume of interconnected pore space in fractures reacts. Depth of Urach3 borehole: 4444m



Long-lasting pumping-tests, KTB-site, 4 km depth: • rate ± 86 m³/d (1 l/s) • 1 year

Water conducting fractures are interconnected over large volumes



Pressure-dependence of hydraulic conductivity

In the Urach borehole (depth: 4444 m) many low- and high-pressure injection-tests of up to 660 bar well-head pressure were carried out. During hydraulic injection-tests with well-head pressures below 176 bar, the natural capacity of the rock to absorb water is tested, resulting in the magnitude of the rock’s natural permeability. → standard hydraulic test, no elastic reaction, no widening of fractures, no creation of new fractures.


Q = 70 m³/d


During hydraulic tests with well-head pressures above 176 bar, permeability of the crystalline basement rocks increases dramatically, due to the elastic reaction of the rock: open fractures were widened. (negative slope).

The pressure-dependence is described in terms of power laws relating injection rate (Q) to fracture width (w)

w = 8.14 10-7 / Q-2.50

Due to the lack of shear stress, rock reacted elastic; therefore no significant remaining increase in hydraulic conductivity after any high-pressure test.

High pressure-tests in the open-hole (and perforated sections), Urach borehole


p = 154.5 Q0.251

864 m³/d 86.4 m³/d 2732 m³/d


In the upper part large variability of permeability (several log-units), with highest values similar to those of gravel-aquifers.

Permeability of crystalline basement

In highly deformed areas granite seems to be more permeable than gneiss.

In weakly deformed areas the conductivity of granite can be very low.

Permeability data are based on hydraulic tests (pumping tests)

•  in a test section H [m] •  transmissivity T [m2/s] of the tested rock •  convert T into hydraulic conductivity K [m/s] •  convert K into permeability κ [m2] or [D],

fluid parameters (ρ, µ) are needed.

Investigation areas: Central Europe

H

total: 21.4 mD

gneisses 5 mD

granites 100 mD

-5 1 -1 -2 -3 -4 0 log K (D)


Permeability decreases with depth: log κ = -1.38 log z - 15.4 with: κ (m2) – permeability; z (km) – depth

4

3

2

1

0

-10 -9 -8 -7 -6 -5 -4

log K

log

dep

th

R = 0.42

slope = -0.146

intercept = 0.972

permeability (K) versus depth (z)K (m/s), z (m)

dept

h (k

m)

K = κ ρ g/µ geophysical modeling Ingebritsen & Manning 1999

hydraulic tests Stober & Bucher 2006

10-1 D 10-4 D 1 D 10-5 D 10-5 D 10 D


Location of KTB test site

modified from Zulu & Duyster, 1997

FederalRepublic

ofGermany

KTB

KTB site: Central Germany two boreholes: 4000 m, 9100 m crystalline basement

.

KTBscientific well

Erzgebirge

Prag ue

Harz

Spessart

Oden-wald

Blac

k Fo

rest

Wroclaw

compressionalfault

str ike-slipfault

normalfault

Variscanbasement

Munich

Alpine orogenic front

Carp

athi

anfro

nt

0 50 100 km

Eger Graben

Upper

Rhin

eG

rabe

n

Franconianlineament


modified from Harms et al., 1997

KTB-boreholes

main hole (HB): depth 9100 m pilot hole (VB): depth 4000 m

Lithological units • paragneisses • amphibolites • paragneisses interlayered with metabasites

KTB-pilot hole casing and cementation: to 3850 m depth open hole: 3850 - 4000 m, 6” bottom hole temperature: 120˚C

1

2

4

5

6

7

8

9

3

Depth(km)

Cretaceous

Triassicforeland sediments

Permo-Carboniferous

Major faults

Falkenberg granite

Undifferentiated basement (ZEV)

Paragneisses

Amphibolites

Paragneisses interlayered with metabasites

SW NE

KTB-main holeFranconianLineament

KTB-pilot hole

Zone of water inflow


During the one year pumpingtest an amount of 23,100 m3 water was removed from the crystalline basement rocks at 4000 m depth. This water derived from a rock-volume of about 4,620,000 m3 (n = 0.5%) or from a radial distance of up to 310 m around the 150 m long open-hole. Water composition was constant during the pumping test: TDS = 62.4 g/kg; pH = 7.8 (at 25°C); Cl = 38.7 g/kg; Ca = 15.8 g/kg; Na = 6.4 g/kg; Gases: N2 = 68% vol.%; CH4 = 31 vol.% Thus the fracture-system in the crystalline basement is interconnected. The fractured Upper Continental Crust is water saturated and behaves like any other near surface aquifer.

115

110

105

100

95

90

85

80

75

70-4 -3 -2 -1 0 1 2 3

log time (d)

wellbore storage

pumping rate:Q = 57.5 l min-1

p = 3.0 barT = 6.10 10 m s-6 2 -1

radial flow

Stober 2004 hydraulic border

pumping rate: 86 m³/d (1l/s)

K = 4.1 10-3 D

Hydraulic border = Franconian lineament

1 year pumping test KTB site


Deep circulation systems (some 1000 m depth): • thermal springs • upwelling of saline water (± constant TDS) Downstream of cold low mineralized water due to the hydraulic gradient occurs in open water conducting fractures being interconnected with each other over large volumes. Faults (damage zone) drain the fracture water and lead it to the surface due to the overall gradient.

Flow of water in crystalline basement Deep circulation-systems (thermal springs) Water flow needs a driving force: Topographic gradient induces a hydraulic gradient


Flow:

Mechanisms of water flowing

Water-conducting features, e.g. permeability +

Some kind of a motor, a driving force

As driving force can act: •  Hydraulic gradient due to topography •  Earth tides •  Thermal or hydrochemical gradients

Da Qaidam

Tianshan

Black Forest

The higher the surface gradient, the deeper the circulation!

Institute of Applied Geosciences, Geothermics Division 22 11/9/18 Ingrid Stober talc veins in peridotite (olivine)

Earth-tides keep fluids in motion and are kept chemically active

Fluids in the Upper Continental crust are generally not stagnant:

In areas with topography we observe deep circulation systems, origin of thermal springs.

Stagnant fluids, an unrealistic concept

As a result, overall equilibrium is not achieved and the fluids unceasingly react with the rock matrix


Summery / Conclusions • large variability in permeability in the upper part of the brittle crust

• granite seems to be more permeable than gneiss (in highly deformed areas)

• decrease of permeability with increasing depth

• interconnected open fracture-system over large volumes

• topographic gradient: deep circulation, thermal springs

• fluids in the Upper Continental Crust are generally not stagnant (earth-tides, deep circulating systems, thermal or hydrochemical

gradients,….) Modelling Crystalline Basement Rocks: gigantic, interconnected, open fracture-systeme (i.e. permeability), fluid flow, deep circulation systems

Thank you very much for your interest!


Selected literature If you are interested in some information please send me an e-mail: [email protected] Stober, I., Zhong, J., Zhang, L., Bucher, K. (2016): Deep hydrothermal fluid–rock interaction: the thermal springs of Da Qaidam, China.- Geofluids, 16, 711-728, doi: 10.1111/gfl.12190. Stober, I. & Bucher, K. (2014): Hydraulic conductivity of fractured upper crust: Insights from hydraulic tests in boreholes and fluid-rock interaction in crystalline basement rocks.- Geofluids, 16, 161-178 (doi: 10.1111/gfl.12104). Stober, I. (2011): Depth- and pressure-dependent permeability in the upper continental crust: data from the Urach 3 geothermal borehole, southwest Germany.- Hydrogeology Journal, 19, p. 685-699, (DOI: 10.1007/s10040-011-0704-7). Bucher, K., Zhu, Y. & Stober, I. (2009): Groundwater in fractured crystalline rocks, the Clara mine, Black Forest (Germany).- Int. J. Earth Sci (Geol. Rundschau), 98, p. 1727-1739 (DOI 10.1007/s00531-008-0328-x). Stober, I. & Bucher, K. (2006): Hydraulic properties of the crystalline basement.- Hydrogeology Journal, 15, p. 213-224 Erzinger, J. & Stober, I. (2005): Introduction to Special Issue: long-term fluid production in the KTB pilot hole, Germany: Geofluids, 5, 1-7. Stober, I., Bucher, K. (2005): The upper continental crust, an aquifer and its fluid: hydraulic and chemical data from 4 km depth in fractured crystalline basement rocks at the KTB test site.- Geofluids, 5, 8-19. Stober, I. (1997): Permeabilities and Chemical Properties of water in Crystalline Rocks of the Black Forest, Germany.- Aquatic Geochemistry, 3: 43-60, Kluwer Academic Publishers, Dordrecht/Netherlands Boston London


Deep cross-formation-flow including flow through high permeable granite + gneiss

In the Upper Rhine Graben

Examples of hydraulic gradients as driving forces

Topographic differences often induce hydraulic gradients

.

1*10-6

1*10-7

1*10-8

1*10-10

permeabilities (K)in m/s

model: BGR, Trippler (1988), Chemistry: Toth (1984)

-4000

800

0

-800

-1600

-2400

-3200

-4800m

-4000

800

0

-800

-1600

-2400

-3200

-4800m

SE WNW ESENW

H o c h w a l d P e c h e l b r o n n S o u l t z R h e i n B a d e n -

B a d e n

0 2 4 6 8 10 km

175

200

225

240

300

300 300

168

170

170

190

200

180

168

169

175169167

170165

250

200150170 HCO3-

SO42-

Cl- TDSincre

asing

280groundwater potential line in mbased on fresh water density

groundwater flow line

groundwater divide

d e p t h r e l a t i v e t o m s l d e p t h r e l a t i v e t o m s l

.

NIEDERROEDERNLAYERS

GRAY SERIES

PECHELBRONNLAYERS

DOLOMITIC ZONE

DOGGERMIDDEL JURASSICLIAS,LOWER JURASSICKEUPER,UPPER TRIASSIC

MUSCHELKALK,MIDDLE TRIASSICBUNTSANDSTEIN,LOWER TRIASSIC

PERMIAN

GRANITIC BASEMENT

FAULT

+1000

- 1000

0

- 4000

- 3000

- 2000

m

NN

+1000

- 1000

0

- 4000

- 3000

- 2000

m

NW SE WNW ESE

Rhin

e

Bade

n-Ba

den

Hoch

wal

d

Pech

elbr

onn

Soul

z

FAIL

LE

VOSG

IENN

E

Assumed boundery of the weathered granit(bottom boundery of the model)

Geological section through the Upper Rhine rift valleyfrom the Vosges to the Black Forest

0 2 4 6 8 10 km

Nach SCHNAEBELE (1948), BREYER (1974) und CAUTRU (1985)

Dept

h re

lativ

e to

m &

l

Dept

h re

lativ

e to

m &

l

FAIL

LE R

HENA

NE

SCHW

ARZW

ALD-

STÖR

UNG

Black ForestVosges

basement


With increasing depth, open fractures tend to be vertically orientated, because vertical pressure increases stronger than horizontal pressure.

Change of fracture-orientation with depth

Deep circulation-systems

after: Brown & Hoek 1978, Valley & Evens 2003

Typical Stress Field

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

0 50 100 150Stress [MPa]

Dep

th [m

]

sV

sH

sh

Vertical fracture σh=min �

σh �

Horizontal fracture σV=min �σV�

Documents

Fluid saturation and Permeability of Crystalline Basement ... · 10 11/9/18 Ingrid Stober Institute of Applied Geosciences, Geothermics Division In 1970s the deep crystalline basement