PRESENT-DAY STRESS MAGNITUDES AND ROCK STRENGTHS IN THE ST. LAWRENCE LOWLANDS : IMPLICATIONS FOR CO2 INJECTION
E. Konstantinovskaya1, M. Malo1, and D.A. Castillo2
1 Institut national de la recherche scientifique, Centre Eau, Terre et Environnement (INRS-ETE), 490, de la Couronne, Québec (Québec) G1K 9A9 Canada [email protected] 2 Baker Hughes, Reservoir Development Services, GeoMechanics, 5373 West Alabama Street, Suite 300, Houston, Texas, 77056 USA
Rock strengths in Paleozoic sedimentary units of the Bécancour area, St. Lawrence LowlandsStress orientations and magnitudes in the St. Lawrence Lowlands
Lithofacies - Mineralogy, Acoustic Data, Porosity Static mechanical properties: Rock strength, Elastic Moduli, Poisson’s Ratio, Compressibitity
A071 Impérial Lowlands No 31476,76 - 1476,82 mKBsiltstone Fm Nicolet
A223 Intermont, Bécancour No 1970,70 - 970,80 mKBQz Ca Dol sandstone Fm Beauharnois
A223 Intermont, Bécancour No 1976,90 - 977,00 mKBQz Ca Dol vf sandstone Fm Theresa
A196 SOQUIP Pétrofina, Bécancour No 11142,84 - 1142,94 mKBQz sandstoneFm Cairnside
A196 SOQUIP Pétrofina, Bécancour No 11165,54 - 1165,645 mKBQz-Fsp sandstoneFm Covey Hill
A250 Junex, Bécancour No 8712,72 - 712,77 mKBcalcareous shaleFm Utica
2 cm
2 cm
2 cm
2 cm
A071 1476,8 mKB 5x in plane-polarized light
A250 749,3 mKB 5x in cross-polarized light
A223 970,7 mKB 10x in cross-polarized light
A223 977,0 mKB 10x in cross-polarized light
A196 1142,9 mKB 5x in cross-polarized light
A196 1165,6 mKB 10x in cross-polarized light
TheresaA223976.90 m
BeauharnoisA223970.70 m
Utica ShaleA250712.72 m
CairnsideA1961142.84 m
LorraineA071 1477.57 m
Covey HillA1961165.54 m
Stress-strain curves Elastic modulii
You
ng M
odul
us E
(GP
a)
Poisson's Ratio ν
0
50
100
150
200
250
300
350
-0,015 -0,010 -0,005 0,000 0,005 0,010 0,015
Diff
eren
tial S
tress
(MP
a)
Radial Strain Axial Strain
0
50
100
150
200
250
300
350
-0,015 -0,010 -0,005 0,000 0,005 0,010 0,015
Diff
eren
tial S
tress
(MP
a)
Radial Strain Axial Strain
0
50
100
150
200
250
300
350
-0,015 -0,010 -0,005 0,000 0,005 0,010 0,015
Diff
eren
tial S
tress
(MP
a)
Radial Strain Axial Strain
0
50
100
150
200
250
300
350
-0,015 -0,010 -0,005 0,000 0,005 0,010 0,015
Diff
eren
tial S
tress
(MP
a)
Radial Strain Axial Strain
0
50
100
150
200
250
300
350
-0,015 -0,010 -0,005 0,000 0,005 0,010 0,015
Diff
eren
tial S
tress
(MP
a)
Radial Strain Axial Strain
0
50
100
150
200
250
300
350
-0,015 -0,010 -0,005 0,000 0,005 0,010 0,015
Diff
eren
tial S
tress
(MP
a)
Radial Strain Axial Strain
Strain rate 5x10-6 s-1
Room temperatureLaboratory data: Drained condition
Stratigraphic unit Rock type Sample
No.Depth(mKB)
ConfiningPressure
(MPa)
CompressiveStrength(MPa)
Differential stress (MPa)
StaticYoung'sModulusE (GPa)
StaticPoisson's
Ratio ν
Density (g/cc)
Lorraine Siltstone A071V 1477,57 20,10 242,65 222,55 28,71 0,32 2,65Utica Calcareous shale A250V 712,72 9,70 227,44 217,74 42,06 0,29 2,70Beauharnois QzCaDol sandstone A223V2 970,70 13,29 264,39 251,10 49,28 0,23 2,62Theresa QzCaDol vf sandstone A223V1 976,90 13,20 308,87 295,67 53,97 0,29 2,69Cairnside Qz sandstone A196V1 1142,84 15,55 314,07 298,52 43,69 0,26 2,56Covey Hill QzFsp sandstone A196V2 1165,54 15,86 188,08 172,22 27,56 0,22 2,49
Calculated parameters:
Stratigraphic unit Rock type Sample
No.
Bulk modulus K
(GPa)
Shear modulus G
(GPa)
Compaction modulus M
(GPa)
Lame's constant λ
Vp (km/s)
Vs (km/s) Vp/Vs
Lorraine Siltstone A071V 26,58 10,87 41,08 19,33 3,94 2,03 1,94Utica Calcareous shale A250V 33,38 16,30 55,11 22,51 4,52 2,46 1,84Beauharnois QzCaDol sandstone A223V2 30,88 19,97 57,50 17,57 4,68 2,76 1,70Theresa QzCaDol vf sandstone A223V1 42,84 20,92 70,73 28,89 5,13 2,79 1,84Cairnside Qz sandstone A196V1 29,84 17,39 53,03 18,25 4,55 2,61 1,75Covey Hill QzFsp sandstone A196V2 16,35 11,30 31,42 8,81 3,55 2,13 1,67
E=3K(1-2ν) M=E(1-ν)/((1+ν)(1-2ν)) ρVp2=K+4G/3E=2G(1+ν) λ=Eν/((1+ν)(1-2v)) G=ρVs2
SUMMARY OF TRIAXIAL COMPRESSIVE TESTStested under as-is condition
0,100
You
ng M
odul
us E
(GP
a)
Poi
sson
's ra
tio ν
Porosity (cores A223/A196)
A250V_Utica calc shale
A223V2_Beauharnois QzCaDol ss
A223V1_Theresa QzCaDol vf ss
A196V1_Cairnside Qz ss
A196V2_Covey Hill Qz-Fsp ss
A071V_Lorraine siltstone
E ν
Density and porosity from core analyses
2
3
4
5
6
100 150 200 250 300 350
Vp
(km
/s)
Differential stress σ1-σ3 (MPa)
ut
bh
th
ca
ch
lor
0
1
2
3
4
100 150 200 250 300 350
Vp/
Vs
Differential stress σ1-σ3 (MPa)
Poi
sson
's ra
tio
You
ng M
odul
us (G
Pa)
Bulk Density, g/cc
0
1
2
3
4
100 150 200 250 300 350
Vs
(km
/s)
Differential stress σ1-σ3 (MPa)
ut
bh
th
ca
ch
lor
2,2
2,25
2,3
2,35
2,4
2,45
2,5
2,55
2,6
2,65
2,7
2,2
2,25
2,3
2,35
2,4
2,45
2,5
2,55
2,6
2,65
2,7
0 2 4 6 8 10 12 14 16 18
Bul
k D
ensi
ty, g
/cc
Porosity (cores), %
2,2
2,25
2,3
2,35
2,4
2,45
2,5
2,55
2,6
2,65
2,7
2,2
2,25
2,3
2,35
2,4
2,45
2,5
2,55
2,6
2,65
2,7
0 2 4 6 8 10 12 14 16 18
Gra
in D
ensi
ty, g
/cc
Gra
in D
ensi
ty, g
/cc
Bul
k D
ensi
ty, g
/cc
Porosity (cores), %
2,45
2,5
2,55
2,6
2,65
2,7
2,75
2,8
2,85
2,9
2,95
2,45
2,5
2,55
2,6
2,65
2,7
2,75
2,8
2,85
2,9
2,95
0 2 4 6 8 10 12 14 16 18
Gra
in d
ensi
ty, g
/cc
Bul
k D
ensi
ty, g
/cc
Porosity (cores), %
Bulk and grain densityA223St. Lawrence Lowlands
2.73
3.00
2.00
2.69
mean value
Beekmantown
A196St. Lawrence Lowlands
2.56
3.00 2.49
6.00
Bulk and grain density mean value
Cairnside
A196St. Lawrence Lowlands
2.47
6.00
Bulk and grain density mean value
2.45
7.00
Covey Hill
0
10
20
30
40
50
600,00 0,10 0,20 0,30 0,40
A geomechanical analysis of the St. Lawrence Lowlands sedimentary basin is important to re-liably estimate the maximum sustainable fluid pressures for CO2 injection that will not cause failure of the caprock or reactivate pre-existing faults thereby inducing a breeched CO2 reser-voir.
The maximum horizontal stress (SHmax) orientations are determined from borehole breakout orientations inferred from four-arm dipmeter caliper data and characterize the Paleozoic sedi-mentary succession of the St. Lawrence Lowlands at depths from 250 m to 4 km. The ave-rage SHmax orientation is estimated N59˚E ± 20˚, varying along the Appalachian front from N69.9˚E±17.5˚ in the Saint-Flavien area to N62.8˚E±4.0˚ in the Bécancour-Notre Dame area and to N35.2˚E±5.6˚ in the Saint-Simon area. Our results are compatible with the regional NE-SW SHmax orientation pattern generally observed in eastern North America.
The stresses/pressure gradients estimated in the Paleozoic succession are: Shmin 20.5±3 kPa/m, Sv 25.6 kPa/m, SHmax 40±7.5 kPa/m, pore pressure Pp 9.8 kPa/m. These results indi-cate a strike-slip stress regime Shmin<Sv<SHmax in the St. Lawrence Lowlands (depths < 4 km). The maximum sustainable Pp under the actual horizontal/vertical stress ratios that would not cause the opening of vertical tensile fractures during CO2 operations is estimated as ~18.5-20 MPa for the depth of 1 km.
The coarse-grained poor-sorted fluvial-deltaic quartz-feldspar sandstones of the Covey Hill Formation are characterised by the lowest bulk density and the highest porosity and permea-bility and have the lowest values of static Young modulus, Poisson’s ratio and compressive strength in comparison to other sandstone reservoir units in the Bécancour area.
The calcareous Utica shale of regional seal is more brittle and has higher Young modulus and lower Poisson’s ratio than the Lorraine shale. The values of Young modulus and differential stress observed at failure point during the triaxial tests demonstrate negative correlation with matrix porosity in tested core samples. Calculated Vp and Vs values have a positive correla-tion with differential stress.
550000
550000
600000
600000
650000
650000
700000
700000
750000
750000
5050
000
5050
000
5100
000
5100
000
5150
000
5150
000
5200
000
5200
000
CO2 Emissions 2009 (t)0
< 1000
10 000 - 50 000
50 000 - 100 000
100 000 - 500 000
500 000 - 1 000 000
1 000 000 - 1 300 000
> 1 300 000
OR
DO
VIC
IAN
444
461
479
455
446
468
472
542
488
AGE (Ma)
LOW
ER
MID
DLE
UP
PE
RK
ATIA
NS
AN
DB
.D
AR
RIW
.H
R.
DA
PIN
.FL
OIA
NTR
EM
AD
OC
PC
ChzBR
Lr
Utica ShaleTrentonBlack River
Chazy
Beekmantown
Potsdam
Grenvillian basement
Lorraine
SAUK-TIPPECANOEDISCORDANCE
Ste Rosalie
Queenston
sha
ly
limes
tone
turb
i-di
tes
molasse
dolomite anddol. sandstone
sandstone
CA
MB
RIA
N
Covey Hill
Cairnside
Theresa
Beauharnois
Pts
Bm
Tr
saline aquifers
__b_
reservoir caprock
Potsdam Covey Hill
NWSE
900
1100
700
1300
500
1500
Ele
vatio
n, m
0.1 s
LorraineUtica
Basement
Yamaska Fault
SÉQUESTRATION GÉOLOGIQUE DU CO2CHAIRE DE RECHERCHE
INRSUniversité d’avant garde
The present study is supported by the Ministère du Développement Durable, de l’Environnement et des Parcs du Québec. We are grateful to the Reservoir Development Services group within Baker Hughes Inc. for supporting this stress analysis. Special thanks are due to F. Brunner, L. Dean, R. Mireault and FEKETE Associates Inc. (Calgary) for the pore pressure evaluations from DST analyses; O. Heidbach, N. Pinet and R. Lefebvre for technical advices and discussions; M Rheault and G.Matton for providing the regional topo-graphic map, R. Thériault for the geological digital maps; B. St-Pierre for helping with caliper data integration; and Y. Duchaine for collecting caliper data. Seismic Micro-Techno-logy kindly provided the seismic interpretation software used in this study.resent study.
Interpreted seismic line in the Becancour area
Diff
eren
tial s
tress
σ1-σ3
(MP
a)
Porosity (cores A223/A196)
150
200
250
300
3500,00 0,02 0,04 0,06 0,08 0,10
0,10
0,15
0,20
0,25
0,30
0,35
0,40
20
30
40
50
60
0,000 0,020 0,040 0,060 0,080
0,10
0,15
0,20
0,25
0,30
0,35
0,40
20
30
40
50
60
2,450 2,500 2,550 2,600 2,650 2,700 2,750
0
500
1000
1500
2000
2500
3000
3500
4000
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
Dep
th, m
Stress and Pressure, MPa
A181 Shmin A181 SHmax
A185 Shmin A185 SHmax
A214 Shmin A214 SHmax
A215 Shmin A215 SHmax
A196 Shmin A196 SHmax
LOT Sv
Ph 12,13 kPa/m Ph 10 kPa/m
Fresh water pressure gradient
10 kPa/m
Pore pressure gradient
12,13 kPa/m
Sv gradient 25,6 kPa/m
Bécancour molasse
Lorraine shale
Utica shale upper Trenton to lower Utica shaly limestone Trenton/Black River limestone
Chazy sandy limestone
Black River limestone
Bauharnois dolomite
Theresa dolomitic sandstone
Cairnside Qz sandstone
Covey Hill Qz-Fsp sandstone
Etchemin River mélange
Les Fonds slate
Grenvillian basement
La Citadelle shaly limestone
Sillery schist
Bourret / Quebec City schist
borehole breakout
4000
0
500
1000
1500
2000
2500
3000
3500
Dep
th, m
Well stratigraphy
A181A196 A185 A214A215
SHmax gradient 40,04 ± 7.5 kPa/m
Shmin gradient 20,5 ± 3 kPa/m
Shmin, MPaS
Hm
ax, M
Pa
Sv = 72.2 MPa
Shmin = 56.77 MPa
SH
max
92-1
12 M
Pa
-20
180
160
140
120
100
80
60
40
180160140120100806040
200180
160140
120
100
80
60
40
0-10
RF
NF
SS
T 0 (MPa)
UCS, MPa
= [(µ2 + 1)1/2 + µ]2σ1 - Pp
σ3 - Pp
NF: Shmin = (Sv – Pp)/3.1 + Pp
SS: SHmax = 3.1Shmin – 2.1Pp RF: SHmax = 3.1Sv – 2.1Pp
S Hmax = S hm
in
Eastern Canada St. Flavien areaBécancour - Notre Dame areaSt. Simon area
n=3
after Plumb and Cox (1987)
n=13 n=2 n=7
N69.9˚E±17.5˚N62.8˚E±4.0˚N35.2˚E±5.6˚
present study
n=12
N59.7˚E±20.3˚N50.9˚E±10.3˚
Summary diagrams for directions of present-day SHmax (*) from borehole breakouts
(*) Number weighted Azimuths
St. Lawrence Lowlands St. Lawrence Lowlands
after Faure et al. (1996)
0
1
2 N
E
S
W0
1
2 N
E
S
W0
1
2
3
4 N
E
S
W0
1
2 N
E
S
W0
1 N
E
S
W
Late Cretaceous-Early Tertiarys1 paleostress
n = 80
N64.3˚E±11.8˚
13579
11N
E
S
W
Saint-BarnabéFault
Logan’s Line
AstonFaultChambly-Fortierville Syncline
A070 A158 A025 A071 A229 A185
TWT,
s 1
2
0 0, km
Chaudière Nappe
Yamaska fault
GRENVILLIAN BASEMENT10 km
625000
625000
650000
650000
675000
675000
700000
700000
725000
725000
750000
750000
775000
775000
800000
800000
5050
000
5050
000
5075
000
5075
000
5100
000
5100
000
5125
000
5125
000
5150
000
5150
000
5175
000
5175
000
St Cath
bert
Fault
St Pro
sper
Fau
lt
DF JCF
Aston Fault
Logan’s Line
Yamaska Fault
GRENVILLIAN BASEMENT
ST LAWRENCE PLATFORM
Normal faults in the Grenvillian basement under the sedimentary cover
Normal faults in the Grenvillan basement at surface
Frontal thrust faults of the Appalachian belt at surface
Stratigraphic contact, base of the St Lawrence Platform
borehole breakouts (2008 WSM)
borehole breakouts (present study)
Quality:ABC
all depths
SH direction inferred from :
M2002
M2002
3
2
1
APPALACHIAN THRUST-AND-FOLD
BELT
A214
A185
A169A177A180A183A202
A181
A215A221A225A227A228
A196
A189
P
P
P
P
P
P
PPP
P
P
P
P
P
P
P σ1 the Late Cretaceous-Early Tertiary paleo-stress, after Faure et al. (1996)
The average SHmax orientation is estimated N59˚E ± 20˚, varying along the Appalachian front from N69.9˚E±17.5˚ in the St. Flavien area to N62.8˚E±4.0˚ in the Becancour-Notre Dame area and to N35.2˚E±5.6˚ in the St-Simon area.
The magnitudes of vertical stress (Sv) are evaluated by integration of density log data in regional wells and correspond to average Sv gradient 25.6 kPa/m. The magnitudes of minimum horizontal stress (Shmin) are estimated from leak-off test data and correspond to Shmin gradient 20.5±3 kPa/m. The SHmax magnitudes are constrained by modeling wellbore failure in stress polygon plots taking into account the values of Shmin, Sv, rock strengths and
other parameters measured for a given depth. The estimated gradient of SHmax is 40±7.5 kPa/m.
The obtained stresses magnitudes are compatible with the strike-slip stress regime Shmin<Sv<SHmax that likely characterizes prevailing in-situ stresses in the Paleozoic succession of the St. Lawrence Lowlands at depths from 250 m to 4 km.
The pore pressures estimated from DST data indicate an average Pp gradient 9.8 kPa/m in the St. Lawrence Lowlands, with locally higher values of 12.17-15.4 kPa/m in the Becancour area.
The maximum sustainable pore pressure that would not cause the opening of vertical tensile fractures during CO2 operations could be preliminarily evaluated as 18.5-20 MPa for depths of 1 km.
The near-vertical NE-SW faults striking at 30˚ to SHmax and the W-E vertical natural fractures observed in the St. Lawrence Lowlands could be reactivated as shear fractures under the in-situ stresses (NE-SW SHmax) if fluid pressures exceeded the critical threshold Pc.Further refinement of the geomechanical model of the St. Lawrence Lowlands area is required to estimate the maximum sustainable injection pressure Pc that would be necessary for shear reactivation of the optimally oriented faults.
The saline aquifers of the Covey Hill Formation represent the most favourable unit for CO2 storage displaying the highest thickness of reservoir rocks, high ef-fective porosity, the lowest bulk density and matrix permeability. After triaxial test data, the Covey Hill sandstones have the lowest values of static Young modulus, Poisson’s ratio and compressive strength in comparison to other sandstone reservoir units in the Bécancour area.
Method:
focal mechanismbreakoutsdrill. induced frac.borehole slotterovercoringhydro. fracturesgeol. indicators
Regime:
NF SS TF U
Quality:
ABC
(2008) World Stress Map
270˚
270˚
280˚
280˚
290˚
290˚
300˚
300˚
30˚ 30˚
35˚ 35˚
40˚ 40˚
45˚ 45˚
50˚ 50˚
55˚ 55˚
60˚ 60˚
CanadaU.S.
ATLANTICOCEAN
St. Lawrence River
ACKNOWLEDGEMENTS
CONCLUSIONS
ABSTRACT
Shear failure in triaxial test σ1>σ2=σ3
σa
σ r = σ3
σa = σ1
τ σn
shear fracture
bedding parallel fracture
5 cm
σ2
σ1
σ3
SS
45˚
Polygon of SHmax estimation constrained by wellbore failure for well A185 SOQUIP et al. Notre-Dame du Bon Conseil No. 1
Breakout interval at depth (TVD) 2701 mAzimuth SHmax N62˚E, Pp 27 MPa, Biot coefficient 0.9, Poisson’s ratio 0.3; Wellbore azimuth N326˚W, wellbore deviation 17˚, breakout width 60˚; Differential mud pressure 0.93 MPa, sliding friction 0.7, internal friction 0.6; T0 and UCS denote tensile and uniaxial compressive strengths, respectively; NF, SS and RF indicate segments with normal faulting, strike slip faulting and reverse faulting stress conditions, respectively.
The SHmax orientations and regional fault patterns in the St. Lawrence Lowlands
The normal faults in the Grenvillian basement are projected from the seismic map of Thériault et al. (2005). The thrust faults are shown after Clark (1964a; 1964b), Globensky (1987), Konstantinovskaya et al. (2009). The interpreted seismic line M2002 is after Castonguay et al. (2006). Abbreviations: DF, Deschambault Fault; JCF, Jacques Cartier Fault; NF, Neuville Fault; SBF, Saint-Barnabé Fault; BT, backthrust of the triangle zone. 1, St. Flavien, 2, Notre Dame - Becancour, 3, St. Simon areas.
BT
A222
Present-day maximum horizontal stress SHmax orientations in eastern Canada and the U.S.
after Heidbach et al. (2008)
CO2 Emissions in the St. Lawrence Lowlands (2009)
Sedimentary succession of the St. Lawrence Platform
after Lavoie (1994)
Determination of :- prevailing stresses (orientations and magnitudes)- fault geometries- rock strengths (reservoir and caprock)
To estimate maximum sustainable pore pressures necessary for the opening of vertical tensile frac-tures and for the shear reactivation of pre-existing optimally oriented faults and fractures
0
40
80
120
160
200
240
280
0 320
She
ar s
tress
τ, M
Pa
Normal Stress σn, MPaσ1 σ1 σ1σ1σ3
Beauharnois quartz carbonate dolomitic sandstoneTheresa quartz carbonate dolomitic vf sandstone
Cairnside quartz sandstoneCovey Hill quartz-feldspar sandstone
Lorraine siltstone
A223 A196
A071 Utica calcareous shale A250
µ = 0.6
µ = 1
40-40 80 120 160 200 240 280 520360 400 440 480
µi = 0.75
µi = 0.52
µi = 0.89
τ = S0 + µiσn
µi is from GR log data0.6 < µ < 1.0
S0
N W
1 169 SOQUIP et al. St Flavien 1 (Cedre) 1974 46˚29' 25" 71˚ 36' 19"2 177 SOQUIP et al. St Flavien 2 1976 46˚30' 38" 71˚ 32' 48"3 180 SOQUIP et al. St Flavien 4 1977 46˚29' 43" 71˚ 34' 01"4 181 SOQUIP et al. St Helene 1 1977 45˚44' 12" 72˚ 46' 24"5 183 SOQUIP et al. St Flavien 6 1977 46˚30' 57" 71˚ 34' 47"6 185 SOQUIP et al. Notre-Dame du Bon Conseil No. 1 1978 46˚00' 41" 72˚ 20' 20"7 189 SOQUIP et al. St Tomas d'Aquin 1 1978 45˚41' 54" 72˚ 59' 05"8 195 SOQUIP et al. St Louis Blandford 1 1980 46˚16' 38" 72˚ 02' 14"9 196 SOQUIP Petrofina Bécancour 1 1981 46˚21' 60" 72˚ 24' 42"
10 202 SOQUIP Lemaire et al. Joly 3 1985 46˚28'50" 71˚37' 40"11 214 BVI et al. St Simon 1 1992 45˚41' 33" 72˚ 48' 42"12 215 SOQUIP et al. St Flavien 8 1992 46˚30' 20" 71˚ 34' 58"13 221 SOQUIP et al. St Flavien 9 1993 46˚31' 16" 71˚ 35' 08"14 222 BVI et al. St Wenceslas 1 1993 46˚10' 55" 72˚ 19' 12"15 225 SOQUIP et al. St Flavien 10 1994 46˚30' 21" 71˚ 34' 56"16 227 SOQUIP et al. St Flavien 12 1995 46˚30' 22" 71˚ 34' 52"17 228 SOQUIP et al. St Flavien 13 1996 46˚30' 44" 71˚ 34' 06"
NN Well No. Name Year Location N WNN Well No. Name Year Location
Name and location of vertical wells analysed in present study
Variations of pore pressures and stresses with depth determined from the stress magnitude ana-lysis in the St. Lawrence Lowlands are compatible with the strike-slip stress regime Shmin<Sv<SHmax.
The present-day NE-SW SHmax stress orientations in eastern North America (Fig. 1) are regionally consistent across the area. The average SHmax stress orientation of N54˚E ± 7˚ is inferred from borehole breakouts as deep as 2 km in eastern Canada and the U.S. (Plumb and Cox, 1987).
Variations of pore pressures and stresses with depth determined from the stress magnitude analysis in the St. Lawrence Lowlands
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