Post on 18-Dec-2015
Heat Flow at the margins of continents: example of the lower
Congo basin
Francis Lucazeau
Claire Perry
Frédéric Brigaud
Bruno Goutorbe
Question
Heat flow has been used for years to constrain subsidence and oil maturation models on divergent continental margins…
But do we really know how surface heat flow varies in space and time ?
– Very few measurements– Local variations– Geodynamic scale
0
1000
2000
3000
4000
Ocean Basin Oceanridge/rise
Continentalrise
Continentalshelf
Tectonic setting
Nu
mb
er o
f h
eat
flo
w d
ata
from Pollack et al, 92 database
Estimating heat flow on continental margins
Conventional measurements
water depths > ~1000 m Depth of BSR
water depths > ~500 m
not observed everywhere Oil exploration data (temperatures, well logs)
availability
non equilibrium temperatures
from White et al, 03
Location of the lower Congo basin margin
2000
2000
Africa
South America
Bouvet
Walvis
Etendeka
Paranà
0 1000 2000
Distance (km)
Lower Congo basin
from White et Mckenzie, 1989
from Contrucci et al, 2004
Possibility for comparison of different data sets
9600
9650
9700
9000
9050
9100
9150
9200
9250
9300
9350
9400
9450
9500
9550
500 550 600 650 700 750 800 850 900 950 1000
GABON
CONGO
RDC
ANGOLA
1076a
1077a
Structural aspects in the lower Congo basin
Water bottom
Pliocene base
Oligocene base
Pliocene to Actual
Miocene
Oligocene
Eoceneto Turonian
Cenomanian
Albian
Salt
StratigraphyDiscontinous BSR
Diapir
Tertiary turbiditic sequence
Time (ms TWT)
5000 m
Slope deposits
Recent heat flow measurements on extensional margins
Study Location WD range (m) Heat Flow (mWm-2 )
Louden et al, 97 Galicia margin 4000 - 6000 47 ± 3 (C and O)
Nagihara et al, 96 Gulf of Mexico 3000 - 3500 40 ± 47 (C and O)
Polyak et al, 96 Alboran sea 600 – 2400 69 ± 6 to 124 ± 8 (C)
Ruppel et al, 95 Carolina 2000 – 4000 49 ± 12 (C and O)
Foucher et al, 92 Gulf of Valencia 1000 – 2000 66 ± 4 to 78 ± 13 (C)
Louden et al, 91 Goban Spur ~ 4000 42 ± 4
Only few academic studies…
… but many studies sponsored by oil industry!
from TDI-Brooks website
Measurements of heat flow in the lower Congo basin
from Sultan et al, 2004
502 m 550 m 557 m
• Most of data unpublished• heat flow higher in the North, but no clear variation E-W
Recent Heat flow / BSR studies
Study Location Agreement Characteristic
Shankar et al, 04 Western India margin No comparison
Lüdman et al, 04 NW Black Sea ?
Martin et al, 04 Nankai prism calibration ODP
Lüdmann & Wong, 03 Sea of Okhotsk Poor
Bouriak et al., 03 Vøring / Storegga calibration conventional
Henrys et al, 03 Hikurangi, New Zeal. No comparison
Grevemeyer et al, 03 Central Chile calibration ODP
Vanneste et al, 03 Baïkal rift Poor Lower values
Nagihara et al, 02 Niger delta Mean Lower dispersion
Rao et al, 01 West India margin No comparison
Kaul et al, 00 Makran Poor Higher values
Golmshtok et al, 00 Baïkal smoother
Ganguly et al, 00 Cascadia margin Good
Shyu et al, 98 SW Taiwan ?
Townend, 97 New Zealand No comparison
Yamano et al, 82 Nankai prism
Estimation of temperature gradient from BSR
_( )BSR water bottomsurface
BSR
T TG
Z
Average velocity above
the BSR ( from seismic lines and boreholes):
1530 +/- 30 m/s
4
3
2
1
0
2 3 4 5 6 7
CongoAngolaZaiangoUT Congo
-5 0 5 10 15 20 25Temperature (°C)
5
10
15
20
25
30
Pre
ssu
re (
Mp
a)
10 % Nacl
0 % Nacl
Gas Hydrate stabilitydomain
Free gas Wa
ter
bo
tto
m (
km)
Temperature (°C)
Comparison of observed BSR depth and predicted depth
0.65 0.7 0.75 0.8 0.85 0.9
300
200
100
0
0 10 20 30 40 50
300
200
100
0
20 30 40 50 60 70
300
200
100
0
Dep
th (
km)
Thermal conductivity (Wm-1K-1) Temperature (°C) Heat flow (mWm-2)
ODP1076a
ODP1077a
BSR
BSR
Location of BSR and estimation of temperature gradient
1076a
1077a
BSR gradient versus surface measurements
Variation thermal conductivity with depth
0 0.2 0.4 0.60
0.4
0.8
1.2
1.6
Con
duct
ivity
(W
m-1
K-1)
Depth of BSR (km)
ODP1077a
ODP1076a
From surface heat flow (= q/G)
Estimation of thermal conductivity for the hydrate domain
0.6 0.7 0.8 0.9 1 1.1
Comparison heat flow estimated from BSR and measurements
Absence of heat flow anomalies related to fluids
Pockmark
Short length-scale anomalies related to conduction
Salt dome Canyon
Recent heat flow studies from oil exploration wells
Study Location Temperatures Conductivity Heat Flow (mWm-2)
He et al, 02 Yinggehai Basin Corrected BHT Measurements 79 ± 7 (6)
He and Middleton, 02 NW Australia ? ? 53 ± 4 (7)
Hu et al, 01 Bohai Basin Corrected BHT, DST Meas. outcrops 66 ± 15 (95)
Forster, 01 Northeast German Basin
Comparison BHT / logs
Lee and Deming, 99 Oklahoma Corrected BHT Measurements 36 ± 6 (9)
Gallardo and Blackwell, 99
Carter et al, 98
Anadarko basin Corrected BHT
profiles
Measurements
Cranganu et al, 98 Oklahoma Corrected BHT
profiles
Measurements (cuttings)
35 to 75
Majorowicz and Embry, 98 Canadian Arctic Corrected BHT, DST Estim., harm. 53 ± 12 (156)
Correia and Jones, 96 Jeanne d’Arc Corrected BHT Measur., harm.
Estimated
57 (35)
29 (35)
Problem of estimating thermal conductivity?
Procedure for estimating heat flow from oil exploration data
« Heat diffusion » equilibrium temp.
Horner equilibrium temp.
0 40 80 120 160 200
70
80
90
100
110
120 « Heat diffusion » equilibrium temp.
Horner equilibrium temp.
0 40 80 120 160 200
70
80
90
100
110
120
Correction for mud circulation
Tem
pera
ture
BH
T (
°C)
Elapsed time (h)
-30 -20 -10 0 10 20 30
0
0.1
0.2
-30 -20 -10 0 10 20 30
0
0.08
0.16
Homogenization with DST
Rel
ativ
e fr
eque
ncy
Norway Angola
Temperature difference (°C)
TERT
PALAEOU CRET
Litho-stratigraphic log Geophysical well logs
Mineral composition
Porosity
Estimation of conductivity
Inversion
Comparison of Heat Flow from oil data with other estimates
Conventional measurements
BSR
Global trend across the lower Congo basin margin
ocean deep offshore shelf
marine measurements Oil exploration wells
~42 mWm-2 ~52 mWm-2 ~70 mWm-2
measurements
BSR
Oil data
What is the heat flow value on the Archean basement?
100 km
-6shear wave velocity variations (%)
+6
from Ritsema & van Heijst, 00from Hartley et al, 96
-10
-20
-30
40
30
20
10
0
-25 -15 -5 5 15 25 35 45 55
100 km
80 km
60 km
40 km
30 km
20 km
10 km
5 km
0 km 84 estimates
Elastic plate thickness from gravity
No value on the Archean Congo craton, but 33 mWm-2 on the Tanzania craton (Nyblade, 97) + indirect evidence for low mantle heat flow
Interpretation of the trend on the lower Congo basin
Two possibilities:- local high mantle heat flow- local high crustal heat production (Pan African)
Evidences of higher heat flow on Mozambique margin
High heat flow
from Nyblade, 97
Heat Flow derived from global 3D seismic model
from Shapiro & Ritzwoller, 2004
Flexural rigidity of continental margins
Best fit model:Low rigidity on the marginhigher rigidity on the ocean
from Watts, 1988
Gravity modelling of theBaltimore Canyon trough
Laboratory experiments of convection with insulating lid
from Guillou and Jaupart, 1995
Heat flow discontinuityat the ocean continent boundary
Convection model geometry
-V +V
To Tc
µm=1019 Pa s µc=1022 Pa s
Tbase=3000 K
D~3
000
km
~ 300 km
Breaking of the Gondwana during Barremian-Neocomian
= 8D
= 6000 km
Temperature and velocity fields at 144 Ma (lower Cretaceous)
3000 km
1500 km
Temperature and velocity fields at 72 Ma (end of Cretaceous)
3000 km
1500 km
Temperature and velocity fields at 0 Ma (present time)
3000 km
1500 km
Comparison of T and velocity fields with and without continents
3000 km
1500 km1500 km
Surface heat flow at 0 Ma(present time)
Continent 0 Continent 1
Same experiencewith no continent
Temperature ratio at the base of continent vs heat production
-V +V
To Tc
~0.5-1.2 µWm-3 for the crust
Internal heating
Amplitude of heat flow at the continent margin
-V +V
To Tc
Ra= 5x106
Wavelength of heat flow at the continent margin
Concluding remarks about heat flow on continental margins
Possibility to combine different sets of data in the lower Congo basin :
– No bias observed between the different sets– Large variations at small wavelengths– Emerging trend across the margin
High mantle heat flow below old margins– Possibly related to perturbations in the convection field– Amplitude is a function of heat production in the continent– Wavelength does not depend on the continent properties
Need for a better knowledge of heat flow and processes on continental margin
– Importance of the slope and shelf domains– Still active oil exploration in the deep offshore comparison with
conventional probe measurements
Statistics on heat flow in the lower Congo basin
Type mean SD min max median skewness mean SD mean SD Number
Conventional 46.9 13.1 16.8 95.6 44.2 1.24 60.7 15.2 0.77 0.11 293
Short probe 46.9 13.2 16.8 95.6 44.0 1.23 60.6 15.2 0.78 0.11 282
Long probe 46.5 10.5 34.9 74.7 45.9 63.9 14.6 0.73 0.05 11
north 57.4 11.4 30.4 95.0 57.5 0.58 62.7 11.5 0.92 0.09 66
south 43.9 11.9 16.8 95.6 42.0 1.85 60.1 16.1 0.73 0.07 227
Oil 63.8 15.2 36.7 132.5 61.9 1.13 55.5 16.8 1.28 0.61 424
bathy > 200m 54.8 6.3 42.8 66.6 56.0 62.1 5.4 0.88 0.05 38
bathy < 200m 64.7 15.5 36.7 132.5 63.3 1.04 54.8 17.4 1.32 0.62 390
Oil (north) 65.8 16.7 40.4 132.5 64.6 0.94 55.0 17.9 1.35 0.66 301
Oil (south) 60.8 9.7 36.7 97.7 62.0 0.31 54.0 16.0 1.24 0.47 89
BSR1 52.2 9.5 8.7 138.1 52.7 1.51 61.8 11.0 0.84 993186
BSR1 (north) 53.7 7.5 8.7 138.1 54.5 0.91 61.6 8.3 0.87 711805
BSR1 (south) 48.4 12.5 26.5 137.9 45.5 2.44 62.2 15.8 0.78 281381
Gradient (mKm-1)
Heat flow (mWm-2)
Cond. (Wm-1K-1)