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
Number of heat flow data
4000
3000
2000
1000
0
Ocean Basin
Ocean
ridge/rise
Continental
rise
Continental
shelf
Tectonic setting
from Pollack et al, 92 database
Estimating heat flow on continental
margins
from White et al, 03



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
Location of the lower Congo basin
margin
Lower Congo basin
South America
Africa
Paranà
Walvis
Etendeka
from Contrucci et al, 2004
2000
Bouvet
0
1000
2000
Distance (km)
from White et Mckenzie, 1989
2000
Possibility for comparison of
different data sets
9700
GABON
9650
CONGO
9600
9550
1076a
9500
9450
1077a
9400
RDC
9350
9300
ANGOLA
9250
9200
9150
9100
9050
9000
500 550 600 650 700 750 800 850 900 950 1000
Structural aspects in the lower
Congo basin
5000 m
Discontinous BSR
Water bottom
Pliocene base
Slope
deposits
Stratigraphy
Pliocene
to Actual
Miocene
Tertiary
turbiditic
sequence
Oligocene
Eocene
to Turonian
Cenomanian
Oligocene base
Albian
Salt
Time
(ms TWT)
Diapir
Recent heat flow measurements on
extensional margins
Only few academic studies…
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
… but many studies sponsored
by oil industry!
from TDI-Brooks website
Measurements of heat flow in the
lower Congo basin
• Most of data unpublished
• heat flow higher in the North,
but no clear variation E-W
from Sultan et al, 2004
502 m
550 m
557 m
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
Lüdmann & Wong, 03
Sea of Okhotsk
Poor
Bouriak et al., 03
Vøring / Storegga
calibration
Henrys et al, 03
Hikurangi, New Zeal.
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
Kaul et al, 00
Makran
Golmshtok et al, 00
Baïkal
Ganguly et al, 00
Cascadia margin
Shyu et al, 98
SW Taiwan
?
Townend, 97
New Zealand
No comparison
Yamano et al, 82
Nankai prism
ODP
conventional
No comparison
No comparison
Poor
Higher values
smoother
Good
Estimation of temperature gradient
from BSR
Temperature (°C)
Gas Hydrate
stability
25
domain
2
20
10 % Nacl
15
0 % Nacl
10
5
Free gas
-5
0
5
3
4
5
6
0
Water bottom (km)
Pressure (Mpa)
30
10 15
20
1
Congo
Angola
Zaiango
UT Congo
2
3
4
25
Temperature (°C)
Gsurface 
(TBSR  Twater _ bottom )
Z BSR
Average velocity above
the BSR ( from seismic
lines and boreholes):
1530 +/- 30 m/s
7
Comparison of observed BSR
depth and predicted depth
Thermal conductivity (Wm-1K-1)
0.65
0.7
0.75
0.8
0.85
Heat flow (mWm-2)
Temperature (°C)
0.9
0
10
20
30
40
50
20
0
0
100
100
100
Depth (km)
0
30
40
50
60
70
BSR
200
200
200
BSR
ODP1076a
ODP1077a
300
300
300
Location of BSR and estimation of
temperature gradient
1076a
1077a
BSR gradient versus surface
measurements
Variation thermal conductivity with
depth
Conductivity (W m-1 K-1)
1.6
From surface heat flow (= q/G)
1.2
0.8
0.4
ODP1076a
ODP1077a
0
0
0.2
0.4
Depth of BSR (km)
0.6
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
Correction for mud circulation
120
TERT
« Heat diffusion » equilibrium temp.
Temperature BHT (°C)
Horner equilibrium temp.
110
PALAEO
U CRET
100
Litho-stratigraphic log
Geophysical well logs
Mineral
composition
Porosity
90
80
Estimation of conductivity
70
0
40
80
120
160
200
Elapsed time (h)
Homogenization with DST
Relative frequency
Norway
Angola
0.2
0.16
0.1
0.08
0
0
-30
-20 -10
0
10
20
30
-30 -20 -10
Temperature difference (°C)
0
10
20
30
Inversion
Comparison of Heat Flow from oil
data with other estimates
Conventional
measurements
BSR
Global trend across the lower
Congo basin margin
marine measurements
ocean
deep offshore
~42 mWm-2
~52 mWm-2
Oil exploration wells
shelf
~70 mWm-2
BSR
Oil data
measurements
What is the heat flow value on the
Archean basement?
No value on the Archean Congo craton, but 33 mWm-2 on the Tanzania craton
(Nyblade, 97) + indirect evidence for low mantle heat flow
-25 -15 -5
5
15 25 35 45 55
40
30
20
10
100 km
0
80 km
-10
-20
60 km
40 km
30 km
20 km
100 km
10 km
-30
5 km
0 km
84 estimates
-6
Elastic plate thickness from gravity
from Hartley et al, 96
+6
shear wave velocity variations (%)
from Ritsema & van Heijst, 00
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
from Watts, 1988
Gravity modelling of the
Baltimore Canyon trough
Best fit model:
Low rigidity on the margin
higher rigidity on the ocean
Laboratory experiments of
convection with insulating lid
from Guillou and Jaupart, 1995
Heat flow discontinuity
at the ocean continent
boundary
Convection model geometry
Breaking of the Gondwana during Barremian-Neocomian
-V
+V
= 6000 km
To
~ 300 km
Tc
Tbase=3000 K
= 8D
µm=1019 Pa s
µc=1022 Pa s
Temperature and velocity fields at
144 Ma (lower Cretaceous)
1500 km
3000 km
Temperature and velocity fields at
72 Ma (end of Cretaceous)
1500 km
3000 km
Temperature and velocity fields at 0
Ma (present time)
1500 km
3000 km
Comparison of T and velocity fields
with and without continents
3000 km
1500 km
1500 km
Surface heat flow at 0 Ma
(present time)
Same experience
with no continent
Continent 0
Continent 1
Temperature ratio at the base of
continent vs heat production
-V
+V
To
Tc
Internal heating
~0.5-1.2 µWm-3 for the crust
Amplitude of heat flow at the
continent margin
Ra= 5x106
-V
+V
To
Tc
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 :
–
–
–

High mantle heat flow below old margins
–
–
–

No bias observed between the different sets
Large variations at small wavelengths
Emerging trend across the margin
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
Heat flow
(mWm-2)
Type
Gradient
(mKm-1)
Cond.
(Wm-1K-1)
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