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Assessment of Undiscovered Oil and Gas Resources of the Mozambique Coastal Province, East Africa
By Michael E. Brownfield
Digital Data Series 69–GG
U.S. Department of the InteriorU.S. Geological Survey
Chapter 10 ofGeologic Assessment of Undiscovered Hydrocarbon Resources of Sub-Saharan AfricaCompiled by Michael E. Brownfield
ATLANTIC OCEAN
SOUTHATLANTIC
OCEAN
INDIAN OCEAN
INDIAN OCEAN
MEDITERRANEAN SEA
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MozambiqueCoastal
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U.S. Department of the InteriorSALLY JEWELL, Secretary
U.S. Geological SurveySuzette M. Kimball, Director
U.S. Geological Survey, Reston, Virginia: 2016
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Suggested citation:Brownfield, M.E., 2016, Assessment of undiscovered oil and gas resources of the Mozambique Coastal Province, East Africa, in Brownfield, M.E., compiler, Geologic assessment of undiscovered hydrocarbon resources of Sub-Saharan Africa: U.S. Geological Survey Digital Data Series 69–GG, chap.10, 13 p., http://dx.doi.org/10.3133/ds69GG.
ISSN 2327-638X (online)
iii
Contents
Abstract ...........................................................................................................................................................1Introduction.....................................................................................................................................................1Tectonic History and Geology of Mozambique Coastal Province, East Africa ....................................4Petroleum Occurrence in Mozambique Coastal Province, East Africa ................................................4
Source Rocks.........................................................................................................................................4Reservoirs, Traps, and Seals ...............................................................................................................7
Exploration ......................................................................................................................................................9Geologic Model ............................................................................................................................................11Resource Summary .....................................................................................................................................11For Additional Information ..........................................................................................................................12Acknowledgments .......................................................................................................................................12References ....................................................................................................................................................12
Figures
1. Map showing Mozambique Coastal Province, Mesozoic-Cenozoic Reservoirs Assessment Unit, Mozambique Channel area, and the Ruvuma Delta along the central coast of East Africa ........................................................................................................2
2. Map showing generalized geology of East Africa ..................................................................3 3. Map showing reconstruction of the early breakup of Gondwana during the
Early Jurassic ................................................................................................................................5 4. Generalized stratigraphic columns of Coastal Mozambique, Mozambique
Channel, and Coastal Tanzania, Coastal Morondava Basin, and the Seychelles ..............6 5. Schematic cross section of the Rovuma River delta, northern Mozambique ....................7 6. Stratigraphic column for the onshore and projected offshore parts of the
Rovuma Basin, northern Mozambique ......................................................................................8 7. Cross section across the Mozambique Channel and the Morondava Basin
showing the top of the oil and gas windows ............................................................................9 8. Schematic cross section of the Zambezi Delta, Mozambique ............................................10 9. Events chart for the Mesozoic-Cenozoic Petroleum System (734301) and the
Mesozoic-Cenozoic Reservoirs Assessment Unit (73430101) .............................................11
Table
1. Mozambique Coastal Province assessment results for undiscovered, technically recoverable oil, gas, and natural gas liquids ....................................................12
iv
Abbreviations Used in This Reportkm2 square kilometer
AU assessment unit
TOC total organic carbon
TPS total petroleum system
USGS U.S. Geological Survey
Assessment of Undiscovered Oil and Gas Resources of the Mozambique Coastal Province, East Africa
By Michael E. Brownfield
Generation of hydrocarbons from drift and post-rift sources began in the Late Cretaceous and, in parts of the offshore, continues today. Hydrocarbons migrated into Cretaceous and Paleogene reservoirs and traps. Traps are mostly structural within the syn-rift section and are both structural and stratigraphic in the post-rift rock units. The primary seals are Mesozoic and Cenozoic mudstone and shale. Rifted passive margin analog was used for assessment sizes and numbers because of similar source, reservoirs, and traps.
The U.S. Geological Survey estimated mean volumes of undiscovered, technically recoverable conventional oil and gas resources for the Mesozoic-Cenozoic Reservoirs Assessment Unit in the Mozambique Coastal Province. The mean volumes are estimated at 11,682 million barrels of oil, 182,349 billion cubic feet of gas, and 5,645 million barrels of natural gas liquids. The estimated mean size of the largest oil field that is expected to be discovered is 1,041 million barrels of oil and the estimated mean size of the expected largest gas field is 7,976 billion cubic feet of gas. For this assessment, a minimum undiscovered field size of 5 million barrels of oil equivalent was used. No attempt was made to estimate economically recoverable reserves.
Introduction
The main objective of the U.S. Geological Survey’s (USGS) National and Global Petroleum Assessment Project is to assess the potential for undiscovered, technically recover-able oil and natural gas resources of the United States and the world (U.S. Geological Survey World Conventional Resources Assessment Team, 2012). As part of this program, the USGS completed an assessment of the Mozambique Coastal Province in 2011 (fig. 1), an area of approximately 648,650 square kilometers (km2). The Mozambique Province contains rift, rift-sag, passive-margin, and drift rocks of Paleozoic to Holocene age. This assessment was based on data from oil and gas exploration wells, discovered and producing fields (IHS Energy, 2009), and published geologic reports. Generalized geology of east Africa is shown in figure 2.
AbstractThe main objective of the U.S. Geological Survey’s
National and Global Petroleum Assessment Project is to assess the potential for undiscovered, technically recoverable oil and natural gas resources of the United States and the world. As part of this project, the U.S. Geological Survey completed an assessment of the Mozambique Province in 2011, an area of approximately 648,650 square kilometers. The Mozambique Province contains rift, rift-sag, passive-margin, and drift rocks of Paleozoic to Holocene age. This assessment was based on data from oil and gas exploration wells and published geologic reports.
The Mozambique Province is a priority province for the World Petroleum Assessment and was assessed in 2011 because of increased exploratory activity and increased interest in its future oil and gas resource potential. The assessment was geology based and used the total petroleum system concept. The geologic elements of a total petroleum system consist of hydrocarbon source rocks (source-rock maturation and hydrocarbon generation and migration), reservoir rocks (quality and distribution), and traps for hydrocarbon accumulation. Using these geologic criteria, the U.S. Geological Survey defined the Mesozoic-Cenozoic Composite Total Petroleum System with one assessment unit, the Mesozoic-Cenozoic Reservoirs Assessment Unit, an area of approximately 464,420 square kilometers. At the time of the assessment, the Mozambique Coastal Province contained only two gas accumulations exceeding the minimum size of 30 billion cubic feet of gas; the province is considered to be underexplored on the basis of its exploration history.
Oil and gas were generated from Permian to Paleogene source rocks. Jurassic Karoo-age lacustrine and continental rocks source rocks average 4.0 to 5.0 weight percent total organic carbon. Lower to Middle Jurassic restricted marine rocks contain as much as 9 weight percent organic carbon, and Cretaceous Type II source rocks contain as much as 12 weight percent organic carbon. Hydrocarbon generation of syn-rift Karoo-age sources began in the Middle Jurassic, whereas the generation from Middle Jurassic to Early Cretaceous syn-rift sources began in the Late Jurassic to Early Cretaceous.
2 Assessment of Undiscovered Oil and Gas Resources of the Mozambique Coastal Province, East Africa
Figure 1. Locations of the Mozambique Coastal Province, Mesozoic-Cenozoic Reservoirs Assessment Unit, Mozambique Channel area, and the Ruvuma Delta along the central coast of East Africa. (Stratigraphic columns for the Mozambique Channel and Rovuma Delta are shown in figures 4 and 6.)
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MozambiqueCoastal
7343
AFRICA
INDEX MAP
Base from U.S. Geological Survey digital data, 2002World Geodetic System 1984 (WGS 84)Prime Meridian, Greenwich, 0°
0 150 300 KILOMETERS
0 300 MILES150
Réunion
MAURITIUS
COMOROSMayotte
ZAMBIA
MALAWI
ZIMBABWE
LESOTHO
SWAZILAND
SOUTHAFRICA
KENYA
BURUNDI
RWANDA
70°E66°E62°E58°E54°E50°E46°E42°E38°E34°E30°E
2°S
6°S
10°S
14°S
18°S
22°S
26°S
30°S
34°S
TANZANIA
MADAGASCAR
MOZAMBIQUE
SEYCHELLES
INDIAN OCEAN
RovumaDelta
Mesozoic-Cenozoic Reservoirs Assessment Unit boundary
EXPLANATIONMozambique Coastal Province boundary
Gas field
Mozambique Coastal7343
Introduction 3
Figure 2. Generalized geology of East Africa. Modified from Ophir Energy Company (2011).
CongoBasin
TANZANIA
KalahariBasin
Beira
MAPUTO
Dar es Salaam
MOGADISHU
Somali OceanicBasin
Continent-oceanicboundary
(COB)
OgadenBasin
RovumaDeltaDavie Fracture Zone
Moz
ambiq
ue C
hann
el
Aswa Shear Zone
Cupa Fault Zone1,0
00
KarrooBasin
Continent-oceanicboundary
(COB)
MandawaBasin
MajungaBasin
MorondavaBasin
MozambiqueBasin
INDIAN OCEAN
MA
DA
GA
SCA
R
Mombasa
0 200 400 600 KILOMETERS
0 600 MILES200 400
EXPLANATION
Bathymetric contour, 1,000 meter line—Location approximate
Continental crust—Palo fill
Permian-Triassic–Early Jurassic—Karoo-age rock
Phanerozoic—Intracratonic basin
ContactFault or fault zone—Dashed where approximate. Arrows show relative motion
Post Early Jurassic—Passive margin basin
Tertiary—Volcanic province
Undifferentiated—Precambrian basement
Graben—Teeth on downthrown side
MOZAMBIQUE
Tsimiro
roFie
ld
4 Assessment of Undiscovered Oil and Gas Resources of the Mozambique Coastal Province, East Africa
The Mozambique Province, which was a priority province for the World Petroleum Assessment, was assessed in 2011 because of increased energy exploration activity and increased interest in its future oil and gas resource potential. The assessment was geology based and used the total petroleum system concept. The geologic elements of a total petroleum system include hydrocarbon source rocks (source-rock maturation and hydrocarbon generation and migration), reservoir rocks (quality and distribution), and traps for hydrocarbon accumulation. Using these geologic criteria, the USGS defined the Mesozoic-Cenozoic Composite Total Petroleum System (TPS) with one assessment unit, the Mesozoic-Cenozoic Reservoirs Assessment Unit (AU) (fig. 1), an area of approximately 464,420 km2. The total petroleum system was defined to include Mesozoic to Paleogene lacustrine and marine source rocks and conventional reservoirs.
Tectonic History and Geology of Mozambique Coastal Province, East Africa
The Mozambique Coastal Province is directly related to the breakup of Gondwana (fig. 3) in the late Paleozoic and Mesozoic (Coster and others, 1989; Reeves and others, 2002; Rusk, Bertagne & Associates, 2003). The province developed in four phases: (1) a pre-rift stage that started during the Carboniferous during which a mantle plume caused uplift, extension, microplate formation, rifting, and volcanism; (2) a syn-rift phase that started during the Permo-Triassic and continued into the Jurassic, which formed grabens and half-grabens and the deposition of possible lacustrine and continental source rocks; (3) a syn-rift–drift phase that began in the Middle Jurassic and continued into the Paleogene, depositing sediments of marine clastic rocks and carbonate and, during periods of restricted-marine conditions, depositing sediments of marine source rocks; and (4) a passive-margin phase that began in the late Paleogene and continues to the present (Envoi—Energy Venture Opportunities International, 2011). The stratigraphic section present in Mozambique Coastal Province is generally the same as the section present in the coastal Morandava Basin, coastal Tanzania, and the Seychelles (figs. 2, 4) (Rusk, Bertagne & Associates, 2003).
The opening of the Indian Ocean began in the Permian and continued into the Jurassic during the syn-rift stage (Reeves and others, 2002). In the Middle Jurassic, Madagascar, India, and north Mozambique separated from Africa (fig. 3) and formed a passive margin and a
carbonate platform that was later covered by Upper Jurassic to Cretaceous marine deposits (figs. 4, 5). During the mid-Cretaceous the passive margin basin again became the site for deposition of open-marine sediments.
A stratigraphic column for the offshore and onshore parts of the Rovuma Basin and Delta along the northern part of Mozambique is shown in figure 6. Since 2006 and the 2011 assessment, several new hydrocarbon discoveries have been found in the offshore part of the delta (Law, 2001; IHS Energy, 2009; IHS Energy, 2012). Three generalized seismic cross sections drawn from onshore to offshore are shown in figures 5, 7, 8. These seismic profiles have imaged potential source rock units and prospects in the offshore parts of northern Mozambique (Law, 2001; Ophir Energy Company, 2011).
Petroleum Occurrence in Mozambique Coastal Province, East Africa
Source Rocks
The Mesozoic-Cenozoic Composite Total Petroleum System was defined to include Mesozoic to Paleocene source rocks and conventional reservoirs (fig. 4). The Permian to Triassic section contains fluvial and lacustrine source rocks averaging 5 to 6 weight percent total organic carbon (TOC); some samples have as much as 17.4 weight percent TOC (Envoi—Energy Venture Opportunities International, 2011). The Lower to Middle Jurassic contains restricted marine Type II kerogen source rocks, marginal marine and deltaic Types II and III kerogen source rocks, and Type I lacustrine source rock (Cope, 2000; Rusk, Bertagne & Associates, 2003). The offshore part of Ruvuma Delta contains Early to Middle Jurassic restricted marine Type II source rocks with TOC contents as much as 12 weight percent (Cope, 2000). Late Jurassic to Early Cretaceous marlstone contains Type II and Type III kerogen with as much as 5 weight percent TOC (Envoi—Energy Venture Opportunities International, 2011). Ophir Energy Company (2007) reports that Aptian shale with TOC contents as much as 9 weight percent. Upper Cretaceous marine sources contain Type II and Type III kerogen with TOC contents as much as 7.4 weight percent and Eocene sources contain Type II and Type III kerogen with TOC contents as much as 12.1 weight percent (Cope, 2000). These source rocks have been found in the Ruvuma Delta in northern Mozambique and southern Tanzania.
Petroleum Occurrence in Mozambique Coastal Province, East Africa 5
Figure 3. Reconstruction of the early breakup of Gondwana during the Early Jurassic (200 Ma). Modified from Reeves and others (2002).
0 100 200 KILOMETERS
0 200 MILES100
HORN OF AFRICA
KENYA
TANZANIA
MADAGASCAR
INDIA
INDIA
SRI LANKA
EAST ANTARCTICA
SEYCHELLES
Mik
ume
Rift
Cambay Rift
Saurastra
Anza Rift
Narmada-Son
Basin
NORT
HM
OZA
MBI
QUE
Selous
Line of latitude or longitude— Oriented as on modern map
EXPLANATION
Precambrian crustal fragment
Rift-related rock
6 Assessment of Undiscovered Oil and Gas Resources of the Mozambique Coastal Province, East Africa
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EXPLANATION
Sandstone
Sandstone and conglomerate
Shale
Sandy shale
Calcareous shaley marlstone
Limestone Reservoir rock, East Africa
Salt
Igneous rock—Extrusive
Igneous rock—Oceanic crust
Basement
Unconformity
Contact—Dashed where location approximate
Extent uncertain
R
Source rock
Potential reservoirOil fieldGas field
CoastalMozambique
Tectonicevents
Tectonicevents
Mozambique Channeland Coastal Tanzania
CoastalMorandava Basin
Envir. Envir.W W
TERT
IARY
CRET
ACEO
USJU
RASS
ICTR
IASS
ICPE
RMIA
NCA
RBON
-IF
EROU
SPR
ECAM
-BR
IAN
Basement
Neo
gene
Pale
ogen
eUp
per
Low
erUp
per
Uppe
rM
ML
UL
Mid
dle-
Uppe
rLo
wer
FluvialDeltaic
Deltaic
Marine
?
?
?
Cont
inen
tal w
ith m
inor
mar
gina
l mar
ine
Zone
s o
f re
serv
oir
pote
ntia
l
Mar
ine
Mar
ine
Cont
inen
tal w
ith m
inor
mar
gina
l mar
ine
Shallowmarine
Deltaic tocont.
Shal
low
mar
ine
to c
ontin
enta
l
Shal
low
mar
ine
lago
onal
toco
ntin
enta
l
Mar
gina
l sag
and
pas
sive
mar
gin
Rift,
mar
gina
l sag
and
drift
Mar
gina
l sag
and
drif
t
Rift
and
mar
gina
l sag
Recu
rren
t rift
ing
and
uplif
t
Recu
rren
t rift
ing
and
uplif
t
Seyc
helle
s-In
dia
brea
kup
Mad
agas
car-
Seyc
helle
s-In
dia
brea
kup
from
Afri
ca
Mad
agas
car-
Seyc
helle
s-In
dia
brea
kup
from
Afri
ca
Rest
ricte
d m
arin
e, o
pen
mar
ine,
and
mar
gina
l mar
ine
Seychelles
SeychellesEast Africa
Drift
Rift
Lithology
?
?
?
Lithology Lithology Lithology
?
?
?
?
?
W EEE
?Re
stric
ted
mar
ine,
shal
low
mar
ine,
and
ope
n m
arin
eSh
allo
w m
arin
e an
d op
en m
arin
eCo
ntin
enta
l with
min
or m
argi
nal m
arin
e
Envir.
R
R
R
R
R
R
R
R
Age
Rifti
ng a
ndm
argi
nal s
ag
Figure 4. Generalized stratigraphic columns of Coastal Mozambique, Mozambique Channel and Coastal Tanzania, Coastal Morondava Basin, and the Seychelles along the east coast of Africa (fig. 1). W, west; E, east; Envir., environment; cont., continental; L, Lower; M, Middle; U, Upper. Modified from Rusk, Bertagne & Associates (2003) and PetroSeychelles (2013).
Petroleum Occurrence in Mozambique Coastal Province, East Africa 7
Rovuma onshore Rovuma offshore
Caravel
Caravel
Ironclad
Jurassic
Cretaceous
Tertiary
EXPLANATION
NOT TO SCALE
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WEST EAST
INDIAN OCEAN
Mecupa Windjammer
Sandstone reservoir rock—Turbidite sandstone unit, deep water fan, and growth-fault-related sand
Carbonate
Basement
Contact
FaultFault—Growth fault, normal fault, and thrust fault
Drill hole and identifier—Approximate depth to target depth
Figure 5. Schematic cross section of the Rovuma River delta, northern Mozambique. Modified from Law (2011). Not to scale.
Oil and gas generation most likely began in the Early Cretaceous for the Upper Jurassic syn-rift sources in the province (Coster and others, 1989). Oil and gas generation began in the Late Cretaceous for the Barremian to Aptian post-rift sources and in the offshore parts of the province the Late Cretaceous post-rift sources began oil and gas generation began in the early Paleogene and is most likely continu-ing today (Coster and others, 1989; Envoi—Energy Venture Opportunities International, 2011). Oil- and gas-generation windows are shown in figure 7 for the Mozambique Channel and the Morondava Basin (Envoi—Energy Venture Opportunities International, 2011).
Reservoirs, Traps, and Seals
The Mozambique Coastal Province and the Mesozoic-Cenozoic Reservoirs Assessment Unit (fig. 1) contain Mesozoic and Cenozoic clastic reservoirs (Coster and others, 1989; Nairn and others, 1991; Cope, 2000; Rusk, Bertagne
& Associates, 2003; Law, 2011). Triassic to Middle Jurassic syn-rift rocks contain possible alluvial fans, fan deltas, fluvial deltas, and lacustrine sandstones reservoirs. The Late Jurassic post-rift rocks contain reef and platform carbonate rocks that are potential reservoirs. The post-rift Cretaceous rocks contain regressive and transgressive marine sandstone, slope-turbidite sandstone and basin-floor fan sandstone reservoirs (Coster and others, 1989). Upper Cretaceous and Cenozoic passive-margin rocks contain possible carbonate reservoirs and Maastrichtian and Paleocene turbidite and basin-floor fan reservoirs (Cope, 2000). Volcanic rocks found within the Karoo age rocks and Cretaceous section may have degraded some of the reservoirs.
The Mesozoic-Cenozoic Reservoirs Assessment Unit (fig. 1) contains sandstone reservoirs that mostly are associated with growth-fault-related structures such as rotated fault blocks within the continental shelf, deep water fans, turbidite sandstone units, and slope truncations along the present-day shelf and paleoshelf edge (Cope, 2000; Rusk, Bertagne & Associates, 2003; Law, 2011). For example, the Rovuma River delta (fig. 5) contains turbidite sandstone units,
8 Assessment of Undiscovered Oil and Gas Resources of the Mozambique Coastal Province, East Africa
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Period Epoch Stage Onshore OffshoreWest EastQuaternary Pleistocene
Cen
ozoi
cM
esoz
oic
Pal
eoge
neC
reta
ceou
sJu
rass
icN
eoge
ne
Pliocene
Miocene
Oligocene
Eocene
CalabrianPiacenzian
ZanclianMessinianTortonian
SerravallianLanghian
BurdigalianAquitanian
Chattian
RupelianPriabonianBartonian
Lutetian
Campanian
SantonianConiacianTuronian
Cenomanian
Albian
Aptian
Barremian
Hauterivian
Valanginian
Berriasian
TithonianKimmeridgian
Oxfordian
Callovian
Bathonian
Bajocian
Aalenian
YpresianThanetianSelandian
Danian
Maastrichtian
Paleocene
Middle
Late
Late
Early
?Chinda
FormationMikindani Formation Rovuma Delta Complex
Pemba Formation
Rovuma Delta Complex
Mifume Formation
Macomia Formation
Pemba Formation
Alto Jingone FormationAlto Jingone Formation
UnconformityPresent coastline
EXPLANATION
Sandstone Continentalclastic rock
Conglomerate
Paralic clastic rock
Marine sandstone
Marine shale, siltstone, and sandstone
Calcareous sandstone
Shelf carbonate
Marl
Contact
Quissanga Formation
Figure 6. Stratigraphic column for the onshore and projected offshore parts of the Rovuma Basin, northern Mozambique. Middle and Lower Jurassic units shown in figure 4, such as the Lower Jurassic salt, are not shown. Modified from Key and others (2008).
Exploration 9
Figure 7. Cross section across the Mozambique Channel and the Morondava Basin (line of section on index map) showing the top of the oil- and gas-generation windows. Cross section is approximately 420 kilometers long, not to scale. Modified after Envoi—Energy Venture Opportunities International (2011).
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INDEX MAP
WEST-NORTHWEST EAST-SOUTHEAST
KILOMETERSSEA LEVEL
4
6
8
10
2
EXPLANATION
Cenozoic
Tertiary
Upper Cretaceous
Lower Cretaceous
Jurassic
Oil field andidentifier
Gas field andidentifier
Triassic to Permian
Basement rock
Volcanic
ContactFault
MnaziBay Field(Offset to
South)
MnaziBay Field
X'
MOZAMBIQUE MADAGASCAR
Île Juan de NovaExclusive Economic Zone
FRENCH SOUTHERN ANDANTARCTIC LANDS
X
IroncladDiscovery(Offset to
North) WindjammerDiscovery(Offset to
North)Manambolo
Gas FieldJuan deNova Island
Shallow anddeepwaterprospect
TsimiroroHeavy Oil
Field BemolangaTar Sands
Top of Oil Window
Top of Gas Window
Davie Fracture Zone Morondava Basin
IroncladDiscovery
MOZAM
BIQUE
MA
DA
GA
SCA
R
MALAWI
Moz
ambiq
ue
Chann
el
RovumaDelta
Majunga Basin
Mor
onda
va B
asin
Mozambique Channel
INDIANOCEAN
X'
X
Line of section
deep-water fan, and growth-fault-related sandstone reservoirs (Law, 2011). A seismic profile reported by Walford and others (2005) interpreted the Late Cretaceous and Cenozoic section showing the Domo Sandstone, a potential reservoir and clinoform packages, channeling, slumping, and growth faults in the offshore part of the Zambezi Delta (fig. 8).
Triassic to Jurassic syn-rift rocks contains structural traps related to graben and half grabens. Lower Cretaceous post-rift rocks (drift and passive-margin) contain stratigraphic traps such as transgressive and regressive sandstones and structural traps including salt structures, drape anticlines, and flower structures (Rusk, Bertagne & Associates, 2003; Law, 2011). Upper Cretaceous and Paleogene post-rift rocks (drift and passive-margin) contain both structural and stratigraphic traps in growth-fault-related structures, rotated fault blocks within the continental shelf, deep-water fans, turbidite units, and slope truncations along the present day shelf and paleoshelf edge.
The primary reservoir seals are Mesozoic and Cenozoic drift and marginal-marine mudstone and shale (Nairn and others, 1991; Cope, 2000). Secondary fault-related seals are
found in Karoo-age grabens and Mesozoic half-grabens, faulted drape anticlines, and inversion-related anticlines (Cope, 2000; Rusk, Bertagne & Associates, 2003).
Exploration
At the time of the 2011 assessment, the Mozambique Province contained five gas fields and no oil fields (IHS Energy, 2009) and is considered to be underexplored on the basis of its limited exploration activity. Recent hydrocarbon shows are limited to the Cretaceous-Tertiary offshore drift and passive-margin section (Law, 2011).
Hydrocarbon shows in exploration wells on the continental shelf and upper slope provide evidence for the existence of an active petroleum system containing Mesozoic source rocks and for the migration of the hydrocarbons into Cretaceous and Cenozoic reservoirs, most likely since the Late Cretaceous.
10 Assessment of Undiscovered Oil and Gas Resources of the Mozambique Coastal Province, East Africa
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INDEX MAP
0
1
3
4
5
2
Well and identifierWell A
A'
Tertiary
Cretaceous
Fault
Jurassic
ContactSeismic reflector
EXPLANATION
AWell A Well B
Top Eocene
Domo Sandstonechanneling
slumping
Seafloor
TWO WAYTIME IN
SECONDS
Top PlioceneTop Miocene
Middle MioceneTop Oligocene
Top Cretaceous
0 5 10 KILOMETERS
0 10 MILES 5
Zambezi River
INDIAN OCEAN
INDIANOCEAN
BeiraA'
A
MOZAMBIQUE
Line of section
Figure 8. Schematic cross section of the Zambezi Delta, Mozambique. Modified from Walford and others (2005).
Resource Summary 11
Figure 9. Events chart for the Mesozoic-Cenozoic Total Petroleum System (734301) and the Mesozoic-Cenozoic Reservoirs Assessment Unit (73430101) in the Mozambique Coastal Province, South Africa. Gray, rock units present; yellow, age range of reservoir rocks; green, age ranges of source and overburden rocks, timing of trap formation, and generation, migration, and preservation of hydrocarbons; wavy line, unconformity. Divisions of geologic time conform to dates in U.S. Geological Survey Geologic Names Committee (2010). Ma, thousands of years ago; Plio, Pliocene; Mio, Miocene; Olig, Oligocene; Eoc, Eocene; Pal, Paleocene; L, Late; E, Early; M, Middle; ?, uncertain.
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icted
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23
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Geologic ModelThe geologic model developed for the assessment of
conventional oil and gas in the Mozambique Coastal Province and the Coastal Plain and Offshore Assessment Unit is as follows:
1. Oil and gas was generated from Permian to Jurassic Karoo-age lacustrine and continental rocks (rift stage). The lacustrine rocks contain TOC values averaging 4.0 to 5.0 weight percent. Early to Middle and Jurassic restricted marine rocks contain as much as 9 weight percent TOC, and Cretaceous marine rocks contain Type II kerogen with as much as 12 weight percent TOC. Generation of hydrocarbons in syn-rift Karoo-age source rocks most likely began in the Middle Jurassic, whereas generation of hydrocarbons in Middle Jurassic to Early Cretaceous syn-rift source rocks began in the Late Jurassic to Early Cretaceous. Generation of early post-rift sources most likely began in the Late Cretaceous. The drift and post-rift source rocks most likely began generating hydrocarbons in the Late Cretaceous. Hydrocarbon generation most likely continues today in the offshore parts of the assessment unit.
2. Generated hydrocarbons migrated into mostly Cretaceous and Paleogene sandstone reservoirs.
3. Hydrocarbon traps are structural within the syn-rift rock units and are both structural and stratigraphic in the post-rift rock units.
4. The primary reservoir seals are Mesozoic and Cenozoic mudstone and shale.
5. The rifted passive margin analog (Charpentier and others, 2007) was used for assessment sizes and numbers because of similar source, reservoirs, and traps.
An events chart (fig. 9) for the Mesozoic-Cenozoic Composite TPS and the Mesozoic-Cenozoic Reservoirs AU summarizes the age of the source, seal, and reservoir rocks and the timing of trap development, generation, and migration.
Resource SummaryAt the time of this 2011 assessment, the Mozambique
Coastal Province contained only five gas accumulations exceeding the minimum size of 30 billion cubic feet of gas; this province is considered to be underexplored on the basis of its level of exploration activity. Using a geology-based assessment, the USGS estimated mean volumes of undiscov-ered, technically recoverable conventional oil and gas resources for the Mesozoic-Cenozoic Reservoirs Assessment Unit in the Mozambique Coastal Province (table 1). The mean volumes are estimated at 11,682 million barrels of oil, 182,349 billion cubic feet of gas, and 5,645 million barrels of natural gas liquids. The estimated mean size of the largest oil
12 Assessment of Undiscovered Oil and Gas Resources of the Mozambique Coastal Province, East Africa
field that is expected to be discovered is 1,041 million barrels of oil and the estimated mean size of the expected largest gas field is 7,976 billion cubic feet of gas. For this assessment, a minimum undiscovered field size of 5 million barrels of oil equivalent was used. No attempt was made to estimate economically recoverable reserves.
For Additional InformationAssessment results are available at the USGS
Central Energy Resources Science Center website: http://energy.cr.usgs.gov/oilgas/noga/ or contact Michael E. Brownfield, the assessing geologist ([email protected]).
AcknowledgmentsThe author wishes to thank Mary-Margaret Coates,
Jennifer Eoff, Christopher Schenk, and David Scott for their suggestions, comments, and editorial reviews, which greatly improved the manuscript. The author thanks Wayne Husband for his numerous hours drafting many of the figures used in this manuscript, and Chris Anderson, who supplied the Geographic Information System files for this assessment.
References
Charpentier, R.R., Klett, T.R., and Attanasi, E.D., 2007, Database for assessment unit-scale analogs (exclusive of the United States) Version 1.0: U.S. Geological Survey Open-File Report 2007–1404, 36 p., CD–ROM.
Cope, M., 2000, Tanzania’s Mafia deepwater basin indicates potential on new seismic data: Oil and Gas Journal, v. 98, issue 33, 6 p., http://www.ogj.com/articles/print/volume-98/issue-33/exploration-development/tanzanias-mafia- deepwater-basin-indicates-potential-on-new-seismic- data.html. Last accessed February 28, 2013.
Table 1. Mozambique Coastal Province assessment results for undiscovered, technically recoverable oil, gas, and natural gas liquids.
[Largest expected mean field size, in million barrels of oil and billion cubic feet of gas; MMBO, million barrels of oil; BCFG, billion cubic feet of gas; MMBNGL, million barrels of natural gas liquids. Results shown are fully risked estimates. For gas accumulations, all liquids are included as natural gas liquids (NGL). Undiscovered gas resources are the sum of nonassociated and associated gas. F95 represents a 95-percent chance of at least the amount tabulated; other fractiles are defined similarly. Fractiles are additive under assumption of perfect positive correlation. AU, assessment unit; AU probability is the chance of at least one accumulation of minimum size within the AU. TPS, total petroleum system. Gray shading indicates not applicable]
Total Petroleum Systems (TPS) and Assessment Units (AU)
Field type
Largest expected
mean field size
Total undiscovered resourcesOil (MMBO) Gas (BCFG) NGL (MMBNGL)
F95 F50 F5 Mean F95 F50 F5 Mean F95 F50 F5 Mean
Mozambique Coastal-Mesozoic-Cenozoic Composite TPS
Mesozoic-Cenozoic Reservoirs AU Oil 1,041 6,268 11,174 18,857 11,682 8,423 15,615 27,238 16,425 225 421 744 444Gas 7,976 93,486 158,654 263,301 165,924 2,915 4,978 8,270 5,201
Total Conventional Resources 6,268 11,174 18,857 11,682 101,909 174,269 290,539 182,349 3,140 5,399 9,014 5,645
Coster, P.W., Lawrence, S.R., and Fortes, G., 1989, Mozambique—A new geological framework for hydro-carbons exploration: Journal of Petroleum Geology v. 12, no. 2, p. 205–230.
Envoi—Energy Venture Opportunities International, 2011, Mozambique Channel (offshore S.E. Africa), Juan de Nova Est Permit, Morondava Basin: Envoi Limited, London, http://envoi.co.uk/wp-content/uploads/2012/11/P191 WessexSEAfricaJuanDeNovaSynopsis.pdf. Accessed March 20, 2013.
IHS Energy, 2009, International petroleum exploration and production database [current through December 2009]: Available from IHS Energy, 15 Inverness Way East, Englewood, Colo. 80112 USA.
IHS Energy, 2012, International petroleum exploration and production database [current through December 2009]: Available from IHS Energy, 15 Inverness Way East, Englewood, Colo.
Key, R.M., Smith, R.A., Smelror, M., Saether, O.M., Thorsnes, T., Powell, J.H., Njange, F., and Andamela, E.B., 2008, Revised lithostratigraphy of the Mesozoic-Cenozoic succession of the onshore Rovuma Basin, northern coastal Mozambique: South African Journal of Geology, v. 111, no. 1, p. 89–108.
Law, Carol, 2011, Northern Mozambique—True “wild-cat” exploration in east Africa: American Association of Petroleum Geologists Search and Discovery article 110157(2011), 39 p.
Nairn, A.E.M., Lerche, I., and Iliffe, J., 1991, Geology, basin analysis, and hydrocarbon potential of Mozambique and the Mozambique Channel: Earth-Science Reviews, v. 30, no. 1–2, p. 81–124.
PetroSeychelles, 2013, The Seychelles licensing initia- tives: NAPE, February 5–8, Houston, Texas, 46 p., http://www.internationalpavilion.com/NAPE%202013%20Presentations/Seychelles.pdf.
Ophir Energy Company, 2007, Hydrocarbon Prospectively of Deepwater Southern Tanzania—East African Petroleum Conference: Arusha, Tanzania, March 7–9, 2007, 26 p.
References 13
Ophir Energy Company, 2011, Exploration in Tanzania and Madagascar—Evolution Securities East Africa Conference: London, January 13, 2011, 27 p.
Reeves, C.V., Sahu, B.K., and de Wit, M., 2002, A re-examina-tion of the paleo-position of Africa’s eastern neighbours in Gondwana: Journal of African Earth Sciences, v. 34, no. 1, p. 101–108.
Rusk, Bertagne & Associates, 2003, Petroleum geology and geophysics of the Mozambique Channel, executive sum-mary: 20 p., http://www.petrocommunicators.com/moz/index.htm. Last accessed March 6, 2012.
U.S. Geological Survey Geologic Names Committee, 2010, Divisions of geologic time: U.S. Geological Survey Fact Sheet 2010−3059, 2 p.
U.S. Geological Survey World Conventional Resources Assessment Team, 2012, An estimate of undiscovered conventional oil and gas resources of the world, 2012: U.S. Geological Survey Fact Sheet 2012–3042, 6 p. Available at http://pubs.usgs.gov/fs/2012/3042/
Walford, H.L., White, N.J., and Sydow, J.C., 2005, Solid sedi-ment load history of the Zambezi Delta: Earth and Planetary Science Letters, v. 238, no. 1–2, p. 49–63.
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ATLANTIC OCEAN
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