New Perspectives – New Plays

in the Douala Basin

of CameroonRichard Bray & Steve Lawrence, ECL, UKSerge E Angoua Biouele, SNH, Cameroon

Exploration Consultants Limited, Highlands Farm, Greys Road,Henley-on-Thames, Oxfordshire, EnglandSNH

EasternGulf of Guinea

Douala BasinLocation

EasternGulf of Guinea

GeologicalSetting

CameroonDouala Basin

Well and Oil Seep Locations

Van Krevelen plot

Tissot & Welte 1978

CameroonDouala Basin

HydrocarbonOccurrences

Cameroon –Rio Muni

StratigraphySource Rocks

Douala Basin

Stable Carbon IsotopeCharacteristics -Seep andReservoired Oils

Douala Basin

OleananeCharacteristics -Seep andReservoired Oils

SOURCE ROCK PROPERTIES FROM

OILS GEOCHEMISTRY 1

Two oil families are present:

Isotopically light with oleanane present – Tertiary source

Isotopically heavy with oleanane absent – Pre-Campanian

source (most likely Albian-Cenomanian)

Co-mingling of these two families occurs

SOURCE ROCK PROPERTIES FROM

OILS GEOCHEMISTRY 2

All oils indicate:

Terrestrially derived oil-prone kerogen deposited in a marine

environment.

Dysoxic depositional conditions – organic preservation favoured

by high sedimentation rate rather than sea-bed anoxia.

Oil maturities indicate source rocks mostly in the early to mid

mature oil windows (some indications of late mature).

Other conclusions concern biodegradation, leakage from trapped

accumulations versus migration from source etc.

Cameroon –Rio Muni

StratigraphySource Rocks

Douala Basin - Souellaba & Matanda Formations - Geochemistry

Douala Basin - Tertiary Petroleum System

Douala Basin – Tertiary Sequence Architecture

Pliocene

Oligo-Miocene

Paleocene-Eocene

Deep waterchannel/fancomplexes

HST

TST

LST

HST - Deltaics showing well developed (basinward) progradationTST - Deep water muds showing local onlap, otherwise parallel reflectorsLST - Deep water sands, chaotic and concave-up reflectors, local progradation

Douala Basin - Seismic Amplitude Map

RMS amplitude 100 msec above base Eo-Oligocene Unconformity

Courtesy of GESeis

EasternGulf of Guinea -Burial HistoryPlots

Marginal Location

Basinal Location

40(C)

80(C)

120(C)80(C)

120(C)

80(C)

120(C)

Age (my)

020406080100120140

0

1000

2000

3000

4000

QPMOEPK

Pliocene

Miocene

SR 1

SR 2

Early Cretaceous

SR 3

Fm

t = 0

40(C)

80(C)

120(C)

160(C)

Age (my)

020406080100120

0

2000

4000

6000

8000

QPMOEPK

Pliocene

Miocene

Paleocene

LateCretaceous

Fm

SR 1

EarlyCretaceous

Douala Basin

Tertiary PetroleumSystem Map

PETROLEUM SYSTEM

In accordance with convention the petroleum system is

classified as hypothetical and described as follows:

N’Kapa/Souellaba – Northern oil seeps (.)

N’Kapa/Souellaba – N’Kapa/Souellaba (.)

CONCLUSIONS 1

Tertiary-sourced petroleum system associated with the mid Tertiary

unconformity.

Source rocks in Souellaba Fm (Oligo-Miocene) or N’Kapa Fm (Paleocene-

Eocene). Source rocks also exist in the Cretaceous section.

Position of source above or below the unconformity is critical to its

maturation history.

Reservoirs are expected to be developed as lowstand channel/fan

complexes within a sediment wedge above the sequence boundary.

CONCLUSIONS 2

More work is needed to positively identify a Tertiary source rock (oils /

well sample geochem).

The stratigraphic framework is poorly constrained. Work is needed to

resolve this (biostrat / seis-strat).

It is crucial to understand the thermal history and the history of uplift

and erosion of the basin (AFTA & high quality VR data).

The petroleum systems approach is a necessary step towards mapping

prospective play fairways.

Thank you for your attentionSNH

Additionalslides follow

Slide 4

EasternGulf of Guinea -Study Wells &Outcrop SampleLocations

Slide 14

Northern Equatorial Guinea - Northern CameroonCross-section

Shale diapir-associatedstructures

Benin

Moudi

Tsavorita

UPPER QUA IBOE

LOWERQUA IBOE

Zafiro

Amatista

AKATA

ISONGO

Alba

BONITO

AKATA

LATE CRETACEOUS

OCEANIC CRUST

SOUELLABA

LOGBABA

OCEANIC CRUST

Toe-thruststructures

Oil migrating fromCre taceoussource rocks

Deep water sands

Oil seeps associated withCretaceous exotics

Cameroon Volcanic Line

Isongo

Post-rift Marine(Albian-Turonian)

N i g e r D e l t a - R i o d e l R e y B a s i n Douala Basin

North-west South-east

MATANDA

LOGBADJECK

WOURI

Channel/fan sands

CONTINENTAL CRUST

Sanaga Delta

MUNDECK

Apt-AlbianSource RocksPost-rift SRs

Albian-Cen

N I G E R I A E Q U AT O R I A L G U I N E A C A M E R O O N

M’Via

Matanda

Souellaba

Slide 16

Rio Muni -Cameroon

ThermalEpisodes &EustaticCurve

Slide 9

S Cameroon - N Rio Muni - Schematic Thermal History

CameroonLicence situationMay 2003