Biofacies and palaeoenvironment & stratigraphy of the ratawi, Minagish and Makhul formations Kuwait, reservoir, source rocks, conventional and unconventional expl plays.

1. Integrated Biostratigraphical Model - numerous fossil groups which are all
environmentally sensitive. For example the diachronous stratigraphical ranges of
key taxa in shallow marine carbonates is a result of environmental control.
The distribution and number of the bioclasts identified contribute to the recognition
of biozones and biofacies – LK1, LK2 and LK3. These are useful for well
correlation and the identification of potential Source and Reservoir intervals.
Semi-quantitative micropalaeontological biofacies analysis of more than 500 thin
sections of core samples from more than 30 wells provides an independent insight
into the environmental history of deposition of the interval.
The thin sections were not taken at regular spaced intervals in the cored sections
and are randomly orientated with the result that species diagnostic features of the
taxa recorded are often not visible. Accordingly, a broad approach had to be taken
for discriminating various species and for the recognition of vertical stacking /
cyclicity of the observed biofacies.
The recorded bioclast data together with core-facies, microfacies and textural data
provide an invaluable technique for determination of both gross and subtle
variations in the depositional environment and for recognition of sea-level changes
and associated flooding events and surfaces.
Biofacies, Palaeoenvironment and Stratigraphy of the
Ratawi, Minagish and Makhul formations, Kuwait.
S. Crittenden1*, M. Al-Baghli1, G. Gega1, A. P. Kadar1 and P. Clews2.
The Makhul, Minagish and Ratawi formations form the oldest
lithostratigraphic units of the Thamama Group and represent a
major 2nd order depositional cycle spanning the latest Jurassic
(Tithonian) and Early Cretaceous (Berriasian and Early
Valanginian) of Kuwait (Figures 1, 2 & 3).
The three formations in Kuwait comprise shallow marine
carbonates and are “informal” lithostratigraphical units defined
and dated by calibration with surface exposures and wells in
neighbouring Saudi Arabia, Iraq and Iran.
OBJECTIVE
To present the applied micropalaeontology technique of
biofacies analysis (thin sections of ditch cuttings and core plus
routine washing preparation of cuttings) for the lower part of
the Thamama Group in Kuwait.
Biofacies Analysis makes a significant independent contribution
to regional stratigraphical resolution, to understanding
depositional continuity and to supporting the recognition of
vertical stacking patterns and depositional cyclicity observed in
the core description and petrographic microfacies studies of
this important hydrocarbon bearing interval.
Materials and Method
Results: Bioclasts - Biofacies - Biostratigraphy
The study interval top is a major temporal hiatus
separating the Early Valanginian from the Late
Hauterivian = KSB40.
The model acts as a broad guide. Observed data
should not be “shoe-horned” to fit the model. The
biostratigraphical data should be used to modify
the model if necessary.
Fig 3: 3rd Order Maximum Flooding Scheme
for the latest Jurassic - earliest Cretaceous (Ref. 7)
Fig 1: Lowermost Cretaceous Conventional Stratigraphy Model
The maximum flooding based stratigraphy of Sharland et al (2004)
indicates four 3rd order depositional sequences within the 2nd order
sequence (duration 16 my). Our evaluation of data indicates up to
six 3rd order depositional sequences may be present as implied by
AROS (Ref. 1). Maximum flooding “intervals” are either deeper water
outer shelf shales or shallow water limestones.
Well F is in an outer ramp deep water carbonate setting.
Fig 2: Well F , Offshore Kuwait (Ref. 1)
Carbonate facies are defined on textures and palaeoecological factors, in predominantly shallow marine
conditions within the photic zone on a flat, laterally extensive carbonate platform. There is a complex
mosaic of facies and differentiation is based upon the degree of restriction of the shallow marine
environment that controls the distribution of texture and grain size and the biotic assemblage (the
biofacies). The biocomponents are dominated by benthonic foraminifera (lituolids, miliolids and small
calcareous genera), echinoid and mollusc debris (rudists, bivalves and gastropods) and calcareous algae
fragments. Minor components include sponge spicules, radiolaria, ostracods, calpionellids and macrofossil
debris (corals, serpulids, bryozoans).
Three major bio-assemblages (defining local biozones - Kuwait) can be identified and approximate the
Makhul Formation (LK1: radiolarite assemblage of restricted platform muddy limestones), the Minagish and
Ratawi Limestone Member (LK2: calcareous algae/foraminiferal assemblage of shallow shelf, clean
carbinates including shoals) and the Ratawi Shale Member (LK3: foraminiferal / ostracod and calcareous
algae assemblage of a mixed clastic and carbonate environment).
Each of these local biozones can be subdivided in to subsidiary biofacies /biozones, laterally and in time.
1 KOC Exploration Studies Team, 2 Independent Consultant.
74th EAGE Conference & Exhibition incorporating SPE EUROPEC 2012
Poster P053, Exploration & Plays session in Poster box 11, June 5, 2012
Biofacies Observations
Textularinids
Cyclamminids
Everticyclamminasp.
Pseudocyclammina
Rotaliids
Miliolids
Charentiaspp
Trocholina
Pfenderinaspp
Lenticulinaspp
Undiffforaminifera
Molluscs
Gastropods
Bivalves
Ostracods
Brachiopods
GreenAlgae
Lithocodium
Echinoderms
Bryozoans
Serpulids
SpongeSpicules
Calpionellids
Calcispheres
VeryShallow
Shallow
Innerramp
Corefacies
Microfacies(Wilson1975)
Mudstone
Wackestone
Packstone
Grainstone
Boundstone
Floatstone
R R R M VR VR M
VR VR ?R VR R C R C R R R M
R R VR C M C R C C M
A M M R A M M C P
R VR R M R M M
M R C? M R C C M VR VR W/P
M R M R R C C C M R C M
M VR? VR M C R VR M
C R? M C C M M M
R? VR M A C R R W
M M M C R M
R M M R M M
R? VR VR R VR VR M
R? VR VR R M VR? R W
R VR? R M R VR? M M
R? VR R VR? M
R R VR M VR R VR? M
M R? R A R C VR VR M
C M VR C A R M VR VR? M
M M R? M C A M C R W
VR VR VR M M R M M
VR M R VR M M M
R VR R? R M
R R VR R M
M R M VR R? M M
R M VR? R VR M R M M
VR VR R R R M
R? VR VR R VR? M
R R VR? VR R R M R M
M R C M R C VR? M
M R? R R M M
C R R M C M VR C M
M VR? R? VR C C R R M M
C M M VR M VR R R M M
C VR R C M
C R VR M R C M M
9659.70
9668.20
9686.70
9702.10 R
9432.00
9435.00
9450.50
9462.30
9472.40
9475.00
9382.70 R
9389.30
9406.00 R
9419.00
9322.10
9334.80
9338.50
9368.90
9371.50
9379.30
9289.70
9299.10
9306.70 R
9314.40 R
A/C
9241.50
9250.50 M
9277.60 R
Minagish
9066.90
9096.40
9153.50
9157.80
9175.70
9184.20
9190.90
9202.50
9205.00
DistalOuterRamp
DistalOffshore(Basinal)
Facies TS Textures (Dunham)
TS Depth
Micriticpeloids
ME-01 Core Thin Section Bio-components
Inner
Ramp
Middleramp
ProximalOuterRamp
Green Algae: maximum numbers recorded at the top of the regressive units (ie. last phase of the high
stand intervals) within low energy inner ramp and lagoonal environments. Common in low energy mid to
outer ramp environments.
Miliolids (f): shallow low energy environment. Present as reworked elements in higher energy shoals and in
tempestite intervals in the Makhul Formation.
Pseudocyclammina spp (f): mid to outer ramp, low to moderate energy.
Trocholina sp. : high spire 5 – 15m water depth, low spire 15 – 25 m water depth.
Dinoflagellate cysts: diverse assemblages are characteristic of relatively deeper water marine environments.
Calcareous nannoplankton: characterise deeper marine waters.
Radiolaria: characterise deeper marine waters – distal / basinal influence
Introduction
Part 1 of 2
BIOZONE LK1 (Makhul Formation facies): radiolarite facies-
calcitised radiolaria, calcispheres and calcitised sponge
spicules. Rare Bositra ?buchi and Saccomma spp. Significant
organic matter. Muddy carbonate.
Relatively deep marine water assemblage. Euxinic, low
energy stratified below storm wave base of an intra-carbonate
shelf / embayment. In wells west of the Kuwait Arch
calpionellids are rare (Fig 4 & 5 Well A & B). In wells east of
the kuwait Arch in a presumed down-dip depositional regime
(deeper water more open marine) calpionellids are common.
Associated foraminfera are rare small agglutinants: Textularia
spp., Ammobaculites spp., & possible cyclamminids.
Allochthonous shallower marine taxa associated with thin
wackestone/packstone beds (tempestites) include miliolids,
lenticulinids & algae, bivalve, echinoderm fragments
Well A
Well B
BIOZONE LK2 (Minagish Formation and Ratawi Limestone
facies):diverse assemblage of echinoid and bivalve debris, calcareous
algae fragments, rare radiolaria, rare ostracods, rare calcispheres, few
sponge spicules, rare to common calpionellids and common benthonic
foraminifera (including rare miliolids). Shallow open marine carbonate.
Comprises lime mudstones, packstones, wackestones and developments
of higher energy regime, clean well winnowed oolitic grainstone shoals,
particularly in the Minagish Formation, and skeletal debris shoals..
Dolomitisation has destroyed contained flora / fauna in some cases.
Species recorded: benthic foraminifera Trocholina spp (high spired and
low spired), cyclamminids such as Pseudocyclammina spp.,
Praechrysalidina spp., small Textularids, Vercorsella sp., Cuneolina sp. ,
Charentia sp., Nautiloculina sp., rare miliolids and small gavelinellids and
frequent small Lenticulina spp.
Sub-biozones and sub-biofacies of various
resolution scale can be identified in some
wells where there is sufficient data and
indicate subtle cycles of deposition and
ariation in assemblage components
associated with differences in water depth
and energy on a carbonate shelf; eg. an
outer ramp low energy setting biofacies (Fig
6 Well C) and a shallow water, high energy
shoal biofacies (Fig 7, 8: well D & Fig 9
Well E)
Fig 4
Fig 5
Fig 6
Fig 7
Fig 8
Fig 9
Well D
Well D
Well C
Well E
Fig 10Well F BIOZONE LK3 (Ratawi Shale
Member):The Ratawi Shale Member is
characterized by a basal calcareous
claystone / argillaceous carbonate to
clastic sedimentation transition interval
that is rapidly replaced upward by
siliciclastic deposits (Fig 10, Well F).
Onshore Kuwait the lower part of the
Ratawi Shale Member contains
microfaunal assemblages comprising
benthonic foraminifera including
abundant Cyclammina /
Everticyclammina spp ., Recurvoides
sp., Trochammina sp., Protopeneroplis
spp., Trocholina spp. and common small
calcareous benthonic foraminifera
including Lenticulina spp., together with
common ostracods, microgastropods ,
mollusc debris, rare calpionellids,
calcispheres, dinocysts and calcareous
nannoplankton consistent with a
shallow marine, inner ramp
environment. Calcareous algae are
absent except in the thin limestone
beds. The recorded foraminiferal
assemblage decreases in number into a
low diversity assemblage in the
overlying sandier and siltier non-
calcareous shales. This permits division
into upper and lower sub-biozones.
A sub-biofacies division reflects a progressive
east to west change in lithofacies of this
member; west of the Kuwait Arch the interval
comprises the biofacies already described.
East of the Kuwait Arch, the calcareous shale
& minor siltstone / limestone sequence yields
a similar biofacies but includes Gavelinella aff.
barremiana, Lenticulina cf heiermanni, L.
munsteri , L. macrodisca and Epistomina
caracolla typical of outer ramp, deeper fully
marine water.
Sparse to common miliolids are recorded from
the Ratawi Shale Member in south Kuwait
suggesting a shallower water depth compared
with wells in the north.

2. Conclusions.
The biofacies study provides an important contribution to the regional
palaeoenvironmental understanding of the Makhul, Minagish and Ratawi formations
in Kuwait.
Higher resolution biofacies studies of particular ‘time slices’ assist in stacking
pattern recognition, sequence definition and correlation in order to aid exploration.
S. Crittenden1, M. Al-Baghli1, G. Gega1, A. P. Kadar1 and P. Clews2.
74th EAGE Conference & Exhibition incorporating SPE EUROPEC 2012
Poster P053, Exploration & Plays session in Poster box 11, June 5, 2012
Chronostratigraphy: Integrated Biostratigraphy uses all available data from all groups studied: eg. calcareous
nannofossils, dinoflagellate cysts, spores and pollen, calpionellids, radiolaria, ostracods, calcareous algae and
foraminifera. All have been used to date the well sections, either in isolation or in an integrated fashion
depending on data available. The proviso is that all are facies dependent / controlled – diachronous nature of
local stratigraphical ranges within a shallow marine environment, and a detailed high resolution
chronostratigraphic biozonation is not possible.
Calcareous nannoplankton:
Due to shallow water palaeoenvironments and post depositional diagenesis, nannofossil assemblages in
samples from the studied wells are of low abundance, low diversity and usually poorly preserved. Many of the
expected stratigraphical marker species commonly reported in deep-sea sediments of Lower Cretaceous age
are absent or only occur sporadically. Semi-quantitative analysis provides a means for assisting in the
identification of marine flooding intervals – floral acme / abundance. FDO (extinction) of Polycostella senaria:
is it a correlatable Time-event (local extinction level) in shallow water shelf carbonates?
Calpionellids:
Characterise deep water, low energy environment. Mostly within laminated calcareous mudstones and
wackstones. Proximal and distal outer ramp setting. Can they be used to indicate marine flooding events?
These pelagic, calcareous unicellular organisms are studied in thin section hence re-study of petrographical
thin sections provides good data. They are however prone to diagenetic obliteration and reworking (in clasts).
Acknowledgments:
This poster is presented with the approval of the Ministry of Oil of the State of
Kuwait and Kuwait Oil Company. The encouragement and advice are acknowledged
of Abdul Aziz Al-Fares Team Leader of the Exploration Studies Group in KOC,
Ghaida Al-Sahlan (Stratigraphy Sub-Team unit head) and team members Irene
Truskowski and Abdel Kadar H. H. Youssef.
Results: e.g. Biostratigraphy Models
I. compactus N. quadratus N. Kampt. minor
N. Stein. minor M. obtusus ?P senaria
R. wisei ?T. sarmatus Z. xenotus
Results: e.g. Palaeoenvironment Model
Results: Depositional Models
T. longa
R. cf. cadischianaL. cf. hungarica
C. cf. simplexC. darderi
C. ellipticaC. alpina
T. carpathica
Data and figures from Al-Rifaiy and Lemone, 1987.
Bars below figures = 50 microns.
Selected References
1. Al-Husseini, M. & Matthews, R. K., 2008. Jurassic-Cretaceous Arabian orbital stratigraphy: The AROS-JK Chart. GeoArabia, v. 13, pp. 89 –
94.
2. Al-Fares, A. A., M. Bouman and P. Jeans., 1998. A new Look at the Middle-Lower Cretaceous Stratigraphy, Offshore Kuwait. GeoArabia, v. 3,
pp. 543 - 560.
3. Al-Rifay, I. A. & Lemone, D. 1987. Calpionellids and the late Jurassic and early Cretaceous stratigraphy of Kuwait and the Gulf Region.
Marine Micropalaeontology, 12, pp. 383-388.
4. Banner, F. T. and Simmons, M. D. 1994. Calcareous algae and foraminifera as water – depth indicators: an example from the Early
Cretaceous carbonates of northeast Arabia. In Simmons, M. D. (ed.). Micropalaeontology and Hydrocarbon Exploration in the Middle East.
British Micropalaeontology Society Publication Series. pp. 243 – 252.
5. Carman, G., 1996. Structural elements of Kuwait. GeoArabia, v.1, pp. 239 – 266.
6. Davies, R. B., Casey, D. M., Horbury, A. D., Sharland, P. R. and Simmons, M. D. 2002. Early to Mid Cretaceous mixed carbonate-siliciclastic
shelfal systems: Examples, issues and models from the Arabian Plate. GeoArabia, v. 7, 3, pp. 541-598.
7. Dunnington, H. V., Wetzel, R. and Morton, D. M., 1959. Iraq: Mesozoic and palaeozoic. Lexique Stratigraphique International., Asie, Volume
III, 10a CNRS. Paris.
8. Hosseini, S. A. & Conrad, M. A., 2008. Calcareous algae, foraminifera and sequence stratigraphy of the Fahliyan Formation at Kuh-e-surmeh
(Zagros Basin) SW Iran. Geologia Croatia, 61/2-3, 215-237.
9. Hughes, G. W. G. 2005. Calcareous Algae of Saudi Arabian Permian to Cretaceous Carbonates. Rev. Esp. de Micropal. V. 37, 1 pp. 131-140.
10. Owen, R. M. S. & Nasr, S. N. 1958. The Stratigraphy of the Kuwait- Basra area. In: Habitat of Oil, AAPG Memoir, 1252 – 1278.
11. Sharland, P., et al. 2001. Arabian Plate Sequence Stratigraphy. GeoArabia Spec Publ. 2
12. Sharland , P., et al. 2004. Chrono-Sequence Stratigraphy of the Arabian Plate. GeoArabia, v 9, 1, Enclosure 1.
13. Steineke, M. & Braamkamp, R. A. 1952. Mesozoic rocks of eastern Saudi Arabia (Abstract) American Association of petroleum geologists, 6,
909.
1 KOC Exploration Studies Team, 2 Independent Consultant.
Biofacies, Palaeoenvironment and Stratigraphy of the
Ratawi, Minagish and Makhul formations, Kuwait.
Part 2 of 2
* Dr Stephen Crittenden is currently a Senior Geologist with Addax Petroleum Ltd, Geneva, Switzerland.