Abstract to accompany the Biofacies poster Copenhagen 2012 EAGE

1. 74th
EAGE Conference & Exhibition incorporating SPE EUROPEC 2012
Copenhagen, Denmark, 4-7 June 2012
P053
Biofacies, Palaeo-environments and Stratigraphy
of the Ratawi, Minagish and Makhul Formations
of Kuwait
S. Crittenden* (Kuwait Oil Company), M. Al-Baghli (Kuwait Oil Company),
G. Gegas (Kuwait Oil Company), A.P. Kadar (Kuwait Oil Company) & P.
Clews (Independent Consultant)
SUMMARY
Three major micropalaeontological biozones / biofacies assemblages are described from the latest Jurassic
(Tithonian) to Early Cretaceous (Berriasian to Early Valanginian) lower part of the Thamama Group in
Kuwait. The thin sections studied and analysed are predominantly from core samples but supplemented
with a small number of ditch cuttings where core was not available. The sample interval was irregular as
the thin sections were originally chosen for reservoir parameter studies that included petrography,
microfacies, porosity and permeability.
Three major bio-assemblages (defining local biozones) can be identified and approximate the Makhul
Formation – radiolarite assemblage of the restricted platform muddy limestones; the Minagish Formation
and Ratawi Limestone Member – calcareous algae / foraminiferal assemblage of shallow shelf, clean
carbonates including oolite / grainstone shoals; and the Ratawi Shale Member – foraminiferal assemblage
of the mixed clastic and carbonate sedimentary environment.
Within these three major bio-assemblages a number of subsidiary biofacies subdivisions, temporal and
spatial, can also be identified. This allows the recognition of vertical stacking patterns and depositional
cyclicity, as observed in the core description and petrographic microfacies studies, of this important
hydrocarbon bearing interval.

2. 74th
EAGE Conference & Exhibition incorporating SPE EUROPEC 2012
Copenhagen, Denmark, 4-7 June 2012
Introduction
The Makhul, Minagisha 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.
This study presents the applied micropalaeontology technique of biofacies analysis (thin sections of
ditch cuttings and core plus routine washing preparation of cuttings). It 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.
Lithostratigraphy
The shallow marine carbonate sediments of the Makhul, Minagish and Ratawi formations (Al-Fares et
al., 1998) form the lower part of the Thamama Group as defined in Saudi Arabia (Steineke and
Bramkamp, 1952). It is underlain by the Hith Anhydrite Formation and the study interval top is a
major temporal hiatus separating the Early Valanginian from the Late Hauterivian – the Late
Valanginian Unconformity, KSB 40 of Sharland et al. (2002) (Figure 1).
Figure 1 The stratigraphy of the Makhul, Minagish and Ratawi formations in Kuwait.
The three formations in Kuwait are informal lithostratigraphical units defined and dated by calibration
with surface exposures and wells in neighbouring Saudi Arabia, Iraq and Iran (Steineke & Bramkamp,
1952: Owen & Nasr, 1958; Dunnington et al., 1959: Hosseini & Conrad, 2008).
Previous biofacies work
This study was aided by the substantial number of helpful taxonomic, stratigraphical and
palaeoenvironmental references that reflect the great deal of attention given to carbonate thin section

3. 74th
EAGE Conference & Exhibition incorporating SPE EUROPEC 2012
Copenhagen, Denmark, 4-7 June 2012
micropalaeontology in the Middle East during the last 50 plus years (Simmons (ed), 1994: Hughes,
2005). The available historical biostratigraphical and biofacies data for the Makhul, Minagish and
Ratawi formations of Kuwait however, are not substantial.
Method
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, originally used for carbonate reservoir parameter
characterization, 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.
Bioclast components
The biocomponents identified are environmentally sensitive and their presence or absence, their
distribution and number and stratigraphical variation contribute to the recognition and delineation
of biozones and biofacies.
Figure 2 The depositional model and biozones of the Makhul, Minagish and Ratawi formations in
Kuwait.

4. 74th
EAGE Conference & Exhibition incorporating SPE EUROPEC 2012
Copenhagen, Denmark, 4-7 June 2012
These biocomponents comprise benthonic foraminifera – lituolids, miliolids and small calcareous
genera, together with calcareous algae, sponge spicules, radiolaria, ostracods, calpionellids and
macrofossils (fragments) such as corals, serpulids, molluscs (rudists, bivalves and gastropods),
echinoid debris and bryozoans (Figure 2).
Biofacies layers and palaeoenvironment
The assemblages are dominated by benthonic foraminifera, echinoid and bivalve debris and
calcareous algae. Three major bio-assemblages (defining local biozones) can be identified and
approximate the Makhul Formation – radiolarite assemblage of the restricted platform muddy
limestones, the Minagish Formation and Ratawi Limestone Member – calcareous algae / foraminiferal
assemblage of shallow shelf, clean carbonates including oolite / grainstone shoals, and the Ratawi
Shale Member – foraminifera assemblage of the mixed clastic and carbonate sedimentary
environment. Within these three major bio-assemblages a number of subsidiary biofacies subdivisions
can also be identified.
Biozone LK1 (Makhul Formation facies)
This biozone characterised by a radiolarite facies comprising calcitised radiolaria, calcispheres and
calcitised sponge spicules, rare Bositra ?buchi and Saccomma spp together with significant amounts
of organic matter is typical of the muddy carbonates of the Makhul Formation west of the Kuwait
Arch. This relatively deep marine assemblage represents a euxinic, low energy, stratified marine
environment below storm wave base of an intra-carbonate shelf basin / embayment. The occurrence
of calpionellids, including Calpionella alpina (Early to Middle Berriasian age) and Tintinopsella
carpathica (Valanginian to Tithonian age) indicates a subtle lateral biofacies subdivision. In wells
west of the Kuwait Arch they are extremely rare or absent while in wells in the offshore area east of
the Kuwait arch in a presumed down-dip depositional regime (deeper water more open marine
connection) they are common.
Associated foraminifera in these lime mudstones are extremely rare – small agglutinants that
includeTextularia spp., Ammobaculites spp., questionable Valvulina spp. and Cyclammina /
Everticyclammina spp. Allochthonous shallower marine species, associated with thin wackstone
and packstone horizons (storm generated turbidites – tempestites), include miliolids and small
lenticulinids together with small fragments of algae, bivalves and echinoderms. This biozone, both
west and east of the Kuwait Arch, can be divided into two sub-biozones; a lower sub-biozone
characterized by the virtual absence of an in-situ fauna / flora and dominantly lime mudstones and an
upper sub-biozone characterized by a diverse but sparse in number in-situ benthonic and planktonic
fauna / flora and with an upward increase in the occurrence of wackestones and packstones.
Biozone LK2 (Minagish Formation and Ratawi Limestone)
This biofacies comprises a diverse assemblage of echinoid and bivalve debris, calcareous algae
fragments, rare radiolaria, rare ostracods, a few scattered sponge spicules, rare to common
calpionellids and common benthonic foraminifera including rare miliolids, all typical of an open
marine, relatively shallow, carbonate ramp. Biozone LK2 comprises packstones, wackstones and
developments of higher energy regime, clean- winnowed oolitic grainstone shoals, particularly in the
Minagish Formation, and skeletal debris shoals together with uncommon developments of low energy
regime lime mudstones.
Dolomitisation of some intervals has destroyed the original texture together with the contained fauna /
flora while in other intervals the fossils have been leached and the moulds replaced by calcite.
Species recorded include the 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

5. 74th
EAGE Conference & Exhibition incorporating SPE EUROPEC 2012
Copenhagen, Denmark, 4-7 June 2012
variation in assemblage components associated with differences in water depth and energy on a
carbonate shelf; eg. an outer ramp low energy setting biofacies and a shallow water, high energy shoal
biofacies.
Biozone LK3 (Ratawi Shale)
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.
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.
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.
Acknowledgements
This abstract is published 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-Sahalan (Stratigraphy Sub-Team unit
head) and team members Irene Truskowski and Abdel Kadar H. H. Joussef.
References
Al-Fares, A.A., M. Bouman and P. Jeans,1998, A new Look at the Middle-Lower Cretaceous
Stratigraphy, Offshore Kuwait. GeoArabia, 3 (4), 543 - 560.
Dunninghton, H. V., Wetzel, R. and Morton, D. M. 1959. Iraq: Mesozoic and Palaeozoic. Lexique
Stratigraphique International., Asie, Volume III, 10a, CNRS.. Paris
Hosseini, S. A. & Conrad, M. A., 2008. Calcareous algae, foraminifera & sequence stratigraphy of the
Fahliyan Formation at Kuh-e-Surmeh (Zagros Basin) SW Iran.Geologia Croatia, 61/2-3, 215-237.
Hughes, G. W. G. 2005. Calcareous Algae of Saudi Arabian Permian to Cretaceous Carbonates.
Revista Espanola de Micropaleontologia, 37 ( 1), 131 – 140.
Owen, R. M. S. & Nasr, S. N. 1958. The Stratigraphy of the Kuwait- Basra area. In: Habitat of Oil,
AAPG Memoir, 1252 – 1278.
Simmons, M. D. (ed.) 1994. Micropalaeontology and Hydrocarbon Exploration in the Middle East.
British Micropalaeontology Society Series. 243 – 252.
Steineke, M. & Bramkamp, R. A. 1952. Mesozoic rocks of eastern Saudi Arabia (abstract). American
Association of Petroleum Geologists, 6, 909.