Sequence stratigraphy and reservoir architecture of the Burgan and Mauddud formations (Lower Cretaceous), Kuwait

Sequence Stratigraphy andReservoir Architecture of theBurgan and Mauddud Formations(Lower Cretaceous), KuwaitChristian J. Strohmenger,1

John C. Mitchell, Howard R. Feldman,Patrick J. Lehmann, andRobert W. BroomhallExxonMobil Exploration Company, Houston,Texas, U.S.A.

Penny E. PattersonExxonMobil Upstream Research Company,Houston, Texas, U.S.A.

Ghaida Al-SahlanKuwait Oil Company, Ahmadi, Kuwait

Timothy M. DemkoUniversity of Minnesota Duluth, Duluth,Minnesota, U.S.A.

Robert W. WellnerExxonMobil Upstream Research Company,Houston, Texas, U.S.A.

G. Glen McCrimmonHibernia Management and DevelopmentCompany, St. John’s, Newfoundlandand Labrador, Canada

Neama Al-AjmiKuwait Oil Company, Ahmadi, Kuwait

ABSTRACT

Anew sequence-stratigraphic framework is proposed for the Burgan andMauddud formations (Albian) of Kuwait. This framework is based on theintegration of core, well-log, and biostratigraphic data, as well as seismic

interpretation from giant oil fields of Kuwait.The Lower Cretaceous Burgan and Mauddud formations form two third-

order composite sequences, the older of which constitutes the lowstand, trans-gressive, and highstand sequence sets of the Burgan Formation. This compositesequence is subdivided into 14 high-frequency, depositional sequences that arecharacterized by tidal-influenced, marginal-marine deposits in northeast Kuwaitthat grade into fluvial-dominated, continental deposits to the southwest.

6Strohmenger, C. J., P. E. Patterson, G. Al-Sahlan, J. C.Mitchell, H. R. Feldman,

T. M. Demko, R. W. Wellner, P. J. Lehmann, G. G. McCrimmon, R. W.Broomhall, and N. Al-Ajmi, 2006, Sequence stratigraphy and reservoirarchitecture of the Burgan and Mauddud formations (Lower Cretaceous),Kuwait, in P. M. Harris and L. J. Weber, eds., Giant hydrocarbon reservoirsof the world: From rocks to reservoir characterization and modeling:AAPG Memoir 88/SEPM Special Publication, p. 213–245.

213

1Present address: Abu Dhabi Company for Onshore Oil Operations, Abu Dhabi, United Arab Emirates.

Copyright n2006 by The American Association of Petroleum Geologists.

DOI:10.1306/1215878M883271

The younger composite sequence consists of the lowstand sequence set ofthe uppermost Burgan Formation and transgressive and highstand sequence setsof the overlying Mauddud Formation. This composite sequence is sand proneand mud prone in southern and southwestern Kuwait and is carbonate pronein northern and northeastern Kuwait. The lowstand sequence set deposits ofthe Burgan Formation are subdivided into five high-frequency depositional se-quences, which are composed of tidal-influenced, marginal-marine deposits innortheastern Kuwait that change facies to fluvial-dominated deposits in south-western Kuwait. The transgressive and highstand sequence sets of the MauddudFormation are subdivided into eight high-frequency, depositional sequences. TheMauddud transgressive sequence set displays a lateral change in lithology fromlimestone in northern Kuwait to siliciclastic deposits in southern and south-western Kuwait. The traditional lithostratigraphic Burgan–Mauddud contact istime transgressive. TheMauddud highstand sequence set is carbonate prone andthins south- and southwestward because of depositional thinning. Significantpostdepositional erosion occurs at the contact with the overlying CenomanianWara Shale.

The proposed sequence-stratigraphic framework and the incorporation of adepositional facies scheme tied to the sequence-stratigraphic architecture allowfor an improved prediction of reservoir and seal distribution, as well as reservoirquality away from well control.

INTRODUCTION

A regional sequence-stratigraphic analysis of the

Lower Cretaceous Burgan and Mauddud formations

was undertaken through a joint study conducted by

ExxonMobil Exploration Company and Kuwait Oil

Company. The study focused on the stratigraphic ar-

chitecture of selectedmajor oil fields throughout Ku-

wait, including the supergiant Greater Burgan field

in southeastern Kuwait, and Raudhatain and Sabiri-

yah fields in northern Kuwait (Figure 1).

Three culminations constitute the supergiantGreat-

er Burgan field: Burgan, Magwa, and Ahmadi. These

three culminations are located near the crest of the

north–south-trending Kuwait arch (Fox, 1961; Ada-

sani, 1965; Brennan, 1990b;Carman, 1996) (Figure 1).

The first well on these structures was drilled in 1938,

followed by wells in 1951 and 1952. Production of

28–368 API oil comes from the Burgan (the major

oil-producing reservoir), the Mauddud (a minor oil-

producing reservoir), and theWara formations (Kauf-

man et al., 1997). The recoverable oil reserves are esti-

mated tobe in the tens of billions of barrels (Christian,

1997).

Raudhatain field was discovered in 1955. It is a

faulted anticlinal dome with production of 28–408API oil from the Ratawi, Zubair, Burgan, and Maud-

dud formations (Milton and Davies, 1965; Adasani,

1967; Al-Rawi, 1981; Brennan, 1990a; Carman, 1996;

Al-Eidan et al., 2001) (Figures 1, 2). The recoverable

oil reserves are estimated to be in the billions of bar-

rels (Christian, 1997).

Sabiriyah field was discovered in 1956. It is an

elongated faulted anticline with production of 28–

328 API oil from the Burgan and Mauddud forma-

tions (Milton and Davies, 1965; Adasani, 1967; Al-

Rawi, 1981; Brennan, 1990a; Carman, 1996; Kaufman

et al., 1997; Al-Eidan et al., 2001) (Figures 1, 2). The

recoverable oil reserves are estimated to be in the bil-

lions of barrels (Christian, 1997).

The Burgan and Mauddud formations are part of

the Wasia Group that overlies the Lower Cretaceous

ThamamaGroup of the Arabian plate (Alsharhan and

Nairn, 1993, 1997). The lower to middle Albian Bur-

gan Formation is themajor oil-bearing sandstone res-

ervoir throughout the Greater Burgan field, as well as

at Raudhatain and Sabiriyah fields innorthernKuwait.

The thickness ranges from approximately 1250 ft

(380 m) at the Greater Burgan field area to approxi-

mately 900 ft (275m) atRaudhatain and Sabriya fields

area (Bou-Rabee, 1996). The overlying upper Albian

Mauddud Formation is a major oil-bearing carbonate

reservoir in northern Kuwait (Al-Anzi, 1995). Thick-

ness of the Mauddud Formation ranges from only a

few feet at theGreater Burgan field andMinagish field

areas (south and southwest Kuwait) to approximately

450 ft (140 m) at the Abdali, Raudhatain, and Sabi-

riyah fields in northern Kuwait (Bou-Rabee, 1996).

214 / Strohmenger et al.

Methodology

The emphasis of this study involved the interpreta-

tionof the sequence-stratigraphic architecturebasedon

correlationof regional stratal surfaces (sequence bound-

aries [SB], transgressive surfaces [TS],maximumflooding

surfaces [MFS], and flooding surfaces [FS]) through-

out Kuwait, as well as on the sequence-stratigraphy-

keyed facies analyses of the Burgan and Mauddud

formations. Approximately 9600 ft (2930 m) of con-

ventional core from 30 wells penetrating the Burgan

Formation and approximately 5000 ft (1520m) of con-

ventional core from35wells penetrating theMauddud

Formation were described sedimentologically. The de-

positional environments interpreted from core were

correlated to well-log signatures and used to develop

the regional sequence-keyed sequence-stratigraphic

framework.More than 100wells were correlatedwith-

in this sequence-stratigraphic context. In addition,

the results from seismic-stratigraphic and biostrati-

graphic interpretations were integrated into this

study.

The identified chronostratigraphic surfaces (SB, TS,

MFS, and FS) were assigned to high-frequency se-

quences (HFS) and numbered sequentially from the

top down; the underlying sequence boundary giv-

ing name to the overlying high-frequency sequence

(Figure 3). TheHFSswere subsequently grouped into the

sequence sets of two third-order composite sequences

(Mitchum, 1977;Mitchum et al., 1977; Vail et al., 1977,

1991;Haqet al., 1987, 1988;Vail, 1987;VanWagoner

et al., 1987, 1988; Sarg, 1988; Haq, 1991; Mitchum

andVanWagoner, 1991; Sarg et al., 1999) (Figure 3).

High-frequency Sequences

High-frequency sequences in the siliciclastic Bur-

gan Formation (Figure 3) are defined by the stacking

patterns and facies distributions. These sequences

may contain lowstand, transgressive, and highstand

FIGURE 1. Location map showing the major oil fields of Kuwait (green) and the wells (black dots) studied.

Sequence Stratigraphy and Reservoir Architecture of Burgan and Mauddud Formations / 215

systems tracts (LST, TST, andHST). Each systems tract

exhibits distinct facies trends, thickness distribu-

tions, and reservoir quality (Strohmenger et al., 2002;

Demko et al., 2003).

The LSTs consist of incised-valley fills (IVF). These

valleys become thinner, as well as more laterally

discontinuous and tidal influenced downdip to the

northeast. Transgressive systems tracts correspond to

retrogradational successions of coarsening-upward,

marginal-marinemudstones and sandstones that grade

intomarine carbonates downdip andmudstone-prone

coastal-alluvial plain deposits updip. Highstand sys-

tems tracts correspond to progadational successions

of coarsening-upward, marginal-marine mudstones

and sandstones that grade updip into mudstone-

prone coastal-alluvial plain deposits (Strohmenger

et al., 2002; Demko et al., 2003).

High-frequency sequences in the carbonate-

dominated Mauddud Formation (Figure 3) are de-

fined by parasequence (PS) stacking patterns, facies

distributions, and microkarst or exposure surfaces.

High-frequency sequences of the Mauddud Forma-

tion may contain TST and HST (Strohmenger et al.,

2002; Demko et al., 2003).

Transgressive systems tracts are generallymoremud

dominated with intercalated sandstones and glauco-

nitic sandstones in the northern Kuwait Raudhatain

and Sabiriyah fields area and grade into siliciclastics

toward the south at Greater Burgan field and toward

the southwest at Minagish field areas. Highstand sys-

tems tracts typically show an upward increase in

grain richness (graining upward) as well as porosity

(Strohmenger et al., 2002; Demko et al., 2003).

Composite Sequences

High-frequency sequences are grouped into se-

quence sets of two third-order composite sequences,

based on the stacking patterns and facies distribu-

tions (Figure 3). Each composite sequence consists

of a lowstand sequence set (LSS), transgressive se-

quence set (TSS), and a highstand sequence set (HSS)

(Strohmenger et al., 2002; Demko et al., 2003).

In the siliciclastic Burgan Formation of Kuwait,

LSSs are characterized by an aggradational stacking

of HFSs dominated by braided fluvial deposits. The

TSS exhibits an overall retrogradational stacking

pattern, dominated by nonmarine facies at the base,

whereas the uppermost HFSs contain increasing

marginal-marinecomponents. TheHSS formsanoverall

progradational succession dominated by marginal-

marine facies, especially in northern Kuwait (Stroh-

menger et al., 2002; Demko et al., 2003).

FIGURE 2. Seismic cross section oriented northwest–southeast showing Raudhatain and Sabiriyah structures andthe interpreted main stratigraphic horizons. Seismic line runs through the center of Raudhatain and Sabiriyah fieldsshown in Figure 1.


TheMauddud TSS shows a lateral change in lithol-

ogy from limestone in northern Kuwait to siliciclas-

tics in southern and southwestern Kuwait. An overall

shoaling-upward or progradational signature char-

acterizes the HSS. Most of the upper HSS is removed

by erosion throughout much of southern and south-

western Kuwait (Strohmenger et al., 2002; Demko

et al., 2003).

BURGAN FORMATION

A regional sequence-stratigraphic analysis of the

Burgan and Mauddud formations reveals that the

traditional lithostratigraphic Burgan-Mauddud con-

tact is a time-transgressive facies boundary (Stroh-

menger et al., 2002; Demko et al., 2003). To define

coeval facies successions in both the Burgan and

Mauddud formations, a chronostratigraphically sig-

nificant regional flooding surface (B100_TS) was de-

fined as the Burgan-Mauddud contact (Figure 3).

Within this chronostratigaphic framework, the up-

permost Burgan and overlying Mauddud formations

form a composite sequence (Figure 3) that becomes

more siliciclastic prone to the southwest and carbon-

ate prone to the northeast. A second composite se-

quence encompasses the rest of the underlying Burgan

Formation (Figure3). This composite sequence is dom-

inated by marginal-marine deposits to the northeast

and nonmarine deposits to the southwest.

The Burgan Formation, as defined in this study,

comprises 19 HFSs (Figure 3). Each of these HFSs

FIGURE 3. Mauddud–Burgan sequence-stratigraphic framework showing the lower and upper third-order compositesequences, as well as the interpreted high-frequency depositional sequences (Raudhatain field type well RA-G). GR =gamma-ray log; MD = measured depth (feet); RES = resistivity log; NEU = neutron porosity log; DENS = density log.


contains LSTs, TSTs, andHSTs, eachwithdistinct facies

trends, thickness distributions, and reservoir quality.

The LSTs of these sequences consist of IVF. These

valleys become thinner, as well as more laterally dis-

continuous and tidal influenced downdip to the

northeast. The TSTs of the Burgan sequences display a

systematic downdip to updip change from marine

carbonates to marginal-marine mudstones and sand-

stones to mudstone-prone alluvial- and coastal-plain

deposits. TheHSTs are dominated bymarginal-marine

sandstones and mudstones downdip and alluvial-

and coastal-plain mudstones and sandstones updip.

The shorelines in these highstands trend northwest–

southeast and are best developed in the northern

Raudhatain and Sabiriyah fields area.

The primary reservoirs in the Burgan Formation

are fluvial and tidal deposits that formed within the

incised valleys (Figure 4). Shoreline sandstones in the

TSTs and HSTs are also potential reservoirs (Figure 4).

However, thesemarginal-marine sandstoneshave low-

er porosity and permeabilities because of their finer

grained and increased clay matrix due to bioturba-

tion. In summary, the sequence-stratigraphic analy-

sis of the Burgan Formation provides an improved

understandingof the spatial and temporaldistribution

of reservoirs that can be used to address exploration-

scale to production-scale issues.

In general, the Burgan Formation is a classic re-

gressive-transgressive-regressive package. It is domi-

nated by sandstone-prone fluvial deposits at its base

FIGURE 4. Sequence-keyed depositional facies models for the Burgan Formation. In these models, the lowstand systemstract consists of incised-valley deposits, whereas the trangressive and highstand systems tracts are composed of wave-dominated shoreface depositional systems. GR = gamma-ray log.


and top andmarginal-marinemudstones, sandstones,

and limestones in the middle parts to the northeast.

The Burgan Formation is bounded at its top by a re-

gional flooding surface, referred to as the Burgan trans-

gressive surface B100_TS (Figure 3). In general, this

boundary is marked by a change from blocky, high

net/gross, fluvial-dominated sandstones of the Bur-

gan Formation below to low net/gross marine mud-

stones, sandstones, and limestones of the Mauddud

Formation above. Within this context, fine-grained

siliciclastics, traditionally included at the top of the

Burgan Formation to the south, are assigned to the

clasticmemberof theMauddudFormation.ThisMaud-

dud clasticmember occurs above the Burgan transgres-

sive surface B100_TS, a regional flooding surface, de-

fined as the top of the Burgan Formation and beneath

the carbonate strata traditionally included within the

Mauddud Formation (Mauddud carbonate member).

Lithofacies and Depositional Environments

Within the Burgan Formation, 22 lithofacies were

identified and define 6 distinct facies. The physical

criteria used to delineate the individual lithofacies in

this study include grain size, composition, sorting,

grading, physical and biogenic sedimentary struc-

tures, stratal boundaries, presence or absence of clay

drapes, organic-rich drapes, organic debris, and dia-

genetic features. For ease of description, each litho-

facies was classified into six categories based on mud

content and apparent reservoir quality. The six cate-

gories range from well-sorted, very clean sand (litho-

facies 1: excellent reservoir quality) tomudstone (litho-

facies 5: very poor reservoir quality) and, ultimately,

to coal (lithofacies 6). In addition, lithofacies were

assigned an alphabetic qualifier to account for subtle

differences in grain size,mud content, dominant sedi-

mentary structures, and type and extent of bioturba-

tion. Trace fossil assemblages were used to infer en-

vironments of deposition,which are based onmodels

proposed by Pemberton et al. (1992a, b). In addition,

our regional database includes two lithofacies that

were not observed in the Burgan strata. They are litho-

facies 3A, coarsening-upward, bioturbatedmudstone

to sandstone; and lithofacies 4C, bioturbated to pla-

nar laminated mudstone to sandstone.

Lithofacies 1A: Trough Cross-bedded Sandstone

Lithofacies 1A (Figure 5A) consists of poorly to

moderately sorted, fine-grained to coarse-grained sand-

stone.Thedominant sedimentary structures are trough

cross-bedding and current-ripple cross-lamination.

Large plant fossils, including compressed branches

and leaves, are common. Mudstone drapes and bio-

turbation are uncommon. Grain size trends are typi-

cally fining upward. Small-scale fining-upward beds

are 0.2–2 ft (0.06–0.6 m) thick and typically asso-

ciated with individual trough cross-bed sets. Larger-

scale, fining-upward trends range from 20 to 50 ft

(6 to 15 m) of thickness.

The cross-bedding and grain-size trends all indicate

deposition in a low-sinuosity fluvial setting. Some

fining-upward trends suggest sedimentation in sandy

point bars. This lithofacies occurs primarily in incised

valleys and in updip braid-plain deposits.

Lithofacies 1B: Trough Cross-bedded Sandstonewith Minor Clay Drapes

Lithofacies 1B (Figure 5B) consists of poorly tomod-

erately sorted, fine-grained to coarse-grained sand-

stones that possess sparse to common clay drapes and

thick-thin couplets. Sedimentary structures are domi-

nated by trough- and current-ripple cross-bedding.

Small mudstone and siderite clasts may be locally

abundant. Small-scale, grain-size trends are typically

fining upward. Large-scale, grain-size trends are ei-

ther coarsening upward or fining upward. Large plant

fossils, such as compressed sticks and leaves, may be

common.Bioturbation is sparse tomoderate.Common

burrow types are horizontal sand-filled tubes with a

circular cross section, approximately 1 cm (0.4 in.) in

diameter (Planolites).

The clay drapes and thick-thin couplets indicate

that some tidal influence occurred during deposition.

This lithofacies occurs at the fluvial to tidal transi-

tion in IVF and at the top of coarsening-upward tidal

bars.

Lithofacies 1C: Current-rippled,Cross-laminated Sandstone

This lithofacies (Figure 5C) consists of well-sorted,

very fine-grained to fine-grained sandstone. Sedimen-

tary structures are characterized by current-ripple

cross-laminationwithminor small-scale troughcross-

bedding. Clay drapes are sparse to absent. This facies

occurs in beds typically a few feet thick with no grain-

size trends. Bioturbation is uncommon. Small plant

fossils, such as small leaves and fine plant fragments,

are common.

Lithofacies 1C occurs in a range of environments.

Where it is associated with coastal-plain deposits, it


represents splays and channel levees. Within distal

incised valleys, this lithofacies represents sedimen-

tation in tidal channels.

Lithofacies 2A: Clay-draped, Current-rippled toLaminated Sandstone

Lithofacies 2A (Figure 6A) consists of well-sorted,

very fine- to fine-grained sandstone. Sedimentary

structures include current-ripple cross-laminations

and minor horizontal laminations, with abundant

thin (<1-mm; <0.04-in.) clay and organic drapes, com-

monly on ripple foresets. Some laminations exhibit

centimeter-scale cyclicity in mud-sand couplets. Sider-

ite cement is common. Bedsets typically fine upward.

Bioturbation is uncommon to moderate and consists

of a low diversity of burrows, including Planolites,

Skolithos, andArenicolites. Fine plant debris and amber

flakes are common.

This lithofacies represents deposition in tidal creeks

or tidal flats.

Lithofacies 2B: Clay-draped, Current-rippled toTrough Cross-bedded Sandstone

Lithofacies 2B (Figure 6B) consists of very fine-

to fine-grained sandstone. The dominant sedimen-

tary structures are current-ripple cross-laminations

to small-scale, trough–cross-bedding with abundant

thin (�1-mm) clay and organic drapes, commonly

on ripple and trough foresets. Bedsets may distinctly

coarsen upward. Bioturbation is sparse to moderate

FIGURE 5. Siliciclastic lithofacies 1, slabbed core photographs. (A) Lithofacies 1A: trough cross-bedded sandstone.(B) Lithofacies 1B: trough cross-bedded sandstone with minor clay drapes. (C) Lithofacies 1C: current-rippled, cross-laminated sandstone, which is interbedded with small-scale, trough cross-beds.


and is characterized by the low diversity of burrows

(mostly Planolites). Fine plant debris and amber flakes

are locally abundant.

This lithofacies is inferred to have been deposited

as subtidal bars in estuaries.

Lithofacies 2C: Clay-draped, HorizontallyLaminated Sandstone

Lithofacies 2C (Figure 6C) is dominated by hori-

zontal laminations, minor current ripples with abun-

dant thin (�1-mm) clay and organic drapes that de-

fine horizontal laminations. Most laminations show

some centimeter-scale cyclicity ofmud-sand couplets.

Lamina and bedsets typically fine upward. Biotur-

bation is sparse to moderate and is characterized by

Planolites, Palaeophycus, Arenicolites, Skolithos, and

Cylindrichnus. Fine plant debris and amber flakes and

pebbles may be locally abundant.

This lithofacies is interpreted to have been depos-

ited on tidal flats and in associated low-energy, tidal

point bars.

Lithofacies 2D: Glauconitic Sandstone

This lithofacies (Figure 6D) consists of fine-grained

to medium-grained sandstone with abundant grains

of glauconite (which are invariably coarser grained

than those of the detrital quartz). Bioturbation ismod-

erate to extensive and is characterized by Thalassi-

noides,Asterosoma, Planolites,Teichichnus, Palaeophycus,

and Scolicia. Siderite concretions are common, par-

ticularly associated with Thalassinoides burrows. This

facies is almost always cemented by calcite and grades

into overlying limestone beds. Mollusk shells and

shell fragments are common.

Lithofacies 2D represents deposition in the distal

parts of low-energy, marine shorelines.

Lithofacies 3B: Bioturbated, Muddy Sandstone

This lithofacies (Figure 7A) consists of poorly to

moderately well-sorted, upper fine-grained to lower

medium-grained muddy sandstone. Bioturbation is

typically extensive and is characterized by multiple

tiers of Thalassinoides, Teichichnus, Asterosoma, Pla-

nolites, Palaeophycus, Skolithos, and Cylindrichnus.

This lithofacies represents deposition along brack-

ish, estuarine, and marine low-energy shorelines.

Lithofacies 3C: HummockyCross-bedded Sandstone

Lithofacies 3C (Figure 7B), which is not often ob-

served in the Burgan Formation, consists of mod-

erately well- to very well-sorted, very fine-grained to

FIGURE 6. Siliciclastic lithofacies 2, slabbed core photographs. (A) Lithofacies 2A: clay-draped, current-rippled tolaminated sandstone. (B) Lithofacies 2B: clay-draped, current-rippled to trough cross-bedded sandstone. (C) Lithofacies2C: clay-draped, horizontally laminated sandstone. (D) Lithofacies 2D: glauconitic sandstone that has been extensivelybioturbated by Teichichnus (Te) and Planolites (Pl) burrows.


lower fine-grained sandstone. The dominant sedi-

mentary structures are hummocky, cross-stratified

beds with wave-rippled and bioturbated upper sur-

faces. Mudstone beds as much as several centimeters

in thickness are only rarely preserved between hum-

mocky bedsets. Bioturbation is typically absent to

sparse, but may increase upward with moderate bur-

rowing at the top of some bed sets. Trace fossils rec-

ognized include Planolites, Palaeophycus, and uncom-

mon Ophiomorpha.

This lithofacies was most likely deposited in ma-

rine, proximal lower shoreface settings.

Lithofacies 3D: Interlaminated Sandstone,Silt, and Shale

Lithofacies 3D (Figure 7C) consists of interlami-

nated, very fine-grained sandstone, silt, and shale.

Sedimentary structures include horizontal bedding,

starved current-ripple cross-lamination, and uncom-

mon syneresis cracks. Depositional strata range from

mostly clay to mostly sand, but are characterized by

sand and mud couplets, thick and thin couplets, and

centimeter-scale cycles of thickening and thinning

sand laminae. Bioturbation is sparse tomoderate and

include trace fossils of Planolites, Palaeophycus, Sko-

lithos, and Cylindrichnus. Plant debris, amber, and

siderite-cemented bands are common.

This lithofacies represents deposition on proximal

(sandy) todistal (muddy) tidal flats, and thecentimeter-

scale cycles are interpreted as neap-spring tidal cycles.

Lithofacies 3E: Current-rippled, InterbeddedSandstone and Mudstone

Lithofacies 3E (Figure 7D) consists of interbedded,

lower medium-grained sandstone and mudstone.

Sedimentary structures are dominated by horizontal

lamination and current-ripple cross-lamination, with

uncommon syneresis cracks. Bioturbation is sparse

tomoderate and is characterizedmostly by Planolites,

Palaeophycus, Skolithos, andCylindrichnus. Plant debris

and amber are locally abundant as well as siderite-

cemented bands.

This lithofacies is interpreted to have been depos-

ited in tidal flats and distal tidal bars.

Lithofacies 3F: Calcareous, Bioturbated Sandstone

This lithofacies (Figure 8A) consists of fine-grained

to lower medium-grained sandstone. Bioturbation

is typically extensive (churned). Mollusk shells, shell

fragments, and foraminifera are locally abundant.

FIGURE 7. Siliciclastic lithofacies 3, slabbed core photographs. (A) Lithofacies 3B: bioturbated, muddy sandstonecontaining shell fragments. (B) Lithofacies 3C: hummocky cross-bedded sandstone. (C) Lithofacies 3D: interlaminatedsandstone, silt, and shale. (D) Lithofacies 3E: current-rippled, interbedded sandstone and mudstone.


This facies is tightly cemented by calcite and grades

into limestone beds above or below.

This lithofacies represents deposition in shallow-

marine shoreline or shoreface settings adjacent to

subtidal carbonate facies.

Lithofacies 3G: Wave-rippled Sandstone

Lithofacies 3G (Figure 8B) consists of well-sorted,

very fine-grained to fine-grained sandstone. Sedimen-

tary structures consist ofwave-ripple cross-laminations.

Clay drapes are common between ripple laminae and

laminae sets. Bioturbation is sparse to moderate and

includes Astersoma, Teichichnus, and Planolites burrows.

This lithofacies is interpreted to have formed in

distal, lower shoreface settings.

Lithofacies 3H: Carbonaceous, Muddy Sandstone

Lithofacies 3H (Figure 8C) consists of very fine- to

fine-grained sandstone with abundant clay and or-

ganic drapes ranging from 5 to 10 mm (0.2 to 0.4 in.)

in thickness.Organic layers range from1mm(0.04 in.)

to a few centimeters in thickness. Sedimentary struc-

tures are dominated by horizontal lamination and

current-ripple cross-lamination. Bioturbation is un-

common to slight and comprises Planolites burrows

and rootworking. Large plant fossils and amber are

very abundant.

This lithofacies represents deposition in flood-

plain, crevasse splay, or levee settings.

Lithofacies 4A: Heterolithic Siltstone to Mudstone

This lithofacies (Figure 9A) consists mostly ofmud-

stone with siltstone to very fine-grained sandstone

stringers (>80% mudstone). Sedimentary structures

include parallel-lamination, silt stringers, uncom-

mon syneresis cracks, and starved current-ripple cross-

lamination. Bioturbation is uncommon to slight and

is characterized by Planolites burrows. Plant fossils

and amber are common to abundant.

Lithofacies 4A is interpreted to represent depo-

sition in flood-plain and abandoned channel-fill

settings.

Lithofacies 4B: Bioturbated to Wave-rippledSandstone to Mudstone

This lithofacies (Figure 9B) is composed of lower

very fine-grained sandstone to siltstone to clay. Sedi-

mentary structures include isolated to amalgamated

FIGURE 8. Siliciclastic lithofacies 3, slabbed core photographs. (A) Lithofacies 3F: calcareous, bioturbated sandstonecontaining shell fragments. (B) Lithofacies 3G: wave-rippled sandstone. (C) Lithofacies 3H: carbonaceous, muddysandstone.


wave-ripple cross-laminations. Bioturbation is slight

to extensive (churned) and is characterized by Aste-

rosoma,Teichichnus,Thalassinoides, Planolites, Palaeo-

phycus, Scolicia, and Skolithos. Fine plant fragments

and mollusk shells are uncommon.

This lithofacies is interpreted as deposition in ma-

rine, distal lower shoreface settings.

Lithofacies 4D: Bioturbated Mudstone

Lithofacies 4D (Figure 9C) is mostly mudstone,

but may grade vertically into siltstone. Bioturbation

is moderate to extensive (churned) and is charac-

terized by mostly indistinct burrows with some dis-

cernible Planolites, Teichichnus, and Thalassinoides

burrows.

This lithofacies is inferred to have been deposited

in offshore to lower shoreface settings.

Lithofacies 4E: Laminated Siltstone

This lithofacies (Figure 9D) is composed of hori-

zontally laminated to wavy laminated siltstone. Bio-

turbation is uncommon to slight and is character-

ized by small (<5-mm; <0.2-in.) indistinct horizontal

burrows.

Lithofacies 4E represents deposition in lacustrine,

flood-plain, pond, and abandoned-channel settings.

Lithofacies 5A: Laminated Gray Shale

Lithofacies 5A (Figure 10A) is composed of dark-

gray, horizontally laminated shale. Bioturbation is

slight to moderate and is characterized by Planolites,

Teichichnus, sand-filled Chondrites, and sparse Zoo-

phycos burrows. Bivalve and gastropod shells range

from sparse to common, and small plant fragments

are uncommon.

This lithofacies is interpreted tohavebeendeposited

in offshore marine settings, below storm-wave base.

Lithofacies 5B: Carbonaceous Mudstone

Lithofacies 5B (Figure 10B) is composed of car-

bonaceous, horizontally laminatedmudstone,which

commonly displays postdepositional, compactional

slickensides. Bioturbation is slight to moderate and

is characterized mostly by rootworking (Figure 11A).

Large leaves and amber (Figure 11B, C) are very

abundant.

This lithofacies represents deposition in clastic

swamp and abandoned-channel settings.

Lithofacies 5C: Laminated Dark Gray Shale

Lithofacies 5C (Figure 10C) is composed of very

dark-gray, horizontally laminated shale. Bioturbation

is uncommon to slight and is characterized by small

FIGURE 9. Siliciclastic lithofacies 4, slabbed core photographs. (A) Lithofacies 4A: heterolithic siltstone to mudstone.(B) Lithofacies 4B: bioturbated to wave-rippled sandstone to mudstone. This core interval has been extensively bio-turbated by Teichichnus (Te), Asterosoma (As), and Planolites (Pl) burrows. (C) Lithofacies 4D: bioturbated mudstone. Theupper interval of this core has been extensively bioturbated by Teichichnus (Te) burrows. (D) Lithofacies 4E: laminatedsiltstone.


Planolitesburrows. Large leaves, sticks,

and amber are very abundant.

This lithofacies is interpreted to

represent deposition in lacustrine,

abandoned channel, and flood-

plain settings.

Lithofacies 6: Coal

This lithofacies (Figure10D) is com-

posed exclusively of coal.

Some coals are rooted and repre-

sent peat swamps. Other coals are

composed of allochthonous plant

detritus and formed in abandoned

channels to estuarine settings with

low clastic input.

Facies, Facies Associations,Depositional Environments, and

Reservoir Quality

The22 lithofacies are grouped into

6 distinct facies. These groupings are

either spatially reoccurring groups

of different lithofacies or thick oc-

currences of the same lithofacies. In

FIGURE 10. Siliciclastic lithofacies 5 and 6, slabbed core photographs. (A) Lithofacies 5A: laminated gray shale.(B) Lithofacies 5B: carbonaceous mudstone. (C) Lithofacies 5C: laminated dark-gray shale. (D) Lithofacies 6: coal.

FIGURE 11. Slabbed core photographs of (A) rooted horizon, (B) amber, and(C) fragment of amber.


turn, the six facies are grouped into two unique facies

associations. The facies associated with each are mu-

tually exclusive (Figure 4).

Facies Association I

Facies association I (Figure 4) consists of four

unique facies, which are interpreted as the normal,

shoaling-upward facies succession of a low-energy,

wave-dominated, shoreline (sensu Walker and Plint,

1992). This facies association is the basic building

block of highstand and transgressive deposits in the

Burgan Formation. The typical idealized vertical

facies succession in this facies association from top

to base is

� carbonaceous facies (lithofacies 1C, 3H, 5B, and

6): coastal-plain and backshore� bioturbated to stratified sandstone facies (litho-

facies 3B and 3C): proximal lower shoreface� bioturbated to interstratifiedmudstones and sand-

stones (lithofacies 2D, 3F, 3G, 4B, and 4D): distal

lower shoreface� bioturbated mudstone facies (lithofacies 5A):

offshore

Lithofacies association I is interpreted to represent

the deposits of a low-energy shoreline environment.

Wave-dominated shoreface sandstones are oriented

along a northwest-southeast belt and primarily occur

in northeastern Kuwait. Shoreface deposits change

facies tomarginal-marine sandstones andmudstones

and offshoremudstones in a northeast transect. They

change facies updip to coastal-plain deposits, which

dominate the southwestern region of Kuwait. The

shoreface deposits are interpreted to represent a low-

energy environment based on the paucity of high-

energy stratification and the presence of strata that

have been moderately to intensely bioturbated by

trace fossil assemblages indicative of open-marine

conditions.

In general, reservoir quality ranges frommoderate

in deposits of the proximal lower shoreface to poor in

the distal lower shoreface and offshore strata. Al-

though sandstone reservoirs may exist within small

(<0.5-km [<0.31-mi]-wide) fluvial channels on the

coastal-plain, for themost part, the coastal-plain part

of this succession is mud prone and nonprospective.

Facies Association II

Facies association II (Figure 4) consists of two

unique facies, which are interpreted as the normal

updip to downdip facies variation in an incised-

valley system (sensu Van Wagoner et al., 1990). The

typical idealized Burgan updip to downdip facies

succession and associated lithofacies are

� cross-stratified sandstone facies (lithofacies 1A

and 1C): fluvial-dominated valley fill� heterolithic tidal facies (lithofacies 1B, 2A, 2B,

2C, 3D, 3E, and 4A): tidal-dominated valley fill

The incised valleys, identified in this study, typi-

cally trend southwest to northeast across Kuwait and

are perpendicular to somewhat oblique to the shore-

line trend of the underlying highstand and overlying

transgressive deposits. Deposits of the incised valley

are characterized by fluvial-dominated facies in up-

dip regions to the southwest and tidal-dominated

facies in the distal regions to the northeast. The

fluvial facies are interpreted as low-sinuosity, braided-

stream deposits based on the prevalence of fining-

upward, fine-grained to coarse-grained, trough–cross-

beds and bedsets. The fluvial strata change facies

downdip to tidal-influenced deposits that possess more

heterolithic lithofacies, indicative of fluctuation-energy

conditions.

Reservoir quality is excellent in the braided fluvial

strata and in the updip parts of themixed fluvial-tidal

systems.However, reservoir quality rapidly diminishes

in the seaward direction as the valley systems thin

and become more mudstone prone.


Nineteen high-frequency depositional sequences

were interpreted within the Burgan Formation, as

defined in this study (Figure 3). From bottom to top,

these are B900, B850, B800, B750, B725, B700, B650,

B600, B550, B500, B450, B400, B350, B300, B250,

B200, B150, B125, and B100 (LST).

In the nonmarine to marine intervals of the

Burgan Formation, high-frequency sequence bound-

aries are interpreted as abrupt vertical changes in

stratal stacking pattern or abrupt basinward shift in

environments of deposition. In the downdipposition,

high-frequency sequence boundaries are evident as

abrupt changes from coarsening-upward marginal-

marine parasequences to blocky fluvial-tidal deposits.

Updip, these sequence boundaries can be traced into

an abrupt change from interpreted low net/gross

coastal-alluvial plain (transgressive or highstand) de-

posits (below) into blocky fluvial (lowstand) deposits

(above; Figure 12). Downdip and laterally, the se-

quence boundaries and transgressive surface become

coincident. However, in the most distal sequences in


FIGURE 12. Regional cross section showing facies distribution and sequence-stratigraphic framework of the Burgan Formation. Note that the fluvial-dominatedsandstones of the incised-valley fills, which constitute the lowstand systems tracts, thicken toward the south in the vicinity of the Greater Burgan field area.The overlying Mauddud clastic member and Mauddud carbonate member also display thickness variations along the depositional transect. The detailedsequence-stratigraphic framework for the Mauddud Formation is shown in Figures 22 and 23. GR = gamma-ray log; MD = measured depth (feet); RES = resistivitylog; DT = sonic log; NEU = neutron porosity log; DENS = density log.

Sequen

ceStratig

raphyan

dReserv

oir

Arch

itecture

ofBurgan

andMau

ddudForm

ations

/227

the BurganFormation, anonlap-

ping successionof carbonates ap-

pears tomark adepositional shelf

break and downdip limit of clas-

ticprogradation ineachsequence.

In more marine-dominated

parts of the Burgan Formation,

the TSs are interpreted at the ver-

tical change from prograding

to retrograding marine parase-

quences. Inmoremedial settings,

these surfaces coincide with the

vertical facieschange, fromblocky,

fluvial-tidal deposits below to

retrograding marine parase-

quences above. In more proxi-

mal (updip) settings, the TSs are

placed at thevertical change from

blocky fluvial-tidal below to low

net/gross coastal- and alluvial-

plain deposits above (Figure 12).

The MFSs of these sequences

are interpreted at major marine

incursions marked by a change

from retrograding to prograd-

ing stacking of marine parase-

quences. In the downdip parts

of themost distal sequences,ma-

rine limestones occur beneath in-

terpreted MFSs (Figure 12).

Lowstand systems tracts pri-

marily consist of incised-valley

systems that are filled by tidal-

influenced sandstones andmud-

stones in the downdip regions

and braided fluvial sandstones

in updip regions (Figure 13A). In

the low-relief, HFSs identified

within theBurganFormation,on-

lapping lowstand clastic wedges,

as well as basin-floor lowstand

fans are absent. Clastic lowstand

deposition appears limited to

IVF. The valleys become thinner

and more discontinuous down-

dip (Figure 13B) and do not ap-

pear to extend to the maximum

downdip progradational limit of

underlying sandstone-prone

highstands. These relationships

strongly suggest that transgres-

sive erosion has modified theFIG

URE13.Depositionalenvironmentandisopach

mapsofalowstandsystemstract

intheBurg

anForm

ation.These

mapsare

interp

retedfrom

thesequence

-stratigraphic

architecture

oftheB100high-frequency,depositionalsequence

,whichistheupperm

ost

lowstandsystemstract

inthelowstandsequence

setofthe

upper,third-ord

erco

mposite

sequence

.(A)Thelowstanddeposits

fillincisedvalleysandare

composedoftidal-influence

dstrata

inthedowndip

positionsandfluvial-

dominatedstrata

intheupdip

regions.(B

)Incisedvalleysbeco

methinnerandmore

disco

ntinuousdowndip.IVF=incised-valleyfills;HST=highstandsystemstract.


primary distribution and thickness patterns in the

most distal (downdip) parts of the Burgan incised-

valley systems.

The TSTs correspond to retrogradational succes-

sions of coarsening-upward strata and display a

systematic downdip to updip change from marine

carbonates, to marginal-marine mudstones and sand-

stones, to mudstone-prone alluvial- and coastal-plain

deposits.

Highstand systems tracts correspond to progada-

tional successions of coarsening-upward, dominantly

marginal-marine sandstones and mudstones down-

dip and alluvial- and coastal-plain mudstones and

sandstones updip (Figure 14). The shorelines in these

highstands trend northwest–southeast and are best

developed in northern Kuwait.

Composite Sequences

The 19 HFSs identified within the Burgan Forma-

tion define four distinct sequence sets that form parts

of two composite sequences. The basal four HFSs

(B900, B850, B800, and B750) stack in an overall ag-

gradational succession and form the LSS of the

lower Burgan composite sequence (Figure 3). This

aggradational sequence set is dominated by braided

fluvial deposits that contain few mudstone breaks

FIGURE 14. Paleogeographic map showing the depositional environments of a highstand systems tract in the BurganFormation. This paleogeographic map is interpreted from the sequence-stratigraphic architecture of the B600 high-frequency, depositional sequence, which is a highstand systems tract in the transgressive sequence set of the lower,third-order composite sequence.


(Figure 12). The basal aggradational sequence set is

overlain by six HFSs (B725, B700, B650, B600, B550,

and B500) that stack in an overall retrogradational

pattern, which constitutes the TSS of the lower

Burgan composite sequence (Figure 3). In the Raud-

hatain and Sabiriyah field area in northern Kuwait,

the basal HFSs in this retrogradational succession are

dominated by nonmarine facies, whereas the upper-

most sequences contain increasing marginal-marine

components (Figure 12). The next four HFSs (B450,

B400, B350, and B300) stack in an overall prograda-

tional succession and comprise the HSS of the lower

Burgan composite sequence (Figure 3). In the north-

ern fields area, these sequences are dominated by

marginal-marine highstand deposits (Figure 12). The

uppermost five sequences (B250, B200, B150, B125,

and the LST of B100) stack in an aggradational pattern

and form the LSS of the upper Burgan and Mauddud

upper composite sequence (Figure 3). In the northern

fields area, these HFSs consist of alternating non-

marine LSTs and marginal-marine TSTs and HSTs

(Figure 12).

Based on this delineation of sequence sets, a com-

posite sequence boundary B900_SB is placed at the

base of the Burgan Formation (Figure 3). In general,

the overlying aggradational, retrogradational, and

progradational sequence sets correspond to the LSS,

TSS, and HSS of the lower composite sequence. It

should be noted, however, that the high-frequency

transgressive surface B725_TS and the high-frequency

maximum flooding surface B500_MFS are used as

composite TS and MFS, respectively, for the lower

composite sequence (Figures 3, 12). The uppermost

aggradational sequence set is interpreted as a second

LSS. The composite transgressive surface B100_TS is

interpreted as the TS of this composite sequence, with

strata in the overlying Mauddud Formation, form-

ing the TSS and the HSS of the younger composite

sequence.

In general, the various sequence sets are thicker

and more sandstone prone in the southwest area of

Kuwait and thinner andmoremudstone prone in the

northeast (Figures 12–14).

Reservoir Quality

Reservoir quality of the Burgan Formation is closely

related to the interpreted depositional environ-

ments. Fluvial-dominated sandstones, which include

lithofacies 1A and 1C, possess the best reservoir-

quality attributes. These lithofacies types have av-

erage porosity and permeability values of 25% and

1600 md, respectively. Tidal-dominated sandstones,

which encompass lithofacies 1B, 2A, 2B, 2C, and 2F,

exhibit moderately good reservoir-quality properties.

Theyhave average porosity andpermeability values of

23% and 270 md, respectively. The marginal-marine

deposits, which include lithofacies 2A, 2E, and 3B,

generally display poorer reservoir quality as a result

of variable extents of bioturbation. Average porosity

and permeability values for these lithofacies are 19%

and 10 md, respectively.

Reservoir Quality Distribution

Stratal distributions, thickness variations, and re-

gional facies architecture of the Burgan systems tracts

can be interpreted from isopach and paleogeograph-

ic maps of these intervals (Figures 13, 14). High-

frequency lowstands of the Burgan Formation consist

of fluvial and tidal deposits that filled incised valleys.

In general, the incised valleys become thinner, nar-

rower, and more tidal influenced downdip to the

northeast (Figure 13). Conversely, the valleys become

thicker, more widespread, and more fluvially influ-

enced updip to the south and southwest (Figure 13).

High-frequency highstands of the Burgan consist of

shoreline deposits, which, in general, trend north-

west–southeast,withmoremarine facies to thenorth-

east and more nonmarine facies toward the south-

west (Figure 14).

The sequence-stratigraphic framework presented

in this paper provides an improved understanding of

the distribution of sandstone-prone lowstands and

marginal-marine highstands in each of the 19 HFSs

identified within the Burgan Formation (Figure 12).

Furthermore, someadditionalnewplay conceptswere

identified. Within the context of the newMauddud–

Burgan boundary, distinct isolated incised-valley sys-

tems in the clastic member of the Mauddud Forma-

tion can be defined. Within the Burgan proper, the

possibility exists that marginal-marine shorelines in

the TSSsmay also contain hydrocarbons off the flank

of structures. This combined structural-stratigraphic

trap would depend onmudstone-prone coastal-plain

deposits in each sequence acting as the updip lateral

seal and marine shales in the overlying sequence

acting as the top seal.

MAUDDUD FORMATION

A sequence-stratigraphic framework for theMaud-

dud Formation has been established using all avail-

able well and core data from Kuwait. The Mauddud

Formation can be described by the TSS and the HSS


as a third-order composite sequence that is composed

of eight high-frequency, depositional sequences. The

top (MAU100_TS) and base (B100_TS) of the Maud-

dud Formation aremarkedbyTSS (Strohmenger et al.,

2002; Demko et al., 2003) (Figure 3).

The lower Mauddud (Mauddud TSS) shows a lat-

eral change in lithology from limestone in northern

Kuwait at the Raudhatain and Sabiriyah fields area to

siliciclastics in southern (Greater Burgan field area;

Figure 15) and southeastern Kuwait (Minagish field

area). The upper Mauddud (Mauddud HSS) is mostly

eroded in southern and southwestern Kuwait (Stroh-

menger et al., 2002; Demko et al., 2003) (Figure 16).

The Mauddud Formation in Kuwait comprises

eight carbonate lithofacies and three siliciclastic litho-

facies. Carbonate lithofacies were deposited in inner

to lower ramp, normal to slightly restricted environ-

ments. Clastic lithofacies were deposited in inner-

ramp (deeper lagoon), nearshoremarine, andoffshore

marineenvironments (Strohmengeret al., 2002;Demko

et al., 2003) (Figures 15, 16), similar to those de-

scribed for the Burgan Formation.

The Cenomanian Wara Formation overlies the

Mauddud Formation and provides a regional top seal

(Figure 3). It characteristically is a slightly calcareous

to noncalcareous marine shale in northern Kuwait

(Raudhatain and Sabiriyah fields area). In southern

(Greater Burgan field area) and southwestern Kuwait

(Minagish field area), glauconite-rich, deltaic sand-

stones are more common.

Lithofacies Types and Depositional Model

Sediments of the Mauddud Formation were de-

posited along a gently northward- and northeast-

ward-dipping homoclinal ramp (Strohmenger et al.,

2002; Demko et al., 2003).

Lithofacies and lithology of the Mauddud Forma-

tion of Kuwait vary by geographic area and time. In

the Mauddud transgressive sequence set, siliciclastic

deposits of southern (Greater Burgan field area) and

southwestern Kuwait (Minagish field area) grade into

carbonates toward the north and northeast (Abdali,

Raudhatain, and Sabiriyah fields area; Figure 15).

The Mauddud Formation can be described by

means of 11 lithofacies types (F1–F11). The facies

scheme follows, in great parts, the one established by

I. Goodall, N. Cross, and D. Payne (1996, personal

communication), C.Hollis, N.Cross, T.Needham, and

B. Jones (1998, personal communication), andN.Cross,

R. Heath, and G. Paintal (1999, personal communi-

cation), with some modifications. Lithofacies types

range from moderate- to high-energy upper-ramp

FIGURE 15. Schematic facies model of the Mauddud transgressive sequence set (upper third-order compositesequence).


deposits (F1, F2, and F3) through medium-energy,

upper- to middle-ramp (F4), and lagoonal deposits

(F4, F5 and F6) to low-energy, lower-ramp (F7, F8,

and F11), and deeper lagoonal deposits (F7, F8, F9,

F10, and F11; Figures 15, 16).

The thickness of the Mauddud Formation increases

toward the north and northeast and decreases to-

ward the south and southwest. The thinning is the

result of reduced accommodation during the lower

MauddudTSS (facies change fromcarbonates to silici-

clastics; Figure 15) and pronounced erosion of the

upper Mauddud HSS in southern (Greater Burgan

field area) and southwestern Kuwait (Minagish field

area) (Figure 16).

Lithofacies 1 (F1): Rudist Floatstone to Rudstone

Lithofacies type F1 (Figure 17A) is rich in rudists or

rudist fragments. Miliolids, conical orbitolinids,

other benthic foraminifera, skeletal fragments, and

echinoderms are common. Discoidal orbitolinids are

uncommon. Nonskeletal grains are peloids. Biotur-

bation is moderate.

This lithofacies type commonly grades into the

high-energy skeletal-peloidal grainstone (lithofacies

F2), as well as into the restricted lagoon nodular,

miliolid-bearing packstone-wackestone (lithofacies

F5). The grain composition (occurrence of miliolids),

as well as the facies-stacking pattern, suggests the

rudist floatstone-rudstone represents a ramp-crest to

inner-ramp,moderate tohigh-water-energy sediment,

deposited laterally or mostly lagoonward of lithofa-

cies F2 (skeletal-peloidal grainstone).

Relatively thick accumulations (as much as 60 ft

[18 m]) of rudist floatstone-rudstone occur within

Mauddud sequences MAU450 and MAU200. Espe-

cially within Mauddud sequence MAU450, rudist

floatstone-rudstone forms very porous intervals that

are easily identified by low gamma-ray- and high-

resistivity-log responses.

Cementation is minor. Dominant cement type is

blocky calcite cement, partly to completely filling the

molds of dissolved rudist shells.

Dominant porosity types are moldic and vuggy

porosity.

The average porosity is 18%, and the typical per-

meability is 5 md.

Lithofacies 2 (L2): Skeletal and Peloidal Grainstone

Lithofacies type F2 (Figure 17B) is rich in conical

orbitolinids, skeletal fragments, and echinoderms.

Other benthic foraminifera, red algae, and green algae

are common. Discoidal orbitolinids and gastropods

FIGURE 16. Schematic facies model of the Mauddud highstand sequence set (upper third-order composite sequence).


are sparse. Nonskeletal grains are coated grains and

peloids. Bioturbation is low.

This lithofacies type frequently shows Glossifun-

gitesburrows and/or, less common, desiccation cracks

(Figures 17B, 18A, B), as well as, also more uncom-

monly, karstification (Figure 18C). Sedimentary

structures indicating intertidal conditions, such as

trough–cross-bedding, fenestral structures (keystone

vugs and sheet cracks; Figure 17B), geopedal fillings

(vadose silt), and circumgranular cracks, are general-

ly limited to lithofacies type F2.

This lithofacies generally occurs at the top of the

Mauddud parasequences and HFSs. The lack of ma-

trix and the overall facies-stacking pattern suggest

the skeletal-peloidal grainstone to represent a high-

energy, shoal (ramp-crest) to upper-ramp deposits.

Cementation varies betweenminor and extensive.

Typical cement types are neomorphosed isopachous

rim cement, blocky calcite cement, and syntaxial cal-

cite cement. Glossifungites burrows as well as karst

fillings are commonly dolomitized.

Dominant porosity type is microporosity. Inter-

particle, intraparticle, andmoldic porosity are minor

porosity types.


meability is 2 md.

FIGURE 17. Carbonate lithofacies types, slabbed core photographs. (A) Lithofacies F1: rudist floatstone-rudstone.(B) Lithofacies F2: skeletal-peloidal grainstone showing Glossifungites (Gl) burrows as well as fenestral structures(keystone vugs). (C) Lithofacies F3: skeletal-peloidal mud-lean packstone showing bioturbation. (D) Lithofacies F4:bioturbated skeletal-peloidal packstone.


Lithofacies 3 (F3): Skeletal and PeloidalMud-lean Packstone

Lithofacies type F3 (Figure 17C) is rich in conical

orbitolinids. Skeletal fragments and echinoderms are

common. Discoidal orbitolinids, other benthic fora-

minifera, and gastropods are sparse. Nonskeletal grains

are peloids. Bioturbation varies from moderate to

high.

This lithofacies type commonly alternates with

lithofacies type F2 (skeletal-peloidal grainstone). The

relatively low mud content and the overall facies-

stacking pattern suggests the skeletal-peloidal mud-

leanpackstone to represent amoderate-energy, upper-

ramp deposit.

Like lithofacies type F2 (skeletal-peloidal grain-

stone), the skeletal-peloidal mud-lean packstone lo-

cally is karstified.

Cementation generally is mi-

nor.Cement types are blocky cal-

citeandsyntaxial calcitecements.

Dominantporosity type ismi-

croporosity. Intraparticle and

moldic porosity are minor po-

rosity types.

The average porosity is 15%,

and the typical permeability is

2 md.

Lithofacies 4 (F4): BioturbatedSkeletal andPeloidal Packstone

Lithofacies typeF4(Figure17D)

is rich in conical and discoidal

orbitolinids and echinoderms.

Skeletal fragments are common.

Other benthic foraminifera, ru-

dist fragments, and thin-shelled

bivalves are sparse. Nonskeletal

grains are peloids. Bioturbation

is high.

This lithofacies typically un-

derlies lithofacies typeF3(skeletal-

peloidal mud-lean packstone)

and, less commonly, lithofacies type F5 (nodular,

miliolid-bearing packstone-wackestone). It commonly

overlies lithofacies type F2 (skeletal-peloidal grain-

stone) and lithofacies type F3 (skeletal-peloidal mud-

lean packstone). Grain composition, texture, and the

overall facies-stacking pattern suggest that the bio-

turbated skeletal-peloidal packstone represents a low-

tomoderate-energy, upper- tomiddle-rampdeposit. It

may also be present behind the high-energy bar de-

posits (lithofacies F1, F2, and F3) in an inner-ramp,

protected lagoonal environment.

Cementation is minor to extensive. Dominant ce-

ment type is blocky calcite cement.

Dominant porosity type is microporosity. Intrapar-

ticle and moldic porosity are minor porosity types.


meability is 0.5 md.

FIGURE 18. Sedimentary struc-tures, slabbed core photographs.(A) Erosional surface with Glossi-fungites burrows. (B) Glossifungitesburrows and/or desiccation crackswith younger sediment infill.(C) Microkarst with sedimentinfill.


Lithofacies 5 (F5): Nodular, Miliolid-bearingPackstone to Wackestone

Lithofacies type F5 (Figure 19A) commonly con-

tains miliolids, conical orbitolinids, other benthic fo-

raminifera, rudist fragments, skeletal fragments, and

thin-shelled bivalves. Sponge spicules are common

and only occur within this lithofacies type. Discoidal

orbitolinids and echinoderms are uncommon. Non-

skeletal grains are peloids. Bioturbation and burrowing

is high, most probably causing its nodular appearance.

This lithofacies type is restricted to the upper

Mauddud (Mauddud HSS; Figure 16) and commonly

over- and underlies the rudist floatstone-rudstone

(lithofacies F1), predominantly within Mauddud se-

quenceMAU200. The grain composition (occurrence

of miliolids), as well as the facies-stacking pattern,

suggests the nodular, miliolid-bearing packstone-

wackestone to represent a low- to moderate-energy,

inner-ramp, restricted lagoonal deposit.

Cementation is minor, and the dominant cement

type is blocky calcite cement.

The dominant porosity type is microporosity. Intra-

particle and moldic porosity are minor porosity types.



Lithofacies 6 (F6): Skeletal Wackestone to Mudstone

Lithofacies type F6 (Figure 19B) is mud rich, light

gray,with sparse skeletal fragments andpeloids. Biotur-

bation is very low. Pyrite framboids are quite frequent.

FIGURE 19. Carbonate lithofacies types, slabbed core photographs. (A) Lithofacies F5: nodular, miliolid-bearing packstone-wackestone. (B) Lithofacies F6: skeletal wackestone-mudstone (C) Lithofacies F7: clay-rich, bioturbated skeletal wacke-stone showing Thalassinoides (Th) and Planolites (Pl) burrows. (D) Lithofacies F8: bioturbated glauconitic packstone.


This lithofacies type is present only in the upper

MauddudHSS (Mauddud sequenceMAU300; Figure 16).

We interpret this lithofacies type to represent a low-

energy, inner-ramp, protected lagoonal deposit.

Cementation (fine-crystalline, blocky calcite filling

thepore space of dissolved skeletal fragments) isminor.

The dominant porosity type is microporosity, and

intercrystalline porosity is present.

Averageporosity and typical permeability (only four

samples analyzed) iswithin the range of lithofacies F5

(nodular, miliolid-bearing packstone-wackestone).

Lithofacies 7 (F7): Clay-rich, BioturbatedSkeletal Wackestone

Lithofacies type F7 (Figure 19C) is rich in discoidal

orbitolinids and echinoderms, aswell as in trace fossils,

including Thalassinoides and Planolites. Skeletal frag-

ments, thin-shelled bivalves, and pelagic foraminif-

era are common. Nonskeletal grains are peloids. Bio-

turbation is very high (solution-seam rich). Pyrite is

common.

This lithofacies typically underlies lithofacies type

F4 (bioturbated skeletal-peloidal packstone) or over-

lies lithofacies type F2 (skeletal-peloidal grainstone)

and lithofacies type F3 (skeletal-peloidal mud-lean

packstone).Grain composition, texture, and theover-

all facies-stacking pattern suggest the clay-rich, biotur-

bated skeletal wackestone to represent a low-energy,

middle- to lower-ramp deposit. It may, however, also

be present behind the high-energy bar deposits (litho-

facies F1, F2, and F3) in the inner-ramp, protected

lagoon environment.

Cementation isminor. The dominant cement type

is fine-crystalline, blocky calcite cement. Dolomiti-

zation occurs along solution seams.

The dominant porosity type is microporosity, and

intraparticle and intercrystalline porosity are minor

porosity types.



Lithofacies 8 (F8): BioturbatedGlauconitic Packstone

Lithofacies type F8 (Figure 19D) commonly con-

tains discoidal orbitolinids, echinoderms, and skeletal

fragments. Conical orbitolinids, thin-shelled bivalves,

and rudist fragments are uncommon. Nonskeletal

grains are glauconite (glauconitized peloids), peloids,

quartz, and pyrite. Bioturbation is high.

This lithofacies type typically overlies sequence

boundaries on top of lithofacies types F2 (skeletal-

peloidal grainstone) and F3 (skeletal-peloidal mud-

lean packstone). We interpret this lithofacies type as

representing periods of low sedimentation rates during

rapid sea-level rise. It dominantly occurs within the

Mauddud TSS. The depositional environment ranges

from inner ramp, lagoonal (Mauddud TSS; Figure 15)

to middle to lower ramp (Mauddud HSS; Figure 16).


ment types are blocky calcite, ferroan dolomite, and

ferroan calcite cement. Ferroan cements aremost com-

mon in southern Kuwait (Greater Burgan field area).

Dominant porosity type is microporosity. Intrapar-

ticle and moldic porosity are minor porosity types.



Lithofacies 9 (F9): BioturbatedGlauconitic Sandstone

Lithofacies type F9 (Figure 20A) is quartz rich and

contains sparse discoidal orbitolinids and skeletal frag-

ments. It is rich in trace fossils, including Teichichnus,

Asterosoma and Terebellina (uncommon). Grain types

are detrital quartz, glauconite, pyrite, and siderite. Bio-

turbation is very high. This lithofacies is similar to

lithofacies 2D (glauconitic sandstone) of the Burgan

Formation but has a higher glauconite content.

Like lithofacies type F8 (bioturbated glauconitic

packstone), this lithofacies typically overlies sequence

boundaries on top of lithofacies types F2 (skeletal-

peloidal grainstone), F3 (skeletal-peloidal mud-lean

packstone), and F10 (bioturbated mud-rich sand-

stone). It dominantly occurs within the Mauddud

TSS (Figure 15). Thebioturbated glauconitic sandstone

is interpreted to represent an inner-ramp, nearshore-

marine, lower-shoreface deposit.


ment types are blocky calcite, ferroan dolomite, and

ferroan calcite cement.

Predominant porosity type ismicroporosity, and in-

traparticle and intergranular porosity types are present.



Lithofacies 10 (F10): BioturbatedMud-rich Sandstone

Lithofacies type F10 (Figure 20B) is intensely bio-

turbated and rich in trace fossils, includingTeichichnus,

Asterosoma, Thalassinoides, Planolites, and Chondrites.

Lithofacies type F10 occurs within the Mauddud

TSS (Figure 15). Relatively thick intercalations (>60 ft;

>18m)occurwithin theMauddud sequenceMAU500.

This lithofacies is similar to lithofacies 3F (calcareous,

bioturbated sandstone) of the Burgan Formation.


The bioturbatedmud-rich sandstone is interpreted to

represent an inner-ramp, nearshore-marine, lower-

shoreface deposit.

Cementation is minor; dominant porosity type is

intergranular.

The average porosity is 12%, and typical perme-

ability is 11 md.

Lithofacies 11 (F11): Dark-gray Shaleand Mudstone

Lithofacies F11 (Figure 20C) shows only sparse

skeletal fragments, thin-shelled bivalves, planktonic

foraminifera, andnannofossils. This lithofacies is sim-

ilar to lithofacies 5A (laminated gray shale) of the

Burgan Formation. Millimeter-scale laminae indi-

cate low bioturbation caused by stressed (lagoon) or

deeper marine, offshore (lower-ramp) environment

of deposition.

Dominant lithofacies type of the Mauddud trans-

gressive sequence set (Figure 15); deposited largely in

an inner-ramp, deeper lagoonal setting, juxtaposed

to lithofacies types F7 (clay-rich, bioturbated wacke-

stone), F8 (bioturbated glauconitic packstone), and F9

(bioturbatedglauconitic sand-

stone; Figure 15). The fact that

it is not highly bioturbated as

it would be expected for off-

shore shales underlying low-

er shoreface deposits (litho-

facies F9 and F10) indicates

a high-stress environment.

The dark-gray shale andmud-

stone are interpreted to rep-

resent a low-energy, deeper

marine, lower-ramp to basin-

al deposit during the Maud-

dud HSS (Figure 16) and the

Wara Formation.

Predominant porosity type

is microporosity.

The average porosity is 5%, and typical perme-

ability is 0.03 md.


Eight high-frequency, depositional sequences were

interpretedwithin theMauddud Formation. Frombot-

tom to top, these are B100 (TST and HST), MAU600,

MAU500, MAU450, MAU400, MAU350, MAU300,

and MAU200 (Figure 3).

Eight SBs, two TSs, three MFSs, and two FSs were

identified. All surfaces, except for one flooding sur-

face (MAU600_FS), can be correlated throughout all

of Kuwait.

Sequence boundaries typically are characterized by

an abrupt change in texture and lithofacies. Glossi-

fungitesburrowsand/ordesiccationcracks are common

in the upper part of each high-frequency sequence

(Figures 18A, B; 21). Karstification is seen locally

(Figure 18C). Evidence of at least periodic exposure,

such as fenestral structures (keystone vugs and sheet

cracks; Figure 17B) and circumgranular cracks, is also

present in the upper part of each high-frequency se-

quence. Sandstone or packstone, rich in glauconite,

FIGURE 20. Siliciclastic lithofa-cies types, slabbed core pho-tographs. (A) Lithofacies F9:bioturbated glauconitic sand-stone showing Teichichnus (Te)burrows. (B) Lithofacies F10:bioturbated mud-rich sand-stone showing Teichichnus (Te)and Thalassinoides (Th) bur-rows. (C) Lithofacies F11: dark-gray shale and mudstone.


typically immediately overlies each high-frequency

sequence boundary (Figure 21), recording periods of

rapid flooding and resulting in low sedimentation rate.

The identified high-frequency sequence boundaries

correspond to combined flooding surface and se-

quence boundaries (FS/SB, Figure 21).

Maximumflooding surfaces are interpreted atmajor

marine incursionsmarked by a change from retrograd-

ing to prograding stacking of marine parasequences.

Floodingsurfacesare interpretedontopof shallowing-

upward parasequences, commonly corresponding to

Glossifungites surfaces (Figure 21).

Mauddud Sequence B100(B100_SB to MAU600_SB)

In northern Kuwait (Raudhatain and Sabiriyah

fields area; Figure 22), this sequence is shale and

mud rich at the base of the TST, grading upward, to

grain rich at the top of the HST. Dominantly tidal-

flat deposits occur in southern Kuwait (Greater

Burgan field area; Figure 23), and dominantly coastal-

plain deposits occur in southwestern Kuwait (Min-

agish field area; Figure 23). The sequence is partly

eroded byMauddud sequence boundaryMAU600_SB

in southern Kuwait (Figure 23).

The sequence consists of lithofacies F11 (dark-gray

shale and mudstone) and lithofacies F9 (bioturbated

glauconitic sandstone) grading upward into lithofa-

cies F7 (clay-rich, bioturbated skeletal wackestone),

lithofacies F8 (bioturbated glauconitic packstone),

and lithofacies F4 (bioturbated skeletal-peloidal pack-

stone) in northern Kuwait (Raudhatain and Sabiriyah

fields area; Figures 22, 23).

Mauddud Sequence MAU600(MAU600_SB to MAU500_SB)

This sequence is composed ofmud-dominated car-

bonates in northern Kuwait (Raudhatain and Sabir-

iyah fields area; Figure 22), dominantly coastal-plain

and tidal-influenced deposits in southern Kuwait

FIGURE 21. Mauddud Formation idealized carbonate parasequence (upper part of a high-frequency sequence)showing shallowing-upward trend of facies from base to top: bioturbated skeletal-peloidal packstone (F4, bluecolor), skeletal-peloidal mud-lean packstone (F3, red color), and skeletal-peloidal grainstone (F2, orange color). Floodingsurface/sequence boundary (FS/SB) is interpreted by Glossifugites burrows or, uncommonly, karstification (microkarst)and is overlain by bioturbated glauconitic packstone (F8) or bioturbated glauconitic sandstone (F9, green color).


FIGURE 22. Field-scale cross section (northwest–southeast) showing facies distribution and sequence-stratigraphic framework of the Mauddud Formationthroughout the northern Kuwait Raudhatain and Sabiriyah fields. Mauddud transgressive sequence set: B100_TS to MAU400_MFS. Mauddud highstand sequenceset:MAU400_MFS toMAU100_SB.Mauddud lowstand systems tract:MAU100_SB toMAU100_TS.GR=gamma-ray log; FAC=Mauddud carbonate and siliciclastic faciesand Burgan deposits (based on core); MD = measured depth (feet); DT = sonic log; NEU = neutron porosity log; DENS = density log.

Sequen

ceStratig

raphyan

dReserv

oir

Arch

itecture

ofBurgan

andMau

ddudForm

ations

/239

FIGURE 23. Regional cross section oriented north–south and east–west showing facies distribution and sequence-stratigraphic framework of the MauddudFormation. Note that chronostratigraphic boundaries (time lines) crosscut the lithostratigraphic boundary between the Mauddud carbonate member (MauddudFormation) and the Mauddud clastic member (Burgan Formation, time equivalent to Mauddud Formation). The proposed sequence-stratigraphic correlationis supported by age dating and palynofacies analyses (T. D. Davies and T. C. Huang, 2000, personal communication). Stratigraphy-diagnostic palynofaciesassemblages are shown as colored dots. Blue dots: only found aboveMauddud transgressive surfaceMAU100_TS (inWara Formation). Yellow dot: only found betweenMauddud sequence boundary MAU100_SB and Mauddud trangressive surface MAU100_TS (Mauddud lowstand systems tract, onlapping on Mauddud sequenceboundary MAU100_SB in southern and southwestern Kuwait). Green dots: only found between Burgan transgressive surface B100_TS and Mauddud maximumflooding surfaceMAU400_MFS (Mauddud transgressive sequence set: lower part of Mauddud carbonatemember in northern Kuwait andMauddud clastic member insouthern and southwestern Kuwait). Red dots: only found below Burgan transgressive surface B100_TS (Burgan lowstand sequence set). No stratigraphy-diagnosticpalynofacies assemblage was found in grain-dominated, shallow-water carbonates between Mauddud maximum flooding surface MAU400_MFS and Mauddudsequence boundary MAU100_SB (Mauddud highstand sequence set). Color codes for Mauddud carbonate and siliciclastic facies as well as for Burgan siliciclasticdeposits are shown in Figure 22. GR = gamma-ray log; FAC = Mauddud carbonate and siliciclastic facies and Burgan deposits (based on core); MD = measured depth(feet); DT = sonic log; NEU = neutron porosity log; DENS = density log.

240

/Stro

hmen

ger

etal.

(Greater Burgan field area; Figure 23), and dominantly

coastal-plain and tidal-flat deposits in southwestern

Kuwait (Minagish field area; Figure 23).

Dominantly lithofacies F11 (dark gray shale and

mudstone) and minor lithofacies F8 (bioturbated

glauconitic sandstone) and lithofacies F7 (clay-rich,

bioturbated skeletal wackestone) occur in the north-

ern fields area. The succession may show upward in-

crease of porosity and permeability and shallowing-

upward lithofacies trend, as well as coarsening-upward

texture in the northern fields area (Figures 21, 22).


Marginal-marine (distal lower shoreface) siliciclas-

tics occur in northern Kuwait (Raudhatain and Sabi-

riyah fields area) and were not eroded by sequence

boundaryMAU450_SB (Figure 22). Dominantly coastal-

plaindeposits occur in southernKuwait (Greater Burgan

field area; Figure 23) and dominantly tidal-influenced

to fluvial deposits occur in southwestern Kuwait (Mi-

nagish field area; Figure 23).


This sequence is composed of grain-dominated

carbonates in northern Kuwait (Raudhatain and

Sabiriyah fields area; Figure 22) and dominated by

marginal-marine (distal lower shoreface) deposits in

southern (Greater Burgan field area; Figure 23) and

southwestern Kuwait (Minagish field area; Figure 23).

The sequence is composed predominantly of litho-

facies F2 (skeletal-peloidal grainstone), with minor

lithofacies F3 (skeletal-peloidal mud-lean packstone)

and lithofacies F4 (bioturbated skeletal-peloidal pack-

stone). Relatively thick accumulations (as much as

60 ft [18 m]) of highly porous lithofacies F1 (rudist

floatstone-rudstone) occur as aerially restricted inter-

calations throughout the northern fields area. This

sequence may show an upward increase of porosity

and permeability and a shallowing-upward lithofacies

trend, as well as coarsening-upward texture (northern

fields area; Figures 21, 22).


This sequence is composed of grain-dominated car-

bonates in northern Kuwait (Raudhatain and Sabiri-

yah fields area), with lithofacies 8 (bioturbated glau-

conitic packstone) commonly overlying Mauddud

sequence boundary MAU400_SB (Figure 22). Litho-

facies F8 (bioturbated glauconitic packstone) overlies

Mauddud sequence boundary MAU400_SB in south-

ern Kuwait (Greater Burgan field area; Figure 23).

Lithofacies F9 (bioturbated glauconitic sandstone)

overlies Mauddud sequence boundary MAU400_SB in


This sequence is dominated by lithofacies F4 (bio-

turbated skeletal-peloidal packstone) in southern

Kuwait (Greater Burgan field area; Figure 23) and

dominated by marginal-marine siliciclastics with

thin, karstified lithofacies F3 (skeletal-peloidal mud-

lean packstone) at the top in southwestern Kuwait

(Minagish field area; Figure 23). It is partly erod-

ed in southwestern Kuwait (Minagish field area;

Figure 23).

The sequence is composed predominantly of litho-

facies F2 (skeletal-peloidal grainstone) and litho-

facies F3 (skeletal-peloidal mud-lean packstone), as

well as minor lithofacies F4 (bioturbated skeletal-

peloidal packstone) and lithofacies F7 (clay-rich, bio-

turbated skeletal wackestone) in the northern fields

area (Figures 22, 23).


This sequence is composed predominantly of litho-

facies F2 (skeletal-peloidal grainstone) and litho-

facies F3 (skeletal-peloidal mud-lean packstone), as


peloidal packstone) and intercalations of lithofacies F1

(rudist floatstone-rudstone) innorthernKuwait (Raud-

hatain and Sabiriyah fields area; Figure 22). It is partly

eroded in the Greater Burgan field area (lithofacies F4:

skeletal-peloidal packstone; Figure 23) and eroded

(not present) in southwestern Kuwait (Minagish field

area; Figure 23).

This sequence may show an upward increase of

porosity and permeability and shallowing-upward

lithofacies trend as well as coarsening-upward tex-

ture in the northern fields area (Figures 21, 22).


This sequence is composed predominantly of litho-

facies F2 (skeletal-peloidal grainstone) and lithofa-

cies F3 (skeletal-peloidal mud-lean packstone), as


peloidal packstone) and lithofacies F1 (rudist float-

stone-rudstone) in northern Kuwait (Raudhatain and

Sabiriyah fields area; Figure 22). The sequence is eroded

(not present) in southern (Greater Burgan field area;

Figure 23) and southwestern Kuwait (Minagish field

area; Figure 23).



This sequence is composed predominantly of

lithofacies F5 (nodular, miliolid-bearing packstone-

wackestone) and lithofacies F3 (skeletal-peloidal

mud-lean packstone), as well as minor lithofacies F4

(bioturbated skeletal-peloidal packstone) and litho-

facies F1 (rudist floatstone-rudstone) in northern Ku-

wait (Raudhatain and Sabiriyah fields area; Figure 22).

The sequence is eroded (not present) in southern

(Greater Burgan field area; Figure 23) and southwest-

ern Kuwait (Minagish field area; Figure 23).

Mauddud Interval MAU100_SB to MAU100_TS

This interval is composed predominantly of litho-

facies F11 (gray shale and mudstones) and lithofacies

F7 (clay-rich, bioturbated skeletal wackestone).

The interval was deposited during the third-order

relative sea-level rise aboveMauddud sequencebound-

ary MAU100_SB (Figures 22, 23) and is not present

in southern (Greater Burgan field area; Figure 23) and


Composite Sequence

The TSS of theMauddud composite sequence starts

at the base of Mauddud transgressive surface B100_TS

and is bounded on the top by Mauddud maximum

flooding surface MAU400_MFS of the Mauddud high-

frequency sequence MAU400. The overlying HSS

is bounded on top by Mauddud sequence boundary

MAU100_SB. The top of the Mauddud Formation is

marked by the transgressive surface MAU100_TS

(Figures 22, 23) that merges with the Mauddud se-

quence boundary MAU100_SB toward southern and

southwestern Kuwait (Figure 23).

The Mauddud TSS shows a lateral change in litho-

logy from limestone in northern Kuwait (Raudhatain

and Sabiriyah fields area; Figure 22) to siliciclastics in

southern (Greater Burgan field area; Figure 23) and

southwesternKuwait (Minagish field area; Figure 23).

An overall shoaling-upward or progradational sig-

nature characterizes the Mauddud HSS. The HSS is

interpreted to be erodeddown to andbelow sequence

boundary MAU350_SB in southern (Greater Burgan

field area; Figure 23) and southwestern Kuwait (Mi-

nagish field area; Figure 23).

Our sequence-stratigraphic interpretation of the

Mauddud Formation contrasts with the previously

used lithostratigraphic correlation. Lithostratigraphic

correlation places the boundary between the Maud-

dud Formation and the underlying Burgan Forma-

tion at the base of the deepest limestone bed. In con-

trast, the sequence-stratigraphic boundary between the

Mauddud Formation and the underlying Burgan For-

mation occurs approximately 100 ft (30 m) deeper in

the clastic section of the Mauddud Formation. The

lithostratigraphic boundary between the Mauddud

carbonate member and theMauddud clastic member

is highly diachronous (Figure 23). The thickness rela-

tionships of the two Mauddud Members are recipro-

cal. The Mauddud carbonate member becomes very

thin in locations where theMauddud clastic member

is thick. Toward the north (Raudhatain and Sabiriyah

fields area), the Mauddud clastic member becomes

very thin to absent, whereas the Mauddud carbonate

member is thinning toward southern Kuwait (Great-

er Burgan field area; Figure 23) and southwestern

Kuwait (Minagish field area; Figure 23).

The sequence-stratigraphic correlation of the

Upper Burgan and the Mauddud presented here is

supported by biostratigraphic and palynofacies data

(T. D. Davies and T.-C. Huang, 2000, personal com-

munication) (Figure 23).

Reservoir Quality Distribution

In general, most Mauddud lithofacies have mod-

erate porosity and overall low permeability. Litho-

facies types F2, F3, F4, F5, and F6 have essentially the

sameporosity-permeability distributions.Only litho-

facies type F1 (rudist floatstone-rudstone) and litho-

facies F10 (bioturbated, mud-rich sandstone) show

higher porosity and/or permeability values. Intervals

that show enhanced reservoir quality are related to

fracturing and faulting (enhanced permeability), the

occurrence ofmicrokarst (Figure 18C), the occurrence

of rudist floatstone-rudstone (lithofacies F1: Maud-

dud high-frequency sequence MAU450; Figure 17A),

or the occurrence of the bioturbated, mud-rich sand-

stone (lithofacies F10: Mauddud high-frequency se-

quence MAU500; Figure 20B).

CONCLUSIONS

Sequence-stratigraphic and biostratigraphic analy-

ses indicate that the traditional lithostratigraphic

Burgan-Mauddud contact is actually a time-transgres-

sive boundary (Figure 23). The uppermost Burgan and

overlying Mauddud formations form a third-order

composite sequence that becomes more siliciclastic

prone toward the south (in the Greater Burgan field

area) and toward the southwest (in theMinagish field

area; Figure 23) and carbonate prone to the north

and northeast of Kuwait near the Raudhatain and

Sabiriyah fields (Figures 22, 23). A lower, third-order


composite sequence encompasses the remainder of

the underlying Burgan Formation (Figure 12). It com-

prises marginal-marine deposits to the northeast

and nonmarine deposits to the southwest of Kuwait

(Figure 12).

Within the Burgan Formation, 19 high-frequency,

depositional sequences are recognized and stack to

form one third-order composite sequence and the

LSS of a younger third-order composite sequence

(Figures 3, 12). Lowstand systems tracts consist pri-

marily of fluvial, incised-valley-fill deposits in southern

and western Kuwait that become thinner, laterally

more discontinuous, and more tidal-influenced in a

downdip direction to the northeast (Figure 13). The

TSTs display a systematic updip to downdip change

from mud-prone alluvial- and coastal-plain strata to

marginal-marine mudstones and sandstones to ma-

rine carbonates. The HSTs are dominated by updip

alluvial- and coastal-plainmudstones and sandstones

and marginal-marine sandstones and mudstones

downdip (Figure 14).

Facies analysis of the Burgan Formation reveals the

presence of 22 lithofacies, which are delineated based

on unique physical criteria, including grain size, com-

position, sorting, grading, and physical and biogenic

sedimentary structures. These lithofacies describe six

distinct facies, which form the basic building blocks

of two facies associations (Figure 4).

The primary reservoirs in the Burgan Formation

are fluvial and tidal deposits of the incised-valley-fill

facies association (Figure 4). Minor potential reser-

voirs are shoreline sandstones of the TSTs and HSTs

(Figure 4). In addition, the possibility exists that

marginal-marine shorelines in the TSSs may contain

hydrocarbons off the flanks of present-day structures.

This combination of structural and stratigraphic trap

would be dependent onmud-prone coastal-plain sedi-

ments in each sequence acting as the updip lateral

seal and marine shales in the overlying sequence

serving as a (very high-risk) top seal.

The Mauddud Formation is sequence stratigraphi-

cally subdivided into eight high-frequency deposi-

tional sequences (Figures 3, 22, 23). The identified

high-frequency SBs, TSs, MFSs, and FS can be cor-

related regionally throughout Kuwait. The Mauddud

transgressive sequence set displays a lateral change in

lithology from limestone in northern Kuwait (Raud-

hatain and Sabiriyah fields area; Figure 22) to silici-

clastics in southern (Greater Burgan field area) and

southwestern Kuwait (Minagish field area; Figures 15,

23), interfingering with what has traditionally been

recognized as the Burgan Formation (Figures 3, 23).

The Mauddud highstand sequence set is carbonate

prone and is mostly eroded in southern and south-

western Kuwait, resulting in a significant southward

and southwestward thinning (Figures 16, 23).

A total of eight carbonate lithofacies and three

siliciclastic lithofacies types were identified within

the Mauddud Formation. Carbonate lithofacies were

deposited in inner- to lower-ramp, normal- to slightly

restricted-marine environments. Siliclastic lithofa-

cies were deposited in a fairly wide range of environ-

ments, including deeper lagoon, nearshore-marine,

and offshore-marine (Mauddud carbonate member),

as well as coastal-plain, fluvial, and tidal, (Mauddud

clastic member) environments.

In general, most Mauddud lithofacies have mod-

erate porosity and low permeability, with micropo-

rosity as the dominant pore type. Intervals with en-

hanced reservoir quality can be related to fracturing

and faulting, theoccurrenceofmicrokarst (Figure18C),

thepresenceof rudist floatstone-rudstone (Figure 17A),

and the distribution of intercalated mud-rich sand-

stone (Figure 18A). Within the context of the new

Mauddud–Burgan chronostratigraphic boundary,

distinct isolated incised-valley systems canbedefined

within the Mauddud clastic member. These IVF are

expected to have reservoir characteristics similar to

those of the underlying Burgan Formation.

The proposed sequence-stratigraphic framework

and the sequence-stratigraphy-keyed facies scheme

result in a predictable distribution of reservoir and

seal facies and allow for a better prediction of the

vertical and lateral distribution of reservoir quality

and reservoir continuity at both field scale and re-

gional scale.

ACKNOWLEDGMENTS

The authors gratefully acknowledge the manage-

ments of ExxonMobil Exploration Company, Exxon-

Mobil Upstream Research Company, and Kuwait Oil

Company (KOC) for their permission to publish this

paper. For valuable discussions, we thank Linda W.

Corwin (ExxonMobil), Daniel H. Cassiani (Exxon-

Mobil), KathleenM.McManus (ExxonMobil), Menahi

Al-Anzi (KOC), Ahmed Al-Eidan (KOC), andMoham-

med Al-Ajmi (KOC). We extend our thanks to David

Awwiller (ExxonMobil) for his detailed reservoir-

quality analyses and to Tom D. Davies and Ting-

Chang Huang for performing the biostratigraphic

andpalynofacies analyses.DoloresA.Claxton (Exxon-

Mobil) is thanked for drafting the figures. We extend

special thanks to Arthur D. Donovan (BP; formerly


with ExxonMobil) for his valuable contributions to

this study. The authors greatly appreciate the thor-

ough and thoughtful reviews of J. R. (Rick) Sarg and

James McGovney.

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Sequence stratigraphy and reservoir architecture of the Burgan and Mauddud formations (Lower Cretaceous), Kuwait

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