Outcrop Analogs to the Offshore Sarawak Miocene Buildups, how effective can

they be? The Subis Limestone as an Example

AbderRahmane Dedeche

SE Asia Carbonate Research Laboratory

(SEACaRL)

Universiti Teknologi PETRONAS

Overview • Background

o Regional setting

o Motives behind this study

o Study area

o Previous studies

• The Subis Limestone o Architecture

o Depositional facies

o Depositional environments

o Depositional cycles

o Facies stacking patterns

o Growth history model

• Analogy Discussion

• Conclusions

Background • The Miocene carbonate buildups of Southeast Asia

are prominent for containing commercial amounts

of natural unassociated gas.

• Accurate depiction of reservoir heterogeneity is

crucial to realistic reservoir modeling.

• Grammer et al. (2004) emphasized the importance

of outcrop analogs in providing a proxy for the

subsurface.

• Published analog studies for the Southeast Asia

carbonates are relatively few (e.g. Noad, 2001;

Bassant et al., 2004)

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Sedimentary Basins in S.E.A.

BINTULU

MIRI

50 MILES

0 50 KM

0

>220 platforms were mapped

Age: Mid – L. Miocene

Size: Up to 7x12 km2

Suai

Subis

Sources : PETRONAS (1999), M. Yamin and Abolins (1999), Haile (1956) Courtesy: M. Yamin Ali/2009

CENTRAL LUCONIA

TINJAR PROVINCE

Niah Caves

Bukit Kasut

Debestone Quarry

Batu Niah

Niah National Park-HQ

to Miri

to

Bintulu

to Miri

Gunung Subis Peak 365m

Previous Work Shell Geologists:

Jordi (1953) Haak (1955)

Sleumer (1977)

Geological Survey

Department: Liechti et al. (1960)

Haile (1962)

Academics: Che Aziz (1993)

Roohi (1994)

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Subis Hill/Platform

4/2/2013 Abder Rahmane Dedeche 8

Batu Niah

Niah Caves Quarry

Structural Setting

4/2/2013 Abder Rahmane Dedeche 9

Trusan fault (Haile, 1962)

Stratigraphic setting

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4/2/2013 Footer Text 11 Nyalau Sands Fm. Tangap Fm.

Setap Shales Fm.

Subis Lst. Mb.

LOWER SEQUENCE

UPPER SEQUENCE Debestone quarry

Niah Caves

1 km

Well Subis-2

Depositional Facies Facies Texture Components Energy Depositional Environment

1 Algal, Miliolid

Wackestone to

Packstone

Wackestone to

packstone

red algae,

benthic foraminifera (lepidocyclina,

milliolids)

low shallow protected subtidal environment (shallow

lagoon)

2 Miogypsinid,

Rhodolith

Packstone to

Grainstone

Packstone,

occasional

localized

grainstones

red algae (rhodoliths),

benthic foraminifera (miogypsina),

gastropods

medium back-reef sand shoal/tidal channel

3 Coral

Framstone

Framestone hermatypic coral (e.g. acropora, faviida),

solitary corals (e.g. porites)

high reef front, reef crest

4 Coral Rubble

Floatstone

Floatstone, matrix:

wackestone to

packstone

coral fragments larger than 2mm,

carbonate mud and sand

medium back-reef

5 Coral Rubble

Rudstone

Rudstone more than 80% coral fragments larger than

2mm

high reef flat

6 Algal

grainstone

Grainstone fragments of articulated coralline red

algae,

benthic foraminifera (amphestigina,

lepidocyclina)

high back-reef sand shoal, beach

7 Algal

bindstone

Bindstone corals (mostly branching and encrusting),

encrusting coralline red algae, encrusting

foraminifera

high reef front, reef crest

8 Skeletal,

peloidal

Wackestone

Wackestone carbonate mud, pelloids,

fine skeletal fragments (mollusks, corals)

low deep protected subtidal environment (deeper

than 20m)

Algal, Miliolid Wackestone to Packstone

Miliolids, Austrotrillina,

Amphistegina, Alveolina,

Marginopora,

Miogypsina and

Lepidocyclina;

Coralline red algae;

Mollusk fragments;

Echinoderm fragments.

Interpretation: Shallow

lagoon.

Abder Rahmane Dedeche

1 mm

Miogypsinid, Rhodolith Packstone to Grainstone

Miogypsina, Amphistegina,

and Lepidocyclina;

Rhodoliths, Coralline red

algae; mollusk fragments;

Echinoderm fragments.

Interpretation: Backreef

sand/grain shoal

Coral Framstone

Massive and branching

corals in growth position,

interstitial material includes

carbonate mud and

foraminifera. (Reef crest)

Coral Rubble Floatstone Coral fragments,

coralline red algae,

foraminifera, and

carbonate mud.

Interpretation: Back-reef

Coral Rubble Rudstone Branching coral fragments,

massive coral fragments,

carbonate mud.

Interpretation: Reef-flat

Skeletal, peloidal Wackestone

Mollusks: specially bivalves

(Pecten sp.), peloids, bryozoa,

Echinoderm fragments, and

carbonate mud.

Interpretation: Deep lagoon

Depositional Environments 1. Reefal

1. Reef-front

2. Reef-crest

3. Reef-flat

4. Back-reef

2. Protected 1. Shallow lagoon

2. Deep lagoon

3. Sand/grain shoals

3. Shallow open marine

M. Yamin and Abolins (1999)

Depositional Cycles • The Debestone Quarry

exposes the lower part of

the outcropping Subis

Limestone which we

divided into three (4rd

order?) sequences.

• Each of these sequences

is composed of several

thinner higher-order

shallowing-upward

cycles(in terms of

depositional environment)

wac

kest

on

e p

acks

ton

e gr

ain

sto

ne

flo

atst

on

e ru

dst

on

e fr

ames

ton

e

Max. flooding surface

sequence boundary

deep lagoon

shallow lagoon

reef flat

back reef

lagoon/shallow open marine

back reef

0m

5m

10m

15m

Shallowing-upward

(Cycle I)

Shallowing-upward

(Cycle II)

Facies Stack. Patterns

Reef-front

Reef-flat

Back-reef

Reef-apron/sand shoal

Shallow lagoon

Deep lagoon

Gr’, Gp’ < A’ Gr’ > A’ Gp’ < A’

Gr’: Growth/Rim Gp’: Growth/Interior A’: Accommodation

4/2/2013 Footer Text 22 Nyalau Sands Fm. Tangap Fm.

Setap Shales Fm.

Subis Lst. Mb.

BUILD-OUT

BUILD-UP

Niah Caves

1 km

BUILD-IN (?)

Well Subis-2

Growth History

4/2/2013 23

100 m 500 m

N N

Niah Caves

Bukit Kasut

Quarries

Reef Back-reef Lagoon Deep lagoon Island samples

Church Reef Platform, Celebes Sea Gunung Subis or Subis Hill (reconstruction)

Namoluk Atoll, Federated States of Micronesia, Pacific Ocean

500 m

N

Bukit Kasut

Quarries

Niah Caves

Reef Back-reef Lagoon Deep lagoon Sand shoal samples

N

Gunung Subis or Subis Hill (reconstruction)

Growth History

Growth History

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100 m 500 m

N N

Niah Caves

Bukit Kasut

Quarries

Reef Back-reef Lagoon Deep lagoon Island samples

Church Reef Platform, Celebes Sea Gunung Subis or Subis Hill (reconstruction)

Growth History

500 m

N

Bukit Kasut

Quarries

Niah Caves

Reef Back-reef Lagoon Deep lagoon Sand shoal Karst surface samples

Little Inagua, The Caribbean

N

Gunung Subis or Subis Hill (reconstruction)

Analogy to producing buildups

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Epting, 1980

Selley, 1998

Conclusions • The Gunung Subis represents an ancient tropical

isolated carbonate platform, rimmed by a coral-

algal reef, enclosing a vast restricted lagoon.

• Eight depositional facies compose the Subis

Limestone in the sampled locations; the most

common components are corals, coralline algae

and benthic foraminifera.

• The Debestone Quarry section is predominantly of

lagoonal and back-reef facies; other reef related

facies also occur towards the top of the outcrop.

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Conclusions • This study supports the division of the Subis

Limestone into two major sequences.

• The quarry outcrop features the building blocks of

the Subis Limestone: the shallowing-upward

depositional cycles.

• The Subis Limestone is characterized by a dominant

aggradational to backstepping growth patterns.

• The Subis Limestone is proven a good architectural

and depositional analog to the Sarawak offshore

buildups. However, digenetically speaking it is likely

of a radical contrast to the former.

4/2/2013 Abder Rahmane Dedeche 29

References Bassant, P., F. Van Buchem, A. Strasser, and A. Lomando, 2004. A comparison of two early Miocene carbonate

margins: The Zhujiang carbonate platform (subsurface, South China Sea) and the Pirinç Platform

(outcrop, southern Turkey), in Integration of outcrop and modern analogs in reservoir modeling: AAPG Memoir 80, p. 153-170.

Che Aziz bin Ali, 1993. Sedimentology and Diagenesis of the E11 Carbonate Builup and the Subis Limestone (Miocene), Sarawak, Malaysia. University of Reading. Unpublished PhD thesis.

Epting, M., 1980. Sedimentology of Miocene carbonate build-ups, Central Luconia, offshore Sarawak. Geological Society of Malaysia Bulletin, 12, 17-30.

Grammer, G. M., P. M. Harris, and G. P. Eberli, 2004. Integration of outcrop and modern analogs in reservoir modeling: Overview with examples from the Bahamas, inIntegration of outcrop and modern analogs in reservoir

modeling: AAPG Memoir 80, p. 1-22.

Haile, N.S., 1962. The Geology and Mineral Resources of the Suai-Baram Area, North Sarawak. Geological Survey Department, British Territories in Borneo.

Hutchison, E.S. 2005. Geology of North West Borneo, Sarawak, Brunei and Sabah. Elsevier B.V. pp131-158.

James, N. P., 1983. Reefs, in: Carbonate Depositional Environments. P. A. Scholle, D. G. Bebout and C. H. Moore (eds.). AAPG Memoir 33, Tulsa, p. 345-462.

Mazlan b. Haji Madon, 1999. North Luconia Province. In: The Petroleum Geology and Resources of Malaysia.

PETRONAS, Kuala Lumpur, pp. 443–454.

Noad, J., 2001. The Gomantong Limestone of eastern Borneo: a sedimentological comparison with the near-contemporaneous Luconai Province. Palaeogeography, Palaeoclimatology, Palaeoecology 175, 273-302.

Roohi, G., 1994. Biostratigraphy of the Subis Limestone, Sarawak. Unpublished thesis. University Malaya.

Selley, Richard C., 1998. Elements of Petroleum Geology. Academic Press. Plate 3.

Sleumer, B. H. G., 1977. Paleoecology and internal architecture of the Subis Limestone complex (Sarawak). Unpublished internal report. Shell Sarawak Bhd. Exp. R. 50108. The Hague 2076. 22p.

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