PREPARED BY : ROZEN REVILENE RAYMOND (15302) SUPERVISOR : MDM. NORSYAZWANI BIN ZAINAL ABIDINPetroleum Geoscience Department, Universiti Teknologi PETRONAS, Malaysia.

DIAGENETIC HISTORY OF CARBONATE FORMATION IN EASTERN SABAH

ABSTRACTThis work presents the diagenetic history of Gomantong Limestone Formation located along the road of Sukau, Sabah. In earlyMiocene, there is a period of tectonic deformation which suggested widespread of uplift followed by carbonate sedimentation (GomantongLimestone Formation) when the depositional environment changed from deep to shallow marine. Overall, diagenetic history in GomantongLimestone is limited and restricted to marine diagenetic environment. Due to high cementation, reservoir quality of Gomantong isrelatively poor.

INTRODUCTION

PROBLEM STATEMENT:The limestone from the Gomantong Formation in the eastern Sabah was depositedon an open shelf which is adjacent to the coastline formed of uplifted LabangFormation. Noad (2001) stated that due to lack of exposure of GomantongFormation rocks thus leads to speculative on the age of the formation. However,detailed study on diagenetic features are still unavailable.

OBJECTIVES:

• To study the microfacies of carbonate in north east Sabah• To understand the diagenetic processes that occur in Gomantong Limestone

during Miocene Period.

METHODOLOGY

FIELD WORK

SELECTIVE ROCK SAMPLING

• THIN SECTIONS• SEM (SCANNING ELECTRON

MICROSCOPY) • X-RAY DIFFRACTION ANALYSIS

• STRIKE & SLIP DIRECTIONS

• SEDIMENTARY LOGGING

CONCLUSION

Generally, the diagenesis events are limited to cementation, dissolution, micritization, compaction and replacement. Diageneticenvironment are said to be in marine environment due to the blocky and equant cements presence. Little diagenesis is due to lackof exposure. It is believed that Gomantong Limestone extended to western Sulu Sea, therefore is is recommended to have a moredetailed study by including stable isotope analysis in future research. Overall, the reservoir quality is highly affected by thediagenesis which decreases the reservoir quality due to cementation.

S1

24-0027 (D) - Calcite - CaCO3 - Y: 50.00 % - d x by: 1. - WL: 1.5406 - Hexagonal (Rh) - a 4.99000 - b 4.99000 - c 17.00200 - alpha 90.000 - beta 90.

Operations: Strip kAlpha2 0.500 | Fourier 20.000 x 1 | Smooth 0.200 | Import

S1 - File: 66.raw - Type: 2Th/Th locked - Start: 10.000 ° - End: 80.000 ° - Step: 0.020 ° - Step time: 1. s - Temp.: 25 °C (Room) - Time Started: 10 s - 2

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ounts

)

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2-Theta - Scale

10 20 30 40 50 60 70 80

RESULT & DISCUSSION

c

B

A

THIN SECTIONS:

Figure A: Wackestone with

abundance of lepidocyclina sp.

(Benthic foraminifera). Grains

to grains contact indicate

mechanical compaction and

shallow burial. Equant-blocky

cements filled in fractures and

present of benthic forams

indicate marine realm as

diagenetic environment.

Figure B: Packetsone with

abundance of broken

fragments of Lepidocyclina sp.

Mechanical compaction

causing the grain to grain

contacts. Minor fractures then

formed and infilled by calcite

cements.

Figure B: Boundstone where

platy corals are bound together.

Chambers of corals have been

neomorphosed and infilled by

calcite cements. Platy corals

indicate depositon at fore reef

and base of the slope

environment.

Diagenetic

Environmentn

Diagenetic Processess

Diagenetic Environment

Shallow

Marine

Shallow –

Moderate

Burial

Moderate –

Deep Burial

Meteoric

Influence

Micritization

Equant Blocky Calcite in

Intergranular Grains

Equant Block Calcite in

Intragranular Grains

Dissolution

Mechanical Compaction &

Fracturing

Blocky calcite cement in

fractures

Stylolites

Replacement by Pyrite

SEM image illustrating blocky equant cementsXRD analysis results showing that

most of the cement is calcite and not

influence by dolomitization

Summary of diagenesis processes with its relative

diagenetic environment proposed.

SEM RESULTS:GEOCHEMICAL ANALYSIS :

References:• Noad, J. (2001). The Gomantong Limestone of eastern Borneo: a sedimentological comparison with the near-contemporaneous Luconia Province. Palaeogeography, Palaeoclimatology, Palaeoecology, 175(1), 273-302.

• Lavenu, A. P., Lamarche, J., Gallois, A., & Gauthier, B. D. (2013). Tectonic versus diagenetic origin of fractures in a naturally fractured carbonate reservoir analog (Nerthe anticline, southeastern France) AAPG bulletin, 97(12),

2207-2232.