One Basin with Several Sediment Sources: Stratigraphic Records of - - PowerPoint PPT Presentation

One Basin with Several Sediment Sources: Stratigraphic Records of the Bunguran Trough, Central South China Sea

AAPG GTW, Kota Kinabalu, 26-27 May 2015 John Jong1, Steven M. Barker1, 2, * Franz L. Kessler3 and Tran Quoc Tan1

1 2 3

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• Regional Geological Overview
• Deformation Kinematics
• Sedimentation profiles
• Mineralogical compositional analysis
• Implication for the Bunguran trough

Talk Outline

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Introduction:

• The sediment supply for the Bunguran Trough - the deepwater depositional setting of the mud-

prone Rajang Delta is thought to have been predominantly sourced from the Borneo hinterland.

• A recent study of Plio-Pleistocene deformation history and the corresponding sedimentation

rates of the Bunguran Trough, together with the results of whole rock bulk mineralogical composition analysis of ditch cuttings from Jelawat-1, suggest sediment inputs from more than

• ne provenance, with a secondary source supply likely from the nearby Natuna High.

Objectives:

• To investigate the Plio-Pleistocene stratigraphic records of the Bunguran Trough based on the

study of the deformation profile of the Bunguran Trough Fold-Thrust Belt to establish a better understanding of the play fairways.

• To investigate mineralogy information from Jelawat-1. The presence of feldspar would be a

useful indicator for a proximate sand source.

• To investigate the recently acquired multibeam and 2D seismic data for indication of sediment

supply from Natuna High area.

Introduction and Objectives of Study

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Study Area Introduction

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Exploration History

Jelawat-1 Mulu-1 Talang-1 Paus-1 Laya-1 Sook-1 Panda-1 Komodo-1 Rusa-1 Macan-1 Bursa-1 CRD-1X Arca-1

Jelawat-1 ST1 (2004) Well type : Exploration, deviated Result : Dry (Tight hole) Total Depth : 3394.1m MDSS Water Depth : 607.7m Well objectives : Late Miocene and early Pliocene turbidite systems Sook-1 ST1 (2003) Well type : Wildcat Result : Wet Gas discovery Total Depth : 1555.5m MDSS Water Depth : 159m Remarks : Good gas shows in Intra- VIII undeveloped sands Laya-1 (2003) Well type : Wildcat Result : Oil & Gas shows Total Depth : 2861.5m MDSS Water Depth : 141.7 m Remarks : Good gas shows in Intra-VI undeveloped sands Mulu-1 (1994) Well type : Wildcat Result : Minor gas show Total Depth : 5055m RKB Water Depth : 1170 m Well objectives : Middle Miocene carbonates & Cycle II formation Paus-1 (2009) Well type : Wildcat Result : Oil & Gas discovery Total Depth : 3658.8m MDSS Water Depth : 1346 m Well objectives : Cycle I (Oligocene- Lower Miocene) Talang-1 (2006) Newfield Well type : Wildcat Result : Gas discovery (deepest play) Total Depth : 3672m MDSS Water Depth : 1137 m Well objectives : Clastic turbidites & pre-MMU section Jintan-1 (1992) Well type : Wildcat Result : Major gas discovery Total Depth : 1710m RKB Water Depth : 130m Well objectives : Cycle V carbonate sequence M3-1 (1970) Well type : Wildcat Result : Gas discovery Total Depth : 1954m MDSS Water Depth : 115m Well objectives : Cycle IV/V Carbonate Natuna D-Alpha (1970) Giant gas field, High CO2 (71%) 222TCF gas, 45TCF methane (5000’ gas column) Macan-1 Result : Wet gas discovery Well objectives : Oligo/Miocene sequence

Dara-1 Dara-2 X1-1

L4-1 112’ NGS in V/VI sands; <10% CO2, Trace of 38 deg. API; Oil recovered in one RFT Hibiskus-1 40’ NGS & oil shows in V sands; 3-4% CO2 contamination Dara-1 Reported high CO2 in Dara-1 and 2 (Scouting) X1-1 (1970) Dry, minor sands in VII; OP > 3000psi near TD (2300m)

Hibiskus-1 L4-1

CRD-X (2009) Oil & gas in Cycle I & II

H aqet ai, 1988 150

100

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F .trllobata

NNI N4 P221Nl 25.5 NP25

OiATT1AII NP24 P2t (pars)

Pliocene and Pleistocene Turbidites

I Bunquran I

Onshore

• Sarawak

Hibiskus Laya Jelawat Mulu REGIONAL TECTONIC EVENTS

Latest Rajang Delta opening (DeepWater in Block F)

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local buln tnve"lon tectonic-.

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Middle Miocene Extension

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Natuna Basin Natuna Basin Central Luconia Central Luconia Balingian Province Balingian Province Baram Delta Baram Delta Half Graben Half Graben Dangerous Grounds Dangerous Grounds

*modified after Jong et al., 2014 *modified after Hutchison, 2004

Regional Geology

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Bunguran Trough

Regional Framework

Satellite-derived Gravity anomaly map (source IHS, Interpretation based on published papers)

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Geoseismic Cross Section

Jemuduk-1ST1 well tested a common play in a deltaic setting; a rollover anticlinal structure bounded by growth faults within the Rajang Delta system. The inboard wells (Nagasari-1, L4.1X, Hibiskus-1, X1.1X, Jemuduk-1ST1 & Laya-1) tested the Pliocene-Pleistocene shelfal-to-shoreface facies, whilst the outboard well (Jelawat-1ST1) tested the Upper Miocene and Pliocene condensed bathyal-to-outer neritic facies. Apart from Jemuduk-1ST1, all wells found mostly poorly developed sands.

*modified after Jong et al., 2014

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• Regional Geological Overview
• Deformation Kinematics
• Sedimentation profiles
• Mineralogical compositional analysis
• Implication for the Bunguran trough

Talk Outline

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Deformation Kinematics

B B’

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Deformation Kinematics

B B’

• U. Cycle V

Seabed

• U. Cycle VIII - H4
• L. Cycle VII - H15
• U. Cycle V - H20

Intra Cycle VIII - H6

• U. Cycle VI – H19.5

Intra Cycle VIII – H7

VIII

Top Cycle VII - H11 Lower Cycle VIII – H10.5

VII VI

B B’

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Deformation Profiling

The rate of shortening is used here as a proxy for the rate of growth and is calculated by measuring the full length of the folded horizon and comparing it with the current day line length. Shortening is simply calculated: Line shortening (m) = Folded length (m) - Present day cross-section length (m) The rate of shortening can then be calculated based on the temporal data and is calculated: Rate of Shortening (m/Ma) = shortening (t1) – shortening (t2) / Time period H11 H15 H10 H6 H6.5 H4 H19 H20

End Miocene Pliocene Pleistocene

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Deformation P

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Deformation Profile: Yu

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Structural Evolution Based on Growth Profiles

Post Cycle VIII Upper Cycle VIII Intra Cycle VIII (2) Lower Cycle VIII Upper Cycle VII Intra Cycle VIII (1) Lower Cycle VII Cycle VI Legend Zero to minimal growth Low rate of growth observed High rate of growth observed

Holocene

• L. Pleistocene

Lower Pliocene

• U. Pleistocene

Upper Pliocene

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Structural Evolution – Two Kinematic Domains

Cycle Megasequence Northeast Megasequence southwest Post Cycle VIII Post Post Upper Cycle VIII Syn Post Intra Cycle VIII Syn Post/Syn? Lower Cycle VIII Syn Syn Upper Cycle VII Syn/Pre? Syn Lower Cycle VII Pre Pre Cycle VI Pre Pre

Northeast Southwest

Cycle VII Cycle VI

Cycle V

Cycle VIII Jelawat-1st

U. Cycle V VIII

VII

V I

VII V I

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0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

500 1000 1500 2000 2500 3000 3500 4000 4500

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5 5.2 5.4 5.6 5.8

Shortening (m) and Shortening Rate Age (Ma)

Growth and Sedimentation Profile - Jelawat

Sedimentation Profile

Max Sedimentation Rate (m/Ka) = True Stratigraphic Thickness (m) / Time period (Ka).

To ground truth these sedimentation rates, studied rates of sedimentation were collected from different basins from around the world in similar geological and sedimentary settings from the literature:

• Nygård et al., 2005, Sejrup, 2004, Laberg, 2001,

Burgess and Hovius, 1998, Sommerfield, 2006

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• The calculated sedimentation rates show a clear declining trend from a very high rate of sedimentation for the recent 600Ka of

~1.5m/Ka, which falls over time to <0.5m/Ka along a power function trend.

• This trend is expected for numerous reasons and one of the key reasons is the resultant compaction that sediments undergo

during burial and thus the apparent systematic decrease in sedimentation rate through time.

• Nonetheless, the deposition during the Lower Cycle VIII shows a potential increase in rate away from the trend which

corresponds to a period of high deformation and thus accommodation space in the frontal syncline where the sedimentation rate is measured.

• This observation potentially also implies that a secondary source from the nearby Natuna High might have contributed to the

sediment supply of the Bunguran Trough during this period, in addition to the main supply from the Rajang Delta.

Key Observations from the Sedimentation Rates

• Present-day clastic outflows (picture

right) from Natuna Island are directed towards DW2F Bunguran Trough depocentre providing further evidence

• f sediment supply from the Natuna

High area.

View on Natuna (airplane perspective). The picture shows competition between clastic outflow areas (to Block 2F)

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• Regional Geological Overview
• Deformation Kinematics
• Sedimentation profiles
• Mineralogical compositional analysis
• Implication for the Bunguran trough

Talk Outline

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Jelawat-1 Mineralogical Composition Analysis

Right - bulk mineralogical composition of ditched cuttings from Jelawat-1 well intervals 2330-3421m (late Miocene –early Pliocene). Lower left –upper Miocene to lower Pliocene paleogeographic map by Shoup et al. (2012) indicating a land bridge connecting the Natuna High to the Borneo landmass.

Pliocene

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• Whilst the majority of grains consist of quartz, there is also a considerable element of

plagioclase and orthoclase. The latter may have biased the wireline interpretation in suggesting the higher clay content.

• Importantly, the presence of feldspar indicates a proximate sand source, given that

feldspars weathered quickly and do not survive multiple phases of reworking.

• In addition, all sandy intervals contain carbonate, probably cement, and fossil fragments;

which are indicative (i) for the proximity of nearby carbonate platforms and, (ii) water depth – carbonate is present, hence the point of sedimentation was above the CCD which corresponds to ca. 800m of water depth.

• A recent study of tectono-stratigraphic framework and Tertiary paleogeography of

Southeast Asia by Shoup et al. (2012) indicates that during the late Miocene –early Pliocene times, Natuna High was an exposed area connected to Borneo landmass and therefore likely a potential sediment source area for the deepwater Bunguran Trough.

Key Observations from Mineralogical Composition Analysis

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• Regional Geological Overview
• Deformation Kinematics
• Sedimentation profiles
• Mineralogical compositional analysis
• Implication for the Bunguran trough

Talk Outline

Significant progradation of the late Miocene to Plio-Pleistocene clastic sequences from Natuna High transporting proximate sandy sediment eastwards to deepwater Bunguran Trough area

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Structural Influence on Sedimentation Pattern

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Summary H7-H10.6

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Structural Influence on Sedimentation Pattern

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Jemuduk-1ST1 does not

• nly prove a working and

active hydrocarbon charging system of the Rajang Delta area; it also suggests potentially better development of sandy sedimentary fairways is possible, more than earlier thought, due to the perceived mud-prone nature of the Rajang Delta deltaic system. The Jemuduk sedimentary fairway would have carried sandy sediments downdip to the Bunguran Trough area forming viable turbidite targets.

Harun Alrashid et al., 2015

Implications of Jemuduk-1ST1 Well Results (PETRONAS, 2014)

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• The Bunguran Trough is dominated by young sediments of late Pliocene, Pleistocene, and even the

Holocene layer is several hundreds of meters thick. By its relative distance from continental shorelines of Borneo, it is logical to expect a clay-dominated environment.

• However, the study of the sedimentation rate and mineralogical composition of the Bunguran Trough

sediments, together with Jemuduk-1 well results, suggest more sand contents than thought possible.

• Additional sediment inputs from nearby Natuna High are suggested. Recently acquired multibeam

and 2D seismic data also supported a secondary source from the Natuna area.

• Additional feeders from now submerged areas of the Dangerous Grounds and Central Luconia

areas could have existed but these remain speculative.

• Overall delivery systems may have changed in transport direction over time.

Conclusions

Understanding the structural kinematics provides a very powerful and predictive tool for play fairway mapping!

THANK YOU

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Acknowledgements We thank contributions from our colleagues in DW2F exploration team and discussions with Operator PETRONAS Carigali in the neighbouring DW3F for a better and a meaningful regional understanding of the

• rigins of sedimentary succession recorded in

Bunguran Trough discussed in this presentation.