The 3-D Seismic Geomorphology of Deep-Water Slope Channel Systems A Case Study from the Deep Water Nile Delta

Transcription

1 Geological Society of Trinidad & Tobago The 3-D Seismic Geomorphology of Deep-Water Slope Channel Systems A Case Study from the Deep Water Nile Delta Nigel E. Cross

2 Presentation Outline Introduction Deep water channel systems The Nile Delta Modern day Slope Process Large-scale character and Channel Sandbodies Case Study The Sequoia Complex Sedimentology Large-Scale Reservoir Architecture Sequence Stratigraphic Context Component Sandbodies Channel System Evolution Conclusions - Implications for Reservoir Heterogeneity 2

3 Deep-Water Channels Major Sediment Pathways Rosetta Delta Channelised debrisflows WDDM Slope Inner fan Slope apron Outer fan Frontaol lobe High-sinuosit y channels and levees Supra-fan (modified from Reading and Richards 1994)

4 Nile Delta Tectono-Stratigraphic Setting 0 Pliocene slope channels in the b WDDM concession (e.g. Sequoia Field) situated above the NDOA high km 8 Plio-Pleistocene Miocene Cretaceous Depth (km) Messinian Salt Palaogene Basement Cross-section modified after Aal et al.,

5 The West Offshore Nile Delta, Egypt E E North 1000 m Water Depth 500 m M E D I T E R R A N E A N S E A Alexandria Port Said N 100 m EGYPT CAIRO Suez 0 10 km Prolific Pliocene gas province with multi-tcf fields 5

6 Pliocene Nile Delta - Large-Scale Character Sapphire 40 Sands Sapphire 70 Sands Unconfined systems with combination traps Taylor et al. (2009)

7 Pliocene Nile Delta - Large-Scale Character Sapphire 40 Sands Sapphire Da Db Dc Dd NDOA/SD Df/S3 Dh/Dq S4 Gas chimn ey 40/ Sapphire 70 Sands Unconfined systems multi-storey slope systems Taylor et al. (2009)

8 Nile Delta Pliocene Slope Channel Elements Amalgamated lateral splays type II Straight mud-filled channel Straight sand-filled discontinuous channels Sinuous sand-filled continuous channels Straight sand-filled continuous channels Sinuous sand-filled discontinuous channels Basal splays Amalgamated lateral splays type I Layered overbanks Sinuous mud-filled channel Layered lateral splays Isolated splays Frontal splays The fundamental building blocks to reservoir architecture Taylor et al. (2009)

9 Present Day East Coast Trinidad Sea-floor Shelf slope higher gradients with straighter channel courses, gravity tectonics and mass transport complexes. Lower slope/base of slope lower gradients with meandering channels. Syn-or post- tectonic deposition with channels diverted around tectnic highs (thrusted structures associated with Barbados accretionary prism. 50 km From Huyghe et al. (2004) Gravity flow processes on the present day deep water slope 9

10 Deep Water Channels Systems in Trinidad Frontal splay complex with channel breakthrough Crevasse splays on the outer bends of channels Sinuous channels Complex arrangement of lateral and frontal splays NB if amplitude = sand then the channels are mud-prone Image courtesy of Adrian Thomas 10

11 The Sequoia System Case Study E E Line of section North 1000 m Water Depth 500 m M E D I T E R R A N E A N S E A Alexandria Port Said N Sequoia Field 100 m EGYPT CAIRO Suez 0 10 km Prolific Pliocene gas province with multi-tcf fields 11

12 The Sequoia Field Geological Overview 0 5 km North Stages Gamma Ray 0 (API) 150 Scale (m) Neutron 0.45 (frac) Densit y 1.95 (g/cc) Resistivity 0.2 (ohm.m) Field Outline V IV 100 III TST 50 Maximum Magnitude Thickness Isopach m II SB I 0 Sequoia channel system - 10 s km long, c.5km wide and up to 200m thick 12

13 Sedimentological Character 10 cm Massive sandstones erosional bases and commonly sharp tops. Graded sandstones Injected sandstone beds Thinly bedded (cmscale) sands and shales Laminated pelagic shales A range of sandstone and thinly bedded, channelised gravity flows 13

14 Large-Scale (Strike) Reservoir Architecture West East West East Correlatable down-lap flooding surface (?mfs) High net-to-gross reservoir Low net-to-gross reservoir W ater-bearing reservoir (perched) Base channel 100 m 0 0 Vert. Exag. x12 Scale 5 km Base channel Major basal erosion surface with nested channelised fill 14

15 Large-Scale (Dip) Reservoir Architecture South North Prograding lobate sand-sheets Correlatable dow n-lap flooding surface (?mfs) Seismic flat- spot (GWC) Highnet-to-gross reservoir Low net-to-gross reservoir W ater-bearing reservoir Perched water Intra-reserv oir grow th fault Base channel Position of NDOA high Perched water in topographic lows unconnected to regional aquifer? 15

16 Sequence Stratigraphical Context Prograding top-seal slope deposits Correlatable seismic down-lap surface Low net-to-gross with thin-beds and small sandy channels High net-to-gross with with well developed channel sandbodies Major slope incision surface Highstand Systems Tract Maximum Flooding Surface Late Lowstand-Transgressive Systems Tract Lowstand Systems Tract Sequence Boundary Lowstand incision with late lowstand to transgressive fill? 16

17 Component Sandbodies Laterally amalgamated channels Aggrading sinuous channels Channels with frontal splays Prograding sandsheets Seismically-defined elements calibrated by core and FMI data 17

18 Laterally Amalgamated Channels North Channel belt 1-2km wide Remnant pods 100 s m scale Channels up to 30m thick 2km Basal part of channel system dominated by laterally stacked channels 18

19 Aggrading Sinuous Channels North Channels 10 s km long and m wide Thickness of 10-20m and stacks up to 80m thick. 2km Medial parts of stratigraphy dominated by aggradational channels 19

20 Aggrading Sinuous Channels North Line A-A Line B-B A A 600 m B B 600 m Aggradational stacking pattern with limited lateral migration 20

21 Channels with Frontal Splays Channel components are 1-2km long and c.100m wide Frontal splays are 1-2km long and 500m and 2km wide d Sandbodies c.10-15m thick b Composite sandbodies built of low efficiency flows 2km Composite channelised sandbodies built of low efficiency flows 21

22 Syn-Sedimentary Tectonics North 1 km 2 km 1 km Channel diversions and ponding suggest syn-depositional tectonics 22

23 Syn-Sedimentary Tectonics Ponding of flows and deflection of flows on to the footwall of syn-sedimentary fault Extensional growth fault Channel course deflected around the tip of synsedimentary normal fault Northward flow Direction Channel diversions and ponding suggest syn-depositional tectonics 23

24 Prograding Sandsheets North Lobate planforms up to 4km wide down-dip Sandsheets are c.10m thick. Fed by very narrow (50-100m wide) sinuous channels Shingled stacking 2km Further suggestion of syn-depositional tectonics? 24

25 Stratigraphic Evolution of the Channel System Stage I III IV VI Sediment Laterally Aggrdational Channel Abandonment Prograding by-pass, with amalgamated sandsheets sinuous frontal erosion maximum splays and slumping channels and flooding leveed Channel channels initiation 6 stages in the evolution of the Sequoia channel system 25

26 Conclusions Impact on Reservoir Heterogeneity Abandoment mudstones (Stage V) at the top of the reservoir provide a seal and isolate the sandsheets above (Stage VI) General upward decrease in sand content through reservoir Smaller composite channels comprising small channels with frontal splays higher potential for isolation (Stage IV) West East Irregular incision surface traps perched water (Stage I) Injected sand has the potential to vertically link otherwise isolated sandbodies (Stage IV) c. 50m c.2km Aggradational sinuous channels promote vertical connectivity (Stage III) Amalgamated channels with high degree of lateral connectivity (Stage II) Thin beds increase lateral connectivity between isolated channels (Stage III) Reservoir heterogeneity intimately linked with channel system evolution 26