An Overview of Deepwater Reservoir Elements in the Eastern Mediterranean
Shelf-Margin Depositional lobe Seafloor characteristics: lobate patterns Delta (sheet) Levees Channel Depositional lobe (sheet) Friedmann et al., 2000 Pirmez et al., 2000 Modern slope of Nigeria
Choosing the best depositional analogs for the Levant Best analogs: Base-of-slope turbidite systems Unconfined area (no major bathymetric highs creating sediment traps) Modern oceanic depths Fed by updip area with large drainage systems Sediments are delivered by submarine canyon (possibly) Best producing analogs: northern Gulf of Mexico (unconfined area), Miocene, Paleogene Okay analogs: intraslope basins (GOM, Angola); Cenozoic-Brazil; Base-of slope unconfined, limited drainage and water depths (Lower Cretaceous, NW Shelf of Australia) North Sea (Upper Jurassic through Eocene). Good published examples for production: Thunder Horse, Mars, Augur (high porosity and permeability values, little diagenesis)
Northern Gulf of Mexico Lowstand Paleogeography Kendrick (1998)
Unconfined deepwater systems: Seafloor image False-color image derived from the GLORIA II side-scan sonar image of the Mississippi Fan surface. Brighter colors: sand-rich, depositional lobes (red and yellow colors) at Sinuous channel the termini of the channels. Blue areas: finer-grained, overbank sediments.. 7 6 Depositional lobes 5 1 4 2 3 Wen et al., 1995
Slope settings: erosional channels and their fill
Unconfined settings: depositional lobes Gardosh, 2012
Unconfined settings: depositional lobes Gardosh, 2012
Deepwater reservoir elements: lobe reservoirs Lobe (Sheet) sands and sandstones: some of the best high-rate, high-ultimate-recovery (HRHU) reservoirs in deep water. Characteristic sedimentary features in cores/outcrops: massive to graded beds with non-erosive bases that have conformable, non-erosive bed contacts Simplest reservoir geometries: good lateral continuity, potentially good vertical connectivity, high aspect ratio (> 500:1), narrow range in grain size (and thus greater porosity and permeability), and few erosional features .
Deepwater reservoir elements: lobe reservoirs Unlike other deepwater reservoir elements, lobe (sheet) sands commonly have an areal extent that exceeds the area of the trap Sealing capacity of interbedded shales is potentially important Diagenesis generally not a problem in “ younger ” reservoirs, i. e. Miocene or younger, or those without significant burial. Commonly certain layers will be more permeable than others; sometimes this is related sorting
Northern Gulf of Mexico Lowstand Paleogeography Kendrick (1998)
Northern Gulf of Mexico: Unconfined lobes now in Foldbelt K2/Timon Shenzi Neptune OBN WAZ & NATS Merge, OBN WAZ & NATS Merge, TTI RTM -2010 TTI RTM -2010 Mad Dog Atlantis Puma Frampton Green Knoll ’ ’ Walker et al, 2012 ’ ’
Fan System Salt near seafloor lower Miocene in early Miocene lobes 10 Miles ? K2 Komodo Shenzi ? Atlantis Puma Mad Dog Dendara Frampton GC AV Green Knoll WR L Walker et al, 2012
Regional correlation of lower Miocene depositional lobes Green Puma Mad Dog Shenzi Komodo Knoll 200 feet 12 Miles 8 Miles 15 Miles 13 Miles Walker et al, 2012
Regional correlation of lower Miocene depositional lobes Green Puma Mad Dog Shenzi Komodo Knoll DD EE upper FF 200 feet lower FF 12 Miles 8 Miles 15 Miles 13 Miles Walker et al, 2012
Depositional lobes: reservoir architecture Mander et al, 2012
Depositional lobes: reservoir architecture 200 feet 3 Miles 7 Miles 7 Miles Mander et al, 2012
Depositional lobes: reservoir architecture 200 feet Mander et al, 2012
Depositional lobes: details in reservoir architecture lobe complex ( or fan) DD fan lobe lobe bed element fan EE complex fan Expected dimensions of architectural elements 0.1 km x 0.1 km x 0.5 m upper (from Karoo FF 5 km x 3.5 km x 2 m basin analog: fan Prelat, and others, 2010) 27 km x 13km x 5 m lower FF 44 km x 29 km x 50 m fan 95 km x 80 km x 170 m (this study) Mander et al, 2012
Depositional lobes: details in reservoir architecture Much of this detail is below seismic resolution Mander et al, 2012
Summary: reservoir lessons learned Although lobe (sheet) sands and sandstones are considered to be some of the best deepwater reservoirs, each field has its own set of characteristics that make it a challenge to produce. Several case studies of fields with lobe (sheet) reservoirs indicate that the initial reservoir models were overly simplistic, and the actual complexity of the reservoir was only discovered with field production. Shales at various scales are important because they, too, are laterally extensive and offer the potential for isolating individual sheet sands and sandstones and packages of sheet sands and sandstones. In some reservoirs, this results in multiple fluid contacts and depletion rates. Development scenarios should make use of the sealing capacity of shales for selective water flooding and horizontal drilling .
Deepwater reservoir elements: channel-fill reservoirs Channel-fill reservoirs: have proven to be great reservoirs in some deepwater settings (Angola (> 4 Bbbls), Nile (> 50 Tcf), Nigeria, Gulf of Mexico, North Sea). Channels have relatively low aspect ratios (30:1 to 300:1) and are considerably longer than they are wide. Channels vary from erosional to erosional/aggradational to purely aggradational (channel-levee) types. On seismic-reflection data, channel fills show a variety of geometries, including shingled reflections (laterally migrated packages), offset patterns with aggradational fill, and entirely aggradational fill. Lithofacies and grain-size distribution are also highly variable in channel-fill deposits and create many baffles and barriers to pressure and fluid communication.
Slope settings: erosional channels and their fill
Treacle (D) Polaris (C) Subregional Strike Line Giza North (B) Giza South (A) 10km Butterworth, 2012 150km
Mid Pliocene-Pleistocene WND Strike Section SW NE MTD Giza Channel P80 MFS Complex Set slide Lobes P78 MFS MTD 200m Leveed channels 2 km Slide blocks Butterworth, 2012
A. Giza South proximal ~ 35km from shelf edge 100ms 100ms 100ms 750m 750m 750m B. Giza North ~ 50km from shelf 100ms 100ms 100ms 750m 750m 750m C. Polaris ~ 75km from shelf distal 100ms 100ms 100ms 750m 750m 750m D. Treacle ~100km from shelf 750m 750m 750m 100ms 100ms 100ms Butterworth, 2012
flattened time slice Stage IV Stage IV III Stage II Stage I Stage 0 400m Abandonment levee Muddy channel Sandy channel element Abandonment levee – along axis Levee (external) Sandy channel element - axis Levee (internal) Lobe Sandy channel - margin Butterworth, 2012
flattened time slice + 100ms flattened time slice + 80ms flattened time slice + 60ms GIZA NORTH-1 GIZA NORTH-1 GIZA NORTH-1 NAB-1 NAB-1 NAB-1 flattened time slice + 40ms flattened time slice + 20ms flattened time slice GIZA NORTH-1 GIZA NORTH-1 GIZA NORTH-1 NAB-1 NAB-1 NAB-1 Butterworth, 2012
GN-1 Butterworth, 2012 • Downdip of Structure: 10m Preservation of Channel Axis • Updip of Structure: Preservation of channel margin and levee Giza North-1-P80-Channel Complex GS-1 A SLT B C SST D E TB F MST SLT G H SST SLT SST MST TB TB Giza South-1-P80-Levee A B SLT C SLT D TB TB MST E TB F G H
Abandonment Amalgamated Lobes & Levees & Levees “ Terminal Lobes ” IV. Constructional Phase Turbidite Silts Injected Sand 145 m “ channel complex set ” III. Switchoff 15m incision Channel “ channel element ” II. Aggradational Margin axis Phase I. Erosion & Bypass 40-50m incision 1.5 km “ channel complex ” Thin Bedded, Laminated Thick Bedded, Graded, Massive Butterworth, 2012 Muddy Debrites
Summary: reservoir lessons learned Although channel fills are internally complex, the complexity is arranged in a hierarchical pattern, which is recognizable at outcrop (large) and seismic scales. It may be more difficult, but not impossible, to identify the hierarchy in wellbores and cores. Because of the extreme complexity of channel fills, reservoir performance can vary laterally within a reservoir. Proper well spacing and orientation are imperative for effectively draining hydrocarbons from channel fills. Proper well placement requires a knowledge of the nature of the fill that can only be determined with sufficient data early in the life of the field. Collect as much static data during drilling (e.g. cores, wireline and image logs, biostratigraphy) and collect dynamic data frequently to monitor. Spectacular failures: Mauritania example
Unconfined settings: deeper targets Gardosh, 2012
Additional potential reservoirs? Large volumes of reserves have been found in the Mesozoic strata in many deepwater margins in the world Need good 3D seismic resolution to accomplish Deeper targets: although largely fine-grained, potential for good sands to develop Local build-ups Possibly fractured Lessons from the Santos Basin, Brazil
: Microbialite carbonates
Finis
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