An Overview of Deepwater Reservoir Elements in the Eastern Mediterranean Depositional lobe Seafloor characteristics: lobate patterns (sheet) Shelf-Margin Delta Levees Channel Depositional lobe (sheet) Friedmann et al., 2000 Modern slope of Nigeria Pirmez et al., 2000 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 Sinuous channel 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 the termini of the channels. Blue areas: finer-grained, overbank sediments.. 7 6 Depositional lobes 5 1 2 Wen et al., 1995 4 3 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 Single Azimuth NATS, Isotropic CAWE - 2003 OBN WAZ, Isotropic SM 2008 Mad Dog Atlantis Puma Frampton 3000’ Green Knoll VE 2.7:1 Walker et al, 2012 9000’ OBN WAZ & NATS Merge, TTI RTM -2010 Fan System Salt near seafloor in early Miocene lower Miocene lobes 10 Miles ? K2 Komodo Shenzi ? Atlantis Puma Mad Dog Dendara Frampton Green Knoll GC AV WR L Walker et al, 2012 Regional correlation of lower Miocene depositional lobes Green Knoll Puma Shenzi Mad Dog Komodo 200 feet 12 Miles 8 Miles 15 Miles 13 Miles Walker et al, 2012 Regional correlation of lower Miocene depositional lobes Green Knoll Puma Shenzi Mad Dog Komodo DD EE 200 feet upper FF 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) lobe lobe element DD fan bed EE fan fan complex Expected dimensions of architectural elements 0.1 km x 0.1 km x 0.5 m 5 km x 3.5 km x 2 m 27 km x 13km x 5 m (from Karoo basin analog: Prelat, and others, 2010) lower FF fan 44 km x 29 km x 50 m 95 km x 80 km x 170 m upper FF fan (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 150km Butterworth, 2012 Mid Pliocene-Pleistocene WND Strike Section SW NE MTD Giza Channel Complex Set P80 MFS slide Lobes P78 MFS MTD 200m Leveed channels 2 km Slide blocks Butterworth, 2012 A. Giza South proximal ~ 35km from shelf edge 100ms 750m 750m B. Giza North ~ 50km from shelf 100ms 100ms 750m 750m C. Polaris ~ 75km from shelf 100ms 100ms 750m distal 750m D. Treacle ~100km from shelf 100ms 100ms 750m 750m Butterworth, 2012 flattened time slice Stage IV Stage IV III Stage II Stage I Stage 0 400m Sandy channel element Abandonment levee Muddy channel Sandy channel element - axis Abandonment levee – along axis Levee (external) Sandy channel - margin Levee (internal) Lobe Butterworth, 2012 flattened time slice + 100ms flattened time slice + 80ms GIZA NORTH-1 flattened time slice + 60ms GIZA NORTH-1 NAB-1 flattened time slice + 40ms GIZA NORTH-1 NAB-1 flattened time slice + 20ms GIZA NORTH-1 flattened time slice GIZA NORTH-1 NAB-1 NAB-1 GIZA NORTH-1 NAB-1 NAB-1 Butterworth, 2012 GN-1 Butterworth, 2012 •Downdip of Structure: Preservation of Channel Axis 10m • Updip of Structure: Preservation of channel margin and levee Giza North-1-P80-Channel Complex GS-1 A SLT B SST C D E TB F MST SLT G H SLT MST SST SST TB TB Giza South-1-P80-Levee A B SLT SLTC TB D MSTE F G H TB TB Abandonment Levees & “Terminal Lobes” Amalgamated Lobes & Levees Turbidite Silts Injected Sand III. Switchoff II. Aggradational Phase Margin I. Erosion & Bypass 1.5 km Channel axis 15m incision “channel element” 145 m “channel complex set” IV. Constructional Phase 40-50m incision “channel complex” Thin Bedded, Laminated Thick Bedded, Graded, Massive Muddy Debrites Butterworth, 2012 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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