GEOCLASTICA Ltd

Dr ROGER HIGGS
rogerhiggs@geoclastica.com

Consulting in Petroleum Sedimentology
& Sequence Stratigraphy

Bude, Cornwall, UK +44 7880 515748


LECTURE: 'THE EMPEROR'S NEW FAN' …

Why Foreland-Basin "Deep-Sea" Flysch Turbidites Are Not Deep & Why This Is Crucial For Oil Companies


It is now clear that ten renowned, outcropping, foreland-basin, "deep-sea" flysch formations (Annot, Brushy Canyon, Bude, Cerro Toro, Hecho, Jackfork, Laingsburg, Marnoso-arenacea, Ross, Skoorsteenberg) are in fact shelfal…

download Higgs AAPG 2008 abstract (78KB)

download Higgs AAPG 2009 Discussion (5 pages, 810KB)

download Higgs IAS 2013 abstract (71KB)

download AAPG 2014 abstract (69KB)

weblink to Higgs AAPG 2014 article & poster (9.5MB)

…based partly on abundant mud-draped scours (wave erosion) and frequent beds with HCS and/or combined-flow ripples. This 'foreland flysch' or 'shelf flysch' is not to be confused with the 'nappe flysch' of the adjacent accretionary prism, comprising trench and ocean-floor strata (with "flysch-type" foram assemblages) scraped off subducted ocean crust, and commonly more structurally deformed than shelf flysch.

Alarmingly, many oil companies use the ten shelf-flysch formations as supposed outcrop analogs for predicting the geometry and architecture of passive-margin deep-sea turbidite reservoirs (slope basins; sinuous leveed channels; base-of-slope fans), despite four major contrasts that, collectively, must profoundly influence sand distribution and lateral-vertical connectivity, as well as sand-body dimensions: (1) continental basement (foreland) vs oceanic; (2) tectonically active vs passive, affecting subsidence rate, seismicity (injectites) and highland proximity (sediment calibre); (3) shallow water (c. 10-100 m) versus deep (0.5-5 km), only the former experiencing intermittent planation (erosion) by storm waves (e.g. levees impossible); and (4) feeder slope short vs long (continental slope), affecting the relative abundance of river-fed turbidites (hyperpycnites) vs slump-induced turbidites. The “analogs”, far from being deep-sea fans and leveed channels, were deposited during times of low eustatic amplitude (hence no Quaternary examples) on 'flysch shelves' indented by submarine-canyon heads. Their highly inappropriate use as analogs for deep-sea-turbidite reservoirs risks billions of dollars in non-optimum borehole placement and, even worse, unwarranted declaration of field economic viability (or non-viability!).

On the other hand, the outcrops are good analogs (and self-analogues) for productive shelf-flysch reservoirs (e.g. Brushy, Jackfork, Marnoso, Puchkirchen-Hall), and are potential analogs for turbidite reservoirs deposited in other intracontinental basins (rift, sag), in arguably shallower water than is generally believed (e.g. Forties Member?).

Stay abreast of this developing, still largely unpublished, sedimentological breakthrough (see 2013-15 references on CV/Publications page). For more details, click on "Outcrop Analog Field Trips" below.

To arrange a presentation at your company offices and/or consultation on your turbidite reservoir issues (including examination of logs, cores, etc.), please email rogerhiggs@geoclastica.com

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Homepage CV & Publications
Bude Turbidite Research Centre Petroleum Sedimentology Course
Turbidite Reservoir Analogs Lecture Outcrop Analog Field Trips
Core & Outcrop Facies Logging Sandstone Porosity Prediction
South America Consulting Bude Geological Walks & Talks
Non-Exclusive Exploration Reports for Sale:
Trinidad Venezuela