Thus far, the subject of deep-marine sands emplaced by baroclinic currents associated with internal waves and internal tides as potential reservoirs has remained an alien topic in petroleum exploration. Internal waves are gravity waves that oscillate along oceanic pycnoclines. Internal tides are internal waves with a tidal frequency. Internal solitary waves (i.e., solitons), the most common type, are commonly generated near the shelf edge (100–200 m [328–656 ft] in bathymetry) and in the deep ocean over areas of sea-floor irregularities, such as mid-ocean ridges, seamounts, and guyots. Empirical data from 51 locations in the Atlantic, Pacific, Indian, Arctic, and Antarctic oceans reveal that internal solitary waves travel in packets. Internal waves commonly exhibit (1) higher wave amplitudes (5–50 m [16–164 ft]) than surface waves (
2 m [6.56 ft]), (2) longer wavelengths (0.5–15 km [0.31–9 mi]) than surface waves (100 m [328 ft]), (3) longer wave periods (5–50 min) than surface waves (9–10 s), and (4) higher wave speeds (0.5–2 m s–1
[1.64–6.56 ft s–1
]) than surface waves (25 cm s–1
[10 in. s–1
]). Maximum speeds of 48 cm s–1
(19 in. s–1
) for baroclinic currents were measured on guyots. However, core-based sedimentologic studies of modern sediments emplaced by baroclinic currents on continental slopes, in submarine canyons, and on submarine guyots are lacking. No cogent sedimentologic or seismic criteria exist for distinguishing ancient counterparts. Outcrop-based facies models of these deposits are untenable. Therefore, potential exists for misinterpreting deep-marine baroclinic sands as turbidites, contourites, basin-floor fans, and others. Economic risks associated with such misinterpretations could be real.
Added on 30 April, 2013
Integrated three-dimensional (3-D) paleomorphologic and sedimentary modeling was used to predict the basin architecture and depositional pattern of Pleistocene forearc basin turbidites in a gas hydrate field along the northeast Nankai Trough, off central Japan. Structural unfolding and stratigraphic decompaction of the targeted stratigraphic unit resulted in successful modeling of the paleobathymetry at the time of deposition. This paleobathymetry was characterized by a simple U-shaped paleominibasin. Subsequent turbidity current modeling on the reconstructed paleobathymetric surface demonstrated morphologically controlled turbidity current behavior and selective turbidite sand distribution within the minibasin, which strongly suggests the development of a confined turbidite system. Among three candidate inflow patterns, a northeasterly inflow pattern was determined as most likely. In this scenario, flow reflection and deflection caused ponding and a concentration of sandy turbidite accumulation in the basin center, which facilitated filling of the minibasin. Such a sedimentary character is undetected by seismic data in the studied gas hydrate reservoir formation because of hydrate-cementation–induced seismic anomalies. Our model suggests that 3-D horizon surfaces mapped from 3-D seismic data along with well-log data can be used to predict paleobasin characteristics and depositional processes in deep-water turbidite systems even if seismic profiles cannot be determined because of the presence of gas hydrates.
Added on 30 April, 2013
Japan has taken a leap forward in natural gas production by conducting the first successful production test of natural gas from marine hydrates. Could this be the“bridge” fuel needed in the coming energy transition?
Added on 01 June, 2013
Explorer Division Column EMD
Every six months, chairs of the Energy Minerals Division committees convene and report on developments in the areas they cover. In this column, we highlight important observations from these recent reports.
Added on 01 February, 2014
The AAPG Energy Minerals Division covers many scientific disciplines and interests – and because previous EXPLORER articles featured shale gas and oil shale, this quarter will focus on highlights from this year’s EMD November Mid-Year Meeting Commodity Reports.
Added on 01 February, 2013
If you have a pulse and have been to an AAPG Annual Convention and Exhibition (ACE) over the past couple of years or so, or a recent AAPG International Convention and Exhibition (ICE) such as those held in Calgary or Milan, you would have noticed.
Added on 01 February, 2012
It’s a new year, with a new EMD Executive Committee and president, and there is renewed interest in unconventional and alternative energy resources.
Added on 01 August, 2011
Gas hydrate, a crystalline compound of water and natural gas, has been touted as a vast potential energy resource for more than a decade – but realizing this potential has persistently remained beyond reach due to technical and economic hurdles.
Added on 01 May, 2010
The circum-Arctic region has ample energy potential, but innovative technology is essential for future exploration. One research geologist explains the need for combining tried and true geology basics with new, creative methods to get the best results.
Added on 01 November, 2010
Explorer Policy Watch
Sitting at his Oval Office desk on Aug. 2, President Obama signed into law the compromise agreed to by the House of Representatives and Senate to lift the nation’s debt ceiling and trim federal spending.
Added on 01 September, 2011