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AAPG Bulletin

Abstract

AAPG Bulletin, V. 100, No. 2 (February 2016), P. 213-235.

Copyright ©2016. The American Association of Petroleum Geologists. All rights reserved.

DOI: 10.1306/09011514210

Mass-transport and slope accommodation: Implications for turbidite sandstone reservoirs

Ben Kneller,1 Mason Dykstra,2 Luke Fairweather,3 and Juan Pablo Milana4

1Department of Geology and Petroleum Geology, School of Geosciences, University of Aberdeen, Aberdeen AB24 3UE, United Kingdom; [email protected]
2Colorado School of Mines, Golden, Colorado 80401; present address: Statoil Gulf Services, 6300 Bridge Point Parkway, Building 2, Suite 500, Austin, Texas 78730; [email protected]
3Department of Geology and Petroleum Geology, University of Aberdeen, Aberdeen AB24 3UE, United Kingdom; present address: Dana Petroleum, 62 Huntly St, Aberdeen AB10 1RS, United Kingdom; [email protected]
4Faculdad de Ciencias Exactas, Fisicas y Naturales, Universidad Nacional de San Juan, San Juan, Argentina; [email protected]

ABSTRACT

Mass-transport events are virtually ubiquitous on the modern continental slope and are also frequent in the stratigraphic record, but the potential they create for stratigraphic trapping within the sea-floor topography is not generally appreciated. Given the abundance of mass-transport deposits (MTDs), we should expect that many turbidite systems are so affected. The MTDs may be very large (volumes > 103 km3 [∼250 mi3], areas > 104 km2 [∼6250 mi2], thicknesses > 102 m [∼330 ft]), and they extensively remold sea-floor topography on the continental slope and rise. Turbidity currents are highly sensitive to topography; thus, turbidite reservoir distribution and geometry on the slope and rise are often significantly affected by subjacent MTDs or their slide scars. Turbidites may be captured within slide scars and on the trailing edges, margins, and rugose upper surfaces of MTDs; developed in accommodation when the mass movement comes to rest; or subsequently resulting from compaction or creep. The filling of such accommodation depends on the properties of the turbidity currents, their depositional gradient, and how they interact with basin floor topography. The scale of accommodation on top of MTDs is determined largely by the dynamics of the initial mass flow and internal structure of the final deposit, and it typically has a limited range of length scales. We present interpretations of a range of previously published and original case studies to illustrate the range of accommodation styles associated with MTD-related topography within the evacuated space of the slide scar, around and on top of the deposits themselves. In fact, several well-known deep-water outcrops probably represent examples of sedimentation influenced by MTDs.

Hydrocarbon reservoirs in many slope settings may be controlled by the accommodation related to MTD topography. At the exploration scale, entire shelf margin and slope depositional systems may be contained within the scars evacuated on the upper slope by mass failure, whereas at the production scale, the rugosity on the top of MTDs creates widespread potential for stratigraphic trapping. The location, geometry, and property distribution of such reservoirs are closely controlled by the interaction of turbidity currents with the topography; thus, an understanding of these processes and their impact on slope stratigraphy is vital to reservoir prediction.

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