Integrated Outcrops and Subsurface Studies
Published:January 01, 2011
Abstract: Mass-transport deposits may act as barriers or baffles to fluid flow in the subsurface, or may conduct fluids via internal structures or lithological connectivity. Conventional seismic and borehole data present radically different scales of observation to assess the likely fluid-flow behavior of mass-transport deposits. Seismic-scale outcrops and high-resolution seismic data bridge this scale gap. Exceptional outcrops of large mass-transport deposits are used to develop strategies to relate core- and seismic-scale observations for the purposes of subsurface prediction of reservoir, baffle, or seal potential, and for prediction of fluid flow through mass-transport deposits in the subsurface. We present here an outline of our approach, and some preliminary results based on two systems of contrasting styles. One is a > 120-m-thick debrite of Carboniferous age in northwest Argentina; the other is an approximately 300-m-thick slide complex of Jurassic-Cretaceous age in Antarctica. Differences in these two systems are assessed by evaluating the internal structure and seismic expression of the deposits, based on forward modeling of the outcrop architecture. Topography on the top surface of mass-transport deposits is defined by very localized (a few meters wavelength and amplitude), localized (a few tens of meters wavelength, a few meters to ~ 10 m amplitude), and subregional (kilometers in wavelength, tens of meters in amplitude) “ponding” or partial confinement of turbidite beds immediately above the mass-transport deposits. Strain histories and strain distributions are complex and variable within deposits, implying that inferences based on limited well data are likely to yield incorrect conclusions regarding direction of movement and slope orientation. This observation is clearly illustrated by the non-coaxial deformation, which is visible in high-resolution seismic data.
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Mass-Transport Deposits in Deepwater Settings
Historically, submarine-mass failures or mass-transport deposits have been a focus of increasingly intense investigation by academic institutions particularly during the last decade, though they received much less attention by geoscientists in the energy industry. With recent interest in expanding petroleum exploration and production into deeper water depths globally and more widespread availability of high-quality data sets, mass-transport deposits are now recognized as a major component of most deep-water settings. This recognition has lead to the realization that many aspects of these deposits are still unknown or poorly understood. This volume contains twenty-three papers that address a number of topics critical to further understanding mass-transport deposits. These topics include general overviews of these deposits, depositional settings on the seafloor and in the near-subsurface interval, geohazard concerns, descriptive outcrops, integrated outcrop and seismic data/seismic forward modeling, petroleum reservoirs, and case studies on several associated topics. This volume will appeal to a broad cross section of geoscientists and geotechnical engineers, who are interested in this rapidly expanding field. The selection of papers in this volume reflects a growing trend towards a more diverse blend of disciplines and topics, covered in the study of mass-transport deposits.