Slope-fan depositional architecture from high-resolution forward stratigraphic models

Nicolas Hawie,Jacob A Covault,Dallas Dunlap,Zoltán Sylvester

doi:10.1016/j.marpetgeo.2017.12.033

Nicolas Hawie, Jacob A Covault + Show 2 more

Open Access

https://doi.org/10.1016/j.marpetgeo.2017.12.033

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Abstract

Submarine fans in tectonically active continental-slope basins are targets of petroleum exploration and production. These slope fans commonly comprise compensationally stacked sandy and muddy architectural elements, including mass-transport deposits, weakly confined to distributary channel-and-lobe deposits, and leveed-channel deposits. The lateral continuity and vertical connectivity of these architectural elements are important uncertainties in reservoir characterization that influence fluid-flow behavior during hydrocarbon production. Here, we use a simple forward stratigraphic model to simulate the stratigraphic patterns and illuminate the likely distribution of fine-scale, sub-seismic heterogeneity in a slope fan. We used published seismic-reflection horizons from the tectonically active Columbus basin, offshore Trinidad, to define the top and base of a Pleistocene submarine fan. We then simulated the stratigraphic evolution of the slope fan with a series of DionisosFlow™ forward stratigraphic models. All variables were kept constant during the simulations in order to test the hypothesis that the autogenic evolution of the surface topography alone, as a result of erosion and deposition, can produce compensational-stacking patterns common in submarine fans. A reference-case model is similar to the thickness trend of published isochron maps of the Trinidad slope fan. The reference-case model also produced patterns of compensational stacking. Varying the time step impacts the heterogeneity of the model. Shorter time steps are characterized by less sediment accumulation, which results in less sediment diversion during the subsequent time step, more gradual migration of channel deposits, shorter offset distances of depocenters, and shorter length-scale heterogeneity compared to longer time steps. Thus, a key characteristic of slope-fan deposits is autogenic compensational stacking, without any external forcing, which governs heterogeneity in these reservoirs. Furthermore, our results suggest that relatively simple diffusion-based models can produce realistic compensation patterns and future work will be focused on higher-resolution model calibration to seismic-reflection data and the influence of input variables on heterogeneity of channel-and-lobe deposits of slope fans.

Highlights

Even though all models show similar patterns of compensational stacking, from a qualitative perspective, shorter time steps result more gradual migration of channel deposits, shorter offset distances of depocenters, and shorter length-scale heterogeneity compared to longer time steps
The controls on the compensational stacking and depocenter evolution are autogenic in these models
The stratigraphic evolution of the depositional sequence offshore of Trinidad is similar to other systems in tectonically active slopes; in slope basins and stepped slopes with abrupt changes in gradient, masstransport deposits are overlain by weakly confined channel-and-lobe and leveed-channel deposits of a submarine fan (Brami et al, 2000; Moscardelli et al, 2006; Wood and Mize-Spansky, 2009)

Summary

Introduction

Submarine fans are depositional sinks of continental-margin sediment-routing systems, where they host stratigraphic archives of Earth history and environmental changes (Clift and Gaedicke, 2002; Fildani and Normark, 2004; Covault et al, 2010; 2011; Fildani et al, 2016).Submarine fans are important reservoirs of natural resources (Pettingill and Weimer, 2002).Early models characterized submarine fans as laterally extensive sheets in cross section with radial- or cone-like depositional morphologies in map view across unconfined basin floors of low relief and with gentle gradients (e.g., Shepard and Emery, 1941; Dill et al, 1954; Menard, 1955; Heezen et al, 1959; Bouma et al, 1985) (Fig. 1). Tectonically active slope basins and stepped slopes with abrupt changes in gradient commonly consist of ponded mass-transport deposits overlain by weakly confined to distributary channel-and-lobe deposits, which transition to perched, downstream-thinning wedges comprising leveed-channel deposits (Beaubouef and Friedmann, 2000; Brami et al, 2000; Beaubouef et al, 2003; Prather, 2003) (Fig. 1); mass-transport deposits and leveed channels are not always present (e.g., Jobe et al, 2017). Such tectonically active slopes are targets of petroleum exploration and production (e.g., the slope basins and stepped slopes of the Gulf of Mexico and the Niger Delta; Damuth, 1994; Pirmez et al, 2000; Sullivan et al, 2004; Prather, 2003; Rowan et al, 2004; Adeogba et al, 2005; Deptuck et al, 2012; Sylvester et al, 2012)

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