Towards the multi-scale characterization of braided fluvial geobodies from outcrop, core, ground-penetrating radar and well log data

Abstract

The integrated application of advanced visualization techniques – validated against outcrop, core and gamma ray log data – was found to be crucial in characterizing the spatial distribution of fluvial facies and their inherent permeability baffles to a centimetre-scale vertical resolution. An outcrop/behind outcrop workflow was used, combining the sedimentological analysis of a perennial deep braided outcrop with ground-penetrating radar profiles, behind outcrop optical and acoustic borehole imaging, and the analyses of dip tadpoles, core and gamma ray logs. Data from both the surface and subsurface allowed the recognition of two main architectural elements – channels and compound bars – and within the latter to distinguish between the bar head and tail and the cross-bar channel. On the basis of a well-constrained sedimentological framework, a detailed characterization of the gamma ray log pattern in the compound bar allowed several differences between the architectural elements to be identified, despite a general cylindrical trend. A high-resolution tadpole analysis showed that a random pattern prevailed in the channel, whereas in the bar head and tail the tadpoles displayed characteristic patterns that allowed differentiation. The ground-penetrating radar profiles aided the 3D reconstruction of each architectural element. Thus the application of this outcrop/behind outcrop workflow provided a solid database for the characterization of reservoir rock properties from outcrop analogues.

The geoengineering approach to the study of rivers and reservoirs

“…Exploration of the possible responses by geo/flow modelling and comparison of synthetic geotype curves with real build-up data can help to constrain the more appropriate architectural scenarios. The clay drapes internal to the compound bars described by Yeste et al (2018) and the calcretes described by Dal' Bó et al (2018) will reduce vertical permeabilityconditions whereby the lateral connectivity will become the critical aspect of pressure support. The model of Yeste et al (2018, fig.…”

“…A Triassic sandstone geobody has been studied by Yeste et al (2018) from the Triassic red beds of the Iberian Meseta (TIBEM) Formation in south-central Spain and interpreted to record the sedimentary dynamics of a fluvial braidplain. This particular example has been highlighted in the literature as an outstanding outcrop analogue for productive reservoirs such as the Algerian TAGI (Trias Argilo-Gréseux Inférieur) (Yeste et al 2018). The analysis of architectural elements in outcrop allows differentiation of the sub-environments of deep perennial channel, compound bar, cross-bar channel and bar tail elements.…”

“…In this section a number of studies on modern systems (Blum 2019;Sinclair et al 2016;Nicholson et al 2019) are compared with ancient counterparts, from the Cenozoic (Stow et al 2016) and Mesozoic (Dal' Bó et al 2018;Yeste et al 2018;Fambrini et al 2019) through to the Paleozoic (Reesink 2016;Ellen et al 2018). In reconciling these two timescales, it is necessary to find common ground between studies which focus on the plan-view (topdown) evolution of fluvial systems (often the focus of modern studies) and the cross-sectional view often employed by studies of ancient relict landforms in the geological record.…”

“…In the previous section a number of authors generated 2D panels (Stow et al 2016;Fambrini et al 2019) and developed 3D reconstructions of outcrop architecture (Ellen et al 2018;Yeste et al 2018). These models and the data collected in the field can be used for training images and statistical datasets for the building of 3D reservoir models (Martinius et al 2014;Beaumont et al 2016).…”

Reservoir architecture and heterogeneity distribution in floodplain sandstones: Key features in outcrop, core and wireline logs

“…away from the channel-belt axis (Ghinassi et al, 2014;Ielpi & Ghinassi, 2014). Tadpole sets with random azimuth and dip angles, between 5°and 25°, represent the foresets of trough cross-bedding (Donselaar & Schmidt, 2005;Viseras et al, 2018;Yeste et al, 2018). Donselaar & Schmidt (2005) have also identified tadpole patterns with unidirectional azimuths and very low dip angles for crevasse-splay deposits.…”