Quantitative Outcrop Analysis and Modelling of the Triassic fluvial Wolfville Formation(Nova Scotia, Canada)

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Abstract

Sub-surface reservoirs are normally characterised by limited information from widely spaced wells (1D sections) and relative low-resolution seismic data (2D or 3D sections) making any derived geological model highly interpretive. The ability of outcrop exposures to study the sedimentary architecture (e.g. stacking patterns, lateral continuation, facies proportions and distribution) at a wide range of scales (km to mm) in continuous 3D accessible sections make them ideal analogues to help bridge the gap in resolution between seismic and well data in reservoir studies.In this study the sedimentary architecture of the outcrop exposures the Late Triassic Wolfville Formation are evaluated using traditional sedimentological (e.g. correlation panels, log sections) and digital (e.g. DGPS, LiDAR, DEM) field techniques to help better understand these often complex fluvial depositional systems for analogue reservoir studies. The sediments of the Wolfville Formation are superbly exposed in both cliff sections and on extensive wave-cut platforms along the shore of the Minas Basin (Nova Scotia, Canada). The succession lies unconformably on Pre-Triassic rocks and forms the earliest syn-rift unit in the Fundy basin. The unit comprises coarse- and fine-grained fluvial sandstones, aeolian dune deposits, and alluvial fan sediments. The laterally extensive and three-dimensional nature of the outcrop exposures offer a valuable insight in the sedimentary architecture of the fluvial system. A detailed sedimentological analysis of the succession allowed the determination of the large-scale sedimentary architecture of this gravelly to sandy bedload fluvial system. In order to characterise the architectural evolution in more detail digital outcrop studies were employed in three carefully selected study areas. The study areas are located along the southern Minas Basin shore within the gravelly and younger sandy-dominated part of the succession.The digital outcrop studies carried out in the study areas collected spatial data using differential GPS and LiDAR (Light Detection and Ranging) equipment. The integration of traditional collected geological and spatial data forms digital outcrop models (DOMs), which allow accurate mapping and evaluation of the geological properties geometry and distribution using novel spatial analysis techniques (e.g. classified point-cloud and perpendicular projection plane method). The results offer a better understanding on the heterogeneity of the depositional system, accurate geostatistical information on the characteristics of sedimentary bodies and genetic units (geometry, distribution and proportion) and provides a high-resolution stratigraphic-structural framework for geocellular outcrop models. In the geocellular outcrop models of the study areas the three-dimensional facies distribution are simulated using various modelling approaches, such as sequential indicator simulations, object modelling and multiple point statistics. The available control of the outcrop models allowed the various facies modelling approaches to be examined. The results are evaluated and discussed using qualitative comparison studies. In addition, these outcrop models provided detailed information on the three-dimensional fluvial architecture.

Keyword(s)

Digital Outcrop Model; Fluvial; LiDAR; Wolfville Formation

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