Comparison of digital outcrop and conventional data collection approaches for the characterization of naturally fractured reservoir analogues

Abstract

In this study, fracture systems developed within faulted, high-porosity sandstones in the decommissioned mines of Alderley Edge, Cheshire, UK are characterized using lidar (Light Detection And Ranging)-based analysis. The geometry of the mine workings prove to be conducive to the extraction of fracture attributes, whilst providing a degree of exposure of a notable Triassicaged reservoir outcrop analogue (Helsby Sandstone Formation) not afforded at the surface.To test the fidelity of the approach, fracture statistics generated from lidar-derived digital outcrop models are compared to an equivalent dataset collected using conventional manual surveys, with digital outcrop and manually acquired fracture attributes used to populate discrete fracture network models. These are upscaled to provide equivalent porous medium properties, enabling the impact of uncertainties introduced into fracture modelling workflows by lidarbased techniques to be assessed.Whilst broadly comparable to fracture attributes obtained using manual surveys, the systematic underrepresentation of fracture properties is observed within lidar-derived dataset, resulting in the underestimation of fracture network flow capacity. The study results suggest that, whilst enhancing data acquisition rates and coverage of exposure surfaces, the use of digital discontinuity analysis may introduce additional biases into fracture datasets, increasing the level of uncertainty within resultant modelled networks.

LiDAR, UAV or compass-clinometer? Accuracy, coverage and the effects on structural models

“…These detailed 3D reconstructions of outcrop geology are applied to a broad range of studies, including sedimentology and stratigraphy (e.g., Hodgetts et al, 2004;Enge et al, 2010;Fabuel-Perez et al, 2010;Eide and Howell, 2014;Rarity et al, 2014;Rittersbacher et al, 2014), reservoir modelling (e.g., Enge et al, 2007;Rotevatn et al, 2009;Buckley et al, 2010), and structural geology (e.g., Seers and Hodgetts, 2014;Bistacchi et al, 2015, among others). Light Detection and Ranging (LiDAR) has been the principal acquisition technique for deriving virtual outcrops in the last decade (e.g., Pringle et al, 2006;Buckley et al, 2008;Jones et al, 2009), though acquiring this type of detailed 3D spatial data requires expensive instrumentation and significant knowledge of processing workflows.…”

Reducing uncertainty and risk through field-based studies

“…centres becoming the norm in the industry, subsurface visualization and digital description has now become routine (Seers & Hodgetts 2014;Pyrcz & Deutsch 2014). With a requirement for sound input data, these advances have led to a resurgence in outcrop description and characterization.…”

Advances in the study of naturally fractured hydrocarbon reservoirs: a broad integrated interdisciplinary applied topic

“…Geologically appropriate outcrop analogues are also frequently studied as proxies for subsurface fracture networks (e.g. Bosworth et al 2012;Rotevatn & Bastesen 2012;Slightam 2012;Sonntag et al 2012;Seers & Hodgetts 2013), often in combination with other subsurface geophysical data. Numerical modelling including the finite element method (e.g.…”

“…Voyat et al 2006) and laser scanning techniques (e.g. Wilson et al 2011;Seers & Hodgetts 2013 to generate 3D digital outcrop models of the exposure (see 'Digital outcrop models' below).…”