An integrated workflow for stress and flow modelling using outcrop-derived discrete fracture networks

Abstract

Fluid flow in naturally fractured reservoirs is often controlled by subseismic-scale fracture networks. Although the fracture network can be partly sampled in the direct vicinity of wells, the inter-well scale network is poorly constrained in fractured reservoir models. Outcrop analogues can provide data for population of domains of the reservoir model where no direct measurements are available. However, extracting relevant statistics from large outcrops representative of inter-well scale fracture networks remains challenging. Recent advances in outcrop imaging provide high-resolution datasets that can cover areas of several hundred by several hundred meters, i.e. the domain between adjacent wells, but even then, data from the high-resolution models is often upscaled to reservoir flow grids, resulting in loss of accuracy. We present a workflow that uses photorealistic georeferenced outcrop models to construct geomechanical and fluid flow models containing thousands of discrete fractures covering sufficiently large areas, that does not require upscaling to model permeability. This workflow seamlessly integrates geomechanical Finite Element models with flow models that take into account stress-sensitive fracture permeability and matrix flow to determine the full permeability tensor. The applicability of this workflow is illustrated using an outcropping carbonate pavement in the Potiguar basin in Brazil, from which 1082 fractures are digitised. The permeability tensor for a range of matrix permeabilities shows that conventional upscaling to effective grid properties leads to potential underestimation of the true permeability and the orientation of principal permeabilities. The presented workflow yields the full permeability tensor model of discrete fracture networks with stress-induced apertures, instead of relying on effective properties as most conventional flow models do.

Is the permeability of naturally fractured rocks scale dependent?

“…Recently, Bisdom et al . [] also introduced a workflow for integrating geo‐mechanics and full‐tensor permeability calculations into outcrop modeling studies. Arguably, these studies may not have investigated sufficiently large samples of the fracture population to reproduce the statistics seen in the field [ Paluszny and Matthai , ; Nick et al ., ; Bisdom et al ., , , ].…”

Upscaling of the single-phase flow and heat transport in fractured geothermal reservoirs using nonlocal multicontinuum method

“…Such numerical applications have been discussed in existing literature studies [52], but not in a computationally efficient multiscale framework. Moreover, in the context of coupled thermo-hydromechanical-chemical (THMC) processes, fracture alteration is an area of research for the geothermal heat recovery [6,7,36,41,42]. Computational expenses are always an issue even for modern computers.…”

The Role of Chemistry in Fracture Pattern Development and Opportunities to Advance Interpretations of Geological Materials

“…Consequently, outcrop fracture studies are an essential element in a strategy for learning about fracture patterns existing at depth. Outcrop fracture mapping is undergoing a renaissance owing to recent advances in remote sensing, drone-based imaging, advanced image processing, and feature extraction of outcrop-based data sets (Bisdom et al, 2014(Bisdom et al, , 2017Hardebol & Bertotti, 2013;Healy et al, 2017;Madjid et al, 2018;Pollyea & Fairley, 2011;Wüstefeld et al, 2018).…”