Multiscale fracture network characterization and impact on flow: A case study on the Latemar carbonate platform

Abstract

A fracture network arrangement is quantified across an isolated carbonate platform from outcrop and aerial imagery to address its impact on fluid flow. The network is described in terms of fracture density, orientation, and length distribution parameters. Of particular interest is the role of fracture cross connections and abutments on the effective permeability. Hence, the flow simulations explicitly account for network topology by adopting Discrete‐Fracture‐and‐Matrix description. The interior of the Latemar carbonate platform (Dolomites, Italy) is taken as outcrop analogue for subsurface reservoirs of isolated carbonate build‐ups that exhibit a fracture‐dominated permeability. New is our dual strategy to describe the fracture network both as deterministic‐ and stochastic‐based inputs for flow simulations. The fracture geometries are captured explicitly and form a multiscale data set by integration of interpretations from outcrops, airborne imagery, and lidar. The deterministic network descriptions form the basis for descriptive rules that are diagnostic of the complex natural fracture arrangement. The fracture networks exhibit a variable degree of multitier hierarchies with smaller‐sized fractures abutting against larger fractures under both right and oblique angles. The influence of network topology on connectivity is quantified using Discrete‐Fracture‐Single phase fluid flow simulations. The simulation results show that the effective permeability for the fracture and matrix ensemble can be 50 to 400 times higher than the matrix permeability of 1.0 · 10−14 m2. The permeability enhancement is strongly controlled by the connectivity of the fracture network. Therefore, the degree of intersecting and abutting fractures should be captured from outcrops with accuracy to be of value as analogue.

Linking Structural and Transport Properties in Three‐Dimensional Fracture Networks

“…While it is understood that macroscale network traits influence the arrangement of the fluid flow field within a fracture network (Edery et al, ; Hyman & Jiménez‐Martínez, ), a direct link between geometric and topological properties of the fracture network and upscaled transport observables is still lacking. With such a wide range of relevant length scales, several orders of magnitude (Bonnet et al, ; Davy et al, ; Hardebol et al, ), it is challenging to identify which features of a fracture network influence which flow and transport properties. However, characterizing how the structure of a fracture network influences transport behavior therein is critical for many civil and industrial engineering applications such as CO 2 sequestration (Jenkins et al, ), aquifer storage and management (National Research Council, ; Neuman, ), environmental restoration of contaminated fractured media (Kueper & McWhorter, ; VanderKwaak & Sudicky, ), hydrocarbon extraction from unconventional shale aquifers (Hyman et al, ; Middleton et al, ), and the long‐term storage of spent nuclear fuel (Follin et al, ; Selroos et al, ).…”

Is the permeability of naturally fractured rocks scale dependent?

“…Renshaw and Park [] highlight fracture aperture as an additional important parameter that shows a complex dependence on fracture length, orientation, state of stress, fluid pressure and the mechanical properties of the fractured rock. In most published stochastic modeling studies, however, aperture is treated as constant [e.g., Hardebol et al ., ]. Where it is varied with fracture length, this pre‐imposes a scale variance.…”

Fracture Detection and Numerical Modeling for Fractured Reservoirs

“…Based on different algorithms, several software packages have been developed. For example, DigiFract [22] is a software package written in Python designed to work directly with fracture data digitized from outcrops and it is based on a geographical information system core that is applied for mapping real fracture data sets and studying the impact of fractures geometries on flow [23]. An integrated workflow for stress and flow modelling using outcrop-derived discrete fracture networks was designed after the fracture image was obtained with Unmanned Aerial Vehicles, in which DigiFract is used to digitize the fracture information [24].…”