The Use of Topology in Analysing Fault and Fracture Networks: Characterization and Connectivity

Abstract

Faults and fractures rarely occur individually or without associated deformation, instead developing and accommodating strain as a network of structures, both minor and major. These networks will comprise a number interacting faults and fractures that display a range of lengths, sizes and orientations with the potential to form an interconnected network. Such a network can strongly affect the porosity and permeability of the surrounding rock mass, providing either connected pathways or barriers to fluid flow. Thus the characterization of fault and fracture networks and assessment of their connectivity is important to hydrocarbon exploration and production. Network topology describes the relationships between geometrical elements within the network and is essential to characterize networks. In 2-dimensions the topology of a fracture network consists of lines, nodes and branches between nodes. Nodes are divided into isolated (I-) nodes, and connecting nodes (X- and Y-nodes). As the ends of branches are marked by nodes we can classify branches into three topological groups: I-I, I-C, and C-C branches. The number and proportion of different node and branch types can be used to calculate key dimensionless parameters that can be used to assess connectivity. The application of topology within fault and fracture networks will greatly improve reservoir modelling and characterization at both geological and production timescales as it relates to the geometry, capacity and compartmentalization of structural reservoirs, and also to connectivity and structural controls on fluid flow. In this contribution we will discuss the concept of topology and illustrate simple topological analyses demonstrating its use for characterization of fault and fracture networks and assessment of connectivity and percolation thresholds. In addition we will explore controls on spatial variations and the development of network topology within fault networks, using examples from the North Sea and comparisons with discrete element models.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016