Title: Methodology for predicting strain and minor fracturing 
Resource Type: document --> technical publication --> report 
Country: EU Projects 
Year: 2004 
Availability: Saltrans Consortium, 2003,Methodology for predicting strain and minor fracturing http://www.weizmann.ac.il/ESER/Saltrans/Deliverables.html 
Author 1/Producer: Saltrans Consortium 
Author / Producer Type: EC Project 
Report / download web link (=direct link): http://www.weizmann.ac.il/ESER/Saltrans/Deliverables.html  
EUGRIS Keyword(s): Contaminated land-->Soil and groundwater processes-->Hydrogeology
Groundwater protection-->Groundwater processes-->Hydrogeology
Water resources and their management -->Water resources and their management Overview
 
Short description: This report comprises Deliverable 5 for the SALTRANS project (EVK1-CT-2000-0062) with the title ‘Methodology for predicting strain and minor fracturing intensity and bulk rock hydraulic properties around major faults’. This deliverable is linked to Work Package 2, and relates to the activity “Quantification of dynamic (evolving) structural changes, due to deformation, poroelasticity and fracture growth processes”. 
Long description: In Narteau & Main (2002a,b), we have succeeded in developing a general model for the development of fractures. The model represents an optimum between exactly solving the equations of elasto-dynamics and the stochastic nature of fracture evolution for a linear viscoelastic medium (strain rate proportional to stress). The method works by nucleating fractures at random, with a probability weighted by the local deformation rate. Once a fracture is nucleated, it perturbs the stress field at all scales up to the maximum fracture length, similar to the renormalisation group approach. This is an improvement on traditional cellular automata that use only the elementary scale, and hence fail to account accurately for stress concentration effects. The fractures then grow, and then coalesce or not depending on interactions specified at their tips, and the rate of healing. The resulting patterns look very realistic, but also predict phenomena such as the evolution of stress and permeability in a way that mimics experimental laboratory tests (e.g. for the case of deformation bands in porous sandstones as in Narteau & Main, 2002a). By tuning the assumed stochastic healing rate and the ratio of the loading rate to the threshold strength for failure, it is possible to map out map out virtually all of the known ‘type’ fracture population morphologies. Deformation at high healing rate produces distributed damage in the form of populations of isolated fractures below the percolation threshold. At intermediate healing rates damage localises on a single percolating mega-fault, which branches into a set of deformation bands if the loading rate is higher. At low healing rates populations resembling joint patterns evolve naturally. Interestingly, when the population statistics are analysed using the entropy based on the population of energetic microstates, the localised megafault and the distributed joint pattern both occur at minima in the Helmholtz Free Energy, thereby possibly explaining why these two particular types are so common in nature. 
Link to Project(s): SALTRANS Methods for assessing salt intrusion and transport in heterogeneous and fractured aquifers
 
Submitted By: Dr Stefan Gödeke WhoDoesWhat?      Last update: 22/10/2006