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Mathematical Modelling of Faulting: Internal Fault Structures and Related Permeability Framework

Moraes, Anderson *1; Lima, Claudio 2; Cristina, Melissa 3; Lavorante, Luca 4
(1) Structural Geology and Tectonics, Petrobras/R&D Centre, Rio de Janeiro, Brazil.
(2) Reservoir Geology, Petrobras/E&P, Rio de Janeiro, Brazil.
(3) Reservoir Characterization and Modelling, Petrobras/R&D Centre, Rio de Janeiro, Brazil.
(4) Information Technology, Petrobras/E&P, Rio de Janeiro, Brazil.

Fault zones are the most ubiquitous of the geological structures and they occur at all scales in a wide variety of tectonic settings. Economic and geologic importance of fault zones have supported many studies developed to better understand the mechanical and hydraulic behaviour of such deformation zones. In particular, for the oil and gas industry to comprehend and quantify the role of fault zones in fluid flow are fundamental not only for exploration and production but also for drilling. Thefore, people in industry have endeavoured to simulate fault zones processes in geologic space and time in a more quantitative fashion.

Fault zones are the result of localization of deformation in a finite volume of rock through the complex interplay of fracturing, rotation, distortion, cementing, dissolution, crushing, slipping, rolling and friction of grains and/or of their clusters. However, an inspection of the present literature shows that most of the models relating to the mechanical evolution of fault zones rely only on a simplistic mohr-coulombian formulation, which could support at most the shearing behaviour of faults.

The present study is concerned with the development of mathematical models for fault zones formation that strive to capture part of the mechanical complexity in fault nucleation and the consequent permeability structure related to fault zones. Therefore, additional flow laws were combined to Mohr-Coulomb criterion in order to establish fracturing, rotation, crushing and slipping processes for the inner fault-related structural framework. This most embracing integrated mechanical model for fault zones genesis enables to reproduce a more realistic model for the fault inner structure, in agreement to empirical and experimental data. In addition, this kind of mechanical analysis suggested different ways of fault localization and distinct contexts for the hydraulic framework inside fault zones. This deterministic model is supported by some field and experimental case studies where fault zones deformation pattern and permeability measurements were reasonably calibrated.


AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California