Predictive Modelling of the Evolution of Geological Structures: Upscaling from Bench-Scale Experiments - The Influence of Compaction and Pore Pressure

A.J.L. Crook¹, S.M Willson², and J.G. Yu^1
1Rockfield Software Limited, Technium, Prince of Wales Dock, Swansea, UK
²BP America Inc, 501 Westlake Park Boulevard, Houston, USA

Reconstruction of the stress and deformation history within sedimentary basins necessitates an integrated modelling framework that properly accounts for the simultaneous evolution of the state variables that describe the internal state of the rock formation due to the imposed boundary conditions. This involves the concurrent computation of displacement, fluid pressure and temperature history together with any additional variables dependent upon the specific physics included in the model.

This paper describes ongoing research on some of the key elements required within this class of simulation methodology and, in particular, it discusses issues related to the application of fully coupled geomechanical and fluid flow models to field scale applications including:

1 The strongly coupled nature of the mechanical deformation and the flow fields.
2 Algorithms for prediction of the onset and evolution of faults.
3 Scale up from laboratory-scale sandbox tests to field scale models.
4 A Constitutive model for the evolution of the material state boundary surface.

This work is an extension of a previously published study (Crook et al., 2006(a)) that focused on predictive modelling of structure evolution in sandbox experiments. In that study the modelling approach was successfully benchmarked by forward simulation of two extensional sandbox experiments that exhibit complex fault development including a series of superimposed crestal collapse graben systems. It was emphasized in that work that no initial perturbations or fault seeding was imposed so that structure evolved solely from the prescribed movement on the basal detachment.

The extension from laboratory-scale to field-scale, which is described in this paper, is non-trivial as there are number of additional deformational mechanisms and physical processes at the field-scale that may be neglected at the laboratory-scale; e.g. mechanical compaction, chemical compaction, evolution of fluid pressure, creep relaxation, etc. Algorithms for treatment of these phenomena will be presented and it will be shown that, depending on the specific conditions associated with the structure evolution, these additional mechanisms may have a large influence on the predicted structural style. Furthermore, it will be demonstrated that adoption of more simplistic assumptions may in some case lead to misleading interpretations of the observed response.

A.J.L. Crook, S.M. Willson, J.G. Yu, D.R.J. Owen. Predictive modelling of structure evolution in sandbox experiments. J. Struct. Geol., Vol. 28, 729-744, 2006
A.J.L. Crook, D.R.J. Owen, S.M. Willson, J.G. Yu. Benchmarks for the evolution of shear localisations with large relative sliding in frictional materials. Comp. Meth. Appl. Mech. Engng., Vol.195, 4991-5010, 2006

 

AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands

 

AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands