Lewis, Helen¹, Stephen A Hall¹, Gary D Couples², Mark Reynolds³, Gillian Pickup¹, Jingsheng Ma³, Xavier Macle⁴ 
(1) Heriot Watt University, Edinburgh, United Kingdom 
(2) Institute of Petroleum Engineering, Heriot-Watt University, Edinburgh, United Kingdom 
(3) Heriot-Watt University, Edinburgh, United Kingdom 
(4) Institute of Petroleum Engineering, Edinburgh, United Kingdom

ABSTRACT: Evolving Upscaled Permeabilities and Seismic Responses in Numerical Models of Deforming Fracture/Flow Systems

There are considerable difficulties in predicting fluid flow through deforming geological materials in general and fractured reservoirs in particular. Recognition and interpretation of the associated seismic/acoustic signature is also a challenging. Aspects of the deforming/flowing system include: distribution/scale of altered effective material properties with deformation; local porefluid; and multiphase issues. Practical outputs include upscaled representations of mechanical and flow behaviours and the damaged materials’ seismic response. 
Numerical simulation ideally requires multiple coupling. Here we report results from a 2D, single-phase system where fractured blocky material is subjected to mechanical and fluid loads. The linear-elastic blocks can move and strain in 2D, and the block boundary discontinuities can open, close, or shear. Converged fluid-velocity and pressure (head) fields enable upscaled permeability calculations. 
The system’s coupled response is intriguing, showing conceptually satisfying, but complex, distinctly non-linear behaviours. We illustrate the flow consequences for a bent layer with different fracture densities and address how the upscaled permeability varies as a function of the global pressure differential; the upscaled stress-strain behaviour of the coupled system is distinctly non-linear. These results indicate that the method is capable of generating new understanding of the hydrogeomechanical coupling of such systems. 
It is also well recognised that, as well as variations with stress state, the instantaneous elastic response of deformed materials differs from that of their undeformed equivalents. Here we illustrate how a simple distribution of fault-associated open fractures under simple far-field loading produces a complex distribution of fracture permeabilities and seismic anisotropy signature.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.