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Numerical and analogue modelling studies |
1 Petroleum and Geosystems Engineering Department, The University of Texas at Austin, 1 University Station C0300, Austin, TX 78712, USA (e-mail: jolson{at}mail.utexas.edu)
2 Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX 78713, USA
3 Geocosm, Austin, TX 78746, USA
Diagenesis and fracture are often linked processes in deformed rock. Empirical observations show that quartz-lined natural fractures are very common in sandstones that have been exposed to temperatures in excess of 90°C. These fractures exhibit crack-seal textures as well as cement bridges propping the fractures open and preserving fracture porosity. These diagenetic effects are examined in the context of detailed fracture characterizations generated by geomechanical modelling. Aperture, length and fracture network geometry are examined in the context of subcritical crack growth and various biaxial loading boundary conditions of varying initial anisotropy. An isotropic initial state results in more polygonal fracture patterns. A small initial anisotropy creates preferential through-going fractures that are later connected by cross-fractures. A larger initial anisotropy results in only one parallel set. The flow connectivity of isotropic and small strain anisotropic patterns appears high based on trace pattern geometry, but when the effects of diagenesis are added, preferentially filling smaller aperture fracture segments, connectivity can be significantly reduced. Finite difference, steady-state flow simulations demonstrate the permeability effects of heterogeneous fracture aperture distributions predicted by the mechanical model and permeability reduction caused by systematic diagenetic fracture sealing.
