Abstract: Modelling Fracture Connectivity in Sedimentary Rocks

T. Rives, K. D. Rawnsley, J. P. Petit

In fractured reservoirs, it is now known that one of the most important parameters controlling fluid flow is fracture connectivity. In the horizontal plane, bedding surfaces have shown that this parameter is often very high if more than one fracture set is present. In cliffs, vertical connectivity is highly dependant on the mechanical layering of the sequence most fractures abut against bedding planes. These observations show that fracture development is strongly influenced by preexisting discontinuities.

To investigate fracture connectivity we have carried out a series of analogue brittle varnish models. Typical fracture patterns are presented in calcareous and clastic sequences and are simulated in the experiments. Analogue fracture patterns, very similar to natural ones are produced in the varnish (orthogonal networks, curving perpendicular and curving parallel tendencies, fan geometries...) which help to understand fracture development chronology and formation mechanisms.

These experiments suggest a methodology for use in stochastic simulations. In particular, fractures should be simulated in chronological order and connectivity must be used explicitly as a constraint.

One main conclusion of this work is that natural tension fracture patterns may be highly connected and should be realistically simulated. Other controls including infilling, aperture variations and in situ stresses must be superimposed into the 3D geometric pattern to investigate fluid flow.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France