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Abstract: Constraining Reservoir Fracture Modelling with Outcrop Studies

Vincent Auzias, Keith Rawnsley, Jean Pierre Petit

In this study the use of quantitative outcrop studies to constrain reservoir fracture modelling is presented. As a case study Clair Field to the west of the Shetland Islands (UK) has been selected. For this example extensive outcrops are available. We aim to quantify the major influences affecting the development of the fractures in the middle and upper Devonian reservoir. These influences include the mechanical properties of the different lithological units in the reservoir and the influence of the reactivation of major fractures in the basement.

The fracture pattern (tension fractures, fracture corridors and faults) is defined at centimetre, metre and kilometre scales in outcrop and aerial photographs. Both cliff sections and horizontal exposures allow the 3D characterisation of the fractures in granitic basement, Devonian flagstones and sandstones.

The relation between the fracture pattern and the stratigraphy is quantified. We show that the exact nature of the fracture pattern is dependent of the stratigraphical position. The influence of the interface between beds on the vertical continuity of the fractures is also quantified using the bedding impedance ratio.

Fractures maps in the basement, Middle and Upper Devonian are presented. These are compared and a fracture development history is proposed.

These measurements are translated into geological rules for constraining reservoir fracture pattern models.

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