A Simplifying Discrete Fracture Network Method for Dynamic Test Simulations

André Fourno
Reservoir Enginneering Division, IFP, Rueil Malmaison, France

The hydraulic characterization of fractured reservoirs, using flow-meter or well tests, is a key point to provide valid flow properties to full-field simulation models. For several years, different methodologies have been proposed to use a Discrete Fracture Network (DFN) model in order to increase the precision of fluid flow simulations. However, the drainage area of a well test in a fractured reservoir is generally large, leading thus to numerous computation nodes, especially for dense fracture networks. In such situations, the required CPU time is often prohibitive. A solution is to reduce the number of fracture nodes. Previous works, presented in MEOS 2005, SPE 93748, proposed a method to simplify the DFN to a "sugar-box" fracture network in the regions located far from the well-bore (the near-wellbore fracture network is not simplified). This simplification is performed through a homogenization procedure keeping the same matrix-fracture storativity ratio and inter-porosity flow parameter.

This paper presents further developments and applications which allow (1) to apply this approach to a Corner Point Geometry grid, (2) to define elliptic simplified zones according to their principal flow directions and (3) to delimit the near-wellbore area where the original DFN has to be preserved.
This approach is validated by comparing the simulated well test responses on both optimized and original DFN models. The well test signature is not affected by the DFN simplification procedure, but the computation time is drastically reduced, by nearly two orders of magnitude. Flows can now be simulated on DFN models at the well drainage area scale in order to match fracture flow properties to field-measured well tests responses, that is an essential step in the field flow modelling process.

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